Cutting metal with a gas cutter: how to use, cut, work, technology

How to properly assemble a cutter with cylinders (oxygen + propane), what is the order of preparatory work? Please tell me a good cutter model.

MAYAK-2-01 gas welding cutter

To work correctly with such equipment, theory alone will not be enough. Before you start, you definitely need to practice at positions with specialists who have experience. Wrong actions can even lead to a tragic accident. Safety precautions should come first here.

Torch Basics

The cutting process with a gas cutter occurs by burning the metal in a stream of oxygen supplied under pressure.
The alloy must first be heated to the required operating temperature using a burning mixture of acetylene and oxygen. The only metals that can be cut using this method are various grades of carbon and non-alloy steel. Stainless steel, non-ferrous metals and alloys cannot be cut with an oxygen-acetylene cutter. To perform this type of work, in addition to the appropriate set of gas equipment, you will need the following:

• Fire extinguisher.
• Protective equipment: special glasses; thick leather gloves; sturdy work shoes with leather soles.
• Appropriate clothing – fire-resistant clothing is recommended, but if not available, well-fitting cotton clothing will do. You should not wear items made of synthetic or flammable fabrics, loose fit, or with torn or worn edges.
• Tools for measuring and marking: ruler, square and pencil made from soapstone.
• Lighter for gas cutter - designed to properly ignite the flame of the cutter. Using regular matches and lighters is very dangerous.

Preparing a place and conditions for safe and comfortable work

To ensure safe work using a cutting torch, you must follow the following rules and recommendations:

• To perform the work, choose only a place in a perfectly ventilated room or in the open air.
• You can cut away from flammable substances and materials.
• The floor in the room should be concrete or earthen.
• The surface of the earth or concrete must be cleared of any foreign objects and materials within a radius of at least 5 m, since sparks from the metal being cut scatter over several meters and can set fire to dry rags, shavings, paper, dried plants or leaves.
• The metal to be cut is placed on a suitable support so that the cutter can be used at a comfortable working height. For these purposes, it is best to use a steel table.
• Do not allow the flame to touch the concrete (especially if it is fresh) - this will cause its expansion and subsequent intense cracking with small fragments of concrete flying out of it.
• It is strictly forbidden to use flammable surfaces as workers, or on which flammable or explosive materials are spilled.
• The location of the metal cut is marked as shown in the video.

Preparing and setting up gas cutting equipment

In order to work safely with a gas cutter, it is important not only to correctly select the appropriate set of equipment, but also to connect and configure it correctly. First, the corresponding tubes are connected to the oxygen and acetylene cylinders. Oxygen hoses and containers are usually green, acetylene hoses are red.

Safety valves (a device that delays flashback flames) should be installed at both ends of the hoses.

The next step is to check that the acetylene supply is working properly. First, close the flow control valve - the T-shaped handle is rotated back several times. On the cylinder, in its upper part, open the valve - turn it 1 turn of the hand. They do this for safety reasons. The acetylene pressure in the cylinder should not be allowed to exceed 1 atm - in case of high pressure, this gas becomes unstable and can even spontaneously explode or ignite. To check that the acetylene pressure is adjusted correctly, do the following:

1. The main valve of the container is unlocked, then the control valve is opened by turning the handle in a clockwise direction. This must be done very slowly, monitoring the readings of the pressure gauge installed at the low pressure outlet. The control valve is opened until the pressure reaches 0.34–0.54 atm.
2. Then blow air from the hose - open the acetylene valve of the cutter until the sound of escaping gas appears. After this, look at the readings of the low pressure gauge. When purging, the pressure value should be stable (if not, then make sure that the regulator is installed correctly).
3. The valve on the cutter is closed.

They check and adjust the oxygen supply - turn off the oxygen supply regulator (twist it down), and then adjust the pressure. To reduce the oxygen supply, twist the pressure gauge knob a few turns back. Then perform the following steps:

1. The main valve on the oxygen cylinder is fully opened. It is double-seated and if it is partially opened, due to the high pressure in the cylinder (150 atm), oxygen escapes around the sealing ring of the valve stem connection.
2. Slowly open the supply regulator, monitoring the readings of the pressure gauge installed at the low pressure outlet until the oxygen pressure is adjusted within the range of 1.7–2.7 atm.
3. Blow out the atmosphere from a hose - open the oxygen valve on the cutter. The cutter has 2 valves for oxygen: one is closer to the hose, controls the flow into the chamber where oxygen is mixed with acetylene to heat the steel (burning the mixture), as well as for supply to the oxygen nozzle for cutting; the other is located further and supplies oxygen to a separate cutting nozzle (until this valve is opened or the special cutting lever is released, oxygen should not leave the cutter mouthpiece). First, the first valve is opened - it is turned several times, ensuring a sufficient flow of oxygen to carry out both functions. After this, open the second (front) valve slightly until the hose is cleared (3–5 s for a 7.5 m long tube).
4. The front valve is closed.

Ignition of the torch and heating of the metal

Before igniting the torch, you must:

• make sure that all connections (valves, pressure gauges, hoses, other fittings) are tight - any gas leak can instantly cause a fire;
• check the place of work again for the absence of flammable materials, strangers (especially children), and animals;
• make sure you are ready to work;
• Wear safety glasses and gloves.

Then the acetylene valve on the cutter is opened, allowing the oxygen in the mixing chamber to escape. A few seconds are enough for this. Then they tighten the valve until you can hear that acetylene is barely coming out. A special lighter for it is placed in front of the cutter, as shown in the video, so that its inner part touches the mouthpiece. Then press the lighter lever. When the sparks produced ignite the acetylene, a small yellow flame should form in front of the mouthpiece.

By tightening the gas supply valve, the flame length is increased to approximately 25 cm. The torch should start at the very mouthpiece of the cutter. The flame will come off or jump when too much acetylene is supplied.

Slowly open the front oxygen valve. In this case, the flame should change color from yellow to blue - at this moment, the supply of such an amount of oxygen will be provided, which is sufficient for the complete combustion of acetylene. The oxygen supply should be increased until the inner tongue of blue flame decreases and contracts towards the mouthpiece.

