One of our products which is made of PA 6.6 retardant treated, injected into a mold with two cavities crack in the union area of flow fronts, strange is that only one of the pieces crack, and we do not have any success whatever we do. THANK YOU FOR ANSWERS!

Hi Valentin, Difficult to say without knowing the full story but there maybe a clue in that one impression is ok, the other not. A few basic things to try first. Are both impressions filling equally, have you conducted a series of short-shots, or even better, are you able to install a pressure transducer in each impression (costly but in my experience worth every penny)? Are the surface temperatures of both impressions equal (both core and cavity)? Is gas venting incorporated in both impressions in the weld-line areas particularly but also at the split-line, if so, is one blocked? Does the product from the "good" cavity not crack at all, or is it just a bit better then the "bad" one? These are just a few very basic things to look at first, you may well have already tried them but as I say, without seeing the full picture and knowing the history of your mould trials it is difficult to be more precise. Hope this helps but if not please do come back to me with more detailed information.

Hi Valentin

I have 2 suggestions. maybe the trouble isn't the injection molding parameters.

Please consider this trouble in 2 directions.
1) The wall thickness of the crack position. maybe too thin.
2) the mold factors: is the runner flow is balance for the 2 cavities ? is there any air trap for the crack position ?
Hope this information is useful for you .
Thanks
Jeson Chen

Hi Valentin,

Not sure if the crack was happened after an ejection , And cannot be able to see the part feature . Pls check the ejection pins status in the tooling . Especially the crack one cavity.

Hi VALENTIN
Both Rita & Jeson have good input on this - i think a mouldflow analysis would help to show if there is hesitation/temp/pressure/shear in the flow causing a bad meld of the 2 flows coming together.

Thanks for answers,I tried most of your suggestions but I will try once with greater attention,is likely to be wrong somewhere ,for more details of mold I can say that was designed to produce four cavities but at this part we work only with 2 cavities because of a defect occurred in the past at this mould,we work with 2 only at this part-number in rest use 4 cavities with no problem, i try to change the position of the bad cavity ,up,diagonal or side by side from good cavity....and one more detail the good cavity not crack at all,even after strength tests and the bad one crack even when i push with my finger...
Thank you all again for your help
Respectfully,VALENTIN

could you please check 4 points
1- ejector position
2- cooling rate of the part
3- sticking in cavity/core side.
4- packing while mould processing