Mold-cavity unit

Injection molding involves two distinct processes. The first is melt generation, mixing, and pressurization and flow, which is carried out in the injection unit of the molding machine. The second is product shaping, which takes place in the mold cavity. Injection molders, therefore, have two distinct parts the injection unit and the mold/clamping unit. The function of the injection unit is to melt the polymer and inject it into the mold the function of the clamping unit is to hold the mold, open and close the mold, and eject the finished product. 

Inevitably, in multi-cavity injection molds, some of the mold cavity gates are located further than others from the sprue that delivers the melt from the plasticating unit. If the runner system that distributes the melt from the sprue to the individual cavities has a constant... 

Injection equipment consists essentially of two parts the injection and clamping units. The injection unit melts the polymer and injects it in the mold. The vast majority of modern injection presses use a reciprocating screw. As in an extruder, the screw rotates, melts the polymer and pumps it. Furthermore, in most injection molding units, the whole screw can also axially move forward, acting like a plunger to inject the resin into the mold cavity through runners and gates. 

Although the transition from compression molding to injection molding has been extensive for phenolics, the same cannot be said for UF Materials, because they are more difficult to mold, possibly because the UF are more brittle than a phenolic resin and so are less able to withstand the stress peaks caused by filler orientation during molding. A combination of compression and injection processes has therefore been developed in which a screw preplasticizing unit delivers preheated and softened material directly to a compression-mold cavity. 

IM is a repetitive process in which melted or plasticized plastic is injected or forced into a mold cavity, where it is held under pressure until removed in a solid state, basically duplicating the cavity of the mold (Figure 5). The mold may consist of a single cavity or a number of similar or dissimilar cavities, each connected to flow channels or runners that direct the flow of the melt to the individual cavities (Figure 6). Three basic operations exist (1) raising the plastic temperature in the injection or plasticizing unit so that it will flow under pressure, (2) allowing the plastic... 

A further development of TM is to plasticize the mbber mixture in a screw-type extmder solidly attached to the press, heat it up and inject it into the transfer cylinder. Closing the clamping unit then fills the mold cavities as in normal TM, Fig. 44 [7]. 

The two wings have the same injection volume so that a single hot runner distributes the melt from the injection cylinder between the two mold cavities. The prior injection unit and the finished part are produced at the same time, whereby... 

Above all, the plasticating and injection unit must convert this gramdate into a homogeneous melt, capable of filling the mold cavity completely. In other words, the ensuing melt must be pourable. For that purpose, the molding compound is heated, until it melts (Figure 3-3). This is achieved by friction... 

The molding compound, which has been homogenized and melted in the plasticating and injection unit, is injected into the mold cavity in the injection operation. There the molding compound soUdifies to form the finished molded part. As soon as the molded part has soUdified, it is removed Ifom the mold by opening the mold at the parting line. 

TYPE PERCENTAGE USED WITH IMM NO. OF MOLD CAVITIES PART SIZE COST/UNIT DOLLARS... 

Molding pressure n. The pressure applied to the ram of an injection machine or press to force the softened plastic to completely fill the mold cavities. It is expressed in force per unit of cross-sectional area of the ram surface acting upon the material. 

Sandwich foam molding, also called coinjection molding may be considered a special form of sandwich molding. Two injection units are used to produce the skin and core as separate operations. First the skin material is injected then, through the same sprue, the core foamant is injected. The mold cavity expands, allowing the core to foam. This is a process that has been patented by ICl of Great Britain. 

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