Asia Rubber Expo & Rubber Tech India 2020" is co-sponsored by AAKAR Exhibition Company and Zhonglian Rubber Co., Ltd. The exhibition will be held in the Chennai Trade Center (CTC) of India from 8 ...Read More
Composition, in the rubber extruder machine, in general, the most basic and most common is a single screw extruder. It mainly includes six parts: transmission, feeding device, barrel, screw, head and die.
The transmission part is usually composed of a motor, a reduction box and a bearing. During the extrusion process, the screw speed must be stable and cannot change with the change of the screw load, so as to maintain the uniform quality of the products obtained. However, in different occasions, the screw must be variable speed to achieve the requirement that a piece of equipment can extrude different plastics or different products. Therefore, this part generally uses AC commutator motors, DC motors and other devices to achieve stepless speed change. Generally, the screw speed is 10-100 rpm.
The function of the transmission system is to drive the screw and supply the torque and speed required by the screw in the extrusion process. It is usually composed of a motor, a reducer and a bearing. On the premise that the structure is basically the same, the manufacturing cost of the reducer is roughly proportional to its outer size and weight. Because of the large shape and weight of the reducer, it means that a lot of materials are consumed during manufacturing, and the bearings used are also relatively large, which increases the manufacturing cost.
For extruders with the same screw diameter, high-speed and high-efficiency extruders consume more energy than conventional extruders. The motor power is doubled, and it is necessary to increase the frame size of the reducer accordingly. But high screw speed means low reduction ratio. For the reducer of the same size, the gear modulus of the low reduction ratio is increased compared with the large reduction ratio, and the load bearing capacity of the reducer is also increased. Therefore, the increase in volume and weight of the reducer is not linearly proportional to the increase in motor power. If you use the extrusion volume as the denominator and divide it by the weight of the reducer, the number of high-speed and efficient extruders is smaller, and the number of ordinary extruders is larger. In terms of unit output, the low motor power of the high-speed and high-efficiency extruder and the small weight of the reducer mean that the unit-output machine manufacturing cost of the high-speed and high-efficiency extruder is lower than that of the ordinary extruder.
Generally, pellets are generally used for feeding, but strips or powders can also be used. The charging equipment usually uses a conical hopper, whose volume is required to provide at least one hour of consumption. There is a cutting device at the bottom of the hopper to adjust and cut off the material flow. The side of the hopper is equipped with a sight hole and a calibration metering device. Some hoppers may also be equipped with pressure reducing devices or heating devices to prevent the raw materials from absorbing moisture from the air, or some barrels also have their own agitators, which can automatically feed or feed materials.
The hopper is generally symmetrical. There is a window on the side of the hopper to observe the material level and feeding situation, and the bottom of the hopper has an opening and closing door to stop and adjust the feeding amount. A cover is added above the hopper to prevent dust, moisture and impurities from falling into it. When choosing hopper materials, it is best to use lightweight, corrosion-resistant and easy-to-process materials. Generally, aluminum and stainless steel plates are used. The volume of the hopper depends on the size of the extruder and the feeding method. Generally, the extrusion capacity of the extruder is 1～1.5h.
There are two kinds of feeding methods: manual feeding and automatic feeding. Automatic feeding mainly includes spring feeding, blast feeding, vacuum feeding, and conveyor belt conveying feeding. Under normal circumstances, manual feeding is used for small extruders and automatic feeding for large extruders.
3. Classification of feeding methods
① Gravity feeding:
Principle-The material enters the barrel by its own weight, including manual feeding, spring feeding, and blast feeding.
Features-simple structure and low cost. But it is easy to cause uneven feeding, which affects the quality of the parts. It is only suitable for small extruders.
② Mandatory feeding:
Principle-Install a device that can apply external pressure to the material in the hopper to force the material into the extruder barrel.
Features-It can overcome the phenomenon of "bridging" and make the feeding uniform. The feeding screw is driven by the screw of the extruder through the transmission chain, so that its speed is compatible with the speed of the screw. The overload protection device can be activated when the feeding port is blocked, thereby avoiding damage to the feeding device.
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