Plastic Manufacturing Leaders - Excelsior are leading manufacturers of plastic products. let us help you bring your own plastic product manufacturing ideas to life.
At Excelsior you can count on our plastic manufacturing expertise to help make your plastic products a reality. With 100 years of history to our name, our rotomoulding experience allows us to create plastic products for clients across a wide range of sectors, including (but not limited to) agricultural, educational, and sporting and leisure.
Like several other forms of plastic manufacturing, rotomoulded products are created using thermoplastics, which can be melted and reformed multiple times without losing any strength and integrity. This allows expert plastic manufacturers like us to create an almost limitless range of shapes from thermoplastics, providing almost endless possibilities for your product. In short, if you can imagine it, we can create it for you.
Rotomoulding in the plastic manufacturing process
Rotomoulding is a form of plastic manufacturing that involves solid thermoplastic pellets being placed inside a hollow mould, which is rotated steadily while being gradually heated. The centrifugal force causes the pellets to melt, disperse and stick to the inside walls of the mould. Once it’s cooled, the result is a hollow, virtually seam-free shape with a consistently even wall thickness. Roto moulding is perfect for creating containers such as grit bins, materials handling products and safety steps, all of which are in our standard range of products.Find Out More
Benefits of rotational moulding for plastic manufacturing
Unlike products manufactured using blow moulded or injection moulded processes, with rotomoulding there are no ‘stress points’ that is, parts of the product which are especially liable to break under physical pressure. Rotomoulding also allows for particularly distinctive shapes and other complex geometries to be made in a single, seamless piece, rather than built from several individually manufactured components. The roto-moulding process also means that different surface textures are possible, which opens up even further design potential for your plastic product ideas.Find out more
An introduction to plastic manufacturing
Plastic is arguably one of the most versatile substances on the planet. Humans have been steadily developing ever more sophisticated plastic manufacturing techniques over the last century, and now plastic is used in almost every industry, incorporated into countless products and technologies designed to make our daily lives safer, more efficient and more convenient.
Some examples of the industries that use plastic include construction, textiles, transport, industrial machinery and manufacturing, the maritime and agricultural industries, and the healthcare sector… just to name a few!
Today, more patents are filed each year for plastic than for glass, metal and paper combined. What’s more, plastic products are filling increasingly more specialised functions, which in turn requires increasingly more specialised plastic manufacturing techniques. Shape-memory polymers, light-responsive polymers and self-healing polymers are all great examples of the sorts of incredible concepts that have now been made a reality.
But while some of the world’s most advanced plastics are developed in labs, the vast majority of plastic products are created using some time honoured plastic manufacturing processes. Many of these have stayed largely unchanged over decades, such as the roto-moulding service we offer right here at Excelsior.
How to choose the right manufacturing process
- 1. The form of the final product
When you’ve got your vision for your own plastic product, deciding on the best plastic manufacturing process will be one of the first major decisions you’ll need to make. It’s not always an easy decision, but various plastic manufacturing processes have different strengths and weaknesses that make them best suited to making different types of products. Below, we’ve provided a quick explanation of what each plastic manufacturing process involves, so you can make a more informed decision about which one’s best for you.
- 2. Volume and cost
Once you know exactly what sort of plastic product you want to manufacture, you’ll think about how many of them you'll need, and what sort of budget you’ve got to dedicate to their production. Will it be a one-off order, or will you be manufacturing them on an ongoing basis?
It’s worth bearing in mind that some manufacturing processes have high upfront costs for tooling and setup, but the products are less expensive individually. This means that certain plastic manufacturing processes like injection moulding might only make financial sense if you’re planning to manufacture your plastic products in large batches.
On the other hand, low volume processes like roto moulding have lower startup costs, but slower cycle times, less automation and greater amounts of skilled labour. All of this means that the costs for individual products remains constant, which makes them better suited to low-volume orders, sometimes as small as ten individual units.
