Wood species, defects. Mechanical properties of wood

Types of knots: a - round; b - oval; c - oblong; g - plastic; d - edge; e - rib; g - stitched; z - group; and - branched

: I - plastic; II - edge; III - end; a - methic; b - frosty; c - shrinkage cracks; g - thrashing

: a, c - change in the cross-sectional shape of the bars with different arrangements of layers at the end; b - the same, boards (core and side); g - longitudinal warping; d - wingedness.

Changes in appearance, violations of the correct structure, integrity of tissues and other shortcomings that reduce the quality of wood and limit its capabilities practical use, are called wood defects.

According to GOST 2140-81, all defects are divided into nine groups:

1 - knots;
2 - cracks;
3 - defects in the shape of the trunk;
4 - structural defects of wood;
5 - chemical stains;
6 - fungal infections;
7 - biological damage;
8 - foreign inclusions, mechanical damage and processing defects;
9 - warped.

Each group includes several types of defects; for some defects their varieties are indicated. Some defects are characteristic only of round timber (logs, etc.), other defects are characteristic only of lumber products (boards, beams, blanks) or veneer. There are defects that occur in two or all three classes of assortments.

Bitches

The most common defect is bitches. They are parts (bases) of branches enclosed in assortment wood. According to the degree of overgrowth, knots are distinguished only in round timber, distinguishing two types: open, i.e. extending onto the side surface of the assortment, and overgrown, detected by swellings and other traces of overgrowth on the side surface.

According to the shape of the cut knots (in lumber and veneer) are divided into round, oval And oblong. A round knot is formed if the base of a branch is cut at a large angle to the longitudinal axis so that the ratio of the larger to the smaller diameter of the knot does not exceed 2. A round knot can be found on the tangential surface of the assortment. An oval knot is formed when the base of a branch is cut at an angle to its longitudinal axis so that the ratio of the larger diameter of the knot to the smaller is 2 - 4. An oblong knot is formed when the base of a branch is cut along or at a small angle to its axis, if the ratio of the larger diameter to the smaller exceeds 4. An oblong knot in the form of a strip tapering towards the core or a strongly elongated oval can be detected on a radial or close to it section.

By position in the sawn assortment differentiate plastic, edge, rib, end And sewing knots. Face knots go out on the wide side (face), edge knots - on the narrow side (edge), edge knots - simultaneously on the adjacent face and edge, end knots - on the short side (end) of the assortment. If a knot penetrates the entire face or edge and extends onto two edges, it is called stitched.

In addition, knots are distinguished in sawn products: unilateral, facing one or two adjacent sides of the assortment, and end-to-end, facing two opposite sides of the assortment.

By relative position in the sawn assortment differentiate scattered, group And branched branches . Scattered are any single knots that are spaced from each other along the length of the assortment at a greater distance than its width. For wide assortments (more than 150 mm wide), the distance between knots must be at least 150 mm. Group knots are two or more round, oval or ribbed knots located on a segment of the length of the assortment equal to its width. For wide assortments, this segment should be 150 mm. With a whorled arrangement of branches, especially characteristic of pine and larch, branched (old name - palmate) knots are formed. They are found on radial or close to them cuts and include two oblong knots of one whorl or one oblong knot in combination with an oval or ribbed knot of one whorl (there may be a third one between them - a round or oval knot).

According to the degree of fusion with the surrounding wood in sawn products and veneer there are fused, partially fused And unfused knots , in which the annual layers have not grown together with the surrounding wood for an area of less than 1/4; more than 1/4, but less than 3/4; more than 3/4 of the perimeter of the knot cut. Among the unfused knots, the ones that fall out are distinguished.

According to the condition of the wood knots in all types of timber are divided into healthy, rotten, rotten And tobacco. Knots in which the wood shows no signs of rot are called healthy. Among this variety of knots in lumber and veneer, the following knots are distinguished: light, colored slightly darker than the surrounding wood; dark, the wood of which is impregnated with resin, tannins and heartwood and is therefore much darker than the surrounding wood; healthy with cracks. Knots in which the rotten zone occupies less or more than 1/3 of the cut area are called rotten and rotten. Tobacco knots are knots whose wood has completely or partially rotted and turned into a loose mass of rusty-brown (tobacco) or whitish color, easily ground into powder.

Characteristics of assortments by knotiness includes an indication of the variety, size and number of knots. In round timber, when identifying the types of open knots based on the condition of the wood, it is sometimes difficult to distinguish tobacco knots from other rotten knots. In this case, probing with a probe is used. If the destruction zone extends to a depth of no more than 3 cm, then such knots, depending on the area of damage, are classified as rotten or rotten, but if the destruction zone extends to a greater depth (often to the core), then these are tobacco knots.

Open knots are measured by their smallest diameter, and the piecing bead is not included in the knot size. Overgrown knots are assessed by the height of the swellings covering them above the side surface of the assortments. In deciduous timber, the diameter of an overgrown knot can be determined by the size of the wound spot or edge whiskers. A clearly visible edge on the smooth bark of some species (birch, beech, hornbeam, aspen) in the form of two dark stripes directed at an angle - whiskers - arises from the pressure of a growing branch on the wood of the trunk. After the branch dies and falls, a wound spot appears in the place of the overgrown knot, most often of a regular ellipsoidal shape.

The size of the thickest part of an overgrown knot in assortments of birch, beech, linden, alder and ash is 0.9, and in aspen - 0.6 of the maximum diameter of the wound spot. In some round assortments, for example in plywood logs, it is important to know the depth of overgrown knots. This allows you to determine the size of the knot-free zone from which high-quality veneer can be obtained. The depth of knots in assortments from the specified rocks can be determined by the ratio between the height and width of the wound spot and the diameter of the assortment at the site where the knot is overgrown.

With a decrease in the specified ratio for a given diameter of the assortment, the depth of the top of the overgrown knot increases. With the same ratio of the sizes of the wound spot, the deeper the knot lies, the larger the diameter of the assortment.

In birch assortments, the depth of the knot can also be determined by the angle between the edges. The greater the angle between the whiskers, the deeper the overgrown knot is located (at a constant diameter of the assortment). At the same value of the angle between the whiskers, the depth of occurrence is greater for assortments of larger diameter. By the length of the mustache you can roughly judge the size of the overgrown knot. The length of the whisker, measured in centimeters, approximately corresponds to the size of the knot in millimeters.

In lumber and sliced veneer, knot sizes are determined in one of two ways:

by the distance between two tangents to the contour of the knot, drawn parallel to the longitudinal axis of the assortment;
along the smallest cross-sectional diameter of the knot.

Round, oval and oblong (or branched) knots that do not extend to the edge are measured as shown in Fig. 5, the first (dimensions a1 a2, etc.) or the second (dimensions b1 and b2, etc.) method. The size of branched knots can be determined as the sum of the sizes of the component knots. The sizes of group knots are determined in the same way. In rotary cut veneer, all knots are measured by the largest diameter of their cross-section. The sizes of knots are expressed in millimeters or in fractions of the size of the assortment and their number is calculated in round timber and sawn products per 1 m or over the entire length of the assortment, in veneer - per 1 m or over the entire sheet area.

Number, size and location of knots depend on the tree species, its growth conditions and the area of the trunk. Shade-tolerant tree trunks - spruce trees have more knots than pine trunks; trees grown in closed stands are cleared of knots earlier and higher than a tree grown in freedom; the butt part of the trunk is less knotty than the apical part. The dimensions of the same knots and the condition of their wood vary along the radius of the trunk. As you move from the bark deep into the trunk to the core, the size of the knots decreases, unfused knots become fused, and the number of rotten and rotten knots decreases.

When using wood, knots in most cases have an impact bad influence- often deteriorate the appearance of wood, disrupt its uniformity and cause curvature of fibers and annual layers, which leads to a decrease in many mechanical properties of wood. Due to their greater hardness compared to the surrounding wood, healthy and especially dark (horny) knots make it difficult to process the wood with cutting tools. Tobacco knots in round assortments are accompanied by hidden core rot.

The degree of influence of the knot on the mechanical properties depends on its relative size, type and nature of the stressed state of the loaded part of the product or structure. The least negative impact is exerted by healthy, round, fully fused knots, and the greatest negative impact is exerted by stitched and grouped knots. The strength of wood decreases most strongly when stretched along the grain, and least when compressed along the grain. When bending, the degree of influence significantly depends on the position of the knot along the length and height of the part. The greatest negative impact is exerted by knots located in the stretched zone of the dangerous section of the bending part, especially if the knot extends to the edge.

According to the data for pine wood blanks, there is close to proportional dependence between the relative size of the knot (as a fraction of the width or thickness of the workpiece) and the strength in static bending and compression along the grain (as a percentage of the strength of pure wood). Consequently, with a knot size of 0.3 and 0.5, the strength will decrease by 30 and 50%, respectively. A similar relationship was found when bending birch and beech wood. In oak wood, the effect of knot size on strength is less pronounced.

Strength increases due to the presence of knots when wood is compressed and stretched in the radial direction across the grain, when the axis of the knot coincides with the direction of the force. Knots also increase strength when shearing along the fibers in the tangential direction, when they are located perpendicular to the shearing plane.

If necessary, wooden plugs (with or without glue) are inserted into the holes remaining after fallen knots. Sometimes knots are specially drilled out and the holes are sealed with plugs. At the same time, the strength of the wood does not increase, since the curvature of the fibers around the plugs still remains.

As the size of the knots increases, the modulus of elasticity during compression along the fibers and static bending decreases, and when stretched and compressed across the fibers in the radial and tangential directions, they increase greatly due to the greater rigidity of the wood of the knots themselves.

The influence of knots on the mechanical properties of pine round timber was investigated. And the decrease in the compressive strength along the fibers of samples with a diameter of 8.5 to 12 cm with an increase in the ratio of the size of the largest knot in the whorl to the diameter of the sample from 0.18 to 0.61 ranged from 4 to 18% compared to pure wood. Approximately the same decrease in strength was found when testing samples for static bending if a large knot was in the stretched zone. For samples with a diameter of 16 cm or more, no significant effect of knots on compressive strength along the fibers was found. Thus, in lumber, knots have a greater influence on strength than in round timber. In round timber, as in lumber, knots have less effect on the modulus of elasticity than on strength.

