Everything You Need To Know About Rotational Molding

Are you a startup business finding a unique yet cost-effective molding process for your plastic products? Rotational molding, also known as roto-molding could be the process you are searching for. The process is ideal for manufacturing versatile and low mass production hollow items. 

Did you know that the rotomolding market forecast predicts that the global rotational molding market will cross the value of $8.82 billion in 2031? You must be wondering how this market is growing immensely.

Figure 1- Rotational Molding Process
Figure 1: Rotational Molding Process

Rotational molding is a complete plastic molding process that does not involve pressure. It is an eco-friendly solution because it produces minimal wastage with the ability to recycle scrap material. It is a simple way to produce high-end seamless products of uniform thickness. 

In this comprehensive guide, we will dig deep into the advantages, drawbacks, working mechanisms, and applications of rotational molding. So, if you are not sure whether roto casting is the right fit for you or not, keep reading!

What is Rotational Molding?

Figure 2- Rotomolding Equipment
Figure 2: Rotomolding Equipment

As we all know that roto-molding process is economical in contrast with other manufacturing processes. But what makes it the best choice is its distinctive capability to produce complex designs according to your manufacturing requirement. Moreover, it is low-cost and beneficial for low-volume production runs. 

But why should I prefer rotational molding over other options?

Roto molding is a plastic molding process mainly used for creating hollow plastic products for various industrial applications.

Do you know the rotomolding technique has been used for manufacturing plastic products for the lastfive decades?

A study suggests that the yearly rotational mold production has increased from 10% to 15% since 1990. It concludes that the rotational molding market is growing continuously with its exceptional benefits.

Whether you want to produce thick double-walled plastic containers or hollow parts, rotational molding is the right choice for you. 

Looking for more in-depth knowledge?

Read Out: Which Plastic Manufacturing Process is Right for Me?

Why You Might Want to Use Rotational Molding

Figure 3- Rotomolding for Plastic Products Production
Figure 3: Rotomolding for Plastic Products Production

To understand why rotational molding could be the best possible fit for your production demand, you must acknowledge the unique features and advantages of roto molding. Understanding the edgy benefits of the process is necessary to make a confident decision.

Let’s find out the top advantages that rotomolding offers;

Low Scrap Rates with Rotational Molding:

The best part of rotational molding is low scrap production, making it an eco-friendly and less-wasteful process. This process produces a low rate of discarded material. Most of the scrap material produced by roto-molding is recyclable. It does not create high scrap material such as sprues, runners, wasteful purges, cut-offs, or gates. 

Rotational Molding Leverages Repetition & Consistency:

The ability to produce consistent premium-quality thick plastic products is the most prominent benefit of roto-molding. You can use a single mold to manufacture different parts without frequent replacements. Therefore, the process is compatible with affordability. 

The repetition and consistency of the process support both high and low-scale production. 

Flexibility:

Unlike other traditional molding processes, the rotational molding process provides flexible design features. You can produce seamless hollow plastic products in high or low production volumes. 

It allows you to accommodate double-walled, thick-walled, undercuts, ribbing patterns, threaded inserts, etc. From complex structure to wall thickness, the process offers a far-fetched flexible manufacturing process.

Efficiency:

The rotational molding process is way more efficient and accessible than injection or blows molding because it is largely automated and functional. The process significantly reduces labor costs and environmental impact.

The rotomolded plastic parts are smooth-textured, resistant, and UV stable to fulfill the requirements of various industrial applications. 

Cost-effectiveness:

If you are inventing a new product, the rotational molding will not leave you financially stressed. The rotomolding machine automatically regulates temperature, reducing the additional labor cost. 

Quality:

“If you do not compromise on quality, rotational molding is the process that will satisfy your requirements.”

The manufacturing process uniformly distributes plastic resin to produce even thick-walled plastic products. Rotocasting produces thicker and more resistant corners than injection and blow molding. It does not involve any joining processes; thus, the product is durable and long-lasting. 

So… What Is The Downside To Rotational Molding?

While rotomolding offers numerous advantages, there are some drawbacks that you should definitely consider before making your final decision. If you are seeking the right manufacturing process for your application, consider the following disadvantages of rotational molding;

Small Design Errors Have BIG Costs with Rotational Molding

There are high chances of design errors and precision due to the absence of pressure. The process uses a molten plastic resin that flows over the mold instead of being forced with pressure. 

It is quite challenging to produce small designs and achieve precise dimensions. If you want to produce high-volume, you must ensure that the design is satisfactory in the first go. 

