Injection Mold Units

Injection molds have two main parts, or platens. Typically the half containing the hollow cavity side is attached to the injection molding machine, and is referred to as the fixed platen. Because the melted plastic enters through this side, it is also called the hot side, or the hot half (Fig. 11.2). 

The section of the mold containing the convex core is usually the piece that moves back and forth to open and close the mold, and is referred to as the moving platen. In some designs, especially in stack molds, the mold cavity is mounted on an intermediate section called the floating platen, rather than directly on the injection molding machine. 

To achieve accurate dimensions in the finished part, the mold cores must be aligned accurately with the cavities. Mold halves have large guide pins in the corners to assure alignment. 

The mold is cooled, usually by water, to solidify the plastic. When the plastic object has been cooled sufficiently to maintain its shape, the mold is opened, along the mold parting line, and the object is ejected. The cycle time in injection molding depends on the size of the molded part, as well as on the molding conditions and on the thermal and mechanical characteristics of the plastic being molded. In some case, the cycle time can be as short as two seconds. 

Injection molds are usually made from high quality tool-grade steel. They may include beryllium copper inserts to improve heat transfer rates for more rapid cooling. Molds are quite expensive, and often contain wear plates that can easily be replaced, so that the molds can be more easily refurbished and have a longer life. 

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In addition to high-speed photography, which was used to obtain the results discussed above, other methods have been used to visualize flow, for example, the tracer method.279"281 A typical experimental device consists of a capillary viscometer connected to a mold, which is a simple model of plunger-type injection molding unit.279 A special device was used to introduce tracers of different colors in regular succession. After sample solidification, it is possible to examine the position of the various colors on the surface (Fig. 4.47 a) or through the volume by cutting sections (Fig. 4.47 b). It can be seen that the tracers are positioned symmetrically near the surfaces and that they have a V-type shape, with the tip oriented toward the stream. 

Ram and piston injection molding units are used in the rubber iudustry [57]. The rubber stock is fed to a heated cyliuder, which is heated to the required temperature aud from there is forced by a hydraulic ram through a nozzle, mold runners, and... 

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. 

Time a resin spends in a given processing machine (an extmder, injection molding unit, etc.) and is subjected to heat and stress. 

This process can also be performed with a screw extruder. There are two ways of doing this. One, the screw-transfer method, uses a plasticating extruder, which not only replaces the preheat and preform portions of the cycle but also loads the pot. Another way of providing the material to be molded is to use a screw injection-molding unit. 

The direct manufacture of prototype molds using the rapid prototyping process offers significant advantages (see also Section 4.7). By LaserCUSING and adapted processes, molds without restriction for prototype and small-series production can be used. Also, highly filled thermoplastics of up to 70% GF can still be manufactured to several thousand injection molded parts on standard injection molding units. 

In some injection-molding units, the hydraulic ram is replaced by a rotating screw (Fig. 1.7b), which transports the polymeric material into a reservoir immediately behind the nozzle. During the injection process, the screw stops rotating and acts as a ram to push the melt into the mold. A better understanding... 

FIGURE 1.11 Typical injection molding unit. (Reprinted by permission of the publisher from Tadmor and Gogos, 1979.)... 

FIGURE 10.3 Flow rate and pressure in the reservoir of an injection molding unit as a function of time. 

Various footwear soles unit soles, inner soles, and outer soles by injection molding... 

The past introduction of TP materials into the area of printed circuit substrates has led to a broader type of application for the circuits. The products can be injection molded and the circuit applied to a molded part which will have a molded-in connector structure used to interconnect the device to the rest of the system. By combining the connector and substrate functions, it is possible to make very compact printed circuit units. 

An ounce is a unit used to represent the capacity of an injection molding machine, showing the polystyrene equivalent weight of polymer for one shot . 

Potente, H., Effen, N., and Liu, ]., Throughput Calculation with Considerations of Leakage Flow on Injection Molding Plasticizing Units, Polym. Eng. ScL, 36, 1557 (1996)... 

Isosorbide polyurethanes, especially those based on aliphatic isocyanates, may be useful in the same applications as conventional polyurethanes i.e. thermoplastics, coatings, and foams. In fact, excellent rigid foams have been obtained from P(I-MDI)(5). Isosorbide has a low melting point of 61°C and it is suitable for use in reactive injection molding processes alone or in the form of a mixture with other conventional diols. In addition, its polymers may also find specific applications due to the anticipated high complexation ability of the two tetrahydrofuran rings in their isosorbide units. 

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