Cracks

Cracks- these are longitudinal tears in wood that are formed under the influence of internal stresses that reach the tensile strength of wood across the grain.

Cracks in round timber and sawn products divided by type into methic, thrashing And frosty that appear in a growing tree, and shrinkage cracks that appear in felled wood.

Methic cracks are internal radial cracks in tree trunks. They are found in all species, especially often in pine, larch, and beech, mainly in overmature stands. The length of the crack along the trunk reaches 10 m or more, sometimes the crack from the butt reaches the living crown. In round timber, metic cracks are visible only at the ends (preferably at the butt), since, starting from the core, they do not reach the bark and are not visible on the side surface. In lumber, these cracks are found both on the ends and on the side surfaces. A simple crack is a meticulous crack (or two cracks directed along the same end diameter) located in the same plane along the length of the assortment. Complex are two or more cracks directed at the end at an angle to each other, as well as one or two cracks directed along the same diameter, but due to the spiral arrangement of the fibers they are not in the same plane. Methic cracks occur as the tree grows. There is an opinion that cracks also form when a tree is felled by hitting the ground. As the wood dries, the size of the crack increases. Methic cracks are not continuous, but intermittent breaks along the length of the assortment.

Peeling cracks - these are peelings (along the annual layer) of wood inside the core or mature wood of the trunks of growing trees; found in all breeds. Shot can be found in round timber only on the ends in the form of arcuate (not filled with resin) or annular cracks, in lumber - on the ends in the form of cracks-holes, and on the side surfaces in the form of longitudinal cracks or grooved depressions. Until now, the reason for the appearance of peeling cracks has not been precisely established. Peel cracks form in places where there is a sharp transition from fine-grained wood to coarse-grained wood. The occurrence of rot can be associated with the formation of internal rot, and in pine and deciduous trees - water layer.

Frosty cracks are external longitudinal tears in the wood of the trunks of growing deciduous (less often coniferous) trees; spread deep into the trunk in radial directions. They are formed when the temperature drops sharply in winter. They look like old cracks caused by a lightning strike. On the surface of the trunk, this defect looks like a long open crack, often with ridges of overgrown wood and bark along the edges. Frost cracks are located in the butt part of the trunk. In round timber, frost cracks are clearly visible on the side surface and ends; on the outside they have the greatest width, go deep into the wood (often to the core), gradually narrowing. In lumber they are found in the form of long radial cracks with the annual layers widening around them.

Shrinkage cracks arise in timber under the influence of internal drying stresses. Cracks spread from the side surface deep into the assortment in radial directions. They differ from metic and frost cracks in that they are shorter along the length of the assortment (usually no more than 1 m) and shallower in depth. These cracks can appear on the end surfaces of round logs and lumber due to uneven drying along their length. At the final stage of drying large-section lumber (usually hardwood), internal cracks (fistulas) sometimes appear, which are discovered when cutting assortments.

By location in the assortment differentiate end cracks located at the ends and not extending to the sides of the assortment, and side cracks, which are located on the sides of the assortment and can extend to the ends. Among the lateral cracks in sawn assortments, a distinction is made between face and edge cracks.

If cracks extend to a depth of less than 1/10 of the thickness of the log (but not more than 7 cm for round timber and 5 mm for sawn products), they are called shallow, if to a greater depth (but do not have a second exit to the side surface) - deep. Through called cracks that extend onto two sides or two ends of the assortment, as well as peeling cracks that extend in two places on one side of the assortment (they can form a groove). In veneer, cracks less than 0.2 mm wide are called closed, and wider ones - dispersed.

Side cracks measured by the depth of the assortment in millimeters, and by the length - in centimeters or, respectively, in fractions of the thickness and length of the assortment. To measure depth, use a thin steel probe. Face metic, peel and frost cracks in round timber, measured by the smallest thickness of the core board or the diameter of the circle into which it can be inscribed, or by the smallest width of the intact peripheral zone of the end. End shrinkage cracks in round timber are measured by depth. In sawn products, end cracks are measured by their length at the end in millimeters or in fractions of that side of the log on which their projection is larger. Peeling end cracks in lumber are measured along the chord, and if the crack occupies more than half the circumference of the annual layer - by diameter. In veneer, cracks are measured along the length, and split cracks are measured along the width; take into account the number of cracks per 1 m of sheet width.

The smallest reduction in strength due to cracks is observed during compression along or across the fibers, the greatest - during tension across the fibers, if the crack is located in a plane perpendicular to the direction of action of the force, as well as during chipping, if the crack coincides with the plane of chipping. During bending, the greatest negative effect is exerted by a crack perpendicular to the direction of the bending force and located in the neutral plane. Here there are no normal stresses, but shear stresses are maximum and the decrease in strength is proportional to the decrease in the area working for shearing. According to the data, cracks do not affect the modulus of elasticity in tension and compression along the fibers, but greatly reduce the modulus of elasticity in static bending in the case when the plane of the crack is perpendicular to the direction of the bending force.

Cracks- one of the main factors reducing the strength of assortments used in construction. Restrictions on the tolerance of cracks are also explained by the fact that they facilitate the penetration of moisture and fungal spores deeper into the assortment.

Trunk shape defects

Convergence. All tree trunks are characterized by a gradual decrease in diameter in the direction from the butt to the top (runoff). If for every meter of trunk height (assortment length) the diameter decreases by more than 1 cm, then this phenomenon is considered a defect - camber. The taper is measured as the difference between the butt and top diameters of round logs (in butt logs, the lower diameter is measured at a distance of 1 m from the butt end), and for unedged lumber - between the width of the butt and top ends. The resulting difference is related to the total length of the assortment and is expressed in centimeters per 1 m or as a percentage.

The trunks of deciduous trees are more tapering than those of coniferous trees. Heavily cambered trunks of trees grown in the wild or in a sparse forest stand. The higher the quality of the planting, the more woody the trunks are, i.e. less runaways. The least camber is characteristic of assortments cut from the middle part of the trunk, the greatest - from the apical part. The curvature increases the amount of waste when sawing assortments and peeling them and indirectly affects the strength, as it causes the appearance of a defect in the lumber - a radial inclination of the fibers.

Compulsiveness. This is a case of camber when there is a sharp increase in diameter in the lower part of the trunk; The diameter of round timber or the width of unedged lumber at the butt end is more than 1.2 times greater than the diameter (width) of the assortment at a distance of 1 m from this end.

Rounded backbone called if the cross-section of the butt part has a shape close to a circle. Ribbed buttock characterized by a multi-lobed cross-sectional shape. Longitudinal depressions are visible on the side surface of the assortment.

Buttiness is measured as the difference between the diameters (for unedged lumber - widths) of the butt end and the cross-section at a distance of 1 m from it. In case of ribbed rib, it is allowed to determine the difference between the maximum and minimum diameter butt end.

Ovality. This is the name for the elliptical shape of the end of round timber, in which largest diameter no less than 1.5 times the smaller one. The defect is measured as the difference between the specified diameters. Ovality accompanies heel or traction wood.

Growths. This is what local thickenings of the trunk are called. They can have a smooth or bumpy barked surface and dormant buds (burls). Sometimes burls can be distinguished from suvels by the presence of shoots on them. Growths are formed as a result adverse effects fungi, bacteria, viruses, chemical agents, radiation, mechanical damage, etc. Features of the formation of growths caused by disruption of growth processes. In a longitudinal section of the suvel, the annual layers are curved and repeat the outer contours of the growth. Burls are characterized by a curled wood structure. In coniferous species, mainly suvels are formed, while in deciduous species, growths of both types are formed. The curling nature of the burl wood and the presence of numerous traces of dormant buds in it creates a very beautiful texture on the cuts. The texture of the burls is especially decorative walnut. Root burls often reach significant sizes.

In walnut and birch they can weigh hundreds of kilograms, and sometimes more than a ton. On the trunks of Karelian birch, spherical thickenings with a characteristic texture are often formed. Suvel wood has high shrinkage along the grain (from 0.5 to 1.0%), low elasticity modulus and low compressive strength along the grain. Burl wood is denser and harder than normal stem wood and has less pronounced anisotropy. Growths are measured by length and width. They make it difficult to use round timber and complicate its processing, but burl wood is highly valued as a material for artistic crafts and raw material for sliced veneer.

Curvature. Curvature of the trunk along the length occurs in everyone tree species. Due to the loss of an apical shoot and its replacement by a lateral branch, due to the tilt of the tree towards better lighting, when growing on mountain slopes and for other reasons, the tree trunk may become curved. Distinguish simple And complex curvature, characterized respectively by one or more bends of the assortment.

Simple curvature is measured as the amount of deflection of the assortment at the point of its curvature (as a percentage of the length of the curved section of the assortment). When cross-cutting a long piece of wood into short pieces, their curvature turns out to be less by approximately the same amount of times as the length of the long piece of wood was cut into equal parts. Complex curvature is characterized by the magnitude of the greatest curvature, measured in the same way as in the case of simple curvature.

Defects in the shape of the trunk increase the amount of waste when sawing and peeling round logs and cause the appearance of radial inclination of fibers in lumber and veneer.

Wood structural defects

Incorrect arrangement of fibers and annual layers

Fiber inclination. Deviation of fibers from the longitudinal axis of the assortment (previously this defect was called cross-layer) occurs in all breeds. In roundwood, the slope is due to the natural spiral arrangement of the fibers; found on the lateral surface in the direction of bark grooves or in debarked assortments along screw cracks. There are two types of this defect in sawn products and veneer - tangential And radial incline. The tangential inclination of the fibers is detected on a tangential section by the deviation of the direction of resin passages, vessels, core rays, cracks and strips of fungal lesions from the longitudinal axis of the assortment.

If these signs are not clearly expressed, then you should draw the marks with a thin, but not sharp, instrument or carry out a test splitting along the fibers; deviation of the mark from the longitudinal axis of the assortment or non-flatness of the surface of the radial split will indicate the presence of a defect.

Inclination of fibers on a tangential surface lumber may not be associated with the spiral arrangement of fibers in the tree trunk, but arise as a result of sawing straight-grained boards (timbers) into small parts when the cuts are directed at an angle to the longitudinal axis of the original assortment. This defect, in contrast to the natural tangential inclination of the fibers, has the same angles of inclination of the fibers on opposite sides of the assortment.

