Method of quenching glass sheets

While a heated glass sheet moves through a quenching section, the glass sheet is blown with air in the same portions so as to be quenched always in the same portions to provide on the glass surface rapidly cooled portions and uncooled portions. Thereby the residual strains on the glass surface are made different to prevent the generation of pieces or splines when the glass sheet is broken.

BACKGROUND OF THE INVENTION 
This invention relates to a method for quenching heated glass sheets with 
air nozzles to strengthen them. 
More particularly, the present invention relates to a method of quenching 
glass sheets wherein a glass sheet moving through a quenching section is 
blown in the same portions throughout the quenching section with air from 
nozzles and is moved while being rapidly cooled in the same portions so as 
to set up the differentials of residual strains on the glass surface. 
A glass sheet used as a windshield of an automobile is heated in a heating 
furnace, is then conveyed to a quenching section, is blown with air and is 
rapidly cooled to be a tempered glass sheet. A compression strain is 
developed on the rapidly cooled glass surface and a tension strain 
corresponding to the compression strain is developed in the interior 
portion which chills gradually, with the strength of the glass being 
determined by the differential rates of cooling between the surface and 
the interior of the glass body. 
Nowadays, a standard tends to be set for the purpose of avoiding the danger 
when a side glass or rear glass of an automobile is broken. This standard 
is to regulate whether or not there are long pieces (called splines) over 
the length of 6 cm. produced when the glass breaks, and the number of 
broken pieces. According to the already set British Standard No. BS 5282 
"Road Running Vehicle Safety Glass," it is required that the number of 
broken pieces per unit area of 5.times.5 cm. of a glass sheet of a 
thickness no more than 4 mm. should be in a range of 40 to 400. Where a 
glass sheet is rapidly cooled and tempered to generate a compression 
strain by quenching the glass surface, if this strain is made large, 
splines will be eliminated but the number of broken pieces per unit area 
will increase. If the strain is made to be below a certain value in order 
to keep the number of broken pieces within an allowable upper limit, 
contrary to the above, splines will be produced. It has recently been 
required to solve this technical problem and it is desired to prevent the 
generation of splines while keeping the number of broken pieces within the 
allowable range defined by the standard. 
The present inventors have made the present invention in order to meet the 
above requirement. Particularly, by obtaining a knowledge that, in 
quenching step, if the glass sheet is partially quenched on the surface 
and the strain differentials are set up on the surface, the generation of 
splines will be able to be prevented while keeping the number of broken 
pieces within a predetermined range. 
SUMMARY OF THE INVENTION 
The present invention contributes to provide a safe tempered glass sheet 
wherein the number of broken pieces when it is broken is kept within a 
predetermined range and the generation of splines is inhibited. 
An object of the invention is to provide a method of quenching a glass 
sheet wherein a heated glass sheet is moved through a quenching section, 
is blown in the same portions during the movement with air from a 
plurality of nozzles so as to provide rapidly cooled portions and uncooled 
portions. 
Therefore, according to the present invention, it is possible to retain the 
strain differentials set up on the surface of glass sheets which is cooled 
to the normal temperature, between the rapidly cooled portion and uncooled 
portion of the glass surface. Therefore, when the glass sheet is broken, 
the generation of splines will be able to be inhibited while keeping the 
number of broken pieces within a required range. 
Another object of the invention is to provide a method of quenching a glass 
sheet wherein air is intermittently jetted out of nozzles arranged as 
opposed to the entire glass sheet moving area in a quenching section, and 
the air jetting nozzles are changed in turn so as to coincide with the 
moving speed and moving direction of the glass sheet by synchronizing the 
intermittent jetting of the air with the movement of the glass sheet to 
provide, on the glass sheet surface, portions blown with air and portions 
blown with no air alternately in the glass sheet advancing direction. 
