carlbud
Mechanical
- Mar 7, 2005
- 23
We have built a cavity to mold a 6" X 6" X 1/2 thick plate of Fortron with 40% glass (similar to ryton R4. We are having trouble with some slight porosity in the center of the parts. We then made the cavity smaller in steps to the point that the cavity is now 3" X 3". The runners are 5/16 dia.and the gate is a full length fan gate along one edge and is .175 thick where it enters the cavity. We have added overflow tabs around the part to get rid of some of the cold material at the end of the part. We have pretty much eliminated the trapped gas voids that we had in the beginning but we still have slight porosity in the center of the .500 thickness. We have tried a variety of injection speeds and pressures along with hold pressures and times. We are running it in a 230 ton press. Our customer wants to use these plates to machine small connectors and the porosity shows up when they cut them. In sampling we skim cut the plates .030 at a pass and the first .170 of depth looks great. When we get past that the material show areas of a slightly different color and some porosity.
In some discussions with the material supplier he mentioned shrinkage voids but I have not been able to get in touch with him again to discuss further. I am thinking that this is what we are struggling with since the porosity seems to be only in the center of the plate. It makes sense that the material will cool faster on the outer surfaces and thus leave nowhere for the hotter material to shrink as it cools without creating voids. We have never molded anything this thick so we have not experienced this before. Also the fact that the customer cuts it up and needs the material to be solid all the way through is a unique situation.
Does anyone have any general advice on how we might improve this situation through molding parameters or tool modification?
Thanks,
Carl
In some discussions with the material supplier he mentioned shrinkage voids but I have not been able to get in touch with him again to discuss further. I am thinking that this is what we are struggling with since the porosity seems to be only in the center of the plate. It makes sense that the material will cool faster on the outer surfaces and thus leave nowhere for the hotter material to shrink as it cools without creating voids. We have never molded anything this thick so we have not experienced this before. Also the fact that the customer cuts it up and needs the material to be solid all the way through is a unique situation.
Does anyone have any general advice on how we might improve this situation through molding parameters or tool modification?
Thanks,
Carl