Radial fiber inclination observed when cutting annual layers on the radial or close to it surface of lumber. This type of fiber inclination (according to the old terminology - artificial cross-grain) is obtained when sawing heavily ragged, knotty and crooked logs. If the saw cuts run parallel to the longitudinal axis of the log, then the annual layers and, consequently, the fibers on the radial surface of the lumber are at an angle to the assortment edge. In this case, closely spaced boundaries of the annual layers are visible on the tangential surface of the lumber, as well as on the peeled veneer.

The grain slope of round timber is measured at the most typical place manifestations of the defect - on the side surface - as a deviation of the fibers from a line parallel to the longitudinal axis of the assortment over 1 m and is expressed as a percentage or centimeters. In butt logs, the slope of the fibers is measured at a distance of 1 m from the bottom end. It is allowed to measure the defect at the upper end along the chord h in centimeters or fractions of the diameter of the end. In sawn products, the slope of the fibers is measured as the deviation h over a length l equal to at least twice the width of the assortment (as a percentage of the length of this section along the longitudinal axis).

In veneer, the tangential slope is measured in the same way as in lumber, and the radial slope is measured by the average width of the cut annual layers, which are calculated on a 100 mm long segment in the area of the tangential surface of the sheet where these layers are most closely located.

The greater the slope of the fibers, the more the strength of the wood decreases. The greatest decrease in strength is observed during tension along the fibers; strength during static bending decreases noticeably; This defect has the least effect on compressive strength along the fibers. According to the data, a fiber inclination equal to 12% causes a decrease in the tensile strength of pine in compression along the fibers by 3%, in static bending by 11%, and in tension along the fibers by 14%. The elastic modulus also decreases significantly with increasing fiber inclination, especially when compressed along the fibers.

The inclination of the fibers increases the shrinkage of assortments in the longitudinal direction and causes the formation of helical warping (winging) of lumber and twisting of pillars. In addition, the slope of the grain makes it difficult to machine the wood and reduces its ability to bend.

Curlyness. This is the name for the tortuous and random arrangement of fibers, which is most often found in hardwoods.

Wavy curliness is expressed in a more or less ordered arrangement of wavy curved fibers and forms a characteristic streamy texture. This arrangement of fibers is observed mainly in the butt part of the trunk, especially in the places where the trunk passes into the roots.

Confused curliness characterized by a random arrangement of fibers; found mainly in wood of burl-type growths.

Typically, twisting is a local defect, as it is limited to individual areas of wood, but sometimes it can be found over a large length of the trunk, for example, in Karelian birch. According to research, such wood is characterized by the presence of large false-wide medullary rays containing clusters of small parenchyma cells. The peculiar brownish patterned pattern is caused by brown pigment found in the cells of the false broad rays and areas of the parenchyma.

By measuring the width and length of the curly part of the surface, the percentage of the surface area of the assortment occupied by the defect is determined. Curling reduces tensile strength and increases toughness and splitting resistance. Mechanical processing of curly wood is difficult. At the same time, curliness (especially confused) creates a beautiful texture, which is highly valued when using wood as a decorative material, so curliness should be considered a conditional defect.

Curl. This is a local curvature of the annual layers of knots and shoots. On the side surfaces of lumber and in veneer, bracket-shaped, curved or closed concentric contours of curved annual layers are noticeable. A curl that extends onto one or two adjacent sides of the assortment is called one-sided; through, it extends to two opposite sides of the assortment.

On the side surfaces of lumber and in veneer, the width and length of the curl are measured, and the number of curls per 1 m or over the entire length of the assortment in lumber and blanks and per 1 m or over the entire surface of the sheet in veneer is counted. Curls surrounding knots, which are acceptable in this assortment, are not taken into account.

The greatest reduction in strength is observed in the presence of through curls under the influence of tensile stresses. Curls also reduce toughness. Curls are especially dangerous for small assortments.

Reactive wood. In inclined and curved trunks and branches, a special wood is formed, which is called reactive wood in the world botanical literature. This defect occurs under the influence of gravity, which causes redistribution of substances that stimulate or suppress growth processes, wind load, growth stress, osmotic pressure and other factors.

Kren. This structural defect of coniferous wood is expressed in an apparent increase in the width of the late zone of annual layers. The lurch wood only resembles the late wood in color. The heel is formed mainly in the compressed zone of curved or inclined trunks, i.e. on the bottom side facing the ground.

Continuous roll is found at the ends of trunks that have been bent for a long time, in the form of a dark-colored area, sometimes occupying more than half of the cross-section, which has oval shape. The core is displaced towards the area of normal wood. In lurch wood, the annual layers are much wider, and within each annual layer the transition from the light to dark zone is less sharp than in normal wood. Typically, the surface of edged wood is smoother than that of normal wood. Continuous roll is more often observed in the butt part of inclined trunks; it can be observed in the stretched zone of curved trunks, as well as in the lower (compressed) zone of branches.

Local roll occurs due to short-term bending of the trunk or the action of other factors. At the end of the trunk it is noticeable in the form of arched areas, covering one or several annual layers.

On the side surfaces of lumber and veneer, continuous and local heel looks like dull dark stripes of varying widths. Rolling is especially common and clearly visible in mature wood species - spruce and fir; In the dark-colored core zone of larch, pine, and cedar, the roll is less visible.

The roll is measured by the width and length of the zone occupied by it; You can also determine the share (in percent) of the area of the assortment side occupied by this defect.

Root tracheids have about round shape cross section; large intercellular spaces remain. The thickness of the walls is 2 times greater than in normal tracheids.

In lurch wood, the cellulose content decreases by approximately 10% and the lignin content increases. Density, end hardness, compressive strength along the fibers and static bending increase, and tensile strength along the fibers and impact strength decrease. The elastic moduli along the fibers decrease, while the shear moduli and elastic moduli in compression across the fibers increase.

Shrinkage across the fibers of lurch wood is approximately 2 times less than that of normal wood, however, shrinkage along the fibers (due to the large angle of inclination of the microfibrils) increases significantly (10 times or more). This causes longitudinal warping and cracking of the lumber.

The limit of hygroscopicity of lurch wood is lower; the permeability of wood to liquids and gases decreases, which is associated with the smaller size of the tracheid cavities and bordered pores; water absorption decreases.

The presence of hemp in pulp pulp reduces the yield of chemically pure cellulose and increases the cost of bleaching. Due to heeling, the quality of wood pulp used in paper production deteriorates; saws become jammed when cutting boards crosswise.

Traction wood. This defect in the structure of deciduous wood is related in origin to heel, but unlike heel, it is formed in the upper (stretched) zone of curved or inclined trunks and branches of some species (beech, poplar, etc.). In beech, after felling the tree, traction wood can be identified by its lighter color with a silver or pearlescent tint. Under the influence of light, air, and also as a result of the removal of moisture during drying, traction wood turns darker brown.

At the ends of the timber, traction wood has the appearance of arched sections that differ in color and structure (fluffy-velvety surface) from normal wood. On the radial surface and in wood veneer with clearly visible annual layers (oak, ash), it is observed in the form of narrow strips - strands. In timber with weakly defined annual layers (birch, maple), defect recognition is difficult. The methods for measuring traction wood are the same as for heeling.

The content of libriform fibers in traction wood increases; they have a smaller diameter, but greater length and significantly thicker walls. The walls of the libriform fibers have a thick gelatinous layer lining the inner surface (from the cavity side). This layer is rich in cellulose and does not become lignified. The total cellulose and ash content is higher, and the lignin and hemicellulose content is lower than that of normal wood.

The density of traction wood is approximately 10-30% higher, shrinkage along the grain is approximately 2 times greater than that of normal wood, but the reduction in shrinkage across the grain is less than that of lurch wood. Compressive strength along the grain is less and tensile strength along the grain and toughness are greater than normal wood.

Internal sapwood

Double core in a pine trunk

Stepson

Dry-sidedness

Types of sprouts: a - open; b - closed

Pine cancer

Pockets

Traction wood makes it difficult to mechanically process lumber, leading to the formation of fleecy and mossy surfaces. The fibers that separate during cutting clog the sinuses of the saws, and the sawing process slows down.

Irregular anatomical formations

False core. This is the name of the dark-colored inner zone of deciduous wood (birch, beech, alder, aspen, maple, hornbeam, linden, etc.). The border of the false nucleus usually does not coincide with the growth rings. It is often separated from the sapwood by a dark, less often light (for example, birch) border.

Distinguish rounded, star-shaped And lobed false kernels, colored dark brown or red-brown, sometimes with a lilac, violet or dark green tint. There is a dark border that divides the core into sections. On longitudinal sections, a wide stripe of one or more of the indicated colors is noticeable.

The causes of the formation of the defect may be age-related tissue differentiation, wound reaction of the tree, exposure to fungi, and the influence of severe frosts.

In round timber, the false kernel is measured by the smallest diameter of the circle into which it can fit; in raw plywood (blocks) the smallest width of the defect-free peripheral zone is measured. In lumber and veneer, the size of the zone occupied by the defect is measured.

False heartwood degrades the appearance of the wood. This zone has reduced permeability, tensile strength along the fibers, and impact strength. The presence of a false core reduces the wood's ability to bend. In birch, the false heartwood cracks easily. In terms of resistance to decay, false heartwood is often superior to sapwood.

Internal sapwood. In the wood of oak, ash (sometimes also in other hardwoods) in the core zone, several adjacent annual layers can form, similar to sapwood in color and other properties. In round assortments, at the ends, among the dark-colored core wood, one or more rings of different widths can be noticeable light color. In lumber, smooth light stripes are visible on radial surfaces or surfaces close to them. On tangential surfaces, the internal sapwood is observed in the form of a more or less wide strip, which wedges out when the annual layers are cut. Internal sapwood is formed as a result of disruption of the normal activity of the cambium, which is caused by frost.

In round assortments they measure outside diameter the rings of the inner sapwood, as well as the width of the ring. In lumber and veneer, the width and length or area of the zone occupied by the defect is measured.

Internal sapwood, like normal sapwood, has significantly less resistance to decay than the core and easily allows liquids to pass through. The shrinkage of internal sapwood is somewhat less than that of heartwood.

Spotting. In the wood of growing deciduous trees, due to wound reactions, exposure to chemical factors, fungi and insects, relatively small dark-colored areas of wood are formed (the color resembles the kernel and core).