The oxygen valve is opened even further - the size of the torch is increased until the length of the internal flame becomes barely greater than the thickness of the steel being cut (for cold-rolled sheets with a thickness of 9.5 mm, it is enough to exceed the flame length by 1.3 mm). When you hear a "snuffing sound" or the blue flame appears feathery and unstable, there is too much oxygen being supplied. It is reduced until the entire flame stabilizes and the internal one takes the shape of a clear cone.

The very tip of the internal flame is brought to the surface of the steel being processed. It is heated until a pool of molten glowing metal forms at the point of contact. The tip of the flame must be kept motionless at a distance of approximately 10 mm from the surface of the steel as shown in the video, so that all the heat is concentrated in one area.

Cutting steel with a gas cutter

The handle of the gas cutting valve is slowly released down - a stream of oxygen is supplied, igniting the molten metal. If a violent reaction immediately begins to occur, then the steel has caught fire and you can continue to gradually increase the oxygen pressure until its stream cuts right through the material. When the reaction does not proceed, the metal is not heated enough to ignite in a stream of oxygen. It is necessary to add oxygen to the heating flame and allow it to heat the steel.

When the oxygen stream begins to cut, the cutter mouthpiece begins to slowly move along the cutting line. In this case, almost all processing products (molten slag, sparks) are blown away by a jet to the rear side of the cutting zone as shown in the video. If this flow comes back or slows down, then you need to reduce the speed of the cutter or stop it and heat the material even more (it is better to work very slowly than to try to cut too quickly). Cutting continues until the intended cut or separation of metal is completed.

Advantages of the method

Gas cutting has many advantages over other types of metal processing. This:

Advantages and disadvantages of gas cutting

• smooth and neat seam (subject to all rules);
• the ability to cut steel up to 80 mm thick, and cut other metal products up to 200 mm thick;
• performing work of increased complexity;
• autonomy, the ability to work in “field” conditions;
• versatility, use for a large number of rolled products;
• the possibility of surface treatment of metal without damaging deep layers;
• high cutting speed (compared to the melting method);
• no possibility of decomposition products getting into the metal;
• The optimum ratio of price and quality.

The cutter can work with metals of any thickness, making straight, rectilinear, contour or arbitrary cuts.

Metal gas cutting process

There is no need to extinguish the flame after cutting the metal. As a result, significant heat loss is avoided. If necessary, the cutting process can be quickly stopped. It is enough to extinguish the flame, and the metal will cool in a short time.

Using oxygen cutting, you can make products with complex shapes, without the possibility of torn seams.

Gas cutting is suitable for cutting for welding, removing the surface layer, eliminating defects, making blanks and cutting rolled metal sheets.

Advantages and disadvantages

Cutting metal with propane has a number of advantages, among which are the following:

1. Gas cutting is in demand in situations where there is a need to cut metal of considerable thickness or create products according to templates that require the production of a curved cut that cannot be made with a grinder. You also cannot do without a gas cutter even when faced with the task of cutting out a disk from thick metal or making a blind hole of 20-50 mm.
2. A gas cutter is a very easy-to-use tool and is lightweight. All home craftsmen who have experience working with gasoline models are aware of the inconveniences associated with large weight, size and noise. In addition to the fact that vibration creates significant inconvenience, the operator is forced to provide serious pressure during operation. Gas models seem to be a more attractive alternative due to the absence of all the above-mentioned disadvantages.
3. Using metal cutting with gas allows you to speed up the work by 2 times, which cannot be done using a device equipped with a gasoline engine.
4. Among most gases, including gasoline, propane has a lower price. For this reason, it is better suited for carrying out a significant amount of work, for example, if there is a task of cutting steel into scrap metal.
5. When using propane cutting, it is possible to create a narrower cut edge than when working with acetylene cutters. At the same time, the method under consideration allows you to create a cleaner cut than what can be done using gasoline torches or a grinder.

Among the disadvantages that propane cutters have, only one should be highlighted: they can only be used for a limited range of types of metals. They are suitable for cutting exclusively low and medium carbon steels, as well as ductile cast iron.

Features of use

Such tools are not suitable for cutting high-carbon steels for the reason that they have a fairly high melting point, which is almost the same as the flame temperature.
This leads to the fact that instead of the release of scale, which looks like a column of sparks, from the back side of the sheet, it mixes with the molten metal along the edges of the cut. As a result, oxygen cannot reach the thickness of the metal, which is why it fails to burn through the material. Difficulties when cutting cast iron are created by the shape of the grains, as well as the graphite between them. True, this does not apply to malleable cast iron. It is impossible to solve the problem if you have to deal with aluminum, copper and their alloys.

It is important to dwell on the following point: the category of low-carbon steels is represented by grades from 08 to 20G, medium-carbon steels - grades from 30 to 50G2. A characteristic feature of carbon steel grades is the presence of the letter U in front of their names.

Oxygen-propane metal cutting

The most common operation with metal is cutting it. And indeed:

• during this operation, the part is “born” in the procurement area of ​​metalworking production;
• the same operation terminates its practical use after disposal;
• shaping, repairs, etc. cannot be done without it.

There are many methods of cutting metal used in industry and everyday life. Not the least of them is gas cutting. We will discuss the most cost-effective, and therefore widespread, oxygen-propane metal cutting (hereinafter referred to as OPRM) in this article.

Metal cutting with oxygen and propane

First, let's figure out how metal is separated by oxygen in general. Cutting with this gas is based on the property of the metal to burn under the influence of a jet of this gas, or more precisely, its combustion temperature. Further, under the influence of its pressure, the resulting combustion products are removed from the cut.

Let's take a closer look at the process. It is divided into two main stages:

• at the first stage, the alloy is heated to the required operating temperature (at which the metal ignites in a stream of oxygen). To do this, use the flame of a burning mixture of heating gas (acetylene, propane, etc.) with oxygen;
• on the second, cutting oxygen is supplied in the form of a narrow jet under high pressure. It leads to the continuous formation of metal oxides throughout its entire thickness (the metal is “burned through”). The cutter moves and burns the metal with a stream of oxygen, removing combustion products along the way. As a result, a cutting line is formed. Heating gas is used only until the working area on the surface of the workpiece is heated to the metal combustion temperature. At the second stage, it is not needed (it is blocked) - the required temperature regime is maintained by oxygen.

