The blow molding process is a bidirectional stretching process. In this process, the PET chain is bidirectionally extended, oriented and arranged, thereby increasing the mechanical properties of the bottle wall , improving the tensile, tensile, and impact strength. Good air tightness. Although stretching helps to increase strength, it cannot be over-stretched. The stretch-blow ratio should be controlled well; the radial direction should not exceed 3.5-4.2 and the axial direction should not exceed 2.8-3.1. The wall thickness of the preform should not exceed 4.5mm.
Bottle blowing machine is carried out between the glass transition temperature and the crystallization temperature, generally controlled between 90-120 degrees. In this interval, PET appears as a high-elasticity, rapid blow molding, cooling and shaping to become a transparent bottle. In the one-step method, this temperature is determined by the length of the cooling time in the injection molding process of the PET plastic bottle blowing machine, so it is necessary to connect the relationship between the injection and blowing two stations.
During the blow molding process: stretching-one blow-two blows, the time of the three actions is very short, but it 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 should be adjusted well; the stretching start timing, stretching speed, pre-blowing start and end timing, pre-blowing pressure, pre-blowing air flow, etc., if possible, can control the overall temperature distribution of the preform. Temperature gradient. During the rapid blow molding and cooling process, there are common problems and solutions in the induced stress in the bottle wall.
1. Upper thickness and lower thickness: delay the pre-blowing time or reduce the pre-blowing pressure to reduce the air flow.
2. Lower thickness and upper thickness: contrary to the above.
3. There are wrinkles under the bottleneck: the pre-blowing is too late or the pre-blowing pressure is too low, or the billet cooling is not good here.
4. Blushing at the bottom: The preform is too cold and overstretched, the pre-blowing is too early or the pre-blowing pressure is too high.
5. The bottom of the bottle has a magnifying glass phenomenon: too much material at the bottom of the bottle, the pre-blowing is too late, and the pre-blowing pressure is too low.
6. There are wrinkles in the bottom of the bottle: the temperature at the bottom 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 turbid: opaque, and insufficient cooling.
8. Local whitishness: Over-stretching, where the temperature is too low, or pre-blowing too early, or touching the stretch rod.
9. Eccentricity of the bottom of the bottle: 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 drawing speed, check the gap between the draw bar head and the bottom mold, delay pre-blowing, reduce the pre-blowing pressure, delay high-pressure blowing, and check whether the preform is eccentric.
Production speed adjustment of blow molding machine
By increasing the exhaust time and increasing the saturation time to slow down the speed, while reducing the overall temperature of the lamp box, the overall temperature of the lamp box needs to be reduced by 1% for each increase of 0.1S. Increasing the speed is opposite to reducing the speed. (The exhaust time is very low at 0.8S, and if it is lower than 0.8S, there will be a bottle skipping phenomenon due to the exhaust is not timely.) No matter the speed is increased or decreased, it should not be too fast. The bottle quality should be adjusted after the bottle quality is stable. Every time you adjust the speed, you must carefully observe the quality of the bottle and adjust the temperature of the light box at any time. Each 0.1S change of the bottle blowing cycle changes the bottle output per hour by about 50. The bottle blowing machine should adjust the bottle blowing speed reasonably according to the speed of the filling machine.