Preforms and their heating, pre-blowing (position, pressure and flow), stretching rods, high-pressure blowing (pressure, position) and molds are the factors in the process that affect the bottle blowing machine.
The preform, also known as the parison, is injection molded of PET pellets. It requires that the proportion of recycled material should not exceed 10% and the number of recycling should not exceed two times. The preform after injection molding or the preform after heating must be cooled for more than 48 hours, and the used preform storage time can not exceed 6 months. Different production dates, especially preforms with long intervals, cannot be mixed. The main reason is that The type of raw materials used in the preform, the ratio of the mixed secondary material and the residual stress in the preform are different, and these factors have a significant impact on the molding process of the blow-molding bottle, and should be specifically treated according to actual conditions.
The heating of the preform is performed by a heating furnace, which is manually set and automatically adjusted. The height of the furnace is about 25mm, about 19.6mm from the conveyor wheel. The preform runs continuously on the transfer wheel through the entire oven, so that the preform is heated more evenly and can be formed better, which overcomes the disadvantages of previous heating and manual rotation of the preform and uneven heating. However, if the heating furnace is improperly adjusted, it will result in uneven distribution of the wall thickness of the blown bottles (such as light weight), defects in the bottle mouth, such as large and excessive bottles, hard necks, etc., and even cause torsional failure of mechanical parts. The temperature in each area can be specifically adjusted according to the molding conditions 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 output of the entire oven heat. When it is not turned on for a long time, when it is turned on again, the initial output power should be set higher, 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°C. The effect is even more pronounced.
Blowing bottle production process and production environment temperature also have a certain relationship, the ambient temperature is generally at room temperature (around 22 °C) is appropriate. If the temperature is too high, the product is prone to condensate agglomeration; the temperature is too low, the product performance is unstable when the machine is started, and the specific operation must be adjusted according to the actual situation and experience.
The role of the pre-blow in the blowing process is to make the preform take shape, while the longitudinal strength of the stretched rod is increased by longitudinal stretching. The entire process is the pre-blown cam pushes the three-way valve to the pre-blow position during the blowing process and is completed by a one-way valve. Pre-blowing position, pressure and flow can all affect the quality of the bottle.
Position: Pre-blowing position in advance, there will be a central bottom of the bottle deflection, thinning, uneven thickness and white foot, upper and lower light, hard neck, and even the bottom of the penetration and other defects; pre-blowing position is wrong, There will be defects such as lower weight, thicker center points, and dents.
Air flow The pre-blowing air flow is controlled by a one-way valve, which is generally 3-4 turns. The air flow is large, the bottom is heavy, the central point is thin, partial, the foot is white, and the wall thickness is uneven; the air flow is small, the center point becomes thick, and the sectional pieces are overweighted.
Pressure: The pre-blowing pressure is preferably 0.8-1MPa. When the pressure is high, it may cause the weight to be lighter and lower, the center point is skewed, the wall thickness of the foot is uneven, whitening, etc. When the pressure is low, it cannot be fully stretched, the bottom is heavy, and the center is thick.
The molding conditions of the bottle's feet and center point have the greatest influence on the quality of the bottle. Improper adjustment often causes fatal defects such as bottle burst (under normal experimental conditions) and leakage.
4. Stretch rod
The stretching rod is a device that stretches the heated preform under pre-blowing together with pre-blowing, and it is reset after high-pressure blowing and before venting. The stretching rod must be able to move up and down vertically and smoothly during the blowing process. The driving pressure is 0.55-0.8 MPa, and the clearance with the bottom mold is 2.3-2.5 mm, ie 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 role of high-pressure blowing is to make the molten material fully stretched, close to the mold wall, so that the bottle is fully formed, while stretching in the transverse direction to increase its transverse strength. The main factors affecting are location and pressure.
The high pressure blowing pressure is generally 3.7-4 MPa, which is determined by its molding characteristics and the nature of the filled beverage (carbon dioxide). There are two positions, namely the position of the high pressure gas and the position of the exhaust gas. The time between the two is the holding pressure time during the molding. The length of this time has a great influence on the stability of the bottle capacity. Insufficient high-pressure gas makes it easy to improperly shape the bottle and insufficiently blow the foot.
The mold is one of the important factors that affect the blowing and forming of the bottle. The bottle body is Huff mould and the bottom of the bottle is independent. It is a typical blow mold. During the production process, it is necessary to keep the mould constant temperature, cleanliness, and vents open.
When the mold heating and cooling system fails, bottleneck defects, bottle tilt, volume, height variation, and bottom-heavy defects are maintained; maintaining the mold temperature also prevents condensation on the surface of the mold. The shrinkage of PET after molding is relatively large, generally 1.8%. After adding glass fiber, the shrinkage slightly decreases, but it still reaches 0.2%-1.0%. In general, high mold temperature shrinkage rate and low mold temperature shrinkage rate are small. In order to maintain the PET bottle volume stability, the mold temperature must be strictly controlled. The bottle body temperature is generally required to be slightly higher at 20-45°C and the bottom requirement is lower at 6-15°C. A high bottom temperature will make the bottom heavier and the center point thicker.
In actual production, there are nozzles and other factors that affect the molding of PET bottles.