The temperature of the blow molding machine is an important factor affecting the wall thickness of blow molding products. In order to ensure the uniform wall thickness of hollow blow molded products, the editor analyzed the performance and influence of temperature on the wall thickness distribution from the previous parison molding, parison inflation, product cooling, and solidification stages of Junkang, and summarized them. Hope this article can help you.
From the three key parts of parison forming, parison inflation process in the mold, and product cooling, we will introduce in detail the influence of the temperature of the hollow blow molding machine on the wall thickness of the blow molding product.
1. The temperature effect of the parison forming stage
The uniformity of wall thickness distribution of the parison directly affects the uniformity and performance of the final product wall thickness distribution. The wall thickness distribution of the parison is mainly affected by two complex phenomena, the die expansion and the vertical elongation.
Expansion will increase the diameter and wall thickness of the parison and reduce its length accordingly; the effect of vertical elongation is the opposite of that of expansion.
The combined effect of these two opposing phenomena determines the size and shape of the parison before the blow mold is closed. Many scholars have done a lot of research on the change and distribution of the diameter and wall thickness of the parison during the extrusion process.
The melt temperature has a direct effect on the expansion and vertical elongation of the parison, and the high temperature parison is cooled in contact with the air after being extruded from the die, resulting in a temperature gradient in the parison in the axial and radial directions, which affects the parison. Wall thickness distribution.
2. The temperature effect of the parison in the inflation stage of the mold
The inflation molding stage is divided into 2 consecutive stages: free inflation from the start of the parison to the contact between the parison and the mold cavity; constrained inflation from the contact between the parison and the mold cavity to the formation of the blow molded part .
The effect of the parison temperature on free inflation is achieved by affecting the modulus of the material. The lower the temperature, the greater the modulus and the harder it is for the parison to deform. Due to the temperature gradient of the parison, the deformation of each part is also different. After the free inflation is over, the parison comes into contact with the die wall and begins the inflation process in the constrained stage. After the parison is in contact with the mold wall, the temperature of the parison is rapidly reduced due to the quenching effect of the mold on the cavity, and the parison is immediately bonded to the mold wall to stop further deformation. The wall thickness at this time is the wall thickness of the part. .
Due to the complexity of the shape of the part, the time when each part of the parison contacts the die wall is inconsistent, and the uneven wall thickness of the parison makes the wall thickness distribution of the part uneven.
3. The influence of temperature in the cooling stage of the product
There are two cooling methods for extrusion blow molding:
A cooling water channel is opened in the blow mold to pass the cooling water, and the cooling water can take away the heat through the heat transfer between the product and the mold surface and between the mold and the cooling water.
By circulating air to cool the inner surface of the part, heat transfer between the air and the part carries the heat away.
Temperature is a very important process parameter in the plastic extrusion blow molding process, which affects the mechanical properties of the wall thickness distribution and production efficiency of blow molding products. In this paper, the influence of temperature on its forming and performance is analyzed from three stages: the forming of the parison, the expansion of the parison in the mold to form the product, and the cooling of the product.
September 12, 2022
July 25, 2022
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