soldering 304L st/st to copper plumbing pipe

[eski1]

hi
is there a better solder to use than general 60/40 which is what we use at the moment . It does work but have a feeling it could be better , we use a small oxy/acetylene torch flux & solder

cheers
chris

 

[tomwalz]

Better in what way; tensile strength, shear strength, temperature, color, cost, suitability for further processing, etc.? Which 60/40? Which flux?

Tom

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessor.com

 

[metengr]

The web site below provides some information regarding selection of various solders and braze metals for joining copper to steel/stainless and other metals. I would also investigate the flux, as well. Solder is convenient to use because of the lower melting temperature (melts about 450 deg F) and lower cost in comparison to braze filler metals which melt at or above 1100 deg F.

http://www.jwharris.com/jwref/chart/

 

[eski1]

ok sorry for being vague

Better in that it adheres to the materials easier
Not sure at this moment what flux & type of 60/40 solder so just assume Im asking what is the best method of joining 3mm thick st/st top hat to 0.9mm copper plumbing pipe

cheers
chris

 

[berkshire]

eski1 (Mechanical)
I think you will find that 95/5 leadfree solder will wetout better on ss than 60/40 tin lead.
You will need a flux with free acid to clean the ss Be careful not to overheat the stainless or you will discolor the metal. Stayfree is a good brand of flux, there are other ss fluxes that contain sal ammoniac as well as hydrocloric acid.
Using resincore (Rosin) will not produce good results on ss.
As with any flux containing free acid it is important to neutralise well after soldering. Baking soda works well for this.
B.E.

 

[unclesyd]

Here is another source of soldering and brazing information and consumables.

http://www.silfos.com/htmdocs/product_support/alloy_selection_guide.html

 

[ctmtwilliams]

I would use silver solder with the stainless copper joint.

 

[rnd2]

We always used minimum 45% silver solder for braise-welding copper pipe to stainless steel. The flux was a liqid-paste containing borax and flouride compounds. As I recall the brazing temp was about 600 deg. C. The application was to pipe oxgen gas at 2,000psi.

Fortune favours the bold and avoids the unprepared.

 

[metengr]

Just a note regarding proper terminology - you have brazing and soldering. These are separate joining processes and are related to the melting temperature of the filler metal - there is no base metal melting.

Brazing is performed when the melting temperature of the filler metal exceeds about 850 deg F. Soldering is performed below this temperature.

 

[tomwalz]

We do millions of brazes a year and I do lots of braze failure anaysis. If it is a wetting issue I always start with the preparation of the materials to be joined.

Copper – take steel wool and rub the copper until it is as bright as you can get it. Stainless steel – watch out for the chrome. If you overheat it you can create chromium carbides which means nothing will stick to it. Stainless steel ordinarily brazes well. If it doesn’t braze well try another grade.

The # 1 reason for wetting problems is cleanliness. Clean the parts with a strong caustic cleaner. (Easy Off oven cleaner works well)

Use lots of flux. Flux is an oxygen interceptor. If you don’t have enough then the oxygen gets to the base metals and cretes and oxide layer which either doesn’t wet, doesn’t wet well or wets sort of but doesn’t bond well.

Before you do anything else try:
Clean both parts well with steel wool – that should work for soldering.

If that doesn’t work get back to us here.

From Dick Blick Art Supplies
60/40 Solder
This 60% tin and 40% lead solder has a melting point of approximately 370° F (188° C) and cools with a shiny bead. Best for working with copper foil. 0.125 diameter.


For different approach see:

http://www.hints-n-tips.com/copper.htm

Tom


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessor.com

 

[berkshire]

tomwalz (Materials)
eski1 (Mechanical) already told us that he was not getting good results with 60/40 tin lead solder.
While this can be made to work on stainless it involves scrupulous cleanliness to get a good wet out.
The 94/6 tin silver or the 95/5 tin antimony do wet out better, with out the scrubbing needed with 60/40 or 50/50 tin lead solders.
By the way I do this type of soldering for a living.
B.E.

 

[berkshire]

Until now I had not picked up on the word plumbing pipe.
If that pipe is used in a potable water system. It is a violation of code, in most parts of the United States and as far as I know the European Union to use lead bearing solder.
B.E.

 

[arto]

passivate the stainless after rubbing with steel wool - or it'll rust.
or use a clean scotchbrite

 

[tomwalz]

berkshire (Aeronautics)

Your knowledge is superior to mine in this area. I just automatically start with cleanliness as I have to start somewhere. In this case he asked about different alloys and I thought it was important to make sure that he was using the current alloy properly.

I often find, as I am sure you do, that many problems attributed to the material have more to do with its application than with the inherent properties of the material.

This is always a problem in failure analysis and general consulting for me. Do I address the issue as described or do I do an indepedent analysis to determine all the factors and offer the simplest, least expensive solution?

Thank you for bringing up this side of the issue.

tom


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessor.com