Cover coat

Waterproof Finishes. Waterproofing results from coating a fabric and filling the pores with film-forming material such as varnish, mbber, nitroceUulose, wax, tar, or plastic. The materials may be appHed as hot melts, eg, waxes or some polymers, as solvent solutions, or as aqueous latexes. The continuity of the film provides the water resistance. Except for tents, tarpauHns, and covers, coated fabrics have been largely replaced by plastics, and by fabrics treated with water and oU repeUents that do not reduce permeabUity to air and water vapor. Eabrics are also commonly laminated to films, such that the total stmeture is waterproof (15), or in some cases water-resistant but breathable (16). 

Adhesion of Enamel to Steel. Cobalt compounds are used both to color and to enhance adhesion of enamels to steel (55). Cobalt oxide is often incorporated into the ground frit at rates of 0.5—0.6 wt %, although levels from 0.2 to 3 wt % have been used. The frit is fired for ten minutes at 850°C to give a blue enamel that is later coated with a white cover coat. 

Oxide s Ground coats Cover coats Aluminum enamels ... 

Eor the cover-coat direct-on process, a ferric sulfate [10028-22-5] Ee2(S0 2> etch is included in the metal pretreatment for rapid metal removal. It is designed to remove ca 20 g/m (2 g/ft ) of iron from the sheet metal surface. Hydrogen peroxide [7722-84-1/, H2O2, is added intermittently to a 1% ferric sulfate solution to reoxidize ferrous sulfate [7720-78-7] EeSO, to ferric sulfate. 

Typical ranges of enamel compositions are Hsted in Table 2. Raw materials (Table 1) for the glass batch include minerals, such as feldspars and quartz, because these are inexpensive sources of Si02 and AI2O2 (see Clays). The batch composition for cover coats is comprised primarily of manufactured chemicals of known, controlled levels of purity to maintain reproducible, clean colors. 

Titanium Dioxide. The recrystallization of titanium dioxide in a cover-coat glass is very important to the development of thin, highly opaque finish coats. Titania, Ti02, is the primary opacifying agent for white finish coats. Two polymorphic forms of titania, anatase and mtile, may be present in... 

A.dherence to Porcelain Enamel Cover Coats Direct to Steel, PEI Bulletin T-29(72), Porcelaiu Enamel Institute, Washiagton, D.C., 1972. 

Belag, m. covering, coating, lining, plating, belagem, v.t. besiege. 

Belegung,/. covering, coating, coat charge, belehren, v.t. instruct, advise. 

Xarzinom, n. (Med.) carcinoma, karzinomatos, a. carcinomatoiis. kaschleren, v.t. cover, coat, line, back hide, conceal. 

Tani, T. Lakeman, C. D. E. Li, J.-F. Xu, Z. Payne, D. A. 1994. Crystallization behavior and improved properties for sol-gel derived PZT and PLZT thin layers processed with a lead oxide cover coating. Ceram. Trans. 43 89-106. 

Lamp covers coated with titanium oxide thin-film photocatalysts... 

The Gehman test is also standardised in BS903 Part A1318 and ASTM D105319. The British Standard is identical to the international method but the ASTM has a rather different layout as it covers coated fabrics as well as rubbers and a single point procedure is added for routine inspection. It only specifies a step temperature change procedure. 

Cover coats such as self-opacified titanium enamels derive their color firoui titanium dioxide crystals nucleated in the glass during tiring of the coating. 

The thickness of the enamel layer varies with the type of use and metai. However, typical thicknesses are from 75 to 150 pm t.3 to 6 mils) for sheet steel, 175 to 359 pin (7 to 14 mils) for hot-rolled steel. 100 to 125 pm 4 to 5 mils) Tor each coat of wet process cast iron (760 lo 7RR C fire). 15 lo 25 pm (0.5 to I mil) for dry process cast-iron base coats and 750 pm (average) to nearly 2250 pm (30 mils to 90 mils) for ihe dusted cover coats (898 to 955 C tires), and 25 to 50 im (I to 2 mils) for aluminum alloys. Stainless steel and copper may have enamel coalings from 40 pm to 175 pm 11.5 to 7 mils) ihick. 

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