Extrusion Blow Molding Failures And Remedies

DIRECTORY:
1. parison vertical stretching

2. parison neck portion narrow

3. parison overall crimping

4. parison edge rolled up

5. parison inflation and rupture

6. parison appear gas bubbles

7. parison leak

8. parison surface roughness

9. parison surface uneven

10. parison surface appears “Shark skin”

11. parison surface appear stripes

12. parison surface appears die core blotting

13. parison appear wrinkles

14. parison appear discoloration and uneven color

15. parison appear contaminat

16. parison sticking on the die head

17. product demoulding difficult

18. deflash difficult to remove

19. cut portion too thin

20. cut portion too thick

21. cut portion is not well integrated

22. cut portion strength insufficient

23. cut portion appear bubbles

24. product wall appear bubbles

25. product rupture

26. too much product flash

27. blowing spilled material

28. blowing gas shortage

29. product burst

30. product breaks at the weld

31. product breaks at the mold line

32. product breaks at the bottom part

33. product blow cracked

34. product surface appears black spots

35. product surface appears rough and pitting

36. product surface appear weld blotting

37. product surface appear orange peel and melt blotting

38. product surface pattern not clear

39. mouth swelling insufficient

40. product warpage

41. product wall thickness uneven

42. product wall ultra-thin

43. product shrinks too much

44. product gel

45. product impact resistance insufficient ,cracking

46. blow molding cycle is too long

47. extrusion load is too large

1.  parison vertical stretching

(1) The temperature of the blank is too high or other process parameters are not properly controlled. The barrel screw and head temperature should be appropriately reduced and the extrusion speed parameters should be adjusted.

(2) The extrusion speed of the parison is too slow. Should be accelerated as appropriate.

(3) The mold closing speed is too slow. Should be accelerated as appropriate.

(4) The moisture content in the raw material is too high. Pre-drying should be carried out.

(5) The melt flow rate of the raw material is too high. Resins with a lower melt flow rate should be used.

(6) The design of the machine head structure is unreasonable. A decentralized hand should be used.

2.  parison neck portion narrow

(1) Raw materials do not meet molding requirements. Resins with higher density or lower melt flow rates should be used.

(2) The melt temperature is too high. The fuselage and head temperature should be appropriately lowered.

(3) The molding cycle is too long. The screw speed should be appropriately increased to shorten the molding cycle.

3.  parison overall crimping

(1) The die core outlet is improperly adjusted and the discharge is uneven. The core gap should be properly adjusted to make it evenly discharged.

(2) The head is not heated uniformly. Check the head heater and temperature control device for damage, and adjust the temperature distribution of the machine head to make it even.

(3) The extrusion speed is too fast. Should be appropriately slowed down.

(4) The design of the head runner is unreasonable. The design should be modified to add a pressure ring. When a thin-walled product is blown , the mandrel is pulled into the head and the parison is hung on the edge of the core , causing the parison to curl. In this regard, the core plane should be placed on the same plane as the core mold plane or the former should be slightly higher than the core mold plane.

(5) The melt temperature is too low. Should be properly improved.

4.  parison edge rolled up

(1) The core temperature is too high and the parison is crimped inward. The core temperature should be appropriately lowered . At the same time, the extrusion speed is appropriately reduced and the core gap is increased.

(2) The temperature of the mandrel is too high and the parison is curled outward. The mandrel temperature should be lowered appropriately.

(3) The core plane processing of the core and the core mold is unreasonable. The core plane should be slightly higher than the core plane

5.  parison inflation and rupture

(1) The inflation ratio is too large. A smaller inflation ratio should be used, usually around 1 : 3 .

(2) The core discharge is uneven. The core gap should be properly adjusted to make it evenly discharged.

(3) The parison extrusion speed is too slow. Should be accelerated as appropriate.

(4) The blow molding speed is too slow after closing the mold. Should be accelerated as appropriate.

