Plasma cutting technology is extremely rarely used in everyday life, but in the industrial sphere it has become very widespread. Due to the fact that with the help of a plasma cutter you can easily, quickly and efficiently cut almost any conductive metal, as well as other materials - stone and plastic, it is used in mechanical engineering, shipbuilding, public utilities, advertising production, for equipment repair and much more. The cut always turns out smooth, neat and beautiful. Those who are just about to master this technology may be interested in a reasonable question: what is a plasma cutting machine, what is the principle of its operation, as well as what types of plasma cutters are there and what each of them is used for. All this will give a general understanding of plasma cutting technology and will allow right choice upon purchase and learn how to operate the device.
How does a plasma cutter work? And what is meant by the word “plasma”? To operate a plasma cutter, you only need two things - electricity and air. The energy source supplies currents to the cutter (plasma torch) high frequency, due to which in the plasmatron there is electric arc, the temperature of which is 6000 - 8000 °C. Then it is sent to the plasmatron compressed air, which is on high speed escapes from the nozzle, passes through an electric arc, heats up to a temperature of 20,000 - 30,000 ° C and is ionized. Air, which has been ionized, loses its dielectric properties and becomes a conductor of electricity. Plasma just like that is this air.
Escaping from the nozzle, the plasma locally heats the workpiece in which it is necessary to make a cut, and the metal melts. The particles of molten metal formed on the frontal surface of the cut are blown away by a stream of air escaping at great speed. This is how metal is cut.
The speed of the plasma flow (heated ionized air) increases if the air flow rate is increased. If you increase the diameter of the nozzle through which the plasma escapes, the speed will decrease. The plasma speed parameters are approximately as follows: at a current of 250 A it can be 800 m/s.
To ensure an even cut, the plasma torch must be held perpendicular to the cutting plane, the maximum permissible deviation is 10 - 50 °. Also great importance has a cutting speed. The smaller it is, the wider the cut width becomes, and the cutting surfaces become parallel. The same thing happens when the current increases.
If you increase the air flow, the width of the cut will decrease, but the edges of the cut will become non-parallel.
The plasma cutting machine consists of power supply, plasma torch And cable-hose package, which connects the power source and compressor with a plasma torch.
The power source for a plasma cutting machine can be a transformer or an inverter, which supplies a high current to the plasma torch.
Plasma torch, in fact, is the main element of the device - a plasma cutter. Sometimes the entire apparatus is mistakenly called a plasma torch. This may be due to the fact that the power source for the plasma cutter is not unique in any way, but can be used together with welding machine. And the only element that distinguishes a plasma cutter from another device is the plasma torch.
The main components of a plasma torch are an electrode, a nozzle and an insulator between them.
Inside the plasma torch body there is a cylindrical chamber of small diameter, the output channel from which is quite small and allows the formation of a compressed arc. In the back side of the arc chamber there is an electrode that serves to excite the electric arc.
Electrodes for air plasma cutting can be made of beryllium, hafnium, thorium or zirconium. Refractory oxides are formed on the surface of these metals, preventing destruction of the electrode. But for the formation of these oxides we need certain conditions. The most common are hafnium electrodes. But they are not made from beryllium and thorium, and the reason for this is the same oxides: beryllium oxide is extremely radioactive, and thorium oxide is toxic. All this can have an extremely negative impact on the operator’s work.
Since it is difficult to directly excite an electric arc between the electrode and the workpiece of the metal being processed, the so-called pilot arc is ignited first - between the electrode and the tip of the plasma torch. The column of this arc fills the entire channel. After this, compressed air begins to be supplied into the chamber, which, passing through an electric arc, heats up, ionizes and increases in volume by 50 - 100 times. The plasma torch nozzle is narrowed downwards and forms a plasma stream from heated ionized gas/air, escaping from the nozzle at a speed of 2 - 3 km/s. In this case, the plasma temperature can reach 25 - 30 thousand °C. Under such conditions, the electrical conductivity of the plasma becomes approximately the same as that of the metal being processed.
