Basic knowledge of PET automatic blowing machine (1)


PET blow molding bottles can be divided into two catego […]

PET blow molding bottles can be divided into two categories, one is a pressure bottle, such as a bottle filled with carbonated beverages; the other is a non-pressure bottle, such as a bottle filled with water, tea, oil, and the like. The tea beverage bottle is a modified PET bottle blended with polyethylene naphthalate (PEN) or a composite bottle of PET and thermoplastic polyarylate. It is classified into a heat bottle and can be heat resistant to 80 ° C or higher; Cold bottles do not require heat resistance. The hot bottle is similar to the cold bottle in the forming process. The author mainly discusses the molding process of pressurized beverage bottles in cold bottles.

1 device

With the continuous advancement of technology and the scale of production, PET bottle blowing machines are becoming more and more automated, and production efficiency is getting higher and higher. Equipment production capacity continues to increase, from the previous production of thousands of bottles per hour to the current production of tens of thousands of bottles per hour. The operation has also evolved from the past manual button type to the current full computer control, which greatly reduces the difficulty of the process operation and increases the stability of the process.

At present, the manufacturers of injection-blowing equipment mainly include SIDEL in France, KRONES in Germany, and Huangyan Lange Machinery Mould Co., Ltd. in Taizhou, China. Although the manufacturers are different, the equipment principle is similar, generally including the blank system, the heating system, the blowing system, the control system and the auxiliary machine.

2 blow molding process

PET bottle blow molding process.

Important factors affecting the PET bottle blow molding process include preforms, heating, pre-blowing, molds and the environment.

2.1 preform

When preparing a blow molded bottle, the PET slice is first injection-molded into a preform, which requires that the proportion of the secondary regrind should not be too high (less than 5%), the number of recovery should not exceed two, and the molecular weight and viscosity should not be too low (molecular weight 31000- 50000, intrinsic viscosity 0.78-0.85 cm3/g). Injection molded preforms can be stored for 48 hours or more. The preforms that have not been used up after heating must be stored for another 48 hours to be reheated. Preforms should not be stored for more than six months.

The quality of the preform depends largely on the quality of the PET material. The material that is easy to inflate and easy to set should be selected and a reasonable preform molding process should be established. Experiments show that the preforms of PET materials with the same viscosity are easier to blow molding than the domestic materials; while the same batch of preforms has different production dates, the blow molding process may also have a big difference. The advantages and disadvantages of the preform determine the difficulty of the blow molding process. The requirements for the preform are pure, transparent, free of impurities, no discoloration, suitable length of the spot and surrounding vignetting.

2.2 heating

The heating of the preform is done by a heating oven, the temperature of which is manually set and automatically adjusted. In the oven, far infrared rays are emitted from the far-infrared tube to radiate heat to the preform, and the fan at the bottom of the oven performs thermal circulation to make the temperature in the oven uniform. The preform rotates while moving forward in the oven, so that the wall of the preform is heated evenly.

The arrangement of the lamps in the oven is generally "zone" shape from top to bottom, with more ends and less in the middle. The heat of the oven is controlled by the number of lamps opened, the overall temperature setting, the oven power, and the heating ratios of the sections. The opening of the lamp should be adjusted in conjunction with the pre-blowing bottle.

In order to make the oven work better, the adjustment of its height and cooling plate is very important. If it is improperly adjusted, it may easily appear in the bottle opening (the bottle mouth becomes larger), the hard head neck (the neck material cannot be opened), etc. during blow molding. defect.