TECHNICAL INFORMATION
415
Glossary of Glass Fabricating Terms
Glossary of Glass Fabricating Terms
anneal —to prevent or remove objectionable stresses in glassware by controlled cooling from a suitable temperature. annealing point, AP —the temperature corresponding to a rate of elongation of 0.0136 cm/min when measured by ASTM Method C 336, Test for Annealing Point and Strain Point of Glass by Fiber Elongation. This test prescribes a rate of cooling of approximately 4 C/min with a fiber of approximately 0.065 cm in diameter, and a suspended load of 1000 g. The annealing point numerically approximates log = 13.0 poises, where internal stress is substantially relieved in a few minutes. annealing range —the range of glass temperature in which stresses in glass articles can be relieved at a commercially desirable rate. For purposes of comparing glasses, the annealing range is assumed to correspond with the temperatures between the annealing point (AP) and the strain point (StP). batch —the raw materials, properly proportioned and mixed, for delivery to the furnace. batch charger —a mechanical device for conducting a batch to the furnace. batch house —the place where batch materials are received, handled, weighed, and mixed for delivery to melting units. bead— (1) an enlarged, rounded edge of a tumbler or other glass article, or any raised section extending around the article. (2) a small piece of glass tubing used around a lead wire. blank —(1) a parison or preliminary shape from which a finished article is further formed, or mold for producing same. (2) any article of glass on which subsequent forming or finishing is required. blister —an imperfection; a relatively large bubble or gaseous inclusion. bloom —a surface film resulting from attack by the atmosphere or from the deposition of smoke or other vapors.
out of an otherwise regular surface.
continuous tank —a glass furnace in which the level of glass remains constant because the feeding of batch continuously replaces the glass withdrawn. Contraction Coefficient —is the decrease in length per unit length per °C change in temperature of the glass when it is cooled from the annealing point to 25°C. This figure is useful in considering the glass for sealing to metals or other materials, because the contraction characteristics influence the final stresses in such seals. cord —an attenuated glassy inclusion possessing optical and other properties differing from those of the surrounding glass. crack-off —the process of severing a glass article by breaking, as by scratching and then heating. cullet —(1) waste or broken glass, usually suitable as an addition to raw batch. (2) foreign cullet — cullet from an outside source. (3) domestic cullet (factory cullet) — cullet from within the plant. (4) the portion of a glass article that will later be cut off and discarded or remelted. Danner process —a mechanical process for continuously drawing glass cane or tubing from a rotating mandrel. density —the weight per unit volume. Values listed are reported in grams per cubic centimeter.
devitrification —crystallization in glass.
dielectric constant —is the ratio of the parallel capacitance of a capacitor with the material as the dielectric to the capacitance of the same capacitor with a vacuum as the dielectric. The dielectric constant determines the amount of electrostatic energy which can be stored in a material per unit volume per unit potential gradient. dielectric loss factor —is the product of the dielectric constant and the dissipation factor. At low values (below 1) the dissipation factor is less than 5% different than the power factor so the power factor can be used for most calculations. The power lost in a dielectric is directly proportional to the loss factor if voltage gradient and frequency remain constant. dielectric power factor —the cosine of the dielectric phase angle or its equivalent expressed in percent and represents the energy lost in the dielectric in an alternating current field.
blower —one who forms glass by blowing. (See also gaffer .)
blowpipe —the pipe used by a glassmaker for gathering and blowing by mouth. Also known as blowing iron. blown glass —glassware shaped by air pressure, as by mouth blowing or by compressed air. blow mold —the metal mold in which a blown glass article is finally shaped. borosilicate glass —any silicate glass having at least 5% of boron oxide (B 2 O 3 ), like Kimble® 33 expansion borosilicate glass. burn-off —the process of severing an unwanted portion of a glass article by fusing the glass. chain marks —marks made on the bottoms of slightly overheated glass articles as they ride through a lehr on a chain belt.
distribution —the thicknesses of the walls of a glass article over its entire area.
down-draw —process of continuously drawing glass downward from an orifice. dummy —a mechanical device, operated by the blower’s feet, for wetting, raising, opening and closing the paste mold in mouth-blown glassware. etch —to attack the surface of glass with hydrofluoric acid or other agent, generally for marking or decoration. etched —(1) treated by etching. (2) weathered so that the surface is roughened.
check —an imperfection; a surface crack in a glass article.
chemical durability —the lasting quality (both physical and chemical) of a glass surface. It is frequently evaluated, after prolonged weathering or storing, in terms of chemical and physical changes in the glass surface or in terms of changes in the contents of a vessel. chip —an imperfection due to breakage of a small fragment
Powered by FlippingBook