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 materials processing process in which 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. As with 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 air mixture, the second - nitrogen, hydrogen, as well as some inert gases, for example, 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 thanks to elevated temperature V work 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, great importance has the fact 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 negative aspects 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 special feature of transformers is that, at 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 the maximum cutting thickness. For non-ferrous metals (copper) it is always less. If in technical passport If the maximum thickness is 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 does not require high qualifications 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. For the device to start working, it needs to be fed compressed air.
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 an industrial environment). 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. With an optimal arc burning mode, the cut line should be smooth and the metal should 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 internal part nozzle and 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 a cutting apparatus, an electric current source, overalls, shoes, a mask, mittens, a hammer, a chisel, and a wire brush. Often, to carry out such work, a plasma cutting machine is made by hand. In terms of power, it may not be inferior to the factory one.
One of the popular types of metal processing is its cutting. There are many ways to obtain the required shape from a single sheet, but in this material we will look at the principle of operation of plasma cutting.
Plasma cutting. In fact, there is a golden mean. The advantages of cutting metal with plasma combine all of the above technologies. The main advantage is that there are no restrictions on the type of material processed. Just in terms of thickness.
- aluminum alloys 120 mm
- copper alloys 80 mm
- steel 50 mm
- cast iron 90 mm
The equipment varies from industrial to household, so the technology is accessible to everyone. Let's take a closer look at it.
Plasma cutting of metal - operating principle
A two-component medium acts as a cutter:
- Electric arc operating according to classic scheme– discharge between cathode and anode. Moreover, the material itself can act as an anode if it is a conductor.
- Gas arc. Heating under the influence of an electric arc (temperature reaches 25000º C), the gas is ionized and turns into a conductor of electric current.
The principle of operation of plasma cutting is shown in detail in this video.
As a result, plasma is formed, which is fed under high pressure into the cutting area. This hot gas stream literally evaporates the metal, and only in the working area. Despite the fact that the temperature of plasma cutting is measured in tens of thousands of degrees, there is practically no impact on the boundary zone.
Important! Correctly selected speed allows you to get a very narrow cut without damaging the edge of the material.
The source of plasma cutting is a plasma torch. 
Its task is to light the arc, maintain the operating temperature, and blow molten metal out of the cutting area. Since plasma cutters are designed for processing any solid materials, including dielectrics, the formation of an electric arc is carried out in two ways: 
Figure a) shows a direct action cutter. Cathode assembly (8) along with the assigned cathode (6) are one of the electrodes. The second electrode (anode) is workpiece (4)– a metal with good electrical conductivity.
The power cable of the plasma torch is connected to it. Plasma cutting tip (5) in this scheme it acts as a housing. From separated from the cathode insulator (7). Gas is supplied inside fitting (1) and forms a plasma jet consisting of electric (2) and gas (3) arc.
Plasma cutting is a new excellent technology that allows you to cut metals of considerable thickness and of any nature, even the most capricious. The cutting object is not a knife, but a dense jet of plasma, which allows you to form a perfectly accurate cut pattern in a given time unit.
This method of working with metal has many advantages, which we will discuss below. Now let's start with physics - we need to understand the essence of the process.
Plasma metal cutting technology gives the leading female role to our beloved electric arc. It is formed between the electrode and the nozzle. Sometimes instead of an electrode there is metal that needs to be cut. Let's figure out what plasma cutting is.
The beginning of the process is turning on the electrical power source and supplying high frequency current to the plasma cutter. The power source turns on automatically after pressing the ignition switch in the device.
First, a so-called intermediate arc is formed - it is temporary and connects the electrode to the tip of the cutter nozzle. This pilot arc is heated to a temperature level of about 8000°C.
This important point general process plasma cutting - you need to remember that the real arc between the electrode and the metal is not formed immediately, but through its intermediate version.
The next stage of the process is the supply of air from the compressor, which is usually attached to the metal cutting machine. The compressor supplies compressed air. This air enters the chamber of the plasma torch, in which a temporary electric arc is located and already heated.