Oxygen cutting, as follows from its definition, can be applied to all metals and alloys. It can only be carried out by those that, under the influence of oxygen, have the following properties:

• their combustion temperature should be lower than this indicator during their melting;
• metal oxides formed during the cutting process must have a melting point lower than that of the metal itself;
• the amount of heat generated during the processing process must be sufficient to maintain the process of constant oxygen cutting;
• The slags formed during the processing of parts must be fluid. This will ensure their easy removal from the work area;
• the alloys and metals being cut should not have high thermal conductivity. These include: low carbon steels. For example, brands from 08 to 20G;
• medium carbon steels. For example, brands from 30 to 50G2;
• malleable cast iron.

ATTENTION ! On the other hand, it is impossible to cut high-carbon steels with oxygen cutting (they have the letter “U” in their designation). This is due to the fact that their melting point is close to the flame temperature. As a result, scale will not be thrown out from the back side of the sheet (in the form of columns of sparks), but will mix with the molten metal along the edges of the cut. This will not allow oxygen to “get” deep into the metal and burn it. The shape of the grains and the graphite between them will interfere with cutting cast iron (malleable cast iron is an exception). Aluminum, copper and their alloys will also not lend themselves to oxygen cutting.

Choosing a flammable gas

When using a conventional flame cutter to cut metal, both propane and acetylene are used as preheating. However, in most cases, propane is used for cutting. The reasons for this choice are the following:

• the cost of propane is significantly lower than acetylene;
• less explosive of propane. It is possible to quickly detect leaks because mercury-containing additives are added to propane cylinders. The specific smell of these additives makes it easy to detect the location of a gas leak (depressurization). In addition, acetylene requires much more careful compliance with safety regulations, which is not always easy to do in a metalworking area;
• when carrying out propane cutting, a narrower cut edge is created than when working with acetylene; -the strong smell of acetylene creates discomfort and is not always acceptable. This is especially true if cutting is carried out in a regular workshop where other workers are also working. Considering the above, preference is given to propane.

Equipment for oxygen-propane metal cutting

The metal cutting operation is carried out with a gas cutter. The figure shows an image of this tool and its controls (valves).

Gas cutter device. East. https://rezhemmetall.ru/gazovyj-rezak-po-metallu.html.

Explanation of the figure. The cutter consists of the following components:

• handle with nipples for connecting oxygen and gas hoses;
• housing with propane and oxygen control valves.

The designs of gas cutters from different manufacturers differ slightly. Typically, they have 3 valves:

• the first is for supplying propane. Red or yellow;
• the second – regulating oxygen (for the heating flame);
• the third is cutting oxygen. All oxygen valves are blue.

Almost all parts of this device are replaceable. Therefore, in the event of a breakdown, it can be quickly repaired right at the workplace. The most common cutters are the “P1-01” model or the more powerful “P2-01 and P3-01P”.

In general, cutting metal with gas requires:

• one propane and oxygen cylinder each. Cylinders must be equipped with gas reducers. It should be borne in mind that the thread on the propane cylinder is reversed and it is impossible to screw an oxygen reducer onto it;
• high pressure hoses (oxygen);
• cutter;
• mouthpiece of the required size.

It is necessary to select the mouthpiece correctly, and the choice should be based on the thickness of the metal. For example, if the workpiece consists of parts of different thicknesses 6...300 mm, then you will need mouthpieces with internal numbers from 1 to 2 and external ones - from 1 to 5.

For small production volumes and in everyday life, mobile posts with the specified equipment are used.

Set of mobile equipment for CPRM. East. https://tutmet.ru/oborudovanie-mashina-stanok-gazovoj-rezki-metalla.html.

Such posts are equipped with everything necessary from cylinders and a cutter to auxiliary clamps.

In large industries, autonomous tables are used. This is gas equipment for cutting metal in automatic mode, which, in most cases, is carried out without the participation of an operator. The most famous of them are “Smena”, “Orbita”, “Secator”, “Quicky-E”.

CNC machine “Start-2” for thermal cutting of metal using a mixture of flammable gas and oxygen. East. https://stanki-tvm.ru/produkciya/stanki-gazovoy-rezki-s-chpu.

How to cut

When starting work, first of all, you need to purge the hoses with oxygen to remove any debris or dirt that has gotten there.

Secondly, check for suction in the cutter channels. To do this you need on it:

• connect the oxygen hose to the oxygen fitting (the heating gas fitting must remain free);
• set the oxygen supply pressure to 5 atmospheres and open the gas and oxygen valves on the cutter;
• Check the free fitting with your finger to make sure: is there air leakage? If not, then you should clean the injector and blow out the cutter channels.

After that they are connected to the device:

• the oxygen hose is attached to a fitting with a right-hand thread using a nipple and a nut;
• propane hose - to the fitting with a left-hand thread in the same way.

Followed by:

• check the detachable connections for leaks. Fix detected leaks by tightening the nuts or replacing the seals;
• check the tightness of the gas reducers and the serviceability of the pressure gauges.

Gas cutting of metal should begin by mechanically removing rust and other contaminants from its surface. The necessity of this operation is due to the following. When carbon burns, CO oxide is formed. When interacting with iron, it increases the carbon content on its surface (especially at the cut site). This leads to the formation of hardened structures in the metal, which will heat unevenly. Which, in turn, will lead to the appearance of mechanical stress at the edges of these structures and, as a consequence, to some shortening of them. As a result: deformations occur and cracks form. Mechanical cleaning of the surface to be cut allows you to avoid such defects.

Next, the workpiece, sheet or other workpiece should be placed in such a position that the cutting gas jet can freely pass through it.

We set the operating pressure on the gas cylinder reducers. Typically, the pressure ratio of the heating gas to oxygen is 1:10. Therefore, we set, atm:

• on propane – 0.5;
• on oxygen – 5.

Further actions have the following sequence:

• open the propane a little on the cutter (a quarter turn of the valve flywheel or a little more) and ignite the gas;
• We rest the mouthpiece of the cutter nozzle against any metal (preferably at an angle) and slowly open the regulating (heating) oxygen.

Be very careful. Do not confuse the preheating oxygen valve with the cutting gas valve.

• by alternately adjusting both valves (opening and closing them), achieve the flame strength we need. The length of the flame (aka its strength) is selected based on the thickness of the metal: the thicker the sheet or other part being cut, the stronger the flame should be. Accordingly, the consumption of oxygen and propane increases. When the flame is adjusted, it acquires a blue color and a crown.