By this method, it is possible to blow the glass surface in the same 
portions with air with the movement of the glass sheet and to retain the 
strain differentials set up on the surface of the glass sheet cooled to 
the normal temperature between the rapidly cooled portion and uncooled 
portion of the glass surface. Therefore, when the glass plate is broken, 
the generation of splines will be able to be inhibited while keeping the 
number of broken pieces within a required range. 
Still another object of the invention is to provide a method of quenching 
glass sheet wherein endless running belts, are provided with a plurality 
of baffle members closing the air nozzles, run in the same direction and 
at the same speed as the glass sheet, to close the nozzles in turn with 
the baffle members and to jet air out of the nozzles between the baffle 
members. 
By such a method, even if the air nozzles are arranged as fixed in the 
quenching section, the air jetting nozzles will be able to be changed to 
coincide with the moving speed and moving direction of the glass sheet. 
A further object of the invention is to provide a method of quenching a 
glass sheet wherein, after the glass sheet is heated in the heating 
section, by the conveying operation of an endless running belt, such as a 
chain, the heated glass sheet is continuously conveyed into and through 
the quenching section which is horizontally provided adjacent to the 
heating section. 
The glass sheet can be heated and quenched in series while the endless 
running belt runs through the heating section and the successive quenching 
section and, when the glass sheet is delivered out of the quenching 
section, the treatment required for the tempering of glass will be 
completed. Therefore, the present invention can make the operation quick 
and is adapted to mass production with simple steps. 
A preferred embodiment of the present invention shall be explained in the 
following with reference to the accompanying drawings so that further 
objects and features of the invention may become apparent.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in FIG. 1, a heating section or furnace 10 and a quenching section 
or station 20 are installed and set on bases 11 to form a horizontally 
continued series of working sections. The inlet end of the quenching 
station 20 is connected to the outlet end of the heating furnace 10. A 
lower half 12a of a chain 12, which is an endless running belt, runs in 
the direction indicated by an arrow A through the heating furnace 10 and 
quenching station 20. An upper half 12b of the chain 12 returns to the 
heating furnace 10 from the quenching station 20 along a horizontal beam 
13 provided above the working sections. The chain 12 is fitted with 
members for engagement with glass sheet 14 so that, when the chain 12 runs 
through the heating furnace 10, the glass sheet 14, put on the chain 
through the inlet end 10a of the heating furnace 10, may be engaged at the 
end of the sheet with these members so as to be conveyed through the 
horizontally long heating furnace 10. Many nozzles blowing high 
temperature air are set in the heating furnace 10. The glass sheet 14 
which is heated on both upper and lower surfaces by this high temperature 
air or such heating means as a heater, and is further supported to float 
by a film of air jetted out of the nozzles, advances in this state through 
the heating furnace 10 and is uniformly heated near to a deformation 
temperature before it reaches the end of the heating furnace 10. 
If the endless running belt running through the heating furnace 10 to 
convey the glass sheet 14 is formed of the chain 12 as described above, 
the accident such as a burning of the endless running belt due to the high 
temperature of the heating furnace 10 will not occur. 
The glass sheet 14 is next conveyed to the quenching station continuously 
as it is by the running of the chain 12, and is then quenched with air on 
both upper and lower surfaces in the same portions thereof by the later 
described air nozzles set in the station 20 while moving through the 
quenching station 20. Thereby the glass sheet 14 is quenched. When the 
glass sheet 14 reaches the end of the quenching station, the sheet is 
delivered onto a receiving stand not illustrated. Thus, the glass sheet 14 
is heated, quenched and tempered in a continuous series of operations. 
The detailed structure of the quenching station 20 is shown in FIGS. 2 and 
3, in which a hollow box-shaped upper header 21 and lower header 22 are 
vertically opposed to each other with a space for running of the chain 12 
being provided between them and are held as connected to vertical beams 23 
and horizontal beams 24. Two air ducts 21a and 22a connected to an air 
feeding source are connected respectively to both headers 21 and 22 so 
that air of a required pressure may be fed into the headers 21 and 22. As 
shown in FIG. 3, a chain guide plate 27 is vertically fitted to the side 
of the lower header 22 by means of a bracket 26 so that the chain 12 
having reached the quenching station 20 through the heating furnace 10 may 
be supported when the upper end of this guide plate 27 enters the space 
between the link plates of the chain. Therefore, the chain 12 runs through 
the quenching station along the guide plate 27 extended horizontally as in 
FIG. 2 while maintaining the height level within the heating furnace. 
