Welding technology of copper
Pure copper is rarely used. The introduction of alloying elements and impurities divides the copper alloys. Such alloys are: copper-Nickel alloys, bronze and brass. Brass is an alloy of copper and zinc. In bronze as the main alloying elements are zinc or Nickel. Copper-Nickel alloy is a alloys of copper with iron and Nickel or manganese. The presence of impurities determines the physico-chemical properties of copper alloys and the choice of welding mode.
At the preparatory stage, just prior to welding, a thorough dressing and cleaning of surfaces. The heat-affected zone and welded edges for that clean up with a wire brush or scraper to Shine, then perform degreasing with gasoline, white spirit or other solvent. Between the welded surfaces of the gap should not be more than 2 mm, for this the parts together shrink or make potholders.
The difficulty in welding copper
· High coefficient of thermal expansion causes residual strain and stress;
· good thermal conductivity leads to high cooling rates of the weld pool. This in turn entails a deterioration in the quality of the weld, and grain growth. To counteract this phenomenon is capable of welding with high heat input;
· high casting shrinkage of the cooling metal involves a substantial deformation of the weld zone and the weld, residual strains and stresses in the cases fixing parts;
· high sensitivity of molten copper to hydrogen contributes to the emergence of water bubbles. This can cause multiple cracks and pores. This phenomenon is called hydrogen disease of copper;
· intensive evaporation from the molten zinc metal may cause porosity of the weld;
· high fluidity of molten copper leads to additional difficulties in welding (especially in the overhead and vertical joints);
· at high temperatures copper is easily oxidized. It contributes to the formation of refractory oxides.
Upon completion of the welding seam prokovyvayut first, and then at a temperature of from 600 to 660 °C is annealed with the aim of obtaining fine-grained structure of the weld and the alignment of the chemical composition.
Before use it is subjected to cleaning by etching with an aqueous solution of nitric acid (75 cm3/liter) or a mixture of hydrochloric and sulfuric acid with a ratio of 100:1 with further rinsing in water after the lye, and then again in flowing pure water. After rinsing, the wire was dried with hot air. For example, copper electrodes before welding calcined, thereby reducing the probability of occurrence of hydrogen disease.
Welding copper alloys and copper are produced in protective environments gases, nitrogen, argon or helium, and mixtures thereof. Maximum efficiency welding is achieved by means of nitrogen, which ensures high efficiency of the arc discharge.
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