Compression sleeve molding

Laminated tubes are made from multilayer materials that usually contain paper as well as plastic, and often also include aluminum foil as a barrier layer. The preprinted tube bodies are sealed into a cylinder, with the edges of the sleeve overlapped and compressed, squeezing some of the plastic out around the raw edges of the foil and paper to make a good seal. Next the tube is cut to length, and finally the head is molded and assembled to the body. To improve the barrier in the head, a premolded insert of polybutylene terephthalate or urea can be incorporated in the injection mold when the head is formed. 

Once the molded part has cooled sufficiently in the cavity, it has to be ejected. This is done mechanically by KO pins, KO sleeves, stripper plates, stripper rings or compressed air, used either singly or in combination. The most frequent problem in new molds is with ejection. Because there is no mathematical way of predicting the amount of ejection force needed, it is entirely a matter of experience. 

Ejector pins often leave compression marks on the molded article. They should not be used on the visible part of the article, if this can be avoided. Another example of an ejector is the sleeve-ejector (Figure 4-12), which is able to transmit greater ejection force. Slccvc-ejectors are primarily employed with moldings, which are axially symmetrical. 

A carbon fiber bicycle wheel rim is fabricated by Sun Rims saving 400 g over an A1 rim and with 30% less carbon than that achieved by competitors using carbon fiber braid. A core of foam is rolled into a circle to fit the mold rim periphery and a braid sleeve drawn over the core with the ends overlapped. Extra pieces of carbon fiber prepreg are positioned at high stress points, the reinforcement is impregnated with epoxy resin and the lay-up is then compression molded. The pressures are sufficient for the overlap joint to be uniformly incorporated into the rim thickness. 

Ejector pin (ejector sleeve, knockout pin, KO pin) n. A rod, pin, or sleeve that pushes a molding off a force or out of a cavity of a mold. Attached to an ejector bar or plate, it is actuated by the ejector rod(s) of the press or by auxiliary hydraulic or compressed-air cylinders. 

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