When the plasma is blown out of the nozzle and touches the workpiece with a torch, a cutting plasma arc is formed - a working one, and the pilot arc goes out. If suddenly for some reason the working arc also goes out, it is necessary to stop the air supply, turn on the plasma torch again and form a pilot arc, and then release compressed air.
Plasma torch nozzle can have different sizes and the capabilities of the entire plasmatron and the technology of working with it depend on this. For example, the amount of air that can pass through this diameter per unit time depends on the diameter of the plasma torch nozzle. The cutting width, operating speed and cooling rate of the plasma torch depend on the amount of air flow. Plasma cutters use nozzles no larger than 3 mm in diameter, but quite long - 9 - 12 mm. The length of the nozzle affects the quality of the cut; the longer the nozzle, the better the cut. But here you need to be careful, moderation is important everywhere, since a nozzle that is too large will wear out and collapse faster. The optimal length is considered to be 1.5 - 1.8 times the nozzle diameter.
It is extremely important that the cathode spot is focused strictly in the center of the cathode (electrode). For this purpose, a vortex supply of compressed air/gas is used. If the vortex (tangential) air supply is disrupted, then the cathode spot will move relative to the center of the cathode along with the arc. All this can lead to unstable combustion of the plasma arc, the formation of a double arc, and even failure of the plasma torch.
The plasma cutting process uses plasma-forming And protective gases. Plasma cutting machines with a current of up to 200 A (can cut metal up to 50 mm thick) use only air. In this case, air is a plasma-forming gas and protective, as well as cooling. In complex industrial portal devices, other gases are used - nitrogen, argon, hydrogen, helium, oxygen and their mixtures.
The nozzle and electrode in the plasma cutting machine are consumables, which must be replaced in a timely manner, without waiting for them to be completely worn out.
It is common to buy plasma cutters in finished form, the main thing is to choose the right unit correctly, then you won’t have to “finish anything with a file.” Although in our country there are “Kulibins” who can make a plasma cutting machine with their own hands, purchasing some parts separately.
Types of plasma cutting machines
Plasma cutters are distinguished by several different parameters. Plasma cutting machines can be portable installations, portal systems, hinged-cantilever machines, specialized structures and installations with a coordinate drive. Especially notable are plasma cutting machines with CNC (Computer Numerical Control), which minimize human intervention in the cutting process. But besides these, there are other gradations.
Devices for manual and machine cutting
It is used for cutting metal manually, when the plasma torch is held in the hands of a human operator and guides it along the cutting line. Due to the fact that the plasma torch is always suspended above the workpiece being processed, a person’s hand may tremble slightly even during normal breathing, all of which affects the quality of the cut. It may have sagging, uneven cuts, traces of jerking, etc. To make the operator’s work easier, there are special stops that are placed on the plasma torch nozzle. Using it, you can place the plasma torch directly on the workpiece and carefully guide it. The gap between the nozzle and the workpiece will always be the same and meet the requirements.
Machine cutting devices They are portal-type plasma cutters and automatic cutting devices for parts and pipes. Such devices are used in production. The quality of the cut with such a plasma cutter is ideal; no additional processing of the edges is required. A software control allows you to make cuts of various shapes in accordance with the drawing without fear of jerking your hand at the wrong moment. The cut is precise and smooth. The price for such plasma metal cutting devices is an order of magnitude higher than for manual machines.
Transformer and inverter plasma cutting machines
There are transformer and inverter plasma cutters.
They are heavier than inverter ones and larger in size, but they are more reliable, since they do not fail in the event of power surges. The switching time of such devices is higher than that of inverter devices and can reach 100%. A parameter such as the duration of switching on directly affects the specifics of working with the device. For example, if the duty cycle is 40%, this means that the torch can run for 4 minutes without interruption and then needs 6 minutes of rest to cool down. 100% PV is used in production, where the machine operates throughout the entire working day. The disadvantage of a transformer plasma cutter is its high energy consumption.
Using transformer plasma cutters, you can process workpieces of greater thickness. The price for a similar air plasma cutting machine is higher than for an inverter one. Yes, and it is a box on wheels.
