Establish optimal reheat-blowing conditions for Pet Preform
In order to produce a uniform bottle sidewall thickness, the RHB conditions must be properly adjusted. Recommended procedures for establishing optimal conditions:
1. The stretching rod should only be used to center the gate of the preform at the bottom of the bottle; do not use it to obtain the orientation. If the speed of the lever can be adjusted, lower it to the center of the gate. Then increase the speed in very small increments until the gate is centered again. Keep the speed setting.
2. Increase the line speed until a slight pearlescence occurs. Then adjust the temperature of each heater to make the pearlescence uniform. The transparent areas indicate that the preforms are hot at this location; the temperature of these areas should be reduced. After the pearl is even, reduce the line speed to the normal setting.
3. If the machine is operating at maximum speed, a different approach is required. Lower the temperature of the heater until a slight pearlescence occurs; then adjust each heater to make the pearl even. After unification, record the settings. The temperature of each is then increased by the same relative amount. For example, if one heater is set to 80 and the other heater is set to 40, and it is desired to increase by 5%, then they are increased to 84 and 42, respectively. By doing so in small increments, the pearls should disappear in a uniform manner.
4. If the thickness of the side wall of the bottle is not uniform, increase the pre-low pressure and check the uniformity again. If this makes the sidewalls uneven, reduce the pre-low pressure.
5. Once the optimum pre-low pressure is established, it is sometimes possible to make further improvements by adjusting the timing of the pre-low pressure relative to the timing of the stretching rod. Therefore, the pre-flow timing is changed to start earlier and later in the sequence, and the results are evaluated to determine which timing is best.
Note: Pre-low pressure and time have a large effect on the thickness of the shoulder and bottom of the bottle. An increase in both generally increases the thickness of the substrate, and a reduction in both generally increases the thickness of the shoulder.
6. If the uniformity cannot be significantly changed by changing the pre-low pressure and its timing, increase the high-pressure blow delay time. The high pressure may come too fast, so the pre-extraction time will not be given to complete the work.
7. If the change in high pressure delay does not provide the required thickness uniformity, try increasing the stretch rod speed in small increments.
8. As a last resort, change the heater profile. When adjusting the machine, do not change more than one variable at a time. If you change two variables at the same time, one change may improve the uniformity of the sidewalls, while the other may make it worse, and the end result is unchanged. This may lead to a wrong conclusion that neither of these changes has any effect.
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