Steam molding

Isotactic Polystyrene. The familiar steam molding of pre-expanded particles has so far not been applied successfully to isotactic polystyrene. However, the polymer has been foamed, according to three disclosed methods. For example, finely divided acetone-insoluble polymer, with a melting point in excess of 200°C., is blended with a liquid selected from methylene chloride, aromatic hydrocarbons, or halogenated aromatic hydrocarbons. This blend is then heated (84). A mixture of molten polymer and methyl chloride, propane, or butane is suddenly depressurized (8). Foam may also be generated in a continuous manner directly from a butyllithium-initiated polymerization conducted in the presence of a 4/1 blend of benzene and petroleum ether (15). 

The production and application in 1967 of 193 million pounds of polystyrene foam reflects considerable scientific, engineering, and commercial activity. The continuing growth of expandable polystyrene in this field is attributed to its ability to be steam molded economically into a variety of useful items. 

Polystyrene (PS) Structural polystyrene foams are molded by injection and expansion-casting methods. They have a strong continuous skin and a foam cote. Their densities are quite high, ranging from 20 to 40 lb/ft3, in contrast to the 1 to 5 Ibs/ft range of the steam-molded and extruded polystyrene foams discussed below (11). Compared to other structural foams, however, the densities are relatively low (see Table 3-1). 

Steam-Chest Expansion. In steam-chest expansion the resin beads in which gas is already present are poured into molds into which steam is injected. The steam increases the temperature close to the melting point and expands within the stmcture to create beads with food cushioning and insulating properties. Expanded polystyrene is widely used in this process for thermal insulation of frozen food packaging. 

By comparison, temperatures as high as 150°C are often required for mold-enclosed hard natural mbber compounds, where mold plattens are directly heated by steam or electricity. Synthetic latex mbber compounds, however, can be vulcanised at temperatures higher than those for natural mbber neoprene and acrylonitrile—butadiene can be vulcanised at as high as 135°C. 

The basic resin for EPS is in the form of beads that ate expanded to a desired density before molding. Densities for packaging parts are typically 20—40 kg/m. Once expanded, the beads are fused in a steam-heated mold to form a specific shape. Most parts are molded of standard-white resins, although several pastel colors are available. 

Calcium Silicate Brick. Sand—lime brick is used ia masonry ia the same way as common clay brick. The bricks, molded from a wet mixture of sand and high calcium hydrated lime, are heated under pressure ia a steam atmosphere. Complex hydrosiUcates are formed that give the bricks high dimensional stabiUty (6). 

Copper(II) oxide [1317-38-0] can also cause porosity in the finished casting by combining with hydrogen formed by the dissociation of water in the mold material to form steam within the melt, thus causing holes during solidification. 

More specific recipes appear in Table 3. The ingredients are added to the elastomers on standard two-roU mills or in internal mixers. Finished compounds are readily extmded, calendered, or molded in standard equipment. Vulcanisation of extmdates is accompHshed in Hve steam autoclaves, Hquid salt baths, fluidized beds, and microwave equipment. 

The development of microporosity during steam activation was examined by Burchell et al [23] in their studies of CFCMS monoliths. A series of CFCMS cylinders, 2.5 cm in diameter and 7.5 cm in length, were machined from a 5- cm thick plate of CFCMS manufactured from P200 fibers. The axis of the cylinders was machined perpendicular to the molding direction ( to the fibers). The cylinders were activated to bum-offs ranging from 9 to 36 % and the BET surface area and micropore size and volume determined from the Nj adsorption isotherms measured at 77 K. Samples were taken from the top and bottom of each cylinder for pore sfructure characterization. 

Process of molding or laminating in wliich fluid pressure is applied, usually by means of water, steam, air or vacuum, to a flexible film or bag that transmits the pressure to the material being molded. 

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