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Analysis of Bending and Folding Phenomenon of Blow Molding

Sep. 29, 2020
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1: Why is the extrusion parison prone to bending? How to solve it?

(1) The main reason for the bending of the parison

In the extrusion blow molding process, the main reasons for the bending of the parison are as follows.

①The flow channel in the die is not smooth or the center of the die is not centered. The die gap is large on one side and small on the other side and the parison will bend to the side of the die gap.

② The uneven heating of the die head causes the temperature of the melt to be uneven, which leads to inconsistent pull effects of the extruded parison due to its own weight.

③Extrusion rate is too fast, causing the melt to accumulate in the die, causing the parison to bend.

(2) Solution

①Check the flow channel of the machine head and adjust the center of the machine head to make the gap of the die uniform.

② Adjust the heating temperature distribution of the machine head to make all parts heated evenly.

③Reduce the extrusion rate.

 Extrusion Blow Molding

2: Why does the extrusion blow molding parison appear curling? How to solve it?

The reason for the curling phenomenon of the extrusion blow molding parison is mainly due to the unreasonable temperature control of the die, which causes the temperature difference between the inner and outer surfaces of the parison. When the extruded parison appears curled to the inside, the die temperature may be too high. If the blank is crimped to the outside, the core temperature may be too high. The main solution is to control the temperature of the die and the core mold to be the same and to keep the temperature of each part uniform. When the extruded parison appears curled to the inside, the die temperature should be lowered at this time. If the parison is curled to the outside, the core temperature should be appropriately reduced.


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