Odd behaviour of brazed joint

Sep 01, 2011 8 Replies
M

Silver-soldered to be precise.



One of the bars of the stainless steel BBQ grill detached itself at one end from the stringer (I hope I am making myself clear, not too sure about the correct terminology). The spot weld simply gave way.



I silver-soldered it back into place using Extra-Easy. On first inspection a good joint, could not force it apart.



After several BBQ uses during which the grill is subjected to far less stress than when I was testing the joint, the latter gave way.



I cleaned the whole thing with Dremel using a wire brush and sanding drum. I re-soldered the joint. Same wire, same flux, both work fine elsewhere. On testing the joint was fine but gave way again after 3 or



4 BBQ uses (the heaviest pressure on the grill is when cleaning it).

I had a good look this time with a magnifying glass: The joint gave way on the bar, there seemed good adhesion on the stringer. I re-cleaned etc. and re-soldered with particular attention on heating the strut preferentially. I am waiting to see if I am third time lucky.



What puzzles me that the joint would deteriorate with relatively light use. The BBQ temp does not reach anywhere near the melting point of Extra Easy (1150F). Is this a case of repeating heating and cooling cycles which stress the joint? Has anyone seen this elsewhere?


Michael Koblic, Campbell River, BC


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P

You don't specify what kind of BBQ, charcoal burns at around 1,200F, and my IR gas grill burner at 1,100F.

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S

Most of the failures I have seen with grills comes from the thermal expansion of the metal.I would suspect that what you're seeing is because the joint doesn't have the same thermal rate as the base stainless.

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R

It may not get hot enough to melt, but I bet it does get hot enough to severely weaken the joint. Add in thermal stress 'cause I'm sure the grill does not heat perfectly evenly and there you go.

Remove 333 to reply. Randy

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D

Are you getting interfacial corrosion?

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W

Brazing/silver-soldering is best when it has large contact area with the right (about .005") gap for the filler material. Perhaps your round/round wire joint just doesn't have the right area; a suitable workaround would be to clean and flux, then wrap thin wire around the joint (like a lashing with string). When you apply heat and solder, this will make a brazed joint with all the area of the thin wire, and with the wire acting as a reinforcing fiber.

You might want to peen the working surface flat, using a block of wood to back the grid, afterward.

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C

Why not just weld the sucker????

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R

You probably simply melted the solder.

Hope This Helps! Rich

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M

I used the BBQ for the first time since the third repair. The temperature of the joint did not exceed 320C (by IR), most of the time it was below 300C. This was, however, considerably higher than the BBQ thermometer indicated. The joint held.

This was a fairly light cooking session. It remains to be seen if the temp stays that low when the BBQ is going all out for any length of time. I am now inclined to believe that it will not.

I guess I shall have to shell out to have this welded or just put a rivet in there or something.

Michael Koblic, Campbell River, BC

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