The arc heats the compressed air, the volume of which increases many times when heated. In addition to heating and increasing volume, the air begins to ionize and transform into a real conductor of electric current. It turns into that same plasma
The small diameter of the nozzle makes it possible to accelerate the flow of this hot plasma to enormous speeds with which the jet flies out of the apparatus. The flow speed can reach three meters per second.
Scheme of plasma cutting operation.
The air temperature is prohibitive, up to 30,000°C. Under these conditions, the electrical conductivity of the air - plasma is almost equal to the conductivity of the metal being cut.
The true terminal arc appears instantly as soon as the plasma flow reaches and touches the metal surface. The temporary arc, in turn, is automatically turned off. The metal begins to melt exactly at the cut point.
Liquid metal drops are immediately blown away by a jet of compressed air. This is the principle of plasma cutting. As you can see, everything is simple, logical and understandable.
Classification of types of plasma cutting
Types of plasma cutting will depend on the environment in which metal work is carried out:
Simple
The main difference between the method is the limitation of the electric arc. Electric current and air are used for cutting. Sometimes gas in the form of nitrogen is used instead of air. If the metal sheet is thin - just a few millimeters - the process can be compared to laser cutting.
With this method, the thickness of the metals should not exceed 10 mm. The method works great for low alloy steels and other soft metals. The cutting element is oxygen, from which a compressed jet is formed, which ultimately turns into plasma.
The cuts produce very smooth edges that do not require further finishing.
Using shielding gas
With this method, instead of air, protective gases are used, which are converted into a plasma stream after conversion in a plasma torch. Quality of cuts in in this case significantly increased due to excellent process protection against influences environment.
Gas for plasma cutting is nothing unusual: it can be hydrogen or argon - the “classic gas”.
With water instead of air
An excellent method with many advantages, one of which is the absence of the need for an expensive and bulky cooling system.
There are other classification criteria for plasma cutting. For example, types of cutting are separation and surface. The first one is used more often.
Another parameter is the cutting method. One type is arc cutting, in which the metal being cut acts as an element of an electrical circuit. Another type is jet cutting, where an electric arc connects electrodes rather than the metal workpiece.
Plasma cutters come in a wide variety of varieties on the market, so they can be classified by brand, manufacturer, and many other technical and commercial parameters.
There is, for example, manual plasma cutting - the most affordable method both in price and ease of execution. There are machine automatic technologies, the devices for which are much more expensive and complex.
Benefits of plasma cutting
The operating principle of plasma cutting.
Most similar technology is laser cutting of metals, so it would be logical to list the advantages in comparison with its “neighbor”:
- Plasma cutting can handle metals of any nature, including non-ferrous, refractory and others difficult to process.
- The speed of the process is much higher than cutting with a gas cutter.
- One of the significant features is the ability to produce cuts of any shape, including geometric patterns and figured cutting of the highest complexity. In other words, plasma cutting is the realization of the most daring creative ideas on metal and other difficult-to-cut materials.
- The plasma cutter does not care about any thickness of metal: speed and quality are in no way lost.
- This method lends itself not only to metals, but also to other materials: it is quite universal.
- Plasma cutting is both faster and more efficient in edge quality than any other mechanical methods cutting
- In this method, it is possible to work not only perpendicular to the metal surface, but at an angle, which helps to master wide sheets of metal.
- From an environmental point of view, this is a completely safe type of working with metal with minimal release of harmful substances or pollutants into the air.
- Excellent time saving due to the absence of the need to preheat the metal.
- Since the method does not use explosive gas cylinders, it is much safer than other methods.
Disadvantages of plasma cutting
No metal processing method is without its drawbacks, and plasma cutting is no exception.
The disadvantages of plasma cutting are as follows:
- The high cost of everything model range plasma cutting machines, including even the simplest manual options.
- Limits on metal thickness for plasma cutting: the maximum thickness is only 100 millimeters.
- This is a noisy way of working because the compressed air or gas is supplied at great speed.
- The equipment is complex, expensive and requires competent and constant maintenance.
Another distinctive positive characteristic of the method is that during the process only a small local area is heated. And this area cools down much faster than with laser or mechanical cutting.
