The automatic control of parison wall thickness includes axial control and radial control. For radial control technology, China is still in the research stage, and relatively speaking, axial control research has matured.

The axial control of the parison wall thickness adopts closed-loop control technology. The user sets the axial variation curve of the parison wall thickness on the touch screen panel of the wall thickness controller. The PLC controller sends corresponding voltage or current signals to the electro-hydraulic servo valve based on the curve. The electro-hydraulic servo drive servo cylinder controls the up and down movement of the center rod, thereby changing the mold clearance of the machine head. At the same time, a sensor (magnetic suspension electronic scale) is installed on the piston rod of the servo cylinder connected to the center rod. The electronic ruler can sense the size of the gap between the machine head mold and provide feedback to the PLC controller, compare it with the standard signal in the PLC controller, and then transmit it to the electro-hydraulic servo valve through the servo power amplifier, and drive the servo cylinder through the servo valve. The oil cylinder drives the center rod to move, and finally controls the mold opening to complete the control of the parison wall thickness.

The parison wall thickness control system is a position control system composed of an electro-hydraulic servo system. The core of control is the position of the central rod, and the control accuracy of the central rod position is the key to determining the effectiveness of parison wall thickness control. Therefore, the research focus of this system is on the position control accuracy of the central rod, that is, the control accuracy of the parison wall thickness and the response speed of the system.

The control method for parison wall thickness is to divide each parison forming process into several points and control the wall thickness of these points separately. The fewer control points, the faster the response speed, but the number of points is too small to achieve the required wall thickness control accuracy, and weld seams (circular patterns) are formed around the billet; Excessive points will cause the system response time to be too long, the servo cylinder will not have time to reflect the received signal, and the billet will have already come out. The traditional wall thickness controller for 200L plastic barrels is 64 points or 128 points. This article studies the 200L double L ring cylinder. Through experimental verification, under the premise of wall thickness control accuracy of ± 1mm and response time of 0.3~0.4 seconds at each point, 256 point wall thickness control is more suitable.

Studied the key technologies of a large capacity hollow blow molding machine head with a capacity of over 200L. Compared with other structural forms, a double spiral flow channel has been designed. The utility model makes the melting of molten materials more uniform, the melt flow smoother, eliminates theoretical seams, and improves the strength of the product; According to functional requirements, optimization methods were used to determine process parameters and dimensions, laying the foundation for the optimization design of large capacity hollow blow molding machines above 200L; On the basis of existing parison wall thickness control, the optimal control point and connection method of control points for 200L double L ring cylinder were studied, which improved the uniformity, accuracy, and product strength of parison wall thickness.

Double head blow molding machine, also known as blow molding machine, adopts a double layer double spiral flow channel head.

When the molten material flows in the inner and outer spiral flow channels, a portion of the molten material flows downwards along the inner and outer spiral flow channels, while the other portion flows downwards along the inner and outer core walls to the storage chamber. This ensures that the molten material flows 360 degrees downwards, allowing for uniform melting of the molten material.