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-   -   Should I Case Harden Shredder Teeth? (https://www.shopfloortalk.com/forums/showthread.php?t=53891)

staybusy 07-15-2022 09:25 PM

Should I Case Harden Shredder Teeth?
 
1 Attachment(s)
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 07-15-2022 10:16 PM

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 07-16-2022 01:16 AM

Quote:

Originally Posted by LKeithR (Post 785964)
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 07-16-2022 01:51 AM

Quote:

Originally Posted by Shade Tree Welder (Post 785966)
...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 07-16-2022 06:49 AM

Quote:

Originally Posted by Shade Tree Welder (Post 785966)
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 07-16-2022 07:28 AM

OH GOD NO !!!!!

"Hard Facing"

OH GOD NO !!!!!

Shade Tree Welder 07-16-2022 07:41 AM

Quote:

Originally Posted by digger doug (Post 785969)
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.)

Ironman 07-16-2022 09:28 AM

Quote:

Originally Posted by Shade Tree Welder (Post 785970)
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.)

I still have some 60 Rockwell tool steel welding rods, I paid $45/lb for them in the 80's.
But like Keith said, you should ask before you invest time and damage on making something like this. That is the purpose of the forum, not to help un-fuck a fuckup.

At this point you can hardface and hope for the best. I would have made these out of T1, it is amazingly tough and yet can be filed. I would cut them out on a CNC plasma table, but then I have one.
https://www.napaonline.com/en/p/FNY4...pressionRank=1

I don't know what you have in Onterrible for farm supply stores, but they can be a good source for small amounts of rod.
At some point it would be good to see your design as well. If I was going to do this, I would set up a roller system with bars to crush and break bones and then into the shredder.

digger doug 07-16-2022 08:14 PM

Quote:

Originally Posted by Shade Tree Welder (Post 785970)
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.)

OH GOD NO !!!
It was a joke, seeing how the OP can't even diagnose a problem with a simple 4x6 bandsaw....:rolleyes:
OH GOD NO !!!

camdigger 07-17-2022 08:48 AM

At this point, I would suggest a hardfacing, but apply it to only one side of the tooth. The tooth will then, in essence, become self sharpening. I used to buy rock bits with that feature. They'd still have a sharp cutting edge with 80% of the tooth worn away.

Once these teeth wear out, I'd replace them with a different profile tooth of a better material. A quick YouTube search for HD grinders should reveal that the heaviest duty shredders have teeth cut in a modified C shape. I've seen shredders with that tooth shape shredding steel barrels full of material feeding a disposal process.

This shredder has multiple teeth on each cutter, but hasaprofile with much more support for the cutting edge than a simple star shape.
https://youtu.be/iWlJGFzjT-g

staybusy 07-18-2022 01:27 AM

1 Attachment(s)
All the local metal suppliers I talked to when sourcing steel weren't able to help me so I just moved forward with random 1" plate. I kind of regret that now that it was 10+ hours of cutting time on the bandsaw but at least progress is being made :D Can always make a better version in the future, this one's low budget as possible.

I was originally trying to get a hardening stainless steel but nobody had any. Even just regular stainless was an issue, because they can't cut 1" plate on their brake - they wanted to waterjet cut it, then the prices start getting crazy. Multiple places didn't bother responding to quote inquiries. Metal shop guy on the phone said regular stainless won't bend or crack against bone.. seems like BS, dunno.

Hardfacing sounds like a good easy solution, didn't know about that. As long as there's no really poisonous compounds that could get into the meat (micro chips or from contact, etc) I'm trying to keep things food grade as possible. How thick does the welded layer need to be and what kind of alloy is it?

Adding hardened tool steel teeth is an option I considered and I think would work well. Making 32 teeth then welding them all on is too much work though.

Here's the case hardening method I planned to use - https://www.youtube.com/watch?v=VpD7NyadLcQ

I don't want the teeth to be too brittle so I think if I temper it afterwards it may have better results.

Added a mock up image of the grinder.

-Single shaft design
-Very compact shredding chamber
-4x 1" thick blades with 8 teeth on each
-2 hp motor
-1:160 planetary gearbox
-feed chute like a juicer (press to apply the cutting force)

LKeithR 07-18-2022 02:23 AM

No point in tempering case hardened material--not that you're going to get much hardening with mild steel. Tempering is a process used to reduce the hardness/brittleness of a block of steel after heat treating. It changes the crystalline structure of the entire piece so, since you won't have any hardness in the core of the material you'll gain nothing by tempering it...

Ironman 07-18-2022 11:27 AM

I think that hardfacing is more benign than case hardening, and the hardness layer is so thin that it would have a short life after wearing through in one spot.
Hardface rods usually contain Chrome, so Chromium hexafluoride gas is something you shouldn't breath. Do it outdoors.