Cooling is only necessary for two constituent elements– cathode and nozzle, as the most loaded. This can be done without any problems using working fluid.
Plasma arc and jet.
The arc begins to work stably as a result of the working relationship between the cathode and the nozzle with steam from compressed hot air. A negative charge is localized at the cathode, and a correspondingly positive charge is localized at the nozzle tip. As a result, an intermediate arc is formed.
Excess moisture is absorbed by a special material located in the reservoir of the plasma torch chamber.
Safety rules for this method are of the strictest nature, because all plasma cutting devices can be very traumatic for the master. This is especially true for models with manual control.
Everything will be fine if you follow the master's recommendations for protective equipment: visor, tinted glasses, safety boots, etc. In this case, you can protect yourself from the main risk factors of this method - drops of molten metal, high voltage and hot air.
Another safety tip is to never tap the cutter on the metal to remove metal spatter, as some craftsmen do. You risk damaging the device, but the main thing is to catch pieces of molten metal, for example, with your face or other unprotected part of the body. Better take care of yourself.
Saving Supplies takes no last place in efficient cutting. To do this, we light the electric arc not too often, but precisely and on time, so as not to interrupt it unnecessarily.
Resource savings also extend to current strength and power. If you calculate it correctly, you will get not only savings, but also an excellent cut without burrs, scale and metal deformation.
To do this, you should work according to the following scheme: first apply a high-power current, make a couple or three cuts with its help. If the strength and power of the current are too high, scale will immediately form on the metal due to significant overheating.
After examining the slices, it will be clear whether to leave the current at this level or change it. In other words, we work experimentally – in small samples.
How to use a plasma cutter?
Electrical circuit of a plasma generator.
Cutting metals using a plasma stream is too serious a task to tackle without prior study and careful preparation. This will help you cut more efficiently from all points of view, and, importantly, minimize the risks associated with industrial hazards.
First of all, you need to know the principle of operation of plasma cutting - to see the whole picture of physical phenomena.
The plasma torch should be kept very close to the surface and edge of the metal, as opposed to laser cutting. When the “start” toggle switch turns on, the temporary electric arc will light up first, and only then the real one, which will be the main cutting element. The torch with the cutting arc must be guided across the material evenly and slowly.
The cutting speed should be strictly controlled. This can be done by observing the sparks with reverse side sheet of metal to be cut. If there are no sparks, this means that the cutting of the metal was incomplete.
This can happen for several reasons: due to too high a speed of the burner or the passage of the apparatus, or too insufficient power of the supplied current, or non-compliance right angle at 90° between the torch and the metal surface.
The fact is that complete melting of the metal occurs only when the plasma cutter is tilted to the metal surface at a right angle and not a degree more or less.
After completing the job, the cutter must be tilted. Air will continue to escape for a short time even after the device is turned off.
Before work, it is not harmful to study the diagram of your device: it is there that you can read the most reliable information on the permissible thickness of the metal that can be cut or made a hole in it. The design of a plasma cutter may vary, it all depends on the functions of its purpose.
Choosing a plasma cutting machine
Buying any technical equipment- a matter for which you do not need to spare time and effort: the risk of an unsuccessful decision and loss of money is too high. And the money here is considerable; you won’t find a plasma cutter cheaper than 500 USD in principle.
First, let's look at the parameters and technical characteristics of the device.
Two large groups of plasma cutters are inverter and transformer. The names speak for themselves.
Open and closed plasma jet.
If you need a compact cutter for working with thin metals, you can opt for an inverter-type cutter. They take little energy, are light and have small dimensions.
At the same time, they work intermittently and easily fail due to changes in mains voltage. The price of such devices is quite reasonable; these are the most inexpensive of all plasma cutters.
Another thing is transformer cutters. Here, both the dimensions and the weight are “all right”: serious devices in all respects.
They consume a lot of energy, but they can work almost without interruption throughout the day. And the thickness of the metal can be greater than when cutting with an inverter model. The cost of such devices is high – from 3,000 to 20,000 USD.
Selecting a plasma cutter by power
We begin our reasoning with the properties and technical characteristics parts that you plan to process and cut. It is this that the power of the cutting device is calculated, because both the nozzle in its diameter and the type of gas used will differ.
