Several processes of hollow blow molding


Author: MULAN -Plastic Molding Manufacturer

Hollow blow molding, also known as plastic molding processing, is a general term for various processes that convert synthetic resin or plastic into plastic products, and is a large production sector in the plastics industry. Using ethylene as the main raw material, propylene, 1-butene, and hexene as copolymers, under the action of a catalyst, the slurry polymerization or gas phase polymerization process is adopted, and the obtained polymer is subjected to flash evaporation, separation, drying, granulation, etc. process to obtain finished products with uniform particles. Including such as sheet extrusion, film extrusion, pipe or profile extrusion, blow molding, injection molding and rotational molding. Processing methods of plastic products: Extrusion: Grades for hollow blow extrusion production typically have a melt index of less than 1 and a medium to wide MWD. During processing, low MI can obtain suitable melt strength. Wider MWD grades are more suitable for extrusion because they have higher production speeds, lower die pressures and a reduced tendency to melt fracture. Blow molding: More than 1/3 of HDPE sold in the United States is used for blow molding. These range from bottles of bleach, motor oil, detergent, milk and still water to large refrigerators, car fuel tanks and canisters. The characteristic indicators of blow molding grades, such as melt strength, ES-CR and toughness, are similar to those used for sheet and thermoforming applications, so similar grades can be used. Injection molding: HDPE has countless applications ranging from reusable thin-walled beverage cups to 5-gsl cans, consuming 1/5 of the domestically produced HDPE. Hollow blow molding grades generally have a melt index of 5 to 10, and there are grades with low toughness and low fluidity and high fluidity grades with machinability. Uses include thin-walled commodity and food packaging; tough, durable food and paint cans; high resistance to environmental stress cracking applications such as small engine fuel tanks and 90-gal trash cans. Rotomolding: Materials using this processing method are generally crushed into a powder material, which is melted and flowed in a thermal cycle. Two classes of PE are used in rotomolding: general purpose and crosslinkable. General-purpose MDPE/HDPE usually ranges in density from 0.935 to 0.945g/CC, has a narrow MWD, makes the product have high impact and minimal warpage, and its melt index generally ranges from 3—8. Higher MI grades are generally not suitable because they do not possess the expected impact and environmental stress cracking resistance of hollow blow molded rotomolded products. High performance rotomoulding applications take advantage of the unique properties of its chemically crosslinkable grades. These grades flow well during the first part of the molding cycle and then crosslink to develop their excellent environmental stress crack resistance, toughness. Abrasion and weather resistance. Cross-linkable PE is uniquely suited for use in large containers ranging from 500-gal storage tanks for transporting various chemicals to 20,000-gal agricultural storage tanks. film: PE film processing generally uses ordinary blown film processing or flat extrusion processing. Most PEs are used for films, general purpose low density PE (LDPE) or linear low density PE (LLDPE) are available. HDPE film grades are generally used where superior stretchability and excellent barrier properties are required. For example, HDPE film is commonly used in merchandise bags, grocery bags and food packaging.

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