The functional characteristics of the exhaust screw

During the extrusion process, the gas that needs to be discharged from the raw material includes three parts: the air brought between the material particles; the adsorbed moisture on the particle powder; the gas or liquid contained in the material, such as the remaining monomer, the low molecular volatiles and the moisture and so on. If these gases are not discharged, in addition to the physical and mechanical properties of the products, chemical and electrical properties will be reduced, pores, bubbles, scars, and surface darkening are also found on the surface or in the temporal part, which seriously affect the appearance of the products, such as the air gap will affect the dielectric strength of the cable; bubbles can affect the dielectric strength of the cable. The monofilament can not be stretched; a hard tube containing water will reduce the pressure of the hard tube; the bubble and scar in the plate will cause waste in the vacuum forming process and so on. It is generally believed that the content of these components in raw materials should not be greater than 0.2% before extrusion, and the surface should be at least less than 0.02% in some cases, such as polyester film. On the ordinary screw, the air and the adsorbed moisture of the raw material can escape from the feeding port when the plastic is extruded or be removed by the drying method before adding the feeding mouth. This process is called pre drying. However, the pre drying needs to increase the drying equipment, consume quite a lot of electricity and labor, so the cost will rise, and the removal of some monomers and some high boiling solvents is not good enough. For some transparent products, the pre drying process is booming, which increases the pollution opportunity of raw materials. In addition, with the development of the extrusion, the plastic (such as polyethylene), which had not high exhaust requirements in the past, could not escape from the mouth of the material as the screw speed increased, and the quality of the products would also be affected.