Tangential spotting most often found in beech. It is noticeable at the ends in the form of spots elongated along the annual layer with a width approximately equal to the width of the annual layer, and up to 2 cm long, and sometimes more.

On tangential sections, longitudinal wide stripes of brown or gray-brown color are visible, on a radial section - narrow stripes with core rays that stand out sharply against a dark background.

Radial spotting found in deciduous trees (usually birch), usually closer to the central part of the trunk; at the ends of the assortments it is noticeable in the form of small spots of dark brown, brown or dark gray color, which are elongated mainly in the radial direction, i.e., along the medullary rays. On longitudinal sections, spotting is observed in the form of longitudinal stripes, tapering at the ends. It occurs under the influence of fungi and insects, as a result of damage to the bark by birds.

Veins, or core repetitions, are constantly found in the wood of birch, as well as other deciduous species (alder, rowan, etc.). The veins are clearly visible on a radial section in the form of brown lines located at the boundaries of the annual layer. When viewed tangentially, they have a loop-like shape. In the veneer, group veins are distinguished between scattered and crowded, in the form of interlacing strips. Core repeats are microanomalies in the structure of wood caused by various reasons.

In round timber, spotting is not taken into account. In lumber and veneer, the length and width of this defect or the percentage of the corresponding surface area of the assortment is measured. The spotting does not have a significant effect on the mechanical properties of large assortments, but cracking occurs in the veneer in places where there are large spots of radial spotting. A large number of veins can reduce the tensile strength of the veneer.

Core. In round assortments, the presence of a core is inevitable, so it is not considered a defect in them. In sawn products, the depth of the core is measured, counting from the nearest face or edge. The core and adjacent juvenile wood significantly reduce the strength of small-section assortments. In large sawn assortments, the presence of a core is undesirable due to the numerous overgrown knots around it. In addition, assortments cut in such a way that the core appears in them, when drying, as a rule, crack due to the anisotropy of shrinkage. The core rots easily.

Displaced core. The defect is expressed in the eccentric location of the core, which makes it difficult to use round timber; it indicates the presence of reactive wood.

Double core. In assortments cut from a trunk near its division into separate tops, two cores, and sometimes more, can be found. Each core has its own system of annual layers and is surrounded along the periphery of the trunk common system annual layers. The cross-section of the trunk takes an oval shape.

In lumber and veneer, the length of the section with a double core is measured, and in round timber only the presence of this defect is noted. Sawn logs with a double core are more prone to warping and cracking. Sawing and peeling of round logs is difficult and is accompanied by an increase in the amount of waste.

Stepson and eyes. This subgroup includes very large or, conversely, extremely small knots.

Stepson It is a stunted or dead second top of the trunk, which penetrates the assortment at an acute angle to its longitudinal axis over a considerable extent. In round timber, the stepson has the appearance of a highly elongated oval, in sawn products and veneer - stripes or ovals with an independent system of annual layers. The defect is measured by the smallest diameter of its cross-section. The stepson violates the homogeneity of the wood structure, and in lumber products, the integrity, reduces strength, especially during bending and stretching.

Eyes - these are traces of dormant buds that have not developed into shoots, which are found in lumber and veneer. The diameter of the eyes is no more than 5 mm. There are scattered and group ocelli (three or more ocelli at a distance of less than 10 mm from each other). In addition, the veneer contains light, almost no different in color from the surrounding wood, and dark eyes. If there are scattered eyes, their number is determined, and if there are group eyes, the width of the zone they occupy is determined. In small assortments, eyes, especially those located in the stretched zone of the dangerous section, reduce static bending strength and impact strength.

Wounds

Dry-sidedness. This is what is called external unilateral necrosis of the trunk. The deepened area devoid of bark is elongated along the length of the assortment, and has bulges along the edges (Fig. 1). This defect occurs in all breeds; it is formed as a result of peeling, bruising, burns or overheating of the bark of a growing tree. In coniferous species, dryness is accompanied by increased resin content. In the dry side area, a sapwood mushroom color often appears; In this case, core stains and rot are shifted to the outer zones of the wood. In round assortments, the defect is measured by depth, width and length. Dry-sidedness changes the correct shape of round assortments, causes curls and disrupts the integrity of the wood at the places of sagging, reduces the yield of lumber and veneer.

Germination. This is the name given to an overgrown or overgrown wound that contains bark and dead wood. When partially healed, the wound is easily detected on the side surface of the trunk. When completely overgrown, the overgrowth is visible only at the end as a blunt-shaped crack and an internal radial crack filled with bark remnants.

Distinguish sprout open, extending only to the side surface of any size or to the side surface and end, and closed, which is found only on the ends of round timber and sawn products. The open wound is less than 2 cm wide, which makes it possible to distinguish it from a wider wound - dry side.

In sawn products and veneer, among open shoots, there are one-sided ones, going out on one or two adjacent sides of the assortment, and through ones, going out on two opposite sides of the assortment.

In addition, veneer may also contain the following types of sprouts: fused- a trace from a closed growth in the form of an elongated section (seam) of twisted wood; light- growth similar in color to the surrounding wood, and dark- a sprout that contains inclusions of bark or is significantly different in color from the surrounding wood.

In round timber, open and closed shoots are measured by the smallest thickness of the core cut (board) into which it can fit. In lumber, shoots are measured by depth, width, length, and their number in pieces per 1 m of length or on the entire side of the assortment is taken into account; in veneer, they are measured by length and the number in pieces per 1 m2 or on the entire sheet area is taken into account.

Sprouting violates the integrity of the wood and is accompanied by curvature of the annual layers. The degree of influence of sprouts on the quality of wood depends on their variety, size, location, quantity, as well as on the nature of the assortment.

Cancer. This is a wound that occurs on the surface of the trunk of a growing tree as a result of the activity of fungi and bacteria. Cancer can be open (an unhealed wound with a flat or uneven bottom, stepped edges, and nodules at the periphery) or closed (an overgrown wound with abnormal thickening of bark and wood tissue near the affected areas). This defect occurs in deciduous and coniferous trees. In coniferous species it is accompanied by severe gumming and tarring of the wood. Open cancer is measured by the width, length and depth of the wound, closed - by the length and thickness of the swelling.

With this defect, the correct shape of the round assortments is disrupted. Due to changes in the structure and increased resin content of coniferous wood, it is difficult to use assortments for their intended purpose.

Abnormal deposits in wood

Grinded. This is the name given to a section of wood heavily impregnated with resin, which is formed as a result of wounding of coniferous tree trunks. Most often, tarring occurs in pine. On round assortments they are detected by the presence of wounds and the accumulation of resin. Tarred areas are darker than the surrounding normal wood and are translucent in thin pieces.

The defect is measured by the length, width and depth or area of the tarred area. Resined wood has significantly lower water permeability, moisture and water absorption, but greater density and reduced impact strength; According to the data, the heat of combustion of wood impregnated with resin increases (by 30% with a resin content of 45%). Tarred wood has increased resistance to decay, but is poorly finished and glued.

Pocket. This defect, which was previously called a resin pocket, is a cavity inside or between the annual layers, filled with resin or gums. Such resin reservoirs are found in conifers containing resin ducts in the wood, especially often in spruce. At the ends, arcuate cracks are visible - holes, the flat side facing the center of the trunk, and the convex side facing its periphery (Fig. 1). On the tangential surface, the pockets are recesses in the form of an oval, elongated in the longitudinal direction; on a radial section they look like short slits.

In sawn products, there is a one-sided pocket that goes out on one or two adjacent sides of the assortment, and a through pocket that goes out on two opposite sides. The size of pockets in Siberian spruce can vary from a few millimeters to 10-15 cm. Pockets arise as a result of subcrustal damage to the cambium when individual sections of the trunk are heated by sunlight during the frosty period.

Small pockets can also form from damage by insects. To improve the extraction of resin from spruce, you can create pockets artificially by applying special tool large subcrustal damage to the cambium.

Pockets are measured by depth, width and length, and their number in pieces is also taken into account (in lumber - per 1 m of length or for the entire length of the assortment, in veneer - per 1 m2 or for the entire sheet area). Resin leaking from the pockets interferes with finishing and gluing of product parts. In small parts, pockets can significantly reduce the strength of the wood.

Water layer. These are areas of core or mature wood with high humidity in a freshly cut state. The defect occurs in the butt part of the trunk both in coniferous trees (pine, cedar, and especially often in spruce and fir) and in deciduous trees (aspen, elm, poplar, etc.).

At the ends of timber with this defect, dark spots of various shapes are visible, and stripes are noticeable on longitudinal sections. After drying, the stains of the water layer turn pale, and small cracks appear in these areas of the wood. The humidity of pine and spruce in the watershed zone is 3-4 times higher than the humidity of healthy wood (kernel or mature wood).

In round timber, the water layer is measured by the smallest thickness of the core cut (board), by the smallest diameter of the circle into which it can be inscribed, or by the area of the zone occupied by the defect. In sawn products, the width and length or area of the zone occupied by the defect is measured.

The reasons for the formation of the watershed have not been fully established. Some researchers believe that this defect in the wood of elm, poplar, fir and some other species is caused by the activity of bacteria. In a number of works, the occurrence of a watershed is associated with the penetration of rainwater through ungrown knots. One of the scientists suggests the fungal nature of the water layer in aspen, in which mechanical properties decrease by an average of 10% (impact strength drops especially noticeably). Water-layered wood differs from healthy wood by increased shrinkage and swelling. An increase in the hygroscopic limit was noticed. The water layer makes it difficult to impregnate wood with antiseptics. Increased ability to absorb water can cause drowning during rafting. According to research, the formation of a water layer in spruce and pine is associated with oversaturation of the soil with moisture. Significant fragility of the water-layered wood of these species is noted. The presence of cracks in the central zone of the watershed in growing trees and the formation of cracks when cut wood dries reduces the yield of high-quality lumber.

