How to cut metal with a gas torch
How to properly cut metal with an oxygen-propane cutter?
Compared to gas welding, gas cutting requires much less skill from a person. Therefore, mastering a gas torch is not that difficult. It is enough to understand how to do it correctly. The most widespread in our time are propane cutters. They use propane and oxygen together, since their mixture gives the highest combustion temperature.
How To Set Up And Operate A Cutting Torch
The propane cutter is designed for manual separation oxyfuel cutting of carbon and low-alloy steels using propane.
To cut metal with gas, you must have one cylinder of propane and one oxygen, high pressure hoses (oxygen), the cutter itself and the mouthpiece of the required size. Each cylinder must be equipped with a reducer to regulate the gas supply. Please note that the thread on the propane cylinder is reversed, so it is impossible to screw another reducer onto it.
The design of gas equipment for cutting metal from different manufacturers differs slightly. Usually all of them have 3 valves: the first is for the propane supply, followed by the regulating oxygen valve, and after the cutting oxygen valve. Most often, oxygen valves are blue, the same that open propane, red or yellow.
The metal is cut using a jet of hot flame that is generated by the cutter. During the operation of the apparatus in a special mixing chamber, propane combines with oxygen, forming a combustible mixture.
The propane cutter can cut metal up to 300 mm thick. Many parts of this device are replaceable, so the device, in the event of a breakdown, can be quickly repaired right at the workplace.
It is very important to choose the right mouthpiece. When choosing it, one should proceed from the thickness of the metal. If the object to be cut consists of parts of different thickness, which varies from 6 to 300 mm, you will need several mouthpieces with internal numbers from 1 to 2 and external numbers from 1 to 5.
Preparation for work
Before starting work, it is imperative to inspect the device to make sure that the torch is fully functional. Then follow these steps:
- The first step is to connect the hoses to the cutting machine. Before attaching the sleeve, you need to purge it with gas to remove any debris or dirt that has got there. The oxygen hose is attached to the right-hand thread with a nipple and nut, the second (for propane) hose to the left-hand thread. Remember to check the torch passages for leaks before attaching the gas hose. To do this, connect the oxygen hose to the oxygen connection, and the gas connection must remain free. Set the oxygen supply to 5 atmospheres and open the gas and oxygen valves. Feel the free fitting with your finger to see if air is leaking. If not, clean the injector and blow out the torch passages.
- Next, check the detachable connections for leaks. If you find a leak, tighten the nuts or change the seals.
- Do not forget to check how tight the mountings of the gas reducers are and whether the pressure gauges are in good working order.
Nuances of metal cutting
Flow diagram of the separation oxy-fuel cutting process.
You need to cut the metal at the right speed. The optimal speed can be determined visually by how the sparks fly away. A stream of sparks at the correct speed flies out at an angle of approximately 88-90 ° to the cut surface. If the sparks are flying in the opposite direction of the torch, the cutting speed is too slow. If the angle of flow of sparks is less than 85 °, this signals an overspeed.
When working, it is always necessary to be guided by how thick the metal is. If over 60 mm, it is better to arrange the sheets at an angle to ensure the drainage of slags, and do the job as accurately as possible.
Cutting thick metal has its own characteristics. You cannot move the torch before the metal has been cut to its full thickness. By the end of the cutting process, it is necessary to smoothly reduce the advance speed and make the angle of inclination of the torch more by 10-15 °. It is not recommended to stop during the cutting process. If work is interrupted for any reason, do not continue cutting from the point at which you stopped. It is necessary to start cutting again and only in a new place.
After finishing cutting, first shut off the cutting oxygen, then turn off the regulating oxygen, last turn off the propane.
Surface and shape cutting
Sometimes it becomes necessary to cut through the metal not through and through, but only to create a relief on the surface by cutting grooves on the sheet. With this method of cutting, the metal will be heated not only by the flame of the torch. The molten slag will also serve as a heat source. Spreading, it will heat the lower layers of the metal.
Surface cutting, like conventional cutting, begins with the desired area warming up to the ignition temperature. By turning on the cutting oxygen, you will create a metal burning center, and by moving the cutter evenly, you will ensure the stripping process along the specified mowing line of the cut. In this case, the cutter must be positioned at an angle of 70-80 ° to the sheet. When supplying cutting oxygen, tilt the torch, creating an angle of 17-45 °.
Adjust the dimensions of the groove (its depth and width) with the cutting speed: increasing the speed, decreasing the size of the groove and vice versa. The depth of the cut will increase if the angle of inclination of the mouthpiece increases, if the cutting speed decreases and the oxygen pressure increases (of course, the cutting). The width of the groove is controlled by the diameter of the cutting oxygen jet. Remember that the depth of the groove should be about 6 times less than its width, otherwise sunsets will appear on the surface.
