Properties of Glass

Forming of Glass

Forming of Glass

Glass is produced by heating its raw material to a temperature above which melting occurs. To obtain optically transparent glass, it is important that the mixture at the elevated temperature be homogenous and nonporous. Homogeneity is achieved by melting and mixing ingredients completely. Porosity, which results from the release of gas bubbles in the molten mixture, can be eliminated by controlling the viscosity of the mixture.

The main forming methods used to fabricate glass are:

  • Pressing

  • Blowing

  • Drawing

  • Fiber forming

Pressing

In this method, the molten mixture of raw materials is poured into a cast iron mold to cast the mixture into the desired shape. The molds used in glass pressing are graphite-coated. These molds are usually heated to ensure an even surface. Pressure is then applied over the mold to yield the desired glass product.

Blowing

In this technique, a temporary shape, called parison, is obtained by glass pressing. This shape is then inserted into a blow mold, and a blast of air is applied. The pressure from this blast of air pushes the material into the contours of the mold to produce the desired shape. Blowing helps produce delicate and intricate objects of art. Nowadays, blowing is an automated process.

Drawing

This method is used to form long pieces of glass, such as rods, fibers, tubes, and sheets, with a constant area of cross-section. This process involves the cold or hot rolling of glass. The surface finish in this method is improved by floating the...