There are two large groups of tree species: coniferous and deciduous. Conifers belong to

Pine - one of the most common and accessible types of wood in Russia. The more common species is Scots pine. The pine tree has a straight trunk, and therefore is comfortable material for construction. Pine, growing in northern forests, is characterized by the greatest straightness of the trunk. Its high abrasiveness also favors the use of pine in construction. Among its other properties, one can note dense and durable wood, a core heavily impregnated with resin, due to which pine wood is less susceptible to rotting. Pine wood is light, which, combined with strength, is very good quality. Early pine wood is yellowish-white (width from 20 to 80 annual layers), sharply different from the reddish-brown core wood. Pine is widely used in the manufacture of various crafts. Pine has properties that should be paid attention to by those who are going to work with it, and especially by those who are going to engage in wood carving. Pine wood is very scratchy and, in addition, has a fairly pronounced striped texture. These two properties of pine significantly limit its use in carved crafts: it is best used when making large elements. As a rule, pine cuts and saws well, especially if the pine has little resin. However, you need to remember that as it dries, its causticity increases and it becomes more difficult to cut. Since pine wood is heterogeneous (pine tree rings are separated from each other by wood with resin ducts), it is poorly suited for making small items and crafts. It is better to use pine in large carvings with large patterns, for example, in house carvings.

Spruce - for the most part its characteristics resemble pine. It is also one of the most common and accessible breeds. However, spruce wood is lighter and has more knots. The knots are located at right angles, and therefore have a round shape in a tangential section. Knots are sometimes so hard that you can break a tool on them. It contains less resin, as a result of which the spruce rots faster. Due to its knotty nature, spruce wood is much more difficult to process. In addition, the following can be noted distinctive features spruce wood: compared to pine, spruce darkens more slowly, although its final tone does not differ from that of pine. Freshly planed spruce wood is slightly lighter than pine wood. Unlike pine wood, late wood of spruce has the appearance of a light brown stripe, which gradually turns into yellowish early wood. Spruce growing in the north is better in quality than spruce growing in the south. The same can be said about pine. The growths on spruce trees are very beautiful, but they are very rare.

In our forests you can find two species cedar: Siberian cedar and Korean cedar. In terms of its characteristics, cedar is somewhat inferior to pine. However, from the point of view of resistance, against rotting and cracking, cedar turns out to be a more advantageous species. Cedar lends itself well to processing. Cedar wood has a pinkish tint. Late wood is yellowish-pink in color, transitions into early wood gradually, without a sharp contrast. Tree rings vary across all sections. Cedar has a very beautiful texture. It is used in carved sculpture and in the manufacture of other carved and turned products.

Wood larches
has high physical and mechanical properties. Its strength is about a third greater than that of pine. Because of this, it is an indispensable material in construction. Larch floors can last for many years, and it is difficult to find wood that is superior to larch. In addition, larch is little susceptible to rotting. Larch is also used in furniture production because it has a fairly beautiful texture. Larch wood has a brownish tint. The sapwood is narrow, approximately 15-20 annual layers wide. The kernel is more different dark color; the transition to sapwood is abrupt. The larch texture looks good after varnishing. Veneer is often made from it for finishing furniture. Larch wood is processed very well and is ideally suited for the manufacture of long products.

WOOD DEFECTS

Wood defects are those damages that entail changes in its appearance, tissue integrity, correctness of its structure and, as a consequence, deterioration in its quality and reduction in the possibilities of its use. Mechanical damage to wood is called defects.

However, a lot depends on the intentions of the person working with the tree. If we are not talking about carpentry and carpentry, but, for example, about carving, you need to remember that a defect in wood can turn into an advantageous property that a carver who approaches his work creatively can take advantage of.

Bitches are the most common wood defect. The disadvantages of knotty wood are the following: the appearance deteriorates, mechanical processing becomes difficult, and strength decreases (when stretched along the fibers and bending). The degree of knotiness of wood must be taken into account when performing joinery and carpentry work. In addition to healthy knots, there may also be rotten knots on the wood. Depending on the degree of decay, such knots are divided into rotten (rot has affected less than 1/3 of the knot), rotten (rot has affected at least 1/3 of the knot) and tobacco (rotten wood has been partially or completely replaced by a loose brown or whitish mass). It must be taken into account that rotten knots not only reduce the strength of the wood, but can also cause gradual rotting of the entire wooden piece.

Depending on the shape, quantity, size and causes of occurrence, several types are distinguished cracks Methic is internal longitudinal cracks extending from the core. Such cracks appear in the tree when it has not yet been cut down, and after cutting, as it dries, they increase in size.

Cracks:

methic

thrashing

shrinkage cracks

Frost cracks (frost cracks) also appear in a growing tree, as can be judged by the specific growths of wood and bark. Such cracks can run through the entire assortment. This must be taken into account, since the ends of the crack can be located in different planes, and therefore, the crack itself can be curved, “not flat”.

Crack cracks are called cracks that form between the annual layers. These cracks also occur in the growing tree and increase during the drying process.

Shrinkage cracks are cracks that appear in an already cut tree as it dries out. Their appearance is caused by stresses inside the wood. Shrinkage cracks are somewhat smaller in size than the cracks listed above, however, they can reach a length of one meter.

Among trunk shape defects It should be noted the convexity, growths and curvature.
Taperedness is a decrease in the diameter of the trunk towards its top or upper cut, exceeding 1 cm per 1 running line. m. Curing increases the amount of waste when processing lumber and reduces their strength. The latter occurs because when sawing materials along the fibers, the integrity of a significant part of them is violated.

A growth is a thickening of the trunk with twisted wood. Build-up occurs on all types of wood, but is most common on hardwood. Wood processing becomes more complicated due to growths. However, the growths have a very beautiful texture, and therefore can be used in finishing furniture and artistic products, primarily as veneer. The growths of elm, walnut and elm are of the greatest value.

Curvature is the curvature of the tree along its axis. The curvature of round timber increases the amount of waste during processing, and also leads to the appearance of radial inclination of the fibers in lumber and veneer.

Wood structural defects, as a rule, also complicate processing and make the wood practically unsuitable for carpentry. At the same time, structural defects in wood have a certain decorative value. In other words, we are again faced with the same situation: a disadvantage, depending on the type of work and its goals, can often turn out to be positive quality. This should never be forgotten, especially for those who want to become an all-rounder.

We will focus on such defects as curling, bending of fibers, curl, resin pocket. There are other vices; We refer those who want to learn more about them to specialized literature, especially since they are of purely special interest, and knowledge about them can hardly be useful to a carpenter or woodcarver.

Defects in the structure of the trunk:

Fiber inclination;

Kren

Curling is a tortuous or random arrangement of wood fibers, which reduces the strength of wood during bending, compression and tension. " " -

The inclination of the fibers is a non-parallel arrangement of wood fibers relative to its axis. With the so-called tangential inclination of the fibers, the resin ducts, core rays, as well as cracks in the wood appear to be twisted and do not run strictly along the log. The tangential inclination of the fibers causes increased shrinkage and warping of wood.

A curl is a local curvature of the annual layers, usually caused by the presence of knots.

The resin pocket is a resin-filled cavity inside the annual layer. This wood defect is found in coniferous species, most often in spruce. It negatively affects the appearance of wood, its strength, gluing ability, and also interferes with its facial finishing.

At fungal infection of wood it begins to rot or changes color. It should be noted that not all fungal infections are very dangerous for wood. Thus, there are fungal infections that only change the color of the wood; they do not affect the mechanical properties of wood, but spoil its appearance and increase water permeability, and can also destroy adhesives and varnishes. Consequently, a number of fungal infections pose a danger primarily to the appearance of wood and products made from it. However, in a significant number of cases, a change in color indicates the beginning of decay. Wood affected by rot is not suitable for use.

The fungus can affect both a growing tree and felled wood.
It must be remembered that wood affected by fungus is a dangerous source of infection. Therefore, it is recommended to carefully inspect the wood before storing it.

Danger insect damage to wood It mainly threatens freshly cut wood. However, insects can also damage dry wood in products.

Defects of wood. Defects are violations of the correct structure of wood and natural damage in the conditions of its growth, storage and operation. Defects disrupt the uniformity and integrity of lumber, reduce the strength of wood, increase its warping and cracking, complicate mechanical processing of wood, increase the amount of waste, and worsen the appearance of products.

Bitches there are open and overgrown (depending on whether they extend onto the side surface of the round assortment or not); round, oval, oblong (depending on the cross-sectional shape on the surface of the assortment) (Fig. 3.10); seam, edge, edge, end, stitched (depending on the position in the assortment); scattered, grouped, branched (depending on the relative location); fused, partially fused, unfused, falling out (depending on the degree of fusion with the wood); healthy (light and dark), healthy with cracks, rotten, rotten, tobacco (depending on the condition of the wood of the knot: tobacco knots indicate the presence of heart rot in the wood, since in round timber the rot can be hidden and not extend to the ends); one-sided and through (depending on whether they intersect through the flat assortment or not).

Cracks(Fig. 3.11) there are metic (radial cracks directed from the center to the periphery of the trunk), simple and complex metic (depending on whether traces of the crack remain at the ends of the assortment in the same plane or not); frosty (radial cracks directed from the periphery to the center of the trunk), accompanied by the formation of characteristic growths on the trunk; shrinkage cracks (radial cracks that appear during the drying process), differing from metic and frost cracks in their shorter length and depth; peeling (arc-shaped or annular cracks between the annual layers).

Convergence- narrowing of the trunk exceeding 1 cm per 1 m of length.

Zakomelistost- a sharp increase in the diameter of the butt part of the trunk; It can be round and ribbed.

Growth- sharp local thickening of the trunk.

Curvature the trunk can be simple and complex.

Kren- apparent thickening of late wood of coniferous species in the compressed zone of the trunk, curved or inclined tree. The similarity between heelwood and latewood is purely external, since heelwood has a completely different anatomical structure. There is a local roll, which affects one or several annual layers, and a continuous roll, which covers half or more of the cross-sectional area of the trunk.

Fiber inclination - non-parallelism of the fibers of the longitudinal axis of the assortment .

Curly - twisted or random arrangement of wood grains . There is a wavy and tangled curl.

Double core- presence of two cores in the assortment .

Resin pocket - a cavity inside the annual layer filled with resin.

Germination - overgrown deadness of a section of the trunk. There are open and closed sprouts.

