Cutting of steel of small, medium and large thicknesses
Cutting of small thickness steel (especially less than 5 mm) is usually accompanied by considerable overheating of metal by heating flame, which leads to increased melting of upper edges and to an increase in the proportion of unoxidized (melted) iron in the slag. This slag is welded to the lower edges of the cut and requires a great deal of labor to remove it.
In addition, when cutting thin-plate steel, warpage from the plane of the plate being cut increases, resulting in coils, as well as greater distortion of the shapes of cut pieces and workpieces.
Normal cutting with conventional equipment is performed when sheets are at least 4 mm thick. Cutting with a heated flame and cutting oxygen in a sequence gives the best results for thinner sheets (see gas- and air-driven oxyfuel cutting). Fig. 78, a), but even in this case sheets with thicknesses below 3 mm are difficult to cut and do not give good results. High quality cutting of thin sheets can be obtained by batch cutting, especially effective for batch production of identical cut parts. It is possible to cut sheets with a thickness of at least 1 mm using batch cutting.
The essence of the steel batch cutting process is as follows. Sheets are stacked in a package and cut with the oxygen jet in one pass of the cutter Up to 50 or more sheets are packaged, depending on their thickness, the number of necessary identical parts and means for assembling packages. In some cases it is suitable to pack sheets with such thicknesses that they can also be cut separately (8-10 mm and more).
Batch cutting has several special features. When cutting with conventional equipment, a close-knit assembly of sheets with minimal gaps between them is very important. In the presence of gaps the heating of the underlying plate is worsened and the oxygen jet starts to spread sideways without cutting through it, dragging the hot slag with it, heating up and burning the already cut through parts and underlying plates. To avoid this, the sheets are straightened beforehand and fastened either with clamps or welding rolls applied at the ends. Presses are sometimes used when squeezing thin sheets.
Due to the fact that the power of heating flame is taken in accordance with the total thickness of the package, the upper sheet overheats strongly and with low thickness it warps, moves away from the underlying and creates a gap. The consequence of this may be that cutting can stop. That is why a thicker sheet (usually 6-8 mm, even when parts are cut from thinner metal) is often placed on top of the pack.
The lower plate part (up to 3 mm thick) is also damaged to a certain extent; it collects a large amount of flowing slag that causes melting of the edges. When cutting the package from the edge, it is useful to assemble it with an offset of the edges. The pack can also be assembled without displacement, but then the cutting should be started with a roll pre-folded on the edge end. You can start cutting in the center of the pack by pre-drilling a through hole. Rapid cooling (sometimes with water) of the cut pieces after cutting is completed to make it easier to separate them.
Cutting with low-pressure oxygen, with large material throughputs, requires less precision in plane alignment of sheets in the pack, allowing for cutting with local gaps. In this case the slow flow of slag facilitates the heating of the underlying plate, because the slag filling the gap prevents the oxygen jet from spreading to the sides and helps to keep its direction. The method of cutting with low pressure oxygen is especially appropriate when cutting sheets with a thickness of 8-20 mm and the gaps between the sheets can be 2-4 mm. When cutting with low-pressure oxygen the number of clamps that compress the pack can be reduced.
Medium-thickness steel cutting modes
Medium-thickness oxyfuel cuts (approx. 12-100 mm) give the best quality results. Oxygen cutting of such metal does not cause technological difficulties and is easily performed with conventional gas cutting equipment both by hand and mechanically.
Cutting medium thickness steel with the usual equipment should be done with oxygen pressure in the reducer working chamber of 2,5-6 kgf/cm2 depending on the thickness of the cut metal.
Approximate technical speeds of machine severing cutting of steel of different thicknesses with the oxygen purity not less than 98,5-99% are given in table. 20.
Using the best thermal preparation of the upper edge for reduction of non-cutting probability, VNIIavtogenmash worked out a method of high-speed straight-line cutting “with angle forward”. f to 50-70° Cutting speeds when the torch is positioned perpendicularly (conventional cutting) and when the torch is positioned “angle forward” (high-speed cutting) are shown in Fig. 106. From the given data it follows that this method enables higher cutting productivity with steel thicknesses up to 30 mm.
