The rotational  molding process is a specialized molding alternative for plastic mold manufacturing. The process uses the principles of centrifugal force to move the molten polymer up against the internal surfaces of a spinning mold and leaving the innermost (central) part hollow. Rotational molding process produces products such as oil and water tanks, traffic cones, and plaster statues.Rotational molding also known as rotomolding is a relatively slow process that’s capable of producing large one piece hollow plastic products at a lower cost than many other plastic molding processes.

The rotomolding process starts with a clogged split mold. The molding component, usually a thermoplastic in the type of granules or pellets, is pre measured and placed into the molding chamber. The chamber is then heated and the component inside is melted. Preferably, the molten material can be distributed easily because it has a low viscosity. The rotation station starts to rotate slowly on multiple axes concurrently such that the molten compound is uniformly coated on the inside surfaces of the mold as the temperature continues to fall in a controlled way. The rotation and cooling continues until the molding component solidifies. The mold can now be opened and the finished product removed.

The rotational cooling, heating, and speeds rates need to be controlled carefully throughout the process. Different from other common plastic molding processes, such as compression, extrusion, and injection moldings, there’s no external pressure applied throughout the entire process of molding. In addition, rotational molding is a very slow process and each rotation usually takes approximately one hour or more.
Steps in the Rotomolding Process:

After selecting the type of resin to be used, a pre-measured amount of plastic resin is loaded into a mold.
The resin melts and combines in a three stage process. Once the resin is placed into a mold, the mold is inserted into an oven and then rotated on two axes at a relatively slow speed until the resin forms a coat on the inner surface of the mold hollow space, fusing into an evenly wall thickness.
While still spinning, the mold is removed from the oven and is cooled slowly.
The spinning ends when it reaches the temperature that the element can easily and safely be released from the mold.

Benefits of Rotational Molding

Design Flexibility
Rotational molded products have thicker outer corners which can help toughen the part.
Unlike other plastic processing methods, rotational molding will provide an evenly wall thickness.
Designers can easily kiss-off ribbing and undercuts, reinforced ribs, and add molded inserts.
Double wall construction
Consistent Wall Thickness
An evenly wall thickness can be maintained to within plus or minus 20 (+-20) percent, giving rotomolding tighter tolerance than injection molding.
Traditionally, metal parts are weakest at the corners, the precise areas where the components undergo the most stress. With blow molding or injection molding, it is hard to achieve total uniformity in wall thickness. On the other hand, with rotational molding, the continuous rotation allows the resin to coat every surface uniformly.
Cost Savings
Rotomolding is a low pressure process and molds are usually a thin hollow shell that describes the outer surface shape of the component. This results in mold costs much less when compared to other molding processes.

Economical
One of the key features of this type of plastic mold manufacturing is the ability to convert large numbers of assembled parts into a single working plastic component. This not only reduces cost and eliminates assembly time, but can also result in a more working component with better ergonomics.

Plastic is less expensive to manufacture and lighter weight for better fuel economy than metal parts.
Ability to Do Small Runs
Because of affordable tooling, rotational molding process makes it more cost-effective to do smaller runs on production.
Shorter Production Times
With rotomolding, it takes as little as 3 months to design and produce a component. Blow molding and injection molding can take at least six months or more to design and produce a product. Rotational molding can get your item to market faster and it is more economically than any other molding process.
Low Pressure/ Stress Free Process
The low processing pressure used in rotomolding has an additional advantage of producing components which are quite stress free, as compared to other type of molding that involve high pressure. This advantage of rotomolding is very vital when considering bulky, load bearing components in applications which must provide stress crack resistance or corrosion.

Rotomolding is a low pressure process, and the power required from the molds is very minimal. This results to its capability to produce complex or large parts on a very short notice, using low-costs molds.
Injection Molding Process
Injection molding technique is considered to be one of the most ordinary plastic part production processes. Injection molding can be utilized for producing products from both thermoset and thermoplastic polymers. The process often starts with loading the polymers in the type of granules or pellets and heating until they melt. The molten polymer is then injected into an assembly room formed by a split die mold. The molten polymer stays in the mold and is either heated-up to cure (thermosets) or cooled down to solidify (thermoplastics). The mold is now opened and the finished part is removed.

Regardless of the less expensive tooling rate, injection molding remains to be the most popular plastic manufacturing process for producing plastic materials in large quantities, thanks to its versatility to make components with complex shapes, and the low operational cost.
Bottom Line
Even though injection molding allows for quick plastic mold manufacturing of simple components, rotational molding produces exceptionally high quality customized plastic molds, even in low quantities. In addition, the parts produced are uniform, stress free, unified, and above all strong.Check out all the benefits we offer in rotational plastic containers.