Plastic extrusion blow molding machinery common defects and how to solve

Date: 11th Jun, 2017

In Plastic extrusion blow molding process, we always encounter a variety of problems. Silver Python machinery which is manufacture of Plastic extrusion blow molding machinery, let us provide some common defects and solutions.

Defect 1
Longitudinal wall thickness is uneven

Cause 1
1. Self-weight sag phenomenon serious
2. The longitudinal difference between the two cross-sectional diameters of the product is too large

Solution 1
1. Reduce the parison melt temperature, improve the parison extrusion speed, replace the use of low melt flow rate of resin, adjust the parison control device
2. Appropriate changes in product design, the use of bottom blowing method

Defect 2
Products transverse wall thickness is not uniform

Cause 2
1. parison extrusion skew
2. Mold sets and mold core temperature difference between inside and outside
3. Product shape asymmetry
4. Billet inflation is too large

Solution 2
1. Adjust the gap width of the die gap, so that the parison wall thickness uniform; before closing the mold, straight billet
2. To improve or reduce the mold set heating temperature, improve the temperature inside and outside the die deviation
3. When the mold is closed, the parison is pre-clamped and pre-expanded so that the parison is properly shifted in the thin-wall direction
4. Reduce the expansion ratio of the parison (replacement mold sleeve, core)

Defect 3
Products warp

Cause 3
1. The cooling is low
2. Blowing air pressure is insufficient
3. Product cooling is not uniform
4. Slab wall thickness difference is large

Solution 3
1. Extend the billet inflation (cooling) time, reduce the mold cooling temperature, parison melt temperature
2. Appropriate increase in inflation pressure
3. Clean, remove the mold cooling pipe scale and obstacles, adjust the mold cooling system design
4. Adjust the parison wall thickness, adjust the parison control device

Defect 4
The inner or outer surface of the product is contaminated

Cause 4
1. The compressed air is not clean
2. Use the corners to be dirty or mixed with debris
3. Part of the resin degradation, or even carbonization
4. Storage tank head oil spill

Solution 4
1. Increase the number of water and oil discharges in soft drinks or petrol separators
2. Strengthen the scrap processing or reduce the amount of its reuse
3. To minimize the equipment downtime, reduce the heating temperature, the timely removal and cleaning machine head die
4. Replace the storage tank seal

Defect 5
The bottom seam of the product is too weak

The following are the same as the ”

1. The speed of the mold is not correct
2. Mold off time is wrong
3. The parison melt temperature is not accurate
4. Mold clip blade design error 5. Mold cooling temperature is insufficient

Solution 5
1. Use fast – slow closing speed
2. Adjust the mold closing time
3. Lower or increase the melt temperature of the parison
4. Appropriate increase the knife-edge angle, deepen the depth of the blade or increase the width of the knife-edge
5. Reduce the cooling temperature of the mold clip seam area

Defect 6
The markings of the products in the parting line are bad

Cause 6
1. Billet inflation pressure is low
2.Defective at the parting line
3. Mold parting surface is not smooth
4.Mold expansion mold

Solution 6
1. Increase the billet inflation pressure
2. Trim the exhaust slot
3. Trimming the mold parting surface, correcting the mold guide column
4. Increase the template locking pressure

Defect 7
Products appear orange peel pattern or pitting

Cause 7
1. Poor mold exhaust
2. Mold leakage or mold cavity condensation phenomenon
3. Parison poor plastic, parison melt fracture phenomenon
4. Blowing air pressure is insufficient
5. Blowing speed slow 6. Blowing ratio is too small

Solution 7
1. Mold parison for sandblasting, additional vent holes
2. Repair the mold, adjust the mold cooling temperature to “dew point” above
3. Reduce the screw speed, increase the extruder heating temperature
4. Increase the inflation pressure
5. Clean the compressed air passage and check that the blower rod is leaking
6. Replace the mold sleeve, mold core, improve the billet inflation ratio

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