1993-04-01

New Joining Methods for Copper/Brass Heat Exchangers 931076

The copper industry has during the last couple of years developed two new joining techniques for copper/brass heat exchangers. The results are promising and they are likely to find industrial applications very soon.
Laser welding can use a modified ordinary lock seam tube mill together with the laser. The welding speed can be at least the same as during normal lock seam tube production and the wall thickness as thin as the thinnest used in lock seam tubes. Results from laser welding of a new tube profile, “double tubes”, is also presented.
Brazing instead of soldering is possible as new materials for brazing now are available. A cheap, non toxid low temperature brazing alloy based on the CuSnNiP system has been developed. Brazing can be done using a fluxless paste made from atomized powder. Both vacuum and inert gas furnaces can be utilized. Modified fin and tube materials that can stand the brazing temperature without excessive grain growth have been developed and are under evaluation. Results from wettability tests on different copper base alloys are reported as well as how the brazing alloy desolves the base material. Mechanical properties of typical heat exchangers joints are shown.
Corrosion properties of joints have also been studied.
The brazing technology has interesting properties. No flux is needed which means that the cleaning after brazing can be avoided and there are no lead or other dangerous metals in the brazing material. Some properties of full size radiators made with the new joining methods are finally reported.

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