Blow back control device for a glass sheet tempering system

A blow back control device (10) for use in a glass tempering system (12) is disclosed as including an air supply member (28) mounted between a glass heating furnace (14) and a quenching station (24). The air supply member (28) supplies a planar jet of high pressure blow back control air generally in a direction of glass sheet conveyance (A) away from an exit opening (20) of the furnace (14) and toward the quenching station (24) at an angle in the range of between 0.degree. and 25.degree. formed between the planar jet of high pressure air and a plane of conveyance of a glass sheet (16) along a conveyor (22) to deflect cooling air, supplied by blastheads (26,26') from entering the furnace (14).

TECHNICAL FIELD 
This invention relates to a blow back control device which has particular 
utility for use in a glass sheet tempering system in connection with the 
tempering of heated glass sheets. 
BACKGROUND ART 
A sheet of glass can be tempered to both increase its mechanical strength 
and improve its breakage characteristics. When tempered glass is broken, 
it collapses into a large number of relatively small, dull pieces instead 
of shattering into sharp pieces as in the case of annealed glass. 
In a glass tempering system, the glass tempering process generally involves 
two steps. First, a sheet of glass is heated in a glass heating furnace to 
its deformation point of about 1200.degree. F. to 1300.degree. F. 
Secondly, the heated glass sheet is removed from the furnace and rapidly 
quenched by the application of cooling gas directed onto the hot glass 
sheet. Rapid cooling sets up high compressive forces near the surfaces of 
the glass sheet which give it desired strength and breakage 
characteristics. 
The quenching operation takes place on a quench ring or roller conveyor, 
depending upon whether a side exit or end exit glass heating furnace is 
utilized, immediately after the glass has left the furnace. Thin glass 
sheets require more rapid application of cooling gas after exiting the 
furnace than does a thicker glass sheet. The close proximity of the 
furnace and quenching station combined with the heating step being 
followed directly by the quenching step can result in cooling gases which 
flow off the glass sheet during the quenching step entering the furnace. 
Cooling gas which enters the furnace is at a significantly lower 
temperature than the normal operating temperature within the furnace. As a 
consequence, the furnace may undergo undesirable temperature swings. Also, 
cooling gas may prematurely cool the glass sheet in the furnace before 
reaching the quenching station. Premature cooling of the glass can 
adversely affect its tempered characteristics or shape and is especially a 
problem with relatively thin glass which requires more quench gases to 
temper properly than does thicker glass. 
U.S. Pat. No. 2,144,320 to Bailey for means for thermally toughening glass 
discloses headers mounted at an exit end of a glass sheet heating furnace. 
The headers are disposed above and below a roller conveyor and deliver 
cooling air directed at an inclination to partitions located adjacent the 
exit end of the furnace. The partitions are said to deflect some of the 
cooling air that tends to enter the glass heating furnace as the glass 
sheet is being quenched. 
DISCLOSURE OF INVENTION 
An object of the present invention is to provide a blow back control device 
in a glass sheet tempering system that prevents cooling gas which is 
applied to quench a heated glass sheet, at a quenching station, from 
entering an associated glass heating furnace adjacent the quenching 
station. 
In carrying out the above object, the blow back control device is used in a 
glass tempering system that processes a sheet of glass that has been 
heated in the glass heating furnace. The furnace includes an exit portion 
having an exit opening through which the heated glass sheet is discharged 
from the furnace by a glass sheet conveyor in a direction of glass sheet 
conveyance. The glass tempering system also includes a quenching station, 
including blastheads, adjacent the exit portion of the furnace for 
applying cooling gas to the heated glass sheet. 
The blow back control device comprises an air supply member mounted 
adjacent the exit opening between the glass heating furnace and the 
quenching station for supplying a planar jet of high pressure air across 
the exit opening. The planar jet of high pressure air is directed for 
supplying blow back control air generally in the direction of glass sheet 
conveyance away from the exit opening of the furnace and toward the 
quenching station at an angle in the range of between 5.degree. and 
25.degree. formed between the planar jet wall of high pressure air and the 
plane of conveyance of the glass sheet along the conveyor. The jet thereby 
peels off and deflects cooling air, supplied by the blastheads and 
travelling along the glass sheet during the tempering, from entering the 
exit opening of the furnace. 
In the preferred embodiment of the invention, the air supply member is a 
conduit including an outlet for delivering the planar jet of high pressure 
air. Preferably, the conduit is a tube mounted perpendicular to the 
direction of glass sheet conveyance. The outlet in the tube is a plurality 
of apertures extending generally linearly along the tube although the 
outlet can be a slit extending along the tube. 
A compressed air supply supplies blow back control air to the blow back 
control device. A controller is operable for regulating the compressed air 
supply to provide maximum air pressure when the glass sheet is exiting the 
furnace and entering the quench station and subsequently reduces the 
pressure during the quenching of the heated glass sheet. 
