Injection machine check valve

Injection Machine Check Valve A free-flowing sliding ring check valve is recommended for use with SPS. A sliding ring check has less restriction and will have a lower pressure drop than other check valve designs. 

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 14-44 Schematic diagram of a check valve in injection molding machines (top) during plastication and (bottom) during injection. 

Injection molding is a cyclic discontinuous process used to form three-dimensional plastic parts (25. 26). Both thermoplastics and thermosets are injection molded. The process is shown schematically in Figure 11 for a reciprocating screw injection molder. This type of a machine has a screw rotating in a barrel similar to an extruder. However, here the melt flow is discontinuous and controlled via a check valve at the tip of the screw. Material is melted in the extruder, and the melt is accumulated in front of the screw tip until sufficient melt is at hand to fill the mold cavity (cavities). 

Plastication unit design. The role of the plastication part of the machine is to mix and melt the polymer and the additives, homogenize, pressurize, and feed the melt to the transfer section of the cylinder through the check valve. Plastication takes place at elevated temperatures (230°C-400°C) depending on the type of the plastic. Polyvinylidene fluoride is injection-molded at the lowest end of the temperature range while PFA is processed at the highest. 

Figure 125. Injection molding machine parts composed of Mo2FeB2-based alloys (a) cylinder (b) auger (c) check valve (d) seal ring (e) auger head.

Advances in simulation technology have led to several attempts to link the results of simulation to the injection-molding machine. One of the difficulties in doing this is that injection-molding machines have characteristics that are not easily accounted for in simulation. For example, the ability of the machine to respond to a desired change in process conditions is not known nor is the performance of the flow check valve. Nevertheless, simulation can be used to get somewhere near an optimum set of process conditions. The setup can then be fine-tuned to optimum performance. 

By virtue of a check valve on the forward end of the soew (Figure 14.22), (he reciprocating screw can push forward without rotation and act just as the plunger in an ordinary injection-molding machine. The screw may remain forward, whereas the melt cools or, in the case of rubber, the polymer in a hot mold cross-links. The steps of the cycle in a reciprocating-screw injection-molding machine consist of the following ... 

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