The extrusion head is an important component in the extrusion production line. Its function is to further compact and plasticize the plasticized melt. After shunting, it enters the annular section channel and is cooled and shaped into pipe blank. The pipe extrusion head is divided into three types: straight through head, right angle head (also known as bending head) and lateral head (side head). Among the plastic pipes, PVC pipes have the largest output and the widest application. Among them, rigid polyethylene pipes account for 75% and soft PVC pipes account for 25%. The following is a further introduction to the PVC pipe head.
1. Straight through head
This type of head axis coincides with the axis of the extruder, which has the advantages of simple structure, easy manufacture, low cost and low material flow resistance; The machine head has the disadvantages of difficult core mold heating and low pipe strength at the joint line caused by the diverter support. It can be seen from the flow channel structure that when the fluid passes through the head, it will go through several stages, such as diversion, compression, stable flow and setting. Here, l is the length of the straight part of the die, L2 is the length of the compression section, and l is the diversion cone part.
2. Right angle head
The mandrel end of this structure is the support end. Since there is no diverter support, the molten material enters from the head end to the opposite side of the mandrel and collects, and only one suture may be generated. In addition to pipes, the right angle head can also produce wire and cable products, which has the advantages of easy core mold heating and suitable for extruding pipes by inner diameter setting method; However, it also has some disadvantages, such as complex structure, difficult mandrel design, high manufacturing cost, large material flow resistance and so on.
3. Lateral nose
The material flow from the extruder first flows through a curved channel and then enters the side of the head. The material flow wraps the mandrel and flows out along the axis of the head. This design can not only make the extrusion direction of the pipe at any angle with the extruder, but also parallel to the screw axis of the extruder. It is suitable for high-speed extrusion of large-diameter pipe, but the structure of the head is complex and the cost is high.
4. Other forms of handpiece
Other types of machine heads include screen plate pipe extrusion machine head, coating pipe machine head, coating pipe machine head, mandrel rotary machine head, etc. The mandrel rotary head uses ordinary polymer particles to mix a certain length of glass fiber online after its plasticization and melting, and makes the melt molecules and glass fiber spirally oriented along the pipe wall of the extruded circular pipe to produce pipes with higher strength, which can meet the needs of engineering practice.