Furnace and method for heating coated glass sheets

A furnace for heating glass sheets that each have a coated surface and an oppositely facing uncoated surface, comprising:

• a housing defining a heating chamber and having entrance and exit ends;
• a roll conveyor for conveying glass sheets to be heated within the heating chamber along a horizontal conveying plane between the entrance and exit ends of the housing with the coated surface facing upwardly and with the uncoated surface facing downwardly and supported by the roll conveyor;
• electric resistance elements for heating the housing within the heating chamber below and above the conveying plane;
• a hot air distributing system including an array of hot air distributors positioned above the roll conveyor between the entrance and exit ends of the furnace, a source of pressurized air that is located outside the furnace and supplies pressurized air to the hot air distributors, the hot air distributors including heat exchangers for heating the pressurized air prior to delivery therefrom as downwardly directed hot air jets toward the upwardly facing coated glass surface of each conveyed glass sheet, and the hot air jets entrain hot air within the heating chamber and the combined flow of hot air provides convective heating of the coated glass surface in addition to the radiant heating thereof by the electric resistance elements;
• and
• a control including a controller for increasing the forced convection heating of the glass sheet by the hot air distributing system during the glass sheet conveyance to balance the heating and the resultant temperature of the upwardly facing coated surface and the downwardly facing uncoated surface of each conveyed glass sheet being heated, and the controller terminating the supply of pressurized air to the hot air distributors below which there is no coated glass sheet being conveyed.

A furnace for heating glass sheets that each have a coated surface and an oppositely facing uncoated surface, comprising:

• a housing including a lower portion having a flat floor and vertical side walls having upper ends, the housing also including an upper portion of a downwardly opening semicircular shape having lower ends located above the upper ends of the vertical side walls of the lower housing portion such that the housing portions cooperate to define a heating chamber having entrance and exit ends;
• a roll conveyor for conveying glass sheets to be heated within the heating chamber along a horizontal conveying plane between the entrance and exit ends of the housing with the coated surface facing upwardly and with the uncoated surface facing downwardly and supported by the roll conveyor;
• electric resistance elements for heating the housing within the heating chamber below and above the conveying plane, the electric resistance elements being mounted on the floor of the lower housing portion below the roll conveyor and on the semicircular upper housing portion above the roll conveyor;
• a hot air distributing system including an array of hot air distributors positioned above the roll conveyor between the entrance and exit ends of the furnace, a source of pressurized air that is located outside the furnace and supplies pressurized air to the hot air distributors, each hot air distributor including an upper manifold, a vertical support tube having an upper end that is supported by the upper manifold extending downwardly therefrom without direct fluid communication therewith, the support tube having a lower end adjacent the roll conveyor, a horizontal delivery tube that extends in opposite directions from the lower end of the supply tube in fluid communication therewith and has opposite lateral ends, the horizontal delivery tube having downwardly opening delivery orifices, a heat exchanger including a heat exchanger tube having an inlet that is fed pressurized air through the upper manifold and an outlet through which pressurized air heated within the heat exchanger tube is fed to the vertical support tube for flow to the horizontal delivery tube and delivery through the orifices thereof as downwardly directed hot air jets, the hot air jets entraining hot air within the heating chamber and the combined flow of hot air providing convective heating of the upwardly facing coated glass surface of each conveyed glass sheet in addition to the radiant heating thereof by the electric resistance elements, and the heat exchanger tube having inclined portions that extend with an inverted V shape between the upper manifold and the pair of opposite lateral ends of the horizontal delivery tube;
• and
• a control including a controller for increasing the forced convection heating of the glass sheet by the hot air distributing system during the glass sheet conveyance to balance the heating and the resultant temperature of the upwardly facing coated surface and the downwardly facing uncoated surface of each conveyed glass sheet being heated, and the controller terminating the supply of pressurized air to the hot air distributors below which there is no coated glass sheet being conveyed.

A method for heating glass sheets that each have a coated surface and an uncoated surface comprising:

• conveying each glass sheet on a roll conveyor along a horizontal conveying plane within a heating chamber of a housing between entrance and exit ends thereof with the coated surface thereof facing upwardly and with the uncoated surface thereof facing downwardly;
• electrically heating resistance elements located both below and above the conveying plane to provide radiant heat to both the downwardly facing uncoated surface and the upwardly facing coated surface of each conveyed glass sheet;
• supplying hot air jets downwardly toward the upwardly facing coated glass surface of each conveyed glass sheet such that the hot air jets entrain hot air within the heating chamber and the combined flow of hot air provides forced convection heating of the coated glass surface in addition to the radiant heating thereof by the electric resistance elements;
• and
• increasing the forced convection heating by the downwardly directed hot air jets during the glass sheet conveyance to balance the heat supplied to and the resultant temperature of the upwardly facing coated surface and the downwardly facing uncoated surface of each conveyed glass sheet being heated.

A method for heating glass sheets that each have a coated surface and an uncoated surface comprising:

• conveying each glass sheet on a roll conveyor along a horizontal conveying plane within a heating chamber of a housing between entrance and exit ends thereof with the coated surface thereof facing upwardly and with the uncoated surface thereof facing downwardly;
• electrically heating resistance elements located both below and above the conveying plane to provide radiant heat to both the downwardly facing uncoated surface and the upwardly facing coated surface of each conveyed glass sheet;
• supplying pressurized air to heat exchangers of hot air distributors located between entrance and exit ends of the housing to supply hot air jets downwardly toward the upwardly facing coated glass surface of each conveyed glass sheet such that the hot air jets entrain hot air within the heating chamber and the combined flow of hot air provides forced convection heating of the coated glass surface in addition to the radiant heating thereof by the electric resistance elements, and the hot air jet supply being terminated at the hot air distributors when there is no conveyed glass sheet below those distributors on the roll conveyor;
• and
• increasing the forced convection heating by the downwardly directed hot air jets during the glass sheet conveyance to balance the heat supplied to and the resultant temperature of the upwardly facing coated surface and the downwardly facing uncoated surface of each conveyed glass sheet being heated.