The principle of MEPER Machine blow molding?

Molding is the primary process in cosmetic packaging materials, and one of the most commonly used plastic molding methods for hollow blow molding is also a rapidly developing plastic molding method. Plastic products are widely used in all walks of life. It can be said that hollow blow molding products have been integrated into our lives. Jiahao briefly described the relevant knowledge of MEPER blow moulding machine for your reference.

What is Blow Molding?

Hollow blow molding is to place the tube blank obtained by extrusion or injection molding in a mold, and blow compressed air into the tube blank to make it close to the cavity wall, and then cool and demold to obtain a hollow product forming method. This molding method can produce various packaging containers such as bottles, pots, barrels, daily necessities and children's toys.

Raw materials for hollow blow molding?

The plastic varieties used for hollow blow molding include polyethylene, polyvinyl chloride, polypropylene, polystyrene, linear polyester, polycarbonate, polyamide, cellulose acetate and polyacetal resin. The consumption of high-density polyethylene accounts for the first place, and it is widely used in the packaging of food, chemicals and processing liquids. High molecular weight polyethylene is suitable for the manufacture of large fuel mash tanks and barrels, etc. Because of its good transparency and air tightness, polyvinyl chloride is widely used in the packaging of cosmetics and detergents. With the development of non-toxic polyvinyl chloride resins and additives, as well as the development of stretch blow molding technology, the amount of polyvinyl chloride containers used in food packaging has increased rapidly, and has begun to be used in the packaging of beer and other beverages containing carbon dioxide gas .

Linear polyester material is a new type of material that has entered the field of hollow blow molding in recent years. Because its products have the advantages of glossy appearance, excellent transparency, high mechanical strength and good preservation of items in the container, and no environmental pollution during waste incineration, it has developed rapidly in packaging bottles, especially It is most widely used in pressure-resistant plastic food containers.

Due to the improvement of resin modification and processing technology, the usage of polypropylene is also increasing year by year.

Classification and characteristics of hollow blow molding process

Extrusion-blow molding: simple production method, high output, low precision, and many applications

Injection-blow molding: high precision, good quality, high price, suitable for large batches of products.

Stretch blow molding: The product is stretched, with high strength and good air tightness. Including extrusion-stretch-blow molding (referred to as extrusion-stretch-blow) injection-stretch-blow molding (referred to as injection-stretch-blow) two methods.

Five precautions for blow molding:

blowing pressure

In blow molding, compressed air has two functions, one is to expand the tube blank and close to the cavity wall to form the required shape; the other is to cool. According to the different types of plastics and the temperature of the parison, the air pressure is also different. Generally, it is controlled between 0.2-0.7 MPa. The most suitable one is to make the shape and pattern of the product show clear pressure after molding. For plastics with low viscosity and easy deformation, take a lower value; for plastics with high viscosity and modulus, take a higher value; use a higher pressure for large-volume and thin-walled products; use a lower pressure for small-volume and thick-walled products .

Inflation speed

In order to shorten the blowing time, so that the product can obtain a more uniform thickness and a better surface, the inflation speed (the volume of air flowing in a unit time) should be as large as possible, but it should not be too large, otherwise it will bring the product Adverse effects: First, a vacuum will be created at the air inlet, causing this part of the parison to sink in, and when the parison is fully inflated, the sinking part will form a diaphragm; Extremely fast airflow pulls off, causing waste.

To this end, it is necessary to increase the diameter of the blowpipe or appropriately reduce the inflation speed.

inflation ratio

Usually the ratio of the size of the product to the size of the parison is called the inflation ratio. When the size and weight of the parison are constant, the larger the size of the product, the greater the inflation ratio of the parison. The size of the inflation ratio is determined according to the variety and nature of the plastic, the shape and size of the product, and the size of the parison. Usually the inflation ratio is controlled at 2 or 4 times.

Mold temperature and cooling time

In order to ensure the quality of the product, the temperature of the mold should be evenly distributed, and the mold temperature is generally maintained at 20-50 °C. If the mold temperature is too low, the extensibility of the plastic at the jaw will be reduced, it will not be easy to blow up, and the product will be thicker in this part, and at the same time, the molding will be difficult, and the contour and pattern of the product will not be clear. The mold temperature is too high, the cooling time is prolonged, and the production cycle is prolonged. The product is demolded and deformed, and the shrinkage increases.

The mold temperature depends on the type of plastic. When the glass transition temperature of the plastic is high, a higher mold temperature can be used; otherwise, the mold temperature should be reduced as much as possible.

Usually, the cooling time is prolonged as the wall thickness of the product increases. Sometimes in addition to cooling the mold, the molded product can also be internally cooled, that is, various cooling media (such as liquid nitrogen, carbon dioxide, etc.) are introduced into the product for direct cooling.

molding cycle

The blow molding cycle includes the processes of extruding the parison, cutting the parison, clamping the mold, blowing, cooling, deflating, opening the horizontal, and taking out the product (subsequent trimming, matching, and packaging).

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