You can cut a figured hole in the metal as follows. First, we outline a contour on the sheet (when marking a circle or flanges, the center of the circle should also be noted). Hole punching should be done prior to cutting. It is always necessary to start cutting with a straight line, this will help to get a clean cut on the curves. You can start cutting the rectangle anywhere except at the corners. Last but not least, the outer contour should be cut. This will help to cut the part with the smallest deviations from the intended contours.
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 it is necessary to cut rather thick metal or cut something according to templates, when a curved cut is required, which simply cannot be done with the same angle grinder. A gas cutter is indispensable if there is a need to cut a disc out of thick metal or punch a blind hole 20-50 mm.
- Light weight and ease of use of the torch is another indisputable advantage. Those who have worked with gasoline counterparts know how heavy, clumsy and noisy they are, vibrate strongly, forcing the operator to make significant efforts during work. Gas models are devoid of all these disadvantages.
- In addition, cutting metal with gas allows you to work 2 times faster than when using a device with a gasoline engine.
- Propane is much cheaper not only than gasoline, but also other gases. Therefore, it is beneficial to use it for large volumes of work, for example, when cutting steel for scrap.
- Propane cut edges are slightly worse than acetylene cutters. However, the cut is much cleaner than with gasoline burners or an angle grinder.
The only drawback of gas cutters (including propane ones) can be considered the limited Spectra metals that can be cut with their help. They can only handle low and medium carbon steels, as well as ductile iron.
Oxygen-propane soldering and welding plant.
It is impossible to cut high-carbon steels with gas, because their melting point is quite close to the flame temperature. As a result, the dross is not ejected in the form of a pillar of sparks from the back of the sheet, but is mixed with molten metal along the edges of the cut. This prevents oxygen from reaching deep into the metal to burn through. When cutting cast iron, the process is interfered with by the shape of the grains and the graphite between them. (An exception is ductile iron). Aluminum, copper and their alloys are also not amenable to flame cutting.
It should be recalled that grades from 08 to 20G belong to low-carbon steels, grades from 30 to 50G2 to medium-carbon steels. In the designations of grades of carbon steels, the letter U is always put in front.
We set 5 atmospheres on the oxygen reducer, and 0.5 on the gas reducer. (Typically a gas to oxygen ratio of 1:10.) All torch valves should be closed.
To work with a cutter, set 5 atmospheres on the gearbox, and 0.5 atmospheres on the gas.
Take the cutter, first open the propane a little (by a quarter or a little more), set it on fire. We rest the nozzle of the cutter against the metal (at an angle) and slowly open the regulating oxygen (do not confuse it with the cutting one). We adjust these valves one by one to achieve the flame strength we need. When adjusting, we open alternately gas, oxygen, gas, oxygen. The strength (or length) of the flame is selected with the calculation of the thickness of the metal. The thicker the sheet, the stronger the flame and the higher the oxygen consumption with propane. When the flame is adjusted (it turns blue and crown), metal can be cut.
The nozzle is brought to the edge of the metal, it is kept 5 mm from the object being cut at an angle of 90 °. If a sheet or product needs to be cut in the middle, the metal should be heated up from the point from which the cut will go. We heat the upper edge up to 1000-1300 °, depending on the metal (up to the temperature of its ignition). Visually, it looks as if the surface has started to “get wet” a little. Warming up takes literally a few seconds (up to 10). When the metal ignites, open the cutting oxygen valve, and a powerful narrowly directed jet is applied to the sheet.
How to properly use an oxygen acetylene torch for cutting
The valve of the torch should be opened very slowly, then the oxygen will ignite from the heated metal on its own, which will avoid a blowback of the flame, accompanied by a pop. We slowly move the oxygen stream along the specified mowing line. In this case, it is very important to choose the right angle of inclination. It should be at first 90 °, then have a slight deviation of 5-6 ° in the direction opposite to the cutting direction. However, if the thickness of the metal 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 by 20-30 °.
To start cutting metal, lower the cutting valve handle in a smooth, slow motion. As a result, oxygen will begin to flow to the combustion site, which should ignite the preheated metal. If the material is hot enough, the reaction will start instantly, after which you can increase the pressure even more until the moment when the metal is completely cut through.
After that, gradually move the torch along the intended direction of the cut. The speed of the cutting movement must be selected so that the resulting slag, sparks and hot metal drops are blown down or flow away from the burner flame.
After making the cut, the site should be carefully inspected for large pieces of molten metal. You should not step on them under any circumstances, as this can lead to burning even a thick sole. A cut sheet or piece of metal is cooled by water or naturally.
