4. Stretching rod The stretching rod is a device for st […]
4. Stretching rod
The stretching rod is a device for stretching the heated preform under pre-blowing while pre-blowing, and is reset after high pressure blowing and before exhausting. The stretching rod must be vertically and vertically moved during the blowing process, the driving pressure is 0.55-0.8 MPa, and the gap with the bottom mold is 2.3-2.5 mm, that is, 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 function of the high pressure blowing is to make the melt fully stretched and close to the mold wall to fully shape the bottle while performing lateral stretching to increase the transverse strength. The main factors affecting it are location and pressure.
The high pressure blowing pressure is generally 3.7-4 MPa, which is determined by its molding properties 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 time in the molding, and the length of this time has a great influence on the stability of the bottle capacity. Insufficient high-pressure gas can easily cause improper bottle formation and insufficient foot blowing.
Mold is one of the important factors that affect the blow molding of bottles. The bottle is a haf mold, and the bottom of the bottle is independent. It is a typical blow mold. During the production process, the mold should be kept at a constant temperature, clean, and vented. When the mold heating and cooling system fails, there will be bottlenecks, bottle tilt, volume, height change, bottom weight and other defects; maintaining mold 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, it is slightly reduced, but still reaches 0.2%-1.0%. Under normal circumstances, the high mold temperature shrinkage rate is large, and the low mold temperature shrinkage rate is small. In order to maintain the stability of the PET bottle volume, the mold temperature must be strictly controlled. Generally, the bottle body temperature is slightly higher, 20-45 ° C, and the bottom requirement is lower, 6-15 ° C. A high bottom temperature will make the bottom heavy and the center point thicker. In the actual production, there are nozzles and the like which will affect the molding of the PET bottle.