Extruder drives

The extruder drive has to turn the extruder screw at the desired speed. It should be able to maintain a constant screw speed because fluctuations in screw speed will result in throughput fluctuations that, in turn, will cause fluctuations in the dimensions of the extrudate. Thus, constancy of speed is a very important requirement for an extruder drive. The drive also has to be able to supply the required amount of torque to the shank of the extruder screw. A third requirement for most extruder drives is the ability to vary the speed over a relatively wide range. In most cases, one would desire a screw speed that is continuously adjustable from almost zero to maximum screw speed. Over the years, various drive systems have been employed on extruders. The main drive systems are  

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The massive gear boxes of the extruder drive has the following design criterions ... 

Extrusion accounts for about 30% of nylon produced and is used in various processes (24). Nylons can be extruded on conventional equipment having the following characteristics. The extruder drive should be capable of continuous variation over a range of screw speeds. Nylon often requires a high torque at low screw speeds typical power requirements would be a 7.5-kW motor for a 30-mm machine or 25-kW for 60-mm. A nylon screw is necessary and should not be cooled. Recommended compression ratios are between 3.5 1 and 4 1 for nylon-6,6 and nylon-6 between 3 1 and 3.5 1 for nylon-11 and nylon-12. The length-to-diameter ratio, L D should be greater than 15 1 at least 20 1 is recommended for nylon-6,6, and 25 1 for nylon-12. 

Compared to conventional processing tasks, the extruder drive motor is usually quite small for degassing processes, because the intake of polymer solutions or polymer melts does not require a high torque consumption. The use of a back vent depends on the amount of... 

Asynchronous motors can operate directly on the AC network current. The resulting speed is constant and dependent on the number of pole pairs and network frequency. However, an extruder drive should at least have variable speed. For this, a frequency converter is used. 

Thus, there are numerous marginal conditions and alternatives to be considered in configuring the drive for a large extruder. That is why the path is difficult and full of repetitive loops before the concept for a large extruder drive is complete. 

In the extrusion of snack foods, cereals and pet foods, cooking prior to extrusion is required. This can be accomplished in a steam pressure cooker integral with the extruder such as shown in Fig. 5.17. Screw diameters up to 10 in. (25 cm) are used in this application yielding typical capacities of 4,000 lb/h (1.8 Mg/h) with a 50 hp (37 kW) extruder drive to 12,000 lb/h (5.4 Mg/h) with a 150 hp (112 kW) extruder drive, depending on formulation and product requirements. 

Figure 6.33 Squirrel cage motor as an extruder drive in zone 1.

See design, motion-control, mechanical and electronic effects drive-system control electric motor electric-motor drive extruder drive-energy consumption injection molding machine-drive system. 

Fig. 42 Extruder drive via gearbox with direct-coupled electric motor, 1935...

A certain amount of energy has to be provided to heat and melt the materials above their transition temperature in the extruder. The energy required for melting can be approximately calculated from the typical specific enthalpy of each polymer. The energy is supplied either by heat transfer through the heated barrel walls or by dissipation, frictional heat, and mechanical energy supplied by the extruder drive. 

Extruder drive system Improve drive mechanism by matching size and speed of motor. Investigate high-efficiency motors 20... 

Extruder drive motors must turn the screw, minimize the variation in screw speed, permit variable speed control (typically 50 to 150 r/min), and maintain constant torque. In selecting drive motors, the three major factors are (1) base speed variation, (2) the presence or absence of brushes, and (3) cost. The speed variation of a drive motor is based on the maximum speed available for the motor. Since this variation does not change when the speed is reduced, screw speed. 

Some early DC extruder drives used fixed-speed AC motors to drive DC generators that produced the variable voltage for the DC motor. Nowadays, the DC motor drives usually operate from a solid-state power supply, since this power supply is generally more cost-effective than the motor generator set. The DC motor drive can be simpler and cheaper than the variable frequency drive, even when the higher cost of the DC motor is included. The smaller number of solid-state devices tends to give the DC drive a better reliability than the variable frequency drive. Brushes and commutator maintenance is the principal drawback to the use of DC motors. If the drive has to be expiosion-proof, the additional expense associated with this option may be quite iarge for a DC drive, more so than with a variable frequency AC drive or a hydraulic drive. A schematic of the DC drive is shown in Fig. 3.4. 

The extrusion process is generally designed such that the majority of the total energy requirement is supplied by the extruder drive. The rotation of the screw... 

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