MXPA01005752A - Forced convection furnace and method for heating glass sheets - Google Patents

Abstract

A forced convection furnace (20) and method for heating glass sheets includes a forced convection heater (42) having lower hot gas distributors (44) located below alternate conveyor rolls (38) to provide upward gas flow both upstream and downstream thereof along a direction of conveyance to provide heating from below of the glass sheets being conveyed within a heating chamber (32) of a housing (22) of the furnace. The forced convection heater (42) also includes upper hot gas distributors (52) for providing heating from above of the glass sheets being conveyed within the heating chamber (32).

Description

FORCED CONVECTION OVEN AND METHOD FOR HEATING GLASS LEAVES TECHNICAL FIELD This invention relates to a forced convection oven and to a method for heating glass sheets (lamellas) in preparation for processing.

BACKGROUND OF THE INVENTION The prior art discloses forced convection ovens for heating glass sheets in preparation for processing, such as modeling, tempering, heat strengthening, annealing (heat setting) and coating, etc. Such forced convection ovens of the prior art for heating glass sheets are described by Kenneth R. Kormanyos United States Patents: 5,669,954; 5,672,191; 5,735,924; 5,762,677 and 5,792,232. In the Kormanyos patents, the glass sheets are transported on a roller conveyor during heating, which is carried out by upper and lower groups of hot gas distributors supplying pressurized hot gas flows to the surfaces REF: 129553 inferior and superior of the glass sheets transported. An associated lower hot gas distributor is located between each pair of adjacent conveyor rollers, so that the spent off gas must flow down between the conveyor rollers and the hot gas distributor. In addition, any broken glass that is placed between the conveyor rollers and the lower hot gas distributors must be removed before further heating of the glass sheets begins.

BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to provide an improved forced convection oven for heating glass sheets. By carrying out the above objective, the forced convection oven for heating glass sheets according to the invention includes a housing having a heating chamber and a roller conveyor which is located inside the heating chamber of the housing and has horizontally extending conveyor rollers for transporting sheets of glass along a direction of transport within the heating chamber for heating. A forced convection oven heater includes: lower hot gas distributors located below the alternating conveyor rollers, and each lower hot gas distributor includes a full hot gas (ventilation system in which air is forced into a confined space of so that the outgoing air pressure is greater than the inlet pressure, and the direction of leakage is outward, rather than inward) and a pair of rows of ducts to supply hot gas from the distributor thereof, for upward flow adjacent to the associated conveyor roller, both upstream and downstream thereof, along the transport direction, to provide heating of the lower part of the glass sheets that are transported inside the heating chamber. The forced convection heater also includes upper hot gas distributors to provide heating above the glass sheets that are transported within the heating chamber by the roller conveyor. In the preferred construction of the forced convection oven, the upper hot gas distributors include: rows of nozzles that align with the nozzle rows of the lower hot gas distributors, to provide the aligned lower and upper locations of the hot gas that collides with the glass sheets that are going to heat up. The preferred construction of the forced convection oven also has the pair of nozzle rows of each lower hot gas distributor constructed to include the nozzles that are laterally spaced from one row to the other laterally in an alternating transverse relationship with respect to the direction of transport. further, the preferred construction of the lower hot gas distributors has a dimension along the direction of transport equal to the diameter of the conveyor rollers. The forced convection heater of the furnace is preferably constructed so that each lower hot gas manifold includes a U-shaped housing, having a pair of spaced apart side portions and a connecting portion extending between its side portions. Each lower hot gas distributor also includes an inverted U-shaped cover received within the U-shaped housing thereof, and has a pair of spaced apart side portions and a cover portion extending between its side portions. The spaced apart lateral portions of the U-shaped housing and the spaced apart portions of the inverted U-shaped cover of each lower hot gas distributor cooperate to define the pair of rows of ducts therein, through which the hot gas flows. up towards the transported glass sheets that are going to heat up. In addition, the inverted U-shaped cover portion of each lower hot gas distributor preferably has an inverted V shape for dropping the broken glass. Two described embodiments of the forced convection heater each have the lower hot gas manifold constructed as previously defined and one embodiment has the U-shaped housing of each lower hot gas distributor made of sheet with its spaced apart side portions formed to define duct ducts cooperating with the spaced apart lateral portions of its inverted U-shaped cover, to define the pair of duct rows of the lower hot gas distributor. In another embodiment, each lower hot gas distributor includes nozzle spacers located between the spaced apart side portions of its U-shaped housing and the spaced apart portions of its inverted U-shaped cover, to cooperate therewith, to define the couple of rows of ducts of the lower hot gas distributor. The preferred construction of the forced convection heater also has the upper hot gas distributors constructed the same as the lower hot gas distributors, but inverted, to provide heating from above the transported glass sheets. In this manner, each upper hot gas distributor has a full hot gas and includes an inverted U-shaped housing, which has a pair of spaced apart side portions and a connecting portion extending between its side portions. Each upper hot gas distributor also includes a U-shaped cover received within the inverted U-shaped housing thereof and has a pair of spaced apart side portions and a cover portion extending between its side portions. The spaced apart lateral portions of the inverted U-shaped housing and the spaced apart portions of the U-shaped cover of each upper hot gas distributor, cooperate to define a pair of rows of ducts therein, through which the gas hot flows from the full hot gas down, to the transported glass sheets that are going to heat up. The upper hot gas distributors can also be incorporated as the modes of the lower hot gas distributors. Specifically, one embodiment has the inverted U-shaped housing of each upper hot gas distributor made of sheet and has its lateral portions spaced apart to define nozzles cooperating with the spaced apart portions of its U-shaped cover, to define the pair of duct rows of the upper hot gas distributor. The other mode of the top hot gas distributor includes nozzle spacers, located between the spaced apart lateral portions of its inverted U-shaped housing and the spaced apart lateral portions of its U-shaped cover, to cooperate with these to define the pair of duct rows of the upper hot gas distributor. Another object of the present invention is to provide an improved method for heating glass sheets. Carrying out the immediately preceding objective, the method for heating glass sheets is carried out by transporting the glass sheets by means of a roller conveyor, on horizontal conveyor rollers spaced along a direction of transport inside a housing of the heating chamber . The flow of hot gas is supplied from the bottom of the roller conveyor upwards, adjacent to the alternating conveyor rollers, both upstream and downstream thereof, along the direction of transport, to provide the heating below of the transported glass sheets. The flow of hot gas is also supplied from the top of the conveyor downwards, to provide the top heating of the transported glass sheets. In the preferred practice of the method, the glass sheets are heated by flows of hot gas which are supplied up and down the aligned nozzles, to provide the aligned lower and upper locations of the hot gas colliding with the glass sheets which they are going to heat up The objects, features and advantages of the present invention are readily apparent from the following detailed description of the best form for carrying out the invention, when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a perspective view of a forced convection oven for heating glass sheets according to the invention. FIGURE 2 is a partial side elevational view of a furnace partially cut to illustrate a roller conveyor and the upper hot gas distributors of a forced convection heater of the furnace. FIGURE 3 is a cross sectional view of the furnace taken along line 3-3 in Figure 2, to further illustrate the construction of the furnace housing, roller conveyor and forced convection heater. FIGURE 4 is a sectional top plan view taken along the direction of line 4-4 in Figure 3, to further illustrate the construction of the forced convection heater. FIGURE 5 is a sectional view taken in the same direction as Figure 2, but on an enlarged scale to illustrate the conveyor rollers, the glass sheet to be heated and the upper and lower hot gas distributors of the forced convection heater . FIGURE 6 is an elevational view illustrating the construction of hot gas distributors of the forced convection heater. FIGURE 7 is a sectional view taken along line 7-7 in Figure 6, to further illustrate the construction of the hot gas distributor. FIGURE 8 is a view taken along the direction of line 8-8 in Figure 6, to illustrate the hot gas distributor. FIGURE 9 is a sectional view illustrating the construction of a hot gas distributor embodiment. FIGURE 10 is an elevational view taken along the direction of line 10-10 in Figure 9, to further illustrate the construction of the hot gas distributor. FIGURE 11 is a plan view taken along the direction of line 11-11 in Figure 9, to further illustrate the construction of a hot gas distributor embodiment. FIGURE 12 is a sectional view taken in the same direction as Figure 9 of another embodiment of the hot gas distributor. FIGURE 13 is an elevational view taken along the direction of lines 13-13 in Figure 12, to further illustrate the construction of this embodiment of the hot gas distributor. FIGURE 14 is a plan view taken along the direction of line 14-14 in Figure 12, to further illustrate the construction of this embodiment of the hot gas distributor.

