Factors affecting the process quality of the blow molding machine

The influencing factors affecting the quality of the blowing process are: preform and its heating, pre-blowing (position, pressure and flow), stretching rod, high-pressure blowing (pressure, position), and mold, etc., which are briefly introduced below: 1. Preform Preform, also known as parison, is injection molding of PET pellets, which requires that the proportion of recycled material cannot exceed 10%, and the number of recycling times cannot exceed twice. The preforms after injection molding or the preforms reused after heating must be cooled for more than 48 hours, and the storage time of the preforms used can not exceed 6 months, and the different production dates, especially the preforms with long intervals can not be mixed, mainly because of the different raw material models used in the preforms, the proportion of secondary materials mixed and the residual stress in the preforms, and these factors have a significant impact on the molding process of blowing bottles, which should be treated according to the actual situation. 2. Heating The heating of the preform is completed by the heating furnace, which is set manually and automatically adjusted. The height of the heating furnace should be about 25mm, and the distance from the conveyor wheel is about 19.6mm. The preform runs continuously through the whole oven on the conveyor wheel, so that the preform is heated more evenly and can be better formed, which overcomes the shortcomings of the previous preform static heating and uneven heating due to manual rotation. However, if the heating furnace is not properly adjusted, it will cause uneven distribution of the wall thickness of the blown bottle (such as light at the top and heavy at the bottom), the bottle mouth becomes larger and exceeds the standard, the hard neck and other product defects, and even causes the torque failure of mechanical parts. The heating temperature of the preform is generally set at 85-120°C, the colorless preform is higher, and the colored preform is lower. Temperature settings that are too high or too low 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 should be considered. In addition, the setting of the output power of the oven also has a great influence on the heating of the preforms, which controls the heat output of the entire 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, and 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, and the ambient temperature is generally room temperature (about 22 °C). If the temperature is too high, the product is prone to condensation point agglomeration; The temperature is too low, the product performance is unstable when the machine starts, 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, the longitudinal stretching of the tensile rod increases 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. The pre-blowing position, pressure and flow rate can all affect the quality of the bottle. If the pre-blowing position is advanced, there will be defects such as deviation and thinning of the center point of the bottom of the bottle, uneven and whitish wall thickness of the foot, light weight at the top and light at the bottom, hard neck, and even bottom penetration; After the pre-blowing position is wrong, there will be defects such as light at the top and heavy at the bottom, thickening of the center point, and depression. The air flow pre-blowing air flow is controlled by the check 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 whitish, and the wall thickness is uneven; The air flow is small, the center point becomes thicker, and the weight of the segmented parts exceeds the standard. Pressure: Pre-blowing pressure is 0.8-1MPa. When the pressure is high, it may cause heavy upper and lower light, deviation of the center point, uneven wall thickness of the foot, whitishness, etc.; When the pressure is low, it cannot be fully stretched, the bottom is heavy, and the center point is thick. The molding of the foot and center point of the bottle has a great impact on the quality of the bottle, and improper adjustment often causes fatal defects such as bottle bursting (under normal experimental conditions) and leakage. 4. Stretching rod Stretching rod is a device for stretching the heated preform under the cooperation of pre-blowing at the same time as pre-blowing, and it is reset after high-pressure blowing and before exhausting. The tensile rod must be able to move vertically up and down smoothly during the blowing process, the driving pressure is 0.55-0.8MPa, and the gap between the stretch rod and the bottom die is 2.3-2.5mm, that is, the thickness of the preform is 1/3-1/2. If the gap is too large, it will cause the center point of the bottle base to shift; The gap is too small, and the center point becomes thinner.