General terms protection of electrical equipment on cranes from emergency situations
According to their purpose, specificity of work and design features, load-lifting cranes belong to the category of equipment that has an increased danger, which is explained by the very process of operation of these mechanisms on sites and in premises where people and valuable equipment are located at the same time.
General requirements for the safety of operation of cranes and crane electrical equipment are formulated in accordance with the “Rules for the Construction and safe operation lifting cranes" and "Rules for electrical installations".
All electrical equipment located in crane control cabins is equipped with grounded metal casings or must be completely closed from the possibility of touching live parts. The control cabin must also contain a device that provides direct or remote shutdown of all supply cable routes running through the crane, with the exception of input devices.
Access to crane platforms where electrical equipment and trolleys that are not protected by casings are located can only be achieved through doors and hatches that have a lock that turns off the power to all sources of electricity in the crane.
The section of the main trolleys, the main current collectors and current leads that remain energized when all intra-crane wiring is disconnected. must have reliable protection from accidental touching. This fence must have a lock with an individual key.
Repair and inspection of current leads can only be carried out when the power to the main trolleys or the general input device located outside the crane is turned off. The circuits of several cranes are powered by general shop trolleys, so a repair area is provided where the trolleys can be disconnected without interrupting the power supply to the remaining cranes.
Cranes are moving installations and are subject to vibrations and shocks during movement, so the possibility of damage to cables and wires on cranes is relatively higher than with their stationary installation. In addition, on a number of cranes, current transfer to moving parts is carried out using flexible hose cables, the damage of which cannot be completely avoided. Taking this into account, the first task of protection is to protect electrical equipment on taps from short-circuit currents.
Short-circuit currents in individual circuits within the tap will be smaller, the smaller the cross-section of the installation wires of these circuits and smaller sizes various current junctions and current connectors. Maximum short-circuit currents in control circuits with a wire cross-section of 2.5 mm2 is 1200-2500 A. In this case, to protect the circuits it is possible to use fuses of the PR series for currents of 6-20 A or any types circuit breakers AP 50, AK 63, etc. Short-circuit currents, A, in electric motor circuits can be approximately determined using the formula
Where I kzyuf - current short circuit in the supply phase, line after 0.04 s; s p - wire cross-section in the circuit under consideration, mm2.
Since the current k.e. should not, before turning it off, destroy the switching device located in this circuit, then when choosing devices and wire cross-sections, it is necessary to observe certain ratios that ensure the thermal resistance of the device. Assuming that the thermal resistance of most devices used in crane electric drives is 10I n for 1 s, then the relationship between the maximum permissible wire cross-section, mm2, and the rated current of the device should be as follows:
Where I n - rated current of the device, A.
The last relationship shows that at possible short-circuit currents. on a feeder of more than 8000 A, it is unacceptable to install 25 A devices due to thermal resistance. Devices for currents of 63 A can only be used with cable cross-sections of no more than 6 mm2, and devices for currents of 100 A - with cable cross-sections of no more than 16 mm2.
At possible short-circuit currents. 12,000 A (limit for cranes) devices with currents of 63 A can only be used with cable cross-sections of no more than 4 mm2, i.e., with rated currents up to 30 A. Devices with a current of 100 A can be used with cable cross-sections of no more than 10 mm2, i.e. at rated currents up to 60 A. Thus, for cranes receiving power from feeders especially high power, it is necessary either to install devices with currents not lower than 100-160 A, or to limit the cross-section of wires to these devices in order to reduce possible short-circuit currents.
Protection cable network tap from short-circuit currents is carried out using an instantaneous maximum current relay, and if necessary can be carried out by automatic installation machines.
Protection of wires from short-circuit currents. is complicated by the large power range of the electric motors of the mechanisms within one crane. In accordance with the rules for electrical installations, protective devices must be designed for an operating current of no higher than 450% of the continuous current of the protected circuit. The same rules for wires and cables operating with intermittent loads, the permissible heating current is determined by the expression
Where I pv and I n - rated cable currents in intermittent and continuous operating modes.
At PV=40% I pv = 1.4 x I n. Thus, the multiple of the protection setting to the permissible current of the wire (cable) should not be higher than 450/1.4 = 320% of the current in the 40% duty cycle mode. Permissible loads on wires and cables within the crane at temperatures environment 45°C are given in the reference tables.
