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The transmission system and heating–cooling unit of a plastic extruder

Time：

2018-12-29

The drive system is responsible for powering the screw, providing the torque and rotational speed required by the screw during the extrusion process. It typically consists of an electric motor, a reducer, and bearings. Under conditions of essentially identical design, the manufacturing cost of a reducer is roughly proportional to its external dimensions and weight. A larger size and greater weight imply higher material consumption during production, and the use of larger bearings further increases costs. For extruders with the same screw diameter, high‑speed, high‑efficiency models consume more energy than conventional units; consequently, the motor power must be increased, and the reducer’s frame size is correspondingly upgraded. However, higher screw speeds…

Moreover, under the assumption of a substantially similar structure, the manufacturing cost of a reducer is roughly proportional to its external dimensions and weight. A larger size and greater weight imply higher material consumption during production, and the use of larger bearings further drives up manufacturing costs.

For extruders with the same screw diameter, high‑speed, high‑efficiency models consume more energy than conventional ones; as motor power increases, the corresponding gearhead size also grows. However, higher screw speeds imply lower reduction ratios. For gearheads of the same size, a lower reduction ratio results in larger gear module dimensions and greater load‑carrying capacity compared to a higher reduction ratio. Consequently, the increase in the gearhead’s volume and weight does not scale linearly with motor power. If one uses extrusion output as the denominator and divides by the gearhead’s weight, the high‑speed, high‑efficiency extruder yields a smaller value, whereas the standard extruder yields a larger one.

In terms of unit output, the lower motor power and lighter weight of the reducer in high-speed, high-efficiency plastic extruders mean that the per-unit‑output manufacturing cost of such extruders is lower than that of conventional extruders.

Heating and cooling are essential conditions for the plastic extrusion process to proceed.

Extruders typically employ electric heating, which is categorized into resistance heating and induction heating. Heating elements are installed in the barrel, die neck, and die head, among other sections. The heating system uses external heaters to warm the plastic inside the cylinder, raising its temperature to the level required for the specific processing operation.

Cooling systems are installed to maintain the plastic within the temperature range required by the process. Specifically, they serve to dissipate the excess heat generated by shear friction during screw rotation, thereby preventing overheating that could lead to thermal degradation, scorching, or difficulties in achieving proper shaping. Barrel cooling is typically categorized into water cooling and air cooling; for small and medium‑sized extruders, air cooling is generally preferred, whereas large units often employ water cooling or a combination of both methods. For the screw of a plastic extruder, central water cooling is the primary approach, aimed at enhancing solid‑material conveyance, stabilizing extrusion output, and improving product quality. Meanwhile, cooling at the hopper serves two purposes: first, to reinforce the transport of solid material and prevent plastic pellets from becoming sticky and clogging the feed throat due to temperature rise; second, to ensure the proper operation of the drive system.