Just Bought Some Torsion Bars. Do They Need To Be Heat Treated?

[Mad Scientist 106]

That's what I thought Mei, but Allan mentioned machining post treatment, and he's an engineer. I think it depends on the application.

 

Might as well see if anyone can do it. Peace of mind if nothing else. Car is out of action for a couple of weeks anyway whilst I get a custom oil cooler made.

Edited August 4, 2013 by Mad Scientist

[allanallen 528 2 Cars]

Hardening Is hardening but the tempering may need to be a bit more specific because of it's use, No?!

 

I've plenty of experience machining heat treated materials and as mentioned I know some of the materials we use change size when treated. I'm used to aerospace junk to be honest. I've no idea about spring steel hence me asking the question, in a round about garbled way

I posted on the topic about my experience of using uk supplied non treated bars, rather than to argue about metal properties which the thread has turned into.

 

I'd say just use them Pete, if they sag send them back then come on here and call us all (or just me) d*ck heads

[petert 554]

Hardening Is hardening but the tempering may need to be a bit more specific because of it's use, No?!.............

 

rather than to argue about metal properties which the thread has turned into.

 

Hardening is not just hardening, nor is tempering just tempering. The metallurgist at the H/T place will know what to do.

 

And it's not an argument, just useful information for those with an interest. I'm sorry for taking it to an academic level. I thought you were also a mechanical engineer?

[Tom Fenton 1,526]

The metallurgist at the H/T place will know what to do.

 

My experience is that he will not, and you need to give them specific instruction on the end condition you want.

[allanallen 528 2 Cars]

 

Hardening is not just hardening, nor is tempering just tempering. The metallurgist at the H/T place will know what to do.

 

I was asking a question rather than stating a fact because as I've already said I'm not mega clued up on the process! My argument comment was made for this exact reason, I wanted to distance myself from the ins and outs but I've been drawn in hence all the questions.

My dealings with h/t is somewhat different to what we're on about here, for instance I'm currently machining some kind of turbine impeller, when Ive finished this op. it will go for testing and heat treatment then I'll get it back and machine it again! This is why I asked about size changes during h/t.

I am indeed an engineer hence my interest but I also have first hand experience of non treated bars which is what I wanted to bring to the table. Sorry to ramble on but I just wanted to explain myself a little as I know I'm blunt and come across as a twat in text

 

An educated guess tells me the tempering of say a leaf spring will be somewhat different to a torsion bar, maybe you could enlighten us so Pete knows exactly what to ask for if he chooses to go down that road. I think making the assumption that the h/t place will know what to do is a recipe for disaster.

[DanteICE 72]

As my father is a Metallurgist and used to be a director at Bodycote (Largest International metal treatment company), would you like me to ask his advice. He was a H/T man at one stage, but he ended up in HIP (Hot Isostatic Pressing) nearer the end; and I think his specialty is Nitriding and Metal Fatigue. He'll definitely be able to help.

 

Geoff

[petert 554]

Definitely get a metallurgist involved if possible.

 

My experience is that 44Rc is the number necessary for the desired spring type properties. So that is what you ask the H/T place to achieve. Test a standard torsion bar if you like. The hardening medium will determine the initial hardness. ie bryne, water or oil. Tempering temperature depends on the desired properties, but is determined by the steel composition. Thus complex steels such as en47 require speciallized techniques if problems such as embrittlement are to be avoided.

 

Long, thin sections move about when hardened, in addition to growing. Expect the bars to bend and be ready to press them back straight. If the splines are already a tight fit they may not fit after hardening. They aren't easy to do and thus the cost involved. Chris P obviously has a good H/T place. Maybe ask him? H/Ting special steels is very different from plain carbon steels. Thus don't be surprised if someone doesn't want the job.

[Mad Scientist 106]

Done some digging today and spoken to those involved.

 

The bars are made from en24t. This is hardened and tempered in its raw form, so apparently does not need treating after machining, hence the "shiny" metal. This material is quite widely used for driveshafts, so torsional strength shouldn't be an issue.

I am waiting to see the engineers information on the manufacture and material, but as yet don't know the actual hardness. I'm fairly confident they are up to spec though now.

 

Initially enquiries into heat treatment before i got this information seem like its quite costly, mainly due to the cost of heating up a furness for 2 bars.

[chipstick 382 1 Cars]

This all sounds like a lot of potential hassle you could be doing without.

[Tom Fenton 1,526]

24t is tough strong and resistant to fatigue, it is not however a spring steel which is clearly what s torsion spring is usually made from.

Personally I would buy from Chris Penrose.

[allanallen 528 2 Cars]

The ones I've seen/got ain't made from 24t! Looks like there's a few places making them then....

[Mad Scientist 106]

FFS!

 

This is not ideal really!

 

 

I'm thinking I should just put them in and see what happens, as I really don't have time for this. Nothing is ever simple with my car!

