LFI process: Molding strong and attractive spa enclosures

Dynasty Spas (Athens, Tenn.) finds a composite alternative to wood hot tub surrounds in a polyurethane (PU)-based long fiber injection (LFI) solution implemented by Romeo RIM Inc. (Romeo, Mich.).


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After a composite spa tub is outfitted with heaters, piping and other hardware, an attractive surround, or cabinet, is needed to hide those working parts. In the past, cabinets were often redwood or, more recently, narrow extruded tongue-and-groove plastic boards molded to resemble wood, which needed to be assembled. Dynasty Spas (Athens, Tenn.) found a cost-effective and durable alternative when it turned to a polyurethane (PU)-based long fiber injection (LFI) solution implemented by Romeo Engineering Inc. (Romeo, Mich.).

LFI was originally developed by Krauss-Maffei Corporation (Munich, Germany, and Florence, Ky.), and Romeo RIM says it was the first molder to use the process in North America. In the LFI process, a robotic mix head equipped with a glass chopper lays down the glass fiber while simultaneously spraying the PU resin mixture into a compression mold. The mold compression cycle ranges from 7 to 15 minutes.

Each surround side panel is molded in one piece, eliminating the extra wood ties, fasteners and staples or glue necessary to assemble smaller-sized components. The mold, which is textured with a woodgrain effect, is first treated with an inmold paint. Romeo then uses trademarked Baydur STR 675 PU resin from Bayer MaterialScience LLC (Pittsburgh, Pa.) to make the part. A glaze is applied, postmold, to the 70-lb/32-kg surround, which has a 35 percent fiber volume. Matt Getty, business unit manager for consumer products at Romeo RIM, says LFI  not only produces an attractive product with exceptional strength-to-weight, dimensional stability, and impact-, heat- and chemical-resistance, but also offers significant processing advantages over other materials/processes.  “Our long fiber injection process uses Bayer’s polyurethane system to manufacture a spa cabinet with the superb impact-resistance and stylish finish that Dynasty Spas desired,” says Getty.

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