Santoprene post mold shrinking

[EPMKnox]

I have a part molded from Santoprene 101-64, after the parts are put into service and are exposed to heat (80 degree C) they shrink. I cannot find any data that says that this normal or how to design around this issue. Anyone else experience this?

 

[johnnymat]

Hi
mould shrinkage in TPE is quite common although at a much lower rate than thermosetting elastomers. how big the problem is depends on the tolerances you are working to shrinkage can occurr as a result of various strain relaxations.see below...

Shrinkage
Due to their anisotropic nature, GLS styrenic TPEs shrink more in the flow direction than in the cross-flow direction. Generally, SEBS TPEs have higher shrinkage and are more anisotropic than SBS TPEs.

Typical shrinkage values for SEBS-based TPEs are 1.3% - 2.5%, whereas those for SBS based TPEs are 0.3% - 0.5 %. Softer SEBS formulations (below 30 Shore A) will shrink more than harder materials. Some grades, such as Dynaflex G7700, G7800, and G7900 Series contain filler, which reduces their shrinkage.

The shrinkage values reported by GLS are determined using a 0.125" thick plaque. It should be noted that shrinkage is not an exact number, but a range value. This range can be affected by the part wall thickness, melt temperature, mold temperature, injection speed, hold/pack pressures and also the time between molding and measuring. As a result, prototyping is strongly recommended for parts with close tolerances to better quantify the realistic shrinkage of a specific grade of material in the application.

Johnnymat