Oxygen cutting of metals (the term “autogenous cutting” can be found in the literature) is actively used in industry for cutting sheet steel and other alloys into workpieces of the required length. Also, this technology is used in a number of repairs and dismantling of structures. Its popularity is due to the comparative simplicity and low cost of equipment, as well as a high degree of security. The article contains information about the technology itself, about the necessary equipment and the basics of safety during oxygen cutting of metals and other materials.
Technology basics
Before starting cutting, it is recommended to heat the metal with the flame of a burner. This applies only to materials with a large cross section. Mentioned flame appears due to the reaction of oxygen with gas. If you neglect this recommendation, the metal will inevitably lead, warpage will occur. However, if the geometrical shape of the cut pieces is not important, for example, during the dismantling of structures from building steels, as well as when cutting thin-walled sheets, gas welding and oxygen cutting of metal is allowed without preheating the products.
High temperatures in the cutting zone are achieved by burning high-purity oxygen from a cylinder. In metal tanks under very high pressure contains from 99 to 99.8% of oxygen. If oxygen of ordinary purity (roughly speaking, atmospheric air) is used for heating, then oxygen of high purity is needed for effective oxygen cutting of the metal.
Surface preparation
If there is a task to saw into a transported piece a large object, which is to be disposed of, then you can not do surface preparation. The cutter will cope with this task as soon as possible. Another thing is the production of new products. In this case, it is important to obtain a quality cut line that is clean of scale and other undesirable inclusions. Oxygen cutting of metal is preceded by thorough cleaning of the material.
There are many methods to eliminate pollution. The most popular of them are surface heating with a gas flame and mechanical cleaning. The first method is the simplest. It allows you to effectively eliminate scale - the worst enemy of a gas welder. Its essence is to warm the metal surface to critical temperatures. The second method is more costly and requires special equipment (sandblasting machines, scrapers, brushes and so on) and skilled workers.
Material requirements
Not all steel grades and alloys can undergo oxygen flux cutting of metals. One of the main conditions is the melting point and the ignition temperature. For the normal course of the process, the first indicator should be significantly higher than the second. It is clear why: otherwise, the material will melt, not burn, which will lead to sagging. The cutting line will have a sloppy appearance, often this makes it impossible to further process the part on machining machines as a result of the displacement of the bases. In addition, such a metal layer may have poor mechanical and physical properties.
Certain elements added to the composition of steels as impurities can adversely affect the process of oxygen-propane metal cutting. So steels are considered the most processed, the carbon content of which does not exceed 0.3%. The cutting speed does not decrease with increasing carbon content, however, the steel becomes prone to overheating, hardening of the surface layer and the formation of quenching cracks, which can serve as stress concentrators and lead to brittle fracture of the entire workpiece.
Hand cutting
Oxygen gas cutting of metal, depending on the degree of automation and mechanization, is divided into mechanized and manual.
Manual welding is advisable to use in small-scale and single-unit production, as well as during the dismantling of structures and structures. Ideal for cutting blanks from pipes, removing gates from cast products and so on.
Oxygen cutting equipment for metals and alloys is characterized by high mobility, ease of operation and reliability. Due to these qualities, this technology is the most common both in industrial enterprises and in repair organizations.
Process mechanization
Over the past decade, robotics has developed very rapidly. Today, robots are used almost everywhere. And oxygen-arc cutting of metals is no exception. Currently, numerically controlled cutting equipment will no longer surprise anyone. These devices can be equipped with several oxygen cutters for metal cutting, which significantly increases their already high productivity. All leading foreign engineering holdings and companies have long been actively introducing similar technology into their production chains, and domestic companies are trying to keep up. The level of mechanization of welding works on average is about 80%.
The essence of oxygen-flux cutting metal
Traditional cutting is far from suitable for all materials. For example, steel alloyed with chrome and nickel is difficult to cut. A similar problem arises when cutting non-ferrous metals and cast irons.
Then oxygen-flux technology comes to the rescue. Its essence is as follows. Flux powder is fed into the cutting zone. This substance ignites and burns during the cutting process, while generating a large amount of heat, which makes it possible to reflow refractory carbides, borides and metal oxides.
Oxygen flux cutting equipment
We can say that for this type of metal cutting , conventional standard equipment is used, additionally equipped with a flux supply device (the so-called flux feeder and an oxygen cutter for cutting metal with a flux supply). The most common installations of this type are construction devices of the Avtogenmash Research Institute “URHS”. This equipment is intended for cutting steels with a high content of chromium and other alloying elements.