The use of plasma cutting is extremely broad, so you only need to talk about your specific needs.
For example, if the thickness metal blanks about 30 mm, a cutter with a power of 90A will be enough for you. It can easily handle your material.
But if your metal is thicker, look for suitable model in the power range from 90 to 170A.
Selecting a cutter based on time and speed of cutting material
The speed of plasma cutting of metal is measured in centimeters per minute. This speed also varies from machine to machine and depends on their overall power and the nature of the metal being cut.
For example, all other things being equal, steel is cut the slowest, and copper and its alloys are a little faster. And even faster - aluminum with its aluminum alloys.
Plasma cutter device.
If speed is important to you, do not forget about such an indicator as the duration of operation without overheating, that is, without interruption. If the technical specification for the machine says that the operating time is 70%, this means that after seven minutes of cutting the machine must be turned off for three minutes to cool down.
Among transformer cutters, there are champions with an operating time of 100%. In other words, they can work all day without shutting down. They cost a lot, of course. But if you have long cuts ahead, consider purchasing “champion” transformer plasma cutters.
A few words about the burner
Again, we evaluate the nature of the metal or other material that we plan to cut. The power of the plasma cutter torch will depend on this. It should be sufficient for a quality cut.
When making calculations, you need to take into account the fact that you may encounter difficult work conditions, which, as luck would have it, must be carried out in the most short time, that is, the cutting should be of a pronounced intensive nature.
We do not lose sight of the burner handle, this an important part for a comfortable, and therefore quality work. Can be fixed on the handle additional elements, which will help keep the nozzle at the same distance from the metal surface. This advice Applies only to manual models of devices.
If you are going to be cutting thin metal, choose a model with a torch that is designed to allow air flow.
If your plans involve massive thick workpieces, buy a cutter with a torch for receiving shielding gas - nitrogen, for example.
For efficient processing For a number of metals, plasma cutting is often used, the operating principle of which is the use of a plasma arc.
1 Metal plasma cutting technology
The plasma arc cutting process that interests us in world practice is “hidden” under the abbreviation PAC. Plasma is a high-temperature ionized gas that can conduct electric current. A plasma arc is formed in a unit called a plasmatron from a conventional electric one.
The latter is compressed, and then a gas is introduced into it, which has the ability to form plasma. Below we will talk about the importance of such plasma-forming gases for the plasma cutting process.
Technologically, there are two cutting methods:
2 Plasma cutting - the principle of operation of the plasma torch
A plasma torch is a plasma cutting device, in the body of which a small cylindrical arc chamber is placed. At the exit from it there is a channel that creates a compressed arc. On the back side of such a chamber there is a welding rod.
A preliminary arc is ignited between the tip of the device and the electrode. This stage is necessary, since it is almost impossible to achieve the initiation of an arc between the material being cut and the electrode. The specified preliminary arc comes out of the plasma torch nozzle, comes into contact with the torch, and at this moment the working flow is directly created.
After this, the forming channel is completely filled with a plasma arc column, the gas forming the plasma enters the plasmatron chamber, where it is heated, and then ionized and increased in volume. The described scheme causes a high arc temperature (up to 30 thousand degrees Celsius) and the same powerful speed of gas flow from the nozzle (up to 3 kilometers per second).
3 Plasma-forming gases and their effect on cutting capabilities
The plasma-forming medium is perhaps the key parameter of the process, which determines its technological potential. The composition of this environment determines the possibility of:
- indicator settings heat flow in the metal processing zone and the current density in it (due to a change in the ratio of the nozzle cross-section to the current);
- varying the volume of thermal energy over a wide range;
- regulation of surface tension, chemical composition and viscosity of the material being cut;
- control of the depth of the gas-saturated layer, as well as the nature of chemical and physical processes in the treatment zone;
- protection against the appearance of underwater marks on metal and (on their lower edges);
- formation optimal conditions for removing molten metal from the cutting cavity.
