26-09-2013, 12:23 PM
MOLDING TECHNIQUES AND ITS MACHINES MANUFACTURERS
TECHNIQUES AND ITS MACHINES .pptx (Size: 383.71 KB / Downloads: 32)
INTRODUCTION
Rotational molding is also known as roto molding. This molding process is best suited for large hollow products such as ball, toys, carboy, ice bucket. In rotational molding product is formed indeed a closed mold or cavity while the mold is rotating bi axial in a heating chamber. To obtain this mold rotation in two planes perpendicular to each other. This spindle is turned on a primary axis, while the mold is rotated on a secondary axis.
MATERIAL
Mostly thermoplastic can be used in rotational molding.
The most popular however continuous to be the polyethylene's
The first powdered plastic to be used in this field.
Both LDPE and HDPE are being rotationally molded today.
Also used are butyrate propionate, polybutylene, nylon, polyacetal, polycarbonate, polyurethane, polyester, polypropylene, polystyrene, poly vinyl chloride.
Some thermo sets are being roto molded on a limited scale.
MOLDS
CAST ALLUMINUM MOLD
SHEET METAL MOLDS
ELECTRO FORMED MOLDS
VAPOR FORM MOLDS
Single spindle rotational molding machine
It is also known as batch type rotational molding machine, because it is the least sophisticated and requires the most manual works.
In a typical batch operation the charged mold is rolled in to the oven for rotational heating.
when the cycle is complete, the mold is removed and a newly charged one in seriated in its place.
The completed mold is then transferred manually on rollers to a cooling station for cure before
Removal of part.
Straight spindle rotational molding machine
It uses primarily molding large parts.
This is a shuttle carriage machine.
It is generally straight line operation with the oven and one side.
The loading and unloading station in the middle
The cooling that in sure positive placement in the station.
Rock and roll machine
Rotational molding with very long length to diameter ratio can be made on equipment called rock and roll machine.
The mold mounted on a cradle is rocked back and forth on a stationary, horizontal axis.
while it is rotated about a moving axis perpendicular to rotating axis.
On some machines the oven may move.
Canoes and kayaks are made with this type of machines.
COOLING
When the parts have been forwarded the molds
Move towards the cooling chamber.
The cooling is carried out
By the cold water spray
or
By forced cold air or a cooled liquid circulating inside the mold.
The mold continuous to rotate during cooling cycle
When the part does not sag away from the mold surface causing distortion
UNLOADING
Finally the molds are opened & removed:
The ejection of product may be done either by manually or by the use forced air or by mechanical means.
Cycle time range from 7 to 15 minutes.
But can be reduced 5 minutes
for small and can be long as 30 min. for very large parts.
Wall thickness of the parts effects cycle time.
Conclusion
Rotational molding is a very important process for big hollow products like water storage tank, which is not produce by blow molding. It is a cheaper process because tooling cost is less in this process.