Welding technology for copper and its alloys
Preparatory operations
The preparatory stage of copper welding involves thorough cleaning of the surfaces. The area around the weld and the welded edges are cleaned with a metal brush or doctor to shine, then degrease with gasoline, white spirit or other solvent. Between the surfaces to be welded gap should not be more than 2 mm, because the parts pressed together.
Difficulties in welding
— Copper welding technology has the following difficulties.
A high coefficient of thermal expansion causes permanent deformations and stresses;
— good thermal conductivity leads to increased cooling rates of the weld pool. This, in turn, leads to deterioration of weld quality and grain growth. This phenomenon can be counteracted by welding with high energy input;
— high casting shrinkage of cooling metal entails a significant deformation of the peri-seam zone and the weld, residual deformation and stresses in cases of rigid fastening of parts;
-molten copper easily absorbs hydrogen, which contributes to the appearance of water bubbles. This can cause multiple cracks and pores. This phenomenon is called hydrogen sickness;
— intense evaporation from the molten metal of zinc can lead to porosity of the weld;
— molten copper is characterized by high fluidity, which causes additional difficulties in welding (ceiling and vertical welds);
— Hot copper easily oxidizes. This contributes to the formation of refractory oxides.
When welding is complete, the weld is first forged and then annealed at 600 to 660 °C in order to obtain a fine grain structure of the weld and to even out the chemical composition.
Welding wire
Before use, it is cleaned by etching with aqueous nitric acid (75 cm³/litre) or a mixture of hydrochloric and sulphuric acids in a 100:1 ratio with a further rinsing in water, then in alkali, and then again in running clean water. After rinsing, the wire is dried with hot air. Quality welding requires pre-calcination of copper electrodes, thereby reducing the possibility of hydrogen sickness.
Protective atmosphere
Welding technology of copper and copper alloys involves the use of shielding gases, nitrogen, argon, helium or their mixtures. Welding in a nitrogen atmosphere is the most efficient, achieving a high efficiency of the arc discharge.
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