BEST WAY TO CARRY OUT THE INVENTION With reference to Figure 1 of the drawings, in general, a forced convection oven for heating glass sheets is indicated by 20 and is constructed according to the invention, to carry out the same method as described more fully later. The oven 20 and the method of the invention will be described in an integrated manner to facilitate an understanding of all aspects of the invention. The forced convection oven 20 includes a housing 22 having the upper and lower housing portions 24 and 26. More specifically, the housing 22 includes an armature 28 and insulator 30 which is supported by the armature to define a heating chamber 32. The adjustable brackets 33 of the oven frame 28 densely place the upper housing portion 26 on the lower housing portion 24. Between the lower and upper housing portions 24 and 26, the seals of the conveyor roller 34 provide the sealing of the chamber of furnace heating 32 as described more fully below. Continuing with reference in Figure 1, and further reference to Figures 2 and 3, the furnace 20 also includes a roller conveyor 36 located within the heating chamber 32 of the housing 22 and, has the horizontally extending conveyor rollers 38 to transport the glass sheets G along a transport direction A (Figures 1 and 2), inside the heating chamber for heating. The conveyor roller 38 as illustrated in Figures 1 and 3, has the ends 40 extending outwardly through the seals 34 on the opposite side sides of the furnace, to be at ambient manufacturing temperature, to allow rotational operation thereof in any conventional manner without any consideration related to heat. As illustrated in Figures 1-3, the furnace 20 includes a forced convection heater 42 that includes lower hot gas distributors 44, which are located as shown in Figures 2 and 5, below the alternating conveyor rollers 38. More specifically, as illustrated in Figure 5, each lower hot gas distributor 44 includes a full hot gas 46 and a pair of duct rows 48 for supplying the hot gas from the distributor thereof for upflow, as it is illustrated by the arrows of the gas jet 50 adjacent the associated conveyor roller 38, both upstream and downstream thereof along the direction of transport A, to provide heating from below of the glass sheets G which are transported inside the heating chamber. The forced convection heater 42, collectively illustrated in Figure 3, as also illustrated in Figures 2 and 5, includes the upper hot gas distributors 52 to provide heating from above the glass sheets that are transported within the chamber of heating by the roller conveyor. With the construction of the furnace as described above and, specifically the construction of the lower hot gas distributors 44 of the forced convection heater, the hot gas which then strikes the glass sheet can escape downward, as shown by the arrows 54 and, there is also room for any broken glass to fall down without requiring any removal of the conveyor 36. Continuing with reference in Figure 5, it will be noted that the upper hot gas distributors 52 include the nozzles 48 that provide the rows of ducts aligned with the duct rows of the lower hot gas distributors 44, so that the flows of the gas jet downward as shown by the arrows 56 provide the lower and upper location of the hot gas colliding with the glass sheets G that are going to heat up.

