Glass manufacturing – Processes – Glass preform treating
Reexamination Certificate
2000-01-10
2001-08-28
Colaianni, Michael P. (Department: 1731)
Glass manufacturing
Processes
Glass preform treating
C065S118000, C065S119000, C065S273000, C065S356000, C065S355000, C219S388000, C219S476000, C432S094000, C432S128000, C432S130000, C432S133000, C432S136000, C432S159000
Reexamination Certificate
active
06279349
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method for heating glass sheets, a furnace for heating glass sheets, and a method for making the furnace that heats the glass sheets.
BACKGROUND ART
Glass sheets are heated for processing such as forming, heat strengthening, or tempering, etc. Such heating is conventionally performed by either electric resistance-type furnaces or by forced convection furnaces. Prior electric resistance-type furnaces are disclosed by U.S. Pat. Nos. 3,934,970 McMaster et al., 3,947,242 McMaster et al., and 3,994,711 McMaster, all of which have lower and upper housing portions that support electric resistance elements that provide radiant heating of glass sheets from below and above at their lower and upper surfaces during conveyance within a heating chamber of the furnace housing. Prior forced convection furnaces are disclosed by the U.S. Pat. Nos. of Kenneth R. Kormanyos: 5,669,954; 5,672,191; 5,735,924; 5,762,677; and 5,792,232, all of which have lower and upper forced convection heaters that provide forced convection heating of conveyed glass sheets from below and above at top and bottom surfaces of the glass sheets.
Electric resistance furnaces for heating glass sheets are less expensive to initially manufacture than forced convection furnaces for heating glass sheets and also can be more easily controlled by less involved control apparatus. In addition, electric resistance furnaces for heating glass sheets also result in a greater percentage of the energy input being transferred into the glass for the heating. However, electrical energy is more expensive than natural gas heating and the radiant heating involved cannot efficiently heat low emission-coated glass. Furthermore, radiant heating cannot uniformly heat glass coated partially with paint bands or reflective coatings used in the automotive industry because the coated area absorb more or less radiant heat than adjacent uncoated areas.
Forced convection furnaces for heating glass sheets are not as efficient as electric resistance furnaces since a certain volume of heated air must be continually removed from the furnace to make up for the volume of combusted gas that is being introduced. However, this loss in efficiency is offset by the lower cost of natural gas as compared to electrical energy such that the operational cost for forced convection furnaces are effectively less than for electric resistance furnaces.
DISCLOSURE OF INVENTION
One object of the present invention is to provide an improved method for heating a glass sheet.
An object of the present invention is to provide an improved method for making a furnace for heating glass sheets.
In carrying out the above object, the method for making a furnace for heating glass sheets in accordance with the invention is performed by providing a glass sheet roll conveyor furnace of the electric resistance heater type having a housing including lower and upper portions for respectively supporting lower and upper electric resistance elements below and above a roll conveyor including conveyor rolls within the furnace. In making the furnace, the roll conveyor and the lower housing portion of the furnace are maintained for supporting the lower electric resistance elements below the conveyor rolls such that electrical power supplied thereto provides heating from below of the glass sheets conveyed by the conveyor rolls. The upper housing portion of the furnace above the roll conveyor is removed. The furnace manufacturing also involves installing another upper housing portion and a gas burner forced convection heater supported thereon above the roll conveyor to provide a dominant mode of external heat for heating the conveyed glass sheets from above.
The preferred practice for making the furnace is also performed by installing the gas burner forced convection heater with hot gas distributors spaced along a direction of conveyance of the furnace. This installation of the forced convection heater is performed with a gas burner on one lateral side of the furnace, with a mixing tube that mixes return air and products of combustion, and with a plenum housing that is located at another lateral side of the furnace to receive the mixed return air and products of combustion from the mixing tube as a hot gas flow that is fed to the hot gas distributors. The preferred installation of the forced convection heater is also performed with the plenum housing having an intake that receives the mixed return air and products of combustion at one lateral side of the plenum housing, and with the plenum housing having a supply blower located therein at another lateral extremity of the plenum housing to provide pressurizing of the mixed return air and products of combustion as the hot gas flow.
The objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.
REFERENCES:
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patent: 5609785 (1997-03-01), Sallinen et al.
patent: 5669954 (1997-09-01), Kormanyos
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patent: 5735924 (1998-04-01), Kormanyos
patent: 5762677 (1998-06-01), Kormanyos
patent: 5792232 (1998-08-01), Kormanyos
patent: 5915958 (1999-06-01), Kurie
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Glafurit, Radiation high convection combi-furnace for GVG-Bietigheim, Glass-Technology International, Jan. 1998, pp. 114-118, Glafurit—Germany.
Brooks & Kushman P.C.
Colaianni Michael P.
Glasstech, Inc.
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