[petert 554]

Fairly sure mine were EN26.

[petert 554]

Further reading reveals EN24 (and EN26) is available in various range of tempers. In the case of EN24, T is the softest, Z being the hardest/strongest.

 

http://www.westyorkssteel.com/alloy-steel/engineering-steel/en24t/

and

http://www.westyorkssteel.com/alloy-steel/engineering-steel/en26w/

 

My bars must have been cut from U temper bar, then brought up to X/Y temper (400+ Brinell or 44Rc) during the HT process. How long does a carbide tool last cutting steel that hard?

Edited August 6, 2013 by petert

[Rippthrough 98]

I'm curious really as this topic often comes up and petert is the only person to have a problem but his bars aren't the same as what we're all using anyway.

As far as I'm aware Chris and the place in Leicester (or wherever it is) are the only folk making them.

 

As for heat treating them, can you even do it after they've been made? I know alot of the materials I work with grow considerably after treatment! What does heat treating do to the properties of the spring steel? I'm sure the correct spec of spring steel shouldn't sag, hence the 'spring' bit?!

 

Since you usually machine it in it's softer tempers to make machining much faster and easier, you usually heat treat them after to bring it back up to a 'spring' temper.

Okay, a lot of aerospace stuff is machined close, hardened, and then finished off by another machine process to make it spot on, or even machined pre-hardened, but that requires good tooling, very tight, rigid and well maintained machinery. Most of which doesn't apply to many engineering shops and spring makers, especially when doing something down to a price.

 

Most EN24 is supplied as En24T which is fairly easy to machine and finish, it really should be hardened to at least the V or W spec, and that's low for a torsion bar or driveshaft really (1000-1200N/mm), but adds almost 50% more yield strength over EN24T (brings it to the 900N/mm area) which is what makes the cheap bars sag over time.

 

For what it's worth, all our race torsion bars and driveshafts are made from S155 - which is basically a much more refined version of EN24 - and hardened to a touch under 1900N/mm tensile, and about 1450n/mm of yield...basic EN24T as supplied is around 900N/mm tensile and 650n/mm of yield.

 

 

edit for more info.

Edited August 6, 2013 by Rippthrough

[allanallen 528 2 Cars]

 

Since you usually machine it in it's softer tempers to make machining much faster and easier, you usually heat treat them after to bring it back up to a 'spring' temper.

Okay, a lot of aerospace stuff is machined close, hardened, and then finished off by another machine process to make it spot on, or even machined pre-hardened, but that requires good tooling, very tight, rigid and well maintained machinery. Most of which doesn't apply to many engineering shops and spring makers, especially when doing something down to a price.

So, an untreated bar of en47 needs to be tempered to make it spring steel or it is already and the tempering just makes it springer?

 

Peter, as Phil says you need decent machines, very rigid tooling and the correct speeds and feeds are paramount. Tip life is dependant on these, a tired machine will destroy tips in seconds. The job I've just finished was a super alloy (astralloy) turbine disc, it's seriously f***ing hard! Tips last a couple of cuts, I'm only using cheapish iscar general purpose tips, better tips would last longer and cut nicer but cost more so it's a bit of a trade off. That's cutting at around 20m/min with steady feeds.

[allanallen 528 2 Cars]

So what's the ideal material for a torsion bar that'll give a similar spring rate to the oe material and not require any treatment, just machining?

[Rippthrough 98]

Depends what the En47 is being used for, it's not a spring if it yields

 

It's been a long time since I tested one but standard bars were around 35RC if I remember correctly. EN26 is usually available in 'W' hardness straight off the shelf so that'd be the easiest thing to use I'd imagine.

[DanteICE 72]

Ok, it has taken my a while to get in contact with my father and show him this thread. After a long, relatively confusing conversation (I'm a programmer not an engineer) he said "Rippthrough sounds like a manufacturer and he knows what he's talking about. People should listen to him."

 

There you go. Oh he did say that heat treating a one off bar would warp the shape and you'd need a straighten it afterwards which would need the proper tools; these tools aren't common.

 

If you want any more clarification I can ask more, but you'll need to give me some questions to ask, because I've less of a clue than you guys.

 

Geoff

[Rippthrough 98]

If you have one hardened, ask them to hang it vertically and quench it the same, should minimise the warping enough that you shouldn't need it straightening after.

[DanteICE 72]

Yeah he spoke about hanging it vertically to avoid warping. He said that at Bodycote they had a machine that would straighten a bar of metal to within thousands of an inch, but the cost would be astronomical for a one off item.

 

So what is it you do Ripp?

[Rippthrough 98]

Professional Keyboard Warrior.

[DanteICE 72]

Professional Keyboard Warrior.

 

Ok let me try that again. What do you do during the week to get money to pay the bills?

[Rippthrough 98]

Man Whore.

 

 

 

 

 

 

 

Design + build shiny bits for muddy cars.

Edited August 12, 2013 by Rippthrough