In the picture you can see that there are some failure, we can avoid them if we put a paper between the mold and part in mold injection process. but it is not feasible. Do you have a similar problem with parts if they are thin? Is there any spray for this problem?
Dear Sara
Have you tried to preheat the mold prior the mold injection process.
The pre-heatment of the mold may help to get rid of the gases in molten
part in order for gases to not trap after the molten part becomes a solid.
Hello Sara,
Assuming that these defects are caused by trapped air, I would recommend you:
1.- To decrease the injection speed for decreasing the turbulence in the melting,
2.- To add vents (small cavities, of 0,025 mm, to release trapped air) in the problematic areas,
3.- Normally air trapped appears in the areas that fill last. So you could try to change your injection gate location (However, this is more costly).
I hope everything goes well!
Dear Khaed and Carlos,
Thanks for your help.
1- Yes, we do preheat the mold for one to two hours before injection.
2- About the subject if they are trapped air defects or not, I should mentioned that I'm not sure. I cut through them, they aren't hollow. They are filled but soft moles on the low-depth surface.
3- The place of moles is different on the surface.
4- We added some vents (thin circular slit), but the problem does not solve.
5- Please, pay attention that we tried porous material like Teflon paper between mold and part, therefore we didn't have this failure. But it is bot efficient and on top of that is time consuming. That's why I am looking for a spray!
I add some more pictures to clear the concept of defects.
Thank you all, in advance.
Dear Sara,
I forgot to ask, which polymer are you injecting? I am asking because maybe you are using a hydrophilic material that requires pre-drying.
Considering that these defects appear in different parts of the mould and it's reduced by adding Teflon paper, I agree that the problem likely comes from the interaction mould/material. Saying this, one option (besides the spray you proposed) is to increase the mould temperature.
Also check the temperature and shear rate used in the injection machine: these moles may be un-molten pellets or in the opposite case, degraded.
It is a compound based on natural rubber.
NR isn't hydrophilic. How mold temperature would be helpful?
Even if it is promising, we have checked the process condition up to now.
The general idea is to reduce the delta temperature between the polymer flow and the mould surface. This normally improves the finishing of the injected component
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