You have to realize that casehardening is about 20 thou thick and underneath is mild steel. Case hardening is done by carbon rich chemicals like cyanide which are used to get carbon into the surface of the steel.
Hardfacing is as thick as you want to lather it on.

mccutter 07-18-2022 12:39 PM

What are you going to use the chopped up bones for?

staybusy 07-18-2022 01:40 PM

1 Attachment(s)
Quote:

Originally Posted by mccutter (Post 786055)
What are you going to use the chopped up bones for?

my dog got lyme disease then developed really bad allergies after being put on doxycycline (very strong antibiotic). gonna feed her raw so I can try to run an elimination diet, hopefully it will cure the allergies. also letting her bury lamb shanks in the backyard, trying to rebuild her gut biome. I notice she's food reactive, if I feed her milk bones she itches like crazy, develops sores and her fur is falling out in places.

Quote:

Originally Posted by LKeithR (Post 786044)
No point in tempering case hardened material--not that you're going to get much hardening with mild steel. Tempering is a process used to reduce the hardness/brittleness of a block of steel after heat treating. It changes the crystalline structure of the entire piece so, since you won't have any hardness in the core of the material you'll gain nothing by tempering it...

I'm not trying to temper the whole piece though, just the case hardened exterior that has carbon content

Quote:

Originally Posted by Ironman (Post 786054)
I think that hardfacing is more benign than case hardening, and the hardness layer is so thin that it would have a short life after wearing through in one spot.
Hardface rods usually contain Chrome, so Chromium hexafluoride gas is something you shouldn't breath. Do it outdoors.

You have to realize that casehardening is about 20 thou thick and underneath is mild steel. Case hardening is done by carbon rich chemicals like cyanide which are used to get carbon into the surface of the steel.
Hardfacing is as thick as you want to lather it on.

I was just gonna use the charcoal method of case hardening.

For hardfacing I was thinking of chopping 2-3 mm off the top of each tooth, then welding on hardened material, after I'd using a grinding wheel to reshape the point. Does that sound ok?

staybusy 07-18-2022 02:02 PM

https://en.wikipedia.org/wiki/Case-h...ng#Carburizing

The carbon can come from a solid, liquid or gaseous source; if it comes from a solid source the process is called pack carburizing.

Packing low carbon steel parts with a carbonaceous material and heating for some time diffuses carbon into the outer layers. A heating period of a few hours might form a high-carbon layer about one millimeter thick.

Check this video - https://www.youtube.com/watch?v=aFqdWXDZiq4 (skip to 9:17 it shows penetration depth)

Interesting document - https://www.dce-darbhanga.org/wp-con...5315f6a1c1.pdf

Ironman 07-18-2022 03:43 PM

Quote:

Originally Posted by staybusy (Post 786058)

I'm not trying to temper the whole piece though, just the case hardened exterior that has carbon content

I was just gonna use the charcoal method of case hardening.

For hardfacing I was thinking of chopping 2-3 mm off the top of each tooth, then welding on hardened material, after I'd using a grinding wheel to reshape the point. Does that sound ok?

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.

Ironman 07-18-2022 03:53 PM

Quote:

Originally Posted by staybusy (Post 786060)
https://en.wikipedia.org/wiki/Case-h...ng#Carburizing

The carbon can come from a solid, liquid or gaseous source; if it comes from a solid source the process is called pack carburizing.

Packing low carbon steel parts with a carbonaceous material and heating for some time diffuses carbon into the outer layers. A heating period of a few hours might form a high-carbon layer about one millimeter thick.

Check this video - https://www.youtube.com/watch?v=aFqdWXDZiq4 (skip to 9:17 it shows penetration depth)

Interesting document - https://www.dce-darbhanga.org/wp-con...5315f6a1c1.pdf

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:rolleyes:

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

greywynd 07-19-2022 08:54 AM

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.


Sent from my iPhone using Tapatalk

staybusy 07-21-2022 06:30 PM

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

Quote:

Originally Posted by Ironman (Post 786064)
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.

Quote:

Originally Posted by Ironman (Post 786066)
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:rolleyes:

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

Oh LOL :D 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?

Quote:

Originally Posted by greywynd (Post 786088)
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.


Sent from my iPhone using Tapatalk

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 07-22-2022 11:00 PM

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?

GWIZ 07-23-2022 02:36 AM

1 Attachment(s)
Quote:

Originally Posted by staybusy (Post 786187)
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.

Kasenit, Try eBay

about 1650 deg, the length of time you heat soak makes a difference.

have no idea why they stopped making it, so be safe and don't breath it. we did use it decades ago in high school.

Ironman 07-23-2022 09:49 AM

3 Attachment(s)
Quote:

Originally Posted by staybusy (Post 786217)
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?

I don't think chrome will be absorbed into the mild steel.

I know you are committed to your design because you have invest so much time into it, but sometime backing up and thinking about it is good.
Here is a video of a bone grinder restore, from back in the day when they needed this stuff. This is an easy thing to construct out of steel. The replaceable cutting tips can be made out of good steel and the rest plain mild stock.
This would also grind meat as well.

mccutter 07-23-2022 02:00 PM

Quote:

Originally Posted by Ironman (Post 786229)
The replaceable cutting tips can be made out of good steel and the rest plain mild stock.

I think Gerry is on to something here. :) What if you drilled/tapped for replaceable carbide tips?


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