It is economically very reasonable to carry out gravity-free cutting. At the moment regimes of gravity-free cutting have been developed based on usage of oxygen of high purity (99,5%), optimum mode, direction and pressure of the cutting oxygen jet so that no slag flows along the cut in the direction opposite to that of cutting (òóê òóê, ÷òîáå). е. with small lagging A), maximal decrease of heating flame power and replacement of acetylene by other flammable (kerosene, propane etc).).
Regimes of gravel-free cutting to obtain II class of quality of cut by recommendations of All-Russian Scientific and Research Institute of Automobile Engineering are given in table. 21.
At small thicknesses (up to 12-15 mm) it is also possible to cut with a slightly less pure oxygen with the cutting torch angled forward (see the table below). Fig. 105).
Cutting medium thickness steel with low pressure oxygen using torches with a larger cutting oxygen channel is not practical.
Cutting thicker steel
Conventional gas cutting equipment is usually designed for cutting steel up to 300 mm thick, but already at the thicknesses above 200 mm some difficulties in cutting appear. Even greater difficulties arise when cutting metal that is more than 300 mm thick. Cutting steel of this thickness is mainly used in metallurgical industry and some heavy engineering enterprises.
Advantages and disadvantages
The advantages of cutting metal with propane over other methods are obvious:
Assembly diagram of a hand torch for cutting steel.
- Gas cutting is used when you need to cut a rather thick metal, or something to cut out on templates, when you want curved cutting, which is simply impossible to do the same angle grinder. The gas cutting torch is indispensable if there is a need to cut a disk of thick metal or punch a blind hole of 20-50 mm.
- The low weight and ease of use of the gas cutter is another undeniable advantage. Those who have worked with gas-powered models know how heavy, sluggish and noisy they are, and that they vibrate a lot, forcing the operator to make considerable effort at work. Gas models don’t have all these disadvantages.
- In addition, cutting metal with gas allows you to work twice as fast as with a gasoline-powered device.
- Propane is much cheaper than gasoline and other gases. Therefore, it is advantageous to use it for large amounts of work, for example, when cutting steel for scrap metal.
- The cutting edge when cutting propane is slightly worse than when using acetylene torches. Nevertheless, the cut is much cleaner than that of gasoline torches or angle grinders.
The only disadvantage of gas torches (propane torches, including) can be considered the limited Spectra of metals that they can cut. Only low- and medium-carbon steels, as well as malleable cast iron can be processed.
Oxygen-propane unit for soldering and welding.
It is not possible to gas cut high-carbon steels, because their melting point is rather close to the temperature of the flame. As a result, the dross is not ejected as a column of sparks from the back side of the plate, but mixed with the molten metal at the edges of the cut. It prevents oxygen from getting deep into the metal to burn it. When cutting cast iron, the process is hindered by the shape of the grains and the graphite between them. (Malleable cast iron is an exception). Aluminum, copper and their alloys also do not lend themselves to gas cutting.
Recall that the low-carbon steels are grades from 08 to 20G, to medium-carbon. grades from 30 to 50G2. Carbon steels, on the other hand, always have the letter U in front of them.
How to work properly with a gas torch: the preparatory stage
Before you start the procedure itself, you need to have the right equipment. It includes:
- fire extinguisher. Handling this type of equipment is dangerous in terms of fire, so a means of extinguishing fires should be available. If there is nothing plastic, oil or other materials that burns easily and quickly around, a standard set of firefighting equipment will do
- Special flame-retardant suit. a fire-retardant tarpaulin welder’s suit and a leather backed welder’s suit. Nylon, synthetics, loose fit, bulging s and cuffs, and ripped edges are prohibited because they are easily flammable. As for footwear, special fire-resistant lace-up boots with leather soles that reduce the risk of injury would be ideal. Necessary equipment includes leather (or spilkovye), canvas with PP mitts or gloves, and goggles;
- metal ruler and angle, universal and other special welding templates, special heat-resistant markers or, at worst, a soapstone pencil for measuring and marking;
- a special torch lighter. The use of matches or a lighter is injurious and is therefore forbidden.
Next, prepare the work area. There are a few rules about this as well:
- It is necessary to perform cutting in a well ventilated room, and the best option. in an open space;
- no flammable objects, such as paper, dry twigs, wood chips, etc., should be within a radius of 5 meters around.;
- you can work with the gas cutter on an earthen or concrete floor;
- A steel table is the best support for this kind of work;
- Take care that the flame does not come into contact with the concrete while cutting. This can cause the latter to deteriorate (it will crack due to expansion).