Now you can start processing the metal (we remind you that processing begins with heating and then separation):

• We bring the cutter nozzle to the edge of the metal and hold it at a distance of 5 mm from the part to be cut at an angle of 90°. In the event that a sheet or other product needs to be cut from the edge, then the metal should be heated from the point from which the cut will begin. We heat the upper edge of the part to a temperature, °C: T = 1000…1300 (the value of the parameter depends on the type of metal being cut and its ignition temperature). Visually, it looks as if the surface has begun to “wet” somewhat. Warm-up time will last only a few seconds (up to 10);
• when the metal ignites, open the cutting oxygen valve. A powerful, narrowly directed jet of cutting oxygen is supplied to the part being cut. The cutter valve should be opened very slowly. In this case, the oxygen will ignite from the heated metal on its own, and this will avoid the backlash of the flame, accompanied by a pop. When cutting has begun, turn off the heating gas (propane).

Important ! From this point onwards it is very important to ensure a continuous supply of cutting oxygen. Otherwise, the flame may go out, the burning of the metal will stop and you will have to start all over again (ignition, adjusting the flame, heating the surface to be cut, etc.).

Subtleties at work

The efficiency of metal cutting is influenced by two main parameters:

• cutting speed;
• cutting depth.

These parameters are greatly influenced by the quality of the heating gas - propane. It is known that in order to detect its leaks (much attention is paid to this, since propane is explosive, but odorless), it is mixed with another gas - butane, which has a specific odor and is easily identified when released into the atmosphere. It is necessary to carefully monitor its concentration, because even if propane contains at least 10% butane, the process of heating the metal before its separation slows down sharply and labor productivity drops.

Propane has one more feature. As the ambient temperature decreases, the density of propane increases, and the fluidity, accordingly, decreases and it flows more slowly to the burner mouthpiece. Therefore, in addition to controlling the concentration of butane, it is necessary to control the temperature of the container in which it is located.

In addition, it is necessary to monitor the oxygen pressure, since this pressure significantly affects the thickness and quality of cutting:

• the pressure is not high enough: it will not allow you to cut through the entire thickness of the metal;
• will make it difficult to remove oxides;

The technologist selects the metal cutting speed based on the properties of the metal. You can check it during operation by emitting sparks and slag:

• if the speed is chosen correctly, the sparks are directed downward at an angle of 85...90°;
• at low speed, the column of sparks advances the cutting movement;
• at excessive speed: there is a lag in the flow of sparks from the cutter;
• There is no through cutting of the workpiece.

When cutting thick metal, it should be taken into account that the cutting jet has the shape of a cone, which expands at the bottom. This can lead to unpleasant consequences: an increase in the width of the cut and the formation of scale at the bottom. To avoid this, it is necessary to increase the supply of cutting oxygen, but it should be taken into account that it can:

• scale appears on the upper edge of the cut;
• increase oxygen consumption.

Metal cutting should be done slowly, conducting a stream of oxygen along a given line. It is very important to choose the right angle of inclination. It should first be 90°, then there should be a slight deviation of 5...6° in the direction opposite to the cutting direction. However, if the metal thickness exceeds 95 mm, a deviation of 7...10° can be allowed. When the metal has already been cut by 15...20 mm, it is necessary to change the angle of inclination to 20...30°.

Sometimes it becomes necessary to perform surface or figured cutting. Surface cutting (hereinafter referred to as SR) consists in not cutting through the metal, but only creating a relief on its surface (by cutting grooves). In this case, the metal will be heated not only by the flame of the cutter, but also by the molten slag - spreading, it will heat the lower layers of the metal. PR begins as usual: the desired area is heated to the ignition temperature. Next, turn on the cutting oxygen and create a source of metal combustion. By moving the cutter evenly, you ensure the stripping process along the specified cut line, but in this case the cutter must be positioned at an angle of 70...80° to the plane being processed. When supplying cutting oxygen, the cutter should be tilted at an angle of 17...45°. The processing scheme is shown in the figure.

Scheme of surface oxygen cutting. East. https://1metallocherepica.ru/instrumenty/pravilnaja-rezka-propanom.html.

The groove dimensions (width and depth) are adjusted as follows:

• changing the cutting speed: increasing the speed, reducing the size of the recess;
• The groove depth will increase if: the angle of inclination of the mouthpiece increases;
• cutting speed will decrease;
• oxygen pressure will increase;

ATTENTION ! It should be remembered that the depth of the groove should be approximately 6 times less than its width. Otherwise, “sunsets” will form on the surface.

Shaped cutting is performed as follows. We mark the outline on the sheet of metal. Please keep in mind that:

• Before cutting begins, holes should be punched;
• When marking circles or flanges, the centers of these circles should be marked.

It is always necessary to start cutting from a straight line - this will help to get a clean cut on the curves. You can start cutting a rectangle anywhere (except the corners). Lastly, the outer contour is cut out. This sequence will allow you to cut out the part with the smallest deviations from the drawing.

Oxygen and propane consumption when cutting metal

Oxygen consumption for metal cutting is calculated using the formula:

Рdet = HL + HKh

In this formula:

• Рdet – the volume of oxygen required to perform a cut, cubic meters;
• N - consumption standards during the working process, cubic meters/m;
• L – total cutting length of the part to be cut, m;
• Kh is a coefficient that takes into account many features of the work process that require gas consumption at: the initial stage: purging;
• adjustment;

The Kh coefficient is usually equal to:

• 1.1 – for single production;
• 1.05 – for industrial (serial) production.

The rate of oxygen consumption “N” for metal cutting depends on the power of the equipment and the cutting mode. It is calculated using the following formula:

H = P/V

In this formula:

• N – oxygen consumption rate, cubic m/m;
• P – permissible gas flow, cubic m/hour. It is indicated in the technical specifications of the equipment used;
• V is the metal cutting speed, m/hour.

The most commonly used gas flow rates (measured in cubic meters per hour) for various cutting speed ranges for certain types of equipment are shown in the following table. Table No. 1

Considering that the cutting speed and thickness of the metal being processed directly depend on the permissible gas consumption, these values ​​can be easily and simply determined by interpolation. Consequently, it is possible to make an aggregated (estimated) calculation of the consumption of various gases, regardless of the type of thermal cutting of metals. For this you only need:

• cut length;
• metal thickness;
• equipment power.

