“Blow molding, also known as blow forming, is a manufacturing process by which hollow plastic parts are formed.” It is used to made hollow parts such as plastic bottles.
Process Material Blow molded parts can be formed from a variety of thermoplastic materials, including the following: Low Density Polyethylene (LDPE) High Density Polyethylene (HDPE) Polyethylene Terephtalate (PET) Polypropylene (PP) Polyvinyl Chloride (PVC)
BASIC PROCESSTWO MAIN PROCESSESTO preform (or parison) of hot plastic resin in a somewhat tubular shape is created.A pressurized gas, usually air, is used to expand the hot preform and press it against a mold cavity. The pressure is held. until the plastic cools.
The blow molding process begins with melting down the plastic and forming it into a parison . The parison is a tube- like piece of plastic with a hole in one end in which compressed air can pass through. The parison is then clamped into a mold and air is pumped into it. The air pressure then pushes the plastic out to match the mold. Once the plastic has cooled and hardened the mold opens up and the part is ejected.
EXTRUSION BLOW MOLDING: In Extrusion blow molding (EBM), plastic is melted and extruded into a hollow tube (a parison). This parison is then captured by closing it into a cooled metal mold. Air is then blown into the parison, inflating it into the shape of the hollow bottle, container or part. After the plastic has cooled sufficiently, the mould is opened and the part is ejected.1)Reciprocating screw. 2)Compressedair.3)Hopper. 4)Granules.5)Barrel. 6)Heaters.7)Grinding, Mixing. 8)Actuatorshydraulic generator.9)Draw plate. 10)Core/Punch.
INJECTION BLOW MOLDING Injection Stage Molten polymer is injected into a heated preform mould. The preform is the partly shaped product that will be used to make the final hollow product by being blown into shape. The preform consists of a fully formed neck with a thick tube of polymer attached. Blowing Stage The preform is passed to the hollow, chilled blow mould. Compressed air is blown through the core rod into the preform material, inflating it and forcing it against the sides of the mould. Ejection The blow formed polymer is allowed to cool. It is then removed from the blow mould and stripped off the core rod. The product then passes to the quality control section and is tested for leaks
Stretch Blow Molding• In the stretch blow molding (SBM) process, the plastic is first molded into a "preform" using the injection molding process. These preforms are produced with the necks of the bottles, including threads (the "finish") on one end. These preforms are packaged, and fed later (after cooling) into a reheat stretch blow moulding machine. In the SBM process, the preforms are heated (typically using infrared heaters) and then blown using high pressure air into bottles using metal blow moulds.
ADVANTAGES:• Well suited to low and high production rates.• Quick product revisions for increased flexibility.• Tooling is less expensive than other molding.• Each part price is less than Rotational Molding.• Trim and flash reusable into finished parts.
DISADVANTAGES:• Environmental Disadvantages effecting.• Process and Material Limitations.• Inability to produce bottles with calibrated neck finishes.• Machines typically dedicated to a narrow range of sizes.• Trimming required