CompositesWorld
Issue link: https://cw.epubxp.com/i/450689
FEBRUARY 2015 48 CompositesWorld FOCUS ON DESIGN helped guide material decisions to enhance composites manu- facturability. He says Ferno's frst requirement was that each leg support up to 318 kg (the iN∫X is rated at 318 kg total). Second, each pair of legs must accommodate, through their length, the pulleys and wires required to raise and lower the legs. Te pulleys and wires are necessitated by another important function factor of iN∫X, as Valentino notes: "Wheel set distance is constant, regardless of cot height, so the legs must adjust their position under the cot to maintain wheel distance." Tis gives the cot, and EMTs, a fxed and unchanging wheel position, which opti- mizes wheel function and maneuverability. To accomplish this, the tops of each set of legs must slide along the underside of the cot as the wheels are raised and lowered. (Leg oper- ation is illustrated in a video available at the Ferno Web site: www.fernoems.com/inx.) To meet all of these design and function requirements, Bendickson and Citadel recommended a two-piece hollow design for each leg. Tis would allow Ferno to place pulley hardware inside the legs during assembly and allow Citadel's fabricators the ability to adjust wall thickness and other design elements more easily to meet load and weight requirements. Tat was a fortuitous decision. Late in the development process, Ferno decided that the weight limit on each leg should be almost doubled, to 590 kg, because designers wanted to ensure that any one leg, if absolutely necessary, would support more weight than the entire cot would ever bear. "We wanted to make sure the legs weren't the weak link," Valentino reports. Tis required, says Bendickson, some changes in sheet molding compound (SMC) charge placement, as well as part wall thickness increases, but was relatively easily done, given the two-piece leg concept. Ultimately, the hollow design evolved to include, at the narrow end of the legs, an I-beam structure, which terminates at attach- ment points under the cot. Te design also features four support arms for the legs, also made by Citadel and also of two-piece, hollow design. Material, manufacturing options Although the decision to go with a composite had been made early, the time had come to make specifc material choices. Carbon fber mat and unidirectional carbon fber were evalu- ated, but Bendickson says carbon fber SMC was selected because the legs "needed fber that ofered a variety of orientations for strength." Supplied by Citadel's Quantum Composites facility (Bay City, MI, US), the SMC, branded AMC 8590, features 12K tow (nominal 25.4 mm fber length) in a vinyl ester resin matrix. Citadel molds the leg halves in a compression-based process. It then machines holes into each half to accommodate support arm attachment points, wheel hardware, fasteners and thread- cutting screws and through-bolts, which are used to attach the leg halves together. Notably, leg halves are not adhesively bonded. Bendickson notes that hole-drilling is, therefore, particularly critical: "Close hole tolerance is needed for good holding power and service on the cot," he says. Already introduced into the EMS market via trade show demonstrations in 2014, the iN∫X, according to Wells, has been well received. Although the iN∫X sports a bigger price tag than the conventional cots on the market, customers reportedly see its value and understand the weight-management advantages the cot provides to EMTs. "We see it as a way to not only help EMTs do their job, but as a way to extend their careers as frst responders," says Wells. Ferno started shipping the frst iN∫X units in January 2015. Read this article online | short.compositesworld.com/EMTcot Ambulatory & Adaptable Ferno worked with Citadel Plastics (North Kingsville, OH, US) to develop the carbon fber/SMC legs, which feature a two-piece shell design that accommodates cables and pulleys for leg extension and retrac- tion. Each leg on the iN∫X is designed for a load of up to 590 kg, which is twice the overall load rating of the entire cot. Source / Ferno Jef Sloan is editor-in-chief of CompositesWorld, and has been engaged in plastics- and composites-industry journalism for 22 years. jef@compositesworld.com