Raw material for Rotational Molding

LLDPE ( Liner Low density Polyethylene) is being used with density of 0.930 to 0.936 gms/ Cm cube and Melt Flow

Index in the range of 3 to 6 gm per 10 minutes. To produce the good quality water tanks by Rotational Molding,

 the material should have following properties.

Other Ingredients

The original LLDPE granules are of natural colour which have to be converted in to either black, white, blue or other colours as per requirement of final product. To produce the colored granules, basic LLDPE granules have to be mixed with colour concentrate which are called as master batches.

These master batches are readily available in market which are to be added along with LLDPE.The master batch should be of grade which is LD based. The master batch with antioxidants are more preferred. Anti oxidants protects the material from oxidation during the molding process which helps to avoid the pin holes on surface of finished product.

Incase of black master batch, carbon contents are very important. Carbon contents act as UV stabilizer. It helps to improve the life of tanks if tanks are exposed to sunlight for longer period and to avoid the crack on tanks.Some other common additives like flame retardants, anti static agents, foaming agents, are also used as per requirements.

A three-arm turret machine is generally used in applications where the oven (1), cooling (2), and servicing (3), cycles for the parts on each arm require relatively equal process time. Four-arm turret machines are used where one part of the process (heating, cooling or servicing) requires up to twice as much time as the other functions.

Rotational moulding, also known as rotomoulding, is a molding  process for creating many kinds of mostly hollow items, typically of plastic.

A heated mold causes the material within to melt and form a puddle at the bottom of the mold cavity. The mold is then slowly rotated (usually around two perpendicular axes) causing the melted material to flow and stick to the walls of the mold. In order to maintain even thickness throughout the part, the mold continues to rotate during the cooling phase. Over the past two decades, improvements in process control and developments with plastic powders have resulted in a significant increase in usage.

Rotational Moulding differs from other processing methods in that the heating, melting, casting and cooling stages all occur after the polymer is placed in the mould with no external pressure applied during forming. The rotational moulding process offers tremendous flexibility in both design and production.