How to choose parallel and conical twin-screw barrel, come and see here ~ ~

Release Time:2023-12-15 13:49

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How to choose parallel twin-screw barrel and conical twin-screw barrel in production and use? It is a question that users often ask when purchasing twin-screw barrel.

classification of twin screw barrel:

According to the rotation direction of the twin screw, it can be divided into the same direction and the opposite direction. The same screw barrel is the same direction of rotation when the two screws are working, and the different screw barrel is the opposite direction of rotation when the two screws are working.

According to whether the axis of the twin screw is parallel or not, it can be divided into two kinds of screw barrels with parallel axis and intersecting axis. Axis parallel to the parallel twin-screw barrel, axis line intersection for the conical twin-screw barrel.

Twin screw barrel and meshing and non-meshing points.

Parallel and conical twin-screw barrels are the same:

All have the conveying mechanism of plastic forced forward, good mixing plasticizing ability and dewatering ability, and basically the same adaptability to the molding process of materials and plastic products.

The difference between parallel and conical twin-screw barrels:

1. Diameter: The diameter of the parallel twin screw is the same, and 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. Length-diameter ratio: Parallel double screw (L/D) refers to the ratio of the effective part length of the screw to the outer circle of the screw, while conical double screw (L/D) refers to the ratio of the effective part length of the screw to the average diameter of the large end and the diameter of the small end.

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

Due to the limitation of the small center distance between the two screws, the parallel twin-screw barrel has limited space for radial bearings and thrust bearings supporting the two output shafts and related transmission gears in the transmission gearbox. Although the designer has exhausted his brains, it cannot solve the reality of bearing capacity, gear module, small diameter and small diameter at the tail of the two screws, resulting in poor torque resistance. Small output torque and poor load resistance are the most significant defects of parallel twin-screw barrel. However, the plasticity of the aspect ratio is the advantage of the parallel twin screw. It can increase and decrease the aspect ratio according to the difference of the molding conditions to meet the requirements of the plastic processing technology, and can expand the scope of application of the parallel twin screw, but it is difficult to do this conical twin screw barrel.

The two conical screws in the conical twin-screw barrel are arranged horizontally, and the two axes are installed in the barrel at an included angle. The center distance between the two axes gradually increases from the small end to the big end, so that the two output shafts of the transmission gearbox have a larger center distance. The gears and gear shafts in these transmission systems and the radial bearings and thrust bearings supporting these gear shafts have a larger installation space, which can install larger radial bearings and bearing thrust, each drive shaft has a shaft diameter sufficient to meet the transmission torque, so large working torque and large bearing capacity are a major feature of the conical twin-screw barrel. This parallel twin screw barrel is incomparable. When the twin-screw barrel is working, the melt will generate a very large pressure (head pressure) at the screw head. The pressure is usually about 14MPA, sometimes even as high as 30MPA or more. This pressure forms a strong axial thrust on the screw, and the thrust is the function of the anti-back bearing.

Parallel twin-screw barrel due to the two screw center distance is small, the bearing capacity of the anti-back bearing and its diameter size, large diameter bearing capacity, obviously with large diameter of the anti-back bearing is impossible. This contradictory situation usually uses several small-diameter anti-retreat bearings in series to bear strong axial force together. The core problem of using this method is that the load borne by each thrust bearing must be uniform and the same. Otherwise, the large bearing will be destroyed in advance due to overload, and the load it should bear will be added to other bearings to overload it. The consequences of this continuous destruction are very serious. It can be seen that the structure of the parallel twin-screw barrel transmission system is more complex. Compared with the structure of the conical twin-screw barrel transmission system, the manufacturing cost of the gearbox is high and the maintenance is more complicated.

The conical twin-screw barrel has an included angle due to the arrangement of the two screws, so the two output shafts of the transmission gearbox have a larger center distance. In the gearbox, two large thrust-aligning ball bearings arranged in a staggered front and back are installed. Enough to prevent the axial force formed by the head pressure, its characteristics are large carrying capacity, low manufacturing cost of the gearbox, and more convenient maintenance.

For users, the purchase of twin-screw barrels is very important, different types of twin-screw barrels have different performance and applications, therefore, it is necessary to find out the performance and application of various twin-screw barrels. For example, the meshing type co-rotating twin-screw barrel because of its high speed, shear rate, combined screw, it is widely used in the modification of the polymer is not easy to thermal decomposition-blending, filling, fiber reinforcement and material reaction extrusion. For example, the meshing-type rotating twin-screw barrel, because of its good mixing and plasticizing function, its biggest feature is the direct molding of PVC powder. Such as changing the geometry of the screw, it can also be used for the molding of other materials, but its strength is still PVC molding. According to the size of the plastic section, determine the amount of extrusion, and then by the amount of extrusion to select the specifications of the twin screw barrel. In the case of plastic processing and molding process conditions are basically the same, the conical twin-screw barrel can adapt to the larger head pressure, and the parallel twin-screw barrel can adapt to the smaller head pressure.