What is the difference between parallel and conical twin-screw plastic machine extruders?

Update:Aug 04,2016
Summary:

The extruder is one of the commonly used plastic machin […]

The extruder is one of the commonly used plastic machines, then what is the difference between parallel and conical twin screw plastic machine extruders?

    1, diameter: parallel twin screw diameter of the same, tapered twin screw diameter and small end of the small end of the different;

    2, concentricity: the center distance of the flat twin screw, the angle between the two axes of the conical twin screw, the size of the center distance varies along the axis;

    3, aspect ratio: parallel double snail (L / D) refers to the effective part of the length of the screw and the outer diameter of the screw, the conical twin screw (L / D) refers to the effective part of the length of the screw and large diameter and small The ratio of the average of the end diameters.

    From the above points, we can clearly see the parallel and conical twin-screw extruder is the most significant difference is the geometry of the screw barrel different, which led to the structure and performance of the many differences, although the two different characteristics, But have their own advantages.

    The parallel twin-screw extruder is limited by the small size of the two screw shafts. In the transmission gear box, the radial and radial bearings and the associated transmission gears that support the two output shafts are limited, although the designer is exhausted Brain juice, but also can not solve the bearing carrying capacity, gear modulus, small diameter, two screws tail diameter of the small reality, resulting in poor resistance to torque results. Output torque is small, poor anti-load capacity, parallel to the twin-screw extruder is the most significant defects. But the aspect ratio of the plasticity is the advantage of parallel twin screw, it can be based on the difference in molding conditions can increase and decrease the aspect ratio to meet the requirements of plastic processing technology, you can expand the scope of parallel twin screw, but this point cone Twin screw extruder is difficult to do.

    Cone twin screw extruder two conical screw horizontal arrangement, the two axes were an angle into the barrel, the center of the two axes from the small end to the big end gradually larger, making the transmission gear box two output shaft Larger center distances, gears and gear shafts in these drive systems, and radial bearings and thrust bearings that support these gear shafts have a large installation space, which can accommodate larger radial bearings and thrust bearings. The drive shaft is sufficient to meet the transmission torque of the shaft diameter, so the large working torque, large bearing capacity is a major feature of the conical twin-screw extruder. This parallel twin screw extruder is unmatched. The twin-screw extruder's twin-screw extruder operates with a very large pressure (head pressure) at the head of the screw. The pressure is usually around 14MPA and sometimes up to 30MPA. The pressure on the screw to form a strong axial thrust, withstand the thrust is the role of only retreat bearing.

    Parallel twin-screw extruder due to the two screw center distance from the small restrictions, bearing bearing capacity and its diameter size, large diameter bearing capacity, obviously with a large diameter stop bearing is not possible. This contradictory situation is usually with a few small diameter stop bearing the role of series together to bear a strong axial force, the use of this method is the core issue of each thrust bearing must bear the same load, otherwise, bear large Of the bearing due to overload and damage in advance, it should bear the load added to other bearings to overload, this damage to the continuity of the consequences is very serious. It can be seen that the parallel twin-screw extruder transmission system structure is more complex, compared with the conical twin-screw extruder transmission system structure, gear box manufacturing costs are high, more complex maintenance.

    Cone-shaped 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 installed two front and rear staggered arrangement of the larger thrust-aligning ball bearings, Enough to prevent the formation of the nose by the pressure of the axial force, which features a large carrying capacity, low cost of gear box manufacturing, maintenance is more convenient.

    For the user, the purchase of twin-screw plastic machine extruder is very important, different types of twin-screw extruder has different performance and application, therefore, must be clear all kinds of twin-screw extruder Performance and applications. For example, the meshing co-rotating twin-screw extruder is widely used for the modification of non-thermally decomposable polymers due to its high rotational speed and large shear rate. The combined screw is widely used for blending, blending, filling Enhance the reaction of the material and squeeze out. For example, the meshing type isotropic rotating twin screw extruder, because of its good mixed plasticizing function, its biggest characteristic is pvc powder direct forming processing. Such as changing the geometry of the screw, can also be used for other materials forming processing, but its strength is still PVC molding processing. According to the size of plastic cross-section size, determine the extrusion volume, and then by the amount of extrusion to select the specifications of twin-screw extruder. In the case of plastic processing molding process conditions are basically the same, the cone-shaped twin-screw extrusion machine to adapt to the larger head pressure, parallel twin-screw extrusion machine to adapt to smaller head pressure.