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What types of screws are there in large plastic blow molding machines?

June 14,2022

The screw of a large plastic blow molding machine is an important part in the production process. Its main function is to plasticize, melt, and transport the raw materials for blow molding. Today, the editor of Yankang wants to popularize the types of screw models of large plastic blow molding machines with you. We will introduce different screw types of blow molding machines from the screw structure, screw diameter and screw length-diameter ratio of plastic blow molding machines.

Screw structure

Ordinary screw
The main feature of ordinary screw is that it is mainly divided into three sections, namely: feeding section, gradual change section and metering section.
The three segments are independent and non-overlapping; the aspect ratio of each segment is different. The basic function is to transport, melt, transport, exhaust and mix raw materials.

Separate screw

The structure of the separation screw is similar to that of the ordinary screw. The difference is that the separation screw replaces the gradual change section of the ordinary screw with the separation section. The main feature is that the melting section of the screw is provided with two main and auxiliary threads and forms two screw grooves.

One of the channels contains solids and the other channel contains liquids. The molten film formed in the solid screw groove barrel is transported into the liquid screw groove through the high-speed and stable rotation of the screw. In the homogenization section of the liquid straight-through screw, the length of the homogenization section is increased accordingly. The melt processed by the screw of this type of blow molding machine is relatively stable, the plastic melt rheology is better, and the performance is relatively high.

Barrier screw

The main feature of the barrier screw is to add an additional barrier section at a certain position of the screw, in order to better improve the mixing capacity.

The longitudinal grooves opened in the barrier section are divided into two groups, one is the feeding trough, the outlet is closed; the other group is the discharging trough, the inlet is closed. All molten material or unplasticized plastic particles are forced to pass through the barrier section, the gap of the barrier section is small, the shear rate is large, and the shear effect is strong. Plastic granules can be plasticized quickly and the melt can be further mixed.

Split type screw

The main feature of the split-flow screw is to add a pin or a split block at a certain position of the screw, in order to increase the mixing capacity of the screw for raw materials.
Pins or diverter blocks serve different purposes in different locations. The mixing and stirring effect of raw materials can be changed in the screw homogenization section; the shear rate can be increased in the melting section. Although the action of the pin or the diverter block is not as fast, it is generally good for changing the mixing effect of the material.

CTM (Cavity Transfer Mixer) screw

It consists of a stator and a rotor, the stator being part of the screw barrel, and the rotor being a cylinder with a smooth head of the screw. Several spherical holes are regularly distributed on the stator and rotor, forming a CTM screw structure. CTM screw is a kind of screw with high mixing efficiency. At the same time, the feeding section of the screw is cooled by water, which can provide enough melt.

Mixing screw

The main feature of the mixing screw is that the mixing of plastics in the processing process can be divided into distributed mixing and dispersion mixing.

Distributed kneading can avoid the yield stress of the fluid and better ensure the quality of the fluid.
Dispersive mixing is a mixing process in which the melt exhibits yield stress.

In the process of plastic processing, the dispersive kneading process will be accompanied by the distributive kneading effect, but the dispersive kneading process will hardly be accompanied by the dispersive kneading effect.

Screw diameter

From ø30mm-ø200mm, the size of the screw diameter represents the size of the extrusion volume.
The choice of a large screw diameter or a small screw diameter should be determined according to the size of the product to be produced, the type of plastic raw materials and the required production level. For products with a larger cross-sectional area, the blow molding machine needs to choose a screw with a larger diameter. On the contrary, for a product with a small cross-sectional area, the blow molding machine needs to choose a screw with a smaller diameter. Such a reasonable configuration can ensure the quality of the product, Save energy consumption and reduce production costs.

The aspect ratio of the screw

The length-diameter ratio of the screw has a certain influence on the plasticizing ability of the screw. The common types of length-diameter ratio are: 11:1, 15:1, 20:1, 25:1, 30:1, etc.

A large aspect ratio can achieve a more adequate and uniform plasticizing effect quality, but the production cost will also be high, so in the production process, we generally achieve a good plasticizing effect with a small aspect ratio.

Since the large plastic blow molding machine is used to produce large plastic products, it needs to process a large volume of raw materials and a large parison, so the performance requirements for the screw are also relatively high. The screw of large plastic blow molding machine generally needs to have the characteristics of strong plasticizing ability, uniform mixing and stirring effect, and stable temperature.

This is the end of the introduction to the types of screw types of large plastic blow molding machines. It is very necessary to choose a screw type with stable performance for plastic blow molding machines. Especially for large plastic blow molding machines, the processing capacity of raw materials is larger and stable screw can greatly improve the processing effect of raw materials, ensure the quality of raw materials, and lay a good material foundation for the production of plastic blow molding products with stable quality.