Rotomolding machines all inherently have the same process and function; to rotate heat and cool. Rotationally molded parts can vary in size ranging from 0.05 litres to 10 000litres and this can be one of the main determinants when selecting which machine to use. In this article we will discuss the various commercial rotational molding machines that are available.

Rock and Roll Machines:

The rock and roll machine functions on two axes, the first axis motion consists of a rocking motion and the second a 360 degree rotation about the perpendicular axis. The image below:

Rock and Roll Machines

Reference: Roto moulding world

It is considered that biaxially rotating machines are an updated version of the rock and roll machine and that the rock and roll machine is best suited for parts which are symmetrical along the central axis perpendicular to the rocking axis. However due to the ease of access to the molds on a rock and roll machine, there is a resurgence in the use of the machine.

Similar in nature to the rock and roll machine is a Rocking Oven, shown below:

rocking oven


A rocking machine is raised above an open oven which is heated by hot air. The molds are secured to the structure which rocks with oven.

Clamshell Machines:

A clamshell machine has a distinct clamshell motion. The oven moves in a clamshell action over the mold and is shown below:

Clamshell Machines


A significant benefit of the clamshell machine is the low floor space requirement; the biaxial rotation is identical of that in a fixed turret machine while also having two support arms connected to the horizontal shaft. Molds are mounted as assemblies on the turntables through the shaft. Once the clamshell oven closes, the axle rotates moving the molds in a spherical motion while also rotating the molds about their axis. The required temperature is obtained through heating and circulating air through the machine. For the cooling cycle, cooled air is circulated and a mist of water is also dispersed. At the end of the cycle the clamshell oven opens and the molds are opened for part removal; the molds are charged with resin and the cycle begins again.