(1) The main influential factors and control methods in the PC extrusion die parison manufacturing process. Extrusion blow molding is primarily the manufacture of parisons whose quality has a significant impact on the properties and appearance of the article. The influencing factors and the control methods in the parison manufacturing process are as follows.
1. The choice of raw materials.
In blow molding, the choice of raw materials is very important. First, the performance requirements of raw materials to meet the requirements of products, followed by the processing of raw materials must meet the blow molding process requirements, the general selection of hollow-grade resin. HDPE blow molding products, the melt flow rate is generally 0.01 ~ 1.O∥ 10min, low MFR resin is conducive to preventing parison sagging, easy to get the average wall thickness parison. However, as the screw speed increases, the low MFR melt tends to be rough.
2 temperature control.
During the extrusion of the parison, PC extrusion mold temperature control is very important. The choice of extrusion temperature depends mainly on the nature of the resin. Extrusion temperature is too low, parison rough surface; extrusion temperature is too high, the melt strength decreased, the product wall thickness. PC blow bottle extrusion temperature control at ± 3 ℃. For PVC heat-sensitive plastic, but also pay attention to control the temperature, to prevent its thermal decomposition.
3.PC extrusion mold-type screw speed.
Screw speed is another important factor affecting the quality of extruded parison.
High extrusion speeds increase yield and reduce parison sagging, but the surface quality of the parison decreases, especially when the shear rate is too high, which can cause some plastics to melt out. Screw speed is easy to produce a lot of friction heat, heat sensitive plastics such as PVC thermal decomposition danger. General blow molding larger extruder, the screw speed control in 70r / min or less.
4.PC extrusion die-type die size and quality.
The die is the main device that determines the size and shape of the parison. Therefore, the inner surface of the die is required to be smooth and the surface roughness is low to facilitate the smooth parison. Die section length of the general choice of 8 times the gap between the die and mandrel spacing.