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Types of Machines Used for Making Rotationally Molded Plastics
Sep 22, 2017

Rotationally molded products are typically hollow with large capacities, such as fuel tanks, with consistent thickness and density. Common molding methods, such as blow molding, extrusion, or injection molding, cannot mold such products; thus, a unique method has been developed, involving a large rotating mold, which is the size of the finished product. For making products, a mold is preheated by a heating system, and then the plastic pellets are introduced into the mold; the mold rotates on different axes, and the softened pellets start to take the shape of the mold. The mechanism ends with the cooling process, where the mold is cooled down.

The process is called as rotational molding, or roto molding, and the machines are called rotomolders.

Rotomolders commonly have four parts: oven, molds, mold spindles, and cooling chamber. Molds give the shape to plastic and are manufactured by two methods, welding or casting. The metal typically is either steel or aluminum. The oven is used for heating the molds, whereas the mold spindles help in giving uniform coating; they are mounted on a rotating axis. The cooling chambers assist in hardening the material by exposing the mold to low temperatures.

Rotomolders come in a variety of designs --carousel, clamshell, rock and roll, vertical, and shuttle machines.

Carousel Type

This is the most common bi-axial machine that, based on an application, can have four and six stations. They are designed in such a way that if one arm remains in the heating station, the other would be the cooling station, and the third arm would be the loading or unloading area.

Clamshell

In this type of machines, a mechanical arm is used for rotating a mold, so that it can be rotated at different axes easily. The advantage of this machine is that the cooling and heating processes are done in the same chamber. This makes the machine compact, so it takes a lot less space than other options. Moreover, the design is less expensive.

Rock and Roll

This machine has a specific application; it fabricates long and narrow parts. The machine can have one or more arms based on the need; machines that have two arms are called shuttle type machines. The arm rotates a mold at 360 degrees at one axis, and concurrently, rocks the mold at 45 degrees along a different axis. The machine is used for making high-volume products and is considered cost-effective due to the use of smaller heating chambers.

Vertical Machines

These machines are also known as over rotational machines. They have different cooling and heating areas and can be loaded and unloaded from the front. Based on the requirements, these machines can be of varying sizes. They are energy efficient because they have small and compact cooling and heating chambers. When it comes to capability, they are the best, still taking a lot less space than multi-armed machines.

Shuttle Type

As the name implies, these machines shuttle the mold between the heating and cooling chambers and can rotate it bi-axially. Shuttle type machines are considered low-cost, as they can produce large-size products. For different needs, the footprint of a machine can be modified.