Rotational Moulding: Definition and Benefits

Introduction

Rotational moulding, also referred to as rotomoulding, is a plastic moulding technique suitable for producing hollow items. It is a casting technique that does not involve pressure, unlike most other plastics processes. Molds for this procedure are generally cheap because they don’t need to handle pressure, so short production runs can be done cost-effectively.

Rotomoulding is basically used for manufacturing a wide variety of products. The procedure can provide product designers with great flexibility as nearly any form can be created with it. There are almost infinite possibilities for the size of mouldings and an abundance of applications.

Rotomoulding Process: How Does It Work?

The idea behind rotational moulding is pretty much straightforward. Powdered plastic material is typically inserted into a hollow mold, often crafted from cast aluminum or sheet steel. 

The mold is shut and turned gradually on two axes. The mold is heated in an oven while rotating, causing the polymer to slowly melt and adhere to the inside of the mold. 

After the polymer powder completely melts, the mould is then transferred to a cooling station where it is cooled using either air or a light water spray. As the part cools, it solidifies. 

Once the material has cooled enough to detach from the surface of the mold, the process is halted and the product is removed from the mold (de-molded).

Although rotational moulding is a simple concept, those with experience in the process know that it is actually very complex. 

It is a type of casting process where there is typically no pressure applied, making it difficult to control the material in the same manner as high-pressure methods like injection moulding. 

Several factors, including ambient temperature and humidity, mold type, material specifications, and powder quality, can impact both production and the final product.

Materials Used in Rotational Moulding

Currently, the industry relies greatly on Polyethylene (PE) with 97% of rotomoulded items being manufactured from this substance. Polyethylene is a much flexible, easily shapeable, & abundant polymer that now plays a leading role in the industry. 

Rotomoulding is a method of casting where powder is typically utilized instead of granules, requiring the material to be milled. Grinding polyethylene at room temperature is quite simple.

The progress of different polymers has been slowed down because the process takes a long time and can be harsh on them. But PVC, Polypropylene, & Polyamide (PA6, PA11 & PA12) are still used in some cases, usually in liquid plastisol form. 

A lot of these non-Polyethylene materials are hard to grind and usually require cryogenic grinding to be turned into powder – a more expensive method. There is a positive rise in research and development to broaden the selection of materials accessible to the industry.

The Benefits of Rotomoulding

Rotomoulding distinguishes itself with various unique features and benefits when compared to alternative moulding techniques.

1: Low Expenses

Since this is a casting procedure, there is no need to feel pressured. This indicates that molds are affordable, and small production runs can be cost-effective. 

If you have a fantastic concept for a new product but are unsure about the sales volume or are interested in a small production run, the low cost of rotomoulding makes it very appealing.

2: Easy to Use

With this procedure, creating intricate forms can be done with ease. Rotomoulding easily handles production complexities like stiffening ribs, moulded inserts, and varied surface textures.

3: Wall Thickness Uniformity

Rotomoulding ensures uniform wall thickness with corners typically having a greater thickness. This enhances the durability and quality of the product. 

Blow moulding, among other processes, stretches the melted material around corners or sharp edges, which can lead to thin areas and vulnerabilities.

4: Multi-working Possibilities

The cost of rotational moulding machines is inexpensive in comparison to other methods, and the necessary investment is minimal. The process allows for a high degree of production flexibility.

There is virtually no restriction on the size of products and multiple products can be molded simultaneously.

The Bottom Line

Another advantage of rotational moulding is the duration of the process. Rotomoulding is faster than both blow moulding and injection moulding. 

Rotational moulding’s quick manufacturing speed makes it ideal for rushed or immediate orders. For instance, at a rotational moulding company, production could start in 3 months or sooner.