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Rotational molding: a brief history

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Martogg Group
Rotational molding: a brief history

Rotational molding uses a heated hollow to form and then fills it with material or a shot of weight. Rotating the mold slowly is done in two directions. The mold's softened material will stick to the surface by this rotation. The mold rotates continuously throughout heating and cooling cycles to maintain an even thickness. The mold does not shrink or deform during cooling. The process was applied to plastics for the first time in 1950s. However, it was limited in its use to plastics and slow in speed. With the advancement of plastic powders, process control has improved and its use has increased.

R. Peters, a British patent holder published the first documented rotational moulding process in 1855. This produces "two centrifugal moves at right angles to each other" using beveled gearing, heat, and heat. This process was used to create artillery and hollow vessels as well as other artilleryshells. It was used to maintain uniform wall thicknesses, density, and other purposes.


Plastics were first introduced to the rotational molding process in the 1950s. Doll heads were the first application. The E Blue box oven machine, which was inspired by the General Motors rear-axle, was used to build this machine. The external electric motor powered it, while the internal motor powered an E Blue-type internal engine. The mold was made of electroformed nickel-copper and the plastic was a liquid, plastisol, polyvinyl chloride. To cool the mold, it was placed in cold water.


Rotational molding was the foundation for many other plastic toys. This method became increasingly popular and sought-after. This was used to create other products such as marine buoys and road cones. This popularity resulted in the development of larger machinery. The direct gas jets were eventually replaced by the indirect high velocity air system. The new heating system was also created.


In Chicago, the Association of Rotational Moulders was established in 1976 to serve as a trade association. The main purpose of this association is to increase awareness about the technology, and the process of rotational moulding.


Rotational molding was introduced for the first time in 1980 with new plastics such as nylon, polycarbonate and polyester. This process is now used in a variety of new ways, such as the creation industrial molds or fuel tanks. Queen's University Belfast has been conducting research since the 1980s. This led to the creation of the "Rotolog", which allows for precise monitoring and control of cooling processes.



Equipment and tooling

There are many sizes for rotational molding machines. These machines typically include ovens, cooling chambers and molds. Because the spindles attach to a rotating axis, each mold is coated with a uniform coating of plastic.


Casting molds and tooling can either be done from welded sheet steel or cast. The fabrication method will often be determined by the part size and complexity. Cast tooling is best for complex parts. Most molds can be made of aluminum or stainless steel. Aluminum molds are typically thicker than similar molds made from steel because it is a soft metal. This thickness does not affect the cycle times, as aluminum has a higher thermal conductivity that steel.


Equipment and standard set-up for rotational molding

All rotation molding systems should include a mold and oven. The molds used for making the part are typically made of aluminum. The final product's quality directly depends on the quality of the mold. The oven heats and turns the part to achieve the desired shape. The cooling chamber is where the part is placed until it cools. To rotate each mold, spindles are attached that provide uniform plastic coating.


  • Rotational molding machines
  • Machine for rock and rolling
  • Rock and Roll's rotating moulding machine at 45 degrees angle
  • 2009 Rock and roll rotational molding machine


This machine can make large, narrow parts. There are several clamshell types. Each has one arm. There are two-arm shuttle-type rolling and rock machines. Each arm rotates 360 degrees in the mold, while the other tip rocks the mold 45deg higher or lower than horizontal. Modern machines heat the mold using forced hot air. These machines are great for large parts that have a high length to width ratio.


Clamshell machine

This machine rotates with a single arm. There are often additional arms at both ends of each arm. The clamshell machine heats and cools the mold in one chamber. It takes up less space than similar shuttle and swing arm rotating moulders. It is affordable for the amount of products it makes. It is also available in smaller sizes for schools interested in prototyping and making high-quality models. An arm can be made from multiple molds.


Machines that can rotate up and down or vertically

The loading and unloading areas are located at the front of the machine, between the heating and cooling areas. These areas are smaller than most rotating machines, and can be either small or large in size. Vertical rotational molding machines are very efficient because of the efficiency and compactness of their cooling and heating rooms. These machines are smaller than horizontal multi-arm carousels machines, but they have the same capabilities.


Shuttle machine

Two arms move the molds from the cooling station to the heating chamber of most shuttle machine. They can be used independently and rotate the molds bi-axially. Sometimes there is just one arm on the shuttle. The mold is moved in a straight line by the machine between cooling and heating chambers.


Machine to swing arm

A swing-arm machine may have four arms and a biaxial movement. Each arm can be operated separately, so you don't have to use them all at once. Each arm is mounted in the corner of an oven and swings in and out of the oven. You can mount a pair of arms on the corner of swing-arm machines to make a four-arm machine with two pivot points.


Carousel machine

This bi-axial machine has become the most popular in business. This machine is available in many sizes and can be outfitted with up to six stations and four arms. There are two types: independent or fixed. Fixed-arm carousels have three fixed arms that must be moved together. One arm will be located in the heating chamber and the other in the cooling chamber. The loading/reloading area will have the third arm. Fixed-arm carousels are best when each arm has the same time. You can move three to four independent-arm carousels at once. This allows you make molds of different sizes and with different thicknesses.

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