Mold is one of the important factors that affect bottle blowing molding. The bottle body is a Huff mold and the bottom of the bottle is independent, which is typical. During the production process of the plastic bottle blowing machine, the mold must be kept at a constant temperature, clean, and vent holes are unblocked.
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 the mold constant temperature can also prevent condensation on the mold surface.
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.
Position: The pre-blowing position is advanced, 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 weight is light, the stiff neck, and even the bottom penetrating defects; after the pre-blowing position is wrong, Defects such as upper lightness and lower heavyness, thickening of the center point, and depression will occur.
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 a great influence on the quality of the bottle. Improper adjustment often causes fatal defects such as bottle burst (under normal experimental conditions) and leakage.
3. Stretch 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 stretching 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.
4. High pressure blowing
The function of 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.