Nylon growth in water 3

[Philrock]

I'm thinking of using a nylon or Nylatron GS roller chain & sprockets in an application which may see a lot of water - possibly even immersion for days at a time. Room temperature. Very low loads and speeds. I know nylon is hygroscopic, but I don't know what to expect in terms of percent dimensional growth. Anybody know the answer or where to look it up?

 

[John2004]

Hi Philrock,

You might want to try Delrin or Acetal instead of Nylon, it has a high tensile strength, good chemical resistance and wear properties, and it absorbs less water & swells less than nylon does. Here is a link to some information about using plastics under water...

http://www.quadrantepp.com/source/acetals.html

Nylon 12 supposed to have the lowest moisture absorption, Here is an in depth report in PDF regarding nylon 6/6 and 12...

http://www.rmb.com/about_rmb/Data_Sheets/Nylon_12_Comparison.pdf

Here's a design guide...

http://www.riversidepolymers.com/designguide.pdf

http://www.riversidepolymers.com/moldingguide.pdf

http://www.wellmaninc.com/Wellman/ermolding/molding guide 2.pdf

Here's an html page with a chart on mechanical properties and water absorption of nylons

http://www.machinedesign.com/BDE/materials/bdemat2/bdemat2_29.html

Sometimes it's possible to submerge nylon under water for 48 hours prior to machining, to account for dimensional changes due to water contact when the part is in use.

As an experiment, I put a 6/6 nylon washer .031" thick X .475" OD X .190" ID in a glass of water for several months. The Thickness hardly changed at all, measuring with dial calipers I think the increase in thickness was about .0008".

With plastics, I think the swelling is proportional to the size of the part. A fairly small part might not change that much, where a larger part would, with the same percentage moisture absorption.

I know

http://www.wmberg.com

has roller chain and sprockets, along with

http://www.sdp-si.com/.

You might also try

http://www.nordex.com

&

http://www.pic-design.com/.

http://www.qtcgears.com/

has a technical reference on gears, the plastic gear section has a chart that list moisture absorption and properties for different plastics.

Hope this might have helped.

John

 

[Philrock]

John2004,

This is a tremendous help - thanks a million!

philrock