Injection molding machines reciprocating

Figure 12.12 Injection molding machine reciprocating extruder terminology and typical design parameters. The nonreturn value (R) is illustrated in Figure 12.13...

Fig. 13. Injection molding machine A, hydiaulic motoi foi turning the screw B, hydraulic cylinder and piston allowing the screw to reciprocate about three diameters C, hopper D, injection cylinder (a single-screw extmder) E, no22le F, fixed platen G, tie rods H, mold I, movable platen , hydraulic cylinder and piston used to move the movable platen and supply the force needed to keep the mold closed and K, machine base.

Figure 20 A horizontal reciprocating screw injection molding machine.

To ensure consistency, the two critical areas for control specific to injection molding are shot size control and temperature control on the injection system, i.e., screw portion for the reciprocating screw machines, and both the screw and ram sections for the screw/ram machines. As mentioned previously, for temperature and cure control, the use of microprocessor controls has significantly improved the performance of injection molding machines, including control of the shot size. 

Journal of Injection Molding Technology 5,No.3, Sept.2001,p.l52-9 MICROCELLULAR FOAM PROCESSING IN RECIPROCATING-SCREW INJECTION MOLDING MACHINES Jingyi Xu Pierick D Trexel Inc. 

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. 

Two systems have been used in injection molding machines to melt and inject the polymer. The most commonly used types use a reciprocating screw, which has many... 

William Willert filed a patent on the in-line, now more commonly known as the reciprocating screw injection molding machine in 1952. In 1953 Reed Prentice Corp. was the first to use Willert s invention, building a 600-ton machine. The patent was issued in 1956. By the end of the decade almost all the injection molding machines being built were of the reciprocating screw type. 

We further assume that the flow is steady in time. We make this assumption because most machines operate continuously, and even in reciprocating machines such as, for example, injection-molding machines, the flow can be viewed instantaneously as steady state. Finally, we assume that the fluid is incompressible and Newtonian, that the flow is fully developed, that is, dvz/dz 0, and that the gravitational forces are negligible compared to viscous forces. 

Fig. 11.30 Effect of preheating 50% by weight E-glass fiber-filled polyamide pulltruded pellets on fiber lengths at the screw tip of a 300-ton 23.86-oz reciprocating injection molding machine. [Reprinted by permission from C. G. Gogos, C. K. Yoon, and J. Brizzolara, Injection Molding Process Development for Long Fiber Reinforced Thermoplastics, SPE ANTEC Tech. Papers, 40, 384 (1994).]...

Fig. 13.2 The injection molding cycle. [Reprinted by permission from R. C. Donovan, An Experimental Study of Plasticating in a Reciprocating-Screw Injection Molding Machine, Polym. Eng. Set, 11, 353 (1971).]...

S. D. Lipshitz, R. Lavie, and Z. Tadmor, A Melting Model for Reciprocating Screw Injection Molding Machines, Polym. Eng. Set, 14, 553 (1974). 

Two-Stage" Injection Molding Machine. Instead of using a reciprocating screw to melt the plastic and to push the melt into the mold, the extruder screw may feed the molten plastic into a separate reservoir, and then a separate plunger can feed the melt into the mold. 

Intermittent accumulator EBM machines use a normal conventional axially fixed continuously operating extruder to prepare the melt. The accumulator is a heated reservoir where the melt is temporarily stored in the intervals between parison extrusion (similar action of a two-stage injection molding machine (IMM) as reviewed in Chapter 4. Also used is a conventional reciprocating IMM that delivers melt through a die into a blow mold. 

Figure 8.4 Schematic of foam reciprocating injection molding machine for low pressure...

Cyro produces a family of acrylic-based resins Acrylite , Cyrolite and XT). All types of injection molding machines can be used to mold these blends. If reciprocating screw machines are used, the screw compression ratio should not exceed 3.5 (to avoid material breakdown). Injection temperature should be the lowest at which the part will fill. Since the material has sparkling clarity, great care should be taken to avoid contamination. 

---