01.
What is PET?
PET is a kind of polyester
Is the abbreviation of English PolyethyleneTerephthalate
Characteristics of PET raw materials
The transparency is as high as 90% or more, the surface gloss is excellent, and it has a glass-like appearance.
Excellent fragrance retention and good airtightness.
Excellent chemical resistance is resistant to almost all organic chemicals, including acids.
Good hygiene, PDA-recognized by the most extensive chemical laboratory in the United States.
No poisonous gas will be generated during combustion.
It has excellent strength properties, and various properties can be further improved by biaxial stretching.
02.
Why do PET raw materials need to be dried before preforms are produced?
Removal of water in PET
Because PET has a certain degree of water absorption, it will absorb a lot of water during transportation, storage, and use. The high content of water will aggravate during production:
-AA (Acetaldehyde) increase in acetaldehyde.
The effect on the smell of the beverage bottle, causing the beverage to change its taste
(But it has little effect on the human body)
-IV (IntrinsicViscosity) viscosity drop.
It impacts the pressure resistance of the beverage bottle and is easy to break.
(The essence is caused by the hydrolytic degradation of PET)
Prepare for high temperature
Prepare for high temperature for PET entering the injection moulding machine for shearing and plasticizing
03.
Water absorption characteristics of PET
The water content of the raw material particles is usually in the range of 0.1-0.3% (1000 to 3000 ppm)
04.
The main points of PET drying
Dry setting temperature 165º-175ºC
Residence time 4-6 hours
The discharge port temperature is above 160º C
Dew point below -30ºC
Dry air flow rate 3.7m³ /h per kg/h
05.
Degree of dryness
The ideal moisture content after drying is approximate: 10to40 ppm (+/- 10 ppm), which is 0.001-0.004%
Excessive drying can also increase:
-AA (Acetaldehyde) increase in acetaldehyde
-IV (IntrinsicViscosity) viscosity drop
(The essence is caused by the oxidative degradation of PET)
06.
How to start to optimize the production cycle
- Opening and closing speed
- Ejection speed
- Adjustment of the distance between the take-out plate and the ejector plate
- Opening time of the nozzle closing valve
- Coordination of injection speed and maximum pressure limit
- Coordination of holding pressure/time with cooling time
- The mould position setting that allows the robot to enter
(Optimization of the cycle to ensure that the average temperature of the mould is appropriate)
07.
Causes and solutions of common quality defects
AA value is too high
1. There are quality problems in the performance of the raw materials → inspect the quality of the raw materials before entering the warehouse
2. Poor drying effect → check the operation of the dryer (such as dew point, drying temperature/time)
3. The barrel heating temperature is too high → try to reduce the temperature under the premise of ensuring quality
4. Screw back pressure is too high → set the back pressure to (400～600Psi) under the premise of quality
5. The cycle time is too long → optimize the cycle time (to avoid too long residence time of the raw materials in the screw)
Yellow bottle preform
1. The drying time is too long/the temperature is too high → release the over-dried raw materials and re-pump and dry them
2. The barrel temperature is too high → reduce the temperature (generally, the temperature of the preform does not produce white fog and increase the temperature by 2～5℃) to the average temperature
3. The blow moulder‘s mold temperature is too high → reduce the temperature to a suitable temperature (275～280℃)
4. The residence time of the raw material in the screw is too long → to empty the high-temperature raw material of the barrel
Excessive wall thickness change rate
1. The screw temperature is too high → appropriately lower the screw temperature
2. The screw back pressure is too large → adjust the screw back pressure to the proper pressure
3. The injection speed is too fast → reduce the injection speed appropriately (3.5～4 S for general injection)
4. Blow moulder‘s Mold cooling water temperature is too high → check the cooling circulating water temperature (9～11℃ ±2℃)
5. The cooling time is too short → lengthen the cooling time (generally set to 3～4 S)
Surface scratches (embroid body/thread)
1. Blow moulder’s Mold has sticky material → clean the mould
2. Blow moulder’s Mold damage → replace damaged parts or repair
3. Take out the board, and the suction tube is damaged → replace the damaged suction tube or repair it