The permissible flow rate (oxygen and propane) is taken from the equipment passport. Cutting speed is found in reference books, which contain special tables or diagrams that connect all the initial data.

The ratio of oxygen and propane when cutting metal

Oxygen cutting is based on the combustion of metal in a stream of technically pure oxygen. From the description above, you know that propane mixed with oxygen is only necessary to heat the metal being processed. The amount of heating gas depends on many factors:

• steel grade;
• material thickness;
• cutting length, etc.

Additional factors affecting consumption are:

• gas consumption at the initial stage of cutting: purging;
• equipment adjustment;

Recommended ratios are indicated in the accompanying documentation for specific equipment. The calculated ratio of gas volumes is determined from reference books, which contain special tables and diagrams that connect all the data. These parameters are indicated in the accompanying technological documentation. In the process of work, they can be adjusted in one direction or another.

If you do not have the specified documentation, then the pressure should be set in accordance with the above ratio. Typically, the pressure ratio of the heating gas to oxygen is 1:10. Therefore, we set, atm:

• on propane – 0.5;
• on oxygen – 5.

Propane consumption, in addition, will depend on the number and duration of warm-ups.

Safety precautions when working with propane

When performing gas cutting of metal, it is necessary to strictly follow safety regulations, since this work is associated with a certain risk. Let's start with protective (work) clothing. It should include:

• fire-resistant suit and hand guards with the same impregnation;
• a welder's mask made of non-flammable plastic with a headband;
• work shoes with high sides.

In addition, it is recommended to use a respirator (to avoid breathing fumes and dust). This recommendation should not be neglected, since a situation may arise in which thick metal is not blown through the first time. In this case, molten splashes (and this is hot metal!) Can fall on a person.

Do not start cutting if there are cracks, breaks or joints in the gas hoses. In case of urgent need, it is allowed to use aluminum or brass tubes at the joint. However, it is better not to risk it and replace them with conditioning hoses as soon as possible.

ATTENTION ! Under no circumstances should steel tubes be used at the joints of gas hoses, as iron can cause a spark and unpredictable consequences.

REMEMBER ! Propane is flammable, and oxygen is oil hazardous, i.e., if oxygen comes into contact with any oil, an explosion will occur. Therefore, do not touch the oxygen cylinder with oil-stained gloves or clothing. And under no circumstances leave oily rags - put everything in containers specially designed for this.

Cylinders should be located at a distance of 10 m from the workplace and 5 m from each other. During work, we must not forget to monitor the gas pressure in the cylinders. It is not allowed to consume all the gas from the cylinder.

During the work, emergency situations may arise.

Don't panic under any circumstances!

If your oxygen hose comes off the fitting or breaks while cutting metal, you must immediately turn off the propane supply to the cutter, and then close both cylinders. If, when igniting the flame and adjusting the cutter, a pop is suddenly heard and the flame disappears, then you should simply close the cutter valves and re-ignite the flame.

Advantages and disadvantages

The advantage of CPRM is the low cost of heating gas - propane, and the disadvantage is that they can only use low- and medium-carbon steels, as well as ductile cast iron. CPRM is advantageous to use for large volumes of work (cutting steel for scrap, etc.). Conventional oxygen cutting of pipes made of chromium and chromium-nickel steels, as well as cast iron, copper and its alloys is practically impossible. To process these parts from these metals, the following is used:

• oxygen-acetylene cutting. The use of acetylene for heating allows you to increase the heating temperature and, accordingly, the thickness of the workpieces being processed. But at the same time the cost of work increases sharply;
• oxygen flux cutting. This method involves feeding powdered flux into a stream of cutting oxygen. This material is designed to burn in oxygen and release additional heat at the cutting site. It should promote the melting of refractory oxides. Molten oxides, in turn, form liquid slags, which flow down and do not interfere with the cutting process. The main component of these fluxes is iron powder of the PZh5M, VM, VS grades and various additives (for example, aluminum powder);
• oxygen-arc (also called gas-electric) cutting. This is a cutting method in which metal, melted by an electric arc, is continuously removed by a stream of gas. The following gases can be used: compressed air;
• oxygen;
• nitrogen, etc.

The most widely used technology is the use of compressed air. This is due to its lowest cost. Air arc cutting is used for:

• smelting defective welds, cavities and cracks;
• V-shaped preparation of edges for welding;
• separation cutting of carbon and alloy steels, cast iron and non-ferrous metals.

It is most widely used for separation cutting of stainless steel up to 20…25 mm thick. The advantage of these types of cutting is the possibility of expanding the range of processed metals, but the disadvantage is the complexity of the technology and increased cost.

Sections: Gas metal cutting

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Cutting Features

The cutter must be moved smoothly along the cutting line and monitor the angle of inclination, which deviates 5-6 degrees against the movement of the tool. When the metal thickness is more than 0.95 m, the deflection is increased by cutting through the metal to a depth of about 20 mm, and the deflection angle decreases again. We have already explained in detail how to cut with a cutter so that the cut is even in the previous section.

How much gas is consumed?

Gas consumption when cutting metal with a propane-oxygen cutter depends on the thickness of the structure and the configuration of the cut. For clarity, we present the table below:

Gas consumption is significantly reduced when surfacing or soldering is performed.

Nuances

The main task of the performer is to maintain the speed correctly:

• normal mode - sparks fly at right angles relative to the surface of the workpiece;
• low speed - flying away from the performer and an angle of less than 85 degrees.

After the process is completed, the oxygen supply is turned off first, and the propane is turned off last.

Negative deformation

Beginning welders are concerned with the question of how to properly use a propane-oxygen cutter so that warping of the surface of the part does not occur. First you need to figure out what factors contribute to the occurrence of these defects:

• with uneven heating of the surface;
• a high cutting speed was selected;
• there was a sharp cooling of the heating area.

To eliminate the occurrence of the listed factors on the workpieces, they are first securely fixed and heated, and the speed is increased gradually. If warping does occur, then the original shape can be returned by firing or tempering, and the sheets can be straightened on rollers.

Kickback hazard

If the jet burns in an incorrect mode, a bang occurs and the flame is drawn inside the product, which leads to an explosion, as the fire spreads through the hoses and reaches containers with gases. To prevent a dangerous situation, the cutter is equipped with a non-return valve, which cuts off the flame and prevents it from spreading.