(5) Surface flaws on the parison. The head splitter should be inspected for damage, cleaned and ground the runner surface to improve surface finish.

(6) Foreign matter impurities are mixed into the raw materials. Replace new materials and clean the machine head and barrel.

(7) Insufficient clamping force. Should be increased appropriately

6.  parison appear gas bubbles

(1) The moisture content in the raw material is too high. Pre-drying should be carried out.

(2) The temperature of the fuselage or the head is too high, and the melt is decomposed by heat. Appropriately reduce the temperature of the fuselage or head, In particular, the temperature of the feed section of the barrel should not be too high, and the residence time of the melt in the barrel should be shortened.

(3) Air enters the barrel from the hopper. The screw speed should be appropriately increased, the number of mesh layers and the number of meshes should be increased, and the extrusion back pressure should be increased.

(4) There is a gas crack on the machine head or the mold or a poor seal at the joint of the machine head. Sealing should be done.

(5) Air leakage from the compressed air storage tank. The joint between the gas tank and the mandrel should be inspected to seal the leak.

(6) The thermal stability of the raw material is insufficient. The formula should be adjusted.

7.  parison leak

(1) The melt temperature is too high. Should be appropriately reduced.

(2) The blow molding pressure is too high or the blow pinhole diameter is too large. The inflation pressure should be appropriately reduced or the diameter of the blowhole should be reduced.

(3) The inflation ratio is not properly controlled. Adjustments should be made.

(4 ) Have localized hot spots on the mold and parison. The heating device should be checked to eliminate hot spots.

8.  parison surface roughness

(1) The surface finish of the parison mold is too poor. The cavity surface finish should be improved.

(2) The melt temperature is too low. Appropriately increase the temperature of the fuselage or head.

(3) Poor plasticization of the melt. The screw speed should be appropriately reduced to increase the temperature of the fuselage and enhance the plasticization of the melt.

(4) The blow molding pressure is too low. The inflation pressure should be increased or the diameter of the blow pinhole should be increased.

(5) Air leakage around the blow pinhole. The leak should be sealed.

(6) The design of the head flow path is unreasonable or the surface is rough. The head flow path should be machined into a streamlined shape with a high surface finish on the runner surface.

(7) Foreign matter is mixed into the raw material. Replace the new material and clean the barrel or the machine head.

(8) The parison is pulled at the die. Should be designed in the edge of the core mold 0 . 3-0 . Rounded corners with a 5mm radius or a diffuser head.

(9) The parison extrusion speed is too fast. Should be appropriately slowed down.

(10) There is condensation on the surface of the mold cavity. The mold temperature should be increased.

(11) When the continuous blow molding is performed, the surface of the parison is rough. The extrusion pressure should be appropriately reduced.

(12) When reciprocating blow molding, the surface of the parison is rough.

The elimination method is 

1 Properly increase the melt temperature.

2 Switch to a resin with a higher melt flow rate.

3 Appropriately reduce the extrusion pressure.

4 adjust the extrusion speed, control the fall time of the parison, Place the extrusion speed outside the unstable zone of melting

9.  parison surface uneven

(1) The melt temperature is too high. The head temperature should be lowered appropriately.

(2) The head is not heated uniformly. The heater and temperature control device should be inspected for damage.

(3) Poor plasticization of the melt. The screw speed should be adjusted to increase the plasticization of the melt.

10.  parison surface appears “Shark skin”

(1) The extrusion speed is not properly controlled. Inappropriate extrusion speeds can cause melt fractures, especially when blowing high density polyethylene hollow products . In continuous blow molding, the extrusion speed and pressure should be appropriately reduced; in reciprocating blow molding, the extrusion speed should be appropriately increased.

(2) The parison forming temperature is too low . Should be properly improved. Generally, the high-density polyethylene has a parison forming temperature of 170-210 degrees and a low-density polyethylene of 150-190degrees.

