Smelting of Frits

In frit manufacture the raw materials of the particular frit recipe are intimately mixed, fed into the furnace and smelted. Various furnace types can be used  

Most enamels melt at ca. 1250°C. Only a few difficult to melt frits require temperatures of ca. 1350°C. The raw materials are smelted, but not, as in glass manufacture, refined. Fig. 5.4-1. schematically. shows the construction of drum and flame-heated tank furnaces. 

In drum furnaces molten frits upon emerging from the outlet are quenched in water forming granules. The smelt from continuous furnaces flows over water-cooled rollers to a crusher, forming flakes. 

Part of the raw material mixture evaporates during smelting fluoride (as hydrogen fluoride, silicon and boron fluorides) and nitrogen oxides are formed in addition to water and carbon dioxide. Effective scrubbing of the flue gases is therefore necessary, which is easier with an electrically heated furnace than with a gas-heated one. 

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