The Single Screw Extruder Pump

In this section we derive a simple mathematical model for the single screw pump. In such a model, we seek relationships between performance and operating variables with the geometrical variables as parameters. 

The single screw as shown in Figs. 6.6 and 6.7 is a relatively simple geometrical configuration that is easy to manufacture, and therefore relatively inexpensive. Thus multiple screws can be retained with a single machine for different applications. 

Albert Aly Kaufman, one of the pioneers of extrusion, who established the celebrated Prodex Extruder Manufacturing Company, used to say What goes in comes out. Don t expect the screw to even-out non-uniform feeding of additives. It can t.  

The extruders used for rubber do not require the length of those used for plastics, because they do not need as long a melting section as plastics do. When the plastics industry adopted the rubber machinery, it imitated the rubber extruder design, but as demands for output and quality mounted, the length-to-diameter ratio of the extruder grew over time, until it leveled off at current values. 

Most screws of SSEs are single flighted, with Ls = Ds, referred to as square-pitched screws. The radial distance between the root of the screw and the barrel surface is the channel depth, H. The main design variable of screws is the channel depth profile that is H(z), where z is the helical, down-channel direction, namely, the direction of net flow of the material. The angle formed between the flight and the plane normal to the axis is called the helix angle, 0, which, as is evident from Fig. 6.8, is related to lead and diameter 

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Another form of positive-acting rotary pump is the single-screw extruder pump typified by the Mono-piunp, illustrated in Figures 3.32 and 3.33. A specially shaped metal helical-rotor revolves eccentrically within a resilient rubber or plastic double-helix, thus creating a continuous forming cavity which progresses towards the discharge of the piunp. A continuous seal is created... 

All of the data in Fig 7.5 were analyzed using linear regression. The summation of the helix and core-regressed flow rates are plotted in Fig. 7.5 as the red dotted line. The experimental superposition for the flows induced by the screw elements essentially overlaid the regression line for the screw configuration rate. Thus, it was concluded that the helix is the pump in the single-screw extruder, and core rotation reduces the flow by dragging the fluid back toward the extruder inlet. 

Equation 7 is not valid for rpumping efficiency can become close to 100%. This is considerably better than the single screw extruder where the optimum pumping efficiency is 33% at a throttle ratio value of 0.33 (r[Pg.44]

The largest volume of thermoplastics is probably processed by means of extrusion. The extmder is the main device used to melt and pump thermoplastics through the shaping device called a die. There are basically two types of extruders single and twin screws. The single-screw extruder is shown in Figure 1.1. The single-screw extruder basically consists of a screw (Fig. 1.2) that rotates within a metallic barrel. The... 

Although the main fimction of the single-screw extruder is to melt and pump polymer, there are a number of other applications. Extruders can be used to remove volatiles such as water or trace amounts of monomers. They can be used to generate foamed polymers as the temperature and pressure history can be controlled. They also serve as continuous mixing and compounding devices. Hence, extruders have a wider range of applications than other pumping devices. 

There are two residence time values of specific interest, and these are the mean residence time, t, and the shortest residence time, fo- The mean residence time was defined in Eq. 6.117 and for the single-screw extruder (i.e., metering section or melt pump) is... 

Mnciple materials and the same between material and screw case of single screw extruder on gear pump principle... 

All single-screw extruders have several common characteristics, as shown in Figs. 1.1 and 1.2. The main sections of the extruder include the barrel, a screw that fits inside the barrel, a motor-drive system for rotating the screw, and a control system for the barrel heaters and motor speed. Many innovations on the construction of these components have been developed by machine suppliers over the years. A hopper is attached to the barrel at the entrance end of the screw and the resin is either gravity-fed (flood-fed) into the feed section of the screw or metered (starve-fed) through the hopper to the screw flights. The resin can be in either a solid particle form or molten. If the resin feedstock is in the solid form, typically pellets (or powders), the extruder screw must first convey the pellets away from the feed opening, melt the resin, and then pump and pressurize it for a down-... 

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