Outsourcing

Are you looking to produce products or components or improve an existing product through the use of rotational molding process?
Do you need a reliable rotational molder / manufacturer, a trusted supplier?
Plastic rotational molded products will deliver cost reductions, increase your performance and will help your overall profitability.
R.M.S is the rotational molding manufacturer and supplier that offers a full service from product development assistance to finished component delivery. We can deliver a custom designed product to meet and exceed your requirements with our state-of the-art equipment. R.M.S has been at the forefront of plastic rotational molding for more than 20 years, a specialist whose continual investment ensures that customers get the quality they rely on, delivered to the schedules they have set.

From concept to production we are a complete, full-service manufacturing partner.

What is Rotational Molding?

Rotational molding is a method for manufacturing hollow plastic products. It is best known for the manufacture of tanks, but designers all over the world now realize that it can be used to make many different types of plastic parts. Some of the sectors that it services include: medical products, consumer products, highly aesthetic point-of-sales products, agricultural and garden equipment, automotive and transportation components, leisure carts and sporting equipment, toys, furniture, and materials handling equipment.

The rotational molding industry is an exciting and innovative part of the plastics manufacturing sector. In recent years, many significant technical advances have been made, and new types of machines, molds, and materials are becoming available. We are able to deliver high-quality, high performance parts at competitive prices.

The Process

The principle of rotational molding of plastics is relatively straightforward. Indeed, the simplicity of the process is a key to its success because it allows the molder to exercise close control over part dimensions and properties. Basically, rotational molding consists on introducing a known amount of plastic in powder, granular, or liquid form into a hollow, shell-like mold. The mold is heated and simultaneously rotated about two axes so that the plastic enclosed in the mold adheres to, and forms a layer against the mold surface. The mold rotation continues during the cooling phase so that the plastic retains the desired shape as it solidifies. When the plastic is sufficiently rigid, the mold rotation is stopped to allow the removal of the plastic product from the mold.

Preparing the Mold

The process begins with filling a hollow mold with a pre-determined quantity of polymer powder or resin. This powder can be pre-compounded to the desired color. The powdered resin is usually polyethylene (PE) although other compounds such as polyvinyl chloride (PVC) can also be used. The oven is preheated by convection, conduction, (or in some cases radiation) to temperature ranges around 260 °C – 370 °C, depending on the polymer used. When the powder is loaded into the mold it is closed, locked, and loaded into the oven.

Heating and Fusion

Inside the oven, the mold is bi-axially rotated (i.e., rotated around two axes) as the polymer melts and coats the inside of the mold. The rotation speed is slow, less than 20 rotations/minute; the process is not centrifugal. During this phase of the rotational molding process timing is critical. If the mold spends too much time inside the oven the polymer will degrade – this will reduce its impact strength. If it spends too little time inside the oven melting of the polymer will be incomplete and it will not fully coalesce on the mold wall, creating large bubbles in the item.

Cooling the Mold

After the melting has been consolidated to the desired level and the timing is right, the mold is removed from the oven and cooled. Cooling of the mold is typically done with air (by fan), water or sometimes a combination of both. Cooling allows the polymer to solidify to the desired shape and shrink slightly so that it can then be handled by the operator and removed from the mold. The cooling time can typically be measured in tens of minutes. It is important that the cooling rate be carefully measured because rapid cooling causes the polymer to shrink too fast and warps the part.

Unloading / Demolding

When it has cooled sufficiently to be handled and the polymer can retain its shape, the mold is opened and the part is removed. The molding process can then be repeated by adding the polymer powder to the mold.

Advantages

• A hollow part can be made in one piece with no weld lines or joints
• The molded part is essentially stress-free
• The molds are relatively inexpensive
• The lead time of the manufacture of a mold is relatively short
• Wall thickness can be quite uniform (compared with other free surface molding methods such as blow molding)
• Wall thickness distribution can be altered without modifying the mold
• Short production runs can be economically viable
• It is possible to make multi-layer parts, including foamed parts
• Different types of products can be molded together on the one machine
• Inserts are relatively easy to mold in
• High quality graphics can be molded in.