I have a problem with a Round Condenser Cover in PPGF30% Black. The material seems too brittle / hard on moulding when compared to competitor samples. Ball drop test failing 200gms from 12 inches. The outer diameter of the part is 300 mm with ID (where fan motor rests) as 100 mm. There are 8 circular ribs (equally spaced of thickness of 2mm each) moving from center towards outer diameter. There are 12 nos of vertical ribs directly connecting the ID to the OD (avg thickness 3.7 mm). 4 nos of fan type gating with runner path 11.5 mm thick. Weight including runner is 290 gms. I hope this gives you fair idea of the part design.

We have tried raw materials from different suppliers with different impact and izod strengths. Nothing seems to be working. Temperature in barrel has been re-calibrated with external thermometer number of times. Temperature set from 220 in nozzle to 160 degrees at hopper on a 350 ton machine. Two different types of impact modifiers have been add (Upto 3% dosing) and trial taken, no positive effect noticed. 2% EVA also added with no result. All trials tried with anealing and dry as well. Mould preheated each time to 90 degrees Celsius. Due to circular nature of part, we are also facing weld lines in the ribs. Breakage happens mostly at weld lines, but frequently outside of the weld line too.

Would really appreciate any inputs from anyone. The entire project seems to be on verge of collapse.

Thanks in advance.

Please send photos of part and runner before degating and after degating. Also send photo of break and if possible show how the part is fixtured for the impact test. You indicate a falling ball, but the normal falling dart impact test uses a cylindrical steel slug with a ball nosed face, is this what you are using (Gardener Impact test.) Since you indicate a fan style gate. What are the gate dimensions and the runner geometry? PPGF30 is a pretty tough resin and you should not have this much difficulty obtaining a good strong part. Are your ribs drafted and polished properly? You could be prefracturing the part during mold open or part ejection. Bear in mind that PP is a semicrystalline resin but can delaminate under conditions of excess shear (Excessively high injection flow rates, excessively high screw speeds, worn or damaged screw flights, flowing past sharp corners in the runner or cavity, etc.)

Your description sounds like inadequate fill and or mold cavity pack out. Do you have vents in the mold? If so where are they located, and how deep are they.

Lastly if you can supply the complete process information including velocities pressures, timer settings,

I may be able to point you toward some things to try after reviewing photos and documentation you send.

Mike Marson
Senior Engineer

I agree with Mike, you should now try to eliminate all causes and forget the resin itself. If you have weldline issues that is due to too difficult filling (too thin part), inadequate wenting or lack of power from injecting. How about the residence time? don't exeed the max value.
Do you have a chance to try moulding in another perhaps stronger machine?

Dear Mike,

Thanks for your very prompt response. Please give me a day to give you all the details you have asked for. I will be in office tomorrow and promise to send them immediately. Meanwhile i would appreciate if i could get your email address to send the details.

Regards,

Ashwin.

Have you done a short shot study to determine if your fill is balanced and the weld lines are where you think they are. Correlate these to the failure mode.
You mention "4 nos" of fan gates. Is this a two plate mold, semi hot or three plate. Your flow path may be excessive and melt temps dropping off.
Waht is the thickness of the part? have you looked at the failed sections to determine if the glass is all being pushed to the walls so that you do not have good mixing throughout the resin. This will cause a weaker part. I've had this happen on thick walled glass filled parts. To the earlier point on gate sizes, are they sized properly to develop proper shear rates for injection. and are you injecting fast enough? If injection rate too slow you will have issues associated with packing as noted above.
just food for thought.