Screw/piston

Easy calibration of direct control lead screw piston drive with flow calibration software... 

Screw-piston injection molding See injection molding. 

Screw-Piston Injection Molding See Injection Molding. 

By using a screw/piston unit, the process of plasticizing and injecting can be controlled separately and is, therefore, better designed. Moreover, in the IM process, the entire process can be optimized by separate control or regulation of the individual processes. This opens up many possibilities and increases the complexity of this process immensely. 

In screw piston injection machines, the material is plasticised more homogeneously and has to stand less thermal stress than in piston injection units, as the plasticising itself happens just shortly after the... 

This is the most common type of unit and will be the basis for further discussion in this section. Thermoplastics as well as thermosets and classical elastomers can be processed with screw piston injection units with the process cycle as described in Chapter 1. 

Injection volume = screw-piston surface x stroke Injection pressure = injection force / screw-piston surface... 

Inj. volume x inj. pressure screw - piston surface x stroke x inj. force stroke x inj. force 1000 1000 screw - piston surface 1000... 

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.

Preforming. Extmsion preforming is easily accompHshed if relatively cool barrel temperatures are used with either a screw or piston type extmder (BarweU). It is important that the gums be used in the appropriate viscosity ranges, and that scorching be avoided. 

Adjusting (screwing) the piston rod further into or out of the cross-head for some single-acting units... 

In much the same manner as pumps, compressors are classified as one of two general classes positive displacement or dynamic (see Figure 3-68) [23]. These two general classes of compressors are the same as that for pumps. The positive displacement class of compressors is an intermittent flow device, which is usually a reciprocating piston compressor or a rotary compressor (e.g., sliding vane, screws, etc.). The dynamic class of compressor is a continuous flow device, which is usually an axial-flow or centrifugal compressor (or mix of the two). 

Another important positive displacement compressor is the rotary compressor. This type of compressor is usually of rather simple construction, having no valves and being lightweight. These compressors are constructed to handle volumetric flowrates up to around 2,000 actual cfm and pressure ratios up to around 15 (see Figure 3-69). Rotary compressors are available in a variety of designs. The most widely used rotary compressors are sliding vane, rotary screw, rotary lobe, and liquid-piston. 

Piston, screw and centrifugal compressors are used. As many chemical processes, such as oil refining, may have cheap waste heat, large absorption systems will also be found. 

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