Foams polyurethane cores

Foamed polyurethane. The basic chemicals are mixed in the liquid state with foaming agents, and swell into a low-density foam which sets by polymerization into a rigid mass. As the swelling material will expand into any shape required, it is ideal for the core of sandwich panels, and the sheet material skins may be flat or profiled. When the panels are manufactured the mixture is injected between the inner and outer skins and expands to the thickness required, adhering to the lining materials. 

Different core materials are used. They include foam, honeycomb core (plastic, paper, aluminum, etc.), ribs, balsa wood, filler spacers, corrugated sheet spacers, etc. Materials such as polyurethane foam, cellulosic foams, and polystyrene foams are widely used as core materials. Plastics, such as glass-reinforced polyester, are frequently used as the skins for panels. Different skin materials are used such as metallic skins alone or in conjunction with plastic skins. 

Certain incinerator chimneys are in hybrid stainless steel with an inner lining in sandwich resin/glass fibres with a core in foamed polyurethane. 

The clean critical size, reflector savings, and temperature coefficients were measured tor two 1.8% enriched cores with water to uranium volume ratios of 4.4 and 6.0 (excluding control rod water channels and axial water gaps). In addition the clean critical size was obtained for the 1.59% enriched core. The clean critical size and reflector savings were also measured for the 1.8% cores containing 18% and 14% voids (ratio of void to water plus voids), respectively. The voids were obtained by inserting low density (9 Ib/ft ) foamed polyurethane void simulators between fuel rows to obtain a uniform displacement of water. These simulators are coated to reduce wafer absorption to a negligible value. The measurements are summarized in Table I. 

Various geometric coring patterns ki polyurethanes (171,175) and ki latex foam mbber (176) exert significant influences on thek compressive behavior. A good discussion of the effect of cell size and shape on the properties of flexible foams is contained ki References 60 and 156. The effect of open-ceU content is demonstrated ki polyethylene foam (173). 

Water-borne adhesives are preferred because of restrictions on the use of solvents. Low viscosity prepolymers are emulsified in water, followed by chain extension with water-soluble glycols or diamines. As cross-linker PMDI can be used, which has a shelf life of 5 to 6 h in water. Water-borne polyurethane coatings are used for vacuum forming of PVC sheeting to ABS shells in automotive interior door panels, for the lamination of ABS/PVC film to treated polypropylene foam for use in automotive instmment panels, as metal primers for steering wheels, in flexible packaging lamination, as shoe sole adhesive, and as tie coats for polyurethane-coated fabrics. PMDI is also used as a binder for reconstituted wood products and as a foundry core binder. 

The foams, marketed by Rohm as Rohacell, are stable at room temperature to hydrocarbons, ketones, chlorinated solvents and 10% sulphuric acid. They may be used under load at temperature up to 160°C. Uses quoted for these materials include bus engine covers, aircraft landing gear doors, radar domes, domes, ski cores and tennis racket cores. Their potential is in applications demanding a level of heat deformation resistance, solvent resistance and stiffness not exhibited by more well-known cellular polymers such as expanded polystyrene and the polyurethane foams. 

The plastic insulants are rigid, homogeneous materials, suitable as the core of sandwich panels. Such a method of fahrication is facilitated when using foamed rigid polyurethane, since the liquids can he made to foam between the inner and outer panel skins and have a good natural adhesion, so making a stiff structural component [40]. 

Since the stiffness of a laminate varies as a cubic relationship with the thickness, there are alternate methods employed to achieve thickness - and hence stiffness - than by using multiple layers of fiberglass and resin. Lightweight core materials, such as end-grained balsa wood, high-density polyurethane foam, PVC foam, and honeycombed materials, are available. These materials are sandwiched in between layers of unsaturated polyester resin to achieve increased laminate stiffness. The common terminology used for this technique is sandwich construction . 

It is mainly used in the industrial production of rigid polyurethane foams. Many other uses are in the fields of coatings, adhesives, sealants and elastomers such as paints, adhesives, weather-resistant sealing materials and foohvear. There is use also in the production of particle board (bonding of wood) and mould cores for the foundry industry (European Union, 1999). 

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 for the mattress core, natural latex is the environmentally preferred stuffing, a rubber-tree product that can be sustainably sourced. Some mattresses are stuffed with a mix of natural and synthetic latex, as the latter substance is cheaper (although chemicals are added in the manufacturing process). Both choices are better than the polyurethane foam found in most conventional mattresses. Still other mattress cores have an innerspring system and batting, often cotton. In-nerspring mattresses are a popular crib choice some people think their firmness prevents SIDS. 

Polyurethane rigid structural foam was one of the earliest applications for RIM. Lightweight and rigidity characterize the material. It consists of a solid skin and a lower density cellular core. Use includes equipment housings, furniture, building components, fancy tires,266 and a variety of industrial and consumer applications (Table 12.1). 

Fig. 6a and b. Volumetric weight distribution of (a) polyurethane foam and (b) polystyrene (1) intermediate (core) layer (2) surface layer... 

Sandwich elements or composites with a core of polyurethane rigid foam are widely used for the construction of walls and fagades as well as for roofs of industrial buildings, warehouses, cold storage facilities, supermarkets, airports, sports facilities, school buildings, garage doors and so on (Sommerfeld, 1996). 

AMS 3725-84 Core, Polyurethane Foam (Polyether), Rigid, Cellular, 7 PP... 

BS 4541 1970 Specification for Polyurethane Interior Foam Cores for Domestic Mattresses for Adults, 9 pp... 

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