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What are the factors that affect the production of bottles by the blow molding machine?

by:Yosion Machinery     2022-04-22
The influencing factors in the process are: preform and its heating, pre-blow (position, pressure and flow), stretch rod, high pressure blow (pressure, position), and mold. 1 Preform The preform, also known as the preform, is injection-molded from PET pellets. It requires that the proportion of recycled materials should not exceed 10%, and the number of recycling should not exceed two times. The preforms after injection molding or preforms used after heating must be cooled for more than 48 hours, and the preforms used should not be stored for more than 6 months. Different production dates, especially preforms with long intervals, cannot be mixed. The main reason is The type of raw materials used in the preform, the proportion of secondary materials mixed in and the residual stress in the preform are different, and these factors have a significant impact on the molding process of the bottle, and should be treated according to the actual situation. 2 Heating The heating of the preform is completed by the heating furnace, which is manually set and automatically adjusted. The height of the heating furnace is preferably about 25mm, and the distance from the conveying 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 formed better, which overcomes the disadvantage of uneven heating due to static heating and manual rotation of the preform 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 (such as light on the top and heavier on the bottom), the bottle mouth will become larger than the standard, the hard neck and other product defects, and even the torsion failure of the mechanical parts. The company mainly produces automatic bottle blowing machines. The heating temperature of preforms is generally set at 85-120 °C, which is higher for colorless preforms and lower for colored preforms. If the temperature is set too high or too low, it will cause product defects, such as tearing, white fog, etc. The temperature of each area can be adjusted according to the molding situation of the product, and the opening of the oven lamp tube should be considered at the same time. 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 whole oven. When the 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 the normal production process. The output power is generally about 80%, especially when the ambient temperature is below 5 ℃. The effect is more pronounced. The bottle blowing production process also has a certain relationship with the production environment temperature. The ambient temperature is generally at 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 is unstable when the machine is started, and the specific operation should be adjusted according to the actual situation and experience. 3. Pre-blowing The function 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-blow position, pressure and flow can all affect the quality of the bottle. 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 foot is uneven and white, the top is heavy and the bottom is light, the neck is hard, and even the bottom penetrates and other defects; Defects such as upper light and lower weight, thickening of the center point, and depression will appear. 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; Pressure The pre-blowing pressure is preferably 0.8-1MPa. When the pressure is high, it may cause the upper part to be heavy and the lower part to be lighter, the center point is skewed, the wall thickness of the foot is uneven, and it is white; when the pressure is low, it cannot be fully stretched, the bottom is heavy, and the center point is thick. The molding 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 burst (under normal experimental conditions) and leakage. 4 Stretching rod Stretching rod is a device that stretches the heated preform under the cooperation of pre-blowing while pre-blowing, and it resets after high-pressure blowing and before exhausting. The stretching rod must be able to move up and down 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 be offset; 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 melt and stick to the mold wall, so that the bottle is fully formed, and at the same time, it is stretched horizontally to improve its horizontal strength. The main influencing factors are location and pressure. The high-pressure blowing pressure is generally 3.7-4MPa, which is determined by its molding characteristics and the properties 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 pressure holding time in the molding process, and the length of this time has a great influence on the stability of the bottle capacity. Insufficient high-pressure air can easily lead to improper bottle molding and insufficient foot blowing. 6 Mould Mould is one of the important factors affecting bottle blow molding. The bottle body is a Huff mold, and the bottom of the bottle is independent, which is a typical blow molding mold. During the production process, the mold should be kept at a constant temperature, clean, and the vent holes are unblocked. When the heating and cooling system of the mold fails, there will be defects such as crooked bottle neck, tilted bottle, volume and height change, and heavy bottom; maintaining the mold constant temperature can also prevent condensation on the mold surface. The shrinkage rate of PET after molding is relatively large, generally 1.8%, and it is slightly reduced after adding glass fiber reinforcement, but it still reaches 0.2%-1.0%. Under normal circumstances, the high mold temperature shrinkage rate is large, and the low mold temperature shrinkage rate is small. In order to maintain the stability of the PET bottle volume, the mold temperature must be strictly controlled. Generally, the temperature of the bottle body is slightly higher, which is 20-45℃, and the bottom requirement is lower, which is 6-15℃. A high bottom temperature will make the bottom heavier and the center point thicker. In actual production, there are also nozzles that will affect the molding of PET bottles.
However, with the increased prevalence of bottle blowing machine, it has become far more affordable.
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