Design & Vision

Design & Vision for Rotational Molding Products

by Design Editor Michael Paloian (Integrated Design Systems, Inc.)

Making the Process Fit the Market

“The versatility of the Rotational Molding process is unmatched by any other plastics molding process.”

The versatility of rotational molding is unmatched by any other plastics molding process because of its wide range of applications, part sizes, levels of productivity and investment requirements. One can become a rotational molder with a minimal investment by building a simple open flame hand cranked machine to mold tanks in sheet metal molds, or invest hundreds of thousands of dollars in automated computer controlled machines, molding complex parts in multiple cast aluminum molds. In industrialized countries within North America, Europe and Australia, rotational molding is expanding into a wide range of markets other than its traditional one, tanks. Molders and mold makers are seeking more profitable markets with a competitive edge. These sophisticated applications require higher investments in equipment, materials, molds and designs. Despite these trends however, the majority of rotationally molded parts are still tanks. This is especially true in economically developing countries within South America, Africa and Asia where the demand for cost effective water storage tanks is almost unlimited, comprising more than 90% of the market. However molders and resin suppliers in these regions are beginning to recognize the unmatched versatility of rotational molding. Their awareness is being stimulated by publications such as this magazine and information being made available through trade associations such as ARM, ARMO and SPE.

For example, rotational molding is perfectly matched to India’s needs because of the wide latitude of investment, manufacturing and design options offered by the process. These characteristics parallel India’s unique extremes in wealth, education, technology, transportation and market requirements. India has a wide range of climates, population densities and religions. Although English and Hindi are the national languages, India has more than twenty-eight distinct languages spoken in and more than 200 different dialects.  These diverse and complex extremes represent a country with a 7000 year history and rapidly changing economy poised for the 21st century. With a population of more than 3.5 times the US in an area slightly greater than 1/3 the US, (1,065,070,607 people in 1,269,338 sq mi) India’s market opportunities are daunting.

Rotational molding has successfully expanded into numerous markets within industrialized nations due to a combination of technological advancements and competition. Although many of these innovations have gradually evolved from spiraling advancements in processing machinery, molds and materials, growth spurts have typically originated with visionary individuals. People who have applied this process to the right application, at the right time, with a good design have opened new market opportunities and become wealthy. These markets have included toys, containers, kayaks, furniture and material handling applications which now account for the majority of US and European rotational molding applications.

As a matter of fact the annual number of new applications for rotational molding has continually splintered traditional markets into new segments at an unprecedented rate during 16 years. Most of the progress has occurred in industrialized countries because of market saturation and pricing pressures placed on molders. Saturated markets have forced prices to drop providing an incentive for manufacturers to seek improved manufacturing efficiency, mold quality, material selection and design. These improvements have also stimulated ideas for new applications that have not previously been considered as viable for rotational molding. Trends toward improved productivity and sophisticated applications have raised the required investments for this process.

Will economically developing countries like India have to wait decades before rotational molding finds its place in applications other than tanks? The answer is emphatically no. Unlike industrialized countries that have taken more than forty years to apply rotational molding to applications other than tanks, India will change much faster. Rotational molding is ideally suited for India and other developing nations. The versatility of the process provides one the choice of entering the business with a minimal investment to mold tanks or a higher investment to mold more profitable specialty products. This article will present how rotational molding can benefit countries such as India based applications unique to its culture.

India is currently going through a period of rapid economic expansion. Its large labor force and democratic capitalist economy are strategically positioned to compete with China as the world’s next dominant manufacturing country. However, unlike China, India might consume most of what it produces by its population of 1.1 billion. The country’s insatiable need for affordable housing, transportation, sanitation, education, food and clothing provide a huge market for goods and services. These basic needs provide opportunities for distinctively Indian products that are ideally suited for rotational molding.

The first of these would be a bicycle-powered rickshaw. Although rickshaws are seen in other parts of the world, India has a variety of bicycle powered rickshaws that are used to transport people and all types of materials. Many of these vehicles are distinctively decorated, inexpensive and light weight. Some of the requirements for a passenger rickshaw other than those previously cited are listed below:

  • It should be easy to enter and exit
  • It should be durable
  • It should be colorful and easily decorated
  • It should be easily assembled to a bicycle
  • It should be easily customized
  • It should be comfortable
  • It should accommodate two people
  • It should be capable of storing personal belongings
  • It should resemble traditional rickshaws

As one can see from the pictures, India’s rickshaws have a minimal structure. They are typically constructed from a combination of aluminum tube and sheet. A soft cushion is added to the seat for passenger comfort. Frequently drivers decorate the exterior with colorfully ornate patterns for aesthetic purposes as well easy identification. A retractable canopy is sometimes included to provide shade or protection from rain. The sides of the passenger compartment are free from any obstructions to provide easy entry and exit.

