GAS WELDING

Gas welding or gas flame weldingbelongs to the group fusion welding, where the basic material is melted by the heat of the flame, which is created by burning fuel gas (acetylene, propane, butane, hydrogen) with pure oxygen or oxygen from the air. The hottest flame produces the combustion of acetylene with pure oxygen (temperature 3,160 ºC), with the release of carbon dioxide (CO2) and water vapor (H2O). Gas welding is performed with additional material, but sometimes without it. It is one of the oldest and most versatile welding methodsle="procedures of welding" href="https://www.sigmat.hr/zavarivanje/strucni-clanci/opce-informacije">welding procedures, but lately it has been less and less represented. It is mainly used today for welding steel pipes and gray cast iron pipes, and it is also used for repairs. The equipment is relatively inexpensive, the flame is more dispersed than the electric arc, causing slower cooling, which leads to higher residual stresses and deformations. A similar procedure is gas cutting, with additional supply of pure oxygen. Oxygen-acetylene flame has a very large industrial application in hard soldering, thermal cutting and local heat treatments.

OprThe gas welding torch consists of a bottleacetylene, oxygen bottles, reduction valves, welding pipes, torches and additional material.strong>Gas flame weldingit is used for welding steel, gray cast iron, copper, aluminum and their alloys. Welding processis simple, the equipment is cheap, but the welding speed is low, while the flammability and explosiveness of the work increases the danger during work.

Equipment for gas welding

Equipment for gas welding consists of an acetylene bottle, an oxygen bottle, reduction valves, a welding pipe, a torch and additional material. Gas flame is used for welding, brazing, brazing, injection molding, straightening, cutting, surface cleaning and many types of surface treatment of materials. Acetylene (as a fuel gas) and oxygen (as a gas that supports burning) are used for welding.

For welding and cuttinge, oxygen is delivered in blue bottles under a pressure of 150 bar. Combustible materials release a greater amount of heat when they burn in pure oxygen rather than in air. Oxygen is obtained by fractional distillation of air (rarely by electrolysis of water because it is a more expensive procedure). The basic principle of fractional distillation is that the air first turns into a liquid state (which is achieved by pressurizing it to 40 bar and subcooling it to -200 ºC). If the liquid air is then heated, it will evaporate the nitrogen that boils at -196 ºC, leaving only oxygen (boiling at -183 ºC) in the fractional distillation apparatus. The specific mass of oxygen at a temperature of 20 ºC and a pressure of 1.013 bar is 1.43 kg/m3.

When withe the oxygen bottle is empty, a certain amount of oxygen must be left in the bottle to avoid the penetration of air and moisture into the bottle (minimum reading on the regulation valve - manometer is 0.5 bar). When handling oxygen bottles, you should make sure that they are always clean (there must be no dirt or grease around the regulating valve), and opening and closing the bottle must be done carefully - no more than half a turn of the valve for opening and closing the bottle).

Bottle acethylene

Acetylene or ethene is supplied in white bottles under a pressure of 15 bar. It is very unstable and explosive when mixed with air or oxygen. As the pressure increases, the explosiveness of acetylene increases, so that 3% of acetylene in a mixture with air is enough to cause an explosion. Likewise, when welding or cutting copper (Cu) or silver (Ag), a reaction of acetylene and the mentioned elements occurs, and compounds are formed that are explosive upon impact or elevated temperatures. For the above reasons, it is necessary to follow the rules that apply to the handling of acetylene and oxygen cylinders in production, transport and storage. Acetylene is a gas from the group of unsaturated hydrocarbons, it is a colorless and non-toxic gas with a characteristic smell. It dissolves in water in a ratio of 1 : 1, and in acetone 1 : 25 at atmspherical pressure and temperature 20 ºC. The solubility of acetylene in acetone increases with increasing pressure, and decreases with increasing temperature. An acetylene cylinder, which has a volume of 40 liters, holds 6 m3 of acetylene at a pressure of 15 bar and a temperature of 20 ºC. A pressure regulator (manometer) is placed at the outlet of the bottle, which lowers the acetylene pressure below 1.5 bar (if the acetylene pressure at the outlet of the bottle exceeds 1.5 bar, gas bubbles may form and combine with air, which may cause gas explosion).

Pri empty bottle, the flow rate of acetylene, that is, the flow rate of acetylene must be less than 1 m3/h, in order to prevent evaporation of acetone from the bottle and freezing of the reduction valve (manometer). Likewise, the bottle must not be completely emptied, but a certain amount of acetylene must be left that corresponds to the pressure on the manometer of 1 to 1.5 bar, depending on the outside temperature. The flame of acetylene and pure oxygen gives a maximum temperature of 3160 ºC, while the flame of butane and propane with pure oxygen gives a maximum temperature of 2830 ºC and 2850 ºC, respectively.