They are used more often in everyday life and in small industries. They are much more economical in energy consumption, have less weight and dimensions, and are most often a manual device. The advantage of an inverter plasma cutter is stable arc burning and efficiency is 30% higher, compactness and the ability to work in hard-to-reach places.
Air plasma cutting and water plasma cutting machine
It is worth noting that there are not only air plasma cutting machines, the operating principle of which and the device were described above, but also water plasma cutting machines.
If in air plasma cutters air acts both as a plasma-forming gas, and as a protective gas, and as a cooling gas, then in water plasma cutters water acts as a coolant, and water vapor acts as a plasma generator.
The advantages of air plasma cutting are low price and light weight, but the disadvantage is that the thickness of the cut workpiece is limited, often no more than 80 mm.
The power of water plasma cutters allows you to cut thick workpieces, but their price is slightly higher.
Operating principle of a water plasma cutting machine is that it uses water vapor instead of compressed air. This makes it possible to avoid using an air compressor or gas cylinders. Water vapor is more viscous than air, so much less of it is needed; the supply in the can is enough for about a month or two. When an electric arc flows in the plasma torch, water is supplied to it, which evaporates. At the same time, the working fluid lifts the negative pole cathode from the positive pole cathode of the nozzle. As a result, an electric arc lights up and the steam is ionized. Even before the plasma torch approaches the workpiece, the plasma arc lights up, which performs the cutting. A bright representative This category of plasma cutter is the Gorynych device; for such a plasma cutting machine the price is about 800 USD.
Depending on whether the material to be cut is included in electrical diagram plasma cutting or not, the type of cutting depends on it - contact and non-contact.
Contact plasma cutting or plasma arc cutting looks like this: the arc burns between the plasma torch electrode and the workpiece. This is also called an arc direct action. The electric arc column is combined with a plasma jet that escapes from the nozzle at high speed. The air blown through the plasma torch nozzle compresses the arc and gives it penetrating properties. Due to high temperature air 30000 °C, its flow rate increases and the plasma has a strong mechanical effect on the blown metal.
Contact cutting is used when working with metals that can conduct electricity. This includes manufacturing parts with straight and curved contours, cutting pipes, strips and rods, making holes in workpieces and much more.
Non-contact plasma cutting or cutting with a plasma jet looks like this: an electric arc burns between the electrode and the forming tip of the plasma torch, part of the plasma column is carried outside the plasma torch through the nozzle and represents a high-speed plasma jet. It is this jet that is cutting element.
Non-contact cutting is used when working with non-conductive materials (non-metals), for example, stone.
Working with a plasma cutting machine and air plasma cutting technology is an entire art that requires knowledge, patience and compliance with all rules and recommendations. Knowledge and understanding of the plasma cutter device helps to perform the work efficiently and accurately, since the operator understands what processes are occurring in the plasma torch and beyond at one time or another, and can control them. It is also important to follow all precautions and safety precautions, for example, when working with a plasma cutter you must wear a welder’s suit, a shield, gloves, closed shoes and thick pants made of natural fabric. Some oxides released during metal cutting can cause irreparable harm to a person's lungs, so it is necessary to work in a protective mask or at least provide good ventilation V work area.
IN Lately The use of plasma flow for cutting materials is gaining increasing popularity. The scope of use of this technology is further expanded by the appearance on the market of hand-held devices that are used to perform plasma cutting of metal.
The essence of plasma cutting
Plasma cutting involves local heating of the metal in the separation zone and its further melting. Such significant heating is achieved through the use of a plasma jet, which is formed using special equipment. The technology for producing a high-temperature plasma jet is as follows.
- Initially, an electric arc is formed, which is ignited between the electrode of the device and its nozzle or between the electrode and the metal being cut. The temperature of such an arc is 5000 degrees.
- After this, gas is supplied to the equipment nozzle, which increases the arc temperature to 20,000 degrees.
- When interacting with an electric arc, the gas is ionized, which leads to its transformation into a plasma jet, the temperature of which is already 30,000 degrees.
