Roto Moulding Services
Rotational Moulding, or roto moulding as it is commonly known is an extremely versatile, relatively cost-effective method of producing hollow plastic components. The process is ideal for the manufacture of simple or complex shapes and because wall thicknesses can be accurately controlled the process lends itself very well to a wide variety of applications ranging from simple products such as safety steps and grit bins to more complex products such as children’s slides, hairdressing furniture and even missile cases.
What is Rotational Moulding?
Rotational moulding, as the name suggests, involves a tool being rotated in an oven whilst being heated and then cooled over a cycle time of approximately 45 minutes to 1 hour.
Polyethylene powder (shot weight) is measured out by the operator and placed into the tool which is manufactured from sheet steel, cast aluminium or CNC aluminium depending on the product design and complexity (see our tooling section for further information). The tool is then clamped shut and moved into the oven chamber. The chamber is heated up to around 220°C to 350°C and the tool rotates on two axes at low speed. As the tool heats up the polymer melts and begins to adhere to the inner surface of the tool until it has completely melted. Once the cook part of the cycle is complete the product is then cooled before it can be removed from the tool. The end product is a hollow, virtually seam free shape with a consistently even wall thickness.
Depending on the product it may be necessary for us to use a cooling jig immediately after the product is removed from the tool. A cooling jig is essentially a frame that is specifically designed to hold the product in order to stop it from shrinking or expanding in order to ensure that the product is dimensionally correct once it has finished cooling. All rotational mouldings are subject to varying degrees of shrinkage once removed from the tool, for some products this may not be a problem but for on others where dimensions are critical, a jig will almost certainly be required. Generally, we advise customers that shrinkage of approximately 1% to 2% is normal for any polyethylene product so this is something to bear in mind at the design stage.
For a brief overview of the process why not check out our new video!
- Why Choose Rotational Moulding?
- Advantages Of Rotational Moulding
- What You Can Expect From Your Products And Tooling?
- What We Need To Get Started With Your Project
Rotational moulding is an ideal process for creating products relatively quickly and cost effectively. Over the years roto moulding has risen in prominence and become far more widespread thanks to an increased awareness of its versatility and the fantastic level of quality that is achievable. This has led to product designers recommending and choosing the process for all manner of products from the very simple to the very complex.
The majority of customers will perhaps not always be familiar with the differences between the major plastic manufacturing processes, i.e. Roto moulding, injection moulding and blow moulding, so to save you time here are some key bits of information to point you in the right direction:
Roto moulding is ideal for creating reasonably complex, hollow parts. To give you some examples, we manufacture a huge variety of products from simple materials handling products such as steps, grit bins and trucks through to complex products including missile cases, twin skin underground housings, children’s playground slides and much more besides.
Roto moulding also has distinct advantages over injection and blow moulding. Relative to injection moulding, roto tools are considerably cheaper, and products are generally far more durable. Relative to blow moulding, rotational moulding permits much more complex, asymmetrical shapes. Wall thickness distribution is more uniform with roto moulding and part size can go well beyond anything which is possible with blow moulding. Relative to injection moulding, rotational moulding has major advantages of low mould cost and the ability to produce complex hollow articles.
Tooling costs are relatively low when compared to injection and blow moulding. Injection moulding tools can cost up to 5x that of a roto tool.
The process is ideal for a huge variety of product sizes and applications ranging from a 20cm equestrian treat toy through to a 2000+ litre water tank.
The ability to run multiple tools on each side of a machine arm meaning that the cycle time per product is reduced and therefore the cost per product reduces.
Wall thicknesses are fairly easy to control, and for most products it is possible to increase the wall thickness substantially if required. We manufacture products with anything from a 2mm to an 8mm wall.
The process is extremely versatile. Parts can be manufactured with moulded-in threaded inserts and a variety of different surface finishes and textures (see below) can be incorporated into the tool and product whether it be logo graphics or embossed contact details for example.
We are regularly asked about product and tooling longevity. The first thing to say is that due to the huge range of products that we manufacture and our lack of control over how those products are used, it is impossible to give any concrete guarantees. However, it is safe to say that provided our products are used correctly, it is extremely rare for MDPE to crack or deform.
Many of our products, such as our grit bins, are specifically designed to be outdoors 365 days a year. Over time you will see a degradation of the colour fastness, our products are UV rated for a Northern European climate however any colour will eventually fade over many years. It also depends on the wall thickness of the product, for example we have known delivery companies to drop our safety steps 6ft onto concrete with nothing other than a small scuff visible, but at 6-7mm thick the material is easily strong enough to withstand that level of abuse! For products shipping to hot countries we would usually recommend a material such as tank grade and would also insist on a higher UV rating which will help to extend the lifespan of the product. If you are in any doubt, please ask for further advice.
Whether it be steel, cast aluminium or CNC aluminium, any tool will give many years’ service without the need for any major repair work. Other than the replacement of the occasional clamp, we have tools that run perfectly and are 25 years old in some cases! It is extremely important to handle and treat tools carefully, they are a significant investment and we always ensure that they are treated as such.
Regular cleaning and inspection is essential, as is regular cleaning of tooling flanges. We always say that with a tool, you get out what you put in, and we pride ourselves in maintaining all our customers’ tools to the very highest standard. Customers are always welcome to visit and inspect their tooling at any time.
Once a design is created, we will need technical drawings in the form of Step files and PDF’s if possible. If you have a target product weight it would be helpful to know although we will always calculate an approximate weight based on an agreed wall thickness.
Once we have enough information we then contact the toolmakers for budget pricing. That can sometimes take up to 1 week depending on the complexity of the project so during that time we calculate budget unit costs and will then email over all costs once we have heard from the toolmakers. We will also cover other costs such as cooling / trimming jigs which are essentially frames which a product sits in in order to prevent it from shrinking or expanding too much, and to retain critical dimensions.
Please note that we are not able to manufacture prototypes. In roto moulding it is not possible due to the fact that in order to manufacture a product a tool is required so we recommend that customers consider methods such as 3D printing if they want to visualise how their concept will look. We do not offer 3D printing on-site but can recommend companies who do.
We work exclusively with LLDPE polyethylene which is sourced from 4 main UK suppliers. We stock 12 standard colours however if a customer wants something bespoke for their project our suppliers are usually able to colour match to a RAL or Pantone reference. The cost increases due to it being a non-standard colour but generally it is always possible to do.Read More
There are lots of available options with roto moulded products, some of which are shown below. We do not have a design team so if assistance is required in developing a design we can help by recommending companies to work with who have an excellent knowledge of roto moulding. We are happy to be involved in that process to ensure that your final design is achievable, and even if it isn’t we will always help toRead More
Inserts - metal inserts are very common in rotational moulding and we have many customers’ own products featuring all manner of inserts as pictured below.Read More