- 3. Lead time
Essentially, how quickly do you need your plastic products completed and ready to go? Some types of plastic manufacturing can create parts within a timescale of just few days, whereas others require tooling and setup that can take weeks or even months. As a general rule of thumb, higher-volume orders tend to take longer to process, so make sure you’re taking that into account!
- 4. Material
There are many different sub-types of plastic material, and each of them has different properties that make it suited to very specific applications. Before you choose a plastic manufacturing process, it’s worth thinking about what requirements you have for your material. What stresses, strains and temperatures will you need it to withstand? Which material will be the safest for your application? For example, if you’re making a plastic product which comes into direct contact with foodstuffs for humans or animals, you’ll need to ensure that it’s food grade plastic to avoid the risk of dangerous contamination.
The different types of plastic
As a synthetic material, plastic can be classed into countless types and sub-types, each with their own unique set of properties that enable them to serve endlessly specific roles. The particular set of plastic manufacturing processes we’re discussing on this page use thermoplastics to create finished products.
Thermoplastics are the most widely used type of plastic. Their main distinguishing feature is their ability to go from solid to viscous forms and back again several times without losing their strength or structure, before they start to eventually degrade.
We use three main types of thermoplastics here at Excelsior: low density polyethylene, medium density polyethylene and high density polyethylene.
- What is low density polyethylene?
Low density polyethylene has the lowest tensile strength and greater flexibility than any other thermoplastic, largely due to its relatively loose molecular structure. It’s semi-rigid, translucent, and surprisingly tough, with excellent resistance against chemicals and weather elements. It’s also exceptionally economical to produce, making it a popular choice for mass produced items.
Low Density polyethylene is used to create products like carrier bags, squeeze bottles and children’s toys, heavy duty sacks, gas and water pipes, and chemical tank linings, to provide just a few examples.
- What is high density polyethylene?
High density polyethylene is principally known for being the strongest, stiffest and toughest types of thermoplastic. It’s chemically inert, resistant to water ingress and solvents, weatherproof, and holds its integrity well even in extreme temperatures, ranging from -60°C all the way up to 800°C.
High density polyethylene is used to make a broad variety of products, including chemical drums, tanks, silos, hoppers, signs, and pipes and fittings.
- What is medium density polyethylene?
Medium density polyethylene combines the advantages of HDPE and LDPE, striking a useful balance between flexibility and raw strength. Medium density polyethylene shares its high resistance against heat and sudden impacts with HDPE, along with a better stress cracking resistance than LDPE.
However, its increased flexibility means that it’s exceptionally useful for making durable water piping, plumbing or waste water plumbing, along with electrical cables. Its high shock resistance also means that it can be used for water containers and oil tanks. It’s an incredibly versatile substance.
Food grade and recycle black plastics
Once you’ve chosen one of these for your own plastic product, you’ll have the choice between specifying it as food grade, or recycle black.
- What is food grade plastic?
Food grade plastic is any thermoplastic that’s been specifically manufactured to be safe for contact with anything that could be consumed by humans or animals. That means it doesn’t contain any dyes or similar ingredients which could be harmful to humans, and it hasn’t been brought into contact with any harmful chemicals during the raw plastic manufacturing process.
We use food grade plastic as standard here at Excelsior, and widely used in the packaging and retail industries, especially for food or medicine.
- What is recycle black plastic?
Recycle black is a particularly low cost and sustainable option made from the offcuts of previous plastic products. It’s a popular choice for anyone on a budget, and for whom colour isn’t an important factor for their plastic product. However, because of the way in which it’s produced, it’s impossible to guarantee that it’s entirely safe for contact with consumables, which is why it’s not possible for us to provide recycle black plastic which has been certified as food grade.
Types of plastic manufacturing
There’s a huge range of plastic manufacturing processes to choose from to create your own plastic product.
Extrusion moulding works by rotating an internal screw to push heated thermoplastic granules through a heated barrel. Once the fused polymer has been squeezed through this barrel, it gradually fills out the hollow of a die waiting on the other side. There, it cools into the finished part, and is then removed from the die. Extrusion moulding has often been compared to squeezing toothpaste from a tube, and to be honest it’s quite an accurate analogy.
