Reciprocating injection machine

Injection Molding. Any standard design plunger or reciprocating screw injection machine can be used for PEA 340, although a reciprocating screw machine is preferred (32). Slow injection into mold cavities avoids surface or internal melt fracture, and control of ram speed is important at low... 

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. 

The use of multinozzle injection machines. In general, this type of machine has a horizontal reciprocating screw that feeds four injection nozzles each connected to a single cavity mold thus minimizing waste. However, one concern with this approach is the need to have the mold accurately lined up (the top and bottom surfaces of the mold will be in the vertical plane) to eliminate compound leakage at the nozzle/mold interface. 

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. 13.1 (a) Reciprocating-screw machine, injection end. (b) Two-stage screw-plunger machine. 

Use is made of screw tip valves, popularly called non-return valve, ball check valve, or sliding ring valve. They are used in reciprocating injection and injection blow molding machines (IMM and IBMM) to control the melt flow in one direction (Chapter 4). There is also the smearhead for IMM, IBMM, and extruder. Back flow will not occur... 

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

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. 

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. 

Injection molding is the most popular and versatile process for manufacturing plastic products. Using a reciprocating injection molding machine as an example, as shown in Fig. 3, polymer pellets are firstly fed into the hopper, which delivers the resin to the plasticizing screw. The screw rotates and the polymer pellets are fed into its channels. 

Reciprocating screw injection machine recommended with 400°C max., cylinder temperature and injection pressure of 1000-1500 kgcm-2... 

A reciprocating-screw machine is an exunder system that has the advantages of screw plastification and ram injection in the same unit. In this design, as the screw rotates, it is pushed backwards by the molten polymer that collects in front of the screw. At a predetermined point, rotation stops and the nozzle moves in the forward position, acting as a ram to force the melt into the mold. It remains forward until the mold gates freeze, then pumps back to repeat the cycle while the mold opens. 

Elco Plastics Ltd of High Wycombe, Bucks, mould the TV screen surround on a Battenfeld BM 2 x 3200/500 S-C co-injection machine. That is, a 500 ton (5 MN) clamp force and two plasticizing cylinders each with 3200 cm swept volume capacity. The reciprocating screws in the plasticizing cylinders were 110 mm diameter with a L D ratio (length to diameter) of 15.5 1. 

Injection machines are classified generally into three types—reciprocating screw, ram or plunger, and two-stage or preplasticizers— described in the paragraphs that follow. Most injection... 

Figure 4-4. Section of In-Line Reciprocating Screw Injection Machine, Showing Screw Zones and...

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