ZhangJiaGang Antron Machinery,Co.,Ltd

Screw structure of plastic granule machine

The screw is a key component of the extrusion system of the plastic pelletizer, and is called the heart of the waste plastic pelletizer. The performance of the screw determines the output of the waste plastic granulator, the plasticization quality of the material, the dispersibility, the temperature of the melt and the power consumption.
The structure of an ordinary screw is mainly composed of screw mandrel, screw edge, drop groove and other parts. The working length of the screw is usually divided into three sections: feeding section, melting section and homogenization section. The feeding section mainly preheats the materials and gradually compacts the loose materials and sends them to the melting section; the function of the melting section is to melt and plasticize all the materials, and to further compact the materials so that the air in the materials is discharged from the feeding section . The homogenization section is to further uniformly plasticize the melted materials, and make them extrude the die head continuously at a constant temperature, a constant pressure, and quantitatively.
1. Screw diameter
The choice of screw diameter is mainly determined by the size and output of processed products. Choose a screw with a large diameter for products with a large section, and a screw with a small diameter for a small section. Try to avoid small diameter screws to produce products with large cross-sections, otherwise there will be less material to be extruded, the head will not be easy to fill, and the phenomenon of material shortage will easily occur. Large-diameter screws produce small-section products, which not only causes low equipment utilization and difficult equipment control. The screw diameter is large and the extrusion speed is high, and the material passes through the die at a high speed, which makes the head pressure too high and damages the machine parts.
2. The effective working length of the screw and the length of each section
The length of each section of the screw is mainly determined by the nature of the processed material. For materials with high crystallinity, high melting temperature and poor thermal conductivity, in order to ensure that the material is basically preheated to the melting temperature at the end of the feeding section, the feeding section should be longer, and vice versa. For materials with small crystallization, wide melting temperature range and high viscosity (PC, PSU...) and poor thermal conductivity, the length of the melting section should be long, and vice versa.
3. Screw length to diameter ratio
In the production process, for the processing of heat-sensitive materials, such as PVC, use a smaller L/D, because too large Z/Q will easily cause the material to stay for too long and cause decomposition. For materials that require higher temperature and pressure, such as fluorine-containing plastics, use larger Z/Q screws for higher prices. For granular materials, after plasticizing and granulating, select smaller Z/Q, and for unplasticized powder materials, the requirement is larger.
4. Spiral groove depth
Ordinary screws usually have deep grooves in the feeding section and shallow grooves in the homogenization section. The volume of the screw groove becomes smaller from the feeding section to the homogenization section, resulting in a compression effect of the material from the feeding section to the homogenization section, which compacts the material and eliminates the gas. The necessary pressure ensures that the material has sufficient density when it reaches the end of the screw.
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