Introduction Of Blow Molding | Advantages And Disadvantages Of Blow molding
Blow molding is a manufacturing process that is used to produce hollow plastic parts by inflating a heated plastic until it fills a mold and formed the desired shape. The schematic of blow molding process is shown in figure.
In this process, the thermoplastic in the form of small pellets or granules is first heated above the melting temperature and molded into a preform using injection molding process. These preforms are used to feed into the blow mold. The preform is heated above the glass transition temperature and formed into a hollow tube which is called parison. The parison is then clamped between two mold halves and inflated by high air pressure until it conforms to the inner shape of the mold.
The air pressure is required as 60 to 140 psi depending upon the material used. The preform is always stretched from the center of the part during the process. This is a single stage process, as both preform manufacturing and bottle blowing are performed in the same machine. The formed part solidified as it is cooled inside the mold. The mold halves are separated and the final product is removed. Final part may be trimmed.
Generally, mold can be made of metal. Cycle time depends upon the finished part wall thickness. If the part wall thickness is 1.5 mm, the cycle time will be 40 to 50 seconds.
- Amount of plastic material
- Melting temperature of plastic material
- Air pressure required
- Cooling time
Different types of thermoplastic material are used, for example: High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE), Polypropylene (PP), Polyvinyl Chloride (PVC), Polyethylene Terephtalate (PET), and Polycarbonate (PC).
Different types of plastic products can be manufactured by this process such as bottles in different shape and size, jars, and containers, ducting, fluid oil tanks, mugs, and toys.
- Low tooling cost
- Fast production rates
- Ability to mold complex part with uniform thickness
- Little scrap generated
- Large hollow shape can be produced
- Produced parts can be recycle
- Limited to hollow parts
- Thick parts can’t be manufactured
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