Defects and elimination of various blow molding processes

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The longitudinal wall thickness of blow molded products is uneven
1. The self-weight sag of the parison is serious
2. The diameter difference between the two longitudinal cross sections of blow-molded products is too large
1. Reduce the melt temperature of the parison, improve the extrusion speed of the parison, replace the resin with low melt flow speed, and adjust the parison control device.
2. Properly change the product design and adopt the bottom blowing method for molding.

The transverse wall thickness of blow molded products is uneven
1. Parison extrusion skew
2. The temperature difference between the inside and outside of the mold sleeve and the mold core is large
3. Asymmetric product shape
4. Excessive blowing expansion ratio of parison
1. Adjust the gap width deviation of the die to make the parison wall thickness uniform; Straighten the mold before closing.
2. Increase or decrease the heating temperature of the die sleeve and improve the temperature deviation inside and outside the die.
3. Before mold closing, pre-clamp and pre-expand the parison to make the parison properly shift to the thin-wall direction.
4. Reduce the blowing expansion ratio of parison

Orange peel pattern or pitting on the surface of blow-molded products
1. Poor mold exhaust
2. Mold leakage or condensation in mold cavity
3. The parison has poor plasticization, and the parison has melt fracture.
4. Insufficient inflation pressure
5. Slow inflation rate
6. The blowing expansion ratio is too small
1. The mold blank shall be sandblasted and the vent hole shall be added.
2. Repair the mold and adjust the cooling temperature of the mold to above the "dew point".
3. Reduce the screw speed and increase the heating temperature of the extruder.
4. Increase the inflation pressure
5. Clean the compressed air channel and check whether the blowpipe leaks.
6. Replace the mold sleeve and core to improve the blow expansion ratio of parison.

Volume reduction of blow molding products
1. The parison wall thickness increases, resulting in the product wall thickening.
2. The shrinkage of the product increases, resulting in the size shrinkage of the product.
3. The inflation pressure is small, and the product is not inflated to the design size of the cavity.
1. Adjust the program control device to reduce the parison wall thickness; Increase the melt temperature of parison and reduce the expansion ratio of parison.
2. Replace the resin with low shrinkage, extend the blowing time and reduce the cooling temperature of the mold.
3. Properly raise the pressure of compressed air

Blow-molded product outline or graphics are not clear
1. Poor cavity exhaust
2. Low inflation pressure
3. The melt temperature of parison is low, and the material plasticization is poor.
4. The mold cooling temperature is low, and the mold has "condensation" phenomenon.
1. Repair the mold, sandblast the cavity or add an exhaust slot.
2. Increase the inflation pressure
3. Properly increase the heating temperature of the extruder and the head, and add an appropriate amount of filler masterbatch if necessary.
4. Adjust the mold temperature above the dew point temperature

Blow-molded products have too many and thick flash
1. Die expansion and insufficient locking pressure.
2. The tool edge of the die is worn and the guide post is offset.
3. During blowing, the parison is skewed.
4. The escape chute at the blank clamping knife edge is too shallow or the knife edge depth is too shallow.
5. Premature start-up of parison charging.
1. Increase the mold locking pressure and properly reduce the inflation pressure.
2. Repair the mold blade, correct or replace the mold guide post.
3. Correct the center position of parison and air blowing rod
4. Trim the mold and deepen the depth of the escape chute or knife.
5. Adjust the filling time of parison

Too deep longitudinal stripes appear
1. Dirty at die mouth.
2. There is burr or notch on the edge of the mold sleeve and core.
3. Color masterbatch or resin decomposition produces dark stripes.
4. The filter screen is perforated, and the material is mixed with impurities and deposited at the die mouth.
1. Clean the die mouth with a copper knife.
2. Trimming die.
3. Reduce the temperature properly and replace the color masterbatch with good dispersion.
4. Replace the filter screen and use the leftover material.

When forming, the embryo is blown out
1. The die blade is too sharp.
2. The parison has impurities or bubbles.
3. Excessive blowing expansion ratio.
4. Low melt strength of parison.
5. Insufficient parison length.
6. The parison wall is too thin or the parison wall thickness is uneven.
7. The container expands and cracks when opening the mold (insufficient venting time)
8. Insufficient mold locking force.
1. Increase the width and angle of the blade appropriately
2. Use dry raw materials, use wet raw materials after drying, use clean raw materials and clean the mold mouth.
3. Replace the mold sleeve and core, and reduce the blowing expansion ratio of mold damage.
4. Replace the appropriate raw materials and properly reduce the melt temperature.
5. Check the control device of the extruder or storage cylinder head to reduce the change of process parameters and increase the length of parison.
6. Replace the mold sleeve or core and thicken the parison wall; Check the parison control device and adjust the die gap.
7. Adjust the bleeding time or delay the mold start time
8. Increase the mold locking pressure or reduce the inflation pressure

Blow-molded products are difficult to demould
1. The cooling time of product expansion is too long, and the cooling temperature of mold is low.
2. The mold is poorly designed, and there are burrs on the surface of the mold cavity.
3. When the formwork is opened, the movement speed of the front and rear formwork is uneven.
4. Die installation error.
1. Properly shorten the blow expansion time of the parison and raise the mold temperature.
2. Trim the mold; Reduce the groove depth, and the convex rib slope is 1:50 or 1:100; Use release agent.
3. Repair the mold locking device to make the front and rear templates move at the same speed.
4. Reinstall the mold and correct the installation position of the two halves of the mold.

The quality of blow molded products fluctuates greatly
1. Sudden change of parison wall thickness
2. The mixed edge and corner materials are not uniform
3. The feeding section is blocked, causing the extruder discharge to fluctuate.
4. Uneven heating temperature
1. Repair parison control device
2. Adopt good mixing device to prolong mixing time; If necessary, reduce the amount of corner return.
3. Remove lumps at the material inlet
4. Reduce the temperature at the material inlet

Post time: Mar-21-2023