30% Glass filled Nylon 6; can I use it in water? 1

[craja67]

I have some elements molded from a Firestone Nylon 6 CG430-203. I use them in a machine that uses a conveyor type belt to screen solids out of influent water channels. I have had issue with tightness and stiffness in the belt and I believe it is due to water absorption.
I need help with information on this material water absorption and desorption rates.
How much will the material grow when submersed in water and how long will it take to absorb water and how long will it take to dry out and come back to its dry size?

 

[patprimmer]

Unfilled nylon 6 typically absorbs about 3% water in air with an average humidity and about 9% if stored at 100% RH.

At 3% moisture content it expands about 1%

At 3% moisture the flex mod is reduced by about 70% and the elongation increases by about 300% although elongation also depends largely on molecular weight and nucleation.

30% glass fibre drastically reduces the effect of the moisture uptake. The %age moisture will be the same for the nylon content only so it becomes 2% and 6% moisture uptake.

At one molecule thick the moisture uptake to equilibrium is virtually instant, however the moisture travels quite slowly through the nylon. The rate depends on concentration gradient and temperature, but for a thick moulding can take months to equalise to the core of the moulding, however most alteration to properties occur before full equalisation of moisture content.

I have data somewhere I could dig up, but reputable raw material suppliers should be able to provide extensive data taking several variables into account.

Regards
Pat
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[craja67]

Pat, thank you for your help. My molded part has various thicknesses, the area I am looking at is a cylindrical boss that has a 1-1/2" OD, 1" ID and is approx 1/4" thick.
In reponse to my on site issue I dropped two elements into a pail of water; at this time they have been submerged for about 20 hours and I have seen little dimensional change.
As for desorption, on site my belt had been out of the water about three days and I did not see a change back to the original dimensions.
Would this be typical rates based on your experience?

 

[patprimmer]

Yes. At 1/4" wall section, significant size changes will take quite a few weeks or even months if it is cold. At 100 deg C it could change to days or even hours.

Regards
Pat
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