With reference to Figures 9 and 12, two different embodiments of the hot gas dispensers are illustrated and are specifically designed to be constructed as the lower hot gas distributors 44 and in the preferred embodiments, they can also be used as the top hot gas distributors. 52. With each of these embodiments, the rows of ducts include the ducts 48 that are laterally spaced from each other from one row to the other in an alternating relationship transverse to the direction of transport. This construction of the duct rows provides uniformity of heating provided by the hot gas to the glass sheets as they are transported for heating. Also, each embodiment of the hot dispensers shown in Figures 9 and 12, when used as the lower hot gas distributor has a dimension along the direction of transport equal to the diameter of the conveyor rollers 38, and is directly located below the associated conveyor roller to have the minimum deflection of the hot gas flow upwards, while preventing the broken glass from falling down on it. As illustrated in Figures 5 and 9-11, the lower hot gas manifolds 44 each include a U-shaped housing 58 that includes a pair of housing members 60 that are L-shaped with the lower flanges 62 that are they insure one with another in any appropriate manner, such as by a soldier. The U-shaped housing 58 includes a pair of spaced side portions 64 and a connecting portion 66 extending between its side portions. Each lower hot gas distributor 44 also includes an inverted U-shaped cover 68, received within the U-shaped housing 58 thereof, and has a pair of spaced apart side portions 70 and a cover portion 72 extending between its lateral portions. The spaced apart side portions 64 of the U-shaped housing 58 and the spaced side portions 70 of the inverted U-shaped cover 68 of each lower hot gas distributor cooperate to define the pair of rows of ducts 48 through which hot gas jets 50 are released, so that the flow of hot gas upwards with respect to the transported glass sheets heated with this flow as previously mentioned, is on the opposite sides of the associated conveyor roller 38, both upstream and downstream thereof as illustrated in Figure 5. Also, the cover portion 72 of the inverted U-shaped cover 68 of each lower, hot gas distributor 44 has an inverted V-shape to facilitate glass tumbling. broken that falls down the roller conveyor. The construction of the lower hot gas manifolds 44 illustrated in Figures 5 and 9-11 is made entirely of die cut sheet. More specifically, the U-shaped housing 58 of each lower hot gas distributor 44 as previously mentioned is provided by the pair of die-cut sheet receiving members 60, and the side portions 64 of the housing are formed as best shown in FIG. Figures 9-11 to define the nozzle lines 48 'cooperating with the spaced apart side portions 70 of the inverted U-shaped cover 68, to define the pair of duct rows 48 of the lower hot gas distributor. This formation of the side portions 64 of the U-shaped housing 58 is provided by the inward formations 74 that extend vertically and have lower rounded ends 76, as shown in Figure 10, so that the adjacent formations provide curved shapes which converge at the inlet end of each nozzle 48. Adjacent to their ends 76, the formations 74 have round openings 78 which facilitate securing the side portions 64 of the U-shaped housing 58 towards the side portions 70 of the cover in FIG. inverted U shape 68, such as by welding. An alternative construction of the lower hot gas distributor is illustrated in Figures 12-14 and, has a U-shaped housing 58 'whose side portions 64' and the connecting portion 66 'are unitary with respect to each other in the same as the side portions 70 and the cover portion 72 'of the inverted U-shaped cover 68'. However, with this embodiment, the nozzle spacers 80 located between the housing and the side cover portions 64 'and 70' cooperate with these to define the pair of duct rows 48 of the lower hot gas distributor. These duct spacers have semicircular ends 81 that provide curved shapes that converge at the input ports of the ducts 48. As illustrated in Figure 5, the preferred construction of the upper hot gas distributors 52 is the same as the distributors of lower hot gas 44 except that they are inverted. The hot gas distributor 46 of each upper hot gas distributor 52 is thus defined by an inverted U-shaped housing 58 and a U-shaped cover 66. The spaced-apart side portions 64 of the U-shaped housing. Inverted 58 of each upper hot gas distributor 52 are connected via their connecting portion 66 and the spaced apart side portions 70 of the U-shaped cover 68 are connected by their cover portion 72. The spaced apart portions of the shaped housing U inverted 58 and the side portions 70 of the U-shaped cover 68 cooperate to define the pair of duct rows 48 thereof, through which the hot gas flows from the hot gas distributor 46 downwardly as shown by the arrows 56 to the transported glass sheets that are to be heated. As previously mentioned, this downward gas flow as illustrated by the arrows 56 is preferably aligned with the upward gas flow 50 of the lower hot gas distributors 44. As shown in Figure 5, each distributor of upper hot gas 52 has its inverted U-shaped housing 58 made of sheet and its spaced-apart side portion 64 formed to define the nozzle conduits cooperating with the spaced apart side portions 70 of its U-shaped cover 68, to define the torque of rows of ducts 48 of the upper hot gas distributor. The alternating mode of the hot gas distributor illustrated in Figures 12-14 can also be used as the hot gas distributor by inverting the position shown in Figure 12, so that its U-shaped housing portion 58 ' it is inverted and its cover 68 'has a U-shape that opens upwards. In this way, with such an inversion, the nozzle spacers 80 define the nozzles 48, through which the hot gas is directed downwards in the direction of the transported glass sheets to be heated. As illustrated in Figures 1 and 3, the forced convection heater 42 includes a plurality of burner assemblies 82 including the burners 84 that are mounted by the furnace housing 22 on a lateral side thereof at locations spaced apart in the portions thereof. of the lower and upper housing 24 and 26. The ends of the nozzles 86 of the burners 84 extend into the heating chamber of the oven 32, so that the combustion products thereof flow into the oven to provide their heating by convection forced Each burner 84, as shown in Figure 3, has an associated mixing tube 88 that opens to the end 86 of the burner nozzle and is mounted by the housing 22 of the furnace. More specifically, the lower mixing tubes 88 are mounted by the lower supports 90 and the upper mixing tubes 88 are mounted by the upper supports 92. A plenum housing 94 associated with each burner 84 is mounted inside the heating chamber 32. of the oven and includes, an inlet 96 extending through the interior thereof from the mixing tube 88 to a blower 98, also located within the distributor housing. The operation of the blowers 98 draws the heated combustion products from the burner 84 and returns the air from the heating chamber 32 in the distributor housing 94 for flow to the hot gas distributors. Each blower 98 is driven by a motor not shown, whose output is connected to an associated driving shaft 100. As illustrated in Figure 4, each distributor housing 94 includes an inclined portion 102 that includes a plurality of elongated rectangular slots 104 into which the associated hot gas distributors are mounted. The lower and upper hot gas distributors have a construction as illustrated in Figures 6-8, wherein the associated housing 58 includes a rectangular mounting portion 106 having a mounting boss 108 secured thereto in any appropriate manner, such as by welding. The mounting portion 106 of each hot gas distributor housing 58 is received within the rectangular slot in the inclined portion 102 of the associated distributor housing 94, to receive the hot gas therein for flow to the duct rows as shown in FIG. described previously. Within the housing 58 of the hot gas distributor, the flow deflectors 110 are provided to distribute the flow of hot gas to the total length of the rows of ducts, between the opposite lateral sides of the furnace housing. As illustrated in Figure 3, adjacent to the lateral side of the furnace housing 22 on which the burners 84 are mounted, the lower and upper baffles 112 are mounted to prevent excessive dragging of the cold ambient air into the heating chamber 32 around of the seals of the rollers 34. Within the furnace heating chamber, there is a slight pressure above the atmosphere, which is prevented from being excessive by the exhaust ducts 114 shown in Figure 1, under the control of the associated dampers 116. Burners 84 as shown in Figure 2, provide a level of heating under the operation of associated controls 118 including associated thermocouples 120 located within associated plenum housings 94, to detect gas temperature hot that is released. Also, the blowers 98 are driven by the electric motors not shown, whose operation is provided by the associated controls 132 that can be coupled with the controls of the burner 118 to provide any desired operation. While the best form for the practice of the invention has been defined in detail, persons familiar with the art for which this invention refers will recognize various alternative forms for the practice of the invention, as defined by the following claims. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Claims (15)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property.

