What Are The Factors That Affect The Quality Of UHMWPE Pipes?
Ultra-high molecular weight polyethylene pipe is the most widely used pipe due to its strong performance advantage. There are three main factors affecting the quality of UHMWPE pipe, among which the mold is the most critical factor.
1. Raw materials are the core
At the core of the raw material for the production of ultrahigh molecular weight polyethylene pipes is molecular weight. Theoretically, the higher the molecular weight of the raw materials, the better the wear resistance. However, as a wear-resistant pipe, other mechanical properties should also be considered, considering the stability of its long-term use. Therefore, the raw material with high molecular weight may not be able to produce ultra-high molecular weight polyethylene pipes with good comprehensive performance, which depends on the mold equipment and processing technology.
At present, the processing technology of ultra-high molecular weight polyethylene pipes has not been standardized, and the manufacturers vary greatly. Mainly in the mold structure and process control. Therefore, the surface of the ultra-high molecular polyethylene pipe produced is not different, but the index is very different. The empirical things here also occupy a relatively large proportion. The raw material of the ultrahigh molecular weight polyethylene pipe is an elastomer when extruded, and the fluidity is zero, which is not good for extrusion.
The core structure of the extruder is a screw-opening full traffic trough, a shallow screw thread and a small screw angle. The theoretical core is to increase the screw thrust as much as possible to reduce the bonding of the raw material to the barrel and the screw. The extrusion force is around 400 kg. Polyethylene pipes are due to the high pressure in the extrusion process, so the thin-walled pipes are difficult to squeeze and the molds are easily biased. Therefore the mold is very important.
The production mold of ultra-high molecular weight polyethylene pipe is a key factor affecting the quality of UHMWPE pipes. The main reasons are as follows:
(1) If the mold compression ratio is unreasonable, it will lead to difficulty in pipe extrusion, or insufficient compactness, poor pressure resistance, and low mechanical properties.
(2) The flow path is not smooth, the raw material is degraded excessively during the extrusion process, and the performance of the ultrahigh molecular weight polyethylene pipe is degraded.
(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 fluctuates greatly, and the operation is difficult. Ultra-high molecular weight polyethylene pipe production operations are mainly based on experience, the main reason is that the mold design is unreasonable. A good mold design will achieve the following effects.
(5) Good operation and stable production. As long as there is no major change in temperature, the appearance of the pipe will not be affected by changes in ambient temperature.
(6) The intrinsic index of the pipe is good, mainly referring to the compactness of the UHMWPE pipe and the degradation of the raw materials.
3. Extrusion process
The extrusion process of ultra high molecular weight polyethylene pipes is also critical to the intrinsic properties of the pipe. Ultrahigh molecular weight polyethylene pipes of different molecular weights have different processing extrusion temperatures.
The molecular weight is 250±500,000, and the temperature during plasticization is about 240 degrees. Too low, the surface of the pipe is smashed, the plasticization is not good; if it is too high, the pipe is good, but the degradation is added. The specific temperature of each material should be summarized by experience. For the same raw material, generally one mold should be adjusted to set a suitable temperature. Therefore, in order to produce high-quality ultra-high molecular weight polyethylene pipes, raw materials, molds, and processing technologies are the core of the three technologies.