Hardening Auger 2

[agpowder]

A number of years ago I designed and made an extruder for making powder coatings. I have been using the prototype machine for 5 years now and made a similar new machine two years ago and both operate well. I am now designing a beefier one that has a stronger gearbox to reduce breakage down time and made the conveying and kneading elements stronger for the same reason. I mainly focused on the metal dimensions to beef the machine up.
My question is, I have an area at the end of the screw conveying section and the begining of the kneading section where I get fast wear, and whilst I have, by virtue of beefing up the metal, probably doubled the wear life I am wondering if I could harden the screw elements at the work end of the machine.
The auger bits are 1.92" long, 1.97" diameter, 1.5" central core diameter with a 1" diameter keyed bore. The flighting without the inner core) has an ID of 1.5", OD of 1.97", pitch 1.92", thickness 0.3125". The parts are being CNC machined out of 4140.
Being these parts are pretty small do you think the movement caused by heat treating would be fairly insignificant? I think I mean the bore itself, do you think and if so how much would you expect the roundness to be out by?
I also want to try treating these parts myself, I have ovens and maybe someone could give a few pointers for me to try? ie, could I heat them to x degF for y minutes and then quench them in water or oil?

 

[swall]

Based on the geometry you have provided, you need to consult an experienced heat treater. Your screw geometry will not only be conducive to warping but also cracking. You can not sucessfully heat treat this yourself.

 

[EdStainless]

I see two options.
One is to coat with hard facing. Braze or weld overlay with stellite or similar products.
The other option would be to harden the flights. Not the full assembly but just the outer edges. You could get 4140 fairly hard.

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Plymouth Tube

 

[agpowder]

The parts that are wearing actually wear as much on the core diameter as the flights, I think I want to investigate the through hardening process.
All I am figuring is that if I can harden them even a little bit then they should last a little longer. I figured that I would like to know what the factors are that enables someone to harden stuff, for instance, if I heat the parts to 450degF and then chuck it in a bucket of water then the hardness may increase by 10% and then if I heat another part to 500degF then the hardness would increase by 20%?????
I dont NEED to harden any of them, I ordered enough to probably last mine and my childrens lifetimes BUT I'm interested in lengthening our factories uptime, and I'm just interested period.

Ian McHattie

http://www.onlinepowdercoatings.com

 

[redpicker]

agpowder, asking for free advice, then copping an attitude when you don't like that advice is just bad form. I don't think you will find that approach works with many people.

swall is aboslutely correct. As evidenced by the information you have in your thrid post, you have no idea how the hardening process works. Commercial heat treaters not only have this knowledge, but are also in a much better position to offer you the help you need. They will have better ideas on how their equipment will be able to process your part and how much distortion you can expect.

To put your request in a bit of a perspective, it is comparable to posting to a medical forum with "I have a pain in my side, I think I may have appendicitis. Where do I have to cut myself so I can reach in and remove my own appendix?".

rp

 

[arunmrao]

rp a star to you.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[EdStainless]

Call a local heat treater.
You may want to rough machine the parts, heat treat, and then finish machine.

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Plymouth Tube

 

[jsokal]

Agpowder,
FYI you would need a furnace, and hardenin is performed at arond 1500°F not 400 or 500°F

Denial ain't just a river in Egypt...Mark Twain

 

[gearcutter]

I would suggest that relying only on the advice of a heat treater is not very good advice at all.
Unless you end up being extremely fortunate in finding a good one; you need to take most of what they say ‘with a grain of salt’.
In your case and without any R&D; knowing or predicting an accurate outcome is next to impossible...............as is the case with most heat treating applications.
Dimensional stability is always going to be a problem whenever there’s a quenching operation involved.
In your case; I would suggest gas or plasma nitriding the part.
If you prepare the parts correctly; you’ll find that there will be minimal distortion..............if any.
If treated correctly; 4140 will allow you to develop a useful case depth of up to 0.50mm and give you hardness at the surface of around 490 – 575HV.
Note that I have specified gas or plasma nitriding and not any of the other types of nitriding available.


Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[agpowder]

Thanks, first Q for gearcutter, when I have my gears made I have the gear guy case harden the spur gears (8620 if memory serves) I have wondered if the teeth are cut before or after hardening, or maybe a combo of both, rough cut, harden, finish grind??
The reason I ask is the actual gear teeth are not all that dis-similar to what I have for these screw flighting.
Case hardening, I have shyed away from because I can allow the element to basically wear completely away, certainly all of the flighting and quite a lot of the core diameter material. The 0.5mm of really hard material would sure enough last loads longer but once it is gone then the remainder will go at the normal rate. Through hardening would factor the wear as a complete multiple.
BTW you are right about the heat treaters, when I ask them "will it move" they say "maybe, maybe not" this is about as useful as a doorknob in a field or a MVP hunter on this forum!
I will however keep your advise for when I have my next gear discussion.
Q for JSOKAl, what would happen to the metal (best case scenario) if I heated it to 1500degF for 20 minutes and then quenched it in water?

