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Silver solder paste

karl

Cast Iron
Joined
Sep 11, 2005
Location
Fayetteville, close to Pond Bank, Pa.
I recently acquired an old filing machine that had a badly worn guide. I made a "patch" and took it to a local shop to have it brazed and they suggested welding as it would be faster and less expensive than braze. It worked fine, but the weld was very hard and difficult for me to mill. My question is, would silver solder paste have worked as I think it wets/flows better than braze and is much easier to machine. Thanks for your help.
Karl
 
silver does not bridge gaps at all, you need tight fit for it to be strong (and clean metal, really clean) - and it is really strong joint when done right. The paste is usually ez or less solder, which is the weaker end of spectrum, and will bridge less gap than a hard or medium silver. Brazing with brass or bronze can bridge a gap, fill a vee and be strong too. Welding is fast and if you can step across it you can weld across it. A lot depends on what broke, condition of break, and stresses it takes to decide method of fixing it. Being that the fix works, your local shop made the right call.
 
A 98% nickel welding rod gives excellent results when repairing cast iron. The trouble with iron based rods is that somewhere between the cast iron and the welding rod alloy in the joint is a layer of iron that has absorbed enough carbon from the cast iron to become a high carbon steel, this has then cooled very fast and is as hard as hades. Nickel doesn't absorb carbon or at least doesn't form a hardenable alloy when it does absorb it. So you end up with a very easy to machine repair.
 
What is your cutting tool made of?
The layer should be hard and want reduced SFM but not "difficult for me to mill".
Silver/braze paste comes in many flavors but needs to be squished or moved as it melts to fill since part of it's volume is flux.
For a repair I'd normally go with braze as it is easier to do and more forgiving, on cylinder head cracks in the chamber you have to go with welding which is fussy to get right.
If your supplier is good at identifying the differing flavors of cast and welding it then this is the strongest.
Bob
 








 
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