The influencing factors that affect the quality of the blowing process include: preform and its heating, pre-blowing (position, pressure and flow), stretch rod, high-pressure blowing (pressure, position), and mold, etc. The following is a brief introduction:
1. Preform
Preforms, also known as parisons, are injection-molded PET pellets. It requires that the proportion of recycled materials cannot exceed 10%, and the number of recycling cannot exceed twice. The preform after injection molding or the preform used after heating must be cooled for more than 48 hours, and the storage time of the used preform cannot exceed 6 months. Different production dates, especially the preforms with too long intervals, cannot be mixed, the main reason is The type of raw material used in the preform, the proportion of the secondary materials mixed in and the residual stress in the preform are different. These factors have a significant impact on the molding process of the bottle blowing, 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 about 19.6mm away from the conveying wheel. The preform continuously runs through the entire oven on the conveying wheel, so that the preform is heated more evenly and can be better shaped, which overcomes the previous disadvantages of the preforms that the preforms are heated in a static state and rotated manually. However, if the heating furnace is not adjusted properly, it will cause uneven distribution of the wall thickness of the blown bottle (such as upper lighter and lower heavy), product defects such as the bottle mouth becoming larger and exceeding the standard, hard neck, and even torsion failure of mechanical parts. The company mainly produces automatic bottle blowing machines.
The heating temperature of the preform is generally set at 85-120℃, the colorless preform is higher, and the colored preform is lower. Setting the temperature 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 preform, which controls the heat output of the entire oven. When the machine is not turned on for a long time and is turned on again, the initial output power should be set higher accordingly, and then gradually reduced to the normal state during normal production. The output power is generally about 80%, especially when the ambient temperature is below 5℃. The effect is more significant.
The blowing production process also has a certain relationship with the production environment temperature. The environment temperature is generally room temperature (about 22°C). If the temperature is too high, the product is prone to freezing point agglomeration; the temperature is too low, the product performance is unstable when the machine starts, the specific operation should be adjusted according to the actual situation and experience.
3. Pre-blowing
The role of pre-blowing in the blowing process is to make the preform take shape, and at the same time to increase its longitudinal strength by stretching the rod longitudinally. The whole process is that the pre-blowing cam pushes the three-way valve to the pre-blowing position during the bottle blowing process, and is completed by the one-way valve. Pre-blowing position, pressure and flow rate can affect the quality of the bottle.
If the pre-blowing position is advanced, there will be defects such as the center point of the bottom of the bottle skewed and thinned, the foot wall thickness is uneven and white, the top is heavy and the bottom is light, the neck is hard, and even the bottom penetrates; after the pre-blowing position is wrong, then There will be defects such as upper lightness and lower weight, thickening of the center point, and depression.
Air flow The pre-blowing air flow is controlled by a one-way valve, generally 3-4 turns are appropriate. The air flow is large, the bottom is heavy, the center point is thin and offset, the feet are white, and the wall thickness is uneven; the air flow is small, the center point becomes thick, and the weight of the segmented parts exceeds the standard.