11.  parison surface appear stripes

(1) There is a dead angle or a streamlined design in the extruder, the socket or the flow path of the machine head . Causes the melt to stagnate, decompose and rupture, The decomposition material stays in the gap of the flow path to cause streaks on the surface of the parison. In this regard, the dead angle of the stagnant material in the flow channel should be repaired.

(2) There are scratches in the flow path of the head. The surface of the runner should be polished to remove scratches.

(3) Poor assembly between the extruder and the adapter, the machine head and the socket, A dead angle is generated. Should be reassembled.

(4) There is a stagnant material in the mold. Appropriately increase the mold temperature and increase the blow pressure.

(5) The temperature of the melt is too high and decomposes due to overheating. The melt temperature should be appropriately reduced to remove the decomposition material.

(6) The temperature difference between the mold temperature and the melt temperature is too large. The mold temperature should be appropriately increased to reduce the temperature difference.

(7) There are foreign matter impurities in the raw materials. It should be purified.

(8) The extrusion back pressure is too low. Should be properly improved.

(9) The head heater is damaged. When the surface of the parison produces clear or undulating streaks, It is likely that the head heater is damaged, so that the melt is pulled in the cold spot area of ​​the handpiece, resulting in surface streaks. In this regard, the head heater should be overhauled.

(10) When a large hollow product is slowly extruded, a large-scale head that continuously and continuously extrudes a thick-walled parison is generally used, and the parison extrusion speed is slow due to the influence of the blow molding cycle. In the case of blow molding, the surface of the product often produces a plurality of uneven stripes which are evenly distributed in the circumferential direction, generally ranging from 15 to 40 , and the wall thickness difference of the stripes is about 0 . 2-1mm or so. These vertical stripes uniformly distributed along the circumference of the extrusion direction are commonly referred to as “watermelon skin” stripes.

The elimination method is 

1 Use a resin with a lower melt flow rate as much as possible.

2 Segment control of the head temperature, reduce the temperature of the shaping section, and increase the temperature at the filter plate.

3 The flow path of the head should be set as symmetrical as possible to avoid unstable flow of the melt.

4 Set the choke section at the melt population of the machine head, and then set a shape-symmetric expansion zone after the choke section so that the melt is symmetrically stretched when entering the machine head.

5 Try not to set the filter plate and not to use the split shuttle head.

6 Appropriately increase the extrusion speed.

7 When two raw materials having different molecular weights or molecular structures are used for blending, eutectic granulation treatment should be carried out first.

12.  parison surface appears die core blotting

(1) There are scratches and damage in the flow path of the head. The head flow path should be ground.

(2) There is a stagnant material in the core . The core should be cleaned .

(3) The melt temperature is too high. The head temperature should be lowered appropriately.

(4) The blowing speed is too slow. Should be accelerated as appropriate.

(5) Insufficient blow molding pressure. Should be properly improved.

(6) The mold temperature is too low. Should be properly improved.

(7) The cavity edge is too sharp. Should be set to 0 at the edge . 3-0 . 5mm radius fillet

13.  parison appear wrinkles

(1) The melt temperature is too high. Should be appropriately reduced.

(2) The head section is too short. It should be lengthened appropriately.

(3) The core discharge gap is improperly adjusted and the flow is uneven . The core gap should be properly adjusted to make the head discharge uniform.

(4) The strength of the melt is too low.

The troubleshooting method is

1 Properly reduce the melt temperature.

2 Appropriately increase the amount of recycled materials.

3 Properly reduce the back pressure of the extruder.

4 Appropriately slow the transfer speed of the parison.

5 Appropriately speed up the clamping.

Before the 6 parison is placed in the blow mold, a small amount of air is blown into the parison to perform pre-blowing treatment.

14.  parison appear discoloration and uneven color

(1) Contamination of the barrel or head flow path. It should be cleaned up.

(2) The melt temperature is too high. The temperature of the fuselage or head should be appropriately reduced to shorten the residence time of the melt in the barrel.