Crane electric drives have the following main types of protective devices:
Maximum protection for disconnecting the electric drive from the network when unacceptable currents occur in the protected circuit;
Zero protection to turn off the electric drive when the power supply from the electrical source is interrupted or interrupted. A type of zero protection is zero blocking, which prevents self-starting of the electric motor when power is restored to the supply line if the control is in the operating position
Ultimate protection to prevent movement of moving structures beyond certain permissible limits.
An important task of the protection system is to prevent unacceptable overloads for all types of electric drives of crane mechanisms associated with malfunction of control circuits, jamming of mechanisms, open brake circuits, etc. This is the difference between the requirements for overload protection of crane electric drives and overload protection for electric drives of continuous operation .
Due to the uncertainty of the load of crane mechanisms, changing heating rates of motors, and their operation under conditions of frequent starts and braking, it is not even possible to set the task of protecting electric drives from thermal overloads. The only condition for preventing thermal overloads of crane electrical equipment is its right choice taking into account any pre-calculated operating modes possible in operation.
Thus, overload protection comes down to monitoring the inrush current during step-by-step starting and protection against jamming of squirrel-cage motors or electric drives with current cut-off. With a properly organized start of the electric drive with stepwise acceleration, the starting current should not exceed 220-240% of the current corresponding to the calculated value.
Taking into account the necessary margin for the spread of both the starting current and the maximum relay setting, the latter should be designed to operate at a current of about 250% of the calculated one, which may be equal to or less than the electric motor current in duty cycle mode = 40%.
According to the above, the maximum current relay in the crane electric drive system has two functions:
1. protection against short-circuit currents. wires (cables) in each pole on direct current and in each phase on alternating current,
2. overload protection, to ensure which it is enough to turn on the relay in one of the poles or one of the phases.
In accordance with the rules, electric drives of cranes must have, i.e., when the power is interrupted, the electric drive must be turned off, and it can be turned on again only after the control element returns to the zero position. This requirement does not apply to floor push-button systems that have self-resetting pushbuttons.
The presence of zero blocking eliminates self-starting of electric drives of cranes, and also eliminates re-starting when various protections are triggered.
Phase loss protection is not used on taps. Analysis possible consequences phase failure outside the tap and an acceptable phase failure protection system showed that, on the one hand, there is currently no satisfactory technical solution for the use of a reliable, cheap and simple apparatus voltage control on the phases, and on the other hand, phase failure within the tap and outside it is unlikely due to the fact that the use of fuses in the main circuit is not currently practiced.
New dynamic braking systems, used instead of counter-switch braking, minimize the risk of a load falling due to phase failure.
Overload protection relay in electric crane drive
To protect the circuits of crane electrical equipment from overloads, an instantaneous electromagnetic relay type REO 401 is used. These relays can be used in both AC and AC circuits. direct current. The relay has two designs. In Fig. Figure 1 shows a general view of the REO 401 relay.
The relay consists of two main components: electromagnet 2 and opening auxiliary contact 1. The coil of the electromagnet 3 is located on the tube 4, in which the armature 5 moves freely. The position of the armature in the tube is adjustable in height and determines the value of the relay operating current. When the current in the coil increases above the operating current, the armature rises up and opens the contacts through the pusher of the contact assembly.
In the second version, relay electromagnets in the amount of two to four pieces are attached to a common base, which also has a common bracket that transmits the forces of any individual electromagnet armature to an auxiliary contact installed on the base. Thus, in this design several electromagnets act on one auxiliary contact.
After the current is turned off, the armature returns under the influence of its own weight. The relay has one normally open auxiliary contact. The auxiliary contact is designed for switching alternating current up to 10 A at a voltage of 380 V and or for DC switching 1 A at 220 V and L/R = 0.05
Rice. 1 . General view of the REO 401 relay
Relay coils for currents above 40 A are made of bare copper. The terminals of these coils are located on a special insulating panel. Coils for currents up to 40 A are insulated. When choosing a relay to install in. complete devices should be guided by permissible load coils in PV mode = 40% and operating range taking into account the required shutdown settings.
REO 401 relays can perform their functions provided that the starting current of the electric drive is less than the current of the braked electric motor when it is turned on at the rated voltage, i.e., protection of short-circuited electric motors and electric drives with current cut-off using the REO 401 relay is impossible. Protection of such electric motors should be carried out using thermal series TRT.
TRT relays have five sizes in the current range from 1.75 to 550 A. Relays of all types are enclosed in a plastic casing and differ in the shape of the reacting thermal element, the presence of an additional heater and the size of the leads. The fifth size relay is mounted on the current transformer. Invarstal bimetal, flown by current and additionally heated by a heater, is used as a reacting thermal element of the relay. The relay has one normally open contact, rated for switching AC 10 A, 380 V at Cos φ = 0.4 and DC 0.5 A, 220 V at L/R = 0.05.
