Common technical problems of PET blow molding machine

Update: 2022/05/07

The blow molding process is a two-way stretching proces […]

The blow molding process is a two-way stretching process, in which the PET chains are extended, oriented and aligned in both directions, thereby increasing the mechanical properties of the bottle wall, improving the tensile, tensile and impact strength, and have a high Good air tightness.
The bottle blowing machine is carried out between the glass transition temperature and the crystallization temperature, generally controlled between 90-120 degrees. In this range, PET is highly elastic and rapidly blow-molded, and becomes a transparent bottle after cooling and shaping. In the one-step method, this temperature is determined by the length of the cooling time during the injection molding process, so the relationship between the injection and blowing stations should be well connected.
In the blow molding process, there are: stretching—one blow—second blow. The three actions are very short, but they must be well coordinated, especially the first two steps determine the overall distribution of the material and the quality of the blow molding machine. Therefore, it is necessary to adjust well; the starting timing of stretching, the stretching speed, the starting and ending timing of pre-blowing, the pre-blowing pressure and the pre-blowing flow rate, etc. If possible, it is best to control the overall temperature distribution of the preform and the inner and outer walls of the preform. Temperature gradient. PET bottle blowing equipment has common problems and solutions for induced stress in the bottle wall during rapid blow molding and cooling.
1. Thick on the top and thin on the bottom: delay the pre-blowing time or reduce the pre-blowing pressure to reduce the air flow.
2. Thicker at the bottom and thinner at the top: Contrary to the above.

3. There are wrinkles under the bottle neck: the pre-blowing is too late or the pre-blowing pressure is too low, or the blank is not cooled well here.
4. White bottom: the preform is too cold, overstretched, pre-blowing is too early or pre-blowing pressure is too high.
5. There is a magnifying glass phenomenon at the bottom of the bottle: too much material at the bottom of the bottle, pre-blowing is too late, and pre-blowing pressure is too low.
6. There are wrinkles in the bottom of the bottle: the bottom temperature is too high, the cooling at the gate is not good, the pre-blowing is too late, the pre-blowing pressure is too low, and the flow rate is too small.
7. The entire bottle is cloudy: opaque, not cooling enough.
8. Partial whitening: Excessive stretching, the temperature here is too low, or pre-blowing is too early, or the stretching rod is touched.
9. Bottom eccentricity: It may be related to the temperature of the preform, stretching, pre-blowing, high-pressure blowing, etc. Reduce the temperature of the preform, speed up the stretching speed, check the gap between the tie rod head and the bottom mold, delay the pre-blowing, reduce the pre-blowing pressure, delay the high-pressure blowing, and check whether the preform is eccentric.

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