Screw feed section

Figure 12.5 Fully compacted solid bed in screw feed section.

Figure 12.44 Side view of a typical, one processing section planetary roller extruder from US Patent 4,192,617 showing relationship of the planetary section components and a single-screw feed section and fully flighted planetary spindles.

The screw consists of a feed section, a rapid transition section, and a metering section a rounded forward end prevents stagnation. The breaker plate that converts the rotary motion of the melt into smooth, straight flow should have as many holes as possible both ends of each hole should be countersunk for streamlined flow. 

Eig. 1. Parts of an extmder A, screw B, barrel C, heater D, thermocouple E, feed throat E, hopper G, thmst bearing H, gear reducer 1, motor , deep channel feed section K, tapered channel transition section and L, shallow channel metering section (15). 

Fig. 10. Mass flow screw feeder designs, (a) Combined tapered shaft and variable pitch screw feeder where A represents a conical shaft and constant pitch (feed section) B, constant shaft and increasing pitch (feed section) and C, constant shaft and constant pitch (conveying section), (b) Stepped shaft screw feeder where A represents a stepped diameter shaft and constant pitch (feed section) and B, constant shaft and constant pitch (conveying section).

It is normal practice to have screws double flighted under the feed section. This is mainly because a single flight, working in conjunction with the feed roll, does not effectively pull in the feed strip in a consistent manner. In some extruder constructions the double flight continues down the length of... 

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-... 

Sikora, J.W., The Effect of the Feed Section Groove Taper Angle on the Performance of a Single-Screw Extruder, Polym. Eng. ScL, 41, 1636 (2001)... 

Figure 6.6 Melting profiles for a 63.5 mm diameter extruder running an ABS resin at 60 rpm for screws with a 8.89 mm deep feed channel, 6 diameters of feed section, and a metering channel depth of 3.18 mm (C = 2.8) (a) 8 diameters of transition section for R = 0.00342, and (b) 4 diameters of transition section for R = 0.00684 [13, 14]. The pushing flights are on the right side of the section photographs...

The metering section of the screw presented above was simulated at 120 kg/h and a discharge pressure of 6 MPa. The screw had to be rotated at a speed of 56 rpm to obtain 120 kg/h. The barrel temperatures were 160, 220, and 275 °C for the feed section through the discharge section, respectively. The simulated axial pressure and temperature are shown in Fig. 9.3. 

The material of construction for the ET screw is critical in order to provide the proper strength in the event of an improper start-up procedure and to minimize cost. The maximum stress that the screw will experience during operation will be in the feed section where the root diameter is the smallest and the torque is the greatest. The calculation of the power that a screw can transmit safely is provided in Section 10.4.5. This calculation ignores the strength contribution from the flight. The safety factor for this screw made from three different materiais is provided in Table 9.6. 

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