In addition, many technical specifications equipment used for plasma cutting also depend on the composition of the environment we describe, in particular the following:
- design of the cooling mechanism for the device nozzles;
- option for mounting the cathode in the plasmatron, its material and the level of intensity of coolant supply to it;
- control circuit of the unit (its cyclogram is determined precisely by the flow rate and composition of the gas used to form the plasma);
- dynamic and static (external) characteristics of the power source, as well as an indicator of its power.
It is not enough to know how plasma cutting works; in addition, you should select the right combination of gases to create a plasma-forming environment, taking into account the price of the materials used and the direct cost of the cutting operation.
Typically, for semi-automatic and manual processing corrosion-resistant alloys, as well as machine and economical manual processing of copper and aluminum use a medium formed by nitrogen. But low-alloy carbon steel is better cut in an oxygen mixture, which absolutely cannot be used for processing aluminum products that are resistant to corrosion of steel and copper.
4 Advantages and disadvantages of plasma cutting
The very principle of operation of plasma cutting determines the advantages of this technology over gas techniques processing of non-metallic and metal products. The main advantages of using plasma equipment include the following facts:
- universality of technology: almost all known materials can be cut using a plasma arc, from cast iron and copper to aluminum and steel;
- high speed of operation for metals of medium and small thickness;
- the cuts are of truly high quality and high precision, which often makes it possible not to make additional machining products;
- minimal air pollution;
- there is no need to preheat the metal to cut it, which makes it possible to reduce (and significantly) the burning time of the material;
- high safety of work due to the fact that cutting does not require gas cylinders, which are potentially explosive.
It is worth noting that according to some indicators, gas technologies are considered more appropriate than plasma cutting. The disadvantages of the latter usually include:
- the complexity of the plasmatron design and its high cost: naturally, this increases the cost of each operation;
- relatively small cutting thickness (up to 10 centimeters);
- high noise level during processing, which occurs due to the fact that gas flies out of the plasmatron at transonic speed;
- the need for high-quality and most competent maintenance of the unit;
- increased level of release of harmful substances when nitrogen is used as a plasma-forming composition;
- impossibility of connecting two cutters for manual metal processing to one plasma torch.
Another disadvantage of the type of processing described in the article is that deviation from the perpendicularity of the cut is allowed no more than an angle from 10 to 50 degrees (the specific angle depends on the thickness of the product). If you increase the recommended value, there is a significant expansion of the cutting area, and this becomes the reason for the need for frequent replacement of the materials used.
Now you know what plasma cutting is and are well versed in all its features.
The power source can be:
- transformer. Its advantage is that it is practically insensitive to changes in power supply voltage and allows cutting workpieces of large thickness, but its disadvantage is its significant weight and low efficiency;
- inverter. Its only drawback is that it does not allow cutting thick workpieces. There are many advantages:
- when powered from it, the arc burns stably;
- Efficiency is 30% higher than that of a transformer;
- cheaper, more economical and lighter than a transformer;
- it is convenient to use in hard-to-reach places.
Plasma torch
A plasma torch is a plasma cutter that is used to cut a workpiece. It is the main unit of the plasma cutter.
The design of the plasma torch consists of the following components:
- cooler;
- cap.
Compressor
A compressor in a plasma cutter is required to supply air. It must provide a tangential (or vortex) supply of compressed air, which will ensure that the cathode spot of the plasma arc is located strictly in the center of the electrode. If this is not ensured, then unpleasant consequences are possible:
- the plasma arc will burn unstably;
- two arcs can form simultaneously;
- The plasma torch may fail.
Principle of operation
The operating principle of the plasma torch is as follows. A flow of high-temperature ionized air is created, the electrical conductivity of which is equal to the electrical conductivity of the workpiece being cut (i.e., the air ceases to be an insulator and becomes a conductor of electric current).
An electric arc is formed, which locally heats the workpiece: the metal melts and a cut appears. The plasma temperature at this moment reaches 25,000 – 30,000 °C. Particles of molten metal appearing on the surface of the workpiece being cut will be blown away from it by the air flow from the nozzle.
Technology
The technology of plasma cutting of metal can be briefly described as follows. All types of metals up to 220 mm thick can be treated with plasma.
