torch brazing - HELP HELP HELP!

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- sub_0001
  
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posted
16 years ago

Sun, Oct 7, 2007 4:48 AM

I am trying to braze some brass fittings to 2-inch dia. K-hard copper pipe. I need the joint to be vacuum tight. I am not having much success. I have lots of leaks.

I am using Sil-Fos 6, a fast flowing phos-copper filler and no flux, oxy-acetylene torch, victor #2 tip, 5 psi oxy/acetylene with slightly acetylene rich flame, outer cone ~2x inner cone.

I am trying to heat the entire joint uniformly before I add filler. I think this may be a mistake. Should I heat one area, add filler, then move to another area?

Can I reheat the fitting when it leaks? I've tried this but it doesn't seem to help much. I'm afraid that after the first heating, scale is forming and subsequent heatings do not cause the filler to wet the oxidized area.

I think I will have to use flux.

Please post any suggestions.

TIA!

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- dcaster
  
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posted
16 years ago

Sun, Oct 7, 2007 6:43 AM

This is how I would do it. It may not be the best way.

After cleaning the pipe and fittings assemble the joint. Apply heat to the fitting and pipe about half an inch away for the joint so as not to oxidize the joint area. When you have the joint close to the right temperature, apply the heat to the fitting with the Sil-phos 6 rod on the crack between the fitting and pipe nearest to where you are heating. When the sil-phos sucks into the joint move the heat further around the joint and keep the sil-phos on the crack close to where you are heating. Continue doing this around the joint.

When you try to get the whole joint hot enough before adding the sil- phos, the metal has a chance to oxidize in the area where there is no flame. Your reducing flame will help keep the metal from oxidizing so you could heat the whole joint if you had multiple flames.

Dan

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- Don Young
  
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posted
16 years ago

Mon, Oct 8, 2007 3:13 AM

In my limited experience I have found that when using only copper, the joint stays nice and bright all the way up to brazing temperature in the flame envelope but oxidizes rapidly if I move the flame away. So I try to complete the joint in the flame but have to be careful not to have too big a flame and overheat the joint. I think a flux is recommended for copper to brass joints.

Another possible problem is having the joint too tight. I do not know the recommended clearance but you have to have enough clearance for the filler to flow completely into the joint for a good job. You can add a bead around the edge of the joint to stop leaks.

Don Young