Dry screw vacuum pump used in plastic industry


Dry screw vacuum pump means that the pump can start pumping under atmospheric pressure and can directly discharge the pumped gas to the atmosphere. There is no oil or other working medium in the pump cavity, and the ultimate pressure of the pump is the same as that of an oil-sealed vacuum pump. Stage or close mechanical vacuum pump.

Dry screw vacuum pump is a kind of pump body with many uses at present. Its application fields are all over various industries. Among them, it can be used as extruder degassing device, gas delivery device, gas extraction and compression device in the plastic product processing industry. Use the following information to understand this knowledge in detail:

1. Extruder degassing

During the process, the thermoplastic plastic is melted in the extruder and degassed in the screw part of the extruder. Dry screw vacuum pumps are used to extract gas and vapor components from the molten material. All low-molecular substances are extracted to obtain the ideal quality of the thermoplastic plastic, with a smooth appearance, higher strength, better insulation performance and lower gas generation speed.

2. Setting table
The plastic material melted and degassed in the extruder enters a continuous section on the sizing table. Typical cross-sections include pipes, door and window materials, wire ducts and medical pipes. The plastic material is drawn into the mold. For cooling and lubrication, a water film is formed between the inner side of the mold and the continuous work piece, and the air is evacuated stably by a dry screw vacuum pump.

3. Foaming

In EPS foam production, a dry screw vacuum pump is first used to suck the pre-expanded polystyrene particles into the mold, and then steam is used to pressurize them. Polymerization is carried out at the end and foamed into foam products. In order to avoid deformation during this process, it is easy to exceed 3 to 4 minutes for large products. The product must be cooled. In the foaming device of these products, a vacuum pump is used for cooling to ensure that it will not be deformed and the moisture in it will quickly evaporate. The evaporation process absorbs the heat of the product and speeds up the cooling process.

4. Pneumatic conveying device

In various stages of production, plastic spherical raw materials must be transferred from one location to another (such as from storage tank to dryer). It can be realized automatically by using a pneumatic conveying device, and the conveying speed can be accelerated. The pipeline is routed from the starting point to the end point and connected to the dry screw vacuum pump or compressor. Because of the material to be transported, it is “loaded” by the air in the pipeline at a faster rate, which can be compared with a hurricane. According to the weight of the material and the length of the pipeline, the design of the system can make the vacuum pump (vacuum transfer) or compressor (pressure transfer) generate enough wind speed to pick up the material and deliver it to the destination without accumulating in the pipeline .

5. Vinyl chloride gas extraction and compression

In the process of producing PVC, vinyl chloride gas is polymerized under the pressure of the autoclave to form polymerized PVC. At the same time, the generated gas is extracted, compressed and liquefied.

Use this kind of dry screw vacuum pump can obtain a clean high vacuum and vacuum environment, so it will not affect the quality of the processed plastic products, which is a main feature that distinguishes dry pumps from other vacuum pumps.

Dry screw vacuum pumps are widely used, mainly in the following aspects:

1) Polysilicon preparation process in low pressure chemical vapor deposition;
2) Semiconductor etching process. Corrosive gases and abrasive particles are often used or generated in these production processes;
3) For some processes that produce particles other than semiconductor processes, the particles are not expected to be mixed into the pump oil, but the particles are expected to be discharged from the pump, a certain type of dry mechanical vacuum pump can meet the requirements;
4) In the chemical industry, pharmaceutical industry, food industry, distillation, drying, deaeration, packaging, etc., organic solvents should be prevented from causing pollution, and dry vacuum pumps are suitable;
5) Used as the fore pump of a general oil-free cleaning vacuum system to prevent oil pollution.

Copyright: EVP Vacuum Pump

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