Technical data of the TRT relay are given in reference books. The timing characteristics of the TRT series relays are shown in Fig. 2. The relay does not operate at 110% of the rated current in continuous mode. At a current of 135% of the rated relay, it operates in 5-20 minutes. At a current of 600% of the rated relay, it operates in a time from 3 to 15 s. The regulator available on the relay allows you to adjust the rated current setting within ±15%. The relay contacts return to the on state 1-3 minutes after the current is turned off.
When choosing a relay, you should be guided by the following conditions:
1) the rms current of the protected circuit must not be higher than the rated current of the heater;
2) with three starts in a row, the relay should not operate;
3) the response time at the starting current should not be higher than the permissible time for the electric motor to remain under current in this mode.
When using the time characteristic of the operation of the TRT relay, it should be taken into account that the possible actual deviations of the operation current are about ±20% of the set current.
Protective panels
In accordance with the requirements, each crane must be equipped with a device designed to supply power to the electric drives of the mechanisms and turn it off, and turning it on, i.e., supplying power, can be carried out after unlocking the switching device using an individual brand key.
Rice. 2. Timing characteristics of TRT series relays.
In turn, the key cannot be removed without performing a shutdown operation. This locking makes it possible to ensure that the crane is brought into a usable state only by a person authorized to operate the crane.
On all types of electric cranes, except construction tower cranes, an individual brand key is used in. For construction tower cranes, the specified key is used to block the main switch (or circuit breaker) in the power cabinet tower crane, to which the flexible power cable is connected.
Rice. 3. Diagram of control circuits of protective panels: a - when controlling cam controllers; b - when controlling magnetic controllers; 1P-ZP - fuses; KB - “return” button; CL - hatch contact; AB - emergency switch; L - linear contactor: MP1, MP2 - maximum relay contacts; KVV, KVN - limit switches; PP - test switch; K12 - zero contacts of controllers.
Depending on the type of crane and type of drive (electric, mechanical), the crane is equipped with a number of instruments and devices that ensure its safe operation:
Limit switches- for automatic stopping of crane mechanisms with electric drive. On mechanically driven valves, limit switches are not used.
Interlock contacts- for electrically blocking the door to the crane cabin from the landing platform, the hatch cover, and the entrance to the bridge deck. All crane doors and guards are blocked by its release device. If any contact is broken, the tap cannot be turned on.
Load limiters- to prevent crane accidents associated with lifting loads weighing more than their lifting capacity. Installation of the device is mandatory on jib, tower, and portal cranes.
Skew limiters- to prevent dangerous distortion of metal structures of gantry cranes.
Load capacity indicator- installed on jib-type cranes, in which the lifting capacity changes with the change in the boom radius. The device automatically shows what the crane's lifting capacity is at the set boom radius. This helps prevent the crane from being overloaded.
Angle indicator- For correct installation jib cranes, except those operating on rail tracks
Anemometer- tower and portal cranes should be equipped with it. It shows the wind speed. The operation of the cranes must stop if the wind speed is above 15 m/s, and when installing elements with a large windage when the wind speed is above 10 m/s.
Anti-theft device- on cranes operating on surface rail tracks to prevent them from being blown away by the wind.
Automatic alarm dangerous voltage - is triggered when the crane boom approaches live wires and power lines. They are equipped with jib cranes (except for railway ones).
Support parts- they are equipped with overhead cranes, tower cranes, and portal cranes to reduce dynamic loads on metal structures in the event of breakdown of the axles of the running wheels.
Stops- installed at the ends of the rail track to prevent the lifting machine from leaving them, as well as on jib cranes, with a variable boom reach to prevent it from tipping over.
Sound signaling device- installed on cranes controlled from the cabin or remotely. They are installed on cranes controlled from the floor.
Dimensional requirements for the installation of cranes moving along overhead rail tracks
The horizontal distance between the protruding parts of a crane moving along overhead tracks and buildings, stacks of cargo and other objects located at a height of up to 2 m from the ground must be at least 700 m, and at a height of more than 2 m - at least 400 mm. These distances must be maintained along the entire length of the rail track and in any position of the rotating part of the crane. The vertical distance from the counterweight console to the platforms where people may be located must be at least 2 m.
