Rotational molding is one of the fastest growing plastic making processes in the world today. As the name suggests, rotational molding machines are responsible for making these plastics. The machine consists of a heated hollow mold which is usually filled with a charge or shot of the material. The machine is then slowly rotated. This causes the soft material inside to disperse and stick to the walls of the machine uniformly.
In order to ensure even thickness, the molding machine is kept rotating at all times while heated and cooled. This ensures that there is no sagging or deformation during the cooling process.
Types of Rotational Molding Machines
There are a variety of rotational molding machines. Each have their own characteristics and used for different kind of purpose. The types of rotational molding machines are listed below:
Rock and Roll Machine
This specialized machine spins or rotates 360 degrees in one direction and can also tip or “roll” up to 45 degrees while spinning. The heating is usually by way of forced hot air. These machines are big space savers and heat cost efficient because of the smaller chamber size.
These machines allow the mold to rotate on two axes. This is made possible by having the mold built onto arms which rotate on two perpendicular axes. While rotating, the molds are moved into an oven where the heat melts the resin. The arms continue to spin as the molds are removed from the oven for cooling.
This type of machine contains only one arm. The clamshell cools and heats the mold in the same chamber. The advantage of this is that it costs less compared to the products it produces. It is very similar to the shuttle except that instead of moving the entire assembly, the oven opens and closes like a clamshell allowing the product to either load, heat or cool without being moved.
Shuttle Rotational Molding Machine
The shuttle gets its name because of how the entire machine is moved out on a slider from the oven for cooling. It is a large oven that houses the bi-axial rotating drum or mold. This mold spins 360 from a spindle at top while the entire portion it is attached to is rotating. The mold is shuttled from loading to oven to cooling.
Swing Arm Machines
These can have up to four arms, each of them independent. This provides for multiple stations and an efficient working environment since each arm is attached to a separate cart. These machines are very useful for products that require longer cooling periods.
Parts of a Rotational Molding Machine
These complex and often times large machines are actually very simple in function. In order for a rotational molding machine to function properly they require the following parts:
- Mold – The mold is made up of welded steel sheet or cast. Molds are typically made from aluminum or stainless steel.
- Oven – The oven is of course used for heating the material and is a key part of the rotational machine.
- Cooling chamber – This part is necessary to ensure that the material is cooled off properly.
- Spindles – The spindles are what allow the mold to rotate. This ensures that the material can spin, which ensures a uniform coating of the plastic.
Products produced by the Rotational Molding Machines
There are numerous number of products that can be and are being produced by a molding machine. These include
- Storage Tanks
- Road Signs
- Pet Houses
- Refuse Containers
- Road Cones
- Rowing Boats
- Playground slides
- Seals for inflatable oxygen masks
- Containers for the transportation of nuclear fissile materials