Blowing die for extrusion

摘要

A die body(10) performs a swiveling movement relative to a core(2) in order to vary the width of an extrudate outlet gap(S). Adjustment of the die body is by a pressure ring(12). The die body(10) is swivel mounted in the upper end of the parison die and the pressure ring(12) is located close to the outlet gap(S). The die body has an upper part(10a) with a spherical cap-shaped outer surface which swivels in a complementary bearing shell(8,9) in the die. A lower part(10b) of the die body is interchangeably connected to the upper part. The bearing shell comprises spherical dish-like upper(8) and lower(9) parts. Positioning of the die body may be performed by four hydraulic cylinders which contact the pressure ring. The four cylinders are arranged as two opposing pairs, offset from each other by 90[deg]. At least two stroke sensors are located around the circumference of the die body and are offset at 90[deg] to each other. Each stroke sensor has a spring-loaded sensing pin facing toward the pressure ring. Signals from the sensors are received by a computer which controls the actuation of the pressure ring according to a program dependent on the received signals. Die body positioners are double acting actuators and can be hydraulic cylinders(21) or spindle drives. Actuators are suspended in a plane orthogonal to the die core axis and passing through the rotation point of the swiveling bearing. Suspension points are universal joints. Each actuator may have two wedge-shaped profiles whose parallel faces lie against opposite sides of the die body lower part(10b) and push in the same direction to swivel the die body. Alternatively, actuators rotate two eccentrically mounted cams which roll on opposite sides of the die body lower part to swivel the die body.