Should I Case Harden Shredder Teeth?

[staybusy]

I have some 1" plate I cut into teeth for a shredder / grinder. As far as I know it's mild steel (sourced from a junkyard). This steel doesn't harden well from heat treatment.

The shredder will be for processing meat, bone, hooves, etc.

I'm wondering how mild steel teeth would hold up to dense bone - lamb shanks, deer femur, cow femur, pigs feet, etc. Will the teeth eventually get warped and chip if I don't harden them?

Is it worth it to case harden the teeth?

Case harden then temper?

Setup will be extreme high torque, very low RPM so no high speed impacts. I don't care about grinding speed at all, only that it can process material.

See pic for tooth profile.

[LKeithR]

In my experience mild steel doesn't case harden well either. The other problem you may have is with the depth of the case hardening itself. The surface of the material may harden somewhat but the underlying material will still be soft and, depending how much load and impact there is, the sharper edges may just break away while the softer material slowly deforms.

I would certainly have made those teeth out of a better material but, since you've already got them made you don't have a whole lot to lose if you use them. The time to ask questions like this is before you buy the material...

[Shade Tree Welder]

Originally Posted by LKeithR

In my experience mild steel doesn't case harden well either. The other problem you may have is with the depth of the case hardening itself. The surface of the material may harden somewhat but the underlying material will still be soft and, depending how much load and impact there is, the sharper edges may just break away while the softer material slowly deforms.

I would certainly have made those teeth out of a better material but, since you've already got them made you don't have a whole lot to lose if you use them. The time to ask questions like this is before you buy the material...

Mild steel will not harden.

I agree use them when they fail, and the only unknown is when not if.

Buy some A2 tool steel and make your next set.

[LKeithR]

Originally Posted by Shade Tree Welder

...Mild steel will not harden...

You can in fact create a very thin skin of hard material on a piece of mild steel by case hardening but it won't stand up to anything more than mild abrasion. If there is any impact involved it will fail quickly because the underlying core is soft and won't support it. So for all practical purposes Ron is right, you cannot harden mild steel--it's just not worth the effort...

[GWIZ]

Originally Posted by Shade Tree Welder

Mild steel will not harden.

I think you missed the question.

Yes, Case harden will help but from the pictures there may be too much back clearance on the teeth.
as Keath mentioned "won't support", may not be enough back support for the pressure generated. "its hard to tell from the picture because I cant judge size or pressure angle.

I had a motorcycle sprocket case hardened, about 0.030-0.050 it did help but the teeth still bent.
its Hard to explain,
with case hardening the teeth bent symmetricly (all the teeth bent the same amount).
stock non hardened sprockets some teeth would bend more than others and stretch the drive chain in spots, the chain would slap up and down so you could not adjust the slack out of the chain.

[digger doug]

OH GOD NO !!!!!

"Hard Facing"

OH GOD NO !!!!!

[Shade Tree Welder]

Originally Posted by digger doug

OH GOD NO !!!!!

"Hard Facing"

OH GOD NO !!!!!

Doug, I did think about that but this is a shredder, so you have to have them somewhat sharp. So weld and then try to grind hard facing...

Run them like they are. The buy some tool steel and do it right.

(PS he likely is not going to want to spend that kinda cash on 10 lbs. of hard facing rod, I have never seen HF rod in small paks.)

[greywynd]

Years ago I had access to a cyanide bath for case hardening, and yes, if things were ideal, we could get around .040” or one millimetre of case.

I’ve also used Kasenit, however it’s no longer sold. Charcoal and bonemeal can also be used.

The toughest part I find for case hardening is finding metal containers to use, along with a heat source that will run long enough, with enough volume of heat. Tool steels one just has to get hot enough then quench, followed by a lower temp heat for tempering. (Tempering can sometimes even be done in kitchen ovens.)

Case hardening requires holding the high temperature long enough to allow the carbon to soak.


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[staybusy]

Sorry for delay in response I think I got covid again, been all dizzy and tired.

Originally Posted by Ironman

for your dog, feed him garlic chopped fine, 10 minutes in the open air to convert the alliin into allicin. Then mix with ground beef and feed it. Eliminate grain from his diet, it's a filler and does no good for a carnivore.
I had St Bernard with issues like that. I know garlic will cure the hair falling out and oozy wet spots. Took about a week.


I would hardface the top and frontside and leave the backside soft. Camdigger may have a better idea. Then tweak the edge with a grinder to sharpen the edge. If you leave one side of the tooth soft it will wear sharpen.

Thanks for the tip, I'll try out the garlic. I already have her on a premium "no grain kibble" but it's still got fillers like peas and oils, and other random crap. It definitely reduced her symptoms but didn't fix everythng.

My only worry about hardfacing is that I'm gonna make a mess of the teeth and add "worm holes", and shitty welds that will make the teeth hard to clean. I'll have to practice welding a bit more before attempting it.

Originally Posted by Ironman

I was wrong in my 20 thou estimate, 40 thou. I used to work in a drill shop where they forged ends on square drill steel, machined a thread on a turret lathe and case hardened in a bath of molten cyanide salt.
This was an open bath with a hood and fan. Times have changed

I hope you plan on broaching a keyway into these cutters before you harden. Afterwards is not a good plan.

Oh LOL I thought you meant 20,000 of an inch. Like a fraction of a hair. I don't know anything about these types of fractions, only ones I use are on a tape measure. Where's a good place to learn?

Originally Posted by greywynd

Years ago I had access to a cyanide bath for case hardening, and yes, if things were ideal, we could get around .040” or one millimetre of case.

I’ve also used Kasenit, however it’s no longer sold. Charcoal and bonemeal can also be used.

The toughest part I find for case hardening is finding metal containers to use, along with a heat source that will run long enough, with enough volume of heat. Tool steels one just has to get hot enough then quench, followed by a lower temp heat for tempering. (Tempering can sometimes even be done in kitchen ovens.)

Case hardening requires holding the high temperature long enough to allow the carbon to soak.


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What temps did you case harden at?

I have a dual burner forge setup with 100lbs propane tank. I could use the 2 burners + extra charcoal on top of the container with forge blower blasting air onto the coals.

[staybusy]

Had an interesting thought.

If you can heat mild steel in a carbon pack and have it absorb carbon, what would happen if you added chromium powder with the carbon?

Is it possible to create a stainless surface layer that way?