Cracking of PC part after couple of days (5-10 days).
Hello, I would like to ask if any of you experienced cracking of PC part after few days. Part is made of polycarbonate and there is a small rectangular shaped part. whole part is about 50×50 mm. Critical rectangular part is 5x7mm. Wall thickness af whole part is cca 1mm. During assembly of electrical motor this critical part is bend down by 5° and hold the motor in proper place. After assembly the bend is 3-4°. The scrap rate is about 10%. Do you have any ideas why it does not crack immediately but later? The issue occurs the first at the moment but I am worried about future lots. Process settings are more or less the same. All proposals are welcome.
Only knowing that your article is quite small, need more tooling detail for better advise:
1) How many cavities and cavity positioning in the tool?
2) What is the machine tonnage?
3) Need the parameter for the speed and screw positioning, such back and injection pressure, machine barrel or hot runner temperature setting
4) Actual tool temperature.
5) Is there sub inserting at bottom of article for air releasing?
6) Pre-heating of resin: temperature and period?
The mold has 1 cavity
Machine is about 150 tons
As I check the process temperatures they we according to recommended parameters (by resin supplier).
Venting is fine. There are no "burn marks". Of course It might be drying but in that case you should see silver lines which are specific for this kind of failure.
If there would be a small notch in the cracked area it might a problem. But if it is there for years why would cracking occurs after couple days and why not before but now in few lots. The parts are stored in room temperature.
Best of luck,
I was also thinking about chemical reaction which where PC can partially lose its properties. I have been told that such chemicals should not be present during molding by supplier or at our shopfloor during assembly. But I can try to ask once more.