Products produced by hollow blow mold machines require uniform wall thickness. Usually, the hollow container below 0.2L can be without the parison wall thickness control device. In other cases, the use of the parison wall thickness control device should be considered, especially for hollow molded products with complex cross-sections. At present, the wall thickness control is usually achieved by changing the die lip gap between the die cover and the die core. According to the shape of the head cover and the core, the adjustment method of the lip gap is also different. The up and down movement of the mold core is generally driven by a hydraulic cylinder.

When the hollow blow molding machine processes plastic hollow containers with simple shapes, it can be realized by a switch-type hydraulic system. The electro-hydraulic reversing valve only accepts power-on or power-off signals to make the hydraulic cylinder go up or down. The distance the hydraulic cylinder moves (that is, the change of the opening of the die) is set by the upper and lower limit nuts, and the speed of the hydraulic cylinder is set by The throttling function of the flow valve is set, and the electrical signal of the electro-hydraulic reversing valve is controlled by a time relay. This control method is simple and inexpensive, but the wall thickness variation law is simple, there are only two wall thickness variations, and it can only be used for hollow containers with simple shapes.