What benefits could a rotationally molded passenger compartment offer versus the current materials and manufacturing methods? A rotationally molded compartment would offer many advantages, some of which are listed below:

  • Less expensive
  • Aesthetically more attractive
  • Lighter weight
  • More durable
  • Less parts
  • Molded in color
  • More functional
  • Easier to assemble
  • More comfortable

The concept in Picture 3 represents just one example how a rotationally molded rickshaw could be designed. This concept is based on a two-piece structure including a passenger compartment and a chassis.  Rotational molding would provide an opportunity to cost effectively attain styling freedoms similar to those in automobiles. Polyethylene with molded in colors would eliminate concerns for chipping, denting, and corrosion. High strength to weight ratios achieved with proper design and material selection would yield a very rigid structure capable of withstanding stresses induced by rough roads. Advantages of maintaining bicycle wheels as part of the cab are their light weight, low cost and popularity. The one piece cab would be much stronger than the welded sheet metal cabs which usually fail at weld joints. Structural integrity would be achieved by integrating the overall form with proper reinforcements such as kiss-offs on the underside of the cab.  A rotationally molded one-piece chassis would also provide added benefits of simplifying assembly to a bicycle frame and eliminating concerns for corrosion. Features for mounting wheels and providing a storage compartment could also be easily included within this module. Contrasting color combinations can be applied for another level of design individuality. Features for easily mounting the chassis to the cab body would enable the compartment to be shipped assembled or separately to the user. The cab could also include features to accept a soft cushion, drain holes, and mounting holes for optional canopies. Exterior surfaces could be decorated with traditional ornate Indian textures or molded in graphics for uniquely individualize cabs.

If one were to travel through a city or drive through any countryside within India, one would immediately notice a common sight, the street vendor. There are millions of street vendors throughout India selling everything from apples to clothing from their transportable vending carts. Almost all these carts are constructed in a similar manner based on an upper wooden deck and a lower steel chassis supporting four bicycle wheels. (pic.5 – Traditional Vending Cart). It is not uncommon to see most vending carts seriously deteriorated and weather beaten. However, vendors must still display their merchandise and be able to easily move these carts after their work day is complete. Carts must be sturdy and affordable since vendors have limited financial resources. Although a rotationally molded vending cart might not be readily affordable to everyone, it could be a viable alternative for a percentage of vendors if it offered specific advantages. Some of these advantages and design possibilities are listed below:

  • Provide a means of attractively displaying merchandise
  • Offer an extended life versus wood
  • Attract more customers based on colors and overall design
  • Provide security with closed compartments
  • Be more easily transported and set up
  • Be lighter weight
  • Store more merchandise
  • Be easily upgraded or custom configured
  • Options for thermal insulation for cold storage

Photo 5 shows a concept for a multicolored, modular, rotationally molded fruit vending cart. This concept is based on an interchangeable set of modules that can be configured to satisfy any number of custom user requirements. The red base unit is designed as a one piece rotationally molded chamber which also acts as a chassis. Bicycle wheels which are traditionally used in vending carts can be attached to the base module and protected by the integrally molded in wheel fenders. Integrally molded in hinge knuckles within the main body and doors provide a structurally robust hinge that would be virtually impossible to break. Pad locked hinged doors would permit vendors to store valuable merchandize within secure compartments in the main base. If the spaces between double walled doors and the main body are filled with polyurethane foam, thermal insulation could be introduced. These compartments might then be used for ice cream or chilled beverages.

A yellow foamed polyethylene deck could be sold separately or as part of the system. Features such as shut-offs and recesses to align the lower main chamber have been included for additional stiffness as well as ease of assembly. Displayed merchandise is improved by adding a foldable rack with features to accept a number of optional tiers. These tiers permit fruits to be displayed without damage. After a day’s work emptied racks can be folded and stored way on the main deck.

An optional rotationally molded roof mounted on four steel posts would shield merchandise from sun and rain. The system could be also be expanded to include modular panels between the roof and deck for added security or display surfaces. Another configuration would include a lower cost system sold without the rotationally molded roof, which would be substituted with a cloth canopy provided by the end user. 

