Gunning mixes

Refractories may be preformed, ie, shaped, or formed and installed on-site, ie, specialties. Iimovations in placement and vessel constmction has led to a greater emphasis on specialty refractory products. Castables, gunning mixes, and plastic and ramming mixes are used either for repair or for complete new constmction of what is known as monolithic linings. The tendency to use monolithics instead of constmctions using shaped products has been steadily increasing. As of the mid-1990s, monolithic installations are as common as conventional shaped product constmction. 

Fixing as constants those variables that are not open to change (for example, selecting a particular type of coating pan, spray gun, mixing baffle design, pan loading, etc.). 

Other common refractory forms include setter tile and kiln furniture, fusion-cast shapes, cast and hand-molded refractories, insulating refractories. castables and gunning mixes, plastic refractories and ramming mixes, mortars, composite refractories, and refractory coatings,... 

Colloidal silica was used in general foundry applications such as gunning mixes, ceramic mold facings for core boxes and the like, mold washes, and semi-permanent molds with renewable facings. It was also used in the production of wallboard (Figure 4). 

Spray-up is similar to hand lay-up except that the glass reinforcement and resin are applied to the gel coat simultaneously by a gun. The gun mixes catalyst and resin and sprays this onto the surface. At the same time, a chopper fitted with rotating blades cuts continuous rovings (strands) of glass fibers into lengths of 1/2 to 1 inch. These are impelled into the stream of resin which carries them onto the mold, wetting them in the process. The layers are rolled to remove air as in hand lay-up. This process is much faster and less labor-intensive than the hand process. 

Two forms of refractories products are universally recognized (1) formed or preshaped refractories, which includes bricks of numerous shapes such as keys, wedges, and arches and (2) monohthics, which includes mortars and cements, plastics, ramming mixes, castables, and gunning mixes. Various classifications exist for these products. 

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