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A. Plug in and unplug kiln during each operational use. This will prevent accidental burnout of kiln elements after firing.II. TEMPERATURE CONTROL
B. Keep the kiln at least 12 inches away from any combustible materials during firing.
C. A sheet of asbestos at least 1/4 inch thick should be kept under the kiln while firing.
D. Do not move the kiln any more than is necessary.
A. Set the control dial to desired setting. The automatic control will maintain a set temperature.
B. The control dial is very accurate. " DO NOT CHANGE THE SETTING."
C. Pyrometer may not read the same as the control dial do to altitude, humidity and/or shipping.
D. If the pyrometer does not read the same as the temperature control dial, it can be reset by turning the small screw on the face of the pyrometer.
E. Pyrometer should be set at working temperature, (i.e., 1050 °F).
F. To annealing borosilicate glass set control dial at 1050 °F.
A. Do not touch heating element while the kiln is plugged in.
B. Do not use any objects that conduct electricity near or around the heating element while the kiln is plugged in, this can results in serious injuries.
A. Clearances height with the door up 32" (-0 +2")
B. Clearances depth 21" (-0 +1")
C. Clearances width 21" (-0 +1")
The annealing of glass is a problem of great practical importance to all glassblowers. When glass is cooled without special annealing treatment, it is usually strained and subject to breakage. Although a polariscope is not absolutely essential in a glassblowing shop, it is a useful piece of equipment.
Annealing in an oven, or kiln, is the most satisfactory method, since the entire piece of glass is heated and cooled uniformly and the temperature control is more accurate. However, if you are working on a small piece of glass, it can be flame annealed then at a later date it can be placed in a kiln with several other pieces for a thorough annealing. Flame annealing consists of heating the glass in a soft, bushy flame (gas- air) until it has been uniformly softened. The glass is at the proper temperature for annealing when it is bathed in a soft, orange (sodium) flame. The annealing temperature is gradually decreased by lowering the flame temperature and this heating is continued until a layer of soot has been deposited from the gassy flame which is used last. The glass should be laid aside to cool in such a manner that the hot glass does not come in contact with any cold surface. Flame annealing requires good technique and judgment on the part of the glassworker, since it is necessary to heat the article uniformly and avoid overheating, with the resultant softening and deformation of the articles being annealed. Some professional glassblowers anneal glass with gas oxygen flames. Excellent results may be quickly obtained this way by the experienced worker. For the beginner, the danger of either not annealing the glass or of over annealing and causing sag, cannot be emphasized too strongly. When at all possible, the use of gas-air burner for annealing is recommended.
The strain points, shown in Table I, is the temperature at which internal strains will be reduced to acceptable values in about four hours, and it may be cooled quickly from this temperature with no damage; at this temperature glass has a viscosity of 1014.5 poises.Annealing point:
Annealing depends on two factors: time and temperature. As the temperature increases, the time to relieve strain is decreased. The annealing temperature shown in Table I is the temperature at which internal strains will be reduced to acceptable values in 15 minutes and which is not high enough to cause the glass to change shape under its own weight; at this temperature glass has a viscosity of 1013.0 poises.Softening point:
The softening point, as shown in Table I, is the temperature at which the sample will deform under stress of its own weight; at this temperature glass has a viscosity of 107.6 poises,Working Temperature:
The working point, as shown in Table I, is the temperature corresponding to a viscosity of 104 poises, an arbitrary viscosity chosen representing the range where most working is usually accomplished. This does not constitute a recommendation as to the proper temperatures for all work.Coefficient of Expansion:
The rate of expansion of glasses is of the utmost importance to the glassblower. The successful joining of glass, either to other types of glass or to other materials, such as metals and ceramics, requires that the material joined have nearly the same coefficient of expansion. The coefficient of expansion is determined by measuring the change in length of glass for a one-degree Centigrade increase in temperature. Table I gives the expansion in centimeters per °C and shows the average coefficient of expansion at the temperature range 0 to 300 degrees °C. (32 to 572 degrees °F.). The joining of glass with different coefficient will develop stresses in the glass and can be easily seen with the polariscope.
This information was provided by GLASS LINE Newsletter. Additional information on annealing and viewing the stress in glass with a polariscope can be obtained from GLASS LINE - Volume 2, Number 5.
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Pyrex® is a registered trademark of Corning Glass Works Corning, N.Y.
Kimax® is a registered trademark of Owens, IL.
Duran® is a registered trademark of Schott Glaswerke, Mainz, W. Germany.
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