Knowledge of PVC extrusion machines

- Nov 06, 2018-

What is the difference between parallel and Conical twin-screw mechanical extruders?

Extruder is one of the commonly used plastic machinery. What is the difference between two types of extruders.

1. DIAMETER: The diameter of the parallel twin screw is the same, but for the conical twin screw is not. The small end diameter is different from the big end diameter;

2. concentric distance: The center distance of the flat twin screw is the same, the axis of the conical twin screw is included angle, the size of the center distance changes along the Axis;

3. Length-diameter: parallel twin screw (L / D) is the ratio of the effective length of the screw to the outer diameter of the screw, while conical twin screw (l / d) is the average ratio of the effective length of the screw to the large end diameter and the small end diameter.

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 barrel, which leads to many differences in structure and performance, although the characteristics of the two are different But each has its own advantages.

The parallel twin-screw extruder has limited space for the radial bearing and thrust bearing supporting the two output shafts and the related transmission gears in the transmission gear box due to the small size of the center distance of the two screws Although the designer tried hard, but can not solve the bearing load capacity, gear modulus, small diameter, the tail of the two small screw diameter, resulting in poor torque results. Output Torque is small, poor load resistance, is the parallel twin-screw extruder the most significant defect. But the plasticity of the aspect ratio is the advantage of the parallel twin screw. It can increase and decrease the aspect ratio to meet the requirement of the plastic processing according to the difference of the forming conditions. It can expand the applicable range of the parallel twin screw But this point conical twin-screw extruder is difficult to achieve.

In the conical twin-screw extruder, the two conical screw rods are arranged horizontally, and the two axes are packed into the barrel at an angle, and the center distance of the two axes gradually increases from the small end to the big end, so that the two output shafts of the transmission gear box have larger center distance The gears and pinion shafts in these transmission systems and the radial and thrust bearings supporting these pinion shafts leave considerable room for installation and can be fitted with large radial and thrust bearings Each drive shaft has enough shaft diameter to transfer torsion distance, so big work torsion distance and big load-bearing capacity is a big characteristic of conical twin-screw extruder. This point of parallel twin-screw extruder is incomparable. When the twin-screw extruder's non-recoil bearing twin-screw extruder is working, the melt will produce very large pressure at the head of the screw (head pressure) , the pressure is usually about 14 MPA, sometimes even up to 30 MPA This pressure on the screw to form a strong axial thrust, thrust against the anti-retreat is the role of bearings.

Parallel twin-screw extruders are limited by the small center distance of the two screws, the bearing load capacity is related to the diameter of the bearing, the diameter of the bearing load capacity is large, it is obviously impossible to use the large diameter of the bearing. The key problem with this method is that each thrust bearing must bear the same load uniformly. Otherwise, the thrust bearing will be subjected to the same load Bearing large bearing because of overload and premature failure, the load it should bear on the other bearings to overload, this kind of continuous damage its consequences are very serious. Compared with the transmission system of conical twin-screw extruder, the gear box has high manufacturing cost and complex maintenance.

The conical twin-screw extruder has a large center distance between the two output shafts of the transmission gear box because of the angle between the two screws. Two thrust self-aligning ball bearings are installed in the gear box The utility model has the advantages of large bearing capacity, low manufacturing cost, and convenient maintenance, and is capable of preventing the axial force formed by the head pressure.

For customers, it is very important to buy twin-screw Plastic Mechanical extruders. Different types of twin-screw extruders have different properties and applications It is necessary to find out the performance and application situation of various twin-screw extruders. For example, intermeshing co-rotating twin-screw extruders are widely used in polymer modification -- blending, filling, fiber reinforcement, and reactive extrusion -- because of their high rotational speed, high shear rate, and combined screws. For example, the intermeshing counter-rotating twin-screw extruder, because of its good mixing and plasticizing function, its biggest characteristic is pvc powder direct molding processing. If you change 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 the plastic section, the amount of extrudate is determined, and then the specification of twin-screw extruder is selected by the amount of extrudate. Under the same plastic processing conditions, the conical twin-screw extruder is suitable for larger head pressure and the parallel twin-screw extruder is suitable for smaller head pressure.