Use such equipment for mechanized cutting, equipping the machine with a flux supply device.
Oxygen flux cutting techniques
The technique is no different from the already traditional methods of classical oxygen cutting. The process itself can be carried out both by hands and mechanized by using auxiliary means, robots and devices. It can also be both dividing and superficial. It is recommended for cutting and cutting steels with a high content of chromium and nickel (that is, for refractory steels).
Features of oxygen-flux cutting of cast iron
During combustion, the flux generates a lot of heat. So much that happens the so-called bleaching of cast iron. The essence of this phenomenon is that carbon transfers from a free state to a bound one. In other words, carbon atoms in a certain area form a chemical compound with metal atoms. This is accompanied by a deterioration in the mechanical properties of cast iron (hardness increases, it becomes more fragile). As a result of accelerated heating and cooling, cracks appear on the surface, which can cause the destruction of the product.
The problem can be solved by preheating the metal and regulating its cooling rate. Only a worker with high qualifications and extensive experience in carrying out such work can cope with such tasks.
Features of oxygen-flux cutting of non-ferrous metals and alloys
Like cast iron, copper must be heated before it can be cut. Heating is carried out to a temperature of 800–900 degrees Celsius. Copper has a high thermal conductivity, so cutting without preheating will lead to significant warping, spatial distortion and marriage.
Alloys based on copper with other elements (brass, bronze and so on) also need to be heated. However, the preheating temperature should not exceed 500 degrees Celsius.
Advantages and disadvantages of oxygen cutting technology
Compared with other alternative methods of cutting sheet material of different grades of steel, this technology is excellent for cutting along curved lines, for cutting holes of large diameter. Also, this method allows to obtain blind holes.
The second, and very significant, advantage is the ease of use of the equipment. The gas cutter has a small mass, so that the welder can work with it for a long time, while not getting tired. This has a positive effect on performance.
Gas is a relatively affordable and cheap type of fuel. And this is the third advantage.
A very significant drawback of the technology is the explosiveness of the substances used. Therefore, violations of technological discipline are not allowed. Ignoring safety precautions can lead to serious consequences.
The rules of operation of the oxygen reducer for metal cutting
Before connecting the gearbox, the worker must ensure that there are no dirt on the threaded surfaces. If any, treat contaminated surfaces with kerosene or solvent. Only after purging the system and removing all foreign particles and elements that can get into the gearbox and disrupt its operation, you can put on and fasten the nut on the gearbox.
Other gearboxes are installed in the same way.
The start of gases is carried out by smoothly opening the cylinder valve. If no abnormalities are observed, the valve can be fully opened. If the gearbox begins to heat up, it is abnormal to make noise, it is necessary to immediately close the flywheel of the oxygen cylinder for cutting metal.
Work safety
After preparatory work, make sure that there are no gas leaks. It can be very dangerous. Only then can the torch be ignited and the flame adjusted.
If you need to make a short pause in the work (no more than two to three minutes), then just shut off the torch valve. In the event that work ceases for a long time, it is necessary to shut off the gearbox and the valve of the gas cylinder.
All work on oxygen cutting of metal is allowed only to workers who have passed all the necessary briefings.
It is forbidden to carry out any work in the vicinity of explosive tanks and flammable materials. If work is carried out in small enclosed spaces, then workers should rest and breathe fresh air regularly.
Welding work in production, which are carried out systematically (not temporary) should be carried out in specially equipped rooms. At the same time, the area of one workplace is at least four square meters. Passages between workstations must be at least 0.8 meters.
The premises should be equipped with a powerful exhaust hood of harmful substances. Its capacity should be 2500-3000 m 3 per 1 m 3 of gas burned.
In the event that more than ten welder jobs are equipped in one room (workshop), the gas should not come to them from cylinders, but centrally from the gas distribution station. The supply of gases from existing gas pipelines is allowed.
Working gas cylinders may only be transported with protective caps. They will prevent the valve from damage and contamination. It is forbidden to transport cylinders over long distances by hand. For these purposes, special devices and carts must be used. The impact of cylinders on the ground or on each other is unacceptable.
An explosive mixture of gas and oxygen may form in an oxygen cylinder for cutting metal in violation of technology and operating procedures. Therefore, it is necessary to approach gearbox adjustment with responsibility.