Design Principle and Working Principle of Drive System of Dual Screw Extruder

A double screw extruder is a machine that melts the plastic into a uniform melt by heating and extrusion and sends the melt to the next process. What are the design principles and working principles of its transmission system? Let's take a look!

Ⅰ. Demission system of the double screw extruder

(1) Reduce the transmission chain as much as possible. The increase of the transmission chain means the increase of the transmission mechanism and the increase of the overall geometric size of the transmission system, which increases the problems of others.

(2) Consider the strength and the continuity of the series, the number of teeth and the moduli for change in the same center distance should decrease in order from large to small, and should not jump to decrease. The helix angle makes the high-speed stage take a large value and the low-speed stage take a small value, so as to increase the axial coincidence of the high-speed stage and achieve smooth operation. The axial force of the low-speed stage is reduced, and the service life of the bearing is improved. The speed ratio distribution should be a non-integer because it is considered that if the processed gear is defective, it will not appear in the same part of the paired gear during work.

(3) The selection of the displacement coefficient of the dual screw extruder should take the best value of the displacement coefficient according to the specific design requirements. Because different displacement coefficients have different effects on the contact strength and bending strength of the gears, all the displacement coefficients of the gears can be taken to be the same. It is easy to calculate in the series design and not easy to make mistakes. Besides, it is best to use all angular displacements, and make the sum of the displacement coefficients greater than 0, so that the bending strength of the tooth root can be improved.

(4) Minimize the sub-box surface of the transmission box as much as possible, and pay attention to the geometric dimensions of the two directions of the horizontal plane of the box body not too large.

(5) The even distribution of torque and the equivalent drive of multiple drives. The uniform distribution of torque and the multi-channel equivalent drive are related to the specific transmission form, as well as the selection of gear teeth and the selection of tooth profile parameters. At the same time, an absolutely uniform transmission of torque must be achieved.

(6) The number of common teeth should be increased as much as possible in the design of the dual screw extruder, which is beneficial to both design and mass production.

Ⅱ. The working principle of double screw extruder

Two screws that rotate in the same direction rotate in the same direction, and it has two possibilities, clockwise and counterclockwise.

But judging from the current popular situation, it is mostly clockwise rotation, and the screw thread must be right-handed. From the perspective of the screw shape, the two screws are exactly the same, and the thread direction is the same.

The two screws of a counter-rotating dual screw extruder rotate in opposite directions. It may have both inward and outward rotation.

For intermeshing counter-rotating dual screw extruder, there is currently less inward rotation. This is because for the feeding section, if the thread of this section is not fully meshed or not fully closed vertically and horizontally, then when the material is added to the screw from the feeding port and driven by the rotation of the two screws, the material will first enter the meshing between the radial gaps of the two screws in the zone, and form a material pile above the two screws, thereby reducing the free space of the available screw grooves, and affecting the ability of the screws to accept materials from the feeder. This is not conducive to filling the screw groove as soon as possible and conveying the material forward, that is, the feeding performance is not good, and it is easy to form a bridge. In addition, the material entering the radial gap of the two screws has a force that separates the two screws, which presses the two screws to the barrel wall from both sides, thereby accelerating the wear of the screws and the barrel.

The above-mentioned disadvantages do not exist when the material is rotated outward. When the material falls on the screw, the material is quickly separated to both sides by the driving of the two screws, fills the screw groove, conveys forward, and quickly contacts the heat cylinder to absorb heat, helping to heat and melt the material. In terms of appearance, the threads of the two counter-rotating screws are in opposite directions, one is left-handed and the other is right-handed, and the two are symmetrical. However, the two screws of the non-intermeshing counter-rotating double screw extruder rotate inward.