Terms of use

They are similar to safety precautions when welding, but have specific additions:

1. It is not recommended to neglect protective equipment, as this leads to injury in the form of skin burns or damage to the cornea of ​​the eyes from flying sparks, so goggles and gloves with long bells up to the elbow are required.
2. The performer's clothing and shoes are made of non-flammable material.
3. Gas cylinders are located no closer than five meters from the cutting site.
4. The flame of the cutter is directed only in the direction opposite to the hoses.
5. Cutting is carried out in rooms equipped with strong ventilation or in open areas.

If the equipment is idle for a long time, it is necessary to carry out preventive maintenance before using the cutter for its intended purpose.

Is it possible for metal to deform?

Gas cutting involves a thermal effect on the material; as a result, deformation changes cannot always be avoided. Deformation consists of lengthening, shortening or bending of a product. The cut part can be turned inward or outward.

There are factors that contribute to metal deformation:

Oxygen cutting process diagram

• uneven heating;
• high flame speed;
• sudden cooling of the heating area.

It is necessary to exclude the effect of these factors, otherwise the resulting defect will have to be corrected. There are several simple ways that allow you to return the workpiece to the correct shape: use firing or tempering, apply steel straightening on rollers.

Deformation can be avoided if the product is pre-fixed and heated, the gas mixture flow rate is observed, and the correct cutting technology is followed. It is important to carry out all the steps sequentially and select the cutting mode based on the thickness and type of material. You cannot start processing with high gas mixture supply rates.

If you don’t have much experience, you should start working with small pieces, rather than cutting products from solid sheets.

Basic design of a cutting torch

Design features of the cutter.

Injection or two-pipe cutter

This is the most popular model due to its design. The name “two-pipe” comes from the division of technical oxygen into two streams. This is done to functionally separate the work of oxygen.

The upper flow of oxygen flows at high speed through the nozzle of the internal mouthpiece. This is an extremely important part of the device - it is directly responsible for the metal cutting phase. This flow is regulated by a special valve, which is usually placed on the outer panel.

The second flow of oxygen goes straight to the injector. The operating procedure in the injector chamber is as follows: oxygen enters the chamber under high pressure and at high speed, as a result of which a rarefied pressure zone is formed in this space. Oxygen is injected in this case.

Nominal gas flow.

Through special side holes in the walls of the chamber, flammable gas is drawn into it - in this case it is ejected. The gases are mixed, the velocities are equalized, and as a result, a flow of a mixture of gases is formed at the exit from the chamber, the velocity of which is lower than that of the injected oxygen, but higher than that of the ejected combustible gas.

At the next stage, the formed mixture of gases enters the tip - first into its head, and then exits through the nozzle between the mouthpieces and forms the same flame in the form of a torch, which heats the metal to its combustion temperature. All gas flows are regulated by their own valves on the outside of the housing - for supplying oxygen and separately for supplying flammable gas to the injector.

Injectorless or three-pipe gas cutter

In this case, the device of the gas cutter is more complicated. Oxygen enters it through two tubes, and the third tube is rightfully occupied by flammable gas. In this welding torch, gases are mixed inside the head; there is no chamber here. This system is safer than the two-chamber model.

The fact is that there is no risk of the so-called “reverse strike”, which consists of a very unpleasant and dangerous phenomenon: the penetration of burning gases in the channels and tubes of the device in the opposite direction.

This model has a significantly higher cost. In addition to this drawback, the three-pipe cutter has one more nuance: when working with it, a very high pressure of flammable gas is required - higher than with an injection apparatus.

Execution technology

The technique is simple, its essence is that the metal is heated to the combustion temperature, and then the place of heating is exposed to the action of pure oxygen, which “cuts” the sheet.

It is important to know that if the melting temperature of the metal is lower than the combustion temperature, then the molten residues will be difficult to remove and the product will be damaged.

Before processing, it is necessary to clean the metal sheet from dirt, rust and paint materials. This can be done using a metal brush or special units.

Features of oxygen cutting

Stages of gas cutting of metal:

• Heating metal to high temperatures.
• Oxidation.
• Blowing slag out of the cut area.

Gas cutting technology

The first step is to heat the material. A flame is supplied through the burner nozzles, which is obtained as a result of the combustion of a gas mixture (oxygen and acetylene). This flame is directed to the desired area (it must warm up to 1100 ˚C). During heating, acid is released, which helps to warm the lower layers of the material.

Once high temperatures are reached, only a stream of technical oxygen is directed to the treatment area. The metal reacts with oxygen to form a molten oxide. The hot jet causes the material at the cutting site to burn. If there are problems with the oxygen supply at this stage, defects may occur.

Standards and dimensions

Welding using a welding torch with gas.
All standard measurements regarding gas cutters are specified in GOST 5191-79. Naturally, the weight and size of the devices are directly related to their power. Weight, for example, comes in only two sizes: the cutters of models P1 and P2 weigh 1.0 kg, and the high-power model P3 weighs 1.3 kg and not an gram more or less.

By the way, the type of combustible gas is also related to the power and size. If powerful P3 cutters operate only on a mixture of oxygen and propane, then smaller devices such as P1 and P2 can operate with any type of gas.

Insert gas cutters:

In addition to the classic models with different powers, there is a separate category - the so-called plug-in gas cutters with a special marking RV. According to GOST, they have a very strange name: tips for a gas torch for cutting metal. In general, they differ from traditional cutters: the mixing of the combustible mixture and oxygen is carried out at the tip itself.

These devices are much lighter in weight than cutters. PB1 weighs 0.6 kg, and PB2 and PB3 only 0.7 kg each. But don't let this apparent elegance fool you. Let's not forget that these are tips for the torch, complete with which they will weigh no less than conventional cutters. What is the advantage then?

The fact is that they can be purchased in addition to an existing burner and, thus, save some money. And the compactness of the entire set, packed in a special case. And one more important detail concerns the nature of flammable gas. The fact is that acetylene is much more expensive than propane.

But for metal welding, acetylene is much more desirable: a torch with it produces a flame with a temperature 400°C higher than the same one with a mixture of oxygen and propane.

Portable models: small ship – short voyage

Cutter device.
The market now offers many portable options for autogens - this is exactly how they are positioned. They are sold as an attachment for a compact collet gas cylinder. But in essence and the principle of operation, these are burners. Most of them provide a flame temperature no higher than 1300°C.

