Carbide Brazing

[sbx]

Hey all,

So, I have a couple upcoming projects that will involve brazing some carbide to steel. I have a large stack of some older slightly worn carbide inserts (SPG, TPG mostly) that are somewhat used up and too large for my smaller South Bend 9. But, I do see a lot of utility in some of them for making a few brazed on bits, and some for scraper blades. Particularly some 6xx IC SPGs for scraping.

I am already getting a green wheel for my bench grinder, but wanted to learn more about what I'd need to braze them on.

Googling, and searching here turned up some good, but seemingly incomplete results.

So far I think it sounds like if I get silver braze in roughly 45-60% in either rod/roll form or maybe more ideally in foil form I'd be ok.

I was planning on using simple MAPP gas (though I may have access to borrow my shop mates Oxy/Act setup) along with some fire bricks for support/heat containment.

Would a welding (Airgas) store have some of what I am looking for?

Any other tips? Thoughts?

Thanks,
sbx

 

[gbritnell]

Hi sbx,
When I was an apprentice we made our own boring bars all the time. The bars were made from drill rod with a pocket for a small carbide insert. The process for silver soldering was to use sheet material. The carbide insert was first cleaned then scrubbed on a piece of emery paper. The pocket was then fluxed and the silver solder shim and carbide insert were put in place. We used an oxy-cetylene torch but a Mapp torch should work as well. As the material is being brought up to temperature and the flux starts to boil it's good to have a piece of rod so that the carbide insert can be held in place until the silver solder starts to melt.
gbritnell

 

[Kernbigo]

I did silver soldering the same on centerless grinder, flatten the siver splder if you only have regular

 

[chips&more]

The Mapp gas should do it, especially if you have 2 torches going at the same time. If you only have round brazing rod and would prefer the flat stuff. Just grab your hammer and give it a few whacks. I would meter the amount brazing material for the job. Meaning, just put enough of it, in pieces, on the work sight to do the job and no more. Make sure you use plenty of flux. And then torch it. The flux can removed with warm water when done…Good Luck, Dave.

 

[Mac1]

If your work isn't too large a propane torch will silver solder. I silver solder my bandsaw blades with propane.

 

[sbx]

Thanks guys. That does clear things Up. I was a little sketchy on how to secure the carbide bit to the blank. But it sounds like just pushing it on will work.

Also - Flux wise. Stay Silv is one I've heard referenced. Any others?

 

[Smudgemo]

I use Gasflux Type U white paste for bicycle frame building. It looks like you can get 1/4lb jars, but my sources only sell 1lb or 5lb jars so I can't say for sure. 45% will surely be better than 56% for this application. Clean everything really well mechanically and with alcohol (it's all about clean with silver), too much flux is better than not enough, watch for the bubbles to stop occurring before trying to melt your silver. Apply heat evenly (probably meaning at the bar more than the insert), and let it cool in still air. If you burn your flux before properly attaching the insert, soak and sand it all off and start over - burnt flux stops working. Sunglasses for eye protection will be more than suitable, and you won't really need a respirator (although I would try to avoid breathing the fumes.) I'd also consider some way to clamp the insert to the bar. It won't take much force, but I find the small bits like to move as the flux wets out in heat.

Just my thoughts/experience.

-Ryan

 

[Kernbigo]

you don't use brazing rod you use silver solder

 

[Dave Smith]

silver solder also comes in flux coated rods along with flat sheets and silver solder wire without flux coating---I just clean both surfaces and put a good amount of flux paste between them---I heat them up hot enough so the silver solder gets sucked in where the flux is and I can see it around all the edges---when using brass rods for brazing metals--it will not get sucked in between joints where the flux is--- like silver solder will. ---I like the thinner silver solder wire for small applications---for bandsaw blades the flux coated silver solder rods work very good for me, and are handy-------I use butane or my choice is usually acetylene and oxygen-------- Dave

 

[Kernbigo]

I use flat sheet silver solder for my band saw blades, with paste flux, and a oxygen propane torch.