Preferably, two tubes are mounted adjacent the exit opening. One tube being 
mounted above the plane of conveyance of the glass sheet and the other two 
being mounted below the plane of conveyance. Most preferably, the planar 
jet of high pressure air jet is directed to strike the plane of conveyance 
at an angle generally of about 16.degree.. 
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.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to FIG. 1 of the drawings, a blow back control device constructed 
in accordance with the present invention is generally indicated by 
reference numeral 10 and is used in a glass tempering system 12. The 
tempering performed in tempering system 12 includes tempering and heat 
strengthening where stresses are much less than conventional tempering. As 
is hereinafter more fully described, the blow back control device 10 
prevents cooling gas used for glass quenching from traveling into a glass 
heating furnace 14. The blow back control device 10 thereby prevents 
temperature swings in the furnace 14 and premature cooling of glass sheets 
still in the furnace. 
As shown in FIGS. 1 and 2, the glass tempering system 12 processes a sheet 
of glass 16 that has been heated in the glass heating furnace 14. The 
furnace 14 includes an exit portion 18 having an exit opening 20 through 
which the heated glass sheet 16 is discharged from the furnace by a glass 
sheet conveyor 22 in a direction of glass sheet conveyance indicated by 
arrow A. As shown, glass heating furnace 14 is a side exit type furnace 
which utilizes a quench ring 23 as the conveyor 22 on which the glass 
sheet 16 is received, supported and conveyed. The blow back control device 
10 has also been used with an end exit glass heating furnace 14 which 
utilizes a roller conveyor for conveying glass sheets 16 out of the exit 
end of the furnace. 
In FIG. 2, the glass tempering system 12 includes a quenching station 24 
which includes upper and lower blastheads 26, 26' that are located 
adjacent the exit portion 18 of the furnace 14 for rapidly applying 
cooling gas to the heated glass sheet 16 immediately after the glass sheet 
exits the furnace. Glass sheet 16 exits the glass heating furnace 14 in a 
direction of glass sheet conveyance illustrated by arrow A. Some of the 
cooling air supplied by the blastheads 26,26' travels along the quenched 
glass sheet 16 toward the exit opening 20 of the glass heating furnace 14. 
With reference to FIGS. 2 and 3 of the drawings, the blow back control 
device 10 comprises an air supply member 28 for supplying a planar jet of 
high pressure air across the exit opening. Air supply member 28 is mounted 
adjacent the exit opening 20 between the glass heating furnace 14 and the 
quenching station 24. Member 28 is mounted so that the planar jet of high 
pressure air is directed for supplying blow back control air generally in 
the direction of glass sheet conveyance A away from the exit opening 20 of 
the furnace 14 and toward the quenching station 24 at an angle in the 
range of 5.degree. and 25.degree. formed between the planar jet of high 
pressure air and the plane of conveyance A of the glass sheet along the 
conveyor 22. The air supply member 28 peeled and deflects cooling air, 
supplied by the blastheads and traveling along the glass sheet 16 during 
the tempering, from entering the exit opening 20 of the furnace 14 and 
thereby from prematurely cooling other glass sheets within the furnace. 
As seen in FIGS. 4 and 5 of the drawings, the air supply member 28 is a 
tube 30 including an outlet 32 for delivering the jet of blow back control 
air. In FIG. 4, outlet 32 is a plurality of apertures 34 extending 
generally linearly along the tube 30. In an alternative embodiment shown 
in FIG. 5, outlet 32 is a slit 36 extending along the tube 30. 
With further reference to FIG. 1 of the drawings, the tube 30, or air 
supply member 28, is mounted generally perpendicular to the direction of 
glass sheet conveyance A. As shown in FIGS. 4 and 5 of the drawings, the 
tube 30 may be shaped to accommodate the shape of the glass sheet 16 being 
quenched and thereby to provide a more effective device for deflecting 
blow back gases traveling along a shaped glass sheet. The blow back 
control device 10 includes a compressed air supply 38 which is regulated 
by a control 40 that provides maximum air pressure when the glass sheet 16 
is exiting the furnace 14 and entering the quenching station 24 when the 
greatest chance of cooling air entering the furnace 14 exists. The 
controller 40 subsequently reduces the pressure during the quenching of 
the heated glass sheet 16. 
As illustrated in FIGS. 2 and 3 of the drawings, two tubes 30,30' are 
mounted adjacent the exit opening 2 of furnace 14. One tube 30 is mounted 
above the plane of conveyance of the glass sheet and the other tube 30' is 
mounted below the plane of conveyance. In the preferred orientation, 
illustrated in FIG. 3, the planar jet of high pressure air is directed via 
mounting of the tube 30 to strike the plane of conveyance of the glass 
sheet at an angle generally of about 16.degree.. 
While the best mode for carrying out the invention has been described in 
detail, those familiar with the art to which this invention relates will 
recognize various alternative designs and embodiments for practicing the 
invention as defined by the following claims.