Nanjing Rubber & Plastics Machinery Plant

(1) Adjusting the speed regulator screw can be fully compensated pressure fluctuations of extruder.

(2) When the speed regulator screw unchanged, the remaining length of polymer melt can be regulated relying on the stabilized voltage screw, which has a good effect on voltage regulation,but only the largest fluctuations is 83163% in the value of regulation.
(3) With lower price, the device is acceptable to the majority of enterprises
(4) It is convenient to clean the screw of an extruder, due to simple structure of the regulator device.
(5) The device is connected to the vertical extruder head, unlike the pressure
fluctuation controller, which requires a direction change of the head.

In the previous studies, a driven method of extruders by variable speed switched reluctance motor drive is put forward. Based on analysis of present states of extruders, the method which could realize flexible numerical control by using variable speed switched reluctance motor to controlling the screw speed on velocity and pressure of extrusion was narrated. In addition, the advantage of saving energy and change of renovated extruders were analyzed. It was proved in practice that the renovated extruders had higher performances in efficiency and capability.

The screw of an extruder driven by switched reluctance motor can be operated through the gear of the motor, which can realize speed control under extrusion rate and the pressure. Generally, an extruder processes its own characteristics: wide range of speed adjustment, steady speed and high precision, small starting current, large starting torque. Due to a small heat-driven system, the occurrence of burning motor and controller is significantly reduced. In particular, it is very efficient to save energy, and the quantity of energy-saving is around 11%, compared with the variable frequency speed regulation system. Such an extruder has made a lot of progress: simple structure, digital control, stepless speed regulation, and high efficiency energy-saving.

(3) There is no burning of motor and controller in an extruder with switched reluctance motor when three-phase input power is absent, and it can only lead to decrease of input electrical power output.

(4) During the operation of an extruder, there is no such an error that leads to short-circuit devices and burning controller, caused by lack of power devices.
(5) There is no belt drive in an extruder, but the screw speed can be adjusted accurately. Due to non-winding and rotor cage of the motor, it processes high mechanical strength and reliability of the transmission.

Over the years, it is a problem for stepless speed regulation in maintaining a large screw extruder torque, due to direction changing of DC motor for speed control, small torque of AC motor, and complex mechanical of speed control, continuously variable high cost and low efficiency of the hydraulic motor, along which many new ways come into being. There are many shortcomings of VVVF, such as low speed electric heat, large energy consumption, low efficiency, torque small, narrow speed range, and the phenomenon of electrical burn, reliability and low running so that people are unsatisfied with VVVF of screw extruder.

An extruder drived by a switched reluctance motor has the following advantages:

(1) The speed of screw with long-term operation can be adjusted from zero to the highest speed in the range of stepless speed regulation, with high efficiency and smaller temperature rise of motor and controller.

(2) When an extruder begins to work, it is not possible to bring about the starting current, which is more than the original rated current 5 to 7 times. Meanwhile, there is no need to start an extruder with lower pressure, for the starting current can be smoothly increased as the current requires. The longer the start-up time is, the smaller the starting current will be. When the starting torque reaches 150% of rated torque, the starting current is only 30% of rated current.

Extruder, which is currently used, is driven by ordinary motor for screw rotation through the reducer. It is only to reach the volume of screw speed and extrusion by pressing the button down. When changing varieties and specifications of products, the adjustment of the volume of melt extrusion or extrusion rate is necessary to readjust the screw speed; when the head pressure begins to change, it is necessary to readjust the screw speed for restoring the pressure; and the auxiliary line likewise, it is necessary to readjust the screw speed.

The screw speed of an extruder is an important process parameter to control the quality of extrusion rate and products. The pressure of material in the barrel increases as speed changes; while the shear strengthening of materials can improve the material temperature, and reduce melt viscosity, which is conducive to the full material and evenly mixed plastics. However, with high screw speed and fast rate of extrusion, melt in the mouth can cause flow instability. Therefore, it is necessary to put weight on the screw speed of a screw extruder.

Screw combination is the key to the development of extruding process. Co-rotating twin screw extruder mainly with a mixing extrusion, screw combination need to take into account of the shape of the main performance and accessories, feeding sequence and location, the location of vents, barrel temperature settings and so on. At the same time, with the various categories of mixture, it is obvious that there is a variety of combinations. The current research mainly depends on a combination of design experience. Nevertheless, the screw combination of twin screw extruder has its own portfolio and basic laws to follow.

Twin screw extruder is characterized as follows: higher speed and in the mating area (in the cross-section of the overlapping part of two screws) there is relative velocity, it can produce a strong uniform shear; Geometry determines that it must be open for its vertical flow channel, so that there is materials exchange between the two screws. In exchange, materials at the bottom of a screw slot will move to another screw at the top of the spiral groove. The opening up of the vertical flow make it possible for horizontal flow channel to be open,which is to achieve the exchange of materials between adjacent slot of the same screw. This makes the twin screw extruder with a good ability of distribution and mixture, so it is the most suitable machine for mixing operations.