A plurality of sprocket wheels 35, 36, 37, 38 and 39 for turning the 
running direction of the chain 12 are provided on the terminal end side of 
the quenching station 20. A motor 30 which is a driving source is set on 
the base 11. The driving force of this motor 30 is transmitted to a 
reduction gear 32 through a chain 31 and is further transmitted to another 
sprocket wheel provided in a bearing 40 for the sprocket wheel 36 so that 
the chain 12 may be run by rotation of the sprocket 36 rotated in unison 
with the another sprocket wheel. 
Many air nozzles 50 are fixed as directed upward on the upper surface of 
the lower header 22. The glass sheet 14 is quenched on the lower surface 
by air jetted out of these nozzles 50 and is supported to float by the air 
pressure in the same manner as in the heating furnace 10. Accordingly, the 
sheet of glass is not deformed by collision with the members, such as the 
nozzles, while moving as heated to the deformation temperature and is 
conveyed to the quenching station 20 from the heating furnace 10 as 
supported to float by the air pressure. As apparent in FIG. 3, the lower 
header 22 is inclined to the horizontal plane so that the side end of the 
glass sheet 14, with which the chain 12 is engaged, may be in the lower 
position and the upper header 21 is also inclined so as to be parallel 
with the lower header 22. All the lower air nozzles 50 are erected at 
right angles with the upper surface of the lower header 22 and are of the 
same length. The upper surface of the nozzles 50 is in a plane inclined by 
the same angle as the angle of inclination of the lower header 22. 
Therefore, in case the glass sheet 14 is supported to float by air from 
the nozzles 50, the glass sheet tends to move toward the lower position 
side by the gravity. 
A member 51 for engagement with the glass sheet is connected to the chain 
12 and passes between both upper header 21 and lower header 22 while the 
chain 12 passes through the quenching station 20 as in FIG. 3. The glass 
sheet 14 moved toward the lower position by the gravity is stopped where 
it contacts with an angle bracket 51a provided at the tip of the member 51 
and moves together with the chain 12 as engaged with the member 51. The 
glass sheet 14 is continuously moved by the member 51 from the heating 
furnace 10. 
The air nozzles 50 of the lower header 22 are provided over the entire 
upper surface of the header 22 so as to be opposed to the entire moving 
area in the quenching station 20. Also, many upper air nozzles 60 are 
provided as directed downward on the lower surface of the upper header 21 
and are arranged in close order over the entire lower surface of the upper 
header 21 so as to be opposed to the entire moving area in the quenching 
station 20. 
In the present embodiment, during the movement of the glass sheet 14 in the 
quenching section, the glass sheet is blown on the entire lower surface 
with air from the lower air nozzles and is blown on the upper surface only 
partially, but in unchanged or the same portions with air from the upper 
nozzles, so that portions blown with air and portions not blown with air 
may be provided only on the upper surface of the glass sheet. However, it 
is possible to blow the glass sheet on the lower surface with air only in 
unchanged portions. Such a method can be attained by an air jetting 
controlling means for the air nozzles 60 explained hereafter, or by a 
means similar to that or by arranging the lower air nozzles 50 linearly in 
the glass sheet 14 moving direction and at intervals in a direction at 
right angles to this moving direction. 
An example of blowing the moving glass sheet 14 with air in same portion 
can be attained by moving the nozzles 60 at the same moving speed in the 
same moving direction as of the glass sheet 14. Further, as another 
example, a plate member which is provided with openings permitting air to 
pass therethrough may be interposed between the nozzles 60 and the glass 
sheet 14 to move at the same speed and in the same direction as of the 
glass sheet 14. Another method wherein the structure can be made more 
simple than each of these methods is adopted in the present embodiment. 
