Extrusion Blow Moulding Machines in blown film production process, film thickness uniformity is a key indicator, wherein the longitudinal thickness uniformity by extruding and pulling speed stability to be controlled, and the film thickness uniformity generally transverse dependant on die precision manufacturing, and with the production process parameter changes, in order to improve thin film lateral thickness uniformity, to introduce automatic transversal thickness control system, control methods of automatic die ( thermal expansion screw control ) and automatic air ring, this paper introduces the principle and application of automatic air ring.
1． Blow Moulding Machinebasic principles: automatic air ring adopts the structure of double outlet, wherein the air to maintain a constant under tuyere, tuyere circumference is divided into a plurality of ducts, each duct by the air chamber, valves, motor and other components, driven by a motor valve to adjust the air duct opening degree, control each duct volume size. In the control process, the thickness measuring probe detects the film thickness signal is transmitted to the computer, the computer to thickness signal and the current set of average thickness were compared, according to the thickness deviation and the changing tendency of operation, the control motor drives the valve to move, when the film is thick, the motor in forward movement, tuyere small; instead, the motor reversely moving air, increased by changing the air ring, each point on the circumference of the air volume adjustment, the cooling rate, the film transversal thickness deviation control in the target range.
2.The control scheme design of automatic air ring is an on-line real-time control system, system object to the distribution in the air ring on a plurality of motor. The fan sent by air ring cooling airflow air chamber constant and then assigned to each passage, driven by the motor to adjust the valve opening and closing movement of air inlet and air quantity, change the mould discharge PET Preform Mouldscooling effect, thereby controlling the thickness of film.