UPVC fittings: Recommended parameters for rigid PVC moulding

[alnigor]

Hello to everyone!

I’m novice in the injection molding process. And will be grateful for any help. I have a question about rigid pvc moulding. What is recommend parameters and profiles of injection speed, injection pressure? I’ve understanding more or less about the temperatures\pressures parameters but which profile I should setup for speed and pressure - slow-fast-slow? In that percentages?

And what could be problem then after standard test (150 ^oC, 15 min) for rain system fittings we see something like:



Thanx a lot!

[rickbatey]

That looks like contamination of a disimilar resin. Say PP or PE in the part. Are you coloring the part? What is the carrier resin for the colorant? That's my best guess.
Now for Process settings the sky's the limit. You need to purchase and read Suhas's books!
Rick.

[MTUHusky]

I agree that looks like contamination but it could be degradation. PVC is extremely susceptible to shear rate and degridation. Shear rate is dependent solely on volumetric flow rate and the radius of the channel that it is passing through. If it is contamination, the solution is simple, find the source and get rid of it. If it is shear rate, now we have to get some details. Is the sprue and runner diameters sized correctly? Are they too long? Are you shooting too fast? A quick test would be to run the mold for 20 -40 minutes at a much slower speed. Try cutting your fill speed in half and see if it improves. If the speed doesn't get the results you need then you need to look at the mold; larger sprue diameter, runner diameter and/or gate diameter. If you know its shear rate then I would also look into a technology called "Melt Flipper" which greatly reduces the shearing at the wall by flipping the melt upside down.

[chrisprocess]

The parts look good in the beginning of the production run then after 15 minutes they turn into that picture?
What do you mean by standard 150 degree test for 15 minute?