Common pipe extrusion molding heads have the following three forms:
1. Straight-through head, also known as flat head. The extrusion direction of the melt in the die is parallel or consistent with the axis of the extruder screw. It is the simplest, most economical, and most commonly used die. The disadvantage is that the shunt trace created by the shunt bracket is difficult to remove. 8.2.2 Typical structure of pipe extrusion head
Pipe extrusion line with straight-through head, equipped with Walthmac gravimetric control system
2. Right-angle nose, also known as cross nose or curved nose. The extrusion direction of the melt in the machine head is at a right angle of 90, which can effectively eliminate the shunt marks produced by the shunt and improve the product quality. The disadvantage is that the core mold design, processing and installation are difficult.
3. Side type head, also known as tubular head. The melt from the extruder to the die has to be turned twice (90° or 45°) and extruded in a direction parallel to the axis of the screw. The advantage is to strengthen the plasticization of the melt and improve the product quality. Production of large diameter pipes. The disadvantage is that the structure is complex and the mold cost is high.
Taking the pipe extrusion molding head as an example, the head is mainly composed of the following parts.
(1) Head body. The function is to assemble the parts of the head and connect it with the extruder.
(2) Grid plate. The grid plate is between the extruder and the die, and its function is to change the melt from a spiral motion to a linear motion, and at the same time, it also prevents a very small number of unplasticized plastics and mechanical impurities from entering the die. In order to further strengthen the filtering effect of the grid, a filter screen with finer holes can be set on the grid to increase the extrusion resistance and make the profile more compact.
(3) Shunt bracket. The main function is to support the diverter and the mandrel, and at the same time to divide the melt into strands, which plays the role of uniform stirring. The small handpiece can be designed with the shunt holder and the shunt in one piece.
(4) Shunt. Also known as the torpedo head, the molten plastic is divided into a tubular parison through a diverter, and further heated and plasticized under the action of shearing force. There is also a heating device in the flow divider of the large machine head to make the melt plasticized evenly.
(5) Adjusting screw. Adjust the gap between the die and the mandrel to ensure that the wall thickness of the profile is uniform.
(6) Mandrel. The mandrel is the part that forms the inner surface of the profile, and the inner wall quality, surface roughness, shape and size of the profile depend on the mandrel.
(7) Mould. The die is the part that forms the outer surface of the profile, and the plastic can get a certain shape and size after passing through the die.
(8)Styling sleeve. The sizing sleeve enables the profile to obtain good surface roughness, reasonable dimensional accuracy and geometric shape.
(9) Clogging. Prevent the leakage of compressed air and maintain a certain pressure in the profile.
