silver braze joints

[ukjimoo]

Hi all

This is my first post on this group and i would be interested if anyone could answer a long standing question of mine that i have never been able to get a definite answer to.
When manufacturing split bearings in the past, i have cut a chunk of SAE660 in half, machined the cut face flat and silver soldered the 2 halfs together. I have then proceeded to manufacture the bearing and found that the joint can barely withstand the stresses of machining. In fact on one occasion, i dropped the bearing on the floor and it broke in two!
Is this because SAE660 is not suitable for silver soldering?
If so why is it widely used for copper boiler bushes.

Best regards
Jim

[jackrae]

SAE660 contains quite a high percentage of lead (up to 8%).
From past experiences, silver solder and lead do not go together. I was always taught that once a joint has had lead on it - forget about trying to get silver solder to stick. Perhaps this is caused by the lead continuously boiling off at the temperatures required to achieve a silvered joint.

I am of the impression that one normally "soft" solders bearing halves together for machine boring rather than silver soldering. This is probably for three reasons : a) the soft solder is both strong enough to do the job, b) it overcomes any possible soldering incompatability and finally, c) does not require "extreme" heat which might well distort the post-machined bearing.
regards
Jack

[ukjimoo]

Thanks for clearing that one up Jack. Looks like in an attempt to get a stronger joint i was actually getting a weaker one by boiling the lead out of the alloy.

Im still a little confused though - I recently made a boiler from a materials kit supplied by a leading ME supplier and the material supplied for the bushes was SAE660. These of course have to be silver brazed. I finished the boiler a couple of years ago and it has a certificate, but do i need to be concerned about a bush blowing out when i steam it?

[jackrae]

As far as I'm aware SAE660 is specified as a "Bearing Bronze" ie designed for bearings
It also contains zinc and aluminium, both of which I would imaging would act as sacraficial elements inside a boiler.
Or to put it another way - perhaps not ideally suitable for use as boiler bushes - but I'm not qualified to provide a definitive answer
One of our learned boiler manufacturers or metallurgists might be able to assist.
It may sound academic suggesting that metals like zinc will become sacrificial but I recall many years ago seeing brass fittings on a full size steam boiler which had been inadvertantly subjected to acidic washing all turning to copper and then weeping.
Jack

Jack

[the_viffer]

I have a boiler made under the "new"ish rules by a highly reputed boiler maker. The bushes are declared made of SAE660.

I was concerned about the lead problem. I spoke to the alloy manufacturer who said that properly handled they did not expect the lead to cause any problem.

[the_viffer]

There is a spec sheet for SAE 660 here anchorbronze.com/c93200.htm which says it is resistant to dezincification and is good for brazing if strain is avoided during brazing and cooling. Sounds like it really is fine for bushes

[ron]

Jim
I don't know if you've tried this but I've found superglue very effective for joining identical parts for machining, sort of thing that might have been soft soldered in the good old days. I clean the parts with thinners to get a good bond and if the joint has a small surface area a sharp chap usually separates them, if not a modest amount of heat will do the job.
Ron