Unitl about myself

5. INDUSTRIAL PLASTICS: 
 
RIGID AND FLEXIBLE FOAMS 
Rigid polyurethane foams in sandwich forms have wide applications as building components. They are also the 
best insulants known today and so have wide application in refrigeration and in buildings, where they are applied in 
fitted slab form or are foamed into cavities at the building site. They can also be applied by spraying about six 
millimetres thickness with each pass of the spray gun. The ability to spray a foaming mixture through a single nozzle is 
a great advantage in application. 
A very important use of rigid foam is for furniture parts to reproduce wood structures; these can be injection 
molded. Polyurethane foam can be screwed and nailed with a retention about equal to white pine lumber. 
A major advance in the manufacture of sandwich structures is a new method of injection molding, in which a 
large machine is used to produce moldings up to 1.2 metres square. Moldings of great strength and any desired 
surface are obtained. 
Flexible foams 
Flexible foams, usually polyurethane, are made in slab form up to 2.4 metres in width and as much as 1.5 
metres high; these are then cut to required shapes or sizes or are molded. The molded foams may be hot molded. 
This involves filling heated aluminum castings and gives a product having high resistance to compression, as for 
automobile seats; or they may be cold molded, a process used particularly for semi-flexible foams with high load-
bearing properties. Used almost exclusively by the automobile industry for crash pads, armrests, and dashboard 
covers, the process involves machine mixing the ingredients and pouring them into aluminum molds lined with vinyl or 
acrylo-nitrile-butadiene-styrene skins, which become the cover material for the part. 
Polystyrene foams are made in a wide range of densities, from expandable beads, either by extrusion through 
slot-shaped openings to 40 times the original volume to form boards directly or by foaming in steam chests to form 
large billets. Using small beads in stainless steel molds, cups can be molded with thin sections. 
Thin sheet for packaging can also be made by the tube extrusion technique. Though packaging is a major use 
for forms made in closed molds, the largest use is for building panels; they can be plastered directly. 
Acrylonitrile-butadiene-styrene can be expanded from pellets and is particularly suitable for wood-grain effects 
and for the production of heavy sections. 
Expanded vinyls can be made from plastisols for flooring or textile linings by calendering with a blowing agent 
and laminating to a fabric base, and by injection molding for insulation and such articles as shoe soles. An improved 
material is now obtained from cross-linked polyvinyl chloride and competes with polyester in glass reinforced plastic. 
 

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