(3) The extrusion friction heat is too high. Should use a smaller compression screw.

(4) The coloring agent is wet and agglomerated. It should be dried or replaced with new materials.

(5) The polyvinyl chloride raw material is insufficiently stirred before adding dioctyl phthalate. Prolonged mixing time

15.  parison appear contaminat

(1) Raw material contamination. The molding system should be kept clean, the resin delivery system should be sealed, and the recycled materials must be clean.

(2) The melt is decomposed by heat. It should be avoided that the molten material stays in the high temperature area for too long.

(3) There is a dead angle in the flow path of the head. The flow path of the machine head should be trimmed to remove dead spots.

16.  parison sticking on the die head

(1) The parison is too long. The stop time of the parison tail outside the mold should be shortened.

(2) The design of the mold blank is unreasonable. The design should be modified so that the parison is “compressed and cooled” at the cut-off port

17.  product demoulding difficult

(1) The draft of the product is not designed. The mold should be modified and the ribs should be designed with a draft angle of 1 : (50-100) .

(2) The groove at the bottom of the product is too deep. The groove depth should be minimized.

(3) The mold temperature is too high. Should be appropriately reduced.

(4) Poor cooling at the blank. The cooling should be strengthened at the cut blank.

(5) The molding cycle is too short. Should be extended appropriately.

(6) The melt temperature is too high. Should be appropriately reduced.

(7) The product sticks to the air intake rod. This is mainly because the temperature around the intake rod is too high, and the cooling of the intake rod should be strengthened. Can intake rod hole drilled 2-8, a pore size 0. 25-0. 38mm, uniform pitch. In addition, the parison temperature should be appropriately reduced .

18.  deflash difficult to remove

(1) The edge of the edge is too wide. Should be appropriate repair narrow, typically 1. 0 ~ 2. 5mm.

(2) The edge of the cutting edge is not flat. The knife edge should be flattened.

(3) The clamping pressure is insufficient. Should be properly improved.

19.  cut portion too thin

(1) The blow molding pressure and the initial blow molding time are not properly controlled. Should be adjusted appropriately.

(2) The mold is poorly exhausted. The surface of the cavity should be sandblasted to improve the exhaust conditions of the mold.

(3) There are too many flashes. The flash should be reduced.

(4) The cut blank is severely damaged. The cut blank should be prevented from being damaged.

20.  cut portion too thick

(1) The slit slit of the blow mold is not properly adjusted. Should be adjusted appropriately.

(2) The incision is damaged. The damaged area should be repaired.

(3) The incision flash is too thick. The amount of flash should be adjusted appropriately.

(4) The melt temperature is too low. Should be properly improved.

21.  cut portion is not well integrated

(1) The parison temperature is too low. Should be properly improved.

(2) The cutting edge is too sharp. The width of the knife edge should be adjusted, generally controlled at 1 . 0-2 . 5mm .

22.  cut portion strength insufficient

(1) The melt temperature is too low. Should be properly improved.

(2) The mold temperature is too low. Should be properly improved.

(3) The design of the cutter structure is unreasonable. After the blade angle should be controlled at 30 ~ 45 ‘, the width of the blade should be controlled at 1. 0-2. 5mm.

23.  cut portion appear bubbles

(1) The rear corner of the cutter is not properly controlled. Should be controlled at 30~45 ‘ .

(2) The mold clamping is too fast. A slow clamping device should be provided.

24.  product wall appear bubbles

(1) The moisture content of the raw materials is too high. Pre-drying and pre-heat treatment should be carried out.

(2) The head is poorly assembled and produces leaking air bubbles. The machine head should be reassembled.

25.  product rupture

(1) The melt droops. For raw materials with low shear rate, the temperature of the head, mold and melt should be appropriately increased to slow down the falling speed of the parison.

(2) The screw temperature is too high. It should be cooled.

