CALCULATING CHANGE IN SIZE OF MOISTURE SATURATED PVC

[DerekCoffyn]

Hello,
How does someone calculate the change in size of a pvc part once it is saturated with water? I understand that it is easy to find the "Water Absorption %" of PVC, but this tells me nothing. Is this % based on mass or volume, and does this directly translate to a proprotional change in dimension? If not, then how do I calculate the size change? Also, how do I calculate the time required to saturate my parts prior to final machining? My parts will be permanently submerged in HCL solution so I hope to saturate prior to final machining for best fit? These parts will be about 5 feet long, so dimensional change could be significant.
Thanks to any and all who provide help,
Derek

 

[patprimmer]

Water absorption is always carried out on a weight weight basis.

In over 40 years in the industry I have never known anyone to be concerned about dimensional change of PVC from water absorption. The level of absorption and consequential swelling are so small that they are considered of no consequence.

In this regard, HCl is not water. It may have a somewhat different reaction, so if you want to predict a final dimension, you need a figure for HCl, not water.

Typically the rate chemicals diffuse through plastics is very slow so time to equilibrium depends on section thickness but is most likely months or even years. typically heat greatly accelerates the rate, but might also change the final result due to annealing.



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

http://eng-tips.com/market.cfm

for site rules