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Silver soldering cast iron?

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AJW18/06/2019 11:29:30
288 forum posts
117 photos

I am modifying a Suffolk centrifugal clutch assembly to drive an alternator which would ideally involve silver soldering my assembly to the cast iron clutch outer.

Never tried silver soldering of cast iron - is it likely?


JasonB18/06/2019 11:59:28
17854 forum posts
1954 photos
1 articles

It can be done but not easy. You need to heat the CI first upto a high temp to drive the carbon to the surface and then wire brush it off before soldering.

Depending on your casting there may be a risk of fracture if it is not heated evenly.

Brazing may be a better option if you have the heating equipment.

speelwerk18/06/2019 14:55:12
361 forum posts
3 photos

The CI must be as clean as possible, I sandblasted it first the few times I have done it. Niko.

AJW18/06/2019 20:56:20
288 forum posts
117 photos

Thanks, I though it could be a problem as there appears to be so much carbon? I think in view of this pieces shape, quite a large 'cup' shaped casting I might be better off making a mechanical fixing to the alternator.


Hacksaw18/06/2019 21:20:05
428 forum posts
173 photos

Later , less well made Suffolks have a pressed steel clutch drum...interchangeable.. Might have one somewhere

AJW19/06/2019 09:38:48
288 forum posts
117 photos

Thanks Hacksaw! The cast one I have is quite a nicely made lump and should suit my purpose well.


CuP Alloys 119/06/2019 10:11:17
234 forum posts

Hi Alan

Yes it is perfectly feasible.

As Jason suggests, first heat the cast iron to red heat in air, (no flux) to burn off the carbon. Allow to cool naturally and clean with a stiff wire brush. Apply a long life flux, like HT5, and proceed normally.

I wouldn't recommend sand blating. If the sand gets into the surface of the cast iron, you would be in a worse place than when you started. You definitely cannot silver solder over sand!



not done it yet19/06/2019 10:18:03
4503 forum posts
16 photos

I’m with JB’s other option. If one can reach brazing temperature, it seems to be the better bet - braze is much, much cheaper than silver, for starters!

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