The principle of plasma cutting. Classification of types of plasma cutting

One of the popular types of metal processing is its cutting. There are many ways to get the desired shape from a solid sheet, but in this material we will consider the principle of plasma cutting.

Plasma cutting. In fact - the 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 being processed. Except for the thickness.

• aluminum alloys 120 mm
• copper alloys 80 mm
• steel 50 mm
• cast iron 90 mm

The equipment is different - from industrial to household, so that the technology is available to everyone. Let's consider it in more detail.

Plasma cutting of metal - the principle of operation

A two-component medium acts as a cutter:

• Electric arc working on classical scheme– discharge between cathode and anode. Moreover, the material itself can act as an anode if it is a conductor.
• Gas arc. Heating up under the influence of an electric arc (the temperature reaches 25,000º C), the gas is ionized and turns into an electric current conductor.

How plasma cutting works is shown in detail in this video.

As a result, plasma is formed, which is fed under high pressure into the cut zone. This hot gas jet literally evaporates the metal, and only in 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 border zone.

Important! Properly 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.


His task is to ignite the arc, to support operating temperature, and blow out the molten metal from the cut zone. Since plasma cutters are designed to process any hard materials, including dielectrics - the formation of an electric arc is carried out in two ways:


Figure a) shows a direct cutter. Cathode assembly (8) along with fixed 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 plays the role of a body. From separated from the cathode insulator (7). The gas is supplied in fitting (1) and forms a plasma jet consisting of electric (2) and gas (3) arc.

) plasma jet is called plasma cutting. The plasma flow is formed as a result of blowing gas over a compressed electric arc. At the same time, the gas heats up and ionizes (decays into negatively and positively charged particles). The temperature of the plasma flow is about 15 thousand degrees Celsius.

Types and methods of cutting with plasma

Plasma cutting is:

• superficial;
• separating.

In practice, separation plasma cutting has found wide application. Surface cutting is used extremely rarely.

The cutting itself is carried out in two ways:

• plasma arc. When cutting steel in this way, the metal being cut is included in the electrical circuit. The arc forms between the torch's tungsten electrode and the workpiece.

• plasma jet. The arc occurs in the torch between two electrodes. The product to be cut is not included in the electrical circuit.

Plasma cutting is superior in performance to oxygen cutting. But if a material of great thickness or titanium is being cut, then oxygen cutting should be preferred. Plasma cutting is indispensable for cutting (especially).

Types of gases used for plasma cutting.

Gases are used to form plasma:

• active - oxygen, air. Used for cutting ferrous metals
• inactive - nitrogen, argon,. Used for cutting non-ferrous metals and alloys.

1. Compressed air. Used for cutting:

• copper and its alloys - with a thickness of up to 60 mm;
• aluminum and its alloys - with a thickness of up to 70 mm;
• steel - with a thickness of up to 60 mm.

1. nitrogen with argon. Applicable for cutting:

• high-alloy steel up to 50 mm thick.

This gas mixture is not recommended for cutting copper, aluminium, and ferrous steel;

1. Pure nitrogen. Used for cutting (h=material thickness):

• copper h equal to 20 mm;
• brass h equal to 90 mm;
• aluminum and its alloys h equal to 20 mm;
• high-alloy steels h equal to 75 mm, low-alloy and low-carbon steels - h equal to 30 mm;
• titanium - any thickness.

1. nitrogen with hydrogen. Applicable for cutting:

• copper and its alloys of medium thickness (up to 100 mm);
• aluminum and alloys of medium thickness - up to 100 mm.

The nitric mixture is unsuitable for cutting all steels and titanium.

1. Argon with hydrogen. Used for cutting:

• Copper, aluminum and alloys based on them with a thickness of 100 mm or more;
• High-alloy steel up to 100 mm thick.

For cutting carbon, low-carbon and low-alloy steels, as well as for titanium, argon with hydrogen is not recommended.

Plasma cutting equipment: types and brief characteristics.

For the mechanization of plasma cutting, semi-automatic and portable machines of various modifications have been created.

