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A SEMINAR ON ROTATIONAL
MOLDING
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What is Rotational Molding?
Is a Casting process used to
make hollow Plastic Products
Also called RotoMolding,
Spin Casting, Slush Casting
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Rotational molding is applied to a much wider
range of applications with an ever-increasingdegree of sophistication
Rotational molding also has few competitors forthe production of large (> 2 m3) hollow objects in
one piece Best known for tanks, but can be used for wide
range of medical products, toys, leisure craft, andhighly aesthetic point-of-sale products
Not Centrifugal Casting
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The Principle
Mold Charging
Mold Heating
Mold Cooling
Part Ejection
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Equipment and Tooling
They normally consist of
Molds
Oven
Cooling chamber Mold spindles
The spindles are mounted on a rotatingaxis, which provides a uniform coating of
the plastic inside each mold
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Rotational molding machines
They usually operate in 4 Stations.
Loading Heating Oven
Cooling Chamber
Unloading
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Rock n Roll Machine
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Carousel type machines
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Shuttle types machines
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Different Process Variables
A measured amount of powder or liquid plasticis introduced
rotational speeds being infinitely variable,usually ranging up to 50 rpm on the minoraxes and 12 rpm on the major axes
A 4:1 rotation ratio generally is used forsymmetrically shaped parts.
A wide variety of ratios are necessary formolding unusual and complex shapes
Cycle time range from 10-45 min
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Materials
PVC
Polycarbonate
Polyester
Nylon Polyethylene
ABS
Phenolic
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Agriculture: storage tanks, spraying equipment tanks
Automotive: interior panels, fuel tanks, ductwork, air-
intake systems, door armrests, wheel arches.
Buildingconstruction: water tanks, septic tanks, highway
barriers
Electricalelectronic: aboveground pedestals,
belowground chambers
Industrial: chemical tanks, cases, shrouds and housings,
control equipment parts
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Marine products: dock floats, hulls, fuel tanks,
seating, fenders, live wells
Material handling: tanks, drums, barrels, hoppers,
IBCs, pallets
Medical equipment: spine boards, anatomical figures,
inflatable masks, implants
Playground equipment: slides, climbing frames,
outdoor furniture
Sports and recreation: toys, kayaks, canoes, helmet
linings, pet products
Transportation: road traffic barriers, cones
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Advantages:1) Manufacturing large, hollow parts such as oil tanks
is much easier by rotational molding than any othermethod
2) Rotational molds are significantly cheaper than
other types of mold
3) Very little material is wasted using this process, and
excess material can often be re-used
4) Consistent wall thickness and strong outside
corners that are virtually stress free
5) Color changes can be made quickly and easily
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Disadvantages:1) Long cycle times-only one or two cycles an hour
can typically occur2) As it is a low pressure process, sometimes
designers face hard to reach areas in the mold
3) Entire mold must be cooled
4) Some plastics will degrade with the long heatingcycles or in the process of turning them into a
powder to be melted.
5) The number of materials that are available for
rotational molding is limited in comparison to
other processes
6) Material costs are higher, due to the need for
grinding pellets of raw material to a fine powder
for molding