Material to Decrease Wetability

Can you expand and clarify your request? Are you using water as a coolant for a brazing operation? Are you brazing copper tube to stainless tube, or some other stainless part? Is brazing material getting on your fixture? Are you trying to prevent corrosion?

I engineer and supervise brazing operations of several types and with different materials, so if you could clarify what you are doing, maybe we can help you with a solution.

This photo is our parts and fixture. Yes, we using water to coolant for brazing operation. we brazing stainless valve body with copper tube. This vavle body have to brazing with two copper tubes. We have control the insert deepth 1mm by fixture and the brazing joint have to full penetrated. The brazing gap is about 0.15mm. Often the brazing material getting on our fixture. Any suggestion will be appreciate! Any questions about this, you can sent email to me. Email: lvzhiyong@danfoss.com

The most economical solution to your problem would be to heat the stainless steel fixtures in air until they become oxidized and dark black. I have found that this oxide makes it impossible to wet the surface of the stailess steel even with flux. It usually requires tha the stainless be heated cherry red and allowed to cool in air.

Quite right, I forgot that one. We heat our stainless parts in a hydrogen/ nitrogen atmosphere & they turn green but the effect is the same.

Any Oxide or Boron Nitride

Any coating of matl with less wettability won't help if a lot of filler metal is flowing over the fixture. You may have to re-design the fixture to prevent it from coming in contact with filler metal. There is also possibilty that you are overheating the filler metal to make it spill from the joint.

Whatever info you have given, I can suggest only this much.

We face similar problems in brazing ceramic/nickel steel/copper assemblies. Sometimes the fixtures have to be nickel steel to match the expansion of the major parts of the assembly. We reduce the risk of brazing the fixture to the assembly by:-

Minimising the contact points by profiling the fixture.

Using inserts of a 'non wetting' material at the contact points.

Using a stop off coating at the contact points, we use a commercially available liquid which is similar to the boron etc suggested earlier.

As suggested, it is also important to control the amount of filler used, could you use a pre-form instead of adding filler by hand?

Hello Nigh, could you please give some informations of "non-wetting" material? Is these material be machineable? could you give me some informations about the commercially available liquid? where could we buy it? It is appreciated if you give me any informations.

Sorry to be so long replying to this, I seem to be missing out on some of the e-mail alerts.

The non-wetting material would have to be chosen to suit your brazing material, we use stainless inserts or jaws when brazing ceramic/metal assemblies with copper based brazing alloys.

The stop-off liquid we use is called nicrobraze & is like a large felt tip pen, I would think that whoever supplies your brazing material would be able to tell you where to get something similar.