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Extrusion blow molding is a method of making hollow thermoplastic parts. Well-known blow molding objects are bottles, buckets, cans, boxes, and all the containers that contain food, beverages, cosmetics, medicines, and daily necessities. Large blow molded containers are commonly used for packaging chemicals, lubricants and bulk materials. Other blow molding products include balls, bellows and toys. For the automotive industry, fuel tanks, car shock absorbers, seat backs, center brackets, and armrest and headrest coverings are all blow molded. For machinery and furniture manufacturing, blow molded parts are shells, door frames, frames, clay POTS, or boxes with an open face.
A common blow molding extrusion plastic is made from high-density polyethylene, the polymer that most milk bottles are made from. Other polyolefins are often processed by blow molding. Depending on the use, styrene polymers, polyvinyl chloride, polyester, polyurethane, polycarbonate and other thermoplastics can also be used for blow molding.
Recent engineering plastics are widely accepted in the automotive industry. Material selection is based on mechanical strength, weather resistance, electrical, optical and other properties.
Three quarters of blow molding products are made by extrusion blow molding. Extrusion is the process of forcing material through a hole or mold to make a product.
Extrusion blow molding process consists of 5 steps: 1. plastic embryo (hollow plastic tube extrusion); 2. 2. Close the flap mold on the mold, clamp the mold, and cut off the mold; 3. Blow to the cold wall of the mold cavity, adjust the opening and maintain a certain pressure during cooling; 4. Open the mold and remove the blown part; 5. Trim the flaps to get the finished product.
Polymer mixing is defined as the process of upgrading a polymer or polymer system through melt mixing. Mixing processes range from the addition of a single additive to the treatment of multiple additives, polymer alloys and reactive mixtures. It is estimated that a third of polymer production in the United States goes through blending. The mix can be customized according to the performance requirements of the final application. Hybrid products have hybrid properties, such as high gloss and excellent impact strength, or precision molding and good stiffness.
The mixed polymer is usually pelleted for further processing. However, blow molding manufacturers are increasingly interested in combining mixing with the next step, such as profile extrusion, to avoid reheating the polymer.
Various types of melt mixing equipment are used, from roller mills and batch mixers to single - and twin-screw extruders. Continuous mixing (extruder) is commonly used equipment because it provides a consistent quality product and reduces operating costs. There are two types of mixtures: distributed mixtures are uniformly distributed in the mixture without the need for high shear stress. Such mixtures are called extensional or laminar mixtures.
Dispersed mixing, also known as strong mixing, in which high shear stresses are applied to break up clumped solids. For example, when the additive pellet is broken, the actual particle size is reduced.
Mixing operations often require two mixing types in one process.