Determination of Plasticizing Degree
The degree of plasticization of PVC hard goods is between 60% and 70%. Excessive or too low degrees of plasticization will affect the physical and other properties of the products. Judging whether the processing technology is suitable and the plasticizing degree of the profiles is ideal, the most fundamental way is to verify the physical and mechanical and other properties of the products. But verifying from the results, it is of a certain limitation and not conducive to production. During actual production, the following methods are used to judge whether the process is suitable and the plasticizing degree is good, and can guide the operators to adjust the process in time.
(1) Observe the material state at the vacuum hole of the extruder.
If the material is powder state or completely loose small bean curd slag, the material is easily sucked by vacuum. It shows that the temperatures in the pre feeding section and plasticizing section are too low, and the material plasticization is not good. If the material plasticization is very good at the vacuum hole, and the full fusion is stuck together and tightly wrapped on the screw rod, indicating that the plasticizing temperature is set too high in the early stage. It is difficult to extract moisture and volatile substance of the full fusion from the dense material. If the material at the vacuum is basically plasticized and roughly stuck into one but slightly loose, with a certain gloss and being moderately coated on the surface of the screw, which indicates that the material is properly plasticized and the front section of the process is set reasonably.
(2) Simple observation of the appearance of extruded embryos and products
If the process is reasonable and the products are properly plasticized, there should be glossy surface, and the inner tendons and outer walls bond strong, the inner and outer surface is smooth. Besides the incisions and products inside and outside don’t have the bubbles. The extruded embryos are of proper soft and hard moderatation, with glossy and smooth surfaces. With the poor plasticization, the product surface is dull , the product is crisp, and the inner tendons are easily broken while the outer wall is stressed, so the material embryo is hard, dark, and is not easy to shape. The surface of the overly plastisized products will be yellower than the normal ones, the port is slags and the products are brittle. The too soft material embryo is not easy to enter the set, from the extruder, dropping the slags. Observing those phenomena with combined actual technological parameters, the process can be judge too high or low.