How to achieve a uniform hardness value in the surface of polyurethane material

[AlpanaSlo]

Hello.
Our production producing Polyurethanes tubes for seals making by injection molding. Lately we faced the problem: Polyurethane tube after mixing in mold and subsequent curing has different surface hardness (difference can vary between ShA 80 and ShA 90). As far as seals are used in machinery with high requirements for phisical and mechanical characteristics, the hardness should vary for 1 or 2 units max.
Probably someone can suggest solutions to this problem?
We have already trued rheology/thixotropy agentsto make the polyurethane system more gomogeneous. Also we tried various catalysts to reduce curing time. Nothing has helped so far.

 

[1503-44]

Post it in a chemical engineering forum.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[JAE]

Wrong forum.