Application of air knife in the production of plastic thermoforming sheet by casting method

Application of air knife in the production of plastic thermoforming sheet by casting method

The key to the production of plastic thermoforming sheet by casting method is to make the sheet closely adhere to the roller. Otherwise, the surface of the sheet will be uneven, the transparency will be reduced, and the secondary processing performance will be deteriorated, which will affect the quality of the final plastic thermoforming product. Therefore, the general equipment is equipped with an air knife, which blows out a certain air pressure and temperature from the air knife slit nozzle, so that the sheet is close to the roller. Some of the air supply methods use a blower, some come from an air compressor. Therefore, some People also call "air knife" "air knife".

The air pressure blowing from the air knife can be adjusted, depending on the thickness, width, material, processing temperature, production speed, opening of the air knife nozzle, etc. The temperature of the airflow can refer to the temperature of the glazing rollers of the "calendering method" and "calendering method". Since most equipment is not equipped with a compressed air temperature control system, the temperature of the general airflow depends on the ambient temperature. Another key function of the air knife is to accelerate the cooling of the sheet and improve the production efficiency at about 20-30 °C. In the production of thermoforming sheets, the opening of the air knife nozzle is usually 0.6 to 1.0 mm, and individual can reach 2.0 mm. Some air knife devices also include two small air knives, which blow and press the edge of the sheet separately to prevent the edge from warping. In order to improve the effect of the sheet attaching to the roller, a vacuum device is installed near the machine head to remove the air between the sheet and the roller and the hot air generated by the molten blank, avoiding the sheet and the cooling roller. The phenomenon that the cartridge is not attached properly due to the generation of air bubbles.

The production method without air knife also exists in actual production. Due to the low production efficiency, the optimal parameters of the sheet attaching roller are not easy to grasp, and are generally less used.

In the way of providing air flow with a blower, pay special attention to the air filter device must be installed at the air inlet of the blower, and cleaned at least once a week. In actual production, due to the lack of timely cleaning, the charging pressure is reduced, the cooling capacity is reduced, the thickness of the sheet is difficult to control stably, and the adhesion is poor; or the damaged filter device is not replaced in time, and the unclean air pollutes the connection. The inner cavity of the pipe and the air knife causes quality problems such as black spots and pits on the surface of the sheet, which affects the cooling effect of the sheet.

If there is a blockage at the air knife outlet, it is recommended to do this first: first open the compressed air valve or blower, scrape the air knife outlet with 0.6-0.8mm thick copper sheet, and open the air duct on one side to let foreign objects Blow out from the air duct interface of the air knife. If the foreign matter is stuck too tightly or too large, it cannot be scraped or blown out, then the movable pressure plate of the air knife nozzle has to be disassembled.

In the air flow provided by the air compressor, pay attention to the quality problems such as oil spots, small hard spots, and material spots on the surface of the sheet due to the unclean separation of oil and water, which causes the gas to be wet. Therefore, it is best to install oil-water filters (which need to be discharged daily) or compressed air drying and cooling devices to improve airflow quality.