Screw thrust bearing

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

The drive system consists of a motor, a speed reducer, and thrust bearing (Figure 14-5). Obviously, the motor turns the screw and is often fairly large, as it takes a lot of power to push high viscosity molten poly-... 

The TSE s have also drawbacks, the main being their cost. Owing to complex design of the screws and the thrust bearings these machines are... 

The extruder screw is designed to develop the pressure required to pump the molten polymer through the die. This pressure also acts on the screw. Since the thrust bearing mechanism supports the drive mechanism into which fits the shank of the screw, the thrust-bearing mechanism resists the axial thrust exerted by the molten polymer on the screw. Pressures of up to 2000 psi can be developed in many extruder operations. 

Thrust bearings absorb the thrust force exerted by the screw as it turns... 

The output of the gearbox is connected directly to the shank of the extruder screw. A thrust bearing is located at this junction (Fig. 2.3). The thrust bearing absorbs the backwards push of the screw generated by the pressure of the polymer at the output end of the screw. 

Without a thrust bearing, it would be very difficult for the screw to rotate because high frictional forces would be generated by the backwards push of the screw into the gearbox. It would be similar to a wheel turning with tens of thousands of pounds of force applied to the hub. The thrust bearing allows the screw to rotate freely and reduces the frictional forces on the shank that are generated by the head pressure on the tip of the screw. 

Thurst load n. In an extruder or screw-injection molder, the rear-directed force in reaction to the forward buildup of pressure in the screw, culminating in the heard pressure acting over the whole screw cross-section, and equal to nif P/4. This force is much less in an injection molder of the same screw diameter because, while the screw is turning, the head pressure is low and when the screw stops, the injection rams take up the thrust. Therefore, their thrust bearings can be much smaller than those of equal-size extruders. 

Figure 5.10 The thrust bearing couples the screw to the gear box. ...

Extruder screws fit into the barrel and are supported by the thrust bearing. The screw s shank length fits into the thrust bearing, while the flighted length contacts the plastic. Extruder screws are specified by their outside diameter (D) and the LID, which is given by... 

Figure 3.9 shows a typical thrust bearing arrangement for a single screw extruder. 

Figure 3.9 Thrust bearing assembly for single screw extruder...

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