Gas Welding Technology
Gas welding and metal cutting allows you to connect metal parts in industry and household. It is a technological process in which a flammable gas substance with pure oxygen is used to bind the edges of surfaces at high temperatures. The distance between them is filled with molten material, the source of which is the filler wire.
Gas welding is a fairly simple technology that has many positive aspects:
- Possibility to perform welding work in standalone mode. It does not require a powerful energy source.
- Availability of simple oversized equipment that is easy to transport.
- Welding process adjustable. The gas torch allows working high temperatures, heating rates and fire angles to be varied.
Large range of uses: processing is used for joining parts of carbon steel, lead, copper, cast iron, brass, bronze, silumin, aluminum and its alloys.
- Large area of heating that creates the conditions for deformation of neighboring elements.
- The gas-welding process refers to work of increased danger. Compressed oxygen, and combustible mixtures require precautions.
- Gas welding is designed for metal thicknesses up to 5 mm.
- Lack of automation of the gas burner.
- High requirements for the profession of a welder.
Features of use
To understand how to properly cut metal with a torch, it is necessary to study the design and know that such equipment is not used for cutting steels with high m carbon, t. к. It is not possible to create a temperature capable of stable melting. When cutting cast iron workpieces or structures, there is a concentration of graphite between the metal grains, which makes it difficult to.
Cannot be used to cut products made of aluminum, copper, and aluminum-based alloys.
Cutting across the surface
Users, of course, are interested in how to use the torch during shape cutting. This technique is performed by the nozzle of the tool, and the molten slag heats the metal, but without exceeding the melting temperature. The torch is placed at an angle of up to 80 degrees, and after oxygen supply, the angle varies from 18-45 0.
Grooves are formed by adjusting the cutting speed, if larger grooves are needed, change the angle of the nozzle and slow down the cutting speed slightly by adjusting the oxygen supply. Width of grooves is changed by adjusting the flow of burning gas through the nozzle, this parameter is equal to 1 to 6, but make sure that there is no overflow.
edges of the notch were clean, the oxygen supply must be increased.
Gas pressure for gas cutting and oxygen consumption
In the table below you will find data on cutting oxygen pressure:
|Thickness of steel to be cut in mm|
|3. 3,5||4. 4,5||4. 4,5||6. 7||8. 11||10. 11||10. 12||12. 14|
The table below will show the oxygen consumption for gas metal cutting:
|Thickness of steel to be cut in mm|
|2,6. 3,0||4,5. 5,0||7,5. 8,5||13,0. 18,0||28,0. 32,0||38,0. 40,0|
Close the torch in reverse order. First of all, it is necessary to cut off the oxygen supply, and only then the combustible gas is cut off.
Basic conditions of gas-oxygen cutting
Not all metals are amenable to oxyfuel cutting. Here are the necessary conditions without which the gas-oxygen cutting process cannot occur:
- The melting point of a metal must be higher than its ignition temperature in oxygen. What is the ignition temperature?? The ignition temperature is the temperature at which the metal begins to oxidize.
- The melting temperature of the metal oxides must be lower than the melting temperature of the metal itself. Otherwise, the oxides will not allow the metal to oxidize. The best known of these metals is aluminum. The melting point of its oxide film is about 2050ºC, which is higher than the temperature of the oxygen flame.
The table below shows the melting temperatures of various metals:
- Metal combustion temperature must ensure an uninterrupted cutting process.
- Metal being cut must not have too great a thermal conductivity. Otherwise, heat generated to heat the metal will be dissipated from the cutting zone. These metals are aluminum and copper.
- Oxides produced by the cutting process must be able to escape from the cutting zone.
- Chemical elements in the metal must not hinder cutting and contribute to the hardening of the metal.
Safety precautions when gas cutting steel
The process of cutting steel is accompanied by a number of hazards: fire, explosion, etc.д. The following rules should be observed:
How to cut metal with an oxypropane torch
For disassembly of metal structures, cutting of any kind of rolled metal before machining or welding, metal cutting is required. And if a sheet or section of small thickness can be cut with a mechanical cutting tool (manual, electric or hydraulic driven). Then to work with metal workpieces of great thickness you need a gas cutter, or in professional slang. autogenous. In this article, the master plumber will tell you how to cut metal with an oxygen-propane torch.
