The preform of the automatic bottle blowing machine and its heating, pre-blowing (position, pressure and flow), stretching rod, high-pressure blowing (pressure, position) and molds will all affect the production speed of the bottle made by the blowing machine.
Preform, also known as parison, is injection molded from PET pellets. It requires that the proportion of recycled materials should not exceed 10%, and the number of recycled materials should not exceed twice. Preforms after injection molding or reheated preforms must be cooled for more than 48 hours, and the storage time of the used preforms cannot exceed 6 months. Different production dates, especially preforms with too long distances cannot be mixed. The type of raw material used in the preform, the proportion of the secondary material mixed in and the residual stress in the preform are different, and these factors have a serious impact on the molding process of the bottle blowing bottle, and should be treated in detail according to the actual situation.
The heating of the preform is completed by the heating furnace, which is set manually and adjusted automatically. The height of the heating furnace is preferably about 25mm, and the distance from the delivery wheel is about 19.6mm. The preform runs continuously through the entire oven on the conveying wheel, so that the preform is heated more evenly and can be shaped better, which overcomes the defects of uneven heating caused by static heating and manual rotation in the past. However, if the heating furnace is not adjusted properly, the wall thickness of the blown bottle will be unevenly distributed up and down (for example, the top is light and the bottom is heavy), the bottle mouth will become larger than the standard, hard neck and other product defects, and even cause torsion failure of mechanical parts. The temperature of each area can be adjusted in detail according to the molding status of the product, and at the same time, the opening status of the oven lamp tube should be considered. In addition, the setting of the output power of the oven also has a great influence on the heating of the preform, which controls the heat output of the entire oven. When the pet bottle blowing machine is not turned on for a long time, when it is turned on again, the initial output power should be set higher accordingly, and then gradually reduced to the normal state during normal consumption. The output power is generally about 80%, especially when the ambient temperature is below 5°C. The effect is more significant.
The bottle blowing production process also has a certain relationship with the production environment temperature. The ambient temperature is generally room temperature (about 22°C). If the temperature is too high, the product is prone to condensation point agglomeration; if the temperature is too low, the product performance will be unstable when the automatic pet bottle blowing machine is started, and the specific operation should be adjusted according to the actual situation and experience.
The role of pre-blowing in the blowing process is to make the preform take shape, and at the same time, it is stretched longitudinally by the stretching rod to increase its longitudinal strength. The whole process is that the pre-blowing cam pushes the three-way valve to the pre-blowing position during the blowing process, and is completed by the one-way valve. Pre-blowing position, pressure and flow can all affect the quality of the bottle.
Position: If the pre-blowing position is advanced, the center point of the bottom of the bottle will be skewed and thinned, the wall thickness of the feet will be uneven and whitish, the top is heavy and the bottom is light, the neck will be hard, and the bottom will penetrate. There will be defects such as light on the top and heavy on the bottom, thickening of the center point, and depression.
Air flow The pre-blowing air flow is controlled by a one-way valve, and it is generally advisable to open 3-4 turns. The air flow is large, the bottom is heavy, the center point is thin and biased, the feet are white, and the wall thickness is uneven; the air flow is small, the center point becomes thicker, and the weight of the segment exceeds the standard.
Pressure: The pre-blowing pressure is preferably 0.8-1MPa. When the pressure is high, it may cause the top to be heavy and the bottom to be light, the center point is skewed, the wall thickness of the foot is uneven, white, etc.; when the pressure is low, it cannot be fully stretched, the bottom is heavy, and the center point is thick.
The shape of the bottle foot and center point has a great influence on the quality of the bottle. Improper adjustment often leads to fatal defects such as bottle bursting (under normal test conditions) and leakage.
4. Stretch rod
The stretching rod is a device that stretches the heated preform under the cooperation of pre-blowing at the same time as pre-blowing. It resets after high-pressure blowing and before exhausting. The stretch rod must be able to move vertically and smoothly during the blowing process, the driving pressure is 0.55-0.8MPa, and the gap with the bottom mold is 2.3-2.5mm, that is, the thickness of the preform is 1/3-1/2. If the gap is too large, the center point of the bottom of the bottle will shift; if the gap is too small, the center point will become thinner.
5. High pressure blowing
The function of high-pressure blowing is to fully stretch the molten material and cling to the mold wall to fully shape the bottle, and at the same time carry out transverse stretching to improve its transverse strength. The main influencing factors are position and pressure.
The high-pressure blowing pressure is generally 3.7-4MPa, which is determined by its molding characteristics and the nature of the filled beverage (carbon dioxide). There are two positions, that is, the position of high-pressure gas and the position of exhaust. The time between the two is the holding time during molding. The length of this time has a great influence on the stability of the bottle capacity. Insufficient high-pressure air can easily cause improper bottle molding and insufficient foot blowing.
The mold is one of the important elements affecting the blow molding of the bottle. The body of the bottle is a half mold, and the bottom of the bottle is independent, which is a typical blow mold. During the production process, the mold must be kept at a constant temperature, clean, and the vent hole should be unblocked.
When the heating and cooling system of the mold fails, there will be defects such as bottle neck skew, bottle tilt, volume and height changes, and bottom weight; maintaining a constant temperature of the mold can also prevent condensation on the surface of the mold.
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