Ian McHattie

http://www.onlinepowdercoatings.com

 

[agpowder]

My mother has a furnace for firing clay porcelin dolls, I could probably quite easily set up some sort of temperature controller. My father uses sort of putty cones that collapse when a particular temp is reached but that would make keeping a constant temp difficult.
I suppose any cracks would likely occur from the broached key radially outwards? I have a half descent surface microspope to crack hunt with.


Ian McHattie

http://www.onlinepowdercoatings.com

 

[EdStainless]

How hard is the material that you are using now?
What is its heat treat condition?
If you want moderate strength then you can heat treat first and then machine.
for higher hardness you will only be grinding after heat treat.
Ion or Plasma nitriding is a good option. Make sure that the starting bar is quenched and tempered, use a tempering temp about the same as the nitriding temp. Then you can machine and surface harden without much risk of distortion.
This may only give you a case, but that 0.050" case may last 5x as long as 0.500" of untreated metal.

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Plymouth Tube

 

[gearcutter]

"The 0.5mm of really hard material would sure enough last loads longer but once it is gone then the remainder will go at the normal rate. Through hardening would factor the wear as a complete multiple."

While your argument may seem logical; in reality however you don't present any facts, R&D or experience in this field.

I fail to understand how an auger could retain any kind of efficiency at moving material if any of its outside diameter has begun to wear away. Surely increasing the toleranced gap between the casing and the outside edge of the flights would not be a desirable outcome.
A wear resistant coating would significantly increase the operating life.



Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[agpowder]

Yes, I have been really thinking about the case hardening aspect for the last hour or so, one point that keeps recurring is I SUSPECT that the outer extremities of the part, also the 0.5mm case are the bit that would see the fastest rate of wear, in fact a convo I had here 2 or 3 years ago keeps coming to mind where a guy that had twinscrew extruder experience told me that the wear the machines see in the first couple of weeks of operation is really accelerated because of the machinery build tolerances.
If my assumption is correct then case hardening is exactly the wrong...or maybe the most ineffective approach.
I was reading earlier today somewhere here on this forum about a part that was made of 1018 and then changed to 304 stainless and the stainless part lasted longer, my first thought, along with someone elses was that that scenario was unlikely. However, one guy mentioned that (actually the guy may have been you) the stainless part was probably work hardening. I wonder if my WORK PROCESS would also cause 304 or some other metal to work harden???
I know even a simple hacksaw operation on 304 and 316 stainless will get harder and harder and Years ago someone said the stainless was work hardening?????? I thought at the time that it was probably the hacksaw blade getting blunt..... Please enlighten me!

Ian McHattie

http://www.onlinepowdercoatings.com

 

[agpowder]

Sorry gearcutter I seem to have posted at the same time. Yes it amazes me as well about the screws being worn out and the machine still operates, we get an operating indication that the time has come to change auger elements by surging in the machine happening actually quite suddenly. Once it starts the surging happens every fiveminutes or so of operation, The surge noise is really scary but by the time the operator can react the surge has finished and the machine is operating normally again.
Now we have 13 0f thes 2" long elements givin about 26" of flights, once the surging starts we dissemble the machine and the last 3 elements (6") are almost completely gone, maybe down to 1.25" diameter. At the end of the 26" long screw flighting is the start of the kneading section which is where the dispersion work starts.
The surging, I think, happens because the screw flightless void fills with product and sticks untill enough axial force from addition product just pushes the slug of product in to the Kneader area.

When you say a wear resistant coating what do you mean; a ceramic liquid coat??? that would be a load harder than a case hardening wouldn't it?

Ian McHattie

http://www.onlinepowdercoatings.com

 

[9627]

I have no professional experience here so just a thought.... can Ti be electroplated onto the items?Seems to be tougher than a Cat D8 where applied on drill bits at only a few microns. Until it gets too hot at least.(Talkin' about titanium....)Interesting topic you have raised. Size does matter.Certainly won't be hard facing with 6mm rods !

 

[agpowder]

I think you have had a great idea, the coating on drill bits does seem to hold up to really extreme wear doesn't it?
I will do some searches and see what I can find about this.
I have found out a bit about ceramic coating and whilst you can quite easily source the liquid product, it does seem to be a bit of a PITA to get the application process to give consistant results. Intaface adhesion seems to be the main problem and once a bit of the ceramic does not stick then the rest of it seems to "peel" off really easily, by pretty much all accounts.
I have found another forum that has described a simple magiver method of hardening the parts which I am also going to give a go to. I have had made 36 of the parts in 4140, only 6 would be needed for the first machine and another 6 for a spare, ready assembled set, thats going top leave 24 for me to play around with hardening. I also have 72 of the parts coming in 1018 and of these I will need 40 for the part and the spare leaving 32 for me to play around with on some sort of hard coating,

Ian McHattie

http://www.onlinepowdercoatings.com

 

[EdStainless]

One nice advantage to a nitride surface is that the hardness drops off gradually. and it is not a coating so it won't peal or flake off.

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Plymouth Tube

 

[arunmrao]

If nitriding is an option,then select a nitriding steel grade instead of 4140. The nitrided layer will be more wear resistant and offer longer life.

Alternately you might consider embedding carbide tips on the wear surface.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year