Chemical stains arise in felled wood as a result of chemical and biochemical processes associated in most cases with the oxidation of tannins. Chemical colors are uniform in color and are usually located in the surface layers of wood with a thickness of 1...5 mm). As the wood dries, they often fade to a greater or lesser extent. The chemical colors include the following: produbina - reddish-brown or brown color of the subbark layers of driftwood of species whose bark is rich in tannins (spruce, oak, willow, etc.); tanning drips - brown spots in the form of streaks on the surface of assorted species whose wood is rich in tannins; yellowness - a light yellow color of the sapwood of driftwood of coniferous species that occurs during drying. Chemical stains do not affect the physical and mechanical properties of wood, but intense colors spoil the appearance of products.

Mushroom sound spots and streaks - areas of abnormal coloration of the core (real, false and mature wood) without reducing the hardness of the wood, which appear in a growing tree under the influence of wood-destroying fungi (the first stage of damage). They do not significantly affect the mechanical properties of wood, but they spoil the appearance and increase the water permeability of wood.

Core rot- areas of abnormal coloration of the core (real, false and mature wood) with reduced wood hardness, which appear in a growing tree under the influence of wood-destroying fungi (second stage of damage). Heart rot significantly deteriorates the quality of wood up to its complete technical unsuitability.

Mold- mycelium and fruiting of mold fungi, which most often appear on damp sapwood during timber storage. Mold appears as a surface coating of blue, green, black, pink or other colors. Mold does not affect the mechanical properties of wood, but deteriorates its appearance.

Sapwood mushroom stains - abnormal coloring of sapwood without reducing its hardness. This defect occurs in felled wood under the influence of wood-staining fungi that do not cause the formation of rot. Therefore, the mechanical properties of wood do not deteriorate, but its appearance deteriorates and water permeability increases.

Browning- brown color of sapwood of different shades, varying intensity and uniformity. Browning occurs in felled wood as a result of the development of biochemical processes and causes a slight decrease in the strength of the wood.

Sapwood rot - abnormally colored areas of sapwood without or with a decrease in wood hardness. Sapwood rot occurs in dead, dead and felled wood under the influence of wood-destroying fungi and spreads deep into the wood from the ends and side surfaces.

External rotten rot - areas of abnormal color, structure and hardness of wood that appear in timber when they are long-term storage under the influence of strong wood-decaying fungi. External rotten rot is characterized by a brown color of various shades and a fissured prismatic structure. Affected wood easily falls apart and is ground into powder. Affected wood is a dangerous source of fungal infection for various wooden structures.

Wormhole - passages and holes made in wood by insects. If the wormhole comes out on two opposite sides of the assortment, then it is called through.

Wood defects. Mechanical damage of artificial origin is called defects. Wood defects include foreign inclusions (stones, sand, wire, nails, metal fragments, etc.); mechanical damage by tools and mechanisms during its harvesting, tapping, transportation, sorting and processing (bark peeling, hacking and sawing, punishment, flake, chipping and tearing, gaff punctures); charring; cut bevel - non-perpendicularity of the end of the longitudinal axis of the assortment; wane - a section of the side surface of the trunk preserved on edged lumber (Fig. 3.16); zakorina - a section of bark preserved on the surface of the veneer; cutting defects are risks (traces of teeth of saws, knives, etc.), waviness (non-flat cut), hairiness and mossiness (tearing of individual fibers), veneer ripples (different levels of wood fibers), burrs and gouges, fringe (tufts of incompletely separated fibers on the ribs of the assortments), burn (from friction with a cutting tool); warping - curvature of lumber products during sawing, drying or storage.

A tree, like any living organism, is subject to many factors that influence its development, including negative ones that can cause various deviations that reduce the quality of industrial wood. The standard defines several main groups of developmental defects.

Bitches- the most common of visible defects, they have a large number of shapes, sizes, types, can be alive or dead, rotten and with great floridity.
Convexity, roughness, growths, curvature from the vertical axis, etc.
Cracks. These can be frost cracks, sprouting, etc., shrinkage cracks, tilting and resin pockets.
Diseases. Defects caused by fungi, diseases and damage by insect pests.
Processing defects.

Now it’s worth looking at them in more detail in order to be able to distinguish them, in order to understand exactly how to buy lumber and how to select it. Based on the assigned tasks, which defects are insignificant and which are categorically unacceptable.

Choosing edged lumber for the construction of a wooden house, rafter system pitched roof and other building structures and structures, you need to understand that any lumber, including softwood, will have its own characteristics.

Wood defects are diseases, damage or deficiencies in the development of a tree caused by natural processes and phenomena. The grade of lumber largely depends on the number of defects. The quality of wood is determined by the provisions of the current standard GOST 8486-86. Let us tell you right away that determining the grade is a rather arbitrary event - for example, among 20 second-grade boards , always, with a careful check of the parameters, you can find several boards of the first grade and several boards of the third grade, if only you have the desire and knowledge. This article is written for those who want to deepen their knowledge.

The main objective of this article is to determine the defects of coniferous wood and study their effect on the quality of lumber used for construction. We will do this work based on many years of practical experience and taking into account GOST 2140-81.

Bitches

Healthy branch

A knot is the place where branches grow from the trunk; they have many varieties in appearance and physical characteristics.

Healthy bitch. It has almost no negative impact on the quality of wood and is light in color. Can only be taken into account to determine the highest quality of lumber.
fused knot. The strongest, the annual rings of the knot are fused with the wood along at least 3/4 of the circumference.
Group. Several nearby individual knots, healthy ones, usually have a small diameter.
Rotten bitch negatively affects the properties of wood; a large number of such defects can lead to complete rejection of lumber.

Depending on their location in lumber, knots can be edge, edge, end and face. The lengths are one-sided (visible only on one side of the lumber) and through (visible on both sides).

Knot-free lumber is the exception rather than the rule. Yes, there is lumber of the "Extra" grade, which has no knots, but its cost is very high, and its use is only possible for some finishing works. Let's divide all the knots into two types - healthy knots, which will not affect physical properties wood, and its use will not in any way affect the quality of the structure or construction. And knots with defects - rotten, tobacco, rib, oblong, stitched and group, which significantly reduce the mechanical properties of lumber, especially if such defects are located along the wood fibers or at their bend.

Thus, you should not use lumber with the indicated knots (photos 2 and 3) for load-bearing structures and support beams, as they can simply break in these places, but you should not be upset or throw away lumber with such defects either. Lumber with this type of defect can be used in those areas of construction where short parts are needed, cutting out a healthy area.

Caused by unfavorable climatic conditions for wood growth or landscape features. The trunk may bend, have visible developmental disorders, etc.

Zakomelistost. At the base, the trunk has a sharply increased diameter, the structure of the fibers in this place is disrupted, they are arranged tortuously. The nozzle area is rarely used for the production of high-grade lumber.
Growths. They can occur at different heights, are most often caused by cancer, and may be a consequence of improper development of individual branches.
Convergence. The tree has a large taper; even with a slight change in length, the diameter of the trunk decreases sharply. Curing significantly reduces the yield of industrial wood. The defect associated with a non-standard trunk shape is mainly a problem for the lumber manufacturer, as it reduces the amount of commercial wood and, accordingly, profits. Of course, such a defect also affects the properties of lumber, since as a result of the non-standard shape of the trunk, such wood features as list.
Kren- this is an uneven inclination of the fibers, usually with a displaced center and curvature of the lines of the annual rings. It is best to look at the code rings at the end of the beam or board. Heeling is a wood defect that will affect the lumber during drying, making it uneven, increasing the risk of warping and cracking. To minimize this effect of heeling, we recommend using atmospheric drying technology. Klin can also affect the impregnation of lumber when painting it, making it uneven due to the different density of annual rings. Kink is a common wood defect that can become a problem when working with wood products, such as furniture, windows, doors and some load-bearing elements. frame structure. It is impossible to eliminate this defect, just like a knot. Minimize the negative impact - perhaps by using the above atmospheric drying technology or purchasing lumber chamber drying. Lumber that has undergone a drying process in a natural way or after drying, it will take its natural shape and will no longer be subject to deformation and cracking.

Cracks and growth

Frosty cracks are caused by unfavorable climatic conditions - the sudden onset of winter and severe frosts.
Crack- a visible defect in lumber associated with rupture of fibers. The decision to use lumber with cracks is made on an individual basis, based on the characteristics bearing loads design and the extent or depth of the crack itself.
Pocket- this is the space between the layers of annual rings, filled with resin. Lumber with such a visible defect will release resin and may spoil the appearance of the product.
Peeling cracks. They are located near the growth rings. They can be in a living tree or in dead wood.
Methic cracks. They have a radial direction, most often appear in dead wood, but can also occur in growing trees.
Germination or porosity- a wound on a wood trunk that is overgrown and has remains of living or dead bark. As a rule, it is enough to cut off the damaged area and use the remaining healthy part of the lumber.
- the central part of the barrel, products with such a defect are susceptible to cracking.

Defects from pests and fungi, types of rot

Quite common defects can lead not only to defects in appearance, but also to significantly reduce the quality of lumber and their structural properties. Often such defects are presented by sellers as “minor”.

Fungal infection. As a result of the development of various fungal formations, the color of the wood changes, but the hardness indicators remain the same as in healthy, unpainted wood. Fungal infections do not disturb the structure of the wood, but only change its color. Fungal spots may appear as long stripes of varying sizes or spots irregular shape. It develops only in living trees; when the lumber is dried, the development of the defect stops. Treatment with antiseptic solutions will also stop the development of fungal growths and can lighten the surface of the lumber before the original color.
. A very unpleasant defect, lumber with wormholes or wormholes is not suitable for making furniture, flooring, load-bearing structures of attic floors, etc. It can be superficial - only the space between the bark and the tree trunk is damaged. This type of damage is not considered critical. And it also happens internally - pest passages are located throughout the entire volume of the tree. It is better not to use lumber damaged by bark beetles and other insects, as the pests can spread and attack healthy wood.
- This is a damage to wood that directly affects the hardness of the lumber. Rot is usually accompanied by a change in color or staining of the wood. Rot can be external and internal, soft and hard. It is better not to use lumber with rot in the construction of load-bearing structures due to low strength indicators.
and fungal infections negatively affect the appearance of lumber. The use of such products is possible after careful treatment with antiseptics or bleaches and complete drying to 12-14% humidity. It would also be a good idea to use such lumber in well-ventilated areas. When purchasing such lumber, it is possible to significantly reduce its cost by bargaining with the seller.

