Plastic Axle

[reyemka]

Hi,

I have an application where I need to use a plastic axle for a pivoting mechanism (20Hz). The axle will have a thin blade attached to one end as well. One of the requirements is cleaning in a microwave steam sterilization bag, so using a metal rod is not an option. I am considering Noryl for the resin and a concern I have is warping. The thin blade is approx 50x22x1.25mmm and the axle is approx 4mm OD and 40mm long. Attached is a simple representation.

Anyone have any advice?

Thanks,

Adam

 

[btrueblood]

Do the blade and shaft/axle need to be the same material? If not, do they need to be a bondable pair?

Suggest you browse Matweb, if stiffness is your design criteria.

Steam-stable polymers with fair rigidity (which I'm assuming is a criteria) would include nylon (not quite sure about microwave due to absorbed water...Pat will know) and polyamide-imide (Torlon), polysulfide, poly-phenyl-sulfone, peek, pfa, pvdf, polyphenylene oxide (Noryl), poly methyl pentene...and a few more that are less rigid and/or less resistant to hot water/steam. How many cycles of steam sterilization the part must endure will affect your choice, as will the degree to which the part can be stiffened by fibers or other fillers...and then you can start comparing costs.

If it had to take a lot of steam, and it can't have reinforcements, and must not warp after molding...I'd look at polysulfone, but that is just from my own limited experience. PS is not very tough stuff.

 

[Pud]

Is the steam at 135ºC autoclave or a domestic type 100ºC sterilizer?

Cheers

H

http://www.tynevalleyplastics.co.uk

It seems to me you have confused a safe drinking limit with what I like to call "lunch"

 

[reyemka]

It's not autoclavable, just home sterilization (100C).

 

[patprimmer]

Noryl is actually a range of PPO/PS alloys. Its properties largely depend on the ratio of PPO to PS, but it is very good to steam, but is very sensitive to solvent stress cracking, sometimes from some very common solvents that go unnoticed in very common household substances like food and cosmetics.

Dimensional stability may be a problem with nylons and hydrolysis resistance may a problem unless properly stabilised. The hydrolysis stabilisers eliminate food contact if that is an issue. Nylons 12 or 6.12 might be best if nylon was on the list or some of the aromatic nylons like Zytel HTN, Grivory or Reny, however I would need to check data re steam.

A good high PPO grade of Noryl might be a good choice. High PPO makes it difficult to mould.

Regards
Pat
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[Pud]

Jeez, nip out for a beer or two and Pat says it all!

mPPO (Noryl, et.al.) my choice at 100C.

(although is it's a one-piece moulding maybe something with a higher flow for the paddle section)

Q: is PA in any guise ok in microwave?

H

http://www.tynevalleyplastics.co.uk

Why be happy when you can be normal?

 

[patprimmer]

PA 6 and 6.6 are definitely a problem in a MW oven. The out gassing of moisture causes them to explode at times.

I am not sure about the low moisture absorbing grades, but you are right, I should have checked or at least warned that a check was required.

Regards
Pat
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[reyemka]

Thanks for the advice.

The proposed design is to make the shaft and paddle from one part, so I was looking at a higher flow Noryl.

 

[Demon3]

Wanted to mention most people don't realise but you can use metals in a microwave. You need to do some work to check what shape you need (avoid sharp edges and points). This may solve your problem. I am sure you can find more info online.

Chris DeArmitt PhD FRSC CChem

 

[patprimmer]

The high flow Noryl grades are the ones with more PS than PPO, so their performance is generally rather lower than the low flow grades.

Regards
Pat
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[cloa]

Also most ceramics are microwave safe too.