Gas cutting of metal; metal processing instruction
The technology of gas cutting of metal has a number of advantages, therefore it is used in various spheres of life. Working with gas burners requires knowledge of technology, equipment design, and safety. Experienced workers achieve the best results.
The choice of cutting gas depends on the properties of the metal workpiece. In addition to technical oxygen, acetylene, coke oven and petroleum gas, methane, propane, butane and mixtures thereof can be used.
Oxygen is used when cutting metal with gas if the material has certain characteristics:
- High thermal conductivity;
- A melting point above the ignition temperature in oxygen;
- The melting temperature of refractory oxides is lower than the melting temperature of the metal;
- The formation of liquid slags during the cutting process;
- The release of 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 jet.
Cutting can be:
- Superficial – the formation of slots and channels;
- Spear – the formation of holes or openings;
- Dividing – 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.
Any burner consists of:
- Valve (not in all models);
- Tip (extension tube);
- Mouthpiece (nozzles).
Mixing of gas with air can take place in the tip or mouthpiece. On valve models, the gas is mixed with oxygen in the head for increased safety. The use of models without a valve allows the use of gas at different pressures. Gas torches 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 jet must be uniform so that the flame does not go out. During combustion, oxides are formed, which are removed by a gas jet.
Gas cutting of metal – instructions for metal processing
Gas cutting is the most popular, as it does not require compliance with the norms for the room and is easy to do. The seam is not torn and neat if stencils are used. All torches are compact and mobile and easy to transport. Many gases can be used. This method allows you to work with thick workpieces and perform complex operations. No power supply required, the mode can be manual or automatic.
- Technology features
- Metal cutting instruction
- Oxygen pressure when cutting metal
- Metal cutting allowances
- Safety precautions for gas cutting of metal
Metal cutting instruction
It is important to correctly connect and prepare the torch. Tubes with closures at the ends are connected to the cylinders. Next, the gas supply is checked (if it is oxygen-propane metal cutting) – the valve closes, the valve on the cylinder opens. Then, observing the pressure gauge, the valve is slowly opened. The pressure should be 0.35-0.55 atmospheres. Then you need to blow through the hose – open the valve. Gas starts to come out with a characteristic sound. If the pressure gauge shows a stable pressure, the valve closes.
The next step is to check the oxygen supply and adjust the pressure. First, the valve on the cylinder opens, then the regulator (flow pressure 1.7-2.7 atmospheres). Oxygen valves on the torch are opened to purge the hose. There are two of them: for feeding into the nozzle and forming a mixture. First you need to open the first, then the second (for 3-5 seconds).
The gas supply valve is opened first to release oxygen, which remains in the mixer after checking. The valve must be turned until you can hear the gas coming out. The lighter in front of the torch should be in contact with the mouthpiece. After pressing the lever, the sparks ignite the gas.
Open the oxygen valve immediately. Its sufficient volume is indicated by a change in the color of the flame to blue. oxygen needs to be supplied to make the torch larger. The gas and oxygen pressure when cutting metal depends entirely on the thickness of the workpiece.
Using the technology of gas cutting of metal, the flame was brought to the material by the tip, heating the surface. After the appearance of the molten metal, oxygen begins to flow, igniting it. The jet increases until the material is fully cut through. At the same time, the mouthpiece moves along the mowing line of the cut. Sparks and slag are removed by a jet.
The optimal cutting speed is determined by sparks – they should fly away at an angle of 85-90 °. If the angle is less, the speed must be reduced. If the workpiece is thick, it must be positioned at an angle so that the slags flow down. It is not recommended to stop without completing the process. At the end of the work, oxygen is first shut off, then gas.
Novice welders are concerned with the question of how to use the propane oxygen cutter correctly so that the surface of the part does not warp. First you need to figure out what factors contribute to the occurrence of these defects:
- With uneven heating of the surface;
- The torch speed is high;
- There was a sharp cooling of the heating place.
In order to exclude the occurrence of the above factors on the workpieces, they are previously securely fixed and heated, and the speed is increased gradually. If warpage does occur, then the original shape can be restored by firing or tempering, and the sheets can be straightened on rollers.
The equipment is classified as explosive, so the work site must be equipped with the following accessories:
- Fire extinguisher;
- Sand box;
- Fire stand with appropriate tools.
Each performer must have a set of protective clothing.
It is not allowed to wear under the protection clothing made of flammable material, for example, synthetics, and the edges of the sleeves should fit snugly around the body so that sparks do not get inside.
They are similar to safety procedures for welding, but have specific additions:
- It is not recommended to neglect protective equipment, since this leads to injuries in the form of skin burns or damage to the cornea of the eyes by flying sparks, therefore glasses and gloves with long sockets to the elbow are required.
- The performer’s clothes and footwear are made of non-combustible material.
- Gas cylinders are located at least five meters from the cutting site.
- The torch flame is directed only away from the hoses.
- Cutting is done 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 torch as intended.
Surface and shape cutting
Surface oxygen cutting scheme.
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. As it spreads, 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 to create an angle of 17-45 °.
Adjust the groove dimensions (its depth and width) with the cutting speed: increasing the speed, decreasing the groove dimensions 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 shaped 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 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 you cut the part with the smallest deviations from the intended contours.
How to properly cut metal with an Oxy-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.
The propane cutter is designed for manual oxygen separation cutting of carbon and low-alloy steels using propane.
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 one.
Take the cutter, first open the propane a little (by a quarter or a little more), set it on fire. We push the nozzle of the cutter against the metal (at an angle) and slowly open the regulating oxygen (do not confuse with the cutting one). We adjust these valves in turn 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), the 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.
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 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 by 20-30 °.