1. can work with both active and inactive gases. The thickness of the cut material ranges from 60 to 120 mm.

• Gas consumption:

1. air - from 2 to 5 cubic meters / hour;
2. argon - 3 m3/hour;
3. hydrogen - 1 m3/hour;
4. nitrogen - 6 m3/hour.

• Travel speed - from 0.04 to 4 m / min.
• Working gas pressure - up to 0.03 MPa.
• The weight of semiautomatic devices is 1.785 - 0.9 kg, depending on the modification.

2. Portable machines use compressed air.

• The thickness of the cut material is no more than 40 mm.
• Compressed air consumption - from 6 to 50 m3/hour;
• Plasma torches are cooled by water or air.
• Travel speed - from 0.05 to 4 m / min.
• Working gas pressure - up to 0.4 - 0.6 MPa.
• The weight of portable machines is up to 1.8 kg, depending on the modification.
• Water-cooled plasma torches can only be operated at positive temperatures environment.
• Semi-automatic and portable machines are suitable for industrial use.

Two sets are available for manual cutting:

• KDP-1 with RDP-1 plasma torch;
• KDP-2 with RDP-2 plasma torch.

Plasma cutting

The device KDP-1 is used for cutting aluminum (up to 80 mm), stainless and high-alloy steels (up to 60 mm) and copper (up to 30 mm).

Maximum operating current - 400 A.

The maximum open circuit voltage of the power supply is 180 V.

Plasmatron RDP-1 works with nitrogen, argon or mixtures of these gases with hydrogen.

The RDP-1 plasma torch is cooled with water, so it can be used at temperatures above 0 degrees Celsius.

The device KDP-2 is inferior to the first one in terms of arc power (only 30 kW). The advantage of this model is that the RDP-2 plasma torch is cooled by air. As a result, the kit can be used outdoors at any ambient temperature.

Completeness of manual cutting devices:

• cutting plasma torch;
• cable-hose package;
• collector;
• lighter for excitation of the cutting arc.

Sets for manual plasma cutting are produced without a console. Such constructive solution rational for performing a limited amount of work with equipment loading no more than 40 - 50%. But for the time of work they have to be understaffed with welding rectifiers and converters.

At the same time, it should not be forgotten that, from the point of view of safety, for manual cutting, the open circuit voltage of the power source is not more than 180 V.

Do-it-yourself plasma cutting of metals: some subtleties of the process.

• The beginning of the process of cutting metals is the moment of excitation of the plasma arc. Starting cutting, it is necessary to maintain a constant distance between the plasma torch nozzle and the surface of the material. It should be from 3 to 15 mm.
• It is necessary to strive to ensure that the current is minimal during operation, because with an increase in current strength and air consumption, the service life of the plasma torch nozzle and electrode decreases. But at the same time, the current level should provide optimal performance cutting.
• Most complicated operation is punching holes. The difficulty lies in the possible formation of a double arc and the failure of the plasma torch. Therefore, when punching, the plasma torch must be raised above the metal surface by 20–25 mm. The plasma torch is lowered into working position only after the metal is pierced through. When punching holes in thick sheets, experts recommend using protective screens with holes with a diameter of 10-20 mm. The screens are placed between the product and the plasma torch.
• Nitrogen is used as the plasma gas for manual cutting of high-alloy steels.
• At hand cutting aluminum using an argon-hydrogen mixture, the hydrogen content should not exceed 20% to increase the stability of the arc.
• Copper cutting is performed using hydrogen-containing mixtures. But brass requires nitrogen or a nitric-hydrogen mixture. At the same time, brass is cut 20% faster than copper.
• After cutting, copper must be cleaned to a depth of 1-1.5 mm. For brass, this requirement is not mandatory.

Plasma cutting is very often used in industries such as shipbuilding, mechanical engineering, as well as in the manufacture of metal structures, 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 - wood, stone and plastic, are quickly and efficiently cut.

Plasma cutting technology allows you to cut sheet metal and pipes, make curved cuts 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 plasma cutting works.

How does a plasma cutter work?

This apparatus consists of the following elements:

• source of power;
• air compressor;
• plasma cutter or plasma torch;
• cable-hose package.

