Common sense of plastic mold
Extrusion blow molding is a method of making hollow thermoplastic parts. Well-known blow molding objects are bottles, barrels, cans, boxes and all containers for packaging food, beverages, cosmetics, pharmaceuticals and daily necessities. Large blow-molded containers are commonly used for packaging of chemicals, lubricants and bulk materials. Other blow molded products include balls, bellows and toys. For the automotive industry, fuel tanks, car shock absorbers, seat backs, center brackets, as well as armrest and headrest covers are blow molded. For machinery and furniture manufacturing, blow-molded parts are shells, door frames, racks, pots or boxes with an open face.
The common raw material for blow molding is high-density polyethylene, and most milk bottles are made from this polymer. Other polyolefins are also often processed by blow molding. Depending on the application, styrene polymers, polyvinyl chloride, polyester, polyurethane, polycarbonate and other thermoplastics can also be used for blow molding.
Near engineering plastics are widely accepted in the automotive industry. Material selection is based on mechanical strength, weather resistance, electrical properties, optical properties and other properties.
3/4 of blow moulded products are produced by extrusion blow moulding. Extrusion is the process of forcing material through a hole or die to create a product.
The extrusion blow molding process consists of 5 steps:
1. Plastic parison (extrusion of hollow plastic tube);
2. Closing the flap mold on the parison, clamping the mold and cutting the parison;
3. To the mold cavity Cold wall inflation type training, adjust the opening and maintain a certain pressure during cooling;
4. Open the mold and remove the blown parts;
5. Trim the flash to get the finished product.
Polymer compounding is defined as the process of upgrading polymers or polymer systems by melt mixing. Compounding processes range from the addition of a single additive to multiple additive treatments, polymer alloys and reactive mixing. It is estimated that one third of U.S. polymer production is compounded. Compounds can be tailored to the performance requirements of the end application. Compounded products have a mix of properties, such as high gloss and good impact strength, or precision moldability and good stiffness.
Compounded polymers are usually pelletized for further processing. However, there is growing industrial interest among blow moulders to combine compounding with further processes, such as profile extrusion, which avoids reheating the polymer.
Various types of melt mixing equipment are used, from roll mills and batch mixers to single- and twin-screw extruders. Continuous compounding (extruders) is a common equipment because it provides consistent product quality and reduces operating costs. There are two types of blending: Distributed blending where the product is evenly distributed in the compound without the use of high shear stress. Such mixtures are called extensional mixing or laminar mixing.
Dispersive mixing, also known as intensive mixing, is where high shear stress is applied to break up cohesive solids. For example, when the additive mass is broken up, the actual particle size becomes smaller.
Blending operations often require two blend types in one process.