PRACTICAL WORK No. 10
Selection and calculation of a tower crane
The choice of tap (Fig. 10) is influenced by:
1. Nature and scope of the structure.
2. Weight of mounted elements.
3. Time frame for installation of the structure.
4. Methods and ways of organizing work.
5. Specifications tap.
Rice. 10. Tower crane diagram
Q = G gr + G basic G base = 10% · G gr
H k = h 1 + h 2 + h 3 + h 4
h 1 – height of the installation area, m,
h 2 – minimum permissible distance 0.5, m,
h 3 – load height, m,
h 4 – height of slings, m.
To calculate the reach of a tower crane, we take the most distant point.
L = b + 0,7 + R, Where R– radius of rotation of the tail section, R≈ 4 m.
Q= 5 t.
The height of the installation area is 12 m.
Q= 5 + 10% · b= 5.5 t.
N cr = h l + h 2 + h 3 + h 4 = 12 + 0.5 + 0.4 + 3.5 = 16.4 m.
L = b + 0,7 + R= l8 + 0.7 + 4 = 22.7 m.
We select a faucet.
Task options
| No. | Cargo weight Q, T | Height of installation area h 1m | Load height h 3m | Object width b, m | No. | Cargo weight Q, T | Height of installation area h 1m | Load height h 3m | Object width b, m |
| 0,4 | 11,5 | 1,3 | |||||||
| 0,2 | 8,5 | 1,4 | |||||||
| 7,5 | 0,5 | 12,5 | 1,6 | ||||||
| 9,5 | 1,7 | ||||||||
| 4,5 | 8,5 | 1,5 | 13,5 | 1,8 | |||||
| 5,5 | 1,1 | 13,5 | 3,6 | 1,9 | |||||
| 3,5 | 9,5 | 0,7 | 6,3 | 14,5 | |||||
| 6,5 | 1,2 | 6,8 | 2,5 | ||||||
| 10,5 | 0,8 | 2,5 | 15,5 | 2,7 | |||||
| 7,5 | 0,9 | 2,2 |
Calculation of self-propelled cranes
The diagram of the self-propelled crane is shown in Fig. eleven.
Rice. eleven. Self-propelled crane diagram
h w ≈ l.5 m,
A≈ 1.5 m,
h≈ l.5 m,
Δ ADE ∞ Δ ABC,
| , | DE = A.E. · = ( H c – h w)( b/2 + 1 m)/ h 4 + h 5, |
L = DE+ D.F.
Example
Cargo weight Q= 8 t.
Height of installation area h 1 = 10 m.
Load height h 3 = 0.2 m.
Sling height h 4 = 3.5 m.
Object width b= 20 m.
Constant values:
Chassis h w = 1.5 m.
Distance to crane axis A= 1.5 m.
Height of pulley block h 5 = 1.5 m.
Stock, h 2 = 0.5 m.
Boom height: Hс = h 1 + h 2 +h 3 + h 4 + h 5 = 8 + 0.5 + 0.2 + 3.5 +1.5 = 13.7 m.
DE = (H c – h w)( b/2 + 1 m)/( h 4 + h 5) = (13.7–1.5)(14/2 + 1)/(3.5 + 1.5) = 19.52 m.
L= 19.52 +1.5 = 21.02 m.
We select the KS-5473 crane.
Task options
| No. | Cargo weight Q, T | Height of installation area h 1m | Load height h 3m | Object width b, m | No. | Cargo weight Q, T | Height of installation area h 1m | Load height h 3m | Object width b, m |
| 0,2 | 8,5 | 1,3 | |||||||
| 0,4 | 9,5 | ||||||||
| 0,5 | 3,5 | 1,5 | |||||||
| 0,6 | 0,8 | ||||||||
| 0,8 | 10,5 | 0,7 | |||||||
| 0,7 | 4,5 | 0,9 | |||||||
| 0,9 | 5,5 | 0,6 | |||||||
| 9,5 | 6,5 | 0,5 | |||||||
| 6,5 | 1,1 | 5,5 | 0,4 | ||||||
| 17,5 | 1,2 | 3,5 | 0,3 |
Calculation of jib cranes
General scheme a tap with a jib is shown in Fig. 12.
Rice. 12. General diagram of a jib crane
DE = A.E. · B.C./AB = (H c – h w)1 m/ h 4 + h 5;
L = DF + DE + b/2;
Q = G gr + G basic; G base = 10% G gr;
H k = h l + h 2 + h 3 + h 4.
