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Silver soldering cast iron?

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AJW18/06/2019 11:29:30
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275 forum posts
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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?

Alan

JasonB18/06/2019 11:59:28
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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
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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
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275 forum posts
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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.

Alan

Hacksaw18/06/2019 21:20:05
406 forum posts
163 photos

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

AJW19/06/2019 09:38:48
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275 forum posts
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Thanks Hacksaw! The cast one I have is quite a nicely made lump and should suit my purpose well.

Alan

CuP Alloys 119/06/2019 10:11:17
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194 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!

Regards

Keith

not done it yet19/06/2019 10:18:03
3372 forum posts
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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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