Processing defects

Processing defects occur on lumber as a result of mechanical stress during sawing of a tree trunk. In other words, such defects are man-made and they are visible; the occurrence of such defects is possible when using old equipment and violations of production technology. Such lumber can be used selectively, since the physical and mechanical properties of wood remain the same as those of lumber according to GOST.

We list the most common processing defects:

- this is a processing defect that does not in any way affect the strength of the structure constructed from it, and the use of such lumber in general construction work will not cause any significant harm.
- wood defect associated with a violation of production technology. Lumber with such a defect can be used selectively, for example, it is suitable for the construction of temporary structures and sheds, as well as scaffolding.
- bark on the end of lumber is the most common type of deviation from grade 1 standards, but at the same time does not in any way affect the quality of lumber used for private house construction. This feature may be important for manufacturers of furniture, windows or doors. If your batch of grade 1 lumber contains boards with a small amount of wane, there is nothing to worry about.

Hidden wood defects

There are also such, it is impossible to determine them before cutting. There are cases when, during sawing, the edged board of a completely healthy blade begins to warp for unknown reasons, the saws become clamped, linear dimensions the boards are broken. It can bend in different directions and take on the shape of a “propeller”. In some cases, long through cracks appear. The reason for this phenomenon is very large internal stresses in the tree caused by various external or internal factors, such as traction wood. Unfortunately, it is impossible to correct any defects in lumber that have arisen; they should be discarded or boards that are not short in length should be cut. Most often, hardwood trees are susceptible to these shortcomings: hornbeam, beech, dut, etc.

Other wood damage

They are not regulated by standards - they are quite rare and have almost no significant effect, but among them there are also very unpleasant ones for sawmills. If the wood was harvested in hunting grounds or in combat areas during World War II, then the wood contains bullets, fragments and shot, nails and ingrown wire. Metal objects saws are damaged; modern high-speed band sawmills are especially afraid of such metal inclusions.

Wood defects are violations of the external shape of the tree trunk, deviations of the structure from normal, as well as internal and external damage that reduces the quality. They are formed during the period of tree growth, during storage and operation. Some types of defects are easily detected by external inspection of the tree. However, most wood defects can be identified only after felling the tree, and sometimes cutting it. The grade of wood depends on the type, nature and size of defects, which sometimes make it completely unsuitable for use.

A complete description of wood defects is given in GOST 2140-81.

In accordance with GOST 2140-81, all defects are divided into nine groups: 1) knots; 2) cracks; 3) defects in the shape of the trunk; 4) structural defects of wood; 5) chemical stains; 6) fungal infections; 7) biological damage; 8) foreign inclusions, mechanical damage and processing defects; 9) warping.

Knots are the most common wood defect, inherent in almost all tree species. They disrupt the homogeneity of the wood structure, complicate mechanical processing and reduce its strength characteristics. The degree of weakening of wood by branches depends on the number of knots, their location, size and connection with the wood of the trunk. Based on the condition of the wood of the knot itself and the degree of its fusion with the wood of the trunk, the following types are distinguished: solid fused, partially fused, solid and non-fused.

An intergrown solid knot has annual layers that are integral with the surrounding wood along the entire length and perimeter of the knot. Fused hard knots are healthy, horny and colored. A healthy knot without signs of rot usually has a slightly darker color than the wood; The horny knot has healthy, rot-free wood and, due to the presence of resinous and tannins in it, is darker in color than the surrounding wood. A painted knot is different in that, being surrounded by healthy wood, it is itself in the initial stages of decay.

A partially fused hard knot is formed as a result of the death of a branch during the life of the tree, when the broken area is partially overgrown with wood, but does not completely grow together with it.

An unfused knot forms holes or rot in the wood, reducing the strength properties of the wood. Unfused knots are falling out, hard, loose and tobacco.

Dropout solids are found in lumber and plywood. They do not have a reliable connection with the surrounding wood and when dry they easily fall out (Fig...

A loose knot is located in the thickness of healthy wood, but it itself undergoes rotting to such an extent that its wood completely or partially loses its original structure.

Tobacco knot - decomposed from rotting and turned into a brown-motley mass; When ground, it easily turns into powder.

According to the shape of the cut on the surface, the assortment of knots is divided into round-oval, stitched (Fig. and clawed (Fig....

For wooden load-bearing structures, wood with only healthy fused knots is allowed. For critical structures made of wood, there should be no knots that are in the stage of decay.

Cracks are formed due to uneven drying of wood, its heterogeneous structure, as well as from various external causes during the life of the tree (frost, strong winds, etc.). They reduce the grade of wood, reduce its mechanical properties and promote decay.

There are cracks in a growing tree (metic, frostbite, frost cracks) and cracks formed in a felled tree - shrinkage cracks.

Metik is an internal longitudinal crack or several cracks passing through the core of the trunk, but not reaching the surface and gradually narrowing from the butt to the top. Methic is most often formed from the swaying of a tree by the wind (Fig...

The shoot is an internal crack running along the annual layer for some distance along the tree trunk. On the end section of the trunk, the peel is usually observed in the form of arcuate cracks. A distinction is made between partial, when the crack occupies part of the annual layer, and complete (ring), if the crack is located around the entire annual layer.

The shock is formed due to severe drying out of the central part of the tree trunk and under the influence of frost (Fig...

Frost crack is a longitudinal crack that is wider on the outer part of the trunk and gradually narrows towards the core.

Frostbite is formed due to uneven compression of wood during strong and sudden cooling of the tree. It can be open (Fig. and closed (Fig...

Defects in the shape of the trunk. Curvature - curvature of the trunk during tree growth in one or more places. Curvature is called one-sided if the curvature of the trunk is directed in one direction, and multilateral when the curvature is directed in different directions.

Tapering is characterized by an increase in the thickness of the log along the axis that exceeds the norm. Lumber from tanned logs is obtained with cut fibers and lower mechanical properties.

Zakomelistost - a sharp thickening of the trunk at the butt (lower) part.

Royka - external longitudinal depressions at the butt part of the trunk. This defect, caused by the growing conditions of the tree depending on the depth and extent of the swarm, can reduce the grade of the logs.

Defects in the structure of wood. The inclination of the fibers is the non-parallelism of the wood fibers (Fig. the longitudinal axis of products (logs, boards, beams, etc.). The inclination increases the strength of wood when splitting, but complicates its mechanical processing and reduces the tensile and bending strength of lumber due to cutting the wood fibers.

Kren - abnormal thickening of late wood in annual layers; characteristic of inclined and crooked trees.

Curling is a wavy or random arrangement of wood fibers, more often found in deciduous trees, mainly in the butt part of the trunk.

Curl is a local sharp curvature of the annual layers under the influence of knots and shoots.

The pith is the narrow central part of the trunk, consisting of loose woody tissue; getting into wooden products, it increases their cracking.

Double core in the form of two cores with independent systems annual layers increases waste during wood processing and increases its cracking.

Stepson - a dead second top or thick branch piercing the trunk at an acute angle to its longitudinal axis. Deteriorates the uniformity and mechanical properties of wood.

Wetlands are areas of core or mature wood that are abnormally dark in color and appear in the growing

tree due to high humidity these areas. This defect often causes cracking and rotting of wood and reduces bending strength.

A sprout, in the form of a woody area of the trunk surface with dead tissue and a radial crack extending from it, occurs in a growing tree when damage heals.

Cancer is a wound that appears on the surface of the trunk of a growing tree due to the activity of fungi and bacteria.

Dry bone occurs in places of damage (cut, burn, bruise, etc.) and is a dead section of the trunk.

Resin - a section of wood heavily impregnated with resin; characteristic only of coniferous species. It reduces impact strength and water permeability, making finishing - varnishing, painting - difficult.

A resin pocket in the form of a cavity filled with resin is found in conifers, most often in spruce. Prevents face finishing and wood gluing.

Some defects (for example, spotting, internal sapwood, etc.) do not have a significant effect on the mechanical properties of wood.

Wood defects and their impact on quality

Vices wood refers to changes in its appearance, violation of the integrity of tissues and cell membranes, the correctness of its structure and damage, reducing the quality of wood and limiting the possibilities of its use.

Defects- wood defects of mechanical origin that arise in it during the process of harvesting, transportation, sorting and mechanical processing.

The effect of a defect on the quality of wood depends on its type, size, location in the material and purpose of the material. It reduces the strength and decorative properties of timber, so the grade of wood is determined with mandatory consideration of the defects present in it.

According to GOST 2140-81 “Defects of wood. Classification, terms and definitions" all defects are divided into groups: knots, cracks, fungal damage, chemical stains, defects in the shape of the trunk and wood structure, insect damage, foreign inclusions and processing defects.

Bitches- the most common and inevitable defect of wood, which are the bases of the branches enclosed in the wood of the trunk. Depending on the degree of overgrowth, knots can be open or overgrown.

Open knots are classified:

according to the shape of the cut on the surface of the assortment - round, oval and oblong; knots according to this characteristic are determined by the ratio of the larger diameter to the smaller one; if this ratio is not more than two, the knot is called round, and if it is in the range from two to four, it is called oval; when the ratio of two diameters is more than four - oblong;

by position in the assortment - sheet, edge, rib, end and stitched; face knots go to the wide side of the assortment (face), edge knots - to the narrow side (edge), rib knots - to the edge, end knots - to the end, stitched - simultaneously to two edges of the same side;

by relative position - scattered, grouped, branched; scattered knots are those located singly and spaced from each other at a distance exceeding the width of the assortment; for wide assortments (width more than 150 mm), the distance between the knots must be at least 150 mm; branched knots are formed when there are two or more knots emerging from one whorl, and are more often characteristic of coniferous species; group knots include two or more knots, regardless of their shape, on a segment of the length of the assortment equal to its width;

according to the degree of fusion with the surrounding wood of the trunk - fused, partially fused, unfused and falling out non-fused; A knot in which the annual layers have not fused with the surrounding wood for less than 1/4 of its perimeter is considered to be fused; in partially fused knots, the annual layers have not fused for more than 1/4, but less than 3/4; in unfused knots, the unfused part is more than 3/4 of the perimeter of the knot; a knot that does not have fusion of the annual layers with the surrounding wood and can fall out when dry is called a falling out;

according to the condition of the wood - healthy, light healthy, dark healthy, healthy with cracks, rotten, rotten, tobacco; a knot that has wood without signs of rot is called healthy; a knot whose wood is light and similar in color To surrounding wood is called healthy light, and a knot whose wood is much darker than the surrounding wood and is richly impregnated with resin is called healthy dark; rotten and rotten are called knots in which the area affected by rot occupies, respectively, less and more than 1/3 of the area of the knot's size; if the wood has completely rotted and turned into a brown mass that easily discolors when pressed, such a knot is called a tobacco knot;

at the exit to the surface - one-sided and through; one-sided knots extend onto one or two adjacent sides of the assortment, through ones - onto two opposite sides of the assortment.

