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What are the common problems in bottle blowing process?
- Apr 13, 2018 -

   Bottle blowing machine is a process of two-way stretch. In this process, PET chains are arranged two-way stretch, orientation, and, thus increasing the bottle wall mechanical performance, can improve the tensile, impact strength, and has good air tightness.Although stretching helps to increase the intensity, it cannot be overstretched, so it is necessary to control the stretching ratio: no more than 3.5 ~ 4.2 in the radial direction, and no more than 2.8 ~ 3.1 in the axial direction.The wall thickness of the preform should not exceed 4.5mm.

   Bottle blowing is between the glass temperature and crystallization temperature, generally controlled between 90 and 120 degrees.In this interval, PET behaves as a high elastic state, rapidly blowing, cooling, and then becoming a transparent bottle.In the one-step method, the temperature is determined by the length of cooling time in the injection process (such as the green wood blowing machine), so the relationship between the two stations should be connected.

    The process of Bottle blowing machine  are: tensile - pre- blowing - blowing, three action time is very short, but be sure to cooperate well, especially the former two step determines the overall distribution of the material, by the quality of bottle blowing.So to adjust good: stretch the starting time, stretching rate, blow the start and end time, air pressure, blowing air flow, etc. If possible, it's best that control the temperature of the bottle preform general distribution, bottle preform, both inside and outside wall temperature gradient.

   In the process of rapid blowing and cooling, there is induced stress in the wall.For an aerated beverage bottle, it can be resistant to internal pressure, which is beneficial, but for a hot filling bottle, it should be guaranteed to be fully released at the glass temperature above.

   Common problems and solutions for bottle blowing machine:

1. Thickness of the upper bottle body: delayed pre-blowing time, or reducing preblowing pressure, reducing air flow.

2. Thin on the bottom: opposite to the above.

3. There is a wrinkle under the bottle neck: the preblowing is too late or the pre-blowing pressure is too low, or the billet is not cool at this point.

4. It's white in the bottom of  bottle: the bottle is too cold;Overstretching;Preblowing too early or preblowing too high.

5. There is a magnifying glass at the bottom of the bottle.Preblowing is too late and the pre-blow pressure is too low.

6. There is a wrinkle in the bottom of the bottle: the bottom temperature is too high (the gate is not cool);Pre - blowing too late pre - blow pressure too low, too low flow.

7. The whole bottle is cloudy (opaque) : not enough cooling.

8. It's white in some part of the bottle : excessive stretching, too low temperature here, or preblowing too early, or touching the stretching rod.

9. Bottle  bottom eccentric: it may be related to temperature, stretching, preblowing, high pressure blowing, etc. Reduce the preform temperature;Accelerate the stretching speed;Check the clearance between the pull rod head and the bottom die;Delay pre - blowing, reduce pre - blow pressure;Delayed high pressure blow;Check whether the  PET preform is eccentric.