Impact Strength vs Time
Submitted by Yee-Huat (Sam) Ho on Tue, 12/23/2008 - 6:04pm
We are trying to run high filler PVC formulation. The interesting part is the pipe will pass the impact in the first few days, but then when we send to our Research & Development Department to do referee test (weeks after), and it fails impact terribly. I understand the impact strength will be reduced by time. However, we cant send it out to market. The customer might send it back and say this pipe fails impact after few months.
ASTM didnt mention about the reduction of impact strength vs time. So we has to assume the pipe will pass the impact the whole time even years after. Any opinion on this issue?
Comments
Change of Properties with time
I direct a lab, so my observations have been from the other side of the table. I have noticed that impact passes and hydrostatic testing (1 h, 36 MPa induced stress at 30C) fails after two hours of the pipes being produced. However, the impact fails and the hydrostatic testing passes after 24 hours.
An improvement in tensile strength but a decline in elastic modulas after 24 h. I suppose it has to do the re-crystallization of the semi-crystalline PVC completing in that time.
I don't know what you mean by "first few days", clause 11 (conditioning)of D4226 requires you to wait 40 h before doing the tests, so if you follow that clause, the results from the lab and the plant floor will be the same. Otherwise check the impact head (shape and weight) in the lab and the plant floor, sometimes small dents make a difference.