The selection of boom equipment for cranes with jib (without jib) is carried out depending on the dimensions of the object:
1. When installing single-story industrial buildings we take a crane with one main boom and work on minimum height equal to approximately 5 m.
2. We do not calculate boom reach.
Let's determine the type of jib tap, design scheme which is shown in Fig. 14.
Rice. 14. Jib crane diagram
Initial data:
Q g = 1.5 t; weight of equipment: Q snap = 0.1 Q= 0.15 m.
Q = Q g + Q equipment = 1.5 + 0.15 = 1.65 t.
Height of installation area h 1 = 7.2 m.
Load height h 3 = 0.3 m.
Sling height h 4 = 3.5 m.
Object width b= 9 m.
Constant values:
Chassis h w = 1.5 m.
Distance to crane axis A= 1.5 m.
Height of pulley block h 5 = 1.5 m.
Stock h 2 = 0.5 m.
DF= 1.5 m.
H k = 7.2 + 0.5 + 0.3 + 3.5 = 11.5 m.
H c =H To + h 5 = 11.5 + 1.5 = 13 m.
m.
L = DF + DE + b/2 = 1.5 + 2.3 + 9/2 = 8.3 m.
We select the MKG-25.01 crane.
Task options
| No. | Cargo weight Q, T | Height of installation area h 1m | Load height h 3m | Object width b, m | No. | Cargo weight Q, T | Height of installation area h 1m | Load height h 3m | Object width b, m |
| 0,5 | 6,5 | 2,5 | |||||||
| 2,5 | 0,2 | 4,5 | |||||||
| 0,7 | 7,5 | ||||||||
| 3,5 | 0,5 | ||||||||
| 1,2 | 0,2 | ||||||||
| 4,5 | 1,4 | ||||||||
| 1,5 | 5,5 | 1,2 | |||||||
| 5,5 | 1,8 | 1,4 | |||||||
| 6,5 | 1,5 | ||||||||
| 1,8 |
Calculation of a crane without a jib
We take a tap without a jib (Fig. 13).
Rice. 13. Crane diagram without jib
Initial data:
Q= 4 t, including weight of equipment:
Q snap = 0.1∙ Q, T;
h 1 = 5; h 2 = 0,5; h 3 = 0,3; h 4 = 3.5 m; h 5 = 1.5 m; h w = 1.5 m; b= 5 m;
H k = h l + h 2 + h 3 + h 4 = 9.3 m;
H c =H To + h 5 = 9.3 + 1.5 = 10.8 m;
.
;
We select a crane brand MKG-16M.
Task options
| No. | Cargo weight Q, T | Height of installation area h 1m | Load height h 3m | Object width b, m | No. | Cargo weight Q, T | Height of installation area h 1m | Load height h 3m | Object width b, m |
| 4,5 | 5,5 | 0,2 | 4,5 | 5,5 | 0,2 | ||||
| 0,4 | 0,4 | ||||||||
| 5,5 | 6,5 | 0,5 | 5,5 | 6,5 | 0,5 | ||||
| 0,6 | 0,6 | ||||||||
| 7,5 | 0,7 | 4,5 | 7,5 | 0,7 | |||||
| 4,5 | 0,8 | 0,8 | |||||||
| 9,5 | 0,9 | 5,5 | 9,5 | 0,9 | |||||
| 5,5 | 8,5 | 8,5 | |||||||
| 1,2 | 4,5 | 1,2 | |||||||
| 1,4 | 9,5 | 1,4 |
Annex 1
MINISTRY OF EDUCATION AND SCIENCE OF RUSSIA
Practical work № _______
Appendix No. 2
MINISTRY OF EDUCATION AND SCIENCE OF RUSSIA
Federal state budget educational institution
higher vocational education
“Izhevsk State Technical University named after M.T. Kalashnikov"
(FSBEI HPE “IzhSTU named after M.T. Kalashnikov”)
Faculty of Quality Management
Department of Life Safety
Course work by discipline
“Safety of technological processes and equipment”
Subject ___________________________________________
Security device - technical device electronic type, installed on a crane and designed to turn off mechanisms in emergency situations or prevent them.
Security device - a technical device of a mechanical, electrical, hydraulic or other (non-electronic) type, installed on a crane and designed to turn off mechanisms in emergency situations or to warn the crane operator (driver) about an emergency situation.
