The preforms of the fully automatic bottle blowing machine and their heating, pre-blowing (position, pressure and flow), stretching rods, high-pressure blowing (pressure, position) and molds are the factors that affect the bottle blowing machine in the process of manufacturing bottles.
- Preforms
The preforms, also known as preforms, are PET pellets that are injected and molded. It requires that the proportion of recycled materials cannot exceed 10% and the number of recycling times cannot exceed two times. The preforms after injection molding or the preforms used after heating must be cooled for more than 48 hours, and the storage time of the used preforms cannot exceed 6 months. Preforms with different production dates, especially those with long intervals, cannot be mixed. The main reason is that the raw material models used in the preforms, the proportion of secondary materials mixed in, and the residual stress in the preforms are different. These factors have a significant impact on the molding process of the bottle blowing and should be treated specifically according to the actual situation.
- Heating
The heating of the preforms is completed by the heating furnace, which is set manually and adjusted automatically. The height of the heating furnace is preferably about 25mm, about 19.6mm away from the conveyor wheel. The preforms are continuously rotated on the conveyor wheel through the entire oven, so that the preforms are heated more evenly and can be better formed, overcoming the shortcomings of uneven heating of the preforms due to static heating and manual rotation. However, if the heating furnace is improperly adjusted, it will cause uneven distribution of the wall thickness of the blown bottles (such as light on the top and heavy on the bottom), excessive enlargement of the bottle mouth, hard neck and other product defects, and even cause torque failure of mechanical parts. The temperature of each area can be adjusted according to the product molding situation, and the opening of the oven lamp should be considered. In addition, the setting of the oven output power also has a great influence on the heating of the preforms, which controls the output of the heat 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 normal during normal production. 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 is also related to 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 coagulation and agglomeration; if the temperature is too low, the product performance will be unstable when the machine is started. The specific operation should be adjusted according to actual conditions and experience.
- Pre-blowing
The role of pre-blowing in the blowing process is to give the preform its initial shape, and at the same time, the longitudinal stretching of the stretching 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 bottle 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.
Position: If the pre-blowing position is advanced, there will be defects such as the center point of the bottom of the bottle being tilted and thinned, the wall thickness of the foot being uneven and white, the top being heavy and the bottom being light, the neck being hard, and even the bottom being penetrated; if the pre-blowing position is wrong, there will be defects such as the top being light and the bottom being heavy, the center point being thickened, and being concave.
Air flow: The pre-blowing air flow is controlled by the one-way valve, and it is generally appropriate to open 3-4 turns. Large air flow, heavy bottom, thin and biased center point, white foot, uneven wall thickness; small air flow, thick center point, and excessive weight of segmented parts.
Pressure: The pre-blowing air pressure should be 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 to be skewed, the foot wall thickness to be uneven, and whitening; 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 the greatest impact on the quality of the bottle. Improper adjustment often causes fatal defects such as bottle explosion (under normal experimental conditions) and leakage.
- Stretching rod
The stretching rod is a device that stretches the heated bottle blank in the cooperation of pre-blowing and pre-blowing. It resets after high-pressure blowing and before exhaust. The stretching rod must be able to move vertically and smoothly up and down during the bottle blowing process. The driving pressure is 0.55-0.8MPa, and the gap with the bottom mold is 2.3-2.5mm, that is, 1/3-1/2 of the thickness of the bottle blank. 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.
- High-pressure blowing
The function of high-pressure blowing is to fully stretch the molten material, close to the mold wall, fully mold the bottle, and at the same time perform lateral stretching to improve its lateral strength. The main influencing factors are position and pressure.
Taizhou Fupusi Machinery Co.,Ltd. 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, namely the position of high-pressure gas and the position of exhaust. The time between the two is the pressure holding time during molding. The length of this period has a great influence on the stability of the bottle capacity. Insufficient high-pressure gas can easily cause improper bottle molding and insufficient foot blowing.
- Mold
The mold is one of the important factors affecting the blow molding of the bottle. The bottle body is a half mold, and the bottle bottom is independent. It is a typical blow molding mold. During the production process, the mold must be kept constant temperature, clean, and the exhaust holes must be unobstructed.
When the mold heating and cooling system fails, there will be defects such as crooked bottlenecks, tilted bottles, changes in volume and height, and heavier bottoms; 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%, which is slightly reduced after adding glass fiber reinforcement, but still reaches 0.2%-1.0%. Generally speaking, the shrinkage rate is large at high mold temperature and small at low mold temperature. In order to maintain the stability of the volume of PET bottles, the mold temperature must be strictly controlled. Generally, the bottle body temperature is required to be slightly higher, 20-45℃, and the bottom temperature is required to be lower, 6-15℃. A high bottom temperature will make the bottom heavier and the center thicker.
In actual production, Taizhou Fupusi Machinery Co.,Ltd. there are also nozzles and other factors that will affect the molding of PET bottles.