Brazing of copper pipes for heat pump and refrigeration applications

Abstract

In heat pumps and refrigeration systems, copper parts play a crucial role. Since heat pumps for space and water heating work under high pressure and are susceptible to vibrations, it is crucial to perfectly weld the copper pipes and heat exchangers to avoid system failures and prevent the leakage of the circulating refrigerants, which are harmful to the environment. The welding of the copper pipes is usually performed by the brazing process in a furnace. The components are subjected to a period of approximately 50 min inside a continuously open oven, varying the temperature from 710 ◦C to 830 ◦C. The oven inlets and outlets are protected by nitrogen curtains to guarantee a suitable internal environment and prevent the contamination of the gas inside the oven. This work analyses which welding methods are most suitable for welding copper, the best joint shape, process time, brazing specimens of a copper alloy, tightness tests, and mechanical properties and composition of the welding samples. From the tests carried out, the appearance of small and large defects is reduced by using a 1 mm thick external ring of filler material and a brazing temperature of 820 ◦C.