There are, of course, portable models of the “professional” range - collet cutters that produce a higher torch temperature - up to 2000 - 2500 ° C, which is generally close in performance to a classic oxygen-propane cutter. But physics is physics: even in these models there is no main component that cuts metal - an oxygen jet that oxidizes this very metal.

Where is a portable cutting torch good? When cutting easily fusible metals or alloys such as tin, brass, bronze, copper. But even these “children’s” options are not cut, but melted. Therefore, compact attachments - cutters are used more for soldering or welding small workpieces made of non-ferrous metals. These can be parts of household devices such as a refrigerator or air conditioner. Welding, not a cutter, in a word.

In any case, be careful when choosing such models; their proposed “portability” is not always justified in the end.

Features of the technology

The choice of gas for cutting depends on the properties of the metal workpiece. In addition to technical oxygen, acetylene, coke oven and petroleum gas, methane, propane, butane and mixtures of them can be used.

Oxygen is used when cutting metal with gas if the material has certain characteristics:

• high thermal conductivity;
• melting point above the ignition temperature in oxygen;
• the melting point of refractory oxides is lower than the melting point of the metal;
• the formation of liquid slag during the cutting process;
• releasing a large amount of heat.

To cut a metal workpiece, it must first be heated. Then the material is burned, the combustion products are removed by a gas stream.

• superficial – formation of slots and channels;
• spear - the formation of holes or openings;
• separating – in the form of a through cut.

Different burners are selected for different jobs. There are several types that are designed to perform different jobs.

• handles;
• valve;
• valve (not on all models);
• tip (extension tube);
• mouthpiece (nozzle).

Mixing of gas with air can occur in the tip or mouthpiece. In models with a valve, gas and oxygen are mixed in the head, which increases the level of safety. The use of models without a valve allows the use of gas with different pressures. Gas cutters for cutting thick metal are equipped with several mouthpieces.

The technology consists of four steps:

• heating the workpiece;
• introducing a gas mixture into the processing area;
• ignition of the material;
• combustion process.

The stream must be uniform so that the flame does not go out. During the combustion process, oxides are formed, which are removed by a gas jet.

Equipment

The main equipment for gas cutting is a cutter. The kit includes: a nozzle for welding and melting.

Thanks to the cutter, you can control the dosage of the gas mixture and oxygen. Also, with the help of this equipment, the flammable mixture is ignited and a flame is supplied to the processing site.

The cutter consists of two blocks: cutting and heating. The first is represented by an oxygen stream outlet tube, a valve and an internal type mouthpiece.

The heating block includes valves that are designed to regulate the pressure of the gas mixture and oxygen. There is also a supply tube, an external mouthpiece, a mixing chamber and an injection cell.

Cutters are either manual or machine. The latter are stationary, so for repair work it is preferable to use manual ones.

Additionally, the following gas cutting equipment is used:

• reducer – designed to reduce pressure;
• device for changing pressure;
• steel cylinder with gas and oxygen;
• connecting hoses.

Before using the equipment, it is important to check its serviceability in order to avoid explosion of the cylinder or reducer. The cutter is pre-purged with oxygen.

Cutting nuances

The cutting process involves speed control, the selection of parameters occurs visually, depending on the number of sparks and their scattering. The stream of sparks generated by the cutting process must be generated at an angle of 90° with respect to the surface. The speed is adjusted if the flow changes direction, in this case the speed is low, requires adjustment.

The thickness of the structure affects the process; in the case of a processed sheet with a thickness of more than 6 cm, it must be placed at a slight angle to allow the slag to drain off. When processing thick products, it is important to maintain an inclination angle of 15 ° more and control the speed. If cutting is stopped in the middle of the path, the process does not resume at this point, but occurs all over again. To avoid rework when working with a thick product, it is necessary to guide the cutter so that the metal is processed along the entire perimeter.

Cutting metal with a gas cutter

After cutting the steel, the supply of cutting gas is turned off. Then the valve on the cylinder is closed, the last step is to close the supply of the combustible mixture.

Safety requirements

Gas equipment that is used in the process of cutting metals, namely an oxygen-acetylene cutter, is classified as explosive and flammable. Therefore, before using a gas cutter, you should follow all mandatory safety recommendations.

To do this, the workplace should be equipped with:

• fire extinguisher. The use of a gas cutter is accompanied by an open flame and high temperatures, so fire extinguishing equipment must be present at the post;
• protective clothing, consisting of: a cotton suit, if possible, impregnated with a fire retardant compound;
• gloves or leggings made of canvas or fairly thick leather;
• boot with leather sole;
• safety glasses with built-in light filters.

When working with a cutter, you should never wear clothing made from synthetics or other easily flammable fabrics, or that do not fit tightly to your body or have heavily worn edges. All this can lead to fire and, accordingly, danger to health and life.

Only various grades and types of unalloyed carbon steel can be cut with gas. Stainless steel, non-ferrous metals and various alloys cannot be cut with a propane cutter.

Disadvantages of processing

Low carbon steel is most suitable for gas cutting, but medium and high carbon steel is not a very suitable material for cutting. Due to the high carbon content, the ignition temperature increases and the melting point decreases. And this condition complicates the cutting process.

It is difficult to cut metal using a gas mixture if it has low thermal conductivity. Therefore, these types of material are not suitable for processing.

Safety rules when gas cutting metal

Gas cutting of metal should only be performed by a qualified and experienced professional. It is important to observe all the key factors of proper processing: oxygen pressure and speed of the procedure. It is necessary to take into account the thickness of the product and the diameter of the cutter nozzle. If the rate of oxidation and metal cutting do not match each other, then the result will be poor-quality processing.

Oxygen cutting involves the use of explosive substances. If safety rules are not followed, there is a high probability of an explosion of the gas-air mixture; it is necessary to monitor the condition of the gas equipment. To protect against burns, you must use personal protective equipment.

A significant disadvantage is the possibility of metal deformation and low cutting accuracy.

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How to choose a better cutter?

