A retrofittable product, the FlushTrim insert, is designed to provide a simple means to separate edge-gated parts from their runners while the parts and runner systems are still in the mold. The inserts are precision machined from hardened tool steel for long life, and they are interchangeable for resurfacing or replacement. Available in three main sizes and a variety of gate openings, they each require a stepped retaining pin and bushing.

For installation, receiving pockets are sunk into the A and B plates and a stepped hole is drilled for the retaining pin. The pin is then inserted into the B plate and moved beyond the face of the mold to receive the insert. Then the pin and insert are pushed into place in the mold, and the bushing is fastened to the pin to retain the in-mold assembly. A large ejector pin close to the insert is used to distribute the degating force over a large area of the part. Adequate distance between the runner and the insert is required to allow the tab to deflect upon ejection and degating.

Here?s how it works: The FlushTrim insert remains stationary in the mold. As the ejector pins move forward, the gate is sheared at the part cavity wall by the sharp edge of the insert. The tab connecting the runner and the cavity is deflected by the insert (see illustration). With a cored part, the retaining pin must be able to clear the core during insert installation so the insert can mate with holding features on the end of the pin. The face of the insert should be in the line of draw; otherwise, the part surface may be marked during ejection.

When degating on a curved surface, a maximum of .5 mm of material can be removed from the insert to accommodate the part?s curvature. Tapered straight and curved seal-offs to properly seat the insert into the mold are required. When degating on curved, cored surfaces, all of the above procedures must be followed.

For optimum gate trim quality, the manufacturer recommends machining the ejector pin to provide a flat close to the FlushTrim insert. This small gap improves the shearing action during ejection, resulting in a cleaner trim. International patents are pending on FlushTrim inserts. They are presently being field tested, and prices have yet to be determined.?Carl Kirkland

Cavity Balancing Systems
Kitchener, ON
Phone: (519) 571-0204
Fax: (519) 570-9824
E-mail: [email protected]