IMM 3/97

We are molding a nylon 6/6, UV stabilized, around a steel insert. The problem we are having is an inconsistent splay on about 1 percent of the parts produced, which is equivalent to $50,000 per year. We have tried the following: installed new dryers, added vents, enlarged gate, installed nylon screw and nozzle, increased diameter of sprue, and increased cycle time. Inserts are loaded robotically, consistent cycle. Any suggestions?

We currently run a similar part using a PA and PPE alloy. We minimized our splay problem by increasing the zone temperatures, near the maximum limit. Countermeasures for shear such as enlarged gates had little effect on our problem. Controlling the regrind ratio provided a more consistent splay pattern. As the viscosity is changed by increased zone temperatures, the shear will decrease, thus reducing splay. Regrind pellet size should also be as consistent as possible. We had our splay analyzed by an outside lab and found that the splay was indeed caused by degradation because of shear
-A. Davidson, Sumitomo Electric Wiring Systems, Scottsville, KY, (502) 237-5419.

First of all, be certain your inserts are clean. Secondly, you might want to preheat them-to remove any surface moisture-to around 100F to 200F prior to molding.
-R. Cianfrocco, Apex Engineering, Pittsfield, MA, (413) 442-1414.

First, I would check the dewpoint of the resin. A new dryer doesn't mean dry material. Incorporate vacuum venting within your tooling.
-M. McGown, Clinton, MA, (508) 368-1243.