Vitreous enamel undercoating for sheet metal objects - where frit includes mixt. of di:phosphate, orthophosphate and aluminate to eliminate need for fluoride flux

摘要

The enamel frit consists of two mixts., viz. (I) a base mixt. of silica flour, feldspar, silicates, borax and alkaline earth cpds. etc.; plus (II) a combination of sodium- or potassium- diphosphate with tert.- sodium- or potassium- phosphate, lithium phosphate, Li2CO3, and sodium- or potassium- aluminate. The constituents in mixt. (II) are pref. present in equal amts. The frit pref. contains 2.5-12.5, esp. 4-6 wt.% of mixt. (II); and mixt. (I) pref. contains as % of the total wt. of the frit, 18-32% silica flour, 14.25% feldspar, 4% NaNO3, 8-10% soda, 22-26% dehydrated borax. The frit is mixed with a liq. and used as the base- or under-coating on sheet metal or objects made out of sheet metal. Conventional frits include a fluoride flux, e.g. CaF2, which creates noxious vapours and creates expensive waste disposal problems. The invention employs no fluoride but still provides an enamel with good fluidity during melting and baking.