Depending on the type of crane (overhead, tower, self-propelled jib, etc.) and the type of drive (electric, mechanical), the crane is equipped with a number of instruments and devices that ensure its safe operation. Such devices include:
a) limit switches designed to automatically stop the mechanisms of electrically driven cranes. On cranes with mechanically driven mechanisms, limit switches are not used. Requirements for equipping lifting machines with limit switches are set out in the Crane Rules;
b) blocking contacts used for electrically blocking the entrance door to the crane cabin from the landing platform, the hatch cover for the entrance to the bridge deck and other places;
C) lifting capacity limiters, designed to prevent crane accidents associated with lifting cargo weighing more than their (taking into account the hook reach) lifting capacity. Installation of the device is mandatory on jib, tower and portal cranes. Overhead cranes must be equipped with a load limiter in cases where their overload cannot be excluded due to production technology. Requirements for installing the device are contained in the Crane Regulations;
d) skew limiters, designed to prevent dangerous skew of metal structures of gantry cranes and bridge loaders due to one of the supports being ahead of the other when the crane is moving. The need to install the device is determined by calculation during design;
e) a load capacity indicator installed on jib-type cranes, in which the load capacity changes with changes in the boom radius. The device automatically shows what the crane's lifting capacity is at the set reach, which helps prevent the crane from overloading;
f) tilt angle indicator (inclinometer) - for the correct installation of jib cranes, except for those operating on rail tracks;
g) anemometer. Tower, portal and cable cranes should be equipped with such a device for automatic feeding sound signal at wind speeds dangerous for work;
h) anti-theft devices used on cranes operating on surface rail tracks to prevent them from being stolen by the wind. The requirements for these devices are set out in the Crane Regulations;
i) automatic dangerous voltage alarm (ASON), signaling the dangerous approach of the crane boom to live wires of the power line. The device is equipped with jib self-propelled cranes (with the exception of railway cranes);
j) phase loss relay - the device is designed to protect against falling loads and booms on electric cranes in the event of a break in any of the three supply phases electrical network, by blocking the operation of the corresponding mechanisms of the lifting machine,
l) supporting parts supplied with overhead cranes, mobile cantilever cranes, tower cranes, portal cranes, cable cranes, as well as cargo trolleys (except for electric hoists) to reduce dynamic loads on the metal structure in the event of breakdown of the axles of the running wheels;
m) stops installed at the ends of the rail track to prevent lifting machines from derailing from them, as well as on jib cranes with variable boom reach to prevent it from tipping over;
m) an audible signaling device used on cranes controlled from the cabin or from a remote control (if remote control). On taps controlled from the floor, a signaling device is not installed.
Instruments and devices providing safe work tower crane
Rice. 3.7. Instruments and devices that ensure safe operation of a tower crane.
1 – anemometer; 2 - load limiter force sensor; 3 – hook lift limiter weight; 4 – hook lift height limiter switch; 5 – boom lift angle sensor; 6 – sound signal; 7 – limit switch of the turret rotation limiter; 8 – limiter alarm panel; 9 – relay block of the load limiter; 10 – limit switch of the crane movement limiter; 11 – inventory track line; 12 – dead-end stop.
During operation, lifting equipment carries out many actions simultaneously. In this case, synchronicity is important. This is the most important factor smooth functioning of the machine. Special devices help control the work process and ensure the safety of the operator and employees present on site, as well as the safety of other mechanisms and property: sensors, stops, etc.
The main purpose of safety devices for lifting equipment is to collect, process and record information about the position of the device, loading, and to prevent uncontrolled movement and impact. According to the requirements, each type of mechanism must have appropriate devices depending on the design features and location. The purpose of the sensors is to detect the slightest malfunctions in operation, sending an alarm signal, which causes a complete stop for diagnostics and repair of the breakdown.
Types of crane safety devices
The operation of industrial and any other lifting equipment can pose a threat to employees performing their duties in the same area. For this reason, all devices are equipped with crane safety devices. The list is as follows:
- limiter - automatically turns off the device drive if the maximum load capacity of the equipment is exceeded;
- limit switch - a fuse that will allow you to automatically turn off the drive when moving parts move beyond the working area;
- boom extension limiter - installed on jib cranes to turn off the mechanism when the minimum or maximum value is reached;
- brake system (installed on actuators) - the main purpose is to reduce the speed of rotation of the devices, to come to a complete stop in order to fix the load in a certain position;
- rotation limiter - prevents rotation of the rotating part in order to prevent breakage of electrical wires;
- load capacity indicator - allows you to prevent overloading of crane equipment;
- anemometer - determines the wind speed at which operation of the device may pose a danger;
- anti-theft device - prevents tower and gantry cranes from derailing under the influence of strong winds;
- additional supports - ensure the stability of the equipment;
- dead-end stops - installed at the edges of rails and beams to prevent the crane from falling off;
- buffer devices - soften the possible impact of the stops against each other (most often rubber cushions are used, wooden blocks, hydraulic type mechanisms).
