Extruder motor drive

FIG. 18-50 Intermeshing corotating twin screw extruder (a) drive motor, (h) gearbox, (c) feed port, (d) barrel, (e) assembled rotors, (f) vent, (g) barrel valve, (h) kneading paddles, ( ) conveying screws, (/) splined shafts, (k) blister rings, (APV Chemical Machinery, Inc.)... 

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-... 

A common indicator in an extruder console is the power, E, consumed by the motor drive in transporting material from feed to product exit. A higher power consumption could mean greater friction during product movement or an overloaded chamber. The torque of extrusion (F) is the energy expended by the motor drive in rotating the screw(s) and is expressed as... 

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. 

SCR drive A variable-speed motor drive widely used today on new extruders in which a silicon-controlled rectifier (SCR) converts alternating current to run a direct-current motor. Unlike AC motors, DC motors have good torque characteristics over a wide speed range. 

Extruder is used to extrudate polymeric materials with a series of subprocesses, including motor-drive control systems and barrel heating/cooling system. Operation and process reflect the input and output of the extrusion process. During extrusion process, each material undergoes a diflerent temporal, thermal, and/or mechanical history. As a result, its final properties may be different from those of the materials subjected to extrusion process [1—4]. 

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. 

Older motor drive systems generally consist of a DC brush motor, a power conversion unit (PCU), and operator controls. A frequent problem with the motor itself Is worn brushes these should be replaced at regular Intervals as recommended by the manufacturer. In troubleshooting an extruder drive, one should follow the procedure recommended by the manufacturer of the drive. A typical troubleshooting guide for a DC motor is shown in Table 11.2. 

It is important to equip the wire extrusion line with sufficient instrumentation to produce a high quality product. Process variables that are routinely controlled and/or monitored are various temperatures, melt pressure inside the extruder, and motor drive speed. Table 8.6 contains a list of process variables, the location of each variable, the impact of each variable, and the methods of its control. 

Motor drive 1. Extruder 2. Take-up capstan 1. Extruder output 2. Line tension 1. Solid state controllers 2. Electronic controllers... 

A 90 kW DC motor drive unit with gearbox was used for the tests, which allowed the connection of different processing units (barrel, screw) 075 x 36 D, 0 50 x 34 D, 0 25 x 25D, see figure 5. A detailed description of this laboratory extruder is already given else were (7, 9). 

The power train on the extruder was also limiting the rate of the process. The extruder was driven by a 190 kW motor with a maximum speed of 1750 rpm and a maximum current of 262 A. The motor was directly coupled to a gearbox with a ratio of 13.91, providing a maximum screw speed of 125 rpm. The maximum torque available to the screw from the drive system was 14,200 Nm. As will be shown later, this gearbox-motor combination did not provide a high enough torque to the screw for this process. 

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... 

The drive unit of a co-rotating twin-screw extruder is, after the processing section, the most important component in the system. It is decisive for dependable operation. The drive unit consists of the motor, safety clutch, and gearbox. The safety clutch and the gearbox will be discussed in the following. 

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