Regardless of the size of the auto-gen and the type of heating gas mixture, cutting is carried out through combustion of metal in a stream of pure oxygen blown through the nozzle of the head into the working area.
Please note! The basic and fundamental condition of gas cutting is that the combustion temperature must be lower than the melting temperature. Otherwise, the metal will melt and flow before it starts to burn. Low carbon steels meet this condition, non-ferrous metals and cast iron do not
Most alloy steels are also not amenable to gas cutting. there are restrictions on the maximum allowable doses of alloying elements, carbon and impurities, beyond which the process of burning of metal in oxygen becomes unstable or generally interrupted.The cutting process itself can be broken down into two phases:
- Heating a limited zone of the part to a temperature at which the metal starts to burn. In order to obtain a plume of heating flame, some of the process oxygen is mixed with the combustible gas in a certain proportion.
- combustion (oxidation) of heated metal in the oxygen stream and removal of combustion products from the cutting zone.
If we consider the classification of only hand torches, the following features are of fundamental importance:
- Type of fuel, power and the method of obtaining a mixture of gases for the heating flame;
- Classification by type of combustible gas: acetylene, propane-butane, methane, universal, MAF;
Please note! kerosene and gasoline torches, though they have the same purpose, belong to the category of fuel torches
- By power: low (cutting metal with thickness from 3 to 100 mm). marking P1, medium (up to 200 mm). P2, high (up to 300 mm). P3. There are samples with increased cutting thickness. up to 500 mm.
- According to the method of combustible gas generation: injector and non-injector.
And if the first characteristic only affects the temperature of the heating flame, and the power. on the limiting thickness of the metal, the third feature is determined by the design of the torch.
The injector, or twin-tube, gas torch is the most common type of design. The process oxygen in the torch separates into two streams.
Part of the flow moves along the upper tube into the head of the tip and exits at high velocity through the central nozzle of the inner mouthpiece. This part of the design is responsible for the cutting phase of the process. Control valve or lever valve is moved outside the body.
The other part enters the injector. The principle of operation of which lies in the fact that the injected gas (oxygen), coming into the mixing chamber at high pressure and high speed, creates there a rarefaction zone and draws flammable (ejected) gas through the peripheral holes. Through mixing, the velocities align and the chamber outlet produces a gas mixture with a velocity lower than that of the injected oxygen, but higher than that of the ejected combustible gas.Then the gas mixture moves along the lower tube to the head of the tip, comes out through the nozzles between the inner and the outer mouthpiece, and forms a plume of heating flame. Each channel has its own valve on the body, which regulates oxygen and combustible gas in the injector.
The sparkless or three-pipe torch has a more complicated design. both oxygen and gas flow to the head through separate tubes.
Metal cutting with gas. Cutting with natural gas.
Natural gas is widely used in many plants as combustible gas for oxyfuel cutting. Due to its high calorific value, it is widely used as a valuable substitute for acetylene in oxygen cutting of steel with thickness up to 300 mm and more, as well as for other types of gas flame treatment of metals.
methane in natural gas.
The basis of natural gas is methane, which reaches 99% in some gas fields.
Natural gas pressure in cylinder.
To the places of consumption natural gas comes through pipelines under low pressure or under pressure of 150 kg/cm2 in cylinders painted red. In case of lack of special cylinders for storage and transportation of natural gas ordinary oxygen cylinders with modified valve and repainted red with corresponding white inscription can be used.
There are special torches for cutting with gases. acetylene substitutes. They differ from acetylene-oxygen torches only by the size of outlet openings of the outer mouthpiece, mixing chamber and injector, which should be somewhat larger.
RZR-55 cutting torch for metal with natural gas.
RZR-55 torch is designed for hand torch cutting of steel with thickness from 5 to 300 mm using natural gas and some other gas-substitutes as well as propane-butane mixture. It is equipped with two outer and five inner nozzles. Technical characteristics of the torch RZR-55 are given in Tab. 1.
