Next time you see one of Herman Miller Inc.'s hot new Red Rocket desks, Composite Products Inc. wants you to take a good look at the feet that hold it up. CPI makes the feet, and the Winona company claims the product marks the first-ever commercial production of a part made by in-line compounding and compression molding of long-fiber-reinforced nylon.
The Red Rocket is part of Herman Miller's low-cost Red product line. The plastics-intensive office furniture is marketed over the Internet.
Glass-reinforced nylon replaces traditional die-cast aluminum for each of three feet that support the entire desk. The Zeeland, Mich., furniture maker looked at glass-filled polypropylene and glass-filled nylon - each much cheaper than aluminum.
``We knew that a plastic molded part would fit the design aesthetic well, but we suspected that most plastic formulations would not be strong enough,'' said Robert Beck, Herman Miller program manager.
According to CPI, the PP part, with a 40 percent glass reinforcement, did not meet Herman Miller's design standards. So CPI switched over to the stronger nylon 6, also at 40 percent glass.
The plastic foot, dubbed the Stonefoot base, is molded with crush ribs so the table leg fits tightly into the foot.
CPI's patented Direct-Feed Thermoplastic technology uses two extruders, synchronized with a compression transfer molding machine. One extruder melts and mixes resin and additives. The material is conveyed, as a low-viscosity melt, through transition tooling to the rotating screw of a second extruder. The reinforcing fibers, usually glass, are fed to the second extruder, where a section of the screw preheats them, then mixes them with the molten resin mix. The preheating opens the fiber bundles and brings the fibers to the proper temperature, so the resin thoroughly wets the glass. A special design of the second extruder imparts gentle mixing of the melt, minimizing damage to the fibers, so they keep their long shape.
To produce the foot for the Red Rocket table, compounded material exits the second extruder and goes to an accumulator, consisting of an open-ended hydraulic piston and cylinder. When the right amount of material builds up, a blade comes down to cut the preform to the designed length. Still hot, the preform moves to a compression mold.
John Busch, CPI's director of business development, said there is an ``enormous market'' for in-line compounding and molding of nylon, particularly with automotive intake manifolds, valve covers and oil pans.
Busch said CPI no longer is signing new licensing deals for its composites technology. Instead, the company wants to focus on molding as its primary business.