The effect appears after ignition plasma-forming gas when a spark is formed in the electric arc circuit (between the tip of the nozzle and the non-consumable electrode. The spark ignites the gas flow, and here it is ionized, turning into controlled plasma (with an extremely high output speed of 800 and even 1500 m/s).
In the outlet hole, due to narrowing, the flow accelerates plasma-forming carrier. A high-speed plasma jet allows you to obtain an outlet temperature of about 20,0000C. A narrowly directed jet of thousands of degrees literally melts the material in the targeted area of influence, heating around the treatment site is insignificant.
Plasma arc method used with the closure of the treated surface into a conductive circuit. Another type of cutting (plasma jet)— works in the presence of third-party (indirect) formation of a high-temperature component in working diagram plasmatron. The metal being cut is not included in the conductive circuit
Plasma jet cutting
Plasma jet cutting of workpieces is used for processing materials that do not conduct electric current. When cutting with this method, the arc burns between the forming tip of the plasmatron and the electrode, and the object being cut does not participate in the electrical circuit. A plasma jet is used to cut the workpiece.
Plasma arc cutting
Conductive materials are exposed. When cutting using this method, the arc burns between the workpiece being cut and the electrode, its column is combined with the plasma jet. The latter is formed due to the supply of gas, its heating and ionization. The gas blown through the nozzle compresses the arc, gives it penetrating properties and ensures intense plasma formation. High gas temperature creates highest speed outflow and increases the active effect of plasma on the melting metal. The gas blows metal droplets out of the cutting area. To activate the process, a direct current arc of direct polarity is used.
Plasma arc cutting is used for:
- production of parts with straight and shaped contours;
- cutting holes or openings in metal;
- production of blanks for welding, stamping and machining;
- processing of forging edges;
- cutting pipes, strips, rods and profiles;
- casting processing.
Types of plasma cutting
Depending on the environment, there are three types of plasma cutting:
- simple. This method involves using only air (or nitrogen) and electric current;
- with protective gas. Two types of gas are used: plasma-forming and protective, which protects the cutting area from environmental influences. As a result, the quality of the cut improves;
- with water. In this case, water performs a function similar to a shielding gas. In addition, it cools the components of the plasma torch and absorbs harmful emissions.
Plasma cutting based on these principles ensures not only high-performance production, but also completely fireproof: the materials used in the technology are not flammable.
Video
Watch videos that clearly explain how plasma cutting works:
Operating principle of air plasma cutting of metal
Air plasma cutting: what is the principle of implementation based on. The cutting plasma is a heated gas with a high electrical conductivity. It is also called ionized. Plasma is generated by a special arc element. This cutting method is commonly called plasma cutting.
A conventional arc is compressed by a plasma torch. Ionized gas is blown into it, with the help of which it can generate hot air. It is capable of processing using elevated temperatures. The metal is cut, melting at the same time.
Metal processing occurs thanks to both a plasma arc and a jet. In the first version metal product there is a direct effect, in the second - indirect. The most common and effective cutting method is direct action. For a material that does not have electrical conductivity (usually non-metallic products), the indirect influence method is used. With any of the options, the material being cut does not lose state of aggregation and its design is slightly subject to deformation.
Working principle of a plasma cutter
Plasmatron is technical device, which forms an electrical discharge between the electrode (cathode) and the surface of the workpiece (anode), this occurs in a gas flow that forms plasma.
The principle of operation of the device: water or gas is used for cooling, plasma-forming gas is used to produce plasma. The gas flow entering the chamber is heated to high temperatures after which it is ionized, thereby acquiring the properties of plasma. Plasma-forming gas and cooling gas are supplied to various channels plasmatron. When power is applied, a so-called auxiliary discharge is formed between the cathode and the nozzle; visually it can be seen as a small torch.
The main (working arc) is formed when the secondary discharge touches the surface being processed, which in this case acts as an anode (plus). Stabilization of the discharge can be carried out by a magnetic field, water or gas; often the stabilizing gas is also plasma-forming. After this, material can be cut, coated, welded, surfaced, or even mined by breaking up rocks.