After that, mark the specific places you will be cutting with a heat-resistant marker.
The most common type of device used in the treatment of steel structures is the two-tube injector torch. The combustible mixture is separated into several streams which makes it possible to adjust the flame power according to the work. The regulating mechanism is on the outside of the body; lever-type instruments are available.
The flow moves along the tube to the tip through the head, the release occurs at high velocity through the central nozzle. The nozzle is responsible for the main function of the torch, the cutting part of the process. part of the gas is transferred to the injector that creates suction under high pressure and thus a combustible mixture is formed. The mixing process is defined by the equalization of the flow velocity.
Mixture formation is performed by the nozzle head into which it enters through the lower tube. The torch is formed between the outer, inner mouthpiece, the consequence of the formation of a combustible mixture. The dual-channel system is equipped with adjustment valves that allow adjustment of both oxygen and auxiliary gas supply to the injector.
Non-injector design is more complicated, as there are tubes for two streams of oxygen and separately for gas. Combustible composition mixing takes place directly inside the head, this design is considered safer action. Higher supply pressure of both oxygen and combustible gases is required to perform actions.
torch sizes are fixed by GOST standards, for production with small parts P1 models with total length not more than 50 cm are used. The more powerful designs are longer in shape, and there are specific elongated designs for tasks where access to the cutting point is difficult.
Advantages and disadvantages
Gas torch is designed for cutting products in production conditions, with a large volume of tasks. Before applying the device, it is important to understand the key features of propane and oxygen metal cutting:
- The mechanism is convenient for making curved cut lines. Stable power allows to cut metal products of different thicknesses into pieces. In situations where the use of a tool, such as an angle grinder, is not possible, a gas torch is used. The task of round work or blind holes can be performed with a gas torch, with no extra effort.
- Gas torch has an advantage over gasoline models. In addition to low weight, the mechanism does not produce excessive noise during operation and is compact.
- Using an apparatus based on the action of flammable gas allows you to speed up execution twice as much, which is not possible with mechanical tools.
- Propane gas as a gas in liquid form is characterized by its low price. Therefore, it is used not only in the processing of products in production needs, but also in the disposal of metal and other actions.
- Using propane as a combustible mixture allows you to make quality cuts. Cutting is carried out on a narrow exceptions, which is a major factor in quality work.
The disadvantages are that some materials can not be processed with a propane torch, such as cast iron and high-alloy steels.
Types of gas torches
Types of gas cutters are represented very widely. Let’s walk through the handheld models, which are subdivided by features.
Working principle of a gas torch.
Type of gas affects the temperature of the flame to heat the metal.
- low power for cutting metal marked P1 and a thickness of 3. 100 mm;
- Medium power. marking P2 and thickness up to 200 mm;
- high power. marking P3 with a thickness of up to 300 mm;
- there are torches for metal with thicknesses up to 500 mm.
Principle design of the gas cutter
Injector or double-tube torch
This is the most popular model by design. The name “double-pipe” comes from the division of the process oxygen into two streams. This is done to provide a functional separation between the oxygen and operating conditions.
The upper oxygen flow goes through the nozzle of the inner mouthpiece at high speed. This is an extremely important part of the machine. it is responsible for the metal cutting phase itself. This flow is regulated by a special valve, which is usually on the outside panel.
The second oxygen flow goes straight to the injector. The procedure in the injector chamber is as follows: Oxygen enters the chamber at high pressure and high speed, resulting in a rarefied pressure zone in this space. In this case, the oxygen is injectable.
Nominal gas flow.
Through special side openings in the walls of the chamber, a combustible gas is drawn into the chamber. it is in this case ejectable. The gases mix and velocities equalize, resulting in a mixed gas stream at the chamber outlet, which has a lower velocity than the injected oxygen, but a higher one than the ejected combustible gas.
In the next stage, the generated gas mixture enters the handpiece. first into its head, and then out through the nozzle between the mouthpieces and forms the very flame in the form of a torch that heats the metal to its combustion temperature. All gas flows are controlled by own valves on the outside of the case. for oxygen supply and separately for fuel gas supply to the injector.
