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Beads. he traditional method of overcoming such defects has been the use of ground and polished plate glass. Plate glass was first produced at Saint Gobain, France, in 1668, by pouring glass into an iron table and rolling it flat with a roller. After annealing, the plate was ground and polished on both sides. Plate glass is now made by rolling the glass continuously between double rollers located at the end of a forehearth. After the rough sheet has been annealed, both sides of it are finished continuously and simultaneously. Grinding and polishing are now being supplanted by the cheaper float-glass process. In this process flat surfaces are formed on both sides by floating a continuous sheet of glass on a bath of molten tin. The temperature is high enough to allow the surface imperfections to be removed by fluid flow of the glass. The temperature is gradually lowered as the glass moves along the tin bath, and the glass passes through a long annealing oven at the end. |
Wholesale Beads Bottles, cosmetic jars, and other glass containers are produced by an automatic process that combines pressing (to form the open end of the container) and blowing (to form the hollow body of the container). In a typical automatic bottle-blowing machine, a gob of molten glass is dropped in a narrow, inverted mold and forced down by an air blast into the lower portion of the mold, which corresponds to the neck of the finished bottle. A baffle then drops over the top of the mold, and a blast from the bottom, up through the neck, partly forms the bottle. The half-formed bottle, called a parison, is held by the neck, inverted, and then lowered into a second finishing mold, in which another air blast blows it out to its finished dimensions. Optical glass differs from other glass in the way in which it bends, or refracts, light. The manufacture of optical glass is a delicate and exacting operation. The raw materials must be of the highest purity, and great care must be taken so that no imperfections are introduced in the manufacturing process. Small air bubbles and inclusions of unvitrified matter will cause distortion on the surface of the lens. Striae, the streaks caused by incomplete chemical homogeneity in the glass, will also cause serious distortion, and strains in glass caused by improper annealing will further impair optical qualities. In recent years a method has been adopted for the continuous manufacture of glass in platinum-lined tanks, using platinum-lined stirrers in the cylindrical end chambers (or homogenizers). This process produces greater quantities of optical glass that are cheaper and superior to glass produced by the earlier method.
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