TECHNICAL INFORMATION
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Glossary of Glass Fabricating Terms
TECHNICAL INFO.
refractive index —the ratio of the speed of light in vacuo to the speed of light in glass.. The value of the refractive index is given for the sodium D line (589.3 mµ and the values listed are for annealed glass. ring —(1) a floating refractory body surrounding a glass surface from which gathers are made. (2) a mold part that forms the rim of a pressed article. sagging process —of forming glass by reheating until it conforms to the shape of the mold or form on which it rests. sealing surface —the portion of the finish which makes contact with the sealing gasket or liner. (See also finish .) seam, n —mark on glass surface resulting from joint of matching mold parts.
from slow solution of a large grain of sand or foreign material.
tank —a melting unit, in which the container for the molten glass is constructed from refractory blocks. temper —(1) the degree of residual stress in annealed glass measured polarimetrically or by polariscopic comparison with a standard such as one or more strain disks. (2) term sometimes employed in referring to tempered glass. (See also tempered glass ). tempered glass —glass that has been rapidly cooled from near the softening point, under rigorous control, to increase its mechanical and thermal endurance. Thermal Conductivity —data has been calculated for three temperatures from compositions. thermal shock resistance —an estimated figure based on the expansion coefficient. updraw —the process of continuously drawing glass of various cross sections, such as cane or tubing, by a method similar to the Fourcault process. volume resistivity —is equivalent to the electrical resistance in ohms across a sample in the form of a cube 1cm x 1cm x 1cm. Because of the wide range of values obtained at the different temperatures, the log 10 of the volume resistivities are listed. Values are on annealed glass. washboard —an imperfection; ripples, waves, etc., on the surface of glassware.
seam, v —to slightly grind the sharp edges of a piece of glass.
seed —an extremely small gaseous inclusion of glass.
sharp fire —combustion with excess air and short flame.
shear mark —a scar appearing in glassware, caused by the cooling action of the cutting shear. silica glass —vitreous silicon dioxide (SiO 2 ). silk screen process —a decorating process in which a design is printed on glass through a silk mesh, woven wire, or similar screen. soda —sodium oxide (Na 2 O). Loosely, a carbonate of sodium. softening point, SP —the temperature at which a uniform fiber, 0.55 to 0.75 mm in diameter and 235 mm in length, elongates under its own weight at a rate of 1 mm/min when the upper 100 mm of its length is heated in the manner prescribed in ASTM Method C338. Test for Softening Point of Glass at a rate of approximately 5 C/min. For glass of density near 2.5, this temperature corresponds to a viscosity of 10 76 poises. stability —(1) resistance to devitrification. (2) chemical durability, resistance to weathering. stain —(1) an imperfection; chemical corrosion on the surface of glass. (2) color applied to glass by absorption at an elevated temperature.
water glass —sodium silicate glass that is soluble in water.
wave —an optical effect due to uneven glass distribution, or to striae.
weathering —attack of a glass surface by atmospheric elements.
working range —the range of surface temperature in which glass is formed into ware in a specific process. The “upper end” refers to the temperature at which the glass is ready for working (generally corresponding to a viscosity of 10 3 to 10 4 poises), while the “lower end” refers to the temperature at which it is sufficiently viscous to hold its formed shape (generally corresponding to a viscosity greater than 10 6 poises). For comparative purposes, when no specific process is considered, the working range of glass is assumed to correspond to a viscosity range from 10 4 to 10 76 poises. Young’s Modulus —the modulus of elasticity. The stress required to produce a unit change of length.
stones —an imperfection or crystalline contaminations in glass.
strain point, StP —the temperature corresponding to a rate of elongation of 0.00043 cm/min when measured by ASTM Method C 336. This test prescribed a linear extrapolation of the data obtained in the annealing point determination to the above designated rate. Internal stress is substantially relieved at the strain point in a few hours. stress —any condition of tension or compression existing within the glass, particularly due to incomplete annealing, temperature gradient, or inhomogeneity. stria —a cord of low intensity generally of interest only in optical glass. (See also cord .)
string —an imperfection; a straight or curled line, usually resulting
NOTE: For additional definitions of terms relating to glass and glass products, see ASTM Standard C162.
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