This is far from full list devices and sensors designed to ensure the safe operation of lifting equipment.
In addition, all easily accessible parts of the crane must be fenced. For this purpose, lightweight metal structures are used that can be removed for carrying out Maintenance, performance checks, configuration, diagnostics and other activities provided for by safety rules.
Lighting and alarm
All types of lifting equipment must be equipped lighting fixtures for work in the dark and at night. The reason for this is also operation in poor visibility (for example, in fog). Installation of a tower crane involves the installation of lamps that fully illuminate work area devices. In this case, the activation must be carried out by an independent electrical device, which must be placed on the portal. The working and equipment cabin, the machine room must also be illuminated. This applies to all types of cranes (tower, bridge, gantry, cantilever) and other types of lifting equipment. Lamps installed on the mechanisms themselves must remain on even after the end of the working day. In addition, lifting equipment in mandatory equipped with an alarm system. The sounds of the device must be clearly audible in places where the load is moving, lowering and lifting, even in strong wind, rain and other adverse weather conditions.
Maintenance Features
When should crane maintenance be performed? Most often it is carried out during activities to check and diagnose the lifting device itself. The adjuster configures the systems taking into account current rules and provisions. When undergoing maintenance, the following is carried out:
- external inspection of devices to check the quality of installation;
- determining the condition and correct connection of electrical wires;
- cleaning from contaminants;
- adjustment of systems and mechanisms;
- integrity definition metal structures, electrical mechanism and other systems;
- checking the integrity of installed seals, serviceability, and operability.
After completing the maintenance, the service technician makes a corresponding entry in the log.
Repair and diagnostics
In case of failure of lifting equipment, it is necessary to conduct a thorough inspection to identify the causes of the failure. Most often, some parts and components require replacement, for example, microcircuits, sensors and circuit boards. Repair is quite difficult technological process, which a professional installer with the appropriate permit and qualifications has the right to perform. If malfunctions are detected, operation of the lifting equipment must be suspended until the breakdown is eliminated. After the repair, the service technician configures the required parameters. The frequency of inspection depends on the type of equipment, its load capacity, operating conditions and other important factors.
Instruments and devices that ensure safe operation of the KB-504 tower crane
1 - anemometer; 2 - load limiter force sensor; 3 - hook lift limiter weight; 4 - hook lift height limiter switch; 5 - boom lift angle sensor; 6 - sound signal; 7 - limit switch of the turret rotation limiter; 8 - limiter alarm panel; 9 - relay block of the load limiter; 10 - limit switch of the crane movement limiter; 11 - inventory track ruler; 12 - dead-end stop.
Instruments and safety devices are designed to automatically shut down the units and mechanisms of the crane when any parameter characterizing the operating mode of the equipment deviates beyond the permissible values.
The main instruments and safety devices installed on cranes include 10.
The movement limiter of a tower crane is designed to automatically turn off the drive of the crane mechanism when it approaches the moving parts of the established restrictions and the engine is turned off.
They must be installed in such a way that the engine of the travel mechanism is turned off at a distance of at least the braking distance to the dead-end stop.
To dampen the residual speed of the crane and prevent it from leaving the end sections of the crane track in emergency situations when the travel limiter or brakes of the crane movement mechanism fail, dead-end stops 12 must be installed at the ends of the rail track (at a distance of at least 0.5 m). in such a way that the crane hits the stops simultaneously.
Boom reach limiters serve to automatically disable the mechanism that ensures a change in boom reach 5 when the boom reaches its maximum or minimum working reach.
The hook lifting height limiter 3, 4 serves to automatically disable the hook lifting mechanism when it approaches the upper extreme position. This limiter consists of a switch 4 and a load 3 with two guide brackets into which the branches of the cargo rope are inserted. When the cargo suspension rests on the load 3 and lifts it, the switch lever 4, freed from the load, opens the contacts electrical supply hook lifting mechanism.
The rotation limiter 7 of the rotating part of the crane serves to prevent rotation of the rotating part of the crane in one direction more than twice, in order to prevent the breakage of live wires when some ends of these wires are fixed on the running frame, and the other on the rotating part of the crane.
