Wet-process enamels for cast iron

Abstract

Wet process enameling of cast iron is becoming of importance because of its application to the enameling of stove parts, sanitary fittings and hardware. This paper is a report of an extended investigation of wet process enamels for cast iron, in connection with the use of a ground coat. Compositions used in dry process enameling have served as a basis for the work, which includes a study of ground coats and white cover enamels. The effect of varying methods of preparing the frits, mill additions, and the relation of composition of the enamels to such properties as adherence, texture and opacity have been carefully studied. Ground Coats.—Sintering of most ground coat frits has been found desirable in order to develop best adherence on the castings. Clay gave best results as a mill addition for the groundvt and feldspar were found to be less satisfactory. Excessive additions of clay or flint produced flaking of the ground coat while feldspar tended to develop blistering. About 15 per cent of clay or 10 per cent each of clay and flint are recommended as mill additions for the ground coats. Excessive additions of any one flux were not desirable, and best results were obtained when sodium, lead and boric oxides were combined in more or less definite pro-portions. Sodium oxide in excess of about 10 per cent gave rise to blistering. Boric oxide increased the firing range of the ground coats and was preferable to lead oxide on this account, although it tended to promote crawling of ground coats high in boric oxide if they were applied somewhat heavily. The best ground coats developed are Rg-26, 17, 1, 25 and 18. Cover Enamels.—Cover enamels were smelted in the usual manner. The mill additions consisted of 5 per cent of clay, 8 per cent of tin oxide, and 45 per cent of water, all based on the weight of the dry frit. For best results, the cover enamel must he adapted to the ground coat in refractoriness. Boric acid increased the firing range of the enamels but tended to promote crawling, although this was less pronounced in the case of the more fusible compositions. Boric oxide improved the opacity when suhsituted for such fluxes as sodium and lead oxides. Cryolite increased opacity but additions above 10 per cent, based on the melted weight, tended to promote crawling. Considering all factors, cover enamels R-14 11, 28, 1 and 18 gave best results.