RUBBER AND SILICONE LSR THERMAL EXPANSION

On 27-03-2013

Materials commonly named "RUBBER" are HOT CURED or HIGH TEMPERATURE VULCANISATION ELASTOMERS (HCR or HTV); they expand under temperature increase influence.Their coefficients of linear expansion will directly be function of "loads" rates; they vary according to polymers.

The usual values are from 2 to 4 x 10E-4  (unity = ° KE-1).
For information, silicones we transform into very big quantities have values from 2 to 3 and often closer to 2.

Sample of HCR, which would see its temperature increasing 130 °C, and by ex from 20 °C to 150 °C, would see a average of its initial length L 20 ° becoming :
  L 150° = L 20° x (1 + 3 x 0,0001 x delta T (130)) = L 20° x (1 + 0,039)
  so 3,9 % increase!
This "average" data is very interesting to keep in mind as equipments are studied and detailed (functions of waterproof coupled with significant thermal constraints).

It will be advisable to allow the HCR to dilate volume in best thus… to flow in the space which has been reserved (compact rubber is not compressible !).

If no, pressures exercised by the HCR component in dilataion process could be too high to exercise important constraints on parts in contact, and because of plastic deformation or break, then lesser performance and break in function return in ambient temperature.