Heat capacity of A-arm rubber mounts 2

[MacGyverS2000]

This may be more of a materials question, but figure with it being car related I may get an answer here...

Does anyone know the heat capacity of the rubber mounts used in the typical A-arm? I'd like to know if the mounts can handle the heat produced during a powder coating session. These sessions typically push 400-500F for 8-10 minutes, but I don't want to degrade the mount. The mounts are an integral part of the component, so removing it before powder coating is not an option.


Dan - Owner

http://www.Hi-TecDesigns.com

 

[patprimmer]

If it is proper cross linked rubber it should handle that no problem. If it is thermoplastic polyurethane then it will melt out at that temp.

Regards

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[MacGyverS2000]

Pat,

I was leaning towards a vulcanized rubber, as well, though I questioned the durability of reheating it. At least one source (Wikipedia) gives contradicting info... in one spot it lists the vulcanization process as taking up to 8 hours, followed in the next sentence as saying tires are cured for 15 minutes at 150C. It also makes mention of thermosets degrading or burning if reheated, though it's unclear if it's specifically talking about thermoset plastics in specific or cross-linked materials in general.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[patprimmer]

I will do some research, but I expect vulcanised natural rubber will withstand that temp and time with minimal damage. There will be some oxidation and maybe some extra cross linking that may make them harder. Rubber is not a single material, but a group of compounds like steel.

Rubber is not my area of expertise, but a few of the major players used to be DuPont and Bayer, and an Italian company and a Yugoslavian company whose names I cannot recall. DuPont should be able to provide actual data.

Regards

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[tom1953]

I'm not an engineer (I'm a chemist in the rubber industry), and I'm not familiar with the application, but regarding rubber, some types of rubber would be more likely to handle the 8-10'/400-500F than others. I would think that natural rubber would not stand up to this exposure very well, as it's not very heat resistant. Natural rubber tends to revert upon extreme heat exposure or long times at lower temps, undergoing chain scission which would reduce the crosslinking not increase it (think old, sticky rubber bands). Most other polymers would crosslink more upon heat aging, giving a harder compound.

There are many types of rubber, natural and synthetic, and EPDM rubber, and other types such as silicone and HNBR (hydrogenated nitrile) are inherently more heat resistant than natural rubber.

Regarding the time of the vulcanization process, it can vary depending on the vulcanization (cure) system, whether it's sulfur cured or peroxide cured, and the thickness of the part. Some injection molded rubber parts can cure in a minute at 400F, for example, while a thick part might take the 8 hours mentioned above at a lower temp such as 250-290F.

Hope this helps.

Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[Compositepro]

It would not be a good idea to take rubber over 400F. While it may not fall apart instantly it will start to degrade and it would be equivalent to losing several years of life of the part. At 500F the rubber will fall apart quickly.

 

[patprimmer]

Tom

Thank you for clearing it up. As I said it was not my area of expertise.

Regards

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[Busa20]

Im from China, we just made a mine vehicle with a natural rubber mounts. we have the same question.

 

[evelrod]

I had all my subframes and suspension bits powder coated in 2004 and our local company would not take the job with the rubber mounts installed. For me, it did not matter as I was replacing all the soft rubber mounts with harder ones or Rose joints. It's just not that big of a job to R&R the bushes!

Rod

 

[MacGyverS2000]

I had an extra rear subframe powdercoated last month, it's waiting on the suspension bolts to come back from the chromer's. I still haven't made up my mind what I'd like to do with the actual A-arms, but it looks like I'll be rinding them down and chroming them, as well... I just can't take the chance of the rubber hardening up.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[mcgyvr]

Might as well swap it with the Prothane or Energy Suspension mounts (if they make them for your application) while its off the car and easy to work on. Stock mounts/bushings are garbage. I just changed out all the rubber mounts on my vehical and its like night and day.

 

[MacGyverS2000]

Replacement mounts for an S2000 are practically non-existent.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[evelrod]

Stock mounts and bushes for much of what I build are non existent in the practical sense. Delrin is cheap and easy to work with. Make your own. Race suspension bushes I use Al or Rose/Heim type joints.

Rod

 

[pennswoodsed]

Dan,
won't chroming embrittle your parts,particularly mount bolts? Seems counterproductive for appearances sake.
Yours,Ed

 

[patprimmer]

Stock rubber mounts are carefully designed and tested to perform the functions hey are designed to for at last the warranty period and often perform far beyond, hardly junk.

If you have different requirements and are prepared to trade of durability and noise and vibration isolation for more exact suspension location, the other materials might suit your specific purposes better.

Like Rod says, acetal (Delrin is a DuPont trade name for acetal) is a good choice for a very hard (relative to rubber) bush.

Depending on service conditions, nylon (Zytel), acetal, PET, polyurethane of various hardness, HDPE, cross linked PE and UHMWPE and PTFE (Teflon) can be used. Each has it's own merit and weakness regards, degree of compliance, fiction properties, heat generated an heat tolerated, wear in clean conditions, wear in dirt and grit, self lubrication, compressive strength, cold flow etc. etc. Also each may be provided with various additive and filler packages suc as PTFE, graphite, molybdenum Disulphide, carbon fibre, aramid powder, silicone oil.

Generally, Polyurethane is best where more compliance is required, Acetal is best where minimal compliance and best compressive strength is required, nylon 66 is best where significant heat is generated and reasonably high compressive strength is required, PTFE is best where minimum friction is required, but compressive strength and cold flow is not an issue and UHMWPE is best where temperature and load is low, but the environment is dirty.

Most can be obtained as bar stock that can be machined and PU can be obtained as liquids parts A & B which can be mixed and poured into a very simple home made mould.


Regards

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[GregLocock]

The problem is that if you go to the parts catalogue and order a suspension bush, because it is the right size then you are unlikely to get one that actually does what /you/ want from your installation.

My corona is just coming up to a quarter of a million miles. The only bushes to shag out (technical term) have been the shocker end bushes.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

Greg

Does that mean for your use the OE bushes are not garbage.

;-)

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patprimmer]

Of all the materials I mentioned above, PTFE is the only one that won't melt by 500F and only nylon ad PTFE will go past 400F

OEM rubber will depend on the type of rubber as indicated by Tom. How to find out what rubber they use is another question. I guess test on rubber bushes from arms damage beyond repair that you might get from salvage yards.

Regards

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[MacGyverS2000]

Ed, A little baking shortly after chroming takes care of embrittlement, not to mention only the frame bolts are under any tensile forces (and that's strictly what force is applied to torque them down, which is not very high at all).


Pat, thanks for the list... when it comes time to work on the A-arms I'll look further into some of those materials. Thank God I have access to the machine shop

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Tmoose]

http://img246.imageshack.us/img246/745/mysterion2az6.jpg

The chromed frame on this Ed Roth show car allegedly failed repeatedly just getting trailered from show to show.
He later commented he did not know he had to bake chrome parts.

Still.........