Pet Preform and their heating, pre-blowing (position, pressure and flow), stretching rods, high pressure blowing (pressure, position) and molds are factors in the process that affect the bottle making of the blow molding machine.
PET preforms, also known as parisons, are injection molded of PET pellets. They require that the proportion of recycled materials should not exceed 10% and the number of recycling should not exceed two. PET preforms after injection molding or PET preforms after heating must be cooled for more than 48 hours, and the PET preforms used should not be stored for more than 6 months. Different production dates, especially long-length PET preforms cannot be mixed. The main reason is that the raw material type of the PET preform, the proportion of the secondary material mixed in and the residual stress in the PET preform are different, and these factors have a significant impact on the molding process of the blowing bottle, and should be treated according to the actual situation.
The heating of the PET preform is done by a heating furnace, which is manually set and automatically adjusted. The height of the heating furnace is preferably about 25 mm, and is about 19.6 mm from the conveying wheel. The PET preform continuously runs through the entire oven on the conveying wheel, so that the PET preform is more uniform in heat and can be formed better, which overcomes the shortcomings of the previous PET preform static heating and manual rotation and uneven heating. However, if the heating furnace is improperly adjusted, it will cause uneven distribution of the wall thickness of the blown bottle (such as light weight), bottle mouth enlargement, hard neck and other product defects, and even cause mechanical component torsion failure. The temperature of each area can be adjusted according to the molding condition of the product, and the opening condition of the oven tube should be considered. In addition, the setting of the oven output power also has a large effect on the heating of the PET 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 accordingly, and then gradually reduced to the normal state 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 blowing production process has a certain relationship with the production environment temperature, and the ambient temperature is generally room temperature (about 22 ° C). If the temperature is too high, the product is prone to agglomeration and agglomeration; the temperature is too low, the product performance is unstable when the machine starts, and the specific operation should be adjusted according to actual conditions and experience.
The role of pre-blowing in the blowing process is to have the PET preform begin to take shape while the longitudinal strength of the stretch rod is increased by longitudinal stretching. The whole process is that the pre-blowing cam pushes the three-way valve to the pre-blowing position during the blowing process, and is completed by the one-way valve. The pre-blowing position, pressure and flow can all affect the quality of the bottle.
Position: The pre-blowing position is advanced, there will be defects such as skewing and thinning of the center point of the bottom of the bottle, uneven wall thickness of the foot, whitening, light weight, hard neck, and even bottom penetration; after the pre-blowing position is wrong, There will be defects such as light weight, center point thickening, and depression.
Air flow The pre-blowing flow is controlled by a one-way valve, generally 3-4 turns is appropriate. The gas flow is large, the bottom is heavy, the center point is thin and partial, the foot is white, and the wall thickness is uneven; the gas flow is small, the center point becomes thick, and the segmented piece exceeds the standard.
Pressure: The pre-blowing pressure is preferably 0.8-1 MPa. When the pressure is high, the upper and lower weight may be light, the center point is skewed, the wall thickness of the foot is uneven, and the white is whitish; when the pressure is low, the foot is not fully stretched, the bottom is heavy, and the center point is thick.
The molding of the foot and the center 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.
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