The resulting plasma jet is characterized by a bright glow, high electrical conductivity and exit speed from the equipment nozzle (500–1500 m/s). Such a jet locally heats and melts the metal in the processing zone, then it is cut, which is clearly visible even in a video of such a process.
In special installations, various gases can be used to produce a plasma jet. These include:
- ordinary air;
- technical oxygen;
- nitrogen;
- hydrogen;
- argon;
- steam produced by boiling water.
Metal cutting technology using plasma involves cooling the equipment nozzle and removing particles of molten material from the processing zone. These requirements are ensured by the flow of gas or liquid supplied to the area where cutting is carried out. The characteristics of the plasma jet generated on special equipment make it possible to use it to cut metal parts whose thickness reaches 200 mm.
Plasma cutting machines are successfully used at enterprises in various industries. With their help, cutting not only metal parts, but also plastic and natural stone. Thanks to such unique opportunities and its versatility, this equipment is widely used in machine-building and shipbuilding plants, in advertising and repair enterprises, and in the public utilities sector. A huge advantage The use of such installations is also that they allow you to obtain a very smooth, thin and precise cut, which is important requirement in many situations.
Plasma cutting equipment
On modern market There are two main types of devices available for cutting metal using plasma:
- indirect action devices - cutting is performed in a non-contact manner;
- direct action devices - contact cutting.
Equipment of the first type, in which an arc is ignited between the electrode and the torch nozzle, is used for processing metal products. Such installations are mainly used in various enterprises; you will not find them in a home craftsman’s workshop or in a repairman’s garage.
In devices of the second type, an electric arc is ignited between the electrode and the part itself, which, naturally, can only be made of metal. Due to the fact that the working gas in such devices is heated and ionized throughout the entire gap (between the electrode and the part), the plasma jet in them has a higher power. This type of equipment can be used to perform manual plasma cutting.
Any plasma cutting machine operating on the contact principle consists of standard set components:
- power supply;
- plasma torch;
- cables and hoses used to connect the plasma torch to the power source and the working gas supply source;
- gas cylinder or compressor to obtain a jet of air at the required speed and pressure.
The main element of all similar devices is a plasma torch, it is this that distinguishes such equipment from conventional welding equipment. Plasma torches or plasma cutters consist of the following elements:
- working nozzle;
- electrode;
- an insulating element that is highly heat resistant.
The main purpose of the plasma torch is to convert the energy of the electric arc into thermal energy plasma. The gas or air-gas mixture coming out of the plasma torch nozzle through a small diameter hole passes through a cylindrical chamber in which the electrode is fixed. It is the nozzle of the plasma cutter that provides the required speed and shape of the flow of the working gas, and, accordingly, the plasma itself. All manipulations with such a cutter are performed manually by the equipment operator.
Considering the fact that the operator has to hold the plasma cutter by weight, it can be very difficult to ensure high quality metal cutting. Often, parts produced using manual plasma cutting have uneven edges, traces of sagging and jerking. In order to avoid similar shortcomings, various devices are used: stands and stops, which allow for smooth movement of the plasma torch along the cutting line, as well as a constant gap between the nozzle and the surface of the part being cut.
Air or nitrogen can be used as the working and cooling gas when using manual equipment. This air-gas jet is also used to blow molten metal out of the cutting zone. When using air, it is supplied from a compressor, and nitrogen comes from a gas cylinder.
Required Power Sources
Although all plasma cutter power supplies operate on AC power, some can convert it to DC power, while others can amplify it. But those devices that operate on DC. Installations operating on alternating current are used for cutting metals with a relatively low melting point, for example, aluminum and alloys based on it.
In cases where too high power of the plasma jet is not required, conventional inverters can be used as power sources. It is these devices, characterized by high efficiency and ensuring high stability of the electric arc, that are used to equip small industries and home workshops. Of course, it will not be possible to cut a piece of metal of considerable thickness using a plasma torch powered by an inverter, but it is optimal for solving many problems. A big advantage of inverters is their compact dimensions, which makes them easy to carry and use for work in hard-to-reach places.
