Seed in Glass Melted in Tank Furnaces

JSGT 1939 V23 T005-T016

 Possible sources of seed in glass are (1) gases resulting from the melting batch, (2) entrapped air in the batch, (3) gases from porous refractory materials. Possible sources of boil are (1) dissolved gases coming out of solution, (2) reaction between glass constituents, (3) reaction between glass and either some agent in the refractories or some foreign matter. In carbon amber glasses there is a strong tendency to boil when reheated, not necessarily to a higher temperature than that of original melting, and the boil may be associated with reaction between the carbon and residual sulphate.

It is considered that reaction between batch constituents is the least likely cause of seed; for quite small particles of batch give rise to large bubbles of carbon dioxide. Entrapped air and moisture are regarded as the most likely sources of small seed, and calculations show the possibility of introducing about 1000 seeds of 0.08mm diameter into 1cc of glass, and a still greater number of small seeds. Even a fairly dense, well-fired refractory may be the source of seed in glass, with the possibility of introducing 280 seeds of 0.075mm diameter into 1cc of glass, and possibly others from pores of smaller diameter. The risk is particularly increased when refractories of fairly high porosity are employed at the working end of a tank furnace. The methods of calculation and procedure for determining seeds in glass are described.

J. B. Murgatroyd, B.A.