Rotational molding, often referred to as rotomolding, is a process used to make hollow products with consistent wall thickness. Thanks to being cost efficient, quick to produce, and very advantageous aspects in terms of design, the process is quite popular. There are several other advantages (and a few limitations) to rotomolding, but before you learn about them, let's have a look at how rotomolding works so that you will understand how these advantages are possible.
How Rotomolding Works
Rotomolding is made from a special blend of resins. These resins may include:
- Acetate butyrate
- Ethylene vinyl acetate
These resins are then, either in powder or liquid form, poured into a hollow mold. The mold will then be rocked or rotated at a low speed across dual axis while it is heated, causing the resin to bind with the shape of the hollow mold. The rotation then continues throughout the cooling process, insuring that the shape is held as the resin hardens before finally being removed from the mold.
The Advantages and Disadvantages of Rotomolding
There are several advantages to rotational molding. Some of the reasons it is so popular include:
- Making a hollow part in one piece means no weld joints
- A virtually stress free product
- Inexpensive molds
- Production time is very short
- It is a very economical process
- There is no waste material; all of the materials are used in production
- There is the ability to make multi-level products
- A wide range of products can be made on one machine
- Inserts are easily molded in
- Molding in high quality graphics is easily done
As great as rotomolding is, there are a few drawbacks to the process. They are:
- A limited choice of materials to work from
- Some geometrical figures are difficult to mold
- There can be a lot of down time during the cooling process
Products Made from Rotomolding
There really are so many uses for this process. The list below is just a small sampling of the things that can be made from rotational molding:
- Storage tanks
- Dog houses
- Garbage cans
- Airplane parts
- Doll parts
- Road cones
- Canoes and Kayaks
- Playground equipment
Additionally, graphics and inserts can be added to other products via rotomolding, such as the numbers on a thermometer, and fire and weather resistance can be added to other products using the process.
The History of Rotational Molding
R. Peters of Britain documented the first use of biaxial rotation and heat in 1855. This rotational molding process was used to manufacture metal artillery shells. The next instances of the process was seen in 1905, when American F.A. Voelke used this method to manufacture hollow wax objects.
Rotational molding developed further, and in the 1920s, R.J. Powell used it for molding plaster of Paris. These early methods using different materials directed the advancements in the way rotational molding is used today with plastics.
The early 1950s saw plastics first being used in the rotational molding process. One of the first uses was in making doll heads. The plastic used was a liquid plastisol. The cooling method consisted of placing the mold into cold water. This process of rotational molding led to the creation of other plastic toys. As the popularity of the process rose, it began seeing more uses, such as manufacturing road cones, marine buoys, and car armrests.
The Engel process was born in Europe during the 1960s. It allowed for the creation of large hollow containers to be created in low-density polyethylene.
New plastics, such as polycarbonate, polyester, and nylon, were introduced to the rotational molding process in the 1980s. This led to new uses for rotomolding, such as making fuel tanks and industrial moldings.