The role of the screw head three small pieces and common problems

Update:27-07-2018
Summary:

The three small pieces of the screw head function in th […]

The three small pieces of the screw head function in the whole screw group, such as sealing, mixing and plasticizing. It is a relatively important part. The quality problems of many plastic products are closely related to the three small parts of the screw head. There are often many three. The details of the small parts have not been handled so that the scrap rate of plastic products has increased significantly, and even forced to stop maintenance. Now I pointed out that the following points hope to bring convenience to all injection molding friends.
 
 1. The overall surface of the three small parts of the screw head is required to be smooth. Except for the assembly part, there can be no right angle acute angles in any place that can be seen from the front. It should be smooth transition. The smooth R size depends on the situation, because the right angle is acute. The dead angle is easy to crack and it is easy to accumulate material, so that the flow of raw materials is not smooth enough. It is easy to have black spots and yellowing during the long period. Remember that the three small pieces are the most prone to yellowing, and many of them are yellowing such as PC.PMMA. It started to turn yellow in three small pieces.
 
2. The design of the two end faces of the aprons is also very important. Now many injection molding machine manufacturers design the combination of the aprons and the mesons to be flat without slope. There are two disadvantages. First, the plane contact has no bevel contact. The face is large, so the service life is much shorter than that of the inclined surface. Second, the junction of the meson without the bevel and the screw head becomes a dead angle. When the raw material stays for a long time, there will be black spots and yellowing. This slope is the most Good 30 degrees is better, 15 degrees is not big enough to accumulate material, 45 degree contact surface is large, it is not easy to accumulate material, but it is easy to violently over the rubber ring when shooting glue.
 
3. The clearance between the left and right sides of the rubber ring should be moderate, to see what raw materials are selected for production or large or small active clearance. Many large machines use thin wall products to shoot rubber. The key point is that the gap between the left and right movements of the rubber ring is too large. There are still a lot of PMMA, PC raw materials in the production of a squeaking sound is because the gap between the left and right aprons is too small and the discharge is not smooth.
 
4. The surface of the threaded part of the screw head is not as hard as other parts. If the hardness is too high, the thread will collapse and the thread strength will decrease. It should be protected by nitrogen after heat treatment. Or the thread can be processed after nitriding. The groove is preferably an R of a circular arc, rather than a right-angle turning tool. The stress is better, and many screw head breaks are in this part.

Details: Extruder Screw