What are the main types of blow molding machine screws?

The screw of the blow molding machine is an important component of the blow molding machine. What are the main types of blow molding machine screws?

The main types of blow molding machine screws are ordinary type, separation type, and mixing type, and their structures and characteristics are as follows:

Blow molding machine screw model one: ordinary screw

The ordinary screw can be divided into three sections in structure, namely the feeding section, the transition section, and the metering section. The three segments are independent of each other and do not overlap, characterized by a length to diameter ratio (L/D) of (20-30)/1; The length of the feeding section is (4-8) D, and the length of the measuring section is (6-10) D. Its function is to carry out solid conveying, melting, melt conveying, exhaust and mixing of raw materials.

Blow molding machine screw model two: separation type screw

The separated screw structure is generally the same as the ordinary screw structure, but the difference is that the separation section is used instead of the gradient section. The length of the separation section is 5-15 times the diameter of the screw. In the separation section, there is a barrier edge (also known as a secondary edge) inside the screw groove, and the gap between this secondary edge and the wall of the machine barrel is greater than the gap between the main edge. When designing, it is advisable to ensure that the melt can smoothly pass through the secondary helix while preventing large-sized solid particles from crossing the secondary helix. The use of this spiral edge can effectively separate the plastic melt from the solid, forming two adjacent spiral grooves. The cross-section of the plastic solid groove gradually decreases along the direction of the spiral groove, while the cross-section of the melt groove gradually increases, reaching the end of the separation section. The solid groove disappears, and the melt groove occupies the entire spiral groove.

Its function is to separate the plastic solid from the melt, which is beneficial for stabilizing the solid bed and reducing or eliminating the degree of damage to the solid bed; And it can make the plastic melt completely or mostly pass through the secondary groove edges. This makes the plastic melt more uniformly and strongly sheared, resulting in better rheological properties of the plastic melt.

Blow molding machine screw model three: mixed screw

The mixing process of mixed screw plastics can be divided into distributed mixing and dispersed mixing. Distributed mixing refers to mixing in which the fluid does not exhibit yield stress, but only increases the spatial distribution between components, and the size of the components does not change. Dispersive mixing is a mixing process that can make the melt present yield stress, which can make the material mass or gel be crushed to a critical size and distributed into the mixture. In the process of plastic processing, dispersed mixing is always accompanied by distributed mixing, but distributed mixing is almost never accompanied by dispersed mixing.