A History of Rotational Moulding
Noel Mansfield Ward

The history of this relatively small but highly specialized sector of the plastics processing industry is not as well documented as that of its bigger counterparts - a situation which this comprehensive account does much to correct. The author, engaged in this field from the 1960s, was in 1976 the first overseas member of the US-based Association of Rotational Molders.

Although patent research traces the rotational casting process back to early Egyptian times in respect of ceramics, the first application relating to plastics was developed in the USA in the early 1950s. This was a doll’s head rotationally moulded using an E Blue box-oven machine based on a General Motors back axle driven by an external electric motor mounted in a steel box and heated by floor-mounted gas burners. The mould was of electroformed nickel-copper with a closure plate across the neck, and the material was a liquid PVC plastisol. After being heated while rotating in the oven the mould was removed and dunked in a bucket of water to cool. To remove the head, a vacuum probe was used to collapse the warm, flexible moulding and to pull it through the neck aperture. The result was a high-quality moulding with no parting line. This new process for the manufacture of dolls’ heads rapidly replaced the papier-mâché method of the day.

Around 1953, a leading UK doll manufacturer, Rosebud Dolls of Raunds, Northamptonshire learned of the American development and the owner, Eric Smith, took his close friend and toolmaker John Orme to the USA to see the new process for making dolls’ heads in action. On his return Smith commissioned Orme to make a similar box-oven machine - the first for rotational moulding in Britain. Orme developed the machine further by introducing a roller-conveyor cooling tank with pneumatic lift, equipped with quick-release mould-carrying plates to increase productivity. Having satisfied Rosebud’s machinery requirements and recognized the potential of the new process, he set up his own company, John Orme Ltd., in Rushden, Northamptonshire, to manufacture rotational moulding machines.

Applications continued to be developed both in Britain and the USA, at first principally in the toy industry, and soon PVC ‘squeaky toys’ and playballs* made their appearance. Machines increased in size to meet growing demand from 26in (66cm) diameter plates to 30in (76cm) and then 42in (107cm). At the same time, the heating method changed from direct gas jets in the bottom of the oven to the indirect
high-velocity air system still used today, to give more even heat distribution and better temperature control. During this period the German company Spangler Kaufman also entered the field with a large machine of box-oven design.

Widening range of uses
As the process became better understood, applications in other markets were developed, including inflatable fenders, marine buoys, car armrests and road cones.
The latter is one of the major success stories for rotational moulding. The original cone was a small black rubber moulding which first made its appearance in the UK in the late 1950s. Peter Luke, a friend of John Orme in the toy trade, came to him with the idea of a red PVC cone incorporating a recess on the underside to hold a weight to stop it moving with wind and vibration from passing vehicles, etc. Orme himself manufactured the cones to start with, but because of his engineering background was more interested in selling machinery than making products. As a result he sold machines and cone moulds to anyone who was interested. The market was slow to develop until the introduction of polyethylene for the application in the early 1960s. Today there are four major manufacturers of road cones in the UK and it is estimated that over ten million cones have been produced in Britain alone.

In comparison to Orme’s approach, in the late 1950s the Davidson Rubber Co. in the USA developed and patented the rotationally moulded PVC car armrest which became the standard method throughout the automotive industry for fixing interior panels to the door. Davidson licensed this process with great success to companies in the UK, Germany, Japan and wherever else cars were made.

In the early 1960s, the process attracted the attention of suppliers of polymers other than PVC on both sides of the Atlantic, and around 1963 the first LDPE rotational mouldings were developed in the USA. Whereas with PVC cooling was achieved by
immersing the mould in a tank of cold water, LDPE in powder form required the mould to continue to be rotated while being cooled with a fine water spray or just air. In Europe the Engel process was developed and was the forerunner of ‘rock-and-roll’
machine design. The concept was to make larger hollow containers such as textile bins in LDPE by rotating an open or closed mould on a chassis housing open gas jets which rocked through approximately 30 degrees, thereby coating the inside of the mould with polymer. Cooling was by switching off the burners and allowing ‘rock-and-roll’ to continue until the moulding could be extracted.

The Engel licence was taken up in the UK by Bowater which made fibreboard drums among other products and recognized this new development as an alternative method of manufacture. Bowater employed three bright young engineers, Dickey Knowles, Earl Duffin and Keith James, to work on this project but after some time decided to abandon it. Duffin left and set up Flextank in a deprived mining village in South Wales which has become one of Britain’s largest rotational moulders, now part of the Tanks & Drums Group, while Knowles established Rotational Moulders Ltd. in New Mills, Derbyshire, not far from the original Bowater plant. (James, on the other hand, made a career move into a large blow-moulding company.) Both the new companies operated for some years using direct-flame ‘rock-and-roll’ machinery to produce a wide variety of LDPE tanks and containers, and spawned a number of similar but smaller operations, mainly in North-west England.

