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Need two materials 1

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Vig16

Vig16

Mechanical
Mar 21, 2007
67
US
I was asked a material question today and I remember that you guys are the materials experts! The part will be rubbing on another plastic part made of PEEK, so we’d like the material to be soft compared to PEEK where the PEEK will wear the material it’s rubbing against. We’re looking to have a disposable and a reusable part made. The requirements of each part are listed below…


Disposable:

Lowest possible heat deflection
Great insulator
Soft material
Lubricous
Iso 10093 biocompatible


Reusable:

Autoclavable
Great insulator
Soft material
Iso 10093 biocompatible
May be 2-shot for strength and softness

Thanks a ton!
 
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My best advice is as follows:

Disposable

Ultra high molecular weight polyethylene UHMWPE

Reusable

POM / Acetal

If Pat and Pud overrule me then listen to them instead. They have actual hands-on experience of such applications.

Chris DeArmitt PhD FRSC CChem

Consultant to the plastics industry
 
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Thanks man! I'll wait to see if I get any resistance, if not, I'll take your advice.

Thanks again!
 
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Sorry about that typo, it's actually 10993, not 10093...I apologize.
 
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Forgot: Are these parts injection moulded? I assume so as you want some soft stuff.

Also, whatever biocompatibility standard is required, there will be various classifications within it - usually for contact with body fluid times.

Cheers

H

 
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The materials don't have to be injection molded, but that'd be ideal.

For the biocompatibility, it will come into contact with bodily fluid, so it must be a medical grade.

Thanks, and please let me know if there are any other useful requirements I left out.
 
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Looking back I think the UHMWPE could be good for both 1 and 2. It is used in hip replacement joints so it is for sure available in implant grades.

Chris DeArmitt PhD FRSC CChem

Consultant to the plastics industry
 
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Not sure of the autoclaving requirement - most plastics are sterilized by EtO or Gamma ray. 135°C might be a bit high for UHMWPE?

So: further reading for you -


UHMWPE moulding flavours (inc medical)

and for softies:


There may be others, but these two are my personal favourites as they have excellent technical support (well, in the UK anyway!)

Cheers

Harry

 
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What do you mean by lowest heat deflection, the material that has the lowest heat deflection temperature rating or the one that deflects least at higher temperatures. A good indication of that temperature is required info before a really good informed recommendation can be made.

Any grades of PE are subject to softening and deforming under load at normal autoclave temperatures.

At a wild guess from what I think you want, low monomer content nylon 6 might be worth consideration. Nylons are or have been used for suture. Additives to increase hydrolysis resistance, thermal stability and heat deflection (up or down) generally ruin biocompatibility.

PET might also be worth a look although it has limited life when autoclaved as does acetal.

Noryl (modified PPO or PPE) might also be worth a look although I am not aware of its bio-compatibility. It is very good foe bearings in constant contact with hot water.

TPX might also serve your purposes depending on what flex mod and creep resistance you require and on whether or not you can get an alocation. Last I heard it was in very short supply with only one manufacturer in the world.

Regards
Pat
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What I meant by lowest heat deflection was that the material cannot come close to surviving autoclave. That part will be a disposable and should fail after autoclave and not be able to be used again.

As far as the Acetal and PET having limited life when autoclaved, that won't work for the reusable part. If I was to have PPO or PPE mechanically grinding along a PEEK part, would the PEEK be able to survive more so than either of those two materials?
 
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Re wear of PEEK exposed to PPO. You may need to do your own tests. I have not seen data for that combo. PPO and PPE are different names for the same material.

If data is available, Sabic, or your PEEK supplier might have it. Others who may have data are DSM or RTP

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
 
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Oh, and PE will serve for the use once as I very strongly suspect it will not wear the PEEK and it will fail a HDT test at autoclave temperatures.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
 
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Thanks! I'll run my tests with PPO and PE and see how that goes!
 
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In looking at the Rockwell hardness of the PEEK compared to the PPO/PPE, the PEEK would be the material to wear as the Rockwell scale is lower than PPO/PPE.

Would you guys happen to have another suggestion for the part to be autoclaved? (If we can get to 20 autoclaves with the material, we'd be happy)
 
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I have read that you can increase the wear resistance of PEEK but manyfold by adding the right filler, for example titanium carbide.

Chris DeArmitt PhD FRSC CChem

Consultant to the plastics industry
 
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That's a good little piece of information to know, Demon. I don't believe that'll help since the PEEK is already molded.
 
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Tribology and plastics is a very compex subject and full of surprises.

One major factor is the change in properties as temperatures rise due to friction. Another is the change of clearance due to change in temperature.

Skin layer characteristics also have a significant effect as does natural tendency to lubricious.



Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
 
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