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Tech Tip April 98

GATE LOCATION

In the past, I have discussed gate design in reference to sizing, freeze times and types. Yet not where the gate should be placed. The placement of the gate is key. This will be determined by the OEM in some cases, usually where it can't be, but if you can influence the placement, the following may be of some help.

Place the gate where it will not interfere with the structure of the part. In other words, you do not want to place the gate in a high stress area where a load is applied or you have flexing going on.

Place the gate where the resulting weld line does not interfere with the structure of the part. With this you must think of where and how is the material going to flow and what is important of the part and function.

Always have the material flow from thick to thin in regards to the wall thickness.

Place the gate or design thereof so the flow front coming out of the gate impinges upon a wall, pin or some such thing. This way, you can minimize the possibility of jetting and having to adjust your molding process.

With cosmetic parts, you can place the gate in an area where a blush does not hurt you. If this is not possible, you can use a different design of gate or runner to minimize the effect. (See previous tips.)

Thanks for the time. More on the subject next time.

Steven L Silvey
Sr. Technical Service
General Polymers Division/
Ashland Chemical