- what is PET?
It’s Polyethylene Terephthalate
Pet 原料的特性
Transparent excellent up to 90%, surface gloss excellent, glass appearance.
excellent fragrance preservation and good air tightness.
excellent chemical resistance, and almost all organic drugs can be resistant to acid.
No toxic gas is produced when burning.
The strength characteristics are excellent and can be further improved by biaxial stretching.
- Why need to dry PET beforeproduct preform ?
Remove the water from PET
1)Because PET can absorb a lot of water during transportation, storage and use because it has certain water absorption.High water content will aggravate in production:
AA(Acetaldehyde)The increase in acetaldehyde.It has an effect on the smell of beverage bottles, leading to the change of beverage flavor (but little effect on human body).
IV(IntrinsicViscosity)Viscosity reduction,It has an effect on the pressure tolerance of beverage bottles and is easy to break.(essentially caused by hydrolytic degradation of PET)
- High temperature preparation for PET entering the injection molding machine for shear plasticizing
- PET的吸水特性
The water content of raw material particles usually ranges from 0.1 to 0.3 percent (1000 to 3000 PPM).
- PET 的干燥要点
Drying setting temperature：165º-175ºC
Drying time : 4-6H
Blanking temperature:more then 160º C
- dew point -30 is below C
Dry air flow:3.7m³ /h/kg
- 干燥的程度
The ideal moisture content after drying is about: 10to40 PPM (+/ -10 PPM), or 0.001-0.004%
Excessive drying also increases:AA(Acetaldehyde) and -IV(IntrinsicViscosity) Viscosity reduction
The essence is caused by oxidative degradation of PET
- 如何优化生产周期
ejection speed
die opening and closing speed
just the distance between the extraction plate and the ejector plate
、opening time of the nozzle shutoff valve
matching of injection speed and maximum pressure limit
coordination between pressure retaining time and cooling time
setting of mold position allowing the manipulator to enter
- 常见质量缺陷的原因及解决方案：
AA is too high
1）. Quality problem of raw materials – check the quality of raw materials before warehousing
2）. Poor drying effect — check the operating condition of the dryer (e.g. dew point, drying temperature/time)
3）. The heating temperature of the gun barrel is too high
4）. High back pressure of screw — set back pressure as (400-600psi) under the condition of quality
5）. Too long cycle time — optimized cycle time (avoid the material staying in the screw for too long)
Preform is faint yellow
1). Excessive drying time/high temperature: release the overdried raw materials and redry them
2), gun barrel temperature too high – temperature decrease (generally in the embryo bottle does not produce white mist temperature increasing of 2 ~ 5 ℃) to normal temperature
3), mold temperature is too high – temperature will drop to the appropriate temperature (275 ~ 280 ℃)
4)The material stays on the screw for too long
The wall thickness changes too much
1)The screw temperature is too high
2)Excessive back pressure of screw – adjust the back pressure of screw to fit pressure
3)Injection speed too fast – reduce the injection speed appropriately (3.5 ~ 4 S for general injection)
4)Mold cooling circulating water temperature of cooling water temperature is too high – inspection (9 ~ 11 ℃ + 2 ℃)
5)Too short cooling time – longer cooling time (generally set as 3-4 S)
There was a scratch on the surface
1) The molds are sticky – cleaning molds
2.) Mold damage: replace damaged parts or repair
3.)Take out the plate and suction tube damaged — replace the damaged suction tube or repair
4.)The position/pressure of the upper lip is too high
5.)Improper position of the extraction plate — check the distance between the suction tube and the lip of the extraction plate (generally set as: 22mm)
Viscosity decreased
1). Storage time of raw materials is too long
2). Poor drying effect — check whether the dryer is normal, maintain the dryer, and check the service time of dry beads (generally 2-3 years)
3). The heat temperature of the gun barrel is too high
4). Excessive back pressure of screw — back pressure shall be set as 400 ~ 600 Psi under the premise of quality
5), mould heating temperature is too high to reduce the temperature of heating temperature, generally set to: 280 ~ 285 ℃
6). The storage time of the bottle embryo is too long or the temperature and humidity in the warehouse are too high
7). If the raw material itself has quality problem, inform the supplier to deal with it
shrinkage strain
1)Too short cooling time —longer cooling time (set as: 3-4s)
2)Dwell times is too short /insufficient injection pressure .
3) Mould cooling water temperature is high
4) The circulating water pressure of mould is low.
There is a defect in the bottle mouth
1)Insufficient injection plastic
2)Low injection pressure.
3) Injection speed is too slow
4)The pressure protection position is too large
5)Mold cooling cycle too low water temperature
Gate wire drawing
1)The hot runner nozzle cannot be closed or the nozzle has worn away
2)The hot runner nozzle is too hot
3)The shut-in valve is delayed for too long
4)Valve needle control valve malfunction maintenance valve needle control valve
Water vapor on the surface
1)Mold cooling water is too low
2)The high temperature or humidity in the workshop caused the mold condensation
3)The mold is leaking
At the bottom of the crystal
1)The temperature of heat flow channel and nozzle is low
2)The pressure is too high
3)Mold cooling temperature water is low or high
4)Mould cold water channel blocked
The bottle white mist
1). Insufficient drying of raw materials — stop to dry the raw materials again.
2)The screw is heated too low
3). Screw skidding —–(generally the production of color oil embryo) will increase the temperature of the gun barrel
4)Low back pressure —–raises back pressure
Burr
1). Die lip, die core seat, die cavity damage —-replace or repair damaged parts
2). Excessive injection pressure—– reduces injection pressure
3). Excessive pressure protection —–reduce pressure protection or pressure protection position
4). The heating temperature is too high —–to lower the heating temperature
5). Low clamping pressure —- increasing clamping pressure (generally: 200 ~ 230Psi)
6). The raw material stays too long in the heating section, —–thus shortening the production cycle
The bottom of the bottle contracts internally
1). Clean the core cooling channel with excessive scale or rust
2). )Loosen the core pipe, remove the mould and tighten the pipe again
3).Insufficient water pressure raise water too (generally: 6 ~ 7 bar)
4). The water temperature is too high.
Scorch
1). The temperature of the nozzle is too high
2). Aging of nozzle heat shield —–replace new nozzle heat shield
3).The cooling water channel at the bottom of the mold cavity is blocked—-
Remove the mold and clean the cavity bottom
4).Insufficient water pressure increase water pressure
5)The water temperature is too high
Fish streak
1). The mold heat flow path temperature is too high
2). The temperature of mold nozzle is too high to lower the temperature of mold nozzle
3). Die injector heat shield aging – —replace the injector heat shield
4). The nozzle needle is not moving well—–maintain the hot runner or replace the valve needle
Gate pinhole
1). The temperature of mold nozzle is too high
2). The position of glue extraction is too small
3). The temperature of mold heat flow passage is too high
4). Poor drying effect of raw materials —– stop to re-dry (about 2-3 hours)
5). The injection speed is too fast——– to slow down the injection speed
6). The pressure and time are too small —– the pressure and time are lengthened
Preform bottom shrinks
1). Insufficient injection amount —— increase injection amount (the remaining position is: 5-8mm)
2). The pressure protection position is too large
3). The cooling water temperature is too high
4). Too short cooling time – —longer cooling time
5). The pressure is too small —– increase the pressure