Extrusion processes single-screw designs

A single-screw extruder (Fig. 12.1) consists of a hollow cylindrical barrel fitted with external heaters. The inner barrel surface is coated with a hard metal liner such as Xaloy to limit wear rates of the barrel and a compatible alloy hard wear surface can be added to the screw flights [27]. A screw is fitted into this cylinder with a specific geometry determined by the polymer and the desired thermal condition of the melt. The screw design chosen will determine the ultimate performance of the extrusion system and is rightly considered the heart of the extrusion process. The screw is driven by an electric motor through a... 

The performance of Double Wave screws was provided earlier by Kruder and others [20-22]. For these trials, the extrusion process was capable of higher rates and lower discharge temperatures than well designed conventional single-flighted screws. Three-dimensional flow simulations for a Double Wave and a Triple Wave section were performed by Fan [23] and Perdikoulias [24], These simulations showed the complex nature of the flows, including the acceleration of the flow as it... 

Most thermoplastic processes utilized for HIPS applications use a single screw to melt and pressurize the polymer. Screw extruders in industry used with HIPS can have screw diameters from 20 to 200 mm and can melt process over 2000 kg/h. Two-stage, vented screw designs are predominantly used for extrusion of HIPS, whereas single-stage reciprocating screws, with a nonreturn valve, are common in the HIPS injection molding process. 

The term dry extruder is applied to a particular type of single-screw machine. These machines were originally designed solely for processing whole soybeans. For this operation, the addition of moisture was not necessary because the high oil content of the beans acted as a lubricant during extrusion. Thus, the machines could reasonably be referred to as dry extruders. ... 

If an extrusion process requires a substantial amount of cooling, this is usually a strong indication of improper process design. This could mean improper screw design, excessive length-to-diameter ratio, or incorrect choice of extruder, e.g., single screw versus twin screw extruder. 

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