Die is the key factor affecting the quality of UHMWPE pipe

UHMWPE pipe is the most widely used pipe because of its strong performance advantages. There are three main factors that affect the quality of UHMWPE pipe, among which mold is the most critical factor.

1. Raw materials are the core

In theory, the higher the molecular weight of the raw material, the better the wear resistance. However, as a wear-resistant pipe, other mechanical properties and long-term stability should be considered. Therefore, high molecular weight raw materials do not necessarily produce UHMWPE pipes with good comprehensive performance, which depends on mold equipment, processing and molding technology. At present, the processing technology of UHMWPE pipe has not been standardized, and the manufacturers are quite different. Mainly in die structure and process control. Therefore, there is no difference on the surface of the produced UHMWPE pipes, but there is a big difference in the indicators. There is a large proportion of empirical things here.

The raw material of UHMWPE pipe is elastomer and has zero fluidity, so it is difficult to extrude. At present, the core structure of the extruder is to open a full access slot on the screw, with shallow screw thread and small screw angle; the theoretical core is to increase the screw thrust as much as possible, and reduce the binding of raw materials, barrel and screw. The squeezing force is about 400 kg. Because of the high pressure in the extrusion process, it is difficult to extrude the thin-walled pipe and the die is easy to deviate. So the mold is very important.

2, mold

The production mould of UHMWPE pipe is the key factor affecting the quality of UHMWPE pipe, because:

① If the design of die compression ratio is not reasonable, it will lead to difficult extrusion of pipe, or insufficient compactness, poor pressure resistance and low mechanical properties.

② The channel is blocked, the raw materials are degraded too much in the extrusion process, and the properties of UHMWPE pipe are decreased.

③ The structure is unreasonable, the plasticization is not good, or the fusion is not good, and the pipe is easy to crack.

④ The structure is unreasonable, the extrusion fluctuation is large, and the operation is difficult.

The production operation of UHMWPE pipe is mainly based on experience. The main reason is that the mold design is unreasonable. Good mold design will achieve the following results.

① Good operation and stable production. As long as the temperature does not change greatly, the appearance of the pipe will not be affected by the change of the external environment temperature.

② The internal index of pipe material is good, which mainly refers to the density of UHMWPE pipe and the degradation of raw materials.

3. Extrusion process

The extrusion process of UHMWPE pipe is also very important to the internal properties of the pipe. Different molecular weight UHMWPE pipes need different extrusion temperature. When the molecular weight is 250 ± 500000, the plasticizing temperature should be around 240 ℃. If it is too low, the surface of the pipe will be lumpy and the plasticization is not good. If it is too high, the pipe will be easy to come out, but the degradation will be increased. The specific temperature of each material should be summarized based on experience. For the same kind of raw material, generally a mold should be adjusted to set a proper temperature. Therefore, in order to produce high-quality UHMWPE pipes, raw materials, molds and processing technology are the three core technologies.