Be Ready for High Tooling Costs for Rotational Molding

Although the tooling cost of rotational molding is cost-effective if your requirement is under 3,000 parts. However, if you have high production demand, replacement, and refurbishment will drastically increase the tooling cost. 

Therefore, other plastic manufacturing processes, such as compression and injection molding are recommended for mass production.

Longer lead times than other technologies

According to Science Direct’s research, rotational molding takes 30 minutes or more to complete its one cycle with 24.5 minutes of heating cycle time. The rotational molding machinery takes eight rotations per minute. This cycle time is way longer than other manufacturing technologies. 

Longer lead times can be a potential disadvantage if you have mass production demands. High cycle time decreases repeatability; thus, impacting the production rates. 

If you are unsure about plastic molding, read our in-depth guide on Plastic Mold.

How does Rotational Molding work?

Figure 4- 4-Step Process of Rotational Molding
Figure 4: 4-Step Process of Rotational Molding

The rotational molding technique is simple and robust. It produces a wide range of plastic products with a high degree of modification. Moreover, the entire process is environmentally friendly, low-cost, and efficient.

Let’s break down the roto-molding process into four steps to understand how powdered plastic transforms into highly durable plastic containers;

Step 1: 

In the first step, the mold is prepared according to the design specifications. Hollow molds for production are usually made of metal. The operators disperse the powdered plastic polymers, typically poly-based resins, over the metal sheet of mold. 

Cast aluminum is the most used raw material in the roto-molding process. 

Step 2:

After loading the mold with powdered plastic, it is passed into the heating chamber. This process allows the plastic polymers to melt uniformly and produce a thick coating on the inner surface of the mold. 

The optimum heating temperature of the mold depends on the chosen raw material and design complexity. 

Step 3:

The mold is slowly rotated between two perpendicular axes after the heating process. During this process, the mold is further heated to a layer to produce thick-walled products. The rotations ensure the even distribution of plastic coating to produce stronger and more seamless products. 

The operator can control the direction of rotation between heating and cooling zones to achieve the required design and parts. 

Step 4:

The mold is cooled down and the plastic is solidified with a water spray. The cooling steps take up to 5-10 minutes, depending on the thickness of the final product. After the plastic inside the mold is hardened, the product is de-molded, and the final inspection is carried out.

The product is further trimmed before the packaging. 

Different Types of Rotational Molding

Figure 5- Rotomolded Products
Figure 5: Rotomolded Products

There are three main types of rotational molding based on the type of machinery and manufacturing technique. Let’s closely analyze the three primary types of rotational molding;

1. Shuttle Rotational Molding:

In this type of roto molding, the molds are attached to a shuttle machine. The shuttle machine performs back and forth movement. It is beneficial to increase the production rate and efficiency of rotational molding.

It is suitable for mass production because it is a continuous process with reduced cycle time.

2. Single-arm Rotomolding:

Single or fixed-arm roto-molding is the simplest type of rotational molding process. As the name suggests, the machinery consists of a fixed arm and the mold is attached to it. The single arm rotates around the vertical axis and simultaneously heats the mold. 

3. Independent-arm Rotomolding:

Another common type of rotational molding is independent arm roto molding. This process consists of machinery with two or more independent arms. The molds are mounted to these independent arms. 

The independent arms allow multiple molds to be heated, cooled, and de-molded simultaneously. This technique is ideal for reducing the cycle time as it supports consistent production. 

What Raw Materials Used in Rotational Molding

Figure 6- Raw Material for Rotational Molding
Figure 6: Raw Material for Rotational Molding

As we have discussed earlier, rotational molding uses powdered plastic polymers that convert into plastic resin when heated.

But which raw material is the best option to manufacture the best-quality hollow articles?

There are a variety of raw material options used in rotational molding. Some of them are as follows;

  • Polyethylene (PE): Polyethylene is the most commonly used type of raw material used in rotational molding. Polyethylene is a flexible, resistant, and cost-effective resin. It is available in both low-density and high-density forms; high-density polyethylene (HDPE) and low-density polyethylene (LDPE).

According to the studies, HDPE has better surface geometry and thermal properties. 