4. The ejection position/pressure of the die lip is too enormous → adjust the ejection position/pressure to a suitable state
5. Improper position of the take-out plate → check the distance between the suction cylinder of the take-out plate and the die lip (generally set as 22mm)
IV drop is too large
1. The storage time of the raw materials is too long → the raw materials are used in a first-in-first-out method
2. Poor drying effect → check whether the dryer is regular, maintain the dryer, and check the use time of the drying beads (generally replaced in 2 to 3 years)
3. The barrel heating temperature is too high → try to reduce the temperature under the premise of ensuring quality
4. Screw back pressure is too enormous → under the premise of quality; the backpressure is generally set to 400～600 Psi
5. Mold heating temperature is too high for blow moulder equipment → lower the heating temperature of the temperature tool, generally set to 280～285℃
6. The preform storage time is too long, or the warehouse environment temperature and humidity are too high → Check the humidity/temperature of the warehouse (generally: below 70%/28) and make a first-in, first-out inventory method
7. The performance of the raw material itself has quality problems → notify the supplier to deal with it
Shrinkage deformation
1. The cooling time is too short → lengthen the cooling time (set to 3～4S)
2. The holding time is too short/the pressure is insufficient → Increase the holding time (set: the total of the three levels 6～8S); increase the holding pressure (first level: 800Psi, second level: 700Psi, third level: 600Psi)
3. Mold cooling water temperature is too high for blowing mouler → reduce water temperature (set to 9～11℃ ±2℃)
4. Mould circulating water pressure is too low → increase water pressure (set to 6～7 Kg)
Unmelted material
1. The screw heating temperature is too low → increase the temperature appropriately
2. The raw material cannot be cut due to the screw slippage → (this phenomenon is usually only found in the production of colour oil). Check whether the colour oil is too high, and replace the colour oil.
3. The screw back pressure is too small → increase the screw back pressure
4. The drying temperature is too low → check whether the screw feed temperature meets the requirements (the standard requirement is 160°C)
Lack of material at the bottle mouth
1. Insufficient injection volume → increases injection volume (the remaining position after injection is generally 5-8mm)
2. The injection pressure is too low → , increase the injection pressure
3. The injection speed is too slow → increase the injection speed (the best injection time is: 3.5～4s)
4. The holding pressure position is too large → reduce the holding pressure position (injection pressure: 900～1200Psi)
5. The holding pressure is too small → , increase the holding pressure
6. Mold cooling circulating water temperature is too low for blowing moulder → increase the cooling water temperature (set to 8～10℃)
Long nozzles, elongated nozzles
1. Poor drying effect of raw materials → stop and re-dry
2. The hot runner valve needle cylinder is blocked → maintain the hot runner
3. The temperature of the hot runner/nozzle is too high → lower the temperature appropriately
4. The pressure holding time is too short → increase the pressure holding time
5. The holding pressure is too small → , increase the holding pressure
6. The cooling time is too short → lengthen the cooling time
Nozzle wire drawing
1. The hot runner nozzle cannot be closed, or the nozzle mouth is worn out → maintain the hot runner cylinder or replace it with a new nozzle
2. The nozzle temperature of the hot runner is too high → reduce the heating temperature of the nozzle
3. The delayed closing time of the nozzle valve is too long → reduce the delayed closing time of the nozzle valve
4. The valve needle control valve fails to → maintain the valve needle control valve
Water vapour traces
1. Blow moulder’s Mold cooling water temperature is too low → increase mould circulating water temperature
2. The temperature of the workshop environment is too high, or the humidity is too high, causing water droplets in the mould → to lower the temperature of the air conditioner
3. Mold leakage of blowing mouder machine → check the cause of mould leakage and its elimination
Bottom crystallization
1. The temperature of the hot runner and nozzle is low → increase the temperature of the nozzle and hot runner
2. The holding pressure is too enormous. Reduce the holding pressure to the third level
3. The mould cooling water is too low or too high → check whether the cooling water temperature is reasonable and then adjust