Technical characteristics of the torch RZR-55.
|Thickness of metal being cut, mm||no. of mouthpiece||Oxygen pressure, kg/cm2||Cutting speed, mm/min||Oxygen consumption, m3/hour||Flow rate, m3/hour|
|external||internal||cutting||heating||natural gas or methane||propane-butane mixture|
Characteristics of cutting torch type UR for cutting with natural gas.
Most often for natural gas, conventional acetylene-oxygen torches with drilled holes in mixing chamber, injector and external nozzles are used. Table below shows characteristics of the cutting torch type UR for operation with natural gas. 2.
When cutting metal with thickness of 250 mm or more it is recommended to deliver oxygen into the cutter by two hoses. separately for heating flame and cutting stream, and the pressure is set by manometers on separate pressure regulators.
Torch characteristics of UR type for cutting with natural gas.
|Metal thickness, mm||No. of the inner mouthpiece||Aperture diameter, mm||Flow rate, m3/hour|
|In the outer mouthpiece||In mixing chamber||Injectors||Natural gas||Oxygen for combustible mixture|
Reducer for natural gas.
A hydrogen pressure reducer painted red with a coupling nut with a left-hand thread and a diameter of 21.8 mm is used for reducing the gas pressure. If no hydrogen pressure reducer is available, a standard oxygen pressure reducer can be used and the coupling nut must be replaced. convenient to use the adapter. allowing to connect a conventional oxygen reducer without any modifications.
After working with natural gas can not be used again for oxygen without prior degreasing.
When working from the pipeline at the workplace it is recommended to install a liquid safety valve.
At pressure in the network not more than 0,02 kg/cm2 a special ZGG-Z post gate for city and natural gas (methane) can be used. Its design and operating principle is similar to that of the acetylene low-pressure valve.
At higher pressures it is necessary to install a shutter of closed type. It is better to use a pressure reducer instead of a valve as it is a reliable blowback preventer and allows working outdoors in winter.
Significantly lower flame temperature created by natural gas-oxygen mixture compared to acetylene-oxygen flame reduces the rate of cooling of the edges heated during cutting. Therefore, the use of natural gas instead of acetylene is especially appropriate for oxygen cutting alloy steels that are prone to cracking. In addition, cutting with natural gas causes less carburizing on the cutting surface. Cutting speed is same as with acetylene. Edge heating time at the beginning of the cut is longer.
Cutting with natural gas produces a cleaner and better cut surface compared to cutting with acetylene. Considerably less deformation of the metal, which is especially important when cutting of small thicknesses.
Cutting with natural gas is equivalent to cutting with acetylene.
Cutting stainless circles/rods
Circuits and rods made of stainless steel have a circular cross-section. The diameter of the workpieces varies: in the case of circles it is up to 300 mm, in the case of bars. up to 80 mm. Plasma cutting technology enables quick and precise cutting of all stainless steel products with a circular cross section.
Manufacturing technology, chemical composition of the material, the special conditions of work with him reflected in GOSTs 7417. 75; 8559. 75; 8560. 78 for the calibrated rod, 14955. 77; 18907. 73 for the polished rod. Grinding wheels are mainly used for manufacturing parts for the machine tool industry. Rods are most often used in construction, repair, architectural work, in the assembly of commercial, food, pharmaceutical equipment and inventory.
After the cutting is complete
Even if the specialist performs gas cutting of metal, the price of which is extremely low, he must comply with safety regulations. And not only before and during, but also after the process. When finished, the equipment must be turned off and the workplace must be tidied up.
First the oxygen supply is stopped, then the fuel gas. Need to make sure that the valves on the cylinders were tightly closed. There is also an accumulation of residual medium in the hose of the torch and the residual medium must be vented to the atmosphere by unscrewing the valve for oxygen supply. It is better to clean the torch nozzles from soot and slag deposits as a finishing work and not to leave it for later.
Then burner is disconnected from hoses. Disassembled equipment should be stored in a designated place.