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1) For extrusion blow molding
pay attention to controlling the drape and wrinkle defects of the parison. If the drape is too long, the wall thickness will be reduced and the excess material cut will also increase; if the drape is not enough and the parison is too short, it cannot be blown.
2) Wrinkle phenomenon
When the parison drops to a certain length, the melt on the parison cannot bear the weight of the parison and produces circumferential stress; generally, higher melt strength, smaller parison diameter expansion, higher extrusion rate and larger die gap are all helpful to improve wrinkles.
3) Uneven wall thickness
Another problem is that the wall thickness is uneven when the parison drops. Usually, a hexagonal nut is installed on the die head to adjust the gap between the core rod and the die.
4) Do a good job of exhaust
To obtain good surface quality of parts, we must pay attention to exhaust. For example, when sandblasting PE material on the mold surface, the sandblasting particle size should be less than 180#, and the blow mold of hard plastic should have exhaust holes, exhaust needles and exhaust grooves. In addition, increasing the blowing pressure is also helpful to improve the appearance of the product.
2. Troubleshooting of blow molding defects in Suzhou
1) Wrinkles
Check whether the die head and the core rod are coaxial
Reduce the temperature of the preform
Increase the die gap or molding section length of the preform
Choose a polymer with smaller preform expansion
2) Uneven length
Check whether there is bridging of the raw materials in the hopper
Check whether the temperature of the barrel feed section is too high
Check whether the screw speed fluctuates
Increase the back pressure of the extruder
Check the temperature control device of the extruder and the die
Check whether the screw and barrel are worn
Check whether the recycled material and the new material are mixed evenly
Check whether the filter screen is broken or partially blocked by impurities
3) Bubble
Strictly dry hygroscopic polymers
Heat the raw materials in the hopper to remove moisture
Reduce the water cooling amount at the extruder inlet
Check and remove impurities in the raw materials
Clear the accumulated material in the extruder and die head to avoid explanation
Increase the back pressure of the extruder
4) Stripes
Remove impurities in the raw materials
Clear the impurities accumulated in the die head
Avoid material accumulation and explanation
Lower the temperature of the preform
Polish or replace the die head
Replace the burned heating coil
5) Gel
Sieve out the powder in the recycled material
Dry raw materials
Improve the dispersing and mixing performance of the screw and reduce the barrel
