Vacuum Drying ─ New Drying Technique for Plastic Materials

Drying process is inevitable and also crucial for every plastics processor to put out high-quality products. Suitable drying technique can help save costs and reduce energy consumption. Accurate evaluation of drying technique and costs is of great significance to pick out advisable drying technique.

What is Vacuum Drying

Vacuum refers to the air state that the air pressure is less than 101,325 Pa (the standard atmosphere is about 101KPa) within the given space. Under vacuum condition, air density is represented by air pressure. It is obvious that the lower the air pressure is, the thinner the air will be.

The boiling point of water is directly proportional with the air pressure. That is to say, the boiling point of water rises as air pressure increases, and vice versa. On the mountain of more than several kilometers, the air pressure is much lower than that at sea level, and the boiling point of water is low because of atmospheric depression. So the water will boil below 100℃on the high mountain.

When the mercury column of barometer reaches 635mmHg (-84.7KPa), the boiling point of water is 56℃. Under this condition, water vapor contained in plastic pellets will evaporate once heated up above the boiling point of water. Water molecules in plastic pellets are activated and ambient pressure is reduced. Vapor is driven out of the plastic materials which can greatly reduce drying time.

Because air pressure is much lower in the vacuum drying hopper in which materials are placed, the vapor in the moist material has lower boiling point than that of vapor in the drying hopper. Moisture will be evaporated quickly and escapes into the hopper. The vacuum pump aspirates and expels the moisture to dry the material. Traditional desiccant dryers are tested by measuring the temperature and dew point, while we measure the temperature and vacuum degree of SVD to ensure drying effect. After obtaining certain temperature and vacuum degree, we assure that the materials are dried.

Why is Vacuum Drying Capable of Saving Energy and Promoting Product Quality

Vacuum drying technique removes regeneration blower and heater system compared with traditional dryers that employ desiccants. In addition, its drying blower is replaced by vacuum pump consuming lower power which can save more energy. By continuous aspiration, the vacuum pump can effectively suction dusts and other impurities in plastic materials to promote product quality.

To meet the requirements of saving energy and promoting product quality for plastics processors, Shini Group has developed SVD series. This series can save more than 50% of energy compared with traditional SCD series and promote product quality effectively. Furthermore, they also have the following features:

 • With neat and eye-catching appearance, the overall design occupies small area.

 • Integration of material drying and conveying.

 • High-efficiency vacuum pump is used to create ultra low vacuity (down to -98KPa) with low noise level (lower than 60dB), simple structure, easy repair and is maintenance-free without oil vapor.

 • Material storage tank and conducting strip are made of duralumin with light weight and high heat transfer efficiency.

 • Cylinder ejection design of the barrelhead is convenient for internal cleaning.

 •  Drying hopper with insulating design avoids heat dissipation and saves energy.

 •  Insulating layer of the drying hopper adopts double-open design to achieve easy maintenance.

 • Hermetic material conveying system avoids materials to be affected with damp.

 • LCD touch screen controller is easy to operate.

•  People-oriented design of 7-day time switch and overheat protector.