The power source for the plasma cutting machine supplies a certain current to the plasma torch. It is an inverter or transformer.

Inverters are quite light, economical in terms of energy consumption, inexpensive, however, they are able to cut workpieces of small thickness. Because of this, they are only used in private workshops and small industries. Inverter plasma cutters have 30% more efficiency than transformer ones and their arc burns better. They are often used for work in hard-to-reach places.

Transformers are much heavier, they spend a lot of energy, but at the same time they have less sensitivity to voltage drops, and with their help they cut thick workpieces.

The plasma cutter is considered the main element of the plasma cutter. Its main elements are:

• nozzle;
• cooler/insulator;
• channel required for supplying compressed air;

A compressor is required to supply air. The principle of operation of plasma cutting involves the use of protective and plasma gases. For devices that rated for current up to 200 A, only compressed air is used for both cooling and plasma generation. They are able to cut workpieces with a thickness of 50 mm.

The cable-hose package is used to connect the compressor, power source and plasma torch. By electrical cable a current begins to flow from the inverter or transformer to excite an electric arc, and compressed air is supplied through the hose, which is required for the occurrence of plasma inside the plasma torch.

Principle of operation

Pressing the ignition button starts the power supply high frequency from the power source (inverter or transformer). As a result, inside the plasma torch, an on-duty electric arc, 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 down, 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 one lights up. She starts heat the workpiece at the cutting point. As a result, the metal melts and a cut appears. On the surface of the metal being cut, small particles of molten metal are formed, which are blown away from it by a stream of air. Thus, the operation of the plasma torch is carried out.

Benefits of Plasma Cutting

Metal cutting work is often carried out on a construction site, in a workshop or workshop. You can use an autogen for this, but not everyone is happy with it. If the amount of work associated with metal cutting is too large, and the requirements for cut quality are very high, then you should consider using a plasma cutter that has the following advantages:

Disadvantages of Plasma Cutting

There are also disadvantages in the operation of plasma cutting. The first of them - the maximum allowable cut thickness is quite small, and for the most powerful units it rarely exceeds 80 - 100 mm.

The next disadvantage is the rather stringent requirements for the 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, then a rather significant expansion of the cut occurs, which results in rapid wear of consumables.

Besides, working equipment quite complex, which makes it completely impossible to use two cutters at the same time, which are connected to one machine.

Conclusion

The principle of plasma cutting is quite simple. In addition, the apparatus used for this has a large number of advantages that are several times greater than the existing disadvantages. If you use it correctly, you can save a lot of time and get a quality result.

For cutting metals, several various methods differing from each other in cost and efficiency. Some methods are used exclusively for industrial purposes, others can also be used in everyday life.

The latter include plasma cutting of metals. The effectiveness of plasma cutting is limited by the experience of the craftsman and the right choice installation.

• What is plasma metal cutting?
• What is the basis for the work?
• What are the areas of application of this method of cutting materials?

Plasma Cutting Basics

To understand the basics of cutting metal using the plasma method, you should first understand what is plasma? The quality of the final result depends on the correct understanding of how the plasma torch works and the principles of working with it.

Thermal plasma treatment of metals depends on the parameters of the working jet of gas or liquid directed under pressure to the treated surface. To achieve the desired results, the jet is adjusted to the following characteristics:

• Velocity - the jet is directed at high pressure to the surface of the material. It can be said that plasma cutting metal is based on heating the metal to a melting point and quickly blowing it out. The operating speed of the jet in this case is from 1.5 to 4 km per second.
• Temperature - for the formation of plasma, it is necessary to heat the air almost instantly to 5000-30000 ° C. Heat achieved by creating an electric arc. When the required temperature is reached air flow ionizes and changes its properties, acquiring electrical conductivity. Plasma metal cutting technology involves the use of air injection systems, as well as dehumidifiers that remove moisture.
• Availability electrical circuit. Everything about cutting metal with plasma can only be learned in practice. But some features must be considered even before purchasing the installation. So, there are plasma torches of indirect and direct impact. And if for the latter it is necessary that the processed material pass electricity and be included in the total electrical network(acting as an electrode), then for the first there is no such need. Plasma for cutting metal in this case is obtained using a built-in electrode inside the holder. This method is used for metals and other materials that do not conduct electricity.

