Two-stage machines

Injection stretch-blow molding may be performed on a single one-stage machine in sequence or on two independent sequential two-stage machines. PET carbonated beverage botties are usually produced by injection stretch blow molding. 

Today, large polyolefin extruders are built as ZSK MEGAcompounders, mainly as 320, 350, and 380 Me sizes. The reason for this is clear from Fig. 14.8 which shows the same relationship as Figure 14.7, but specifically for polyolefin applications, here with the ZSK Me limit curve for maximum throughput. Normally, the torque limit is only reached with LLDPE and FfDPE if pressure is also built up by the ZSK and the powder from the polymerization reactor is coarse enough to prevent intake problems. With PP or melt-charged LDPE or two-stage machines for bimodal polyethylene, the torque required is well below the Me limit curve. 

Multiple-screw extruders can involve either two screws (twin-screw design) or four screws. A typical four-screw extruder is a two-stage machine, in which a twin-screw plasticating section feeds into a twin-screw discharge section located directly below it. The multiple screws are generally sized on output rates (Ib/h) rather than on L/D ratios or barrel diameters. 

Efficiencies for the rotary-vane pump are based on a two-stage machine operated as a dry compressor. 

Industrial air compressors also have intercoolers. These compressors are two-stage machines. That means air is compressed part way in one cylinder and the rest of the way in another. As with turbochargers, the first compression raises the air temperature. An intercooler is often installed between the cylinders. Compressed air flows through the intercooler tubes. Either atmospheric air or cooling water flows around the outside. Cooling the air before the second compression reduces the power required there. 

Not running at rated speed Horsepower higher at increased suction pressure Two-stage machine not operating in tandem Valve parts left in crank-end when operating on head-end... 

Fig. 13.31A depicts the wall of a preform as it exits a reheat oven. Fig. 13.31B depicts the wall of a preform as it leaves the single-stage process second station. Fig. 13.31C depicts the ideal that is sought on both processes. A single-stage process will produce a more optically clean container. The two-stage machine will produce the best barrier bottle plus better wall distributioa... 

One alternative approach to the two-stage steam moulding process is that in which impregnated beads are fed directly to an injection moulding machine or extruder so that expansion and consolidation occur simultaneously. This approach has been used to produce expanded polystyrene sheet and paper by a tubular process reminiscent of that used with polyethylene. Bubble nucleating... 

Poly(ethylene terephthalate) film is produced by quenching extruded film to the amorphous state and then reheating and stretching the sheet approximately three-fold in each direction at 80-100°C. In a two-stage process machine direction stretching induces 10-14% crystallinity and this is raised to 20-25% by... 

In the more favored multi-stage axial flow design the bladeing is of the impulse type (known as a Rateau or Curtis type stage) or of the reaction type. It is popular among manufacturers to design multi-stage machines with a combination of these two types, and the most common combinations are ... 

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