10[Comprehensive]Common Problems With Blow Molding Products

10[Comprehensive]Common Problems With Blow Molding Products

Today you’re going to see 10 comprehensive common problems with blow molding products.

In fact:

In the process of extrusion blow molding, there are always many technical problems. Yankang Plastic Machinery would like to share with you the reasons for these problems and the corresponding solutions, hoping to provide you with relevant suggestions for solving problems.

Let’s dive right in.

  • 1.The uneven vertical wall thickness of blow molding products
  • 2.The non-uniform horizontal wall thickness of blow molding products
  • 3. Orange peel pattern or pitted on the surface of the blow molding products
  • 4.Volume reduction of blow molding products
  • 5.Unclear outline or text of blow molding products
  • 6.Too much flanging and thickness of blow molding products
  • 7.Excessively deep vertical stripes
  • 8. The moulded embryo is blown apart when forming
  • 9.Difficulty in mold release of blow molding products
  • 10. The quality of blow molding products fluctuates greatly

1.The uneven vertical wall thickness of blow molding products


①The dead weight droop phenomenon is serious.

②The diameter of the longitudinal two cross-sections of the blanks is too different.


①The casting reduces the melt temperature of the billet, improves the extrusion speed, replaces the resin with lower melt flow speed, and adjusts the control device of the billet.

②To properly change the product design, using the bottom blow molding.

2.The non-uniform horizontal wall thickness of blow molding products


①The extruding of the extruded blank is skewed.

②The temperature difference between the inner and outer core is large.

③An asymmetrical appearance.

④The blow ratio of the blank is too large.


①The width deviation of the die gap is adjusted to make the wall thickness even. Before the closed mold, straighten out the mold.

②Increase or decrease the heating temperature of the mould sleeve and improve the deviation of the internal and external temperature of the mould.

③The preclamping and pre-expansion of mold billet are carried out before the plate is closed so that the mold billet is offset in the direction of a thin wall.

④The billet expansion ratio is reduced bypass.

3. Orange peel pattern or pitted on the surface of the blow molding products


①Exhaust of exhaust mold is poor.

②Water leakage in the upper mould or condensation in the mould cavity.

③Due to the poor plasticization of the moulded blank, the melting fracture of the moulded blank is short of the blowing pressure.

④Air inflation is slow.

⑤Her blow ratio is too small.


①The blank of jig mold was sandblasted and the air vent was added.

②Repair the mold and adjust the cooling temperature of the mold above “dew point”.

③Lower the screw speed and raise the heating temperature of the extruder.

④To increase air pressure.

⑤Clean air passages and check for air leakage through the air shaft.

⑥Die change the mold cover, mold core, high billet expansion ratio.

4.Volume reduction of blow molding products


①The thickness of the blank wall increases, resulting in the thickening of the product wall.

②The increase in shrinkage of contaminated products leads to a reduction in product size.

③Flat blowing air pressure, products are not blown to the size of the cavity design.


①The main control device of the regulating program reduces the thickness of the blank wall. The melt temperature of the improved billet decreases the mold expansion ratio.

②Contact to replace the resin with a lower shrinkage, extend the blowing time, reduce the mold cooling temperature.

③To properly increase the pressure of compressed air.

5.Unclear outline or text of blow molding products


①Exhaust in the exhaust cavity is poor.

②Air pressure at the inlet is low.

③The melt temperature of the medium blank is low, and the material plasticization is not good.

④Mold cooling temperature is low, mold “condensation” phenomenon.


①Trim the mold, sandblast treatment of the cavity or add an air vent.

②Air pressure increases.

③Increase the heating temperature of the extruder and its head properly, and add appropriate filler ingredients if necessary.

④Adjust the mold temperature above the dew point temperature.

6.Too much flanging and thickness of blow molding products


①The pressure of locking die is insufficient.

②Insert die blade wear, guide column deviation.

③The blank is deflected when blown out

④The discharge chute at the blank edge of the profile clamp is too shallow or the depth of the blade is too shallow.

⑤The air charging of the vermiform blank starts too early.


①To increase the mold pressure lock, suitable for reducing the blowing pressure.

②Repair the die blade, correct or replace the die guide.

③Center position of calibration blank and blowpipe.

④Trim the mold to deepen the depth of the discharge chute or knife.

⑤The filling time of blank is adjusted.

7.Excessively deep vertical stripes


①The lip is dirty.

②Insert the mold, the core edge has burr or notch.

③Brown pigment or resin decomposition to produce dark streaks.

④Passing through the hole, material mixed with impurity deposit in the die.


①Clean the die opening with the copper cutter at the front.

②Blanking die.

③The temperature should be lowered appropriately and the dispersed pigment should be replaced.

④Replace the filter panel and use the stained leftover material.

8. The moulded embryo is blown apart when forming


①The blade edge is too sharp.

②The blank has impurities or bubbles.

③The blow ratio is too large.

④The melt strength of the blank is low.

⑤The length of the blank is insufficient.

⑥The thickness of the blank wall is too thin or uneven.

⑦The pressure vessel is expanded and cracked during mold opening (insufficient air release time).

⑧The mold locking force is insufficient.


①Suitably increase the width and angle of the blade.

②Dry raw materials are used in the air, wet raw materials are used after drying, and clean raw materials are used. Clean up the die.

③Replace the cover and core to reduce the blow ratio.

④Replace proper raw materials and lower melt temperatures.

⑤The department checks the control device of extruder or cylinder head, reduces the change of technological parameters, increases the length of billet, changes the mould sleeve or core, and thickens the blank wall. Check the blank control device; Adjust die clearance.

⑥Adjust the air release time or delay the starting time of mold.

⑦To increase the clamping pressure or reduce the blowing pressure.

9.Difficulty in mold release of blow molding products


①The cooling time is too long and the mold cooling temperature is low.

②Dial mold design is not good, the cavity surface has burr.

③The moving speed of front and back plates are not uniform when starting mold.

④Error in mold installation.


①The elastane shortens the billet inflation time and increases the mold temperature.

Blanking dies; Reduce the depth of the groove and the gradient of the convex rib is 1:50 or 1:10 demoulding agent.

②Repair the locking device to make the front and back templates move at the same speed.

③Reinstall the mold and correct the placement of the two halves.

10. The quality of blow molding products fluctuates greatly


①The thickness of the blank wall changed suddenly.

②The mixing of side and corner return materials is uneven.

③The filling section is blocked, causing fluctuations of extruder output.

④The heating temperature is not uniform.


①Key repair blank control device.

②A good mixing device is used to extend mixing time. Reduce the amount of side – Angle recycling when necessary.

③Remove the clotting at the vent.

④To reduce the temperature at the inlet.

⑤Replace electrical heating cabinet.

Above is 10 comprehensive common problems with blow molding products.

For more information about blow moulding machines, please enter the blog of Yankang Plastic Machinery(click it).


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