Injection molding plunger-type

Injection molding is not new. A patent was issued in 1872 for an injection-molding machine for camphor-plasticized CN, celluloid. Almost all of the machines used today are reciprocating or two-stage screw types. Both types employ a reciprocating Archimedean-like screw similar to that of a screw extruder. A few are of the plunger type. 

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. 

Z molding compound (ZMC) was first prepared in France in 1979. This compound needs a special type of injection machine—a combination of plunger and screw—and was indigenously developed by Billion in France. The machine uses a screw to homogenize and measure the shot. The injection is made like a plunger by the displacement of the screw and inner barrel inside the main barrel. Compared to SMC, ZMC parts have lower mechanical properties, but higher performance when compared to conventional injection molded BMC. 

Fluoropolymers can be injection-molded in plunger or ram-type equipment but a screw machine works best with this family of plastics. The screw-type injection molding machines have a number of advantages including those listed in Table 6.23. Various components of screw-type machines for processing fluoropolymers are described in this section. 

The majority of commercial blend grades has been developed specifically for injection molding and thus can be processed in conventional machines as long as the processing conditions recommended by the blend manufacturer are followed. Reciprocating screw machines are preferred over plunger-type ones. 

FIGURE 2.7 Schematic drawings of (a) a plunger-type preplastidzer and (b) a screw-type preplasticizer atop a plunger-type injection molding machine. (After Lukov, L. J. 1963. SPE/., 13(10), 1057.)... 

An extruder. Fig. 17, has essentially the same structural components as the plasti-fication unit in a screw-type injection molding machine. Fig. 11. The screw in this case is not an axial plunger in the extruder it only rotates. The significance of extrusion per se is the continuity of the process. The method is used to produce plates, tubing, profiles, films, etc. 

The early injection molding machines were plimger machines. The plastic was melted in a heated cylinder and injected into the mold by the plunger. This type of machine is no longer found, except in research laboratories, for making very small quantities of experimental articles. Plunger machines are not discussed in this book. 

There are two types of machines that can be used for injection molding—one fitted with a plunger and the other a screw type injection unit, the latter being preferred for carbon fiber applications. Section 17.9.2 explains the functions of the individual parts of an injection molding machine and describes the terminology used for this application. 

Nevertheless, a terpolymer of styrene-maleic anhydride and acrylonitrile (S/MA/AN) met the specifications of superior thermal properties but it was difficult to injection mold using the plunger-type presses available in the early 1940 s. This objection was overcome by blending with NBR, SBR, or HIPS. 

The injection-compression mold has lateral sealings of plunger type (Figure 1.65) to ensure that the cavity is tightly closed during injection. 

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