4. Blow moulder equipment ‘s Mold cold water channel is blocked → maintain mould water circulation channel
White mist on the bottle
1. Insufficient drying of the raw materials → stop the machine and re-drys the raw materials
2. The screw heating temperature is too low → , increase the screw heating temperature
3. The screw slips → (generally only appears when producing coloured oil preforms), increase the barrel temperature
4. Backpressure is too low → increase back pressure
Preform black spots/contamination
1. The raw materials are contaminated, or there are impurities in the raw materials → release the raw materials with impurities (the extractor should always pay attention to whether the raw materials are contaminated)
2. The raw materials are contaminated during drying → release the raw materials with quality problems
3. The barrel temperature/hot runner/nozzle temperature is too high → reduce the temperature to an appropriate temperature
4. The production environment or equipment is too clean and hygienic → keep the workshop and equipment clean and hygienic
5. Preforms stored in the warehouse are contaminated → keep the warehouse environment sanitary and the packaging intact
Flash
1. Die lip, mould core seat, mould cavity are damaged → replace or repair damaged parts
2. The injection pressure is too high, → reduce the injection pressure
3. The holding pressure is too large, → reduce the holding pressure or the holding position
4. The heating temperature is too high, → reduce the heating temperature
5. The clamping pressure is too low → , increase the clamping pressure (generally: 200～230Psi)
6. The residence time of raw materials in the heating section is too long → shorten the production cycle
Peel the bottom of the bottle
1. The temperature percentage of the nozzle is too high or too low, → adjust the temperature of the nozzle to moderate
2. The nozzle mouth is worn out → replace the new nozzle and the new nozzle heat insulation sleeve
3. The hot runner valve needle is deformed or worn → replaced with a new valve needle
4. The third level of holding pressure is too large → reduce the holding pressure
Internal shrinkage of the bottom of the bottle
1. Excessive scale or rust in the mould core cooling pipe→Clean the mould core cooling passage
2. The mould core water pipe is loose → remove the mould and reinforce the water pipe
3. Insufficient water pressure → increase the water too much (generally: 6 ～ 7 bar)
4. The water temperature is too high → adjust the water temperature of the chiller
Scorch
1. The nozzle temperature is too high, → reduce the heating percentage of the nozzle
2. The nozzle heat insulation sleeve is aging, → replaced with a new nozzle heat insulation sleeve
3. The cooling water channel at the bottom of the mould cavity is blocked → remove the mould to clean the bottom of the mould cavity
4. Insufficient water pressure → increase water pressure
5. The water temperature is too high, → reduce the water temperature
Fishbone stripes
1. The temperature of the hot mould runner is too high → reduce the temperature of the hot runner
2. The heating temperature of the mold nozzle is too high → reduce the temperature of the nozzle
3. The mould nozzle heat insulation sleeve is aging → replace the nozzle heat insulation sleeve
4. The valve needle of the nozzle does not move smoothly → maintain the hot runner or replace the valve needle
Nozzle pinhole
1. The temperature of the mould nozzle is too high → lower the temperature of the nozzle
2. The glue drawing position is too small → increase the glue drawing position appropriately
3. The mould hot runner temperature is too high → lower the hot runner temperature
4. Poor drying effect of raw materials → stop and dry again (approximately 2 to 3 hours)
5. The injection speed is too fast → to slow down the injection speed
6. The holding pressure and time are too slight → increase the holding pressure and time
Shrinkage of preform bottom
1. Insufficient injection volume → increases injection volume (the remaining position is: 5～8mm)
2. The holding pressure position is too large → increase the holding pressure
3. The cooling water temperature is too high → reduce the cooling water temperature
4. The cooling time is too short → lengthen the cooling time
5. The holding pressure is too small → increase the holding pressure
Having your own blow moulder today
If you’re interested in purchasing a bottle blow molding machine to make PET bottles on your own, please contact us for a quick quote on a dependable bottle blower moulder for your consideration.
