Dry resin question

[Josue]

I experience some dimencional trouble with a products made with PBT,, I know we most review the process , mold etc, 5why..., but we have variation lot to lot of resin some times,,

does the dry process (temp, time,,) in a resin (PBT) could affect or have some relation with the resin shrinkage?

how affect the humidity or "over dry" (high temp + abnormal time at the dryer)?

B.R

[brentb]

Suhas has done much research on this topic. I am sure he will comment,but is waiting out of modesty!


KOM

brent

[Suhas]

Thanks Brent, I like to see other views since I am not always right. I am a blend of the theory plus experience and so 1/2 and 1/2. So sometimes I will struggle too! I remember after my research was published a couple people pounced on me - it was funny. But over the years these have been proven right.

Josue, I will send you my paper on overdrying. I have your email ID. Anyone else wants it, please let me know. suhas@fimmtech.com.

Thanks,
Suhas

[Josue]

Thank you very much Suhas, very interesting investigation and information,,I understand better, I didnt put so much attention to this "small" but important details

by the way,, today we set back this mold to produce with PBT,, we didnt find any trouble, we make maintenance and check water flow, etc... we set to dry new bag of resin, we restart and found the parts at "nominal" speck :),, now i will keep some sample of this "good resine" and try to find the Ng resin to send to the lab to compare properties,, im not sure what speck or if i could get some results to indicate a diference of properties,,,

B.R

[Suhas]

Josue,
Make sure to size your hopper correctly. So the residence time in the hopper should not be more than about 6 hours for PBTs. Also, if you shut the machine down for more than 2-3 hours for any reason, make sure to turn the dryer down to 80 - 90 deg F but keep the air flow going. So it will not pick any moisture and the same time there is no high heat to degrade the additives. As I mention in the paper, it is mostly the loss of the low molecular weight additives that causes some of the problems.
Regards,
Suhas