1. A forced convection oven for heating glass sheets, characterized in that it comprises: a housing having a heating chamber; a roller conveyor located within the housing heating chamber and having horizontally extending conveyor rollers for transporting glass sheets along a transport direction within the heating chamber for heating; and a forced convection heater including lower hot gas distributors located below the alternating conveyor rollers, each lower hot gas distributor includes a full hot gas and a pair of rows of ducts to supply hot gas from the plenum thereof, to the upward flow adjacent to the associated conveyor roller, both upstream and downstream thereof, along the transport direction, to provide heating of the lower part of the glass sheets that are transported inside the heating chamber and, the forced convection heater also includes upper hot gas distributors to provide heating above the glass sheets that are transported within the heating chamber by the roller conveyor.

2. A forced convection oven for heating glass sheets according to claim 1, characterized in that the upper hot gas distributors include dies rows that are aligned with the dies rows of the lower hot gas distributors, to provide locations lower and upper aligned hot gas that collides with the glass sheets that are going to heat up.

3. A forced convection oven for heating glass sheets according to claim 1, characterized in that the pair of duct rows of each lower hot gas distributor include nozzles that are laterally spaced from one row to the other in one row. an alternating relationship transverse to the direction of transport.

4. A forced convection oven for heating glass sheets according to claim 1, characterized in that the lower hot gas distributors have a dimension that is equal to the diameter of the conveyor rollers.