One of India’s most valuable resources is its children, who hold the future in their hearts and minds. Their success as adults and India’s destiny will depend on the quality of their education. Today, many of India’s schools lack proper facilities including furniture to adequately satisfy the needs of their hundreds of millions of students. Most of India’s classroom furniture consists of a simple desk and two chairs for each pair of students. Designs are very basic, drab, and uncomfortable because of their painted wood construction. Wooden furniture tends to chip, restricting designs to simple shapes that can be very uncomfortable and have a limited life within environments of highly active young children.

Rotationally molded classroom furniture could cost effectively replace wood with colorful, long lasting tables and chairs. Tables would no longer have to consist of a wooden slab fastened to four legs. Instead, table surfaces could be designed with softer edges and shapes. They could include storage compartments for books, papers and pens. Desks could be designed with four detachable legs for compact shipping. Chairs would be designed for comfort with ergonomically contoured backs and seats mounted to a separate base for easy shipping. Playful colors can be molded as an integral part of the seat to add to enhance the atmosphere of a cheerful learning environment. Chair bases could provide a swivel and tilt feature for added comfort. Rotationally molded furniture would provide a longer life cycle than wood. They would be lighter, chip resistant and very durable. Splinters, broken joints and sanitary problems associated with wood are nonexistent with rotationally molded polyethylene furniture. Rigidity and flatness of the table surface would be optimized with foamed polyethylene. Granite colors can be specified to enhance appearance and the surface texture of desks.

Rotational molding doesn’t have to be limited to portable products. It can be also be used to create parts for permanent architectural structures such as bus stops. Many times the most obvious applications for rotational molding go unnoticed during our daily lives. Bus stop stands of every type are located on thousands of streets throughout India. They are used by millions of people each day who are patiently waiting for trip to their place of work or home. Unfortunately many of these bus stops look run down, have no place to sit and are filled with unsightly graffiti.  Bus stops, like most architectural structures express the culture they are in. Some are frivolous, others classic and many are very functional. India’s architecture is represented by a variety of colors, forms and styles based on its many cultural influences.

The concept shown in Photo 13 illustrates one possible design for a rotationally molded bus stop well suited for India. This system includes only three rotationally molded modules based on 120 cm increments, which permit custom configurations for various length bus stops. Modules would be shipped to a site within compactly stacked pallets and assembled to a steel or aluminum frame on site. The roof would be contoured with a pattern of crisscrossed ribs as shown in Photo 14. The outer ribs would enhance water drainage while the perpendicular ribs on the underside kiss-off to the outer ribs forming a very rigid roof. Attachment points on the underside would permit roof panels to be mounted to the superstructure. Alternating lap joints on the ends of roof panels provide a location for extruded gaskets to be compressed. These sealed joints prevent rain water from entering the bus stand without the labor of caulking.

Molded in slots impart rigidity, design appeal and water drainage to rotationally molded benches. Simple rigid bench designs are easily molded and assembled to the steel super structure with conventional hardware. Similar use of patterned circular openings in the surrounding walls adds rigidity to panels as well as providing a spacious perception for awaiting passengers. Open walls also deter application of graffiti to surfaces. A variety of specific color combinations and traditionally ornate Indian motifs could be substituted for a more obvious expression of Indian culture. After the structure has been erected, wall and roof panels would be quickly assembled, followed by benches. The result would be a cost effective dramatic departure from conventional bus stops used today. Advertising and other information could be restricted to specific areas by placing rotationally molded panels along the top or within limited regions on walls.

These are only a few applications that demonstrate the versatility of rotational molding and its potential applications within emerging economies in countries like India. It is the author’s intension to simulate interest in this process by applying it to products that can be socially beneficial as well as profitable. Markets in India, China and South America represent unlimited opportunities for rotational molders. Concepts such as these will be transformed into reality when visionaries within the industry expand their markets by improving technology and setting their sites on bigger horizons.

Note: This article has been adapted for the RotoWorld® website from Design & Vision RotoWorld® 2005 Issue 1. JSJ Productions, Inc. is the publisher and owns all copyrights herein.

 

Michael Paloian is President of Integrated Design Systems, Inc., Great Neck, New York and Design Editor for RotoWorld® magazine. Over the past 25 years, Mike has developed a broad range of plastic products utilizing various processing methods including rotational molding. Mike’s B.S. degree in Plastics Engineering and Masters in Industrial Design, combined with his extensive experience, has formed the bases for his branded and unique insights into the field of plastics part design.