Intermeshing-gears extruder

Equipment used for (a) low- and (b) medium-pressure agglomeration (a.l) screen extruder, (a.2) basket extruder, (a.3) cylindrical-die screw extruder, (b.l) flat-die extruder, (b.2) cylindrical-die extruder, (b.3) intermeshing-gears extruder. 

In an extruder of this type a system of intermeshing gears is used to force the plastic towards and through the die. A gear pump can be fitted to a single-screw extruder in order to obtain steadier pressure and smoother output, or it may be used to extrude fibres from polymers which at processing temperatures are liquids of low viscosity. 

Rolls may be either side-by-side with material extruded through one or both of the rolls, or one or more small rolls may be fitted inside a larger die roll. In yet another design, two intermeshed gears are used and material is extruded through die holes located in the gear root. 

A third type of pump is used largely for pumping at high rates, often with a white liquid color.This is a progressive cavity pump. Like the gear pump, it is very linear and can handle high viscosities. It has a convoluted tubular stator and a convoluted rodlike rotor, which intermesh, moving the liquid forward, much like an extruder screw. 

In medium-pressure agglomeration equipment (Fig. 8.42), the perforated support (die) can be either flat (a), concave (b), or convex (c). For all three designs, intermeshing, toothed executions have been proposed in the patent literature [B.42] to avoid slippage and improve extrusion as well as extrudate quality, but only the so called gear pelleter , in which the convex dies (Fig. 8.42c) are hollow gears with extrusion channels between the teeth, has reached commercial importance (see below). 

In contrast, in twin-screw extruders with intermeshing screws the relative motion of the flight of one screw inside the channel of the other pushes the material forward almost as if the machine were a positive displacement gear pump which conveys the material with very low friction. In twin-screw extruders, heat is therefore controlled independently from an outside source and is not influenced by screw speed. This fact becomes especially important when processing a heat-sensitive plastic like PVC. 

Fig. 2. Intermeshing corotating twin-screw extruder A, motor B, gear box C, feed port D, clam shell barrel E, vent port F, screw shafts G, conveying screws H, kneading paddles I, barrel valve and J, blister rings. Courtesy of APV Chemical Machinery Inc.

A) BerstorfT ZE 25 x 33D Corotating twin-screw extruder, closely intermeshing 25 33 0.88 Neutral kneading block at 14D Mixing gears at 18D, 23D, and 28D... 

Planetary roller extruders (PRE) have been used for many years in the compounding of temperature sensitive polymers and rubber compounding [57-64]. PREs are comprised of long helically geared components comprising a driven central shaft, freely rotating planetary spindles and a stationary, temperature-controlled outer cylinder, all of which must closely intermesh. The planetary spindles are located between the central shaft and the outer cylinder. To illustrate this relationship. Fig. 12.43 shows... 

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