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Up Topic Welding Industry / Technical Discussions / Brass blocks to thin copper tubing
- - By gittings00 Date 04-01-2003 04:12
I'm not a welder. My guys are TIG welding brass blocks to thin copper tubing in an application that needs to hold internal pressure.

We have a problem with leaking welds. I'm told by our senior guy that *even* he couldn't produce 100% without leaks. Is that realistic??

I know they preheat the brass blocks, but not with any precision. Should that be done in a fashion to produce constant temperatures? Any idea how hot it should be?
Parent - - By colins (*) Date 04-01-2003 15:52
It sounds as if there could be a couple of causes for your problem
A) the difference in thickness between the the thin copper tubing and the thick block. The block is acting as a huge heat sink and removing heat too quick, essentially quenching the weld. As so the joint detail between the two pieces may be a problem

B) The chemistry between the block and the tubing may be incompatible, What if any filler material are they using ?

It seems that there are too many unknowns right now to make any strong reccomendations. Would you mind sharing more details of this situation ?

Parent - - By jwright650 (*****) Date 04-02-2003 14:04
Filler Rod, and Actual Thickness of materials would be a great help along with the ASTM #'s of the base materials. From these items you can determine proper heat treatment(preheat/postheat), and proper filler metal to mix in the puddle for the ASTM # you provide and any special considerations that need to be addressed. Any codes/specs. that are applicable for the type welding you are doing?
John Wright
Parent - - By gittings00 Date 04-03-2003 12:44
It already sounds like our process is not sufficiently controlled, based on the details that you guys are looking for.

Here's what I know at the moment:

1) Filler material is Silcon Bronze.

2) Preheating is done by putting brass blocks into a steel tube and heating with an acetylene torch. The temperature probably varies from piece to piece. Copper is not preheated.

3) No codes - only reqmt is a clean weld that holds pressure and does not fail during temperature cycling between ~0F to ~150F

I will research the details you guys talk about and post again.

Thanks a bunch for sharing your knowledge!!
Parent - - By billvanderhoof (****) Date 04-04-2003 04:00
Why not make the tubes slip into the brass and braze with the material refrigeration guys use. Those connections hold up for years at temperatures that exceed your range.
Parent - By jwright650 (*****) Date 04-04-2003 12:16
Bill is referring to silver solder, which comes in varying %'s of silver. 10% or 15% is common. I have used it to connect the refridgerant lines to the compressor and it holds up against vibration as well.
John Wright
Parent - By dee (***) Date 04-07-2003 01:14
I agree with Bill,
There are various alloys, not all of them true silver solder, used in refrigeration. They'll all handle vibration and pressure to at least a couple hundred PSIG; they vary in temperature range... this is a classic silver solder application and if properly cleaned and fluxed they'll all turn out very well.

Harris makes at least two silver solder alloys, but a Sid Harvey, R.E. Michael, or similar HVAC or plumbing service distributor may have stuff in stock, as well as advice, that might be harder to come by through "welding" channels. In any event specify cadmium free. There are solder/flux pastes I am aware of that may be worth the trouble of trying to find if you have a large production of these things.

Parent - By DavidP66 (*) Date 04-09-2003 18:24
try using silver brazing it with the JW Harris Safety-Silv 45 filler with thier white flux. I used to use this in the navy and the 45 works on many things Cu/Cu, Cu/Brass SS/SS
Up Topic Welding Industry / Technical Discussions / Brass blocks to thin copper tubing

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