Polyurethane foam molding, mold-filling

Civil engineering uses include large diameter pipe for culverts and air ducts and energy-absorbing highway safety devices such as crash barriers filled with polyurethane foam and barrels filled with sand installed around bridge abutments. On a more down-to-earth level, the components of portable privies are frequently rotationally molded. 

Recendy, storm doors have been constmcted of advanced thermoplastic composites. Stampable, glass-mat reinforced polypropylene sheet is used to create a high strength outer skin. These compression molded skins are welded together using a friction or ultrasonic process then injection molded with a polyurethane foam core to produce an insulated structure. New technology for window frames incorporate the pultrusion of frame channels to produce a thermoset composite channel that can be filled with fiber glass for further insulation enhancement (12,31,33,34,48,49,54—56,60—67). 

As an example glass RP boats in use are visually almost indistinguishable from traditional, but more expensive, wooden craft. Slightly higher tech is the Raptor Sportjet, an advanced personal watercraft (PWC) produced in North America. Although hand laid in glass fiber molds and room temperature cured, the all-glass prototype incorporates 0°/90° woven fabric and stitched triaxial reinforcement as well as chopped strand mat. Hull cavities are filled with two-part polyurethane foam for buoyancy and noise reduction. 

Reaction injection molding (RIM) is a fast, low-pressure, low-temperature, low-cost process for one-step conversion of reactive liquids into large finished solid plastic products. Liquid polyol and liquid diisocyanate are mixed by impingement, pumped instantly to fill a large mold cavity, and polymerize/ cure rapidly to form a thermoset polyurethane product. The cured polymer may be a stiffly flexible product such as automotive bumper covers, front ends, and trim or a rigid foamed product such as furniture and housings (cabinets) for computers, business machines, TY and radio. 

BP Chemicals have developed a polyurethane (PU) system for the production of integrally-molded sand-insulated carpets. The carpet is laminated with a PU backing to improve shape retention. It is then placed in a mold and PU foam is injected to fill the space between the car floor contours and the carpet. A carpet made with the system has been in use in the Fiat Turbo Uno. 

Recently, prototype molds are being fabricated from particle-filled polyurethane and epoxy syntactic foams using computer-aided multiaxis routers. Plugs, used to mechanically prestretch polymer sheet, are also usually machined from syntactic foams. For certain pol5miers, heated aluminum plugs or solid nylon plugs are desired. 

Acoustic barriers consist of a low-density layer and a heavy (usually highly filled) layer. Glass fibers, foams, EVA, SEES compounds (injection molded), asphalt-ics, and thermoset polyurethanes are used. 

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