Injection molding stages

Fig. 7. The thickness distribution of the blown prodncts at different melt tempaatures during injection molding stage.

Blends of polypropylene (PP) and liquid crystalline polymer (LCP) processed without melting the LCP were compared with conventional melt processed blends. In a first stage, PP was blended with 20 wt% of LCP in a twin-screw extruder with the take-up speed varied to achieve blends with different LCP fiber dimensions. In the second stage, these blends were processed both below and above the Tm of the LCP by extrusion and injection molding. 

We can explain the injection molding process with reference to the molding cycle illustrated in Fig. 13.2. The cycle consists of four stages injection, packing, cooling, and ejection. 

Pj hydraulic back pressure for an injection-molding plasticator (Eq. 10.22) maximum power rating for the motor in watts Pr pump ratio for a two-stage screw... 

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. 

PHENOL-FURFURAL RESIN, A phenolic resin that has a somewhat sharper transition than phenol-formaldehyde from the soft, thermoplastic stage to the cured, infusible state and can be fabricated by injection molding since it has little tendency to harden before curing conditions are reached. 

The so-called RIM-process (reactive injection molding) is a current realization of the reactive molding process. The heart of the process is the shock mixing of the reactive ingredients, which is achieved by collision of two jets injected at a pressure of 10 - 20 MPa. The reactive mixture is injected into the mold in a laminar flow regime the pressure at this stage does not exceed 0.1- 0.4 MPa.259 The practical development of this method relies on automatic control systems and modem high quality equipment. 

Figure 4.70. Processability diagram (moldability) for the stage of mold filling in reactive injection molding dependence of material temperature (or average temperature on flow rate G). I - premature filling II - poor impregnation mixing III - flow instabilities.

The poppy plant produces raw opium. Crude refineries modify the opium into a brown paste that is molded and dried into bricks. More sophisticated laboratories are found in Bangkok, Karachi, and Hong Kong. These labs change opium into what is known as number three heroin, a smokeable form. Purification of heroin to the injectable fourth stage (number four heroin) involves a volatile chemical combination that can result in catastrophic explosions. 

H.H. Chiang. Simulation and verification of filling and post-filling stages of the injection-molding process. Technical Report 62, Cornell University, Ithaca, 1989. 

S, -W. Kim. Three-Dimensional Simulation for the Filling Stage of the Polymer Injection Molding Process Using the Finite Element Method. PhD thesis, University of Wisconsin-Madison, 2005. 

L.-S. Turng and S.-W. Kim. Three-dimensional simulation for the filling stage of the polymer injection molding process using the finite element method. To be published, 2005. 

Fig. 13.31 Schematic representation of the stages of the gas-assisted injection molding process for a container handle.

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