Collection and adjustment of equipment
- the fitting is pre-checked for defects. If available, the surface is processed with an ordinary file. Otherwise, a reducer installed on a defective fitting can “poison”, that is, little by little gas can pass;
- then the reduction gears are installed: blue. to the oxygen cylinder, red. to the propane cylinder. In this case, you should make sure that the rubber gaskets are in good condition, as well as that there are no traces of fat or oil on the valves;
- Hoses in accordance with the direction of the thread (left-hand or right-hand) are installed on the gearboxes and the torch using the clamps supplied with the equipment. Before installing them, make sure that there is no damage to their surface;
- kickback valves are mounted on matching torch fittings.
After assembling the equipment, it must be configured, while checking its serviceability. The procedure is as follows:
- the supply of acetylene is checked by opening the appropriate valve for 1 turn of the hand. In this case, the pressure should not exceed a level of 1 atmosphere. The optimum pressure, which is recommended to be set using a control valve, is 0.34-0.54 atmospheres;
- then purge the hose by opening the valve on the torch until the sound of gas escaping under pressure;
- the oxygen pressure is adjusted in the same way. For him, the recommended level is 1.7-2.7 atmospheres;
- after that, the hose is purged by sequentially opening the rear and then the front of the two valves that regulate the amount of oxygen supplied.
All the necessary instructions for assembling and setting up the equipment are contained in the delivery set. They need to be carefully studied and followed when working with the torch, which is easy enough to learn.
- a set of purchased equipment used to cut metal;
- tools that are used for marking and measuring (ordinary ruler, tape measure, square, special pencil);
- a special lighter, usually supplied with the rest of the equipment (the use of matches or ordinary lighters is prohibited).
A work station used for gas cutting metals should be located either outdoors or in a workshop or workshop equipped with well-ventilated ventilation. In this case, the floor, according to fire safety requirements, must be earthen or made of concrete. You should also carefully monitor that there are no flammable and flammable materials and products near the working place of the gas cutter. Within a radius of 5 meters from the metal cutting site, the floor or ground is cleared of debris, rags, dry grass and any other objects that could potentially catch fire.
Gas equipment that is used in the process of cutting metals, namely the oxy-acetylene torch, is classified as explosive and flammable. Therefore, before using the gas torch, you should follow all the mandatory safety recommendations.
For this, the workplace should be equipped with:
- fire extinguisher. The use of a gas torch is accompanied by open flames and high temperatures, therefore fire extinguishing means must be present at the post;
- protective clothing, consisting of:
- cotton suit, if possible, impregnated with fire retardant;
- gloves or gaiters made of tarpaulin or sufficiently thick leather;
- boot with leather soles;
- protective goggles with built-in light filters.
When working with the cutter, under no circumstances should you wear items of clothing made of synthetics or other easily flammable fabrics, as well as those that do not fit snugly to the body or have severely frayed 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 gas cut. Stainless steel, non-ferrous metals and various alloys cannot be cut with a propane cutter.
Newbie tips for using a gas torch
Before using the torch, follow the safety instructions. After. go to setting and cutting.
Due to the appearance on the market of construction tools of various types of cutters, affordable and relatively easy to use, the question of how to use a cutter is becoming increasingly important. In order to competently and safely perform work using such equipment, you must first study its features and operating rules.
Igniting the torch and preparing the metal
- once again make sure that the connections of the used shut-off valves are tight and not damaged;
- clean the working area within a radius of 4-5 meters from debris and other easily flammable materials and objects;
- put on a full set of workwear.
This is followed by opening the acetylene valve on the torch and letting off the oxygen in the mixing chamber. Then, by adjusting the valve, a barely audible gas outlet is achieved. A special lighter is brought to the cutter and turned on. A small, yellow flame should appear in front of the torch.
For operation, it is necessary that the flame length is 25 cm.This is achieved by adjusting the acetylene supply valve.
The next stage is the launch of oxygen. It is carried out by opening the corresponding valve until the color of the flame turns from yellow to blue. This means that the amount of oxygen is sufficient to completely burn the incoming acetylene.
how to cut with a torch. oxygen acetylene welding cutting torch
For efficient operation, the oxygen supply is increased until the length of the blue flame inside the tongue does not exceed the thickness of the steel to be cut. If the torch generates a characteristic “puffing” sound or the flame is unstable, slightly reduce the amount of oxygen supplied.
Before starting to cut the metal, its surface must be heated. To this end, the cutter is brought to the steel sheet so that the internal flame is at a distance of approximately 1 cm from it.The steel is heated until a puddle of molten material appears on its surface.
Working with a gas torch presupposes careful observance of safety precautions, as well as rules and instructions for working with the equipment. At the same time, it does not present any particular technological complexity and can be easily performed with an acceptable result in terms of quality, even without special education. It is interesting to know the opinion of experts about professional secrets that probably exist in large numbers. They can be expressed in the Комментарии и мнения владельцев to the article.