This work serves as the basis for beginning an improvement and optimization process of the brazing system and parameters currently used by an industrial company in heat pumps.

In the manufacturing of water heaters, coils play a crucial role. This structure is responsible for allowing water circulation and heating. For this reason, it is essential that this component is long and has high thermal conductivity. Therefore, the coil is made up of a series of welded and bent copper tubes. The welding of these copper tubes is usually done through the brazing process in a furnace.

In this process, the components are subjected to a period of approximately 50 minutes inside a continuously open oven, where temperatures vary from approximately 710 °C to 830 °C.

To guarantee the integrity of the internal environment, the oven inlets and outlets are protected by nitrogen curtains, thus preventing contamination of gas inside. Inside the furnace, a mixture with 5% hydrogen order to reduce the formation of slag.

After leaving the oven, the coils cool naturally to room temperature.

The base material used in the tests was a copper tube of type CW024, rolled product with 99.90% pure copper, and the filler material is a copper-silver-phosphorous alloy BCuP 281a, according to the ISO 17672 standard.

These tubes have a nominal outer diameter of 9.55 mm and a thickness of 0.8 mm, while the filler material is in the form of a ring with an outer diameter of 11 mm and sections of thickness 1 mm and 1.5 mm.

The work involved analyzing which welding methods are most suitable for welding copper; define the best shape of the joints; see how to reduce the process time, brazing specimens of a copper alloy; test the test pieces for tightness; carry out micrographs of the welding samples; and analyze the welding using microcomputed tomography.

For the tests carried out in this investigation, the best results were obtained by brazing the specimens at a temperature of 820 °C and using a ring of outer filler material 1 mm thick.

This article is shared by António B Pereira and José P Res.