Operating principle of a gas cutter.
We offer a block of useful information that will help you better navigate the specifications and technical characteristics of cutters in advance:

• Nipples are made of brass and aluminum. Brass options are more durable.
• If possible, choose models with aluminum rather than plastic handles. No matter how heat-resistant the plastic is, it will “float” in any case faster than aluminum.
• The handle should be quite massive: the diameter should be at least 40 mm.
• The valves should work well. This means turning without much effort.
• Lever-controlled devices are more convenient and economical to use, they save gas.
• Valve spindles must be made of stainless steel, and not brass, which is too short-lived. There are “combined” options; they occupy a middle position in terms of durability.
• The best materials for the cutter body are metals: brass, copper, stainless steel.
• We remember that acetylene cutters are more expensive. We monitor the material from which the parts that have direct contact with the flammable gas are made before mixing in the chamber. Attention! They should not be made of copper or its alloys, where the copper content is not less than 65%.
• If the design of the device is collapsible, this is better: it is easier to clean and repair.
• Only copper! Only copper outer mouthpiece!
• The correct internal mouthpiece for an acetylene-type cutting torch should also be made of copper. But in an oxygen cutter for metal it is made of brass. These are the nuances.
• Be sure to check with the seller the status of spare parts and consumables.

What to look for when choosing a gas cutter

The selection of a quality tool directly depends on the result. If certain parameters are neglected, certain properties of the cutter are lost and safety parameters are reduced. Propane and oxygen are explosive substances that require compliance with certain operating requirements:

• The handle is made of aluminum alloys; plastic is used with cheaper tools; over time it melts and loses its shape.
• A brass nipple will last longer than an aluminum structure, as it has a greater resistance to deformation.
• The rotation of the valves should be done with little force to stop the process in case of an unusual situation. The recommended valve size is at least 4 cm.
• The most reliable spindles are made of stainless steel and can withstand up to 1500 cycles without replacement; brass spindles cannot withstand such a service life. The most suitable option is combination spindles, which have a favorable price-quality ratio.
• The design of the cutter must be dismountable; maintenance is carried out to extend its service life. Mouthpiece material is copper.

Valve-type oxygen-propane cutter

It is necessary to pay attention to the availability of repair kits and spare parts for the cutter. If they are not available for free sale, problems may arise during repairs.

Advice from experienced people: how to use

Instructions on how to use a gas cutter can be divided into general provisions and professional “minor” notes, which in fact are the most valuable practical assistants.

Table of cutting metals with a gas cutter.

First the general points:

• Only with a mask! We carry out any work with any gas cutter only in a welder’s mask or special glasses. Working with an autogen is an activity with a sea of ​​risks; safety precautions must be carried out for real and not childishly.
• We choose clothing and gloves with fire-resistant properties. If there are none, well: at least the minimum requirement is not to wear synthetic clothes.
• There must be a fire extinguisher at the workplace with all the correct expiration dates, etc. Fire extinguishing equipment must also be placed nearby in accordance with fire safety regulations.
• Before work you need to stock up:
• a ruler, a special pencil, a square and a tape measure;
• a special lighter, which is usually included with the equipment.
• When working, it is important to choose the right location. The torch flame must be located in front of the supply hoses. The hoses, in turn, should be positioned so that they do not interfere with you during the process.
• Another safety rule: gas cylinders should not be closer than 5 meters to you during operation.
• Ventilation should be excellent throughout cutting, preferably working outdoors.
• The floor in the workshop should be either concrete or earthen.
• If you haven't worked with your cutter for a long time, or are starting to use a new device, check the channels: they should be clean. In addition, always check the vacuum level in the chamber that is formed by oxygen. First, remove the propane hose - this must be done with the valves on both the cutter and the cylinder tightened. Then open the oxygen and gas valve on the cylinder at operating pressure. The injector is checked simply: put your finger on the gas nipple, if everything is correct, you will feel air being sucked into this nipple. Close the oxygen, all the valves and then connect the hose with flammable gas to the cutter: you can work.

Scheme of cutting metal with a cutter.
Stages of action during cutting, propane cutters:

1. First, an oxygen cylinder: set the operating pressure.
2. Then a cylinder with flammable gas: we also set the working pressure. The reference point is oxygen pressure. The propane pressure should be about ten times less. If the device is three-pipe, then the difference will be five times.
3. Slowly open the oxygen and gas valve, ignite the gas and use the valves to create the pressure of the heating flame.
4. The manual gas cutter is ready for work, now the actual cutting of the metal with the cutter.
5. A stream of igniting oxygen begins to flow to the combustion site. If the metal is heated sufficiently, the desired reaction will begin immediately. In this case, the oxygen supply pressure can be further increased until the metal is completely cut through.
6. Now the autogen can be moved in the desired direction - along the line of the planned cut. The speed of movement must be determined as you go, it will depend on how the sparks and slag flow or are blown down from the burner.
7. After cutting, carefully inspect the work area for any remaining pieces of molten metal. God forbid you step on these - they will even burn through the thick soles of your boots.
8. Cooling of parts is carried out either with water or naturally.
9. After finishing cutting, you need to finish the work process, which is no less important than starting work.
10. First we tighten the oxygen valve.
11. The flame valves are closed next - the propane valve first, the oxygen valve next.
12. We tighten the valves on the cylinders.
13. We release the hoses from the gas: open and then alternately close the valves of the heating mixture on the device.

Sources

• https://tutmet.ru/polzovatsja-rezat-rabotat-gazovym-rezakom-nastrojka.html
• https://stanok.guru/oborudovanie/raznoe/rezka-metalla-kislorodno-propanovym-rezakom.html
• https://printeka.ru/metally/kak-pravilno-rezat-gazovym-rezakom-metall.html
• https://tutsvarka.ru/oborudovanie/gazovyj-rezak
• https://msmetall.ru/instrument/kak-rezat-relsy-rezakom.html
• https://WikiMetall.ru/oborudovanie/kak-polzovatsya-rezakom.html

Surface and figure cutting

In some situations, it may be necessary to create a relief on the surface by cutting a groove into the sheet. If you decide to use a similar cutting method, then heating of the metal will be provided not only by the flame of the cutter. Molten slag will also make a contribution. Becoming liquid, it will spread over the entire surface, which will lead to heating of the lower layers of the metal.

The first step in performing surface cutting is heating the selected area to the ignition temperature. After you start supplying cutting oxygen, you will create a metal combustion zone, and thanks to the uniform movement of the cutter, the cutting line will receive a clean edge. The operation itself must be performed in such a way that the cutter is at an angle of 70-80 degrees with respect to the sheet. When cutting oxygen begins to flow, the cutter is positioned so that it forms an angle of 17-45 degrees from the surface being processed.