Due to its long chain structure and the flexibility of molecular chain, generally, when the polymer is placed at a certain temperature, from the action of external force, the formation and recombination of macromolecules undergo a series of intermediate states to the equilibrium state suitable for external force, which is a relaxation process, and its deformation changes with time. Because the relaxation time t * of the polymer is very short near the high elastic state or viscous flow temperature, if the deformation time T1 > > t * during molding.
Then it can be obtained from equation (3) when the external force action time t = T1. The upper and lower molds are installed between the upper and lower molds of the press, the plastic raw materials are directly added into the mold cavity, the mold is closed, the plastic fills the mold cavity under heat and pressure, and the plastic parts are obtained after curing and shaping. Formed hollow plastic products have good quality, accurate overall dimensions, no splicing joints, uniform wall thickness, multi-mode molding production and high degree of automation.
It is very suitable for mass and efficient production of small containers. After the shortage, the investment in equipment and forming mould is large, and skilled operators are required for operation and production. Plate thickness is related to die lip and three roll spacing. The temperature control of the extrusion die body is to prevent the melt from cooling down in the die body. It is generally set at about 185 ℃. In the production process of most products, it is no problem to set the temperature in this range. Individual products (bellows) are higher than this, up to 190 ℃.
The machining accuracy and fitting accuracy of each part have a significant impact on the uniformity of the slit. The fluctuation or unevenness of extruder discharge will also cause the unevenness of die discharge. The fluctuation or unevenness of extruder discharge is mainly caused by uneven clearance between screw and barrel, excessive extrusion back pressure or uneven heating of extruder.
