Extruder is one of the commonly used plastic machinery, so what is the difference between parallel and conical twin-screw plastic mechanical extruder?

1, diameter: the diameter of the parallel twin screw is the same, the small end diameter of the conical twin screw is different from the big end diameter;

2, concentric distance: the center distance of the flat twin screw is the same, the two axes of the conical twin screw are included, and the size of the center distance changes along the axis;

3, lengthdiameter ratio: parallel twin screw (L/D) refers to the effective part of the screw length and the outer circle of the screw ratio, conical twin screw (L/D) refers to the effective part of the screw length and the diameter of the big end and the diameter of the small end of the average ratio.

From the above points, we can clearly see that the most significant difference between parallel and conical twin-screw extruders is the geometry of the screw barrel is different, which leads to many differences in structure and performance, although the two characteristics are different, but have their own advantages.

Parallel twin screw extruders are limited by the small size of the center distance between the two screws. In the transmission gear box, the radial bearings and thrust bearings that support the two output shafts and the related transmission gears have limited space, although the designer has tried his best, But it can not solve the bearing capacity, the module of the gear, the small diameter, and the reality of the small tail diameter of the two screws, resulting in poor torque resistance. The output torque is small and the load resistance is poor, which is the most significant defect of parallel twin screw extruder. But the plasticity of the length-diameter ratio is the advantage of parallel twin screw, it can increase and reduce the length-diameter ratio according to the difference in forming conditions to meet the requirements of plastic processing technology, can expand the scope of application of parallel twin screw, but this conical twin screw extruder is difficult to do.

Conical twin screw extruder two conical screw horizontal arrangement, two axes in an Angle into the barrel, the center distance of the two axes from the small end to the big end gradually larger, so that the transmission gear box two output shaft has a larger center distance, these transmission system gears and gear shaft as well as supporting these gear shaft radial bearings and thrust bearings have a larger installation space, It can be installed with larger specifications of radial bearings and thrust bearings, each drive shaft has enough to meet the transmission torque diameter, so the large working torque, large load bearing capacity is a major feature of the conical twin screw extruder. This parallel twin screw extruder is incomparable. Double screw extruder work, the melt in the screw head will produce a very large pressure (head pressure), the pressure is usually about 14MPA, sometimes even up to 30MPA or more, this pressure on the screw to form a strong axial thrust, resist the thrust is the role of the stop bearing.

Parallel twin screw extruder due to the limitation of the small center distance between the two screws, the bearing capacity of the stop bearing is related to its diameter, the diameter is large, the bearing capacity is large, obviously with a large diameter of the stop bearing is impossible. This contradictory situation is usually the use of a number of small diameter stop bearing in series together to bear a strong axial force, the use of this method of the core problem is that each thrust bearing must bear the load to be uniform and the same, otherwise, bear the large bearing due to overload and damage in advance, the load it should bear is added to other bearings to overload it. The consequences of the damage of this continuity are very serious. It can be seen that the transmission system structure of parallel twin screw extruder is more complex. Compared with the transmission system structure of conical twin screw extruder, the manufacturing cost of gear box is high and the maintenance is more complicated.

Conical twin screw extruder because of the arrangement of two screw Angle, so the transmission gear box two output shaft has a larger center distance, in the gear box is equipped with two before and after staggered arrangement of the larger thrust aligning ball bearings, enough to prevent the axial force formed by the head pressure, its characteristics of large bearing capacity, low gearbox manufacturing cost, more convenient maintenance.

For the user, the purchase of twin-screw plastic mechanical extruder is very important, different types of twin-screw extruder have different performance and application occasions, therefore, it is necessary to figure out the performance and application of various twin-screw extruder. For example, meshing twin screw extruder in the same direction because of its high speed, large shear rate, combined screw, it is widely used in the modification of polymer that is not easy to thermal decomposition. — Blends, fillings, fiber reinforcement and reaction extrusion of materials. For example, the meshing type cross-rotating twin-screw extruder, because of its good mixing plasticizing function, its biggest feature is the direct molding processing of pvc powder. Such as changing the geometry of the screw, it can also be used for molding processing of other materials, but its strength is still PVC molding processing. According to the size of the plastic section, determine the amount of extrusion, and then choose the specifications of the twin-screw extruder by the amount of extrusion. In the case of plastic processing and forming process conditions are basically the same, the conical twin-screw extruder can adapt to the larger head pressure, and the parallel twin-screw extruder can adapt to the smaller head pressure.

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