Parison or extrusion blow molding machine

(1) Control of the thickness and length of the parison

When the parison is extruded from the die of the machine head, expansion will occur, making the diameter and wall thickness of the parison larger than the gap between the die, and the parison hanging on the die will sag due to its own weight, causing elongation and extrusion of the end wall When the thickness becomes thinner, there are mainly the following ways to control the size of the parison during the extrusion process.

1. Adjust the gap of the die, generally design a conical die, drive the mandrel to move up and down through a hydraulic cylinder, and adjust the gap of the die as a variable for the control of the wall thickness of the parison.

2. Change the extrusion rate. The faster the extrusion rate, the larger the diameter and wall thickness of the parison due to die expansion.

3. Change the parison traction rate and periodically change the parison traction rate to control the wall thickness of the parison.

4. Pre-blowing method. When the parison is extruded, the parison is cut off by a special tool to make it back, and the method of blowing air before the parison enters the mold is called the pre-blowing method. The pre-blowing air volume is automatically changed while the parison is extruded, and the wall thickness of the bottomed parison can be controlled.

5. Program control of parison thickness, which is a control method to control the wall thickness and weight of blow molded products by changing the wall thickness of the extruded parison cross section.

(2) Requirements for the quality of the parison

The requirements for parison quality in extrusion blow molding production mainly include the following.

①The size, melt viscosity and temperature of each batch of parison are uniform.

②The appearance quality of the parison is better, because the parison has defects, the defects will be more significant after inflation.

③The extrusion of the parison must be synchronized with the time required for mold clamping, inflation, and cooling.

④ The parison must be extruded at a stable speed with uniform thickness.

⑤ The parison should be extruded at as low temperature as possible, and the temperature is stable.