The number of knots, sizes and their location largely depend on the type of tree, part of the trunk and growing conditions. The trunks of light-loving species (pine) have fewer knots than the trunks of spruce. Trees grown in freedom are cleared of knots to a lesser extent and much later in time than trees grown in closed stands. There are fewer knots in the lower (butt) part of the trunk than in the top part.

Knots worsen the appearance of wood, disrupt the uniformity of structure and sometimes integrity, cause bending of fibers and annual layers, and complicate mechanical processing. Knots, especially edge, oblong, stitched and group knots, reduce the strength of wood when stretched along the grain and in bending. Tobacco knots indicate the presence of hidden internal rot in the wood. The second most important wood defect is cracks. They are divided into metic, frost, shrinkage and peeling cracks. They appear in a growing tree and increase in size in felled wood as it dries. All types of cracks violate the integrity of timber and in some cases reduce their mechanical strength.

Methic cracks- radially directed cracks in the core, extending from the core, not reaching the bark and having a significant extent along the length of the assortment. The length of a meticulous crack can be more than 10 m. Depending on the location, round assortments are divided into simple and complex. A simple meticulous crack is one or two cracks directed along the same diameter and running in the same plane along the length of the assortment. Two or more cracks located at the end at an angle to each other, as well as one or two cracks directed along the same diameter, but located along the length of the assortment in different planes - this is a complex metic crack.

Scratch crack - a crack between the annual layers that occurs in the heartwood or mature wood. They are formed in a growing tree, have a short length along the height of the trunk and are not visible from the outside.

frost crack- external longitudinal sections of wood from trunks of growing trees. It spreads deep into the trunk in radial directions (usually in the butt part).

Trunk shape defects are expressed in various deviations from the normal shape of the trunk and are formed during the period of tree growth. These include convexity, rumpiness, growths, curvature, and ovality.

Convergence represents a gradual decrease in the thickness of timber or the width of unedged lumber throughout its entire length. If for every meter of trunk height (assortment length) the diameter decreases by more than 1 cm, this phenomenon is regarded as a defect. Coniferous tree trunks are less shaggy than deciduous trees.

Zakomelistost- a sharp increase in the diameter of the butt part of timber and the width of lumber. Roughness and roughness make it difficult to use timber for its intended purpose, increase the amount of waste when sawing and peeling, cutting lumber, and cause the appearance of a radial inclination of the fibers.

Growths and curvature often found on all species, especially deciduous trees, make it difficult to use timber for its intended purpose and complicate their processing. Growths are local thickenings of the trunk, sometimes with smooth surface and the correct structure of the wood, as well as with an uneven surface and twisted

structure of wood, which are called burls. Curvature is the curvature of the trunk along its length. A distinction is made between simple and complex curvature, which is characterized by one or more assortment bends, respectively.

To the vices The structure of wood includes the inclination of the fibers, heel, curl, etc.

Fiber inclination(cross-layer) - deviation of the fibers from the longitudinal axis of the assortment, leads to increased shrinkage and warping. The slope of the fibers makes it difficult to mechanically process wood, reduces the ability to bend, as well as the strength of lumber when stretched along the grain and in bending.

Kren- local change in the structure of coniferous wood. It is expressed in an apparent increase in the width of the late zone of annual layers. Formed in the compressed zone of curved or inclined trunks. Kren increases the hardness of wood and its strength in compression and static bending; reduces tensile strength; increases shrinkage along the fibers, causing cracking and longitudinal warping of lumber; reduces water absorption of wood and this makes it difficult to impregnate it, and also worsens its appearance.

Traction wood observed at the ends in the form of arcuate sections, on radial surfaces - in the form of narrow stripes (strands). It increases the tensile strength of wood in tension along the fibers and static bending, increases shrinkage in all directions, especially along the fibers, which contributes to the appearance of warping and cracks, complicates processing, leading to the formation of hairiness and mossy surfaces.

Curlyness- curvature of fibers. Reduces the tensile, compressive and bending strength of wood, increases strength when splitting and chipping in the longitudinal direction, and makes it difficult to mill wood.

Curl occurs in the form of partially cut, bracket-like curved contours formed by curved annual layers. There are one-sided and end-to-end curls. Reduces the compressive and tensile strength of wood along the grain, as well as the flexural strength. The strength of the material decreases noticeably when the curls are located in the stretched zone of the dangerous section. Resin pocket found in coniferous wood; can be one-sided or through, reduces the strength of wood. Resin leaking from the resin pockets spoils the surface of the products and interferes with their front finishing and gluing.

Sprouting- partially or completely overgrown bark on the trunk or dead wood as a result of damage; occurs in a growing tree when damage caused to it heals and is accompanied by the development of tar, fungal core spots and stripes of core rot. Violates the integrity of the wood and is accompanied by curvature of the adjacent annual layers. Germination can be open or closed.

Grinding- found in wood only from coniferous species. It does not significantly affect the mechanical properties, but significantly reduces the flexural toughness, reduces water permeability, and makes facial finishing and gluing difficult.

False core- dark-colored inner part of the trunk of deciduous non-core species. The cross-sectional shape can be round, star-shaped or lobed. This defect spoils the appearance, is characterized by poor permeability, reduced tensile strength along the fibers and fragility. In birch, the false heartwood cracks easily.

Water layer- occurs in the form of wet, dark spots of various shapes and sizes, causes cracking, reduces impact strength and is accompanied by rot.

Chemical stains in most cases, it is a consequence of the oxidation of tannins contained in wood. These include: dents, tanning streaks, yellowness, which do not affect the physical and mechanical properties of wood, but with intense coloring they worsen the appearance of the materials.

Fungal lesions in wood arise from the development of fungi in it, which are divided into wood-staining and wood-destroying.

Mushrooms are among the simplest organisms that reproduce by spores and vegetatively. Growing trees and felled wood become infected with spores - tiny microorganisms that have high viability and adapt well to unfavorable conditions. Spores are carried by wind or water over considerable distances and, entering the tree trunk through cracks and wounds, begin to develop.

Fungi develop on wood at a certain humidity (optimal - 40-60%) and temperature (optimal - 20-30 ° C).

Under favorable conditions, spores germinate and form hyphae (thin threads), which intertwine with each other and form the mycelium of the fungus or mycelium. Hyphae that penetrate the wood secrete enzymes, the latter convert cellulose and lignin into substances that dissolve in water and are absorbed by the fungus.

Based on the nature of their nutrition and the degree of destruction of wood, mushrooms are divided into two types. In the first case, fungi feed on lignin or cellulose, which leads to the destruction of the cell wall, and therefore the entire wood. Fungi that cause such changes in wood are called wood destroyers. In the second case, the color of the wood changes and only partially its physical and mechanical properties. These mushrooms are called wood staining.

The mechanical properties of wood affected by rot sharply deteriorate, and the ability to resist stress is completely lost. The density of such wood is reduced by 2-2.5 times, water permeability increases. Rotten wood warps sharply when it dries.

Wood-staining fungi feed on reserve organic substances (proteins, fats, carbohydrates) that accumulate in the cavities of wood cells. The optimal temperature at which the development of a common wood-staining fungus (blue stain) occurs is 20-25 C. At a temperature of 7-8 ° C, the growth of the mycelium begins to slow down. The required humidity for the development of blue fungi is 22-163%. The optimal humidity for mycelium is 33-82%. Affected wood becomes gray in color with bluish or greenish tints. The strength of wood decreases by 7-12%, humidity and permeability to liquids increases. Wood-destroying fungi and borer beetles easily develop on such wood.

Under the influence of wood-staining fungi, mushroom sound spots and stripes, in felled wood - mushroom sapwood stains. These defects do not significantly affect the quality of wood; they slightly reduce the strength when shock loads, spoil the appearance and increase the water permeability of wood.

Core rot- areas of abnormal coloration of the core, which, based on color and nature of destruction, are divided into variegated sieve, brown fissured and white fibrous core rot. This defect significantly affects the mechanical properties of the material. Depending on the extent of wood rot damage, its grade is reduced to the point of complete unsuitability.

Mold represents individual spots or a continuous coating of green, blue, black or another color. It does not affect the mechanical properties of wood, but worsens its appearance.

. Browning appears in felled wood as a result of the development of biochemical processes involving fungi; it precedes

sapwood rot and is observed only on fresh cuts of wood. Browning little changes the strength of the material under static loads and hardness, but reduces the impact strength of wood during bending, worsens its appearance, and in beech it reduces water permeability.

Sapwood rot occurs in dead, dead and felled wood under the influence of wood-destroying fungi, as well as during long-term and improper storage. This defect reduces the strength of the material during static bending by 22%, and during compression along the fibers - by 20-25%.

Rotten external rot sharply reduces the mechanical properties of wood; the destruction process can continue not only in undried, but also in relatively dry material. Affected wood is a dangerous source of fungal infection for wooden structures and structures, since it easily falls into pieces and is ground into powder.

Insects mainly damage unbarked, freshly cut timber. Some of them make passages only in the bark, while many go deeper into the wood.

Worm-hole depending on the depth of penetration, it can be superficial (does not affect the mechanical properties), shallow and deep (violate the integrity of the wood and reduce the mechanical properties). Wormholes facilitate the penetration of fungi and the development of rot.

Study of wood defects

Defects found in wood significantly affect the nature of its use, the quality of furniture and other products. Many wood defects are not allowed not only on the front, but also on all surfaces of finished furniture. The ability to determine the type of defect, its size and impact on the quality of finished wood products is one of the tasks of a commodity expert for this group of goods.

(Study of the range of wood materials and semi-finished products In the production of furniture, in construction and other sectors of the national economy, various wood materials and semi-finished products are widely used - boards, bars, veneer, glued, lined decorative plywood, particle boards, wood fiber and joinery boards, bent-glued and bent-propyl parts and etc.