Rotational Moulding


The Roto Process


The principle of rotational molding of plastics is simple. Basically the process consists of introducing a known amount of plastic in powder, granular, or viscous liquid form into a hollow, shell-like mold.7–9 The mold is rotated and/ or rocked about two principal axes at relatively low speeds as it is heated so that the plastic enclosed in the mold adheres to, and forms a monolithic layer against, the mold surface. The mold rotation continues during the cooling phase so that the plastic retains its desired shape as it solidifies. When the plastic is sufficiently rigid, the cooling and mold rotation is stopped to allow the removal of the plastic product from the mold. At this stage, the cyclic process may be repeated. The basic steps of (a) mold charging, (b) mold heating, (c) mold cooling, and (d) part ejection are shown below

Machinery Available.

Equipment :

Mould movement and mould heating are the two most important functions of a rotational molding machine. From the movement point of view, these machines can be divided in two categories :


1. Rock and roll type.

2. Bi-axial rotational type.


Rock and Roll type:

Ideally, biaxial rotation is required for uniform product quality, but rock & roll machines does not permit such biaxial movement. Therefore Rock & roll machines are not useful in moulding tanks economically. 

In rock and roll type machines, mould rock in one direction and roll in another direction. Rocking is in 180 degree and rolling is around Y axis .Moulding is carried by direct heating. LPG or kerosene burners are provided just below the mould . Mould is directly heated during molding cycle hence there is no temp. control. This type machines are not recommended because tanks reduced on these machines are neither gives productivity nor cost effectively. These machines are unable to produce the tanks economically to compete today's market.


Bi-axial Rotational type:

In Bi-axial type machines mold is heated in closed furnace where hot air is used to heat the mould. The Mold is mounted on a arm which rotate the it in two direction hence the process is called as biaxial process. The process is control by diff parameter of molding therefore in biaxial it is possible to produce qualitative and economical tanks.


Following are the advantages of using this type of machine.

  • Cost effective machine running cost is very less
  • High Productivity
  • Consistent quality
  • Uniform wall thickness
  • Accurate Process control
  • User-friendly machine operation




Further, the bi-axial rotation machines are categorized into:


Two Arm Machine

Three Arm Machine

Independent Arm Machine

Clamshell Machine