26.  too much product flash

(1) The melt temperature is too high. Should be appropriately reduced.

(2) The parison is bent. The symmetry uniformity of the parison should be adjusted.

(3) Poor clamping. The clamping process should be checked.

(4) The mold clamping force is insufficient. Should increase the clamping force.

(5) The initial blow molding time and pressure control were improper. Should be adjusted appropriately.

(6) The cutting edge is too wide. The knife edge should be narrowed.

(7) The cutting edge is not straight. The flatness of the knife edge should be corrected.

27.  blowing gas shortage

(1) The melt temperature is too high. Should be appropriately reduced.

(2) The blowing pressure is too high. Should be appropriately reduced.

(3) The mold is separated. The clamping force should be appropriately increased.

(4) The exhaust port is too large. Should be appropriately reduced. The exhaust port should be designed to be deep 0 . 8mm , length 1-4mm , and gradually deepened to the edge of the mold.

28.   Blowing gas shortage

(1) The gas supply line is blocked and the inflation is poor. The gas supply line and pressure should be checked to remove obstructions and ensure that the air supply is unobstructed.

(2) The cut blank is too sharp. The cross section of the blank should be 3-5mm .

(3) The temperature at the blank is too high. The mold should be cooled evenly.

29.  product burst

(1) Mold separation. Appropriately increase the clamping force or use a blow molding machine with a large clamping force.

(2) The product is poorly cooled. The cooling time should be extended as appropriate.

(3) The parison bursts. Resin with higher melt strength or a larger gauge die should be used.

30.  product breaks at the weld

(1) The melt temperature is not properly controlled. If the temperature of the melt is too high or too low, the product will break at the weld line and should be properly controlled.

(2) Improper mold temperature control. Should be adjusted appropriately.

(3) The molding cycle is too long. Should be shortened as appropriate.

(4) The blow mold cut area is faulty. Exclusion should be checked.

31.  product breaks at the mold line

(1) Insufficient clamping force. Should increase the clamping force.

(2) The mold is misaligned and misplaced. The alignment should be corrected.

(3) The mold clamping line is poorly cooled. The cooling conditions at the mold line should be improved.

(4) The mold is poorly vented. The cavity surface should be sandblasted.

32.  product breaks at the bottom part

(1) The temperature of the fuselage or head is too low. Should be properly improved.

(2) The mold is not well cooled. Cooling should be strengthened.

(3) Improper blow molding pressure control. Should be adjusted appropriately.

(4) The mold opening is too fast. The mold should be opened only after the air pressure in the product has completely disappeared.

33.  product blow cracked

(1) The temperature of the melt is too low, and small holes appear in the product along the stitching line or the broken line, and cracks appear in the gap. The melt temperature should be increased appropriately.

(2) The mold clamping force is insufficient, and the mold slightly expands during the blow molding process, causing the product to blow. The clamping force should be properly increased.

(3) The blow molding pressure is too high, and the parison rapidly expands when inflated, causing the product to blow. The blow molding pressure should be appropriately reduced.

(4) The mold closing speed is too fast, and the product breaks at the pinch line. The mold closing speed should be appropriately reduced.

(5) The slit of the mold clip is too sharp or too blunt. If the incision is too sharp, the parison will be cut. If the incision is too blunt, the mold will be closed poorly, which will cause the product to blow. The width of the slit should be adjusted appropriately.

(6) The blow ratio is too large, and the parison is blown too thin, causing the product to blow. The inflation ratio should be appropriately reduced.

(7) Foreign materials are mixed with foreign matter impurities. Foreign matter impurities should be removed to purify the raw materials.

34.  product surface appears black spots

(1) The melt is overheated and decomposed to carbonize. The fuselage or head temperature should be lowered appropriately.

(2) The decomposition melt and impurities in the barrel or the head flow path are gradually peeled off and then extruded. The runner system should be cleaned up.

(3) The raw materials are mixed with impurities. The raw materials should be purified and the filter replaced.

