The processing process of plastic material is mainly the melting, flow and setting of the colloidal particles to cool into the collection. It is a process of cooling after heating. It is also the process of changing the plastic from the particles to the different shapes. The following will explain the processing process at various stages.
(1) the melting device heater (heater) allows raw material pellets to melt gradually into fluid flow, which is mainly based on different raw materials to adjust suitable temperature. Raising the temperature will accelerate the flow of raw materials, increase efficiency, but do not always guarantee good rate, so we must get the right balance. The good effect and the characteristics of high thermal cracking of PP are the guarantee of smooth flow of raw materials to the head of the die during production, in order to avoid the shortage of filling or the phenomenon of reflux. The flow of reflux represents the faster flow of raw materials than the output rate, and the increase of the average flow efficiency at the end, equal to the increase of MFR, is one of the methods that can be used in processing, but it also causes the MFR distribution not to lead to the increase of the instability, which may lead to the increase of the adverse rate. However, the relationship between PP products and applications is not a product with high dimensional precision, so the impact is not large.
(2) the most of the screw PP processing is the screw driven flow, so the influence of the screw is very large, the diameter of the screw affects the output, the compression ratio affects the pressure value of the output and the effect of the finished product. This also includes the mixing effect of a variety of materials (color parent, additive and modifier). The main flow of raw material depends on the heating device, but the friction of the raw material will also produce friction heat, which can accelerate the fluidity, so the screw compression is smaller than the small driving flow, the speed must be increased, and the friction heat will be more compressed than the larger screw. The heating of raw materials is not only a heater, but also the friction heat and residence time must be included. If the mixing effect is particularly good, sometimes two stages of different screw or biaxial bar shall be designed and divided into different sections, so as to achieve various mixing effects.
(3) die or die plastic re - molding depends on the mold or die head, the finished product is stereoscopic, the mold is also more complex, but also to consider the shrinkage problem. All other bar shaped and needle like continuous die heads are classified into special shapes and irregular shapes. Attention should be paid to the immediate cooling stereotypes. Most of the design of plastic machinery is like syringe needle, and the extrusion force driven by snails will cause great pressure on small exports and improve production efficiency. When the die head is designed as a plane, how to make the raw material distribute on the whole surface and the design of the die head is very important.
(4) the cooling ejection mold also has cooling water cooling material design besides pouring gate and pouring raw materials. Pressure forming is achieved by cooling the waterway inside the roller to achieve cooling effect. Besides, there are wind knives. The cooling water is directly drilled in the blowing bag, and the cooling way of hollow blow and so on.
(5) the extension of the finished product reprocessing will enhance the effect, for example, the packing belt by the front and back roller drive speed varies, the finished product matching to the extension part of the tensile strength is not easy to tear, but the transverse is very easy to tear open. The molecular weight distribution also affects the extended effect of high speed production, and all the finished products include the unequal extension of the fiber, and the vacuum and the compression molding can also be seen as another form of extension.
(6) shrinkage of any raw material has the problem of shrinkage. The cause of shrinkage is internal stress caused by thermal expansion, cold contraction and crystallization. Generally speaking, thermal expansion and cold shrinkage are easy to overcome. It can extend the cooling time and keep pressure at work. Compared with non crystalline materials, the crystalline materials tend to have greater shrinkage differences, with PP about 1.6%, but only about 0.4%. This difference should be overcome in the mould, or the additive to reduce the shrinkage rate is often overcame, and the LDPE is often added to the plate to improve the necking problem.