A important method of making film and sheet is known as calendaring. In this process the plastic compound (composed of resin, filler, plasticizer and color pigment) is passed between a series of heated rollers. It comes out from the rolls squeezed into film or sheet. Thickness is controlled by a combination of squeezing and altering the speed of the finishing rolls. The finished product is cooled by passing through water-cooled rolls. The finished product is cooled by passing through water-cooled rolls. Vinyl floor tile, cellulose acetate sheeting and films are some of the applications.
Advantages Of Air Refrigeration : 1. The refrigerant used namely air is cheap and easily available. 2. There is no danger of fire or toxic effects due to leakages. 3. The weight to ton of refrigeration ratio is less as compared to other systems. Disadvantages Of Air Refrigeration : 1. The quantity of Refrigerant used per ton of refrigeration is high as compared to other systems. 2. The COP of the system is very low. Therefore running cost is high. 3. The danger of frosting at the expander valves is more as the air contains moisture content.
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