The double-head blow molding machine, that is, the blow molding machine adopts a double-layer double-helix flow channel head.

When the molten material flows in the inner and outer spiral flow channels, part of the molten material flows downward along the inner and outer spiral flow channels, and the other part of the molten material flows downward along the inner and outer core walls to the storage cavity, so that the molten material can be guaranteed to flow down 360 degrees, so that the molten material is evenly fused.

Product Introduction

Storage-type heads are divided into center-feeding type and side-feeding type. Side-feeding type is a very widely used method. In the storage-type side-feeding hollow blow molding machine, the role of the head is to fuse the molten material and form a parison. The key to the fusion of the molten material is the flow channel in the head. At present, some enterprises in my country have developed a double-layer heart-shaped envelope flow channel, but the double-layer heart-shaped envelope flow channel has a short flow channel length, a large pressure drop, and poor circumferential uniformity after the molten material is fused. This paper refers to foreign materials to study a double-layer double-helix flow channel, as shown in Figure 1.

In Figure 1, the outer core is provided with two outer spiral flow channels which are symmetrically wound at 180 degrees, and the inner core is provided with two inner spiral flow channels which are symmetrically wound at 180 degrees. The inner spiral flow channels and the outer spiral flow channels are arranged symmetrically at 180 degrees, and the winding angle of each spiral flow channel (inner spiral flow channel and outer spiral flow channel) on the outer core and the inner core is 360 degrees, so that the molten material on the 360-degree outer wall surface of the outer core and the inner core can be fully and evenly fused. During operation, the molten material enters the outer cylinder of the die head from the inlet, passes through the diversion hole of the diversion core sleeve, and is successfully diverted by the diversion cone on the outer core. The molten material flows to both sides of the diversion cone, and after turning 90 degrees through the guide flow channel, it is guided to the inner and outer core diversion. Part of the molten material flows downward in a spiral from the outer spiral flow channel on the outer core, and the other part flows into the inner spiral flow channel of the inner core through the guide flow hole. When the molten material flows in the inner and outer spiral flow channels, part of the molten material flows downward along the inner and outer spiral flow channels, and the other part of the molten material flows downward along the inner and outer core walls to the material storage cavity, so that the molten material can be guaranteed to flow down at 360 degrees, so that the molten material is evenly fused.

There are two types of automatic control of the wall thickness of the parison: axial control and radial control. For radial control technology, my country is still in the research stage. Relatively speaking, the research on axial control is more mature.

The axial control of the wall thickness of the parison 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 transmits the corresponding voltage or current signal to the electro-hydraulic servo valve according to the curve, and the electro-hydraulic servo drives the servo cylinder to control the up and down movement of the center rod, thereby changing the die gap of the die head. At the same time, a sensor (magnetic suspension electronic ruler) is installed on the piston rod of the servo cylinder connected to the center rod. The electronic ruler can sense the size of the die gap of the die head and feedback it 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 then drive the servo cylinder through the servo valve. The cylinder drives the center rod to move, and finally controls the opening of the die, completing 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 part of the control is the position of the center rod, among which the center rod position control accuracy is the key to determine the parison wall thickness control effect. Therefore, the research focus of this system is the center rod position control accuracy, that is, the parison wall thickness control accuracy and the system response speed.

The control method of the parison wall thickness is: divide each parison forming process into several points, and control the wall thickness of these points respectively. The fewer the control points, the faster the response speed, but too few points cannot achieve the desired wall thickness control accuracy, and a weld seam (ring pattern) is formed around the parison; too many points will cause the system response time to be too long, and the servo cylinder will not have time to respond to the received signal, and the parison has already come out. Traditional 200L plastic barrel wall thickness controllers are 64 points or 128 points. This paper studies the 200L double L ring barrel. After experimental verification, it is more appropriate to use 256-point wall thickness control under the premise of meeting the wall thickness control accuracy of ¡À1mm and the response time of each point of 0.3 to 0.4 seconds.

The key technologies of the head of a large-capacity hollow blow molding machine above 200L are studied. The designed double-layer double-helix flow channel form is compared with other structural forms. It makes the melt fusion more uniform, the melt flow more smoothly, eliminates the theoretical seam, and improves the strength of the product; according to the functional requirements, the optimization method is used to determine the process parameters and dimensions, laying the foundation for the optimization design of large-capacity hollow blow molding machines above 200L; based on the existing parison wall thickness control, the optimal number of control points and the connection method of the control points of the 200L double L ring barrel are studied, which improves the uniformity and precision of the wall thickness and the strength of the product.