Manual Wheelchair Materials
The materials used to build a manual wheelchair vary greatly. How the wheelchair will be used, and the price of the chair, can mean the difference in durability, aesthetics, function, ride, comfort and cost.
The majority of manual wheelchairs are made of either aluminum or steel. High-end, meaning ultralight wheelchairs or sport wheelchairs, are typically being constructed of exotic materials such as high performance aluminum, titanium and advanced composites. The choice of one material over another depends on the material’s strengths and weaknesses and how that chair will be used.
If you watch what goes on in the aerospace industry, you see those trends gliding into the manual wheelchair market. This happens because the two industries deal with similar issues (e.g., strength versus weight, cost, and reliability). This can be seen in the progression from steel alloys, to aluminum, titanium and more recently advanced composite materials.
The types of common alloy steel typically used in manual wheelchairs are mild steel (AISI 1040 or 1060), chromium-molybdenum alloy steel (AISI 4130) or chromium-nickel-molybdenum alloy steel (4340 and 8620).
The types of aluminum used in manual wheelchairs are SAE 2024, SAE 6061, and SAE 7075, though SAE 2024 is not used as often as the other two.
Advanced composites also have been making the transition to wheelchair design from aerospace and industrial applications. Composites are carbon fiber, fiberglass, and Kevlar®. Composites come as cloth, tape or yarn and are woven to form special layers that are held together by resin (i.e. often epoxy-based). To achieve greatest strength a minimum amount of epoxy must be used while wetting all of the fibers. To increase the strength and stiffness of structural components, a foam (e.g., Styrofoam, urethane, or PVC) core is used to separate the cloth layers.
Composites also can be molded into elaborate shapes, which open a multitude of possibilities for wheelchair design. Molding, specifically for curved pieces, allows for the design of wheelchairs with fewer joints. This is important since the majority of frame failures occur at joints (bolted or welded). Also, complex shapes provide the greatest benefit to individuals who use a wheelchair because:
On the other hand, the ability to produce complex shapes can be considered a downside of composites; these shapes may require intensive manual labor, which is not cost effective. However, new technologies in the production of composite components and frames are being introduced which should reduce the manufacturing costs. Composites are currently used in order to reduce the weight of the casters and the rear wheels, while improving the aerodynamics of the rear wheels, which is important for racers. Also, the Everest and Jennings Barracuda uses composites in the frame.
The different types of material are used depending on the desired functionality of the wheelchair.
Material with a high strength-to-weight ratio (e.g., aluminum, titanium, or composite) may allow for an inconspicuous wheelchair, so the individual is seen before the wheelchair in a social setting. An inconspicuous wheelchair also means a lighter wheelchair, allowing for easier propulsion and maneuverability. Reduction in weight may also lead to a reduction in secondary injuries such as repetitive stress injuries. These injuries may be a result of wheelchair propulsion or lifting the wheelchair during car/van transfers.
Though cost may not be a primary concern to the individual, it automatically becomes one as soon as a third-party payer gets involved. Obtaining a lighter, more durable, and consequently more expensive wheelchair with exotic materials (e.g. titanium and composites) may be justified by a reduction in the dollars per life cycle and in the costs incurred while treating a repetitive stress injury. Therefore, the selection of the material used in manual wheelchairs is a function of the durability, aesthetics, function, ride comfort, and cost of the wheelchair, as well as the wheelchair purchaser.
Once the required material characteristics are known, the most appropriate material and associated manufacturing process can be selected to meet the overall needs of the consumer.
Cooper, R. A., Rehabilitation Engineering: Applied to Mobility and Manipulation, 1995, Institute of Physics Publishing, Ltd., Philadelphia, ch. 7, pp. 255 – 290.
Cooper, R. A., Wheelchair Selection and Configuration, 1998, Demos Medical Publishing, Inc., New York, ch. 3, pp. 43 – 88.
June, R. R., "Aerospace Materials" in The Engineering Handbook, Dorf, R. C., ed., 1995, CRC Press, Inc., Boca Raton, FL, ch. 175, pp. 1849 – 1855.
Cooper, R. A., "A Perspective on the Ultralight Wheelchair Revolution", Technology and Disability, v. 5, pp. 383-392, 1996.
Cooper, R. A., Robertson, R.N., Lawrence, B., Heil, T., Albright, S. J., VanSickle, D. P., and Gonzalez, J., "Life-Cycle Analysis of Depot versus Rehabilitation Manual Wheelchairs", Journal of Rehabilitation Research and Development, v. 31, pp. 45-55, 1996.
Cooper, R. A., Gonzalez, J., Lawrence, B., Rentschler, A., Boninger, M. L., and VanSickle, D. P., "Performance of Selected Lightweight Wheelchairs on ANSI/RESNA Tests", Archives of Physical Medicine and Rehabilitation, v. 78, pp. 1138-1144, 1997.
Cooper, R. A., DiGiovine, C. P., Rentschler, A., Lawrence, B. M., and Boninger, M. L., "Fatigue-Life of Two Manual Wheelchair Cross-Brace Designs", Archives of Physical Medicine and Rehabilitation, v. 80, pp. 1078-1081, 1999.
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