Transformer-type power supplies have higher power, with the use of which both manual and mechanized cutting of metal using a plasma jet can be carried out. Such equipment is distinguished not only by high power, but also by higher reliability. They are not afraid of power surges that can damage other devices.
Any power source has one important characteristic, as the on-duration (DS). For transformer power supplies, the duty cycle is 100%, which means that they can be used the whole working day, without a break for cooling or rest. But, of course, such power supplies also have disadvantages, the most significant of which is their high power consumption.
How is manual plasma cutting performed?
The first thing you need to do in order to start using a machine for plasma cutting of metal is to put together all its component elements. After this, the inverter or transformer is connected to the metal workpiece and to the alternating current network.
Plasma cutting is very often used in industries such as shipbuilding, mechanical engineering, as well as in the manufacture of metal structures, public utilities, etc. In addition, a plasma cutter is quite often used in a private workshop. With its help, any material that conducts current, and some non-conductive materials such as wood, stone and plastic, are quickly and efficiently cut.
Plasma cutting technology allows you to cut sheet metal and pipes, perform figured cut or make parts. The work is carried out using high temperature plasma arc. To create it, you only need a power source, air and a cutter. In order for the work to be done quite easily, and the cut to be smooth and beautiful, you should find out how the principle of operation of plasma cutting is carried out.
How does a plasma cutter work?
This apparatus consists of the following elements:
- power supply;
- air compressor;
- plasma cutter or plasma torch;
- cable-hose package.
The power source for the plasma cutting machine supplies the plasma torch with a certain current strength. It is an inverter or transformer.
Inverters are quite lightweight, economical in terms of energy consumption, inexpensive in price, however, they are capable of cutting workpieces of small thickness. Because of this, they are used only in private workshops and small industries. Inverter plasma cutters have 30% more efficiency than transformer cutters and have a better arc burn. They are often used for work in hard-to-reach places.
Transformers are much heavier, consume a lot of energy, but at the same time have less sensitivity to voltage changes, and with their help they cut workpieces of large thickness.
The plasma cutter is considered the main element of the plasma cutter. Its main elements are:
- nozzle;
- cooler/insulator;
- a channel necessary for supplying compressed air;
A compressor is required to supply air. The operating principle of plasma cutting involves the use of protective and plasma-forming gases. For devices that designed for current up to 200 A, only compressed air is used for both cooling and plasma creation. They are capable of cutting workpieces up to 50 mm thick.
The cable-hose package is used to connect the compressor, power source and plasma torch. By electrical cable current begins to flow from the inverter or transformer to initiate an electric arc, and compressed air is supplied through the hose, which is required for plasma to appear inside the plasma torch.
Principle of operation
When you press the ignition button, the supply of high frequency current from the power source (inverter or transformer) begins. As a result, a pilot electric arc is formed inside the plasma torch, the temperature of which reaches 8 thousand degrees. The column of this arc begins to fill the entire channel.
After the pilot arc has arisen, compressed air begins to flow into the chamber. Breaking out of the pipe, he passes through an electric arc, heats up, while increasing in volume by 50 or 100 times. In addition, the air begins to ionize and ceases to be a dielectric, acquiring the properties of conducting current.
The plasma torch nozzle, narrowed downwards, compresses the air, creating a flow from it, which begins to escape from there at a speed of 2 - 3 m/s. At this moment, the air temperature often reaches 30 thousand degrees. It is this hot ionized air that is plasma.
At the time when the plasma begins to escape from the nozzle, it comes into contact with the surface of the metal being processed, the pilot arc goes out at this moment, and the cutting arc lights up. She starts heat the workpiece at the cutting site. As a result, the metal melts and a cut appears. Small particles of molten metal form on the surface of the metal being cut and are blown off by a stream of air. This is how the plasma torch operates.
Advantages of plasma cutting
Metal cutting work is often carried out on a construction site, in a workshop or workshop. You can use autogen for this, but not everyone is happy with this. If the amount of work involved in cutting metal is too large, and the requirements for the quality of the cut are very high, then you should consider using a plasma cutter, which has the following advantages:
Disadvantages of plasma cutting
There are also disadvantages to plasma cutting. The first of them is the maximum permissible thickness The cut is quite small, and for the most powerful units it is rarely more than 80 - 100 mm.
