Preform and its heating, pre-blowing (position, pressur […]
Preform and its heating, pre-blowing (position, pressure and flow), stretch rod, high-pressure blowing (pressure, position) and mold, etc. These are the factors that affect the bottle blowing machine in the process.
1. Preforms 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. The heating of the heating preform is completed by the heating furnace, which is manually set and automatically adjusted. The height of the heating furnace is about 25mm, and the distance from the conveyor wheel is about 19.6mm. 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 preform that is not uniformly heated due to static heating and manual rotation. 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 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 decrease 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 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 longitudinal stretching by the stretching rod. 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 all affect the quality of the bottle. Position: The pre-blowing position is advanced, and the center point of the bottom of the bottle will be skewed and thin, the foot wall thickness will be uneven and white, the top heavy and the bottom light, hard neck, and even bottom penetration defects; after the pre-blowing position is wrong, Defects such as upper lightness and lower heavyness, thickening of the center point, and depression may occur. 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. Pressure: The pre-blowing pressure should be 0.8-1MPa. When the pressure is high, it may cause the top and bottom to be light, the center point is deviated, the foot wall thickness is uneven, and white, etc.; when the pressure is low, it cannot be fully stretched, the bottom is heavy, and the center point is thick. The shape of the bottle foot and center point has the greatest impact on the quality of the bottle. Improper adjustment often causes fatal defects such as bottle burst (under normal experimental conditions) and leakage.
4. Stretching rod The stretching rod is a device that stretches the heated preform under the cooperation of the pre-blowing while pre-blowing. It is reset after high-pressure blowing and before exhaust. The stretch rod must be able to move vertically and steadily 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 bottle bottom will shift; if the gap is too small, the center point will become thinner.
5. The function of high-pressure blowing and high-pressure blowing is to make the melt fully stretch, close to the mold wall, so that the bottle is fully formed, and at the same time, it is stretched laterally to improve its lateral 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 nature 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 in molding. The length of this time has a great influence on the stability of the bottle volume. Insufficient high-pressure air may cause improper bottle molding and insufficient foot blowing.
6. Mould is one of the important factors that affect bottle blow molding. The bottle body is a Huff mold with an independent bottom, which is a typical blow mold. During the production process, keep the mold constant temperature, clean, and unblocked vent. When the mold heating and cooling system fails, the bottleneck will be tilted, the bottle will be tilted, the volume and height will change, and the bottom will become heavier. Maintaining a constant temperature can also prevent condensation on the mold surface. After PET molding, the shrinkage rate is relatively large, generally 1.8%. After adding glass fiber reinforcement, it decreases slightly, but still reaches 0.2%-1.0%. Under normal circumstances, high mold temperature shrinkage rate is large, low mold temperature shrinkage rate is small, in order to maintain the stability of PET bottle volume, mold temperature must be strictly controlled. Generally, the temperature of the bottle body is slightly higher, 20-45°C, and the bottom temperature is lower, 6-15°C. High bottom temperature will make the bottom heavier and the center point thicker.