Nucleated Nylon 6/6/6

[Jim]

Hello all, We have been running a variety of lens housings for a few years with nucleated Nylon 6/6. We are currently in the process of switching to a nucleated Nylon 6/6/6. This is a cost reduction move. We have been experiencing micro-voids, or pits, with the new material. Have been in touch with the resin tech. people and have tried their suggestions of higher back psi., longer residence time, and higher melt temperature. So far, we have had very little luck. Being a nucleated resin, we are thinking that we are getting air trapped in the melt, or some partially melted pellets. Have not been able to pin down the root cause of the problem, hoping that some of you may have had some experience with this material. We have switched to larger barrel machines to try to maximize residence time, and always check the moisture content before molding. One other suggestion was using a Pulsar Barrier/mixing screw, not to winged on laying out that kind of money. The product gets plated after molding, which tends to enhance the defect. We have some tech. reps. coming in to help, but any input from you guys would be most appreciated.

Thanks,
J.P.

[M&M]

Pits on the surface correct J.P.? If so I don't see it being trapped air but you could increase the venting with less clamp or some P/L 'tape' to prove that out. and lack of resin is, well a lack of resin so the question would be how to get more resin where the void is right. Being a nuked resin it is going to set-up double quick and I would guess that there PA6 part is going to make it quicker then the 6/6. So the heat aspect in the barrel makes sence and I would try some extra mold temp also like a lot gues to prove it is or it isn't going to help. Failing that how about a double quick injection speed to see if there is a gain to be made from theadded shear throught the gates. If that does help maybe that shear could be added with a smaller ID nozzle tip in place of the lower fill time, and go back to the same fill time as the PA 6/6.

[Jim]

Thanks, Mike.....gonna run some parts Monday afternoon with the tech. reps., will post some results.

[rickbatey]

What is the steel/water temps? Could be you are on the low end (or high end) for the resin. Could you also be too hot/excessive residence time for the melt? Those tricky nucleated, appeareance modified, UV or FR resins seem to NEVER process like the sheets state! Keep us posted! Rick.

[Jim]

Update on the nuked nylon; went with hotter molds, higher melt. temps, longer residence time, and higher back pressure. Kind of goes against some of my thinking about nylon with the higher back psi., faster screw speed, but it works with this type of resin. Thanks to Mike and Rick for the input.

J.P.