The next drawback is the rather stringent requirements for deviation from the perpendicularity of the cut. Deflection angle should not be more than 10 - 50 degrees and it depends on the thickness of the part. If these limits are exceeded, a fairly significant expansion of the cut occurs, which results in rapid wear of consumables.
Besides, work equipment quite complex, which makes it completely impossible to use two cutters at the same time, which are connected to one device.
Conclusion
The operating principle of plasma cutting is quite simple. In addition, the apparatus used for this purpose has a large number of advantages that are several times greater than the existing disadvantages. If you use it correctly, you can significantly save time and get high-quality results.
Today it is difficult to imagine heavy industry without the use of welding and metal cutting. On most industrial enterprises Those involved in the processing of metal products use a special cutting method - plasma.
Plasma cutting is a material processing process in which the cutting element is a plasma jet.
Few people know how to do plasma cutting of metal with their own hands and what are the main stages of this process. Most often, the thickness of the processed products is less than 20 cm. It is for cutting metal of this thickness that plasma devices are used.
Characteristics of cutting products using plasma
Those who use an oxygen cutter to separate metal know that plasma cutting differs from this method in many ways. Here, instead of a cutting gas, a plasma jet is used. Like conventional welding, plasma cutting uses an electric arc. It ignites directly between the surface of the object and the electrode. The supplied gas becomes plasma. An interesting fact is that the temperature of the latter can reach several tens of thousands of degrees (from 5 to 30 thousand). In this case, the jet speed often reaches 1500 m/s. Plasma cutting of metal is suitable for products up to 20 cm thick. As for the gas supplied to the nozzle, it comes in several types: active and inactive.
The first category includes oxygen and an air mixture, the second includes nitrogen, hydrogen, as well as some inert gases, such as argon. The choice of one gas or another depends on the metal. If it is a ferrous metal, then it is recommended to use active gases. Inactive ones are more suitable for non-ferrous metals (aluminum, copper) and their alloys. Manual plasma cutting can be surface and separation. The latter is used much more often. You need to know that this method of cutting metal is the most automated. Plasma cutting involves the use of special automatic (programmable) machines.
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Positive and negative sides
Plasma cutting has its positive and negative sides. The advantages, firstly, include the ability to use equipment for cutting any metal. This is achieved due to the increased temperature in the working area. Secondly, an important aspect is high speed. This ensures the best productivity. Thirdly, plasma cutting is great for cutting out products of various geometric shapes. This cannot be achieved using the simple gas method. Fourthly, it is of great importance that such metal cutting is accurate and fast. Here, the likelihood of receiving low-quality products is significantly reduced, since the work is automated.
Fifthly, everyone knows that simple oxygen cutting can pose a danger to humans and others. Plasma cutting is the least dangerous. Sixth, such work can be carried out both on outdoors, and under water. It is also important that the cost per 1 m of material is much lower; due to all this, plasma cutting is increasingly used at large industrial facilities. As for the negative aspects of this process, the equipment is quite expensive, so this technique is rarely used at home.
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Which device to choose
Plasma cutting of metal begins with the preparation of equipment. To do this, you will need to choose a quality device. There are 2 types of equipment: inverter and transformer. Inverters are familiar to many, as they are used for welding. They replaced transformers. Inverter units are small in size, they are compact, aesthetically pleasing and consume less energy. When purchasing equipment, you need to pay attention to such characteristics as operating time and power. The disadvantage of such a unit is that it is quite sensitive to power surges in the network.
Transformer-type cutting equipment is the most reliable and durable. A feature of transformers is that when high power they can be used for automated cutting. The manual method is also used. If metal cutting is supposed to be carried out in a private workshop or at industrial facilities, then it is more advisable to purchase a transformer-type device. It is also widely used in automobile manufacturing. It must be remembered that any plasma cutting is an expensive pleasure.