Anemometer 1 (Fig. 14) consists of a wind speed sensor, a control unit, and a cable (connecting, power and load). It is designed to determine the speed of air flow (wind) in industrial conditions identifying dangerous wind gusts and activating warning devices. When the wind speed reaches more than 90% of Vpr, the preliminary light and sound alarm “ATTENTION” is activated. With a further increase in wind speed and the gusts reach the maximum value, the light and sound alarm “LIMITING SPEED” is activated. If the gust of wind lasts longer than the delay time, the “DANGER” alarm is activated and the external load relay is activated.
Figure 14
The plower is used to clear the rails of snow or debris; it is installed at a distance of 10 mm from the rail head.
A supporting part standing between the wheels of the undercarriage at a distance of 20mm from the rail head in case of wheel failure.
Buffer. This invention relates to buffers designed to mitigate the possible impact of a crane or trolley on stops, as well as cranes on each other. To soften the impact (damping) in lifting cranes, rubber and rubber materials are used.
Crane buffers (cast buffers with a monolithic rubber element or in the form of a cylinder made of polymer material) are used on bridge, gantry and even tower cranes.
Gantry crane safety devices and devices
The crane lifting capacity limiter (Fig. 15) (technical name - load moment limiter) must be “able” to disable automatic mechanisms for changing the boom reach in load lifting situations and/or load lifting mechanisms, for many of which the crane’s lifting capacity has been recorded to be exceeded by 10% (tower and jib cranes), by 15% (portal cranes), by 25% (overhead cranes). It is not necessary to disable other crane mechanisms, such as the slewing and/or traveling devices.
Moreover, the crane's load limiter must be activated if, when lowering a loaded boom, its reach will be increased to a position at which the specific gravity of the load exceeds that specified for of this type tap.
The following condition must be fulfilled: after installed limiter the crane's lifting capacity will turn on, lowering the load and/or turning on other mechanisms should be available immediately, without blocking the components.
Figure 15
The crane's load limiter structurally consists of a force sensor and a disconnecting device; moreover, there is a special corrective invention that automatically (programs) sets the moment of operation of the limiter depending on the load and boom radius. Based on the type and design of sensors, limiters are divided into spring limiters, load limiters, torsion bars and others. The sensor is connected to in different parts tap. As a rule, the sensor is built into the jib pulley system, and for other cranes (bridge type) it is built into the cargo pulley system.
Limiter for the movement of the crane trolley (Fig. 16)
Figure 16 (a - with a switching line, b - with a switching stop)
Lever limit switch (Fig. 17)
Figure 17 (a - schematic diagram, b - use of the KU-703 switch as a limiter for the upper position of the crane hook suspension)
In the mechanism for lifting the load of cranes, limit switches KU-703 are used (Fig. 17b), installed on the frame of the cargo trolley under the leveling blocks (Fig. 93, b). A double-armed lever with a counterweight is attached to the switch shaft, to the free end of which an auxiliary weight is suspended on a thin rope (chain). When the hook suspension approaches the uppermost position, it lifts the auxiliary load. The counterweight turns the released double-arm lever and the limit switch opens the necessary contacts. To prevent the auxiliary load from swinging, the latter is connected with a bracket to one of the branches of the cargo rope.
In addition to the upper position of the hook suspension, in practice it is often necessary to limit its lower position, limited by the length of the cargo rope (it must be remembered that additional turns must always remain on the winch drum, for example, when lowering the load into wells, pits, etc.)
Skew limiter, triggered by torsional deformations of the rigid support (Fig. 18)
Figure 18
An angular rod 2 is installed on the support 1, which, when a misalignment occurs, rotates along with the support. When turning the rod with its horizontal part, it acts on limit switch 3, which is connected to the motor circuit of the movement mechanism of the “run-out” support. When the support runs out, the motor of the movement mechanism is turned off, and when the supports are aligned, it turns on again.
IN last years Skew limiters with synchro-type sensors are increasingly used on cranes and material handlers. Structurally it is done like this. A non-drive trolley is attached to each of the supports, from the running wheels of which the synchronous synchronizers rotate through the multiplier. The magnitude of the signal generated by the synchronizers depends on the path traversed by the trolleys when moving the crane or material handler. Selsyns are connected to a bridge circuit and when uniform motion both diagonal supports measuring bridge balanced. When one of the supports runs out, the balancing of the bridge is disrupted and the generated signal, which is fed into the electrical control circuit of the support movement motor, turns it off.