reduce the linear expansion of Nylon 3

[toolmantwo]

How can we reduce the linear expansion of a molded part, once molded? It is 6/6 nylon.

I understand fiberglass reinforced 6/6 nylon would not expand as much, yet we have stock that is just 6/6 nylon.

Are there any treatments that could help to reduce the amount of linear expansion when elevated to higher temperatures like from 70 F to 110 F?

Any input is very welcome
Thanks, John

 

[insideman]

No.

 

[patprimmer]

Increasing crystalinity by annealing theoretically has an effect. It might be so slight that it might not even be measurable without the most sophisticated of equipment.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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[toolmantwo]

Thanks insideman, and Patprimmer.
It looks like we may re-design the part to add Glass filled Nylon and this can be a reduction of expansion as compared to unfilled.

 

[patprimmer]

Be careful with the design to position the gate so that the glass will orientate along the axis which requires the reduced co-efficient of expansion, as the glass will have a much greater effect in direction of flow. It will also have more effect on thin mouldings vs thick mouldings as the glass orients itself most when close to the surface

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[RichGeoffroy]

Toolmantwo:

Thermal expansion/contraction is less of a mechanical phenomenon and more of a thermodynamic event. Thermal expansion is the result of increased free-volume that arises from the added vibrational (thermal) energy. The more you heat the polymer, the more is vibrates, creating additional free-volume around each molecule, thus expanding the volume of the part.

Inorganic fillers and reinforcements experience the same phenomenon, but to a lesser degree --- about an order of magnitude less than organic polymers. Thus, adding inorganic fillers will reduce the change in volume (or linear dimension) based on its content in the composition --- not through any reinforcing effect.

Also remember, the coefficient of linear expansion is not linear. The coefficient of expansion is fairly constant up to the Glass Transition Temperature (Tg). It changes significantly in the glass transition region and again in the rubbery plateau.



Rich Geoffroy
Polymer Services Group
POLYSERV@aol.com