Top ten questions about blow molding products

In the process of extrusion blow molding, there are always many technical problems. The following is the reason why the Zhizhi Plastics Network shares the problems and the corresponding solutions. I hope to provide suggestions for solving the problems.
First, the longitudinal wall thickness of the blow molded product is uneven:
cause:
1 parison sag is serious
2 blow molding products longitudinal two cross-sectional diameters differ too much
solution:
1Reducing the melt temperature of the parison, increasing the extrusion speed of the parison, replacing the resin with a lower melt flow rate, and adjusting the parison control device
2 Appropriate change of product design, using bottom blowing method
Second, the lateral thickness of the blow molded product is uneven:
cause:
1 parison extrusion skew
2 The mold sleeve has a large temperature difference between the inside and the outside of the core
3 product shape is asymmetrical
4 parison blow ratio is too large
solution:
1Adjust the deviation of the gap width of the die to make the wall thickness of the parison uniform; before the mold is closed, the straightening type is bad.
2 Raise or reduce the heating temperature of the mold sleeve to improve the temperature deviation inside and outside the mold
3 Pre-clamping and pre-expansion of the parison before closing the mold, so that the parison is appropriately deflected toward the thin wall
4 reduce the billet blow ratio
Third, the appearance of blow molding products appears orange peel pattern or pitting:
cause:
1 mold exhaust failure
2 mold leaks or condensation in the mold cavity
Poor plasticization of the 3 parison, melt fracture of the parison 4 Insufficient inflation pressure
5 inflation speed is slow
6 inflation ratio is too small
solution:
1 mold parison is sandblasted, additional vent hole
2 repair the mold, adjust the mold cooling temperature to above the "dew point"
3 reduce the screw speed and increase the heating temperature of the extruder
4 lift inflation pressure
5 Clean the compressed air passage and check if the blower is leaking
6 Replace the mold sleeve and core to increase the blow ratio of the parison
Fourth, the volume of blow molding products is reduced:
cause:
1 parison wall thickness increases, resulting in thickening of the product wall
2 product shrinkage rate increases, resulting in shrinking product size
3The inflation pressure is small, and the product is not inflated to the cavity design size.
solution:
1 adjust the program control device to reduce the parison wall thickness; increase the parison melt temperature and reduce the parison die expansion ratio
2Replace the resin with small shrinkage, prolong the blowing time and reduce the mold cooling temperature.
3 properly raise the pressure of compressed air
5. The outline or graphic of the blow molded product is not clear:
cause:
1 cavity exhaust failure
2 low inflation pressure
3 parison melt temperature is low, material plasticization is poor
4 mold cooling temperature is low, the mold has "condensation" phenomenon
solution:
1 repair mold, cavity blasting or add exhaust vent
2 increase the inflation pressure
3 Appropriately increase the heating temperature of the extruder and the head, and if necessary, add an appropriate amount of filler masterbatch.
4 adjust the mold temperature to above the dew point temperature
6. Blowing products are too much and too thick:
cause:
1 mold expansion mold, insufficient clamping pressure
2 mold edge wear, guide column offset
3 when the inflation is inflated, the parison is skewed
4 The escape groove at the edge of the blank is too shallow or the depth of the blade is too shallow.
5 parison inflation started too early
solution:
1 Lifting mold clamping pressure, suitable for reducing inflation pressure
2 repair the mold edge, correct or replace the mold guide column
3 Correct the center position of the parison and the blowing rod
3 trim the mold to deepen the depth of the escape trough or knife
4 adjust the parison inflation time
Seven, there are too deep vertical stripes:
cause:
1 die dirty
2 mold sleeve, burr or notch on the edge of the core
3 color masterbatch or resin decomposition produces dark stripes
4 filter mesh hole, material mixed with impurities deposited in the die
solution:
1 use a copper knife to clean the die
2 trimming the die
3 Properly lower the temperature and replace the disperse color masterbatch
4 Replace the filter plate and use the scraped scrap
Eight, the embryo is blown during molding:
cause:
1 mold blade is too sharp
2 parisons have impurities or bubbles
3 inflation ratio is too large
4 parison melt strength is low
5 parison length is insufficient
5 type blank wall is too thin or the parison wall thickness is uneven
6The container bursts when the mold is opened (the deflation time is insufficient)
7 mold clamping force is insufficient
solution:
1 Appropriately increase the width and angle of the knife edge
2 use dry raw materials, use dry materials after drying, use clean materials; clean the die
3 Replace the mold sleeve, the core, reduce the bad blow ratio
4 Replace the appropriate raw materials, properly reduce the melt temperature
5 Check the control device of the extruder or storage cylinder head, reduce the variation of process parameters, increase the length of the parison 6 replace the mold sleeve or core, thicken the parison wall; check the parison control device; adjust the die gap
7 adjust the deflation time or delay the mold start time
8 Lifting the clamping pressure or reducing the inflation pressure
Nine, blow molding products are difficult to demould:
cause:
1 product inflation cooling time is too long, mold cooling temperature is low
2 poor mold design, burr on the cavity surface
3 When the mold is opened, the moving speed of the front and rear templates is not balanced.
4 mold installation error
solution:
1 Properly shorten the billet inflation time and raise the mold temperature
2 trimming the mold; reduce the groove depth, the slope of the rib is 1:50 or 1:100; use the release agent
3 Repair the clamping device so that the front and rear templates move at the same speed
4Re-install the mold to correct the installation position of the two mold halves
Ten, the quality of blow molding products fluctuates greatly:
cause:
1 parison wall thickness suddenly changes
2 mixed corner blending material is unevenly mixed
3 The feed section is clogged, causing the extruder to fluctuate
4 heating temperature is not balanced
solution:
1 repairing parison control device
2 Use a good mixing device to extend the mixing time; if necessary, reduce the amount of corner return
3 remove the agglomerates at the mouth
4 material or foreign matter. Reduce the temperature at the mouth
5 replacement electric heating cabinet

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