Machine Design

Composite keeps deep-drawn luggage cover gleaming

Interior parts for public buses are designed for durability, safety, and appearance, an exacting balance that leaves little margin for tradeoffs. One such part, thr luggage cover for use on mass transit buses is produced by composites specialist Amtech LLC in Wapato, Wash.

The cover measures 5 × 4 × 3 ft. and is fabricated in a deep-draw vacuum-forming process that generates a remarkable 40 in. (1,016 mm) draw. The interior layer is glass-reinforced epoxy vinyl ester resin; the core is a proprietary bonding material; and the outer layer is 0.180 in. gauge thermoplastic sheet from Boltaron in Newcomerstown, OH.

The original laminate had a gel coat surface that didn’t withstand the harsh conditions and occasional abuse the luggage covers receive in service and during assembly. “The finish didn’t hold up well in the field and needed numerous repairs,” he says.

In contrast, the proprietary Boltaron sheet, Grade 4800, with impregnated color, ensures that part-to-part aesthetics are consistent. The sheet also works better in deep-draw vacuum forming, getting greater surface texture resolution with fewer surface contaminants during forming.

The material deters graffiti vandals because the specified sand finish doesn't let graffiti from felt pens and other markers adhere well. It is easy to clean.

The extruded sheet is fire retardant and designed specifically for mass transit interiors. It meets ASTM E-162 and ASTM E-662 requirements for flammability and low smoke emissions and FTA, UMTA, and Docket 90A guidelines. The material has good impact strength, abrasion resistance, stain and chemical resistance, and thermoformability. It comes in custom colors and a range of textures, and maintains lot-to-lot consistency. The sheet is available in 0.040 to 0.250 in. gauges, widths to 60 in., and lengths to 120 in.

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