Manufacturing Lime for the Glass Industry

The glass industry, as most others, has placed more rigid specifications on their raw materials in order to make a better finished product which can match the requirements of the high standards of today. The manufacturer of lime and limestone products has therefore a very definite task to perform in controlling the quality and uniformity of his product, be it limestone or burned lime. The present annual consumption by the glass industry is 216,074 tons of burned lime, which represents nearly 9 per cent of the total lime production, and an additional 162,050 tons of limestone. The choice between burned lime and limestone rests with the glass manufacturer, since both are used with good success. There are certain advantages to burned lime: namely, lower shipping cost per ton of oxide and generally more careful inspection of the material shipped. There is generally also less danger of overcrowding a furnace when burned lime is used in the mix since it occupies less space and melts closer to the front end of the tank. In order to be able to manufacture a lime suitable for the glass industry, the lime first of all must have a low iron content and, secondly, must be of uniform chemical composition to insure a proper batch mixture. A good grade of glass-making lime must contain less than 0.15 per cent iron oxide and have a very uniformly low ignition loss. Other impurities such as celestite must be very low. This is especially important in sheet and window glass manufacture.