First, what is PET?
PET （Polyethylene terephthalate） is one kind of polyester
Is the abbreviation of English PolyethyleneTerephthalate
Characteristics of PET raw materials
* Excellent transparency of over 90%, excellent surface gloss and a glassy appearance.
* Excellent fragrance retention and good air tightness.
* Excellent chemical resistance, with acid as the head is almost resistant to all organic drugs.
* Good hygiene, PDA – recognized by the largest chemical laboratory in the United States.
* No toxic gases will occur when burning.
* Excellent strength properties, and can be further improved by biaxial stretching.
* The most complete PET preform quality defect solution in history
Second, why should the PET material be dried before the production of the preform?
A. Remove moisture from PET
Because PET has a certain water absorption, it absorbs a lot of water during transportation, storage and use. High levels of water are exacerbated in production:
– AA (Acetaldehyde) an increase in acetaldehyde. The odor of the beverage bottle causes the beverage to taste (but has little effect on the human body)
– IV (Intrinsic Viscosity) viscosity drop. It has an influence on the pressure resistance of the beverage bottle and is easily broken. (essentially caused by hydrolytical degradation of PET)
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B. Prepare for high temperature preparation for PET into the injection molding machine for shear plasticization.
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Third, the water absorption characteristics of PET
The moisture content of the raw material granules usually ranges from 0.1 to 0.3% (1000 to 3000 ppm).
The most complete PET preform quality defect solution in history
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Fourth, the main points of PET drying
Dry set temperature 165o-175oC
Residence time 4-6 hours
Feeding port temperature above 160o C
Dew point below -30oC
Dry air flow 3.7m3 / h per kg / h
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Fifth, the degree of drying
The ideal moisture content after drying is approximately: 10to40 ppm (/- 10 ppm), ie 0.001-0.004%
Excessive drying is also exacerbated:
-AA (Acetaldehyde) increase in acetaldehyde
-IV (IntrinsicViscosity) viscosity drop
(essentially caused by oxidative degradation of PET)
How to proceed to optimize the production cycle
Opening and closing speed
Ejecting speed
Adjustment of the distance between the take-up plate and the ejector plate
Opening time of the nozzle closing valve
Injection speed and maximum pressure limit
Matching pressure/time with cooling time
Mold position setting that allows the robot to enter
(Optimization of the cycle to ensure that the average temperature of the mold is appropriate)
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7. Reasons and solutions for common quality defects
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1. AA value is too high
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A. The quality of raw materials has quality problems. → The quality of raw materials is checked before entering the warehouse.
B. poor drying effect → check the operation of the dryer (such as: dew point, drying temperature / time)
C. the barrel heating temperature is too high → under the premise of ensuring the quality, try to reduce the temperature
D. the screw back pressure is too high → set the back pressure under the premise of quality (400 ~ 600Psi)
E. the cycle time is too long → optimize the cycle time (to avoid the raw material staying in the screw for too long)
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2. The bottle is yellowed
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A. The drying time is too long/the temperature is too high. → The over-dried material is discharged, and the material is dried again.
B. the temperature of the barrel is too high → the temperature is lowered (generally, the preform does not produce a white fog temperature increase of 2 ~ 5 ° C) is the normal temperature
C. the mold temperature is too high → the temperature is reduced to the appropriate temperature (275 ~ 280 ° C)
D. the raw material stays in the screw for too long → empty the raw material of the barrel
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3. Wall thickness change rate is too large
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A. The screw temperature is too high → adjust the screw temperature appropriately
B. the screw back pressure is too large → adjust the screw back pressure to the appropriate pressure
C. the injection speed is too fast → appropriate to reduce the injection speed (usually 3.5 ~ 4 S when injected)
D. the mold cooling water temperature is too high → check the cooling cycle water temperature (9 ~ 11 ° C ± 2 ° C)
E. the cooling time is too short → lengthen the cooling time (usually set to 3 ~ 4 S)
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4. Surface scratches (embroid body / thread)
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A. the mold has adhesive → clean the mold
B. mold damage → replace damaged parts or repair
C. remove the plate suction tube damaged → replace the damaged suction tube or repair
D. the lip ejection position / pressure is too large → adjust the ejection position / pressure to the appropriate state
E. The position of the take-up plate is not correct. → Check the position of the suction plate and the lip of the plate (generally set to: 22mm)
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5. IV falls too big
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A. raw materials storage time is too long → raw materials to achieve first-in-first-out method
B. poor drying effect → check whether the dryer is normal, maintain the dryer, check the dry bead use time (usually 2 to 3 years replacement)
C. the barrel heating temperature is too high → under the premise of ensuring the quality, try to reduce the temperature
D. the screw back pressure is too large → under the premise of quality will be back pressure, generally set: 400 ~ 600 Psi
E. the mold heating temperature is too high → reduce the heating temperature of the warmer, generally set: 280 ~ 285 ° C
F. the preform storage time is too long or the warehouse environment temperature, humidity is too high → check the wet / temperature of the warehouse (generally: 70% / 28 or less), do a first-in-first-out inventory method
G. the quality of the raw material itself has quality problems → notify the supplier to deal with
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6. Shrinkage deformation
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A. the cooling time is too short → lengthen the cooling time (set: 3 ~ 4S)
B. The holding time is too short / the pressure is insufficient → the holding pressure is extended (set to: 3 to 8S); increase the holding pressure (level 1: 800Psi, level 2: 700Psi, level 3: 600Psi)
C. the mold cooling water temperature is high → reduce the water temperature (set: 9 ~ 11 ° C ± 2 ° C)
D. the mold circulating water pressure is low → increase the water pressure (set: 6 ~ 7 Kg)
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7. Unmelted material
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A. The screw heating temperature is too low → the temperature is raised appropriately
B. the screw slips can not cut the raw materials → (general production of color oil only has this phenomenon) Check whether the color oil is too high, replace the color oil
C. the screw back pressure is too small → increase the screw back pressure
D. the drying temperature is low → check whether the screw feed temperature meets the requirements (normal requirement is 160 ° C)