Another important point What should be taken into account is that plasma cutting of thick metal is practically not performed, as this leads to increased material costs and is inefficient.

Characteristics and principle of metal cutting with plasma

The basic working principle of plasma metal cutting can be described as follows:

Since the process is associated with instantaneous heating of the cut material to liquid state, the thickness of the metal during cutting is:

• aluminum up to 120 mm;
• copper 80 mm;
• carbon and alloy steel up to 50 mm;
• cast iron up to 90 mm.

There are two main material processing methods that affect the performance of plasma cutting. Namely:

1. Plasma-arc - the method is suitable for all types of metal that are able to conduct electric current. Plasma arc cutting is usually used for industrial equipment. The essence of the method is that the plasma is formed due to the arc that appears directly between the surface of the material being processed and the plasma torch.
2. Plasma jet - in this case, the arc occurs in the plasma torch itself. The plasma-jet processing option is more versatile, it allows cutting non-metallic materials. The only drawback is the need to periodically replace the electrodes.

Plasma cutting of metal works like a regular arc, but without the use of conventional electrodes. But the efficiency of the processing method is directly proportional to the thickness of the material being processed.

Plasma cutting speed and accuracy

As with any other form heat treatment, during plasma cutting of metal, a certain melting of the metal occurs, which affects the quality of the cut. There are other features that are characteristic of this method. Namely:

The quality of work performance largely depends on the professionalism of the master. Clean and precise cut with minimum deviation from required dimensions can only be performed by an employee with a specialized education. Without proper preparation, curly cutting is unlikely to succeed.

Plasma cutting of non-ferrous metals

Used in the processing of non-ferrous metals different ways cutting depending on the type of material, its density and other specifications. For cutting non-ferrous alloys, the following recommendations are required.

Where is plasma cutting used?

The use of plasmatrons is not in vain so popular. With relatively simple operation and low cost of manual installation (compared to other cutting equipment), it is possible to achieve high performance regarding the quality of the cut.

The use of plasma cutting of metal has become widespread in the following areas of production:

The use of plasma cutting machines has not replaced manual settings. So artistic cutting of metal with plasma allows you to make unique details that exactly match the artist’s intention, for use as decorative ornaments for fences and stairs, as well as railings, barriers, etc.

Plasma metal cutting - advantages and disadvantages

Almost no industrial enterprise, one way or another connected with rolled metal, can do without metal cutting. Fast cutting sheet material blank, decorative curly cutting metal with plasma, cutting out precise holes - all this can be done fairly quickly using a plasma torch. The advantages of this method are as follows:

• High productivity and processing speed. Compared to the conventional electrode method, it is possible to perform 4 to 10 times more work.
• Profitability - the plasma method wins a lot against the background of standard methods of processing materials. The only limitations are related to the thickness of the metal. It is impractical and economically unprofitable to cut steel thicker than 5 cm using plasma.
• Accuracy - deformations from heat treatment are almost imperceptible and do not require additional processing afterwards.
• Security.

All these advantages of plasma cutting of metal explain why the method is so popular not only for industrial but also for domestic purposes.

But speaking of the pros, it is necessary to note some negative aspects:

• Restrictions related to the thickness of the cut. Even with powerful installations maximum density The processed surface cannot be higher than 80-100mm.
• Strict requirements regarding the processing of parts. The master is required to strictly adhere to the angle of inclination of the cutter from 10 to 50 degrees. If this requirement is not observed, the quality of the cut is violated, and the wear of components is also accelerated.

Comparison of plasma and laser metal cutting

difference laser cutting metal from plasma lies in the methods of influencing the surface of the material.

Laser systems provide greater productivity and speed of processing parts, while after the operation a lower percentage of reflow is observed. The disadvantage of laser equipment is its high price, as well as the fact that the thickness of the material being cut must be less than 20 mm.

