The three small pieces of screw head play the functions of sealing, mixing, plasticizing and other functions in the entire screw group. It is a relatively important part. The quality problems of many plastic products are closely related to the three small pieces of screw head. There are often many three Failure to deal with the details of small parts has greatly increased the scrap rate of plastic products, and even forced to shut down for maintenance.
1. The overall surface of the three small parts of the screw head is required to be smooth. Except for the assembly part, any place that can be seen from the front must not have a right-angled acute corner and a smooth transition. The size of the smooth R depends on the situation, because the right-angled acute angle Dead corners are easy to crack, not to mention, it is easy to accumulate materials, so that the flow of raw materials is not smooth. extruder screw barrel It is easy to have black spots and yellow in a long period. Remember that the three small pieces are the most prone to yellowing. Many PC, PMMA and other yellowing phenomena are It was in the three small pieces that it started to turn yellow.
2. The design of the two end faces of the rubber ring is also particularly important. Now many injection molding machine manufacturers design the joint surface of the rubber ring and the meson to be flat without slope. This has two disadvantages. First, the plane contact does not have the inclined surface contact. The surface is large, so the service life is much shorter than that of the inclined surface. Second, the junction of the meson without the inclined surface and the screw head becomes a dead corner, and the raw material stays for a long time, there will be black spots and yellowing. This slope is the most inclination 30 degrees is better, 15 degrees is not big enough, it is easy to accumulate materials, and the contact surface of 45 degrees is large, and it is not easy to accumulate materials, but it is easy to overwhelm the rubber ring when shooting glue.
3. The left and right movement gap of the rubber ring should be moderate, depending on what raw material is produced. Large or small movement gap. Many large machines make thin-walled products. The focus of injection is unstable because the left and right movement gap of the rubber ring is too large. There are also many PMMA and PC raw materials that have a rattling noise during production because the gap between the left and right movement of the rubber ring is too small, which results in unsmooth discharging.
4. The surface of the threaded part of the screw head does not need to be as hard as other parts. Too high hardness will easily cause the thread to jump off and the thread strength will decrease. It should be protected by blocked nitrogen before heat treatment. Or the thread should be processed after nitriding. Retraction of the threaded part The groove is best to be an R of a circular arc, rather than directly cut out by a right-angle turning tool. That way, the stress is better, and many screw head fractures are in this part.