Gas Welding

Although the oxyacetylene process has been introduced long time ago it is still applied for its flexibility and mobility. Equipment for oxyacetylene welding consists of just a few elements, the energy necessary for welding can be transported in cylinders.Process energy is obtained from the exothermal chemical reaction between oxygen and a combustible gas, Figure 1.2. Suitable combustible gases are C2H2, lighting gas, H2, C3H8 and natural gas; here C3H8 has the highest calorific value. The highest flame intensity from point of view of calorific value and flame propagation speed is, however, obtained with C2H2. C2H2 is produced in acetylene gas generators by the exothermal transformation of calcium carbide with water, Carbide is obtained from the reaction of lime and car- bon in the arc furnace.C2H2 tends to decompose already at a pressure of 0.2 MPa. Nonetheless, commercial quantities can be stored when C2H2 is dis- solved in acetone.

Acetone disintegrates at a pressure of more than 1.8 MPa, i.e., with a filling pressure of 1.5 MPa the storage of 6m3 of C2H2 is possible in a standard cylinder (40 l). For gas ex- change (storage and drawing of quantities up to 700 l/h) a larger surface is necessary, therefore the gas cylinders are filled with a porous mass (diatomite). Gas consumption during welding can be observed from the weight reduction of the gas cylinder.