bluc wrote:So for silver soldering(not soft solder) what flux do i need for copper to stainless?
I got this from a friend who built his still using copper tubes and stainless ferrules.
Tri-clamps are made from Austenitic stainless steel. Austenitic stainless steels are non-magnetic.
The Austenitic steels are based on the 18% chromium 8% nickel composition although the chromium addition can vary
from 15-22% and the nickel from 6-11%. These steels cannot be hardened by heat treatment and must rely for their
mechanical properties on mechanical working. This means that any thermal joining treatment will reduce the
mechanical properties in the 'heat affected zone'.
Austenitic steels if heated between 55O °C and 750 °C will precipitate complex Chromium Carbide. This will render the
material susceptible to a rapid corrosion process known as weld decay. The degree of this precipitation will be a function
of the carbon content but it is obvious that most thermal joining processes will be a potential hazard. The steels can be
stabilised by the addition of either niobium or titanium and all Austenitic steels that are to be brazed or welded should
either be in this condition or have a low carbon content. (302, 303, 304, 310, 316, 321, 325 and 347).
Fluxes
The use of a flux is essential when brazing stainless steel in air. With components where the joint area can be easily
heated up to brazing temperature, Easyflo flux can be used. However, should prolonged heating be necessary, a flux
metal reaction will take place when this flux is used. This reaction will form a film on the surface of the stainless steel so
that it cannot be 'wetted' by the brazing alloy, and the addition of fresh flux will not remove this film. In these instances
it is necessary to use Tenacity Flux No 6 flux. This has improved high temperature properties and does not react with
stainless steel. The only problem is that the residues are not water-soluble and have to be removed with caustic soda, or
mechanical methods, such as grit blasting.
Tenacity flux can be bought from BOC but they have to get it in. They don't have it on their shelves.