Posted by Valerie Weihman on January 06, 1998 at 20:01:10:

In Reply to: Re: Welding precious metals posted by Tony Truong on January 03, 1998 at 22:43:47:

: >>>>> Hi, enjoyed the detailed explanation above on brazing. I have a question going in the reverse direction. How do you unsolder or unbraze a silver-soldered joint between stainless steel and brass without destroying optical components housed within?

:

:Also, I recently ran across a material called "Heat Paste" advertised to stop

"heat cold" to protect parts being soldered/welded. Do you know if this stuff

works?

There are many brands of heat resisitant pastes. Some work better than others - depends upon application. Yes, they do work. You can weld 1/4" and sometimes closer to rubber seals and other sensitive objects. Need to experiment to so which type is best. There are some that are a very thick clay-like consistency (Eutectic-Castolin brand is called "Form-a-jig"). They are good for supporting the parts while heating. There are other pastes that rather goop around and are hard to clean off.

My concerns with the heat paste materials is that they not make any gases or compounds that would cause porosity in the welds when making them. Since you are using this material to protect parts as you remove the silver braze material, that criterion would not come into play.

Since we are talking about removing silver braze near a heat sensitive area, it is important to know about what shape and size the parts are. You could FAX a little sketch of a detail where the two parts and the glass come together. It would be easier to give a good answer knowing those things. My FAX is 608-246-6806 and add my name (Valerie Weihman) to it.

There is always a question when one talks about silver solder what is the temperature that it melts at. If it is truly a solder, it melts below 840 degrees F. If a silver alloy, it is above 840, usually quite a bit above that. Trouble is, everyone uses the term silver solder (even the manufacturers), so it makes it rather hard to determine the temp. It probably is silver solder, though, to join the stainless.

If it is a low-temp material, I would say to add the heat to the part with a soldering-type iron. If the joint configuration is like two cylinders together, then the tip of the soldering iron must be pointed to get down into the crevice. The soldering iron is heated by electricity or by a flame. Because of the proximity of the glass, this indirect method of heating by soldering iron is a good idea. You can also heat by induction (an induced maganetic field).

I hope that you have one of these items to experiment on if it is small, delicate and expensive! Anyway, a picture is worth a thousand words. Are you just repairing one, setting up for reclaim of parts, repairing a few here or there? These things influence the choice of action too.

Follow Ups:

>>> Hi, enjoyed the detailed explanation above on brazing. I have a question going in the reverse direction. How do you unsolder or unbraze a silver-soldered joint between stainless steel and brass without destroying optical components housed within? : : : :Also, I recently ran across a material called "Heat Paste" advertised to stop : "heat cold" to protect parts being soldered/welded. Do you know if this stuff : works? : There are many brands of heat resisitant pastes. Some work better than others - depends upon application. Yes, they do work. You can weld 1/4" and sometimes closer to rubber seals and other sensitive objects. Need to experiment to so which type is best. There are some that are a very thick clay-like consistency (Eutectic-Castolin brand is called "Form-a-jig"). They are good for supporting the parts while heating. There are other pastes that rather goop around and are hard to clean off. : My concerns with the heat paste materials is that they not make any gases or compounds that would cause porosity in the welds when making them. Since you are using this material to protect parts as you remove the silver braze material, that criterion would not come into play. : Since we are talking about removing silver braze near a heat sensitive area, it is important to know about what shape and size the parts are. You could FAX a little sketch of a detail where the two parts and the glass come together. It would be easier to give a good answer knowing those things. My FAX is 608-246-6806 and add my name (Valerie Weihman) to it. : There is always a question when one talks about silver solder what is the temperature that it melts at. If it is truly a solder, it melts below 840 degrees F. If a silver alloy, it is above 840, usually quite a bit above that. Trouble is, everyone uses the term silver solder (even the manufacturers), so it makes it rather hard to determine the temp. It probably is silver solder, though, to join the stainless. : If it is a low-temp material, I would say to add the heat to the part with a soldering-type iron. If the joint configuration is like two cylinders together, then the tip of the soldering iron must be pointed to get down into the crevice. The soldering iron is heated by electricity or by a flame. Because of the proximity of the glass, this indirect method of heating by soldering iron is a good idea. You can also heat by induction (an induced maganetic field). : I hope that you have one of these items to experiment on if it is small, delicate and expensive! Anyway, a picture is worth a thousand words. Are you just repairing one, setting up for reclaim of parts, repairing a few here or there? These things influence the choice of action too. : " />

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