Segment of screw

When the material moves forward along the screw, it experiences changes in temperature, pressure, viscosity and so on. This change is not the same in the whole length of the screw. According to the changing characteristics of the material, the screw can be divided into adding (sending) material section, compression section and homogenizing section.
①, plastic and plastic three states
Plastic has thermosetting and thermoplastic two categories, thermosetting plastic molding curing, can not be reheated melting forming. The thermoplastic molding products can be reheated and fused to form other products.
With the change of temperature, thermoplastics produce glassy state, high elastic state and viscous fluid state, and with the repeated change of temperature, the three states produce repeated changes.
a. Different characteristics of polymer melts in three states:
Glassy - plastic appears as a rigid solid; The thermal motion energy is small, the intermolecular force is large, and the deformation is mainly contributed by the deformation of bond Angle. The deformation is recovered instantaneously after removing the external force, which belongs to the general elastic deformation.
High elastic state - plastics appear as rubber-like substances; The deformation is caused by segment orientation, which contributes to the conformation stretching of macromolecules, and the deformation value is large. After removing the external force, the deformation can be restored but has time dependence, belonging to high elastic deformation.
Viscous flow state -- plastic presents as a high viscosity melt; The thermal energy further intensifies the relative slip motion of chain molecules. The deformation is irreversible and belongs to plastic deformation
b. Plastic processing and three states of plastics:
Plastic glass state can be machined. High elastic state can be stretched processing, such as drawing textile, extrusion pipe, blow molding and hot forming. Viscous flow state can be coated, rolled and injection processing.
When the temperature is higher than the viscoelastic state, plastic will produce thermal decomposition, and when the temperature is lower than the glass state, plastic will produce embrittleness. When the plastic temperature is higher than the viscous flow state or lower than the glass state trend, the thermoplastic tends to serious deterioration and destruction, so in the processing or use of plastic products to avoid these two temperature areas.