Compared to a laser, a plasma torch has a lower cost, a wider scope and functionality.

Today it is difficult to imagine heavy industry without the use of welding and metal cutting. On most industrial enterprises involved in the processing metal products, a special cutting method is used - plasma.

Plasma cutting is a material processing process in which the cutting element is a plasma jet.

Few people know how do-it-yourself plasma cutting of metal is carried out and what are the main stages this process. Most often, the thickness of the processed products is less than 20 cm. It is for cutting metal of such thickness that plasma devices are used.

Characteristics of cutting products using plasma

Those who use an oxy-fuel cutting torch to cut metal know that plasma cutting differs in many ways from this method. Here, instead of cutting gas, a plasma jet is used. As with conventional welding, plasma cutting uses an electric arc. It is ignited directly between the surface of the object and the electrode. The supplied gas then becomes a 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 velocity 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 can be of several types: active and inactive.

The first category includes oxygen and air mixture, the second - nitrogen, hydrogen, and some inert gases, such as argon. The choice of one or another gas 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 frequently. 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 possibility of using equipment for cutting any metal. This is achieved thanks to elevated temperature in the work area. Secondly, an important aspect is the high speed of work. This ensures the best performance. Thirdly, plasma cutting is great for cutting products of various geometric shapes. Simple gas method this is impossible to achieve. Fourth, great importance has the fact that such metal cutting is accurate and fast. Here, the probability of obtaining low-quality products is greatly reduced, since the work is automated.

Fifth, everyone knows that simple oxygen cutting can be dangerous to humans and others. Plasma cutting is the least dangerous. Sixthly, such work can be carried out both outdoors and under water. It is also important that the cost per 1 m of material is much less, because of all this, plasma cutting is increasingly being used at large industrial facilities. As for negative sides 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 need to choose a quality device. There are 2 types of equipment: inverter and transformer. Inverters are familiar to many, since they are used for welding. They replaced the transformers. Inverter units are small in size, they are compact, aesthetic and consume less energy. When purchasing equipment, you need to pay attention to such characteristics as the duration of work in active mode and power. The disadvantage of such a unit is that it is quite sensitive to power surges in the network.

Equipment for cutting by the type of transformers is the most reliable and durable. A 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 expedient to purchase a transformer-type apparatus. It is also widely used in the manufacture of automobiles. It must be remembered that any plasma cutting is an expensive pleasure.

The device will be expensive. An important criterion when choosing equipment is the maximum cutting thickness. For non-ferrous metals (copper) it is always less. If the technical data sheet indicates a maximum thickness of 10 mm, then this indicator refers to non-ferrous metals.

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Features of manual arc plasma cutting

For cutting metal products, a manual method is often used. Its peculiarity is that it does not require high qualifications to cut the product. Any person can perform the work, 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 inspection of the equipment, nozzle, electrodes. The nozzle and electrodes must be securely fastened. To save materials, it is advisable to strike the arc as infrequently 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 equipment to a central pipeline (if cutting is carried out in 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 step is to set up the equipment. To do this, you need to choose the right current strength. It is preferable to start cutting at high current. In this case, several test cuts are made. An incorrectly selected mode can lead to overheating of the metal and its splashing. At optimal mode arcing, the cut line must be even, and the metal must not be deformed.

If it is required to cut sheet material, then the burner nozzle is placed close to the metal surface. To do this, turn on the power button on the device. Soon after this, the duty arc should light up, and after it the cutting one. The arc must be directed at an angle of 90° to the metal. The burner moves from top to bottom. If automatic plasma cutting is fast, then with the manual method, the torch must be moved slowly. At the end of the work, it is advisable to briefly stop the advance of the torch in order to complete the cutting.

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Cutting various metals

Cutting a particular metal may have its own characteristics. Today, cutting of sheet material is more often used. It is usually represented by steel. Often you have 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, in 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 inside nozzle and electrode. Such an electric arc is necessary in order for the 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. With regard to 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 machine, source electric current, overalls, footwear, a mask, mittens, a hammer, a chisel, a metal 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.