- Blow moulding
Blow moulding creates hollow plastic products by using compressed air to inflate specially designed pieces of plastic (called parisons) into the desired shape. A parison is shaped very similarly to a test tube, complete with a hole at one end to allow air into it. It’s first heated in an oven, and then placed inside a mould. A high pressure jet of air is then blown down through the opening, until the parison has expanded to completely fill the mould.
This plastic manufacturing method is often used to create plastic drinks bottles and similar containers. Alternatively, blow moulding might be used to inflate a sheet of warmed plastic into the shape of a dome, which is a popular way to create hemispheres for shop displays.
- Extrusion blow moulding
As the name suggests, this is a combination of the two techniques above. As with extrusion moulding, the process starts with thermoplastic polymers being extruded into a narrow tube shape, suspended in the centre of an open die. Then the die is closed to seal both ends, before compressed air is forced into the cavity, causing the plastic tube to expand until it takes the form of the finished hollow product.
- Injection moulding
This is one of the most widely used forms of plastic manufacturing. It involves taking a polymer in granule form, and heating it until it’s fused, before forcing it into a closed mould. This next part of the process bears a strong similarity to extrusion moulding, in that a screw mechanism is used to force the polymer along the length of a heated barrel. As soon as it reaches the end, it’s injected into a waiting mould.
- Vacuum forming
Vacuum forming is one of the oldest forms of plastic manufacturing, dating back to the 1930s. It starts with a plastic sheet being clamped in a frame, which is then moved into the close vicinity of a heating element. This softens the plastic to make it more malleable - think the bouncy bit of a trampoline. The frame is then lowered onto a waiting mould, which is completely covered by the soft plastic.
This is where the vacuum comes in. All the air is abruptly drawn from the space between the plastic and the mould, so that there are no bumps or bubbles in the finished plastic part. Then the plastic is given time to cool, although sometimes fans and sprayed mist are used to accelerate the process. After that, it’s trimmed by hand or a CNC machine, before the plastic is finally detached from the mould as a single, unbroken part.
- Roto moulding
Roto moulding, or rotational moulding, is a unique process that’s exceptionally well suited to creating hollow thermoplastic products, such as drums, storage tanks or litter bins. In a nutshell, the roto moulding process begins with plastic granules being placed into a mould. This mould is then gradually heated like an oven, as it’s spun on both vertical and horizontal axes.
This rotation generates centrifugal force that throws the molten plastic outwards from the centre, so that it sticks to the inner walls of the mould. The plastic product is then cooled, often by air or water, and finally opened to remove the hollow plastic part.
The rotational moulding manufacturing process
We’ve outlined the basics of the process above, but here’s a little bit more detail.
An operative measures out the required amount of polyethylene powder, before placing it into a pre-made mould. The mould is then clamped shut, and relocated to an oven chamber.
There, the tool is subjected to temperatures of between 220°C and 400°C, as it’s rotated on two axes at significant speeds. Inside, the powder heats up and begins to melt. The centrifugal force generated by the rotation results in the powder being thrown outwards so that it adheres to the inside of the mould.
This part of the process generally takes between 45 minutes to an hour, which provides enough time for the molten plastic to be distributed across the entire inner surface. Then the mould is taken from the oven, and then cooled.
If the product concerned is of a particularly technical nature, at this stage we normally use a wooden cooling jig here at Excelsior. This ensures that the product doesn’t shrink too much, which can result in warping. It also helps to retain critical features, such as stiffening ribs.
The rotational moulding manufacturing process And that’s all there is to it! You can read more about the specific advantages of rotomoulding here. If you’ve got any further questions, or if you need any specific advice, or if you just want to discuss the details of your own plastic manufacturing project, we’re always happy to help - feel free to use the details on our Contact page to get in touch with us.
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