The device will not be cheap. An important criterion when choosing equipment is maximum thickness cutting For non-ferrous metals (copper) it is always less. If the technical data sheet indicates a maximum thickness of 10 mm, then this indicator applies to non-ferrous metals.
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Features of manual arc plasma cutting
The manual method is often used for cutting metal products. Its peculiarity is that it is not required highly qualified to cut the product. The work can be performed by anyone, knowing all the main stages of the process. By purchasing a plasma cutter, you can cut not only metal, but also tiles, wood and other materials. Plasma cutting manually begins with an inspection of equipment, nozzles, electrodes. The nozzle and electrodes must be securely fastened. To save materials, it is advisable to strike the arc as rarely as possible. In order for the device to start working, compressed air must be supplied to it.
For this purpose, you can use cylinders that are filled with air, a compressor, or connect the equipment to a central pipeline (if cutting is carried out in industrial conditions). The most reliable devices are equipped with a special control device, with the help of which the incoming air is distributed in the device.
The next stage is setting up the equipment. To do this, you need to select the correct current strength. It is preferable to start cutting at a high current. In this case, several test cuts are made. An incorrectly selected mode can lead to overheating of the metal and its spattering. At optimal mode When burning an arc, the cutting line must be smooth and the metal must not be deformed.
If it is necessary to cut sheet material, then the burner nozzle is placed close to the surface of the metal. To do this, turn on the power button on the device. Soon after this, the pilot arc should light up, followed by the cutting arc. The arc should be directed at an angle of 90° to the metal. The burner moves from top to bottom. If automatic plasma cutting has a high speed, then when manual method The burner must be moved slowly. At the end of the job, it is advisable to briefly stop the advance of the torch to complete the cutting.
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Cutting various metals
Cutting a particular metal may have its own characteristics. Today cutting is more often used sheet material. It is usually represented by steel. It is often necessary to cut aluminum. If welding of this metal is difficult due to the formation of protective film in the form of aluminum oxide, cutting aluminum is quite simple. It is important to remember here that air and active gases do not need to be used.
Plasma cutting of aluminum is performed using argon or nitrogen.
Argon and nitrogen are chemically less active elements, therefore, during the process of cutting and heating the metal, an oxide film does not form on it. Another common material is steel. In this situation, cutting is carried out without the use of protective gases. Air arc plasma cutting is excellent for products made of of stainless steel. This is the most affordable way cutting
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Plasma jet cutting
Unlike the arc method, when cutting with a plasma jet, the metal does not participate in the formation of an electrical circuit. The electric arc itself is present, but it is formed directly between the inside of the nozzle and the electrode. Such an electric arc is necessary for plasma to form. This makes it possible to cut materials that do not conduct electricity. The plasma in this situation is high-speed. Most often, this method is used to separate sheet material. As for the use of electrodes, electrodes based on various tungsten alloys are suitable for plasma cutting.
It must be remembered that in order to cut materials using a plasma flow, you need to have available necessary tools and materials. They include cutting apparatus, source electric current, overalls, shoes, mask, mittens, hammer, chisel, metal brush. Often for implementation similar work The plasma cutting machine is made by hand. In terms of power, it may not be inferior to the factory one.
Cutting materials using plasma flow is high-tech, effective way their quality processing. Manual plasma cutting, carried out with appropriate equipment, expands the scope of this type of work.
2 Basic classification of plasma cutting equipment
All devices for plasma cutting are divided into:
- indirect action – for non-contact cutting;
- direct action - for contact.
The first type of cutters are used for processing non-metallic materials. This technique is specific and is not in demand outside of production. In the non-contact method, an electric arc is ignited between the electrode and the nozzle of the plasma torch.
Direct acting devices cut various metals. When working with them, the part to be cut is included in the electrical circuit of the plasma device, and an electric arc is ignited between it and the electrode located in the nozzle. The flow of ionized gas is heated throughout the entire area between the point of its exit and the surface of the workpiece - the plasma jet has more power than in devices of the first type. Manual plasma is performed only with the help of equipment of this type, contact method.
