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Silver brazing carbide to steel - relatively long joint

highroadtoolco

Plastic
Joined
Dec 27, 2020
Location
Golden, Colorado
Hi, I'm hoping someone can chime in on whether to expect problems with this set of parts. I've been asked to quote a set of blades with a brazed on carbide cutting edge.

I've brazed carbide tooling (3/4") in the past for hand scraping with good results however this blade/carbide joint will be approximately 2.7" long. My rough calcs show this will have .013" of differential expansion (between steel backer and carbide insert) at 800 degree brazing temp. Sounds like a lot to me.

I've got two options at this point shown in the pics. The full length joint has the 2.7" brazed joint. The other is closer to 1.25". Part thickness is .1"
Plan to use what I've got on hand which is Safety silv 56 and high temp flux.

Anyone have any experience with a long joint like this? Any suggestions as to which is the safer bet or is this bound to be an exercise in frustration?
Thanks!
 

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Dumb question, but those aren't huge pieces. Any chance of a redesign to make it a wholly carbide part, maybe with an abutting steel backer if toughness is an issue?
I like the idea and did consider it but it's just a small run of prototype blades and the holes kind of threw me. No EDM in the shop. Any suggestions for an inexpensive way to pop those 1/4" holes?
 
I like the idea and did consider it but it's just a small run of prototype blades and the holes kind of threw me. No EDM in the shop. Any suggestions for an inexpensive way to pop those 1/4" holes?

DIY diamond drill - a copper or brass tube and diamond grit paste as the cutting medium. Works by embedding the diamond into the end of the tube, spin it in a mill or even a drill press at 1-2K. Dab, grind, lift and brush some more paste in, repeat.
 
DIY diamond drill - a copper or brass tube and diamond grit paste as the cutting medium. Works by embedding the diamond into the end of the tube, spin it in a mill or even a drill press at 1-2K. Dab, grind, lift and brush some more paste in, repeat.
Thanks for the suggestion, I'll try it out. That's certainly an inexpensive method. Hoping that .1 DOC won't take too awful long.
 
Play around with the speed, and you'll want a fairly thin tube (like 1/32" wall) and coarser grit. Don't press down too hard, you'll deform the tube. I would flush the zone with a very light oil every so often, then load a fresh dose of diamond paste.



I wouldn't go finer than 60 micron, maybe a little coarser would cut faster. Water or oil carrier is whatever you think will work better for you, if water than don't use the light oil I suggested above, use a water flush.
 
Just remembered something (it's me age ) ..... I dodn't know what you call it, but back in the day, on large tool tips Big Jim used to put a piece of thin copper inbetween the carbide and steel (fluxing all faces) and holding the TC tip down with a ''pricker'' as the sil sol melted so any excess was squeezed out .

FWIW thin sil sol sheet is my go too for tipping work, IIRC mines <> 0.010 thick
 
Play around with the speed, and you'll want a fairly thin tube (like 1/32" wall) and coarser grit. Don't press down too hard, you'll deform the tube. I would flush the zone with a very light oil every so often, then load a fresh dose of diamond paste.



I wouldn't go finer than 60 micron, maybe a little coarser would cut faster. Water or oil carrier is whatever you think will work better for you, if water than don't use the light oil I suggested above, use a water flush.
Well I had some 20-40 micron on hand and had to give it a try. Not too shabby. I cut .035" deep in a few minutes so it shows promise. I think I'll order up some 60 micron as you suggest if I decide to pursue this method further.
Thanks for sharing!
 

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Well I had some 20-40 micron on hand and had to give it a try. Not too shabby. I cut .035" deep in a few minutes so it shows promise. I think I'll order up some 60 micron as you suggest if I decide to pursue this method further.
Thanks for sharing!

Cool! You can even try thinner wall stainless tubing if you want to play around more. Thinner tube (to perhaps .010" wall) should cut faster, but be more fragile.
 
Just remembered something (it's me age ) ..... I dodn't know what you call it, but back in the day, on large tool tips Big Jim used to put a piece of thin copper inbetween the carbide and steel (fluxing all faces) and holding the TC tip down with a ''pricker'' as the sil sol melted so any excess was squeezed out .

FWIW thin sil sol sheet is my go too for tipping work, IIRC mines <> 0.010 thick
Hey thanks again,
Sounds like a similar principal of trimetal brazing strips mentioned. That appears to have a copper core. I'm curious whether these blades with only a .1" land would be well suited for that? Seems helpful for the thermal expansion issues but would it also weaken the joint?
 
Your best bet is a perfect 'preform' of trimet. This is a thin copper sheet coated with the braze alloy. The copper sheet allows some movement as the alloy goes from liquid to solidus. I still think that with that length you'll have cracking. **Before you quote it and get in trouble, have a braze alloy vendor visit to discuss the job. Ring up Bellman Melcor, Lucas Milhaupt etc.
 
Since they expand at different rates one part of the trick is is pour lots more heat into the carbide than what the steel sees.
This easier said than done.
SOP is to stuff the part into a bucket of sand as fast as possible after the braze. Slow cooling is your friend.
 
I wonder if putting some narrow slits into the steel part so it can give a bit lengthwise would be a good idea. If they're just a narrow saw cut about 1/4" deep, and maybe not near the mount holes, they shouldn't affect function too much.
 
I wonder if putting some narrow slits into the steel part so it can give a bit lengthwise would be a good idea. If they're just a narrow saw cut about 1/4" deep, and maybe not near the mount holes, they shouldn't affect function too much.
Thanks for the suggestion. I like the thought but I failed to mention this is intended for the food processing industry so those slits could be a disadvantage for cleaning.

I've decided to attempt a couple parts of the second design (with the smaller insert). I'll experiment with trimet brazing strips. I was hoping to simplify by making full carbide blades but the customer is justifiably concerned about breakage during install.
 








 
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