Learned something new today

[decorn33]

I tend to carry my panniers on the bike all the time, so i was surprised to find the forward support snapped off the left side frame when I demounted the bags to work on the rear wheel.  I carried the frame and the loose piece to my local weld shop to be reattached.  The welder did his work while I waited, and presented the finished repair saying that he couldn't figure out why the weld kept popping until he realized that these frames weren't welded together at the factory, they were silver soldered. So I now have a silver soldered frame with one weld.

[nhmaf]

Welding on those light alloys tends to cause a lot of localized stress from expansion&shrinkage.   Soldering is much lower temp and lower stress inducing.

[tvrla]

I went through the same thing trying to gas weld a joint that came loose on a pannier frame.

[suecanada]

Sooooo, you fellows are saying that to fix the luggage rack, it should be silver soldered? Not welded? Just asking just in case something happens on the road and no one to ask but a welder to advise.

Any one out there explain what cold soldering is? It sounds like something one could use on the road??

[montmil]

Sue, I'm only familiar with what a poorly soldered electrical connection -improper cleaning, flux, and solder temperature- is known as a "cold solder" joint. Re-do required.

[decorn33]

The hell of it is, the weld worked, but it's ugly in comparison to the other joints. AND if I had known, I would have tried a silver solder repair myself first.  My frames are black, so now I also have a re-paint to accomplish. (Can't think of a nicer machine to have to work on though.)

[Barry]

Welding melts the parent metal even when a filler material is also applied. Soldering or brazing of any sort relies on a filler material to 'glue' the joint together. The temperature at which the filler materials melt varies with higher temperatures generally making a stronger joint. There's not much strength in soft solder unless the joint has a large surface area.  For any sort of tube joint silver solder is the minimum that will be strong enough.  

The only cold soldering I can think of is conductive paint used to repair heated screen elements and the like.



Very approximate figures:-


Soft solder  170 - 200 deg C

Hard solder or silver solder 400 - 600 Deg C

Brazing  600 - 1000 Deg C