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BLOW MOLDING:Blow molding is a process by which hollow plastic parts are manufactured. This process is also known as blow forming. PROCEDURE:In very basic terms, plastic is melted down, clamped into a mold, and then air is blown into the heated plastic untill it fills a mold and forms the desired shape to produce hollow parts. All types of hollow plastic parts can be made through this process such as plastics bottles.Process MaterialBlow molded parts can be formed from a variety ofthermoplastic materials, including the following:? Low Density Polyethylene (LDPE)? High Density Polyethylene (HDPE)? Polyethylene Terephtalate (PET)? Polypropylene (PP)? Polyvinyl Chloride (PVC)Types of Blow molding:Following are the three main types of blow molding:• Extrution Blow molding• Injection Blow molding• Stretch Blow moldingEXTRUSION BLOW MOLDINGIn this type of blow molding, the process begins with melting down the thermoplastic resin by extruder and forming it into a parison. The parison is a tubelike 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 until it fills the mold and forms the desired shape to produce hollow part. Once the plastic has cooled and hardened, the mold opens up and the part is ejected. All types of hollow plastic parts can be made through this process such as plastic bottles.Types of Extrusion blow molding:Continuous Extrusion molding:In extrusion molding, plastics is continuously extruded and the individual parts arecut off by knife.Intermittent extrusion molding:In straight intermittent extrusion, extruder screw run ,stops and pushes melt out.Here, accumulator is used to gather the mold now a days. Injection blow molding:Injection blow molding is used for producing hollow objects in largequantity .the main product of this process are jars ,PET bottles etc.The main steps of the injection blow molding are,Injection :Extruder barrel and screw assembly melts the polymer. Then it is injected through heated cavity and core pin, where preform forms.Blowing :Preform passed to the hollow chilled mold. The compressed air is blown through core rod into preform, inflating it and forcing it against the sides of the mould.Ejection :The final product is cooled, ejected from blow mold and stripped off the core rod. The product then passes to the quality control section and is tested for leaksStretch blow molding:Stretch blow molding is the common method for producing soda bottles. 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 preformsare 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.Factors in blow molding:• Parison characteristics:Size, shape ,straightness, wall thickness, mechanical strength.• Inflation pressure:pressure will be set according to the process. Here, stretch blow moldingpressure is less needed .• Mold design • Blow ratio=Mold diameter/Parison diameterHere ,the blow ratio must be 1.5 to3ADVANTAGES OF BLOW MOLDING:• Well suited to low and high production rates.• Quick product revisions for increased flexibility.• Low tooling cost than other molding.• Each part price is less than Rotational Molding.• Trim and flash reusable into finished parts.• Less time spent on the mold-creation process• Little scrap generated.DISADVANTAGES OF BLOW MOLDING:• Only for hollow parts .• Defect may be seen .• Thick parts can not be manufactured.• Environmental Disadvantages.• Process and Material Limitations.• Inability to produce bottles with calibrated neckfinishes.• Machines typically dedicated to a narrow range ofsizes.• Trimming requiredBlow Molding Applications• Milk bottles• Pharmaceutical bottles• Antifreeze bottles• Polypropylene bottles• Coliseum seats• One-piece chair• Ice chests and coolers• Double-wall player case• Garbage cans• Drums• Fuel tanks

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