3 Devices for manual plasma cutting of metals
They consist of a plasma torch, a power source, a set of cables and hoses with which the plasma torch is connected to the power source and gas cylinder or a compressor. A plasma torch (plasma cutter) is the main element of such equipment. Sometimes, by mistake, the entire apparatus is called this way. This may be due to the fact that the power sources used for plasma cutters do not differ from similar devices and can be used together with welding equipment. And the only element that distinguishes plasma apparatus from another device, and is a plasmatron. Its main components:
- nozzle;
- electrode;
- heat-resistant insulator located between them.
A plasma torch is equipment that converts the energy of an electric arc into thermal energy of plasma. Inside its body there is a cylindrical chamber with an output channel (nozzle) of a very small diameter. An electrode is installed in the back of the chamber, which serves to form an electric arc. The nozzle is responsible for the speed and shape of the plasma flow. A manual plasma cutting machine is used to cut metal manually - the operator holds the plasma torch in his hands and moves it over the cutting line.
Since the working tool is suspended all the time, and therefore can be subject to movement due to involuntary movements of the performer, this invariably affects the quality of cutting. The cut may be uneven, with sagging, traces of jerks, and so on. To facilitate and improve the quality of work, there are special stands and stops that are placed on the plasma torch nozzle. They allow you to place the equipment directly on the workpiece and guide it along the cutting line. In this case, the gap between the metal and the nozzle will always meet the requirements.
At manual cutting The plasma-forming and protective gas (for cooling the nozzle and removing cutting products) can be air or nitrogen. They are supplied from the main line, a cylinder or a compressor built into the equipment.
4 Power sources for hand-held plasma cutting machines
All power sources for hand-held devices operate from alternating current mains. Most of them convert the received electricity into direct current voltage, while the rest only serve to amplify alternating current. This distribution is due to the fact that plasma torches operating on direct current have a higher efficiency. Alternating current used in a number of cases - for example, for cutting aluminum and its alloys.
The power source can be an inverter or transformer that supplies a high current to the plasmatron. Inverters are usually used in small industries and at home. They have smaller dimensions, weight and are much more energy efficient than transformers. Inverters are most often included in manual apparatus For . The advantages of inverter devices include efficiency, which is 30% higher than that of transformer devices, stable combustion of the electric arc, as well as compactness and the ability to carry out work in any hard-to-reach places.
The disadvantages are power limitations (maximum current is usually 70–100 A). As a rule, inverter machines are used when cutting workpieces of relatively small thickness.
Transformer power supplies get their name because of the low-frequency transformers used in their design. They have much larger dimensions and weight, but at the same time they can have higher power than inverter sources. Transformer devices are used for manual and mechanized cutting of metals of various thicknesses. They are more reliable because they do not fail during power surges. The duration of their activation is higher than that of inverter devices and can reach values of 100%.
The switching duration (DS) has a direct impact on the specifics of working with the equipment. For example, if manual plasma cutting of metal, the equipment for which has a duty cycle of 40%, lasted 4 minutes without a break, then the device must then be given 6 minutes of rest in order for it to cool down. Devices with 100% duty cycle are used in production, where the device is operated throughout the entire working day. A significant disadvantage of transformer equipment is high energy consumption.
5 Operating principle of manual plasma cutting machines
After the manual plasma cutting installation has been assembled (all connections and connections of its elements have been made), the metal workpiece is connected to the device (inverter or transformer) with the cable provided for this purpose. The equipment is connected to the electrical network, the plasma torch is brought to the material being processed at a distance of up to 40 mm and the pilot (initiating ionization) electric arc is ignited. Then the gas supply is turned on.
After receiving a plasma jet, which has high electrical conductivity, at the moment of its contact with the metal, a working (cutting) electric arc is formed. At the same time, the attendant switches off automatically. The working arc maintains the continuity of the process of ionization of the supplied gas and the formation of a plasma flow. If for some reason it goes out, then you need to stop the gas supply, turn on the plasma device again and light the pilot arc, and then turn on the gas.