Casting film production line in the cooling device
Casting production line in the cooling device mainly by the rack, cooling roller, peel roller, refrigeration system and air knife, auxiliary devices.
Chill rolls are a key component in cast films and have a length slightly larger than the die width of about 400-5000 mm in diameter. Chill roll surface should be hard chrome, polished to mirror finish. The molten resin is extruded from the lip of the head slit to the surface of the cooling roller to be rapidly cooled to form a film. The cooling roller also has a traction effect. The rate of heat transfer between the cast film and the casting roll depends on the enthalpy of the plastic used.
The way of film cooling is single-sided cooling and double-sided cooling two, double-sided cooling is divided into single-roll sink cooling and two-roll cooling two ways. Single roller cooling structure is simple, the use of more common. Double-sided cooling single roll sink, the cooling effect is better, but the film from the water through the film surface easy to bring water, the need to increase the water removal device, the level of trough to be strictly controlled and adjusted, should maintain balance without fluctuations. Double roller cooling effect, but the equipment is huge, high investment. The diameter of the double-sided chill roll is smaller than the cast chill roll, about 150-300 mm.
In the extrusion of the cast film, the main cooling takes place on the casting roll and the rest of the cooling takes place on the other cooling rolls. The cooling roller relies on forced water circulation to cool. In order to improve the cooling effect and reduce the temperature difference on the surface of the roller, the cooling roller is designed to be jacketed, and the roller is hollow. In order to facilitate the media back to the middle of the jacket with a spiral clamp. Chill rollers with temperature control make temperature control more accurate.
The air knife is a narrow slit nozzle for blowing compressed air and is a device that cools the film with the cooling roll to form the same width as the length of the cooling roll. Knife lip surface smooth, high precision. The role of air knife blown film and the air ring is different from the air knife through the air flow is to make the film close to the cooling roller surface, thereby enhancing the cooling effect, the output more transparent film. Throughout the width, the air velocity should be uniform, otherwise, the film quality is not good. Air knife gap is generally 0.6 a 0.8 mm angle of the air knife directly affects the quality of the film, so the angle of the air knife for the cooling roll should be adjustable. In addition there are two small air knife, a separate inflatable air pressure on the edge of the film to prevent the edge of the warp. The method of increasing the effect of the film roll, as well as the use of vacuum chamber device, the use of vacuum principle to the air between the film and the surface of the cooling roller, so as to avoid bubbles between the film and the roller.
After passing through the device, the temperature profile of the PP sheet is as follows:
(a) (b) show different cooling rates respectively;
(a) shows the temperature distribution at slow cooling;
(b) shows the temperature distribution during rapid cooling.
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