Conventionally, the design of a plasma torch can be represented as several main elements:
- insulator;
- electrode;
- nozzle;
- mechanism for supplying plasma-forming gas;
- arc chamber.
Design and principle of operation of a plasmatron with a combined nozzle and channel
A special feature of a plasmatron using air plasma cutting is the combination of a channel and a nozzle. The air passes through the nozzle channel to the outside. The operating principle is similar; when power is supplied, an auxiliary discharge is formed between the cathode and the nozzle. The air, twisted in a spiral, stabilizes and compresses the column of the working discharge. It also prevents the electric arc from touching the walls of the nozzle channel.
Types of plasma torches
Plasmatrons can be divided into three global types
- electric arc;
- high frequency;
- combined.
Devices operating on the basis of an electric arc are equipped with one cathode, which is connected to a DC power source. For cooling, water is used, which is located in the cooling channels.
The following types of electric arc devices can be distinguished:
- with a straight arc;
- indirect arc (indirect plasma torches);
- using an electrolytic electrode;
- rotating electrodes;
- rotating arc.
Automatic: operating principle
The automatic plasma cutting machine has:
- Remote Control,
- plasma torch
- work table for workpieces.
Cutting machine (China)
Photo source: ru.made-in-china.com
The control panel adjusts preset programs if cutting deviates from the set parameters. For quick corrections during operation and selection of optimal cutting conditions.
An electric current is passed through a sheet installed on the desktop. A primary electric arc runs between the surface of the sheet and the plasmatron. In which compressed air is heated to the state of plasma. The primary arc is hidden in a hot ionized jet, which cuts the metal.
Cutting starts from the middle or from the edge. The more often the arc is interrupted and a new spark is ignited, the shorter the resource of the nozzle and cathode becomes. A competent automatic cutting operator selects cutting modes according to the table and based on specific conditions (metal thickness, nozzle diameter). Thanks to this, you can achieve significant cost reductions. At the end of the operation, the machine will independently notify the operator, turn off and remove the plasma torch from the material.
What gases are used, their features
Plasma cutting of metal is a process of penetration and removal of the melt due to the heat received from the plasma arc. The cutting speed and quality are determined by the plasma-forming medium. Also, the plasma-forming medium affects the depth of the gas-saturated layer and the nature of physical and chemical processes at the cut edges. When processing aluminum, copper and alloys made on their basis, the following plasma-forming gases are used:
- Compressed air;
- Oxygen;
- Nitrogen-oxygen mixture;
- Nitrogen;
- Argon-hydrogen mixture.
IMPORTANT! For some grades of metal, the use of certain plasma-forming mixtures is unacceptable (for example, mixtures containing nitrogen or hydrogen cannot be used for cutting titanium).
All gases used when performing plasma treatment are conventionally divided into protective and plasma-forming.
For domestic purposes (thickness up to 50 mm, arc current less than 200 A), compressed air is used, which can be used as a protective or plasma-forming gas, and in more difficult conditions industrial purposes Other gas mixtures are used that contain oxygen, nitrogen, argon, helium or hydrogen.
Advantages and disadvantages of plasma cutting
Processing metals with devices or plasma cutting machines gives a number of advantages.
- Compared with an oxygen torch, a plasma cutter has a higher power, and correspondingly, productivity, and in this parameter it is second only to industrial-scale laser systems.
- Plasma cutting is beneficial with economic points of view with metal thickness up to 60 mm. For cutting materials with a thickness of more than 60 mm, it is recommended to use oxyfuel cutting.
- Modern plasma cutters are different high precision and high-quality processing metals The cut is “clean”, with a minimum width, due to which it practically does not require additional grinding.
- Also, plasma-arc processing is characterized by versatility of use, safety and low level of environmental pollution.
Among the shortcomings One can note the modest thickness of the cut (up to 100 mm), as well as the impossibility of simultaneous operation of two plasma cutters and compliance with strict requirements for deviations from the perpendicularity of the cut.
Plasma cutting capabilities
The scope of application of plasma cutting is very diverse, due to its versatility and the range of processed metals and metal alloys. Automated and manual plasma cutting of materials is widely used in enterprises and in many industries to perform processing:
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