Gas welding and gas cutting are welding and cutting of metal materials by using the heat released by the mixed combustion of combustible gas and combustion-supporting gas as a heat source. There are many types of combustible gases, such as acetylene, hydrogen, natural gas, and liquefied petroleum gas (mainly propane). At present, the most common application is acetylene gas, followed by propane.
Welding materials for gas welding and gas cutting
Oxygen: Oxygen is a combustion-supporting gas in gas welding and gas cutting. Oxygen cannot burn itself, but it can help other combustible materials burn. Air separation is commonly used in the industry to produce oxygen. The oxygen used for gas welding and gas cutting is divided into two grades according to purity: the first grade purity is not less than 99.2%; the second grade purity is not less than 98.5%. Oxygen can be supplied in a human oxygen cylinder, or it can be piped. The former is flexible and convenient; the latter is safe and stable, more economical, and more effective in large and medium-sized enterprises.
Acetylene: Acetylene is obtained by the interaction and decomposition of calcium carbide (CaC2) and water, and its molecular formula is C2H2. Acetylene is a colorless gas with a special odor. It has a density of 1.179 kg / m3 under standard conditions and is lighter than air.
Acetylene is a combustible gas. When it is mixed with oxygen, the flame temperature is 3000 ~ 3300 ℃, so it is enough to melt the metal quickly for welding and cutting.
Acetylene can be dissolved in a large amount in acetone solution, so that we can take advantage of this property of acetylene, store it in acetylene bottles (containing acetone solution and activated carbon in the bottle) for storage, transportation and use.
It must be noted that acetylene is an explosive and dangerous gas. When the pressure of acetylene reaches 0.15 ~ 0.2MPa and the temperature is 580 ~ 600 ℃, acetylene will explode on its own. The gas mixture of acetylene with oxygen and air is also explosive. Therefore, the acetylene generator that has just been installed in the calcium carbide should first be discharged after the air acetylene is used. When installing acetylene, special care should be taken to avoid open flames and Mars. And should prevent oxygen from flowing back into the acetylene generator.
Propane: The molecular formula of propane is C3H8, which is heavier than air. The flame temperature of propane is 2000 ~ 2700 ℃, which is lower than the temperature of acetylene flame. Therefore, the preheat time should be longer when cutting with propane gas. Propane gas cutting has a smooth and clean cut, does not carburize, and is not easy to slag on the lower edge. It is easy to remove slag if it is slag; small deformation when cutting thin plates. If mechanical cutting is used, the cutting surface roughness is very small, and many workpieces do not need to be machine Processing to improve work efficiency. The following table shows the performance comparison between acetylene gas and propane gas.
As can be seen from the table, liquefied petroleum gas (mainly propane) also has a certain degree of explosiveness, but it can cause a small range of explosion in the air; it is much smaller than acetylene, and its burning speed is relatively small, so Much safer than when acetylene is used.
Since propane gas is heavier than air and will deposit, ventilation must be strengthened. Special attention must be paid to safe ventilation when working in containers and cylinders.
Propane is inexpensive and easy to obtain. Using it to replace acetylene for gas welding and gas cutting of metals has great economic significance.
Gas welding wire: The selection of welding wire during gas welding should be based on the composition of the weldment, the mechanical properties of the base metal, the weldability of the base metal, and the special technical requirements of the weldment. Common types of gas welding wires are welding wire for carbon structural steel, welding wire for alloy structural steel, welding wire for cast iron, and the like.
Gas welding flux: In order to prevent the oxidation of metals, eliminate the formed oxides, and improve the wettability, when welding non-ferrous metals, cast iron and stainless steel, gas welding fluxes must usually be used. The styling gas welding flux is in powder form and sealed in bottles. Each bottle weighs 500g.
