Re: Do cracks/holes in bells NEED patching?


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Posted by dp on March 13, 2003 at 11:47:45:

In Reply to: Do cracks/holes in bells NEED patching? posted by Mr Bent Bell on March 13, 2003 at 11:06:26:

Cracks that can be properly dressed (where the edges can be aligned and cleaned into nice continuous, seam-like non-jagged surfaces) can be "silver soldered" - a process which uses a fairly hard, stiff tin/copper/silver content rod to butt-fill a very thing gap between the edges of a properly-prepared joint (formerly known as a crack.) It is high-level artisan work in every sense of the term, which might help you to understand why patching is so prevalent (low cost and relatively time-efficient.) It's important to know though that "silver soldering" the way I have described it is NOT like the soldering of ferrules and the like, in those cases temperatures are 500-600 degrees F, your typical tin-based solders flow well when the joint and solder are a little above 500F. Silver soldering requires high temp, but still well below about 900 degrees F. Above that temp, you're talking about brazing, still hotter--it's bona-fide welding, where the base metal is flowed into the joint (neither would be recommended if you want a pretty-looking repair!) Part of the reason this is high-artisan-level work is that there is a very narrow temperature range for the work piece to get a consistent durable joint that will clean up well and remain aesthetically pleasing. This temp range varies from horn-to-horn due to material difference, differences in the physical nature of the actual repair, influenced by shop conditions like temp and humidity. A lotta variables to consider.

I hope this helps some, you might want to check the below link to Dan Oberloh's pages describing variuos types and flavours of repair work, there is a lot of good technical information laid out in a fairly easy to grasp way. Dan is a metallurgist and jeweler by training, and (in my mind) certainly qualifies as the artisan-type I have mentioned.

Regards,

Dale Phelps
Los Gatos California USA



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