Flameless or three-tube gas torch
In this case the structure of the gas torch is more complicated. Oxygen enters it through two pipes, the third pipe is by right the combustible gas. In this welding torch, the gases are mixed inside the head. there is no chamber. This system is safer than the dual-chamber model.
The fact is that here there is no risk for the so-called “blowback”, which consists in 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. Besides this disadvantage, the three-pipe torch has another nuance: it requires a very high pressure of combustible gas. higher than with the injector device.
Principle of the gas torch design
Injector or double-tube torch
This is the most popular model by design. The name “two-pipe” comes from the separation of the process oxygen into two streams. This is done to functionally separate the oxygen work.
Upper oxygen stream pours at high velocity through the nozzle of the inner mouthpiece. This is an extremely important part of the machine. it is directly responsible for the cutting phase of the metal. This flow is controlled by a special valve that is usually on the outside panel.
The second oxygen flow goes straight to the injector. The order in the injector chamber is as follows: oxygen enters the chamber at high pressure and high speed, resulting in a rarefied pressure zone in this space. The oxygen is injected in this case.
Nominal gas flow rate.
Combustible gas is drawn into the chamber through special side openings in the walls. in this case, it is an ejected gas. Mixing of gases, speeds are equalized, as a result at the chamber outlet a gas mixture flow is formed which has lower speed than injected oxygen but higher speed than ejected combustible gas.
The next stage is when the generated gas mixture enters the tip. first into its head and then out through the nozzle between the nozzles, forming the flame in the form of a plume that heats the metal to its combustion temperature. All gas flows are controlled by their own valves on the outside of the body. for oxygen supply and separately for fuel gas supply to the injector.
Nozzle or three-pipe gas torch
In this case, the construction of the gas torch is more complicated. Oxygen enters it through two pipes, the third pipe is by right the combustible gas. In this welding torch, the gases are mixed inside the head, so there is no chamber. This system is safer than the two-chamber model.
The fact is that there is no risk of the so-called “blowback”, which is a very unpleasant and dangerous phenomenon: the penetration of burning gases in the channels and pipes of the apparatus in the opposite direction.
This model has a much higher price. In addition to this disadvantage, the three-tube torch has another nuance: it requires a very high pressure of combustible gas in operation. higher than with the injector machine.
Standards and dimensions
Welding with a welding torch and gas.
All standard measurements, concerning gas torches, are stipulated in GOST 5191-79. Naturally, the weight and size of the units are directly related to their power. Weight, for example, only comes in two values: The P1 and P2 torches weigh 1.0 kg, and the high-power P3 model weighs 1.3 kg, and not a gram more or less.
By the way, the type of combustible gas is also related to power and size. If powerful P3 torches work only with a mixture of oxygen and propane, then smaller P1 and P2 torches can work with any gas.
Plug-in gas torches:
Besides classic models with different power there is a separate category. the so called plug-in gas cutters with special marking RV. According to GOST they have a very strange name: torch tips for metal cutting. They are actually different from conventional torches: The mixture of fuel mixture and oxygen is mixed in the tip itself.
These devices are much lighter in weight than the torches. RV1 weighs 0.6 kg, and RV2 and RV3 weigh only 0.7 kg each. But don’t let this apparent elegance mislead you. Let’s not forget that these are nozzles for the torch, complete with which they will weigh no less than conventional torches. What’s the advantage then?
That they can be added to an existing torch and thus save some money. And the compactness of the whole set, packed in a special case. And one more important detail about the nature of the combustible gas. The fact is that acetylene is much more expensive than propane.
But for welding metal is much more desirable exactly acetylene: a torch with it gives a flame with a temperature above 400 ° C than the same with a mixture of oxygen and propane.
Handheld models: a small ship sails small
The structure of the torch.
There are many portable variants of autogenes on the market now. this is how they are positioned. They are sold as an attachment to a compact collet gas cylinder. But in its essence and principle of operation it is a burner. Most of them provide the temperature of the torch is not more than 1300 ° C.
there are, certainly, and portable models of “professional” number. collet torches giving the temperature of torch higher. up to 2000. 2500 °С that in general is close to indicators to the classical oxypropane torch. But physics is physics: even in these models there is no main component that cuts the metal. the oxygen jet, which oxidizes this very metal.
Where a portable gas torch is good? When cutting easily fusible metals or alloys like tin, brass, bronze, copper. But even these “baby” versions don’t cut, they melt. So compact torch heads are used more for soldering or welding small non-ferrous workpieces. It can be parts of household appliances like refrigerators or air conditioners. Welding, not a torch, in a word.
