Preformed Shapes

Preformed shapes are made from refractory castables and ramming mixes. After shapes are formed, they are dried and tempered at the manufacturer s plant. Therefore, they can be put into service immediately. At the site, expenditures involving molds, installation, and heat-up can be reduced. Preformed shapes, such as burners, injection lances for pig iron or steel treatment, gas purging systems, or impact blocks for the bottoms of steel ladles, are examples of functional refractory products. Some of the advantages in using the preformed shapes are as follows  

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The refractory used to constmct the hearth can be in the form of bricks, preformed shapes, or monolithic. Often a furnace design utilizes all three. Openings or passageways through the walls are fashioned in the same manner as windows in a brick building. 

Preforms. Preformed shapes may be made by depositing glass fibres on to a preform mould. The fibres are then held together by spraying them with a binder. 

The reinforcements amenable to RTM are similar to those used for pultrusion, except that they need not be continuous in nature. Thus, E-glass, S-glass, aramid, and carbon fibers are commonly used, as are discontinuous filaments such as wood fiber and polyesters. Even metal and ceramic fibers can be used in this technique. In one method, the preform is fabricated by spraying 12- to 75-mm-long chopped fiber rovings onto a preshaped screen. A binder sprayed with the fibers keeps them in place and holds the preform shape, which is then placed in the mold. 

B. Reaction cavities with very stiff walls and preformed shapes... 

B. Reaction Cavities with Very Stiff Walls and Preformed Shapes and Sizes Silica Gel and Zeolites... 

Refractories may be preformed (shaped) or formed and installed on-site. Castables, gunning mixes, and plastic and ramming mixes are used either for repair or for complete new construction of what is known as monolithic linings. The use of monolithics instead of constructions using shaped products has increased monolithic installations have become as common as conventional shaped product construction. 

There are several common forms of solid epoxy adhesives. These include film, tape, powder, and preformed shapes. Certain formulations are better suited for specific forms. For example, casting of tape or film adhesive from solvent solutions lends itself to working with multicomponent hybrid systems, where each resin can be solubilized and blended together in a universal solvent. B-staged systems are generally more brittle and better suited for powders or preformed adhesives. 

During sintering, a powder of particles of a given size is pressurized at elevated temperatures in a preformed shape so that the interface between the particles disappears. Microfiltration membranes can thus be obtained from PTFE (polytetra-fluoroethylene), PE (polyethylene), PP (polypropylene), metals, ceramics, graphite and glass, with pore sizes depending on the particle size and the particle-size distribution. Porosities up to 80% for metals and 10-20% for polymeric membranes can be reached with pore sizes varying between 0.1 and 10 pm. Most of these materials have excellent solvent and thermal stability. 

The early type of catalytic cracking units involved the use of a fixed-bed operation and this type of processing has been largely supplanted by the fluid- and moving-bed types of operation. The catalysts are used in the form of powder, microspheres, spheres, and other preformed shapes. The catalysts employed are either synthetic silica-alumina composites or natural aluminosilicates. Other catalysts, such as silica-magnesia, alumina-boria, silica-zirconia, and silica-alumina-zirconia have found limited commercial application and, at present, the synthetic silica-alumina and natural clay catalysts dominate the field. 

SERPENT The preformed shape of explosive composition or an integral... 

After molding, the sheet is typically turned into rods or other preform shapes to facilitate subsequent machining operations by orthopedic manufacturers. Thus, the final shape of UHMWPE stock material today is not necessarily dictated by the conversion method. 

One-part epoxy adhesives include solvent-free liquid resins, solutions in solvent, liquid resin pastes, fusible powders, sticks, pellets and paste, supported and unsupported films, and preformed shapes to fit a particular joint. Two-part epoxy adhesives are usually comprised of the resin and the curing agent, which are mixed just prior to use. The components may be liquids, putties, or liquid and hardener powder. They may also contain plasticizers, reactive diluents, fillers, and resinous modifiers. The processing conditions are determined by the curing agent employed. In general, two-part systems are mixed, applied within the recommended pot life (a few minutes to several hours), and cured at room temperature for up to 24 hours, or at elevated temperatures to reduce the cure time. Typical cure conditions range from 3 hours at 60°C to 20 minutes at 100 C. ... 

Parison A hollow tube or other preformed shape of thermoplastic compound which is inflated inside a mold in the blow-molding process. 

Near-net-shape configuration n. In reinforced plastics molding, designating a fibrous-preform shape very close to the shape the perform will take after resin impregnation and curing in the mold, such that no lay-up and little or no trimming after molding are required. 

Parison n. The hollow tube or other preformed shape of molten thermoplastic that is inflated inside the mold in the process of blow molding. Most commonly, the parison is extruded immediately before blowing, but parisons are also injection molded and may also be chilled and stored, to be reheated before blowing. In the earliest application of blow molding, a pair of calendered sheets joined along the edges was used as the parison. 

The research groups of Tormala (Tampere University, Finland), Tunc (Johnson andjohnson, New Jersey, USA) and Ikada (Kyoto University,Japan) have developed methods for producing what are termed self-reinforced PL and PG devices. The process published by Tunc and Jadhav for PL devices has been identified as an orientrusion process. These technologies involve the molding and orientation of a preformed shape. The oriented preform is then machined or further processed during the manufacture of the device. This orientation results in a finished device with significantly improved tensile and flexural strength (Lautiainen et al., 1994 Vainionpaa et al., 1987 Tunc and Jadhav, 1988 Shimamoto et al., 1995 Ikada et al, 1990). 

Foam-based catalytic combustion was one of the earliest applications, and a number of novel designs have been suggested [27-30]. These include combustion of hydrogen [27], light hydrocarbons [28, 29]rand natural gas [30]. Ceramic foams are attractive for combustion devices because of improved turbulence and mixing, together with preformed shapes configured to suit specific equipment. 

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