A forced convection oven for heating glass sheets according to claim 1, characterized in that the lower hot gas distributors each include a U-shaped housing having a pair of spaced apart side portions and a connecting portion that it extends between its side portions, each lower hot gas distributor, also includes an inverted U-shaped cover coupled within the U-shaped housing thereof, and has a pair of spaced apart side portions and a cover portion that is extends between its side portions, and the spaced apart lateral portions of the U-shaped housing and the spaced apart portions of the inverted U-shaped cover of each lower hot gas distributor cooperate to define the pair of rows of ducts therein, a through which the hot gas flows upwards to the transported glass sheets that are to be heated.

6. A forced convection oven for heating glass sheets according to claim 5, characterized in that the inverted U-shaped cover portion of each lower hot gas distributor has an inverted V-shape.

7. A forced convection oven for heating glass sheets according to claim 5, characterized in that the U-shaped housing of each lower hot gas distributor is made of sheet and has its lateral portions spaced apart to define the ducting of the nozzles, which cooperate with the spaced apart lateral portions of its inverted U-shaped cover, to define the pair of duct rows of the lower hot gas distributor.

8. A forced convection oven for heating glass sheets according to claim 5, characterized in that each lower hot gas distributor includes nozzle spacers located between the spaced apart side portions of its U-shaped housing and the spaced apart side portions thereof. its inverted U-shaped cover, to cooperate with it, to define the pair of rows of ducts of the lower hot gas distributor.

A forced convection oven for heating glass sheets according to claim 1, characterized in that each upper hot gas distributor has a full hot gas and includes an inverted U-shaped housing having a pair of spaced apart side portions and a connecting portion extending between its side portions, each hot gas distributor also includes a U-shaped cover received within the inverted U-shaped housing thereof, and has a pair of spaced apart side portions and a portion of cover extending between its side portions and the spaced lateral portions of the inverted U-shaped housing and the spaced apart portions of the U-shaped cover of each upper hot gas distributor cooperating to define the pair of duct rows of the same, through which the hot gas flows from the full hot gas down to the glass sheets transported that are going to heat up.

10. A forced convection oven for heating glass sheets according to claim 9, characterized in that the inverted U-shaped housing of each upper hot gas distributor is made of sheet and has its side portions spaced apart to define the conduits of the sheets. nozzles, which cooperate with the spaced lateral portions of their U-shaped cover, to define the pair of duct rows of the upper hot gas distributor.

11. A forced convection oven for heating glass sheets according to claim 9, characterized in that each upper hot gas distributor includes nozzle spacers located between the spaced side portions of its inverted U-shaped housing and the laterally spaced portions of its U-shaped cover, to cooperate with it, to define the pair of duct rows of the upper hot gas distributor.

12. A method for heating glass sheets, characterized in that it comprises: transporting the glass sheets by means of a roller conveyor on horizontal conveyor rollers spaced along a transport direction inside the heating chamber of the housing. supplying hot gas flow below the roller conveyor upwards, adjacent to the alternating conveyor rollers, both upstream and downstream thereof, along the transport direction, to provide heating from below the transported glass sheets; and supplying hot gas flow from above the conveyor downwards, to provide heating from above the transported glass sheets. A method for heating glass sheets according to claim 12, characterized in that the hot gas flows are supplied up and down the aligned nozzles to provide the aligned lower and upper locations of hot gas striking the leaves of glass that are going to heat up. A method for heating glass sheets according to claim 12, characterized in that the hot gas flows supplied upwards and downwards are supplied through the lower and upper hot gas distributors, which have a dimension equal to the diameter of the conveyor rollers. A method for heating glass sheets according to claim 12, characterized in that the hot gas flows supplied upwards and downwards are supplied through lower and upper hot gas distributors which are formed of sheet. FORCED CONVECTION OVEN AND METHOD FOR HEATING GLASS LEAVES SUMMARY OF THE INVENTION The present invention relates to a forced convection oven (20) and a method for heating glass sheets, including a forced convection heater (42) which has lower hot gas distributors (44) located below alternating conveyor rollers (38), to provide gas flow upstream and downstream thereof, along a conveying direction, to provide heating from below the glass sheets that they are transported inside the heating chamber (32) of a housing (22) of the furnace. The forced convection heater (42) also includes upper hot gas distributors (52) to provide heating from above the glass sheets that are transported inside the heating chamber (32).