(4) There are impurities in the blown air. The impurities in the tank should be checked.

35.  product surface appears rough and pitting

(1) The melt temperature is too low. The head temperature should be increased appropriately.

(2) The mold temperature and ambient temperature are too low. The mold temperature and production environment temperature should be appropriately increased.

(3) The surface finish of the mold cavity is too poor. Should be ground and polished.

(4) The mold is poorly exhausted. The mold exhaust conditions should be improved.

(5) Blowing air pressure is insufficient. The blow molding pressure should be appropriately increased to enlarge the size of the inflatable die hole.

(6) The raw material does not meet the molding requirements, and the melt flow rate is too low. Resins with higher melt flow rates should be used.

36.  product surface appear weld blotting

(1) The clamping pressure is insufficient. Should be properly improved.

(2) The mold clamping line is poorly cooled. Cooling should be enhanced and pre-blow molded.

(3) The mold clamping surface is not flat or the surface has foreign matter adhered, resulting in a loose mold clamping. The mold face should be flattened or cleaned to fit snugly.

(4) The mold temperature is too low. Should be properly improved.

(5) The blow molding pressure is too low. Blow pinholes should be increased or increased as appropriate.

(6) The temperature of the machine head is not properly controlled. Adjustments should be made. Before starting the machine, the core temperature must reach the molding temperature.

(7) The structure design of the machine head is unreasonable, and there is a dead angle in the flow channel. The dead angle of the stagnant material should be repaired.

37.  product surface appear orange peel and melt blotting

(1) The molding temperature is improperly controlled, and the melt temperature is too high or too low. Should be adjusted appropriately.

(2) The mold temperature is too low. Should be properly improved.

(3) The temperature of the head is too high. Should be appropriately reduced.

(4) The surface of the cavity leaks cooling water. The mold should be inspected for leaks and sealed.

38.  product surface pattern not clear

(1) The melt temperature is too low. Should be properly improved.

(2) The blow molding pressure is insufficient. Should be properly improved.

General blow molding pressure It depends on factors such as parison temperature, mold temperature, product size and thickness. When the parison and mold temperature are high and the product is small, the blow pressure should be lower, and vice versa. The pressure should meet two basic requirements: First, after the parison is clamped, the inflator must be inflated as soon as possible so that the parison is cooled before it contacts the mold; Second, the inflated parison must be in close contact with the inner wall of the cavity during cooling to ensure the clarity of the surface pattern of the cavity. Blowing pressure should be lower, the control should be made in the gas flow velocity is low, large air, so that air can be prevented occur near the low-pressure gas into the region, the parison retraction or pulling off the parison; second stage blow molding, blow The plastic pressure should be higher and high enough to allow the pattern in the cavity to form clearly on the surface of the product .

39.  mouth swelling insufficient

Mold expansion refers to a certain expansion and expansion phenomenon when the parison leaves the machine head, sometimes referred to as machining expansion or parison expansion. The amount of die expansion has a large influence on the molding of the product and its surface quality.

(1)   Insufficient expansion of the die

The troubleshooting method is 
1 Appropriately increase the melt temperature.
2 Properly accelerate the transfer speed of the parison.
3 Appropriately increase the back pressure of the extruder.
4 Reduce the use or try not to use recycled materials.
5 speed up the clamping speed.
6 blow lighter products .

(2) The die expansion is too large.

The troubleshooting method is 
1 blow the heavier product .
2 Properly reduce the melt temperature.
3 Appropriately slow the transfer speed of the parison.
4 Properly reduce the back pressure of the extruder.
5 increase the amount of recycled materials.
6 Appropriately slow down the clamping time, can be delayed by about 2s .
7 Reduce or eliminate pre-blowing of the parison before clamping.

40.  product warpage

(1) The blowing time is too short. Should be extended appropriately.

(2) The blowing speed is too slow. Should be accelerated as appropriate. It should be inflated immediately after clamping.

