Is a parallel twin-screw extruder good, or a conical twin-screw extruder? This is a question often asked by the user when choosing a twin-screw extruder. Twin-screw extruder classification According to the direction of rotation of the twin-screw, the extruder can be divided into the same direction and different directions of the two extruders, the same direction of the extruder is the two screws work in the same direction of rotation, different extrusion Outrigger refers to the opposite direction of rotation when the two screws are working. According to whether the axial line of the twin screw is parallel or not, it can be divided into two types of extruders, where the axis lines are parallel and the axis lines intersect. The axis line is parallel to the twin-screw extruder, and the axis line intersects with a conical twin-screw extruder. Twin screw extruders also have meshing and non-meshing points. Parallelism and conical twin-screw extruders have the same features: they have a forward-pushing mechanism for plastics, good plasticizing ability and dewatering ability, and have basically the same adaptability to the molding process of materials and plastic products.

The difference between parallel and conical twin-screw extruders：

1. Diameter: The diameter of the parallel twin screw is the same, and the diameter of the small end of the conical twin screw is different from that of the big end.

2. Concentricity: The center-to-center distance of the flat twin-screw is the same. The two axes of the conical twin-screw are at an included angle. 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 length of the screw to the outer diameter of the screw, and conical twin screw (L/D) refers to the length of the effective part of the screw and the diameter of the big end and small The ratio of the average of the end diameters.

From the above, we can clearly see that the most significant difference between the parallel and conical twin-screw extruders is that the screw barrels have different geometry, which leads to many differences in structure and performance, although the characteristics of the two are different. But there are their own advantages. Parallel twin-screw extruders, due to the small size of the center distance of the two screws, in the transmission gearbox, the space for the radial bearings and thrust bearings supporting the two output shafts and the associated transmission gears is limited, despite the designer's fee. Despite all the brains, it is impossible to solve the bearing bearing capacity, the module of the gear, the small diameter, and the small diameter of the tail of the two screws, resulting in poor torque resistance. The small output torque and poor resistance to load are the most significant drawbacks of parallel twin-screw extruders. However, 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 requirements of the plastic processing technology according to the difference in molding conditions, and the applicable range of the parallel twin screw can be expanded, but this point Twin-screw extruders are difficult to achieve.

Conical twin-screw extruder: Two conical screws are horizontally arranged, and the two axes are loaded into the barrel at an included angle. The centerline of the two axes gradually increases from the small end to the big end, making the two output shafts of the transmission gear box. With a large center distance, the gears and gear shafts in these transmission systems and the radial bearings and thrust bearings supporting these gear shafts have a large installation space. It can accommodate larger radial bearings and thrust bearings. Each drive shaft has a shaft diameter sufficient to meet the transmission torque, 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. When the twin-screw extruder of the twin-screw extruder works, the melt will produce a very large pressure (head pressure) at the head of the screw. The pressure is usually around 14 MPA and sometimes even up to 30 MPA. The pressure exerts a strong axial thrust on the screw, and the thrust is the function of stopping the bearing.

1. The parallel twin-screw extruder is limited by the small center distance of the two screws. The bearing capacity of the anti-return bearing is related to its diameter. The large bearing capacity of the diameter is large. Obviously, it is impossible to use a large-diameter, non-return bearing. This contradiction is usually achieved by connecting several small-diameter, non-returning bearings in series and cooperating with strong axial forces. The central problem in using this method is that each thrust bearing must bear the same load, otherwise, it can withstand large loads. The bearing was destroyed prematurely due to overload and the load it was subjected to was overloaded on other bearings. The consequences of this continuous destruction were very serious. It can be seen that the structure of the drive system of the parallel twin-screw extruder is relatively complex. Compared with the conical twin-screw extruder drive system structure, the manufacturing cost of the gear box is high and the maintenance is complicated.

2. The conical twin-screw extruder has an included angle due to the arrangement of the two screws. Therefore, the two output shafts of the transmission gear box have a large center distance. Two thrust-adjusting thrust balls are arranged in the gear box. The bearing is enough to prevent the axial force formed by the head pressure, which has the characteristics of large bearing capacity, low manufacturing cost of the gear box and convenient maintenance. For users, the purchase of twin-screw extruders is very important. Different types of twin-screw extruders have different properties and applications. Therefore, it is necessary to clarify the performance of various twin-screw extruders and Application occasions. For example, intermeshing co-rotating twin-screw extruders, due to their high rotational speeds and high shear rates, combined screws, are widely used for the modification of non-thermally decomposable polymers - blending, filling, fiber Reinforcement and material reaction extrusion. For example, intermeshing counter-rotating twin-screw extruders, because of their good mixing and plasticizing function, their greatest feature is the direct molding of PVC powder. If you change the geometry of the screw, it can also be used for molding other materials, but its strength is still PVC molding. According to the size of the plastic cross-section, determine the amount of extrusion, and then choose the size of the twin-screw extruder from the amount of extrusion. In the same plastic forming process conditions, the conical twin-screw extruder can accommodate a larger head pressure, parallel twin-screw extruder can adapt to a smaller head pressure.