In any case, be careful when choosing such models are not always their proposed “portability” in the end justified.
Gas cutting metal. instructions for metal processing
Gas cutting is the most popular because it does not require compliance with room norms and is easy to do. The seam is not torn and neat if stencils are used. All torches are compact and mobile, easy to transport. Multiple gases can be used. This method makes it possible to work on thicker workpieces and perform complicated operations. No power is needed, it can be manual or automatic.
In some cases it is not economically feasible to use an acetylene gas cutter. In this case, it is not reasonable to have two torches that work on different types of fuel. Therefore, universal oxygen gas cutters are especially popular at large production facilities. Their main feature is the ability to run on different fuels.
The vast majority of all-purpose units are used for hand cutting unalloyed or low carbon steel. Propane/acetylene torch is the most common. The first type of gas is used for materials up to 200 mm thick; the second type is used for materials over 300 mm thick.
In some cases, it is not economically feasible to use an acetylene gas torch. Having two cutting torches using different fuels makes no sense. Therefore, at large production facilities, universal gas/oxygen torches are especially popular. Their main peculiarity is the ability to work with different types of fuel.
The vast majority of universal units are used for hand cutting unalloyed products or steels with a low percentage of carbon in their composition. Propane/acetylene torch is the most common. The first type of gas is used to process materials up to 200 mm thick, and the second type. over 300 mm.
Features of technology
The choice of gas for cutting depends on the properties of the metal workpiece. In addition to technical oxygen, acetylene, coke and petroleum gas, methane, propane, butane and their mixtures can be used.
Oxygen is used when cutting metal with gas, if the material has certain characteristics:
- high thermal conductivity;
- melting point higher than the ignition temperature of the oxygen;
- The melting point of refractory oxides is lower than the melting point of the metal;
- The gas and air mixture can cause the formation of liquid slag during the cutting process;
- high heat generation.
To cut metal, it must first be heated. Then the material is burned, the combustion products are removed by a jet of gas.
Different torches are selected for different applications. There are several types that are designed for different applications.
Gas can be mixed with air at the tip or nozzle. Models with valve mix gas and oxygen in the head, for improved safety. Using models without a valve allows you to use gas at different pressures. Gas torches for cutting thick metal come with several nozzles.
The jet should be uniform so that the flame does not go out. Oxides are formed during combustion, which are removed by the gas jet.
A small gas cutter or torch in your
Palm-sized, ultra-portable torch is not a spy movie prop but a real gas-cutting device. It is reminiscent of turbo-charged lighters that have become very popular and do not go out even in strong winds. This effect is achieved by accelerating the gas flow in a small turbine nozzle and forming a torch in a special nozzle. During prolonged combustion the lighter’s upper part begins to heat up and even melt. The mini-torch uses special materials and design solutions to avoid this. The gas jet is also accelerated and formed by a specially shaped nozzle that creates a narrow, high-temperature plume. Gas supply lasts only a few minutes and can be refilled from a standard collet with a nipple.
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It will not cut five-millimeter steel angle with this device, but it is quite capable of doing it:
It is inexpensive, and the prudent owner can just have it in the house just in case.
Gas torch with their own hands
This version of a small-sized and uncomplicated gas cutter for assembly with their own hands does not require expensive parts, but at the same time demonstrates the stability and sufficient efficiency of work. Can be used to cut copper wire and sheets.
In order to make the device, you will need:
- two systems for infusions (droppers);
- A soccer ball needle;
- an air tank pump;
- Propane bottle for filling lighters;
- some copper wire;
- electrical soldering iron, solder, flux;
- a hot glue gun;
- nipple from a car wheel;
- velvet file.
- bend the needle from the dropper at an angle of 60° in about a quarter of its length from the plastic adapter;
- Drill a small hole in the needle for pumping balls and pass into it a bent needle from a syringe so that its tip protrudes by 2-3 mm;
- wrap copper wire around the hole and seal it hermetically;
- Connect the plastic tubing from the dropper to the shanks of both needles;
- Connect the thin needle to the compressor and the thick needle to the propane bottle;
- Use plastic clamps to regulate gas supply.
Be careful and cautious when making the torch and working with gas.