Common problems and solutions of PET preform
The blowing process of blow molding process is a two-way stretch, in this process, the PET chain is two-way extension, orientation and alignment, thus increasing the mechanical properties of bottle wall, improve the tensile, tensile, impact strength, and has very good air tightness. Although stretching helps to increase strength, but it can not be stretched too much, to control the ratio of tensile expansion: the radial should not exceed 3.5 ~ 4.2, the axial should not exceed 2.8 ~ 3.1. The wall thickness of the preform should not exceed 4.5mm.
Blowing bottles are carried out between the glass temperature and the crystallization temperature, usually between 90~120 degrees. In this interval, PET exhibits high elasticity, rapid blow molding, and cooling to form a transparent bottle. In one step, the temperature is determined by the cooling time in the injection process (e.g., the root blowing machine), so the relation between injection and blowing two stations should be adjusted.
Blow molding process: Stretching - blow once - two blows, three action time is very short, but must cooperate well, especially the first two steps determine the overall distribution of material, bottle blowing quality is good or bad. Therefore, to regulate the starting time, the tensile tensile pre blow speed, start and end time, pre blow pressure, pre blow flow, if possible, the best to control the temperature distribution of the preform overall, the temperature gradient in the outer wall of the bottle blank. In the process of rapid blow molding and cooling, there is induced stress in the bottle wall. For inflatable beverage bottles, it is good for internal pressure resistance, but for hot bottling, it is necessary to ensure that it is released above the glass temperature. Common problems and Solutions
1., the thickness of the upper and lower: delayed pre blowing time, or reduce pre blowing pressure, reducing gas flow.
2. thick and thin: Contrary to the above.
There are 3. fold bottleneck: pre blow too late or pre blow pressure is too low, or the cooling is not good.
4. bottom white: the bottle is too cold; too stretched; pre blown too early or pre blowing too high pressure.
5. bottom has magnifying glass phenomenon: the bottle bottom material is too much; pre blown too late, pre blowing too low.
There are 6. fold: the bottom of the bottle bottom temperature is too high (gate cooling bad); pre blow too late pre blow pressure is too low, the flow is too small.
7., the whole bottle cloudy (opaque): insufficient cooling.
8., partial white: excessive stretch, where the temperature is too low, or pre blown too early, or hit the tensile bar.
9. bottles bottom eccentric: with the preform temperature, stretching, pre blowing, high pressure blowing and so may be related. Reduce the preform temperature; speed up the drawing; check the clearance between the tie rod and the bottom die; postpone the pre blow; reduce the pre blowing pressure; delay the high pressure blow; check whether the preform is eccentric.