Roto Molding: Complete Manufacturing Guide and Industrial Applications

Roto molding is quite a simple and relatively less expensive technique to produce a wide range of products. Let’s explore its process and pros and cons now!

Roto molding is a century-old method that has gained the trust of many manufacturers who look to produce consistent, high-quality goods.

This article will provide a thorough explanation of rotational molding and how it might lessen a company’s burden.

Scroll down for more details!

1. What is Roto Molding?

Roto molding or rotational molding is a cost-effective manufacturing method for producing an unlimited number of hollow plastic components. Resins are added to a heated, rotating mold, and then they are distributed and fused on the inside surfaces. As a result, seamless parts with consistent wall thickness and additional material in corners to withstand pressures and shocks are produced.

Therefore, this technique is suitable for creating components with stable, high-quality walls. It may employ foaming for rigidity and thermal insulation and integrate features like spin weld attachments and inserts. Because rotomolding eliminates pinch-off seams and weld lines, it provides a final product without the need for further operations (in contrast to blow molding and thermoforming).

2. How Does The Roto Molding Process Work?

The roto molding process consists of 5 simple steps:

Powdered plastic material is poured into a hollow mold.
After starting a biaxial rotation, the mold is moved inside an oven.
The mold keeps rotating while the resin gradually melts and covers the mold’s walls.
Once the melting process is finished, the mold is transferred to a cooling station to cool down by air or a fine mist of water. During the cooling stage, the resin solidifies into the desired form.
After stopping the rotation, open the mold and remove the finished object.

Though the rotational molding process is simple, its casting process (with no pressure involved) is quite complicated, making material management challenging compared to high-pressure techniques like injection molding. The type of mold, material specifications, powder quality, and ambient temperature and humidity all have an impact on manufacturing and the final product.

3. Materials Used in Rotomolding

The most common material used in roto molding is Polyethylene (PE), accounting for 97% of rotomolded products. This material is versatile, available, and easy to mold. It can be easily ground to powder, which is suitable for this technique (which usually requires powder over granules).

Other options for rotomolding include:

Polypropylene (PP): Although this material has poor impact strength at cold temperatures, it has great resistance to cracking from chemical and environmental stress, superior stiffness, and a higher thermal distortion temperature.
Nylons (PA): Because of their excellent technical performance, nylon materials are perfect for rotational molding applications. Though some nylon types (Nylon 6) require an inert atmosphere (usually nitrogen), making the roto molding process a bit complicated, its low cost can make up for the challenge.
Polycarbonate (PC): It’s a translucent, high-strength polymer with built-in flame retardancy. Polycarbonate may need extensive technological processing due to its poor impact resistance.
Plasticized polyvinyl chloride (PVC): It’s a liquid substance that resists certain chemicals and has good weathering and aging qualities. Each grade has different flexibility, impact, and temperature performance.

4. What Machines Are Used In Vacuum Forming?

There are 4 types of machines used in vacuum forming:

DIY machines

DIY machines can be customized to fit certain tasks and save money. The basic supplies required for this machine include wood sheets, glue, clamps, sanding tape, an oven, varnish, and a vacuum cleaner. The procedure is simple and doesn’t need a high level of mechanical expertise.

Tabletop machines

Tabletop machines are commonly used to shape plastic sheets under vacuum pressure. The machine includes a frame, heating element, vacuum system, and material-holding rollers. For longevity, the frame is usually composed of metal or wood, and ceramic or nichrome wire is commonly used as heating components. A roller keeps the plastic sheet in place while a vacuum cleaner or pump creates the vacuum.

Single heater machines

The machine consists of a single heater or infrared heater, a frame, molds, a vacuum pump system, and a cooling system. The single heater is especially used to heat the plastic sheet to make it soft before being cast on the mold. The machine’s simple design and operation make it popular for smaller-scale manufacturing or prototyping.

Double heater vacuum forming machines

The machines are perfect for vacuuming forming because they include two heating stations that heat plastic materials more quickly and uniformly, enabling more effective material shaping. The main parts of the machine are the heating element, vacuum equipment, frame, shaping table, and cooling part.

5. Advantages and Disadvantages of Rotational Molding

5.1. Advantages

Rotational molding is a preferable molding method due to certain benefits:

Low tooling costs since there is no pressure, which makes molds affordable and economically feasible in small quantities.
Complex structures like molded inserts, stiffening ribs, and various surface textures are simple to construct.
The strength and integrity of the product are increased by uniform wall thickness, with corners often being thicker.
Great production flexibility with low equipment costs and minimal investment.
There is no restriction on product size; thus, several items can be molded at once.

5.2. Disadvantages

Yet, rotomolding has some downsides, including:

Long cycle times: At eight rotations per minute, a single component might take up to three hours to complete.
Limited material options: Only poly-based resins may be used since the technique requires conversion from granules to fine powder and good heat stability.
Expensive raw materials: These include high demands for thermal stability, necessary additives, and grinding expenses.
Low repeatability: Quality problems arise because soft metal needs to be replaced every 3,000 cycles.
High labor costs: Higher work intensity is needed due to a lack of automation and mechanization.

6. Applications of Roto Molding

Rotational molding is used to produce many products in different industries, including:

Watercraft products: kayaks, canoes, pontoons, etc.
Kid toys and playground equipment
Big trash cans, recycling bins
Containers to store water and chemicals
Coolers for food and beverage
Agricultural tanks
Barriers
Carts and carriers

7. FAQs about Rotomolding

What is the typical cycle time for roto molding?

The typical cycle time for roto molding is longer than that of other molding methods (such as injection molding). It usually lasts around 20-60 minutes, depending on the size and complexity of the desired produced components.

Can rotomolding be used for prototyping?

Yes. It can simplify prototyping since it has quite a short lead time, benefiting quick turnaround. Plus, in rotational molding, manufacturers don’t need expensive molds for each design iteration. Therefore, you can take advantage of its cost-effective iteration.

How does the cost of rotational molding compare to other methods?

Rotomolding is much less expensive than other methods due to the low cost of machining the mold before heating.

8. Conclusion

Roto molding is a plastic molding technique that produces hollow objects without applying pressure. Its low tooling cost and production flexibility make it a popular choice among manufacturers.

If you’re looking for high-quality plastic materials for the process, check out the engineering plastic compounds and filler masterbatch from EuP Egypt. We offer PP, PE, and PC compounds with enhanced additives, guaranteeing businesses to achieve the products’ requirements. Contact us today to get consultation and free samples.