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8. Bottle mouth shortage
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A. Insufficient injection volume → increase injection volume (the remaining position after injection is generally 5~8mm)
B. the injection pressure is too low → increase the injection pressure
C. the injection speed is too slow → speed up the injection speed (optimal injection time: 3.5 ~ 4s)
D. the pressure holding position is too large → reduce the pressure holding position (injection pressure: 900 ~ 1200Psi)
E. The holding pressure is too small → increase the holding pressure
F. the mold cooling cycle water temperature is too low → increase the cooling water temperature (set: 8 ~ 10 ° C)
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9. Long nozzle extension nozzle
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A. The drying effect of raw materials is poor → stop and dry again
B. hot runner valve needle cylinder blockage → maintenance hot runner
C. hot runner / nozzle temperature is too high → properly lower the temperature
D. the pressure holding time is too short → lengthen the pressure holding time
E. The holding pressure is too small → increase the holding pressure
F. the cooling time is too short → lengthen the cooling time
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10. Injection port drawing
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A. The hot runner nozzle cannot be closed or the nozzle mouth is worn out → maintenance hot runner cylinder or replacement of new nozzle
B. The hot runner nozzle temperature is too high → lower the nozzle heating temperature
C. the nozzle valve delay closing time is too long → reduce the nozzle valve delay closing time
D. valve needle control valve failure → maintenance valve needle control valve
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11. Water and gas traces
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A. The temperature of the mold cooling water is too low → increase the temperature of the circulating water of the mold
G. The ambient temperature of the workshop is too high or the humidity is too high, causing the mold to hydrate the water → lowering the air conditioning temperature
C. the mold leaks → check the mold leakage and eliminate
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12. Bottom crystallization
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A. The hot runner and nozzle temperature are low → increase the nozzle and hot runner temperature
B. the pressure is too large → reduce the pressure of the third level
C. The mold cooling water is low or high → check if the cooling water temperature is reasonable and then adjust
D. mold cold water channel blockage → maintenance mold water circulation channel
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13. Bottle white mist
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A. Insufficient drying of raw materials → stop and dry the raw materials
B. the screw heating temperature is too low → increase the screw heating temperature
C. screw slip → (general production of color oil embryos appear) will increase the temperature of the barrel
D. back pressure is too low → increase back pressure
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14. Preform black spots / pollution
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A. The raw materials are polluted or have impurities in them. The raw materials with impurities are released (the feeder should always pay attention to whether the raw materials are contaminated)
B. The raw materials are contaminated during drying → the raw materials with quality problems are released.
C. barrel temperature / hot runner / nozzle temperature is too high → reduce the temperature to the appropriate temperature
D. The production environment or equipment is too clean and hygienic → keep the workshop and equipment clean and hygienic
E. The preforms are stored in the warehouse and contaminated → keep the warehouse sanitation and the packaging intact
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15. Flash
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A. Die lip, core holder, cavity damage → replace or repair damaged parts
B. the injection pressure is too large → reduce the injection pressure
C. The holding pressure is too large → reduce the holding pressure or holding position
D. the heating temperature is too high → lower the heating temperature
E. the clamping pressure is too low → increase the clamping pressure (generally: 200 ~ 230Psi)
F. the raw material stays in the heating section for too long → shorten the production cycle
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16. Bottom peeling
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A. The nozzle temperature is too high or too low → the nozzle temperature is adjusted to moderate
B. the mouth of the nozzle is worn → replace the new nozzle and the new nozzle insulation sleeve
C. hot runner valve needle deformation or wear → replace the new valve needle
D. The third stage of the holding pressure is too large → reduce the holding pressure
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17. Internal shrinkage of the bottom of the bottle
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A. Excessive scale or rust of the core cooling pipe → cleaning the core cooling passage
B. the core transport pipe is loose → demoulding from the new tightening water pipe
C. Insufficient water pressure → raise water too (generally: 6 to 7 bar)
D. the water temperature is too high → adjust the temperature of the chiller into the water
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18. Scorch marks
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A. the nozzle temperature is too high → reduce the nozzle heating percentage
B. nozzle nozzle insulation aging → replace the new nozzle insulation sleeve
C. The cooling water passage at the bottom of the cavity is blocked → the mold cavity is cleaned and the bottom of the cavity is cleaned.
D. Insufficient water pressure → increase water pressure
E. the water temperature is too high → lower the water temperature
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19. Fishbone stripes
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A. The mold hot runner temperature is too high → lower the hot runner temperature
B. The mold nozzle heating temperature is too high → lower the nozzle temperature
C. mold nozzle insulation sleeve aging → replace nozzle insulation sleeve
D. The nozzle valve needle does not move smoothly → maintain the hot runner or replace the valve needle
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20. Injection pinhole
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A. The mold nozzle temperature is too high → lower the nozzle temperature
B. The position of the glue is too small → adjust the position of the glue
C. The mold hot runner temperature is too high → lower the hot runner temperature
D. the raw material drying effect is poor → stop from the new dry (about 2 to 3 hours)
E. the injection speed is too fast → slow down the injection speed
F. The pressure and time are too small → lengthen the pressure and time
21. The bottom of the embryo shrinks
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A. Insufficient injection volume → increase injection volume (remaining position: 5~8mm)
B. the pressure holding position is too large → increase the pressure
C. the cooling water temperature is too high → reduce the cooling water temperature
D. the cooling time is too short → lengthen the cooling time
E. the pressure is too small → increase the pressure of pressure