  • Polypropylene (PP): Polypropylene is another widely used plastic resin for rotomolded products. It has comparatively lower sturdiness and temperature range than polyethylene. However, it is a versatile, UV-stable, and chemical-resistant material.
  • Polycarbonate (PC): Polycarbonate is a type of raw material that you can use where impact resistance and transparency are required. It is a sturdy, strong, and reliable material option.
  • Polyvinyl chloride (PVC): PVC resin is often used for preparing pipes, fitting and automotive products due to its high chemical resistance and strength. PVC spreads evenly and makes thick layers in the rotational molding process. 

Other than these materials, manufacturers use nylon, polystyrene, acrylics, etc for producing rotational molded plastic products. 

What industries can you use Rotational Molding?

Rotational molding produces versatile products that have a wide range of applications in the industrial and commercial sectors.

Following are the key areas that use roto-molded products;

Aerospace:

Rotomolding has been used widely for manufacturing thermoplastic components in the aerospace industry. These components include water tanks, ducting, drip pans,and air handling parts.

Automotive:

The automotive industry leverages the versatility of roto-molding for the production of fuel tanks, truck mudguards, components, toolboxes, ducting, and dashboards/instrumental panels of vehicles. 

Medical:

Another popular sector that utilizes rotomolded products is the medical sector. Several medical equipment such as trash bins, medical containers, kidney-shaped dishes, plastic bedpans, and urinals, are manufactured with roto molding.

Electronics:

In the electronic field, roto molding is used to produce a range of products due to its reliability and affordability. Protective cases and different enclosures of products such as speakers, phones, tablets, and laptops are manufactured with rotational molding. 

Moreover, wire organizers, display ranks, and battery cases are the most common types of plastic molded products.

So Is Rotational Molding the Right Option for My Project?

Figure 7- Rotational Molding- The Future of Molding
Figure 7: Rotational Molding: The Future of Molding

Although rotational molding has tremendous advantages and diverse applications, it is not suitable for all types of applications. 

If you have an ongoing project, you must find out if the rotational molding is the right option for you or not. 

Start with Financial Considerations

If you are considering rotational molding for your project, the first thing you must consider is tooling and material cost. The material and tooling cost of rotational molding is cost-effective. However, rotational molding would not be the right choice if you have high production demand. 

Calculate the production demand, material cost, equipment cost, and transportation before finalizing the process.

Next, Let’s Talk about Design Considerations

Although rotational molding flawlessly produces complex and compact designs. However, it is crucial to finalize the mold design to reduce the chances of defects. Analyze your design complexity, geometry, and the number of parts to decide whether roto molding would be beneficial for you or not. 

Getting Production Right for Rotational Molding

Cycle time is something you must consider before deciding the process for plastic production. Processes with minimum cycle time and the ability to produce multiple products at once are feasible. 

Rotomolding has a higher cycle time than other plastic products manufacturing processes. It is suitable for low-scale production because high-volume runs will increase labor and tooling costs. 

Rotational Molding vs Injection Molding: What’s the Difference?

Rotational molding and injection molding are the two most popular processes for plastic parts production. The fact that these two are widely used for manufacturing plastic products, you must be curious to know how they are different.

Let’s find out together!

  1. Raw Material: Raw material used for rotomolding primary contain PP, PE, and PVC. In contrast, injection molding has a wide range of material for selections. You can use different thermosets and thermoplastics in injection molding.
  2. Production Run: Production volume is one of the common dissimilarities between injection and rotational molding. Injection molding is efficient for high-volume production, whereas rotational molding is profitable for less than 3,000 parts production.
  3. Flexible Design: Rotomolding can produce different shapes, sizes, and designs for hollow parts but is not suitable for small sized complex shaped parts. However, you can produce small complex shaped parts with extreme precision through injection molding. 
  4. Manufacturing Costs: Rotational casting is comparatively less costly (up to 3000 parts) than injection molding. It has less scrap rate and labor cost, which makes it more cost-effective than injection molding. 

Related Guide: Everything You Need To Know About Injection Molding

Kemal: The Best Choice for Rotational Molding Services

Kemal is a top-notch rotational molding service provider that focuses on providing custom rotational molding services according to your requirements. With our own factory, we are ISO 9001 certified with qualified technicians and engineers. 

With 28 years of experience in CNC machining, injection molding, mold manufacturing, and 3D printing, we also provide pre-sale and after-sale services to our customers. Our customer care is available 24/7 to address your queries and provide professional consultation. 

From prototyping to high-volume production, Kemal ensures superior-quality and faultless final products. We offer advanced facilities and strict inspection & testing to provide accuracy and precision.

So, if you are the one looking for top-quality rotational molding services – Contact us today for a free quote.

Put your parts into production today

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