(3) The melt temperature is too high. The molding temperature should be appropriately lowered.

(4) The product is not properly cooled. If the temperature of the product after demolding is still high, the cooling time of the mold should be extended appropriately. If the top and bottom of the product are warped, the cooling should be enhanced on the cut surface of the mold. If the product wall thickness is different, the cooling should be strengthened at the thick wall. The cooling circuit of the mold should be set according to the cooling requirements.

(5) The cooling sizing mold is not properly heat treated. Quenching should be performed to prevent warpage of the mold.

41.   product wall thickness uneven

(1) The head is not heated uniformly. The head heater should be inspected for damage and the installation position is correct. The head should be heated evenly.

(2) The adjustment of the gap of the machine head is improper, the melt pressure in the flow path of the machine head is inconsistent, and the discharge is uneven. The head clearance should be adjusted according to the wall thickness distribution.

(3) The center of the head is inconsistent with the center of the blow mold. The alignment should be recalibrated.

(4) The head or mold core is not vertical. The vertical should be recalibrated.

(5) The drive belt of the extruder slips and the discharge amount changes. The drive belt should be overhauled and tightened.

(6) The extrusion speed is too slow. Should be accelerated as appropriate.

(7) The melt temperature is too high. Should be appropriately reduced.

(8) The mold design is unreasonable. The mold design should be modified.

(9) Raw materials do not meet molding requirements. Resins with a lower melt flow rate should be used.

(10) The mold temperature distribution is not uniform. The cooling circuit of the mold should be adjusted to make the temperature distribution uniform.

(11) The blowing speed is too slow. Should be accelerated as appropriate.

(12) The inflation ratio is too large. Should be appropriately reduced.

(13) The extruder feed is unstable. The hopper should be inspected for blockage or “bridge” and the temperature of the hopper heater should not be too high.

42.  product wall ultra-thin

(1) The parison is extended. The extrusion speed should be increased appropriately.

(2) The melt temperature is too high. Should be appropriately reduced.

(3) The inflation ratio is too large. Should be appropriately reduced.

43.  product shrinks too much

(1) The product wall is too thick. The thickness should be appropriately reduced to make the wall thickness as uniform as possible.

(2) The mold temperature is too high. Should be appropriately reduced.

(3) The melt temperature is too high. The molding temperature should be appropriately lowered.

(4) The blow molding pressure is insufficient. Should be properly improved.

(5) The blowing time is too short. Should be extended appropriately.

(6) The shrinkage of the raw material is too large. Resins with lower density and shrinkage should be used.

44.  product gel

(1) Poor plasticization of pellets. Appropriately increase the material temperature or use a heated hopper, the parison should be able to reach the average temperature before entering the blow molding.

(2) Raw material contamination. The resin and recycled materials should be purified.

45.  product impact resistance insufficient ,cracking

(1) The shape and structure design of the product is unreasonable. Sharp angles should be eliminated and wall thickness should be avoided.

(2) The melt temperature is too low. The body temperature should be properly increased. First, the temperature of the feed section of the fuselage should be increased.

(3) The raw material does not meet the molding requirements, and the melt flow rate and density are too high. The raw materials should be replaced.

46.  blow molding cycle is too long

(1) The molding temperature is too high and the cooling time is too long. The melt temperature should be appropriately reduced to increase the blow pressure and reduce the wall thickness. And shorten the cooling time as appropriate.

(2) The mold temperature is too high. Should be appropriately reduced.

(3) Improper selection of raw materials. Resins with higher melt flow rates and higher densities should be used to facilitate low temperature molding.

47.  extrusion load is too large

(1) The melt temperature is too low. The molding temperature should be appropriately increased.

(2) The screw compression ratio is too large. The screw should be replaced.

(3) The resistance of the head is too great. The head compression ratio should be reduced.

(4) The motor pulley drive ratio is too large. The gear ratio should be reduced.


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