In Scandinavia, Cipax developed the Engel process and licensed a complete package of machinery, moulds and know-how in various parts of the world. They developed one of the first rocking-oven machines for the manufacture of boats, fish-boxes, canoes, etc. In the USA the ‘rock-and-roll’ concept was taken up by Rototron who themselves developed a total manufacturing and marketing licence package which has been sold to many countries. In parallel with the ‘rock-and-roll’ process developments, McNeil, a rubber machinery manufacturer in Akron, Ohio and John Orme in the UK developed and patented three-station machines which could process both PVC and LDPE, McNeil designed a carousel-type machine with three arms fitted to a turret which indexed from the free-standing oven to a cooling station and then to an unloading/loading position.

By comparison and based upon his experience with box-oven designs, Orme designed a three-arm machine configured like a Ferris wheel with an overhead oven, cooling station at the rear and the unloading/loading station on the ground at the front. The cranked arm carried two rotating mould plates side by side and was designated the 2/36 model, each mould plate being 36in (91cm) in diameter. As a result of the market pressure to mould larger products in LDPE, both McNeil and Orme developed larger machines. However, Orme found that the practical height of the Ferris wheel design was restricted even after constructing a three-foot deep pit and for larger machines he therefore reverted to either a shuttle- or carousel-type design.

While these developments in machine design were emerging in the UK and USA during the late 1960s, Kraus Maffei in Munich, Germany decided to use a different heating medium - hot oil. The concept was to achieve more effective heating and more accurate temperature control by pumping pre-heated oil around the mould while it was being rotated in two planes simultaneously. This required the construction of double-skin moulds at considerable cost and the passage of hot oil through rotating joints. This approach has been used successfully for the moulding of nylon6 (liquid caprolactam) domestic oil storage tanks in Germany and for other special applications but, although still promoted, has found only limited commercial success with polyolefins due to the high mould costs.

In the same period, Ernst Rheinhardt, a German industrial oven manufacturer, developed a carousel-type machine which differed from that of McNeil in that the oven retracted in an effort to reduce heat loss by having only one door. This design has proved attractive to some moulders. Another German company, Spangler Kaufmann, specialized in box-oven type machines for PVC applications but did not develop designs to accommodate PE resin. In Italy, Caccia developed PVC mixing equipment in the mid-1950s and soon found a demand for rotational moulding machines from the users of its mixers. Caccia manufactured box-oven machines for the toy industry and in the mid-1960s developed a carousel-type machine based on the McNeil concept.

McNeil machines dominated the US market from 1963, but by 1970 Akron Crane emerged as an alternative manufacturer in addition to Rotodyne, Fabrimould and Rotational Engineering Inc. in the UK, Orme headed the local market and, after its acquisition by USM Corporation of Boston in 1968, actively exported machines and know-how to many parts of the world. In Europe, Rheinhardt and Caccia steadily expanded the market as the process became more widely appreciated. At the K75 exhibition in Dusseldorf, Orme demonstrated for the first time in public, a six-station production machine moulding PE grass catchers, PVC playballs and other products in the same cycle. Ferry Industries Inc. from Stow, Ohio - the leading machinery supplier today - entered the US market in 1982 with an Orme manufacturing licence.

A professional association
The Association of Rotational Moulders (ARM) was formed in Chicago in 1976 by a small group of PE processors: 20 years on the membership has grown to 357 with half of it based overseas. Through active participation by its members, rotational moulding technology has been pulled together and ARM has been largely responsible for the development of market awareness of the process, particularly in the USA.

The 1980s saw the process recognized for its growth potential by more of the larger material suppliers world-wide, and new materials and grades became available to satisfy increasingly demanding product specifications. Polycarbonate, polyesters, PP, LLDPE, nylon and (for a time) ABS complemented LDPE and HDPE, and cross-linked grades encouraged numerous new applications such as lighting globes, fuel tanks and various industrial mouldings. Although tanks of all kinds and shapes have traditionally formed the volume market, PE toys were developed around this time and rapidly became one of the largest single outlets for rotational moulding.

The process has not justified significant independent research, but important work at Queen’s University, Belfast from the late 1980s onwards has led to a much improved scientific understanding of the rotational moulding process and resulted in the development of the Rotolog system for continuous in-mould temperature measurement. This is a major step forward towards automatic process control and transition from art to science for the ‘rotomoulders’ of tomorrow.

What of the future? Will the next 30 years be as exciting for the process as those past? Will press-button technology replace the bucket for material dispensing? Will computers make operators redundant? We now have the technology - when will its employment be justified.

Pictures show (top) typical dolls and toys moulded on Orme machines, (middle) an early box-oven, and (bottom) a large inspection chamber produced by rotational moulding.

*Harry Grimshaw, ‘The birth and development of the Frido vinyl playball’, plastiquarian no.12, 13-15, 1993