According to this method, even if the plate member in which the openings 
are formed is not used or the upper air nozzles 60 are arranged in a fixed 
position, the same portions on the glass surface can be blown with air. 
This method is characterized in that air is intermittently jetted out of 
the nozzles 60 and stopped as synchronized with the movement of the glass 
sheet by changing the air jetting nozzles 60 in turn to coincide with the 
moving direction and moving speed of the glass sheet 14. 
Means of controlling the air jetting out of the upper air nozzles 60 shall 
be explained in detail hereafter. 
As shown in FIGS. 4 and 6, two pairs of sprocket wheels 70 and 71 are 
incorporated at both ends within the upper header 21 and the two sprocket 
wheels forming a pair are connected with each other through a shaft 72. 
Chains 73 which constitute endless running belts are provided between the 
sprocket wheels 70 and 71 of the respective pairs. As shown in FIG. 4, 
these chains 73 are provided so that the running direction B of the lower 
half 73a may be in the same direction as the running direction A of the 
glass sheet conveying chain 12 shown in FIG. 1, i.e., the moving direction 
of the glass sheet 14. As shown in FIG. 6, baffle members 74 are crosswise 
provided on a pair of the chains 73, are integrally connected respectively 
at both ends to the pins and link plates of the chains 73 and are arranged 
at regular intervals over the entire length of the chains 73. In the 
illustrated embodiment, the baffle member 74 is made flat, narrow and 
long, but its configuration and surface area can be freely determined 
correspondingly to the selection of the upper air nozzles 60 to jet air, 
that is, the portions of the surface of the glass sheet 14 to be blown 
with air. 
The upper air nozzles 60 are inserted and fixed at the base ends into the 
lower surface plate 21b of the upper header 21 and openings 60a provided 
at the base end faces open in and communicate with a space within the 
upper header 21 so that the upper header 21 may serve as a supporting 
member for the upper air nozzles 60 and a distributing member for 
distributing air to all the nozzles 60. When the baffle members 74 advance 
in the direction B in FIG. 4 with the running of the chains 73, the baffle 
members 74 will slide in contact with the openings 60a at the base ends of 
the nozzles 60. Thus, the upper air nozzle 60 will be closed by the baffle 
member 74 and the jetting of air out of the nozzle 60 will stop. After the 
baffle member 74 passes, and only before the next baffle member 74 
arrives, the opening 60a will open and will jet air. 
The space within the upper header 21 is filled with high pressure air from 
the air feeding source through the ducts 21a. Therefore, high pressure air 
acts on the baffle member 74 which is thereby pressed against the opening 
60a of the nozzle 60 so that the leakage of air into the nozzle 60 may be 
positively prevented. In the present embodiment, in addition to the above 
structure, the baffle member 74 is formed of an elastic material such as a 
flexible synthetic resin material so that the baffle member 74 may be 
easily pressed into elastic contact with the nozzle 60 by its own 
flexibility, and the close contact of the baffle member 74 with the nozzle 
60 may be further improved in addition to that provided by the high air 
pressure. 
A device for driving the chains 73 for moving the baffle members 74 shall 
be described hereafter. 
A sprocket wheel on which a chain 80 is engaged is provided in a bearing 
part 40 shown in FIG. 2. Therefore, the sprocket wheel of a chain 33 
driven by the motor 30, the sprocket wheel 36 of the glass sheet conveying 
chain 12 and the sprocket wheel of a chain 80 are coaxially triplicately 
arranged in this bearing part 40. The chain 80 is driven by the motor 30 
together with the chain 12. The driving force of the chain 80 is 
transmitted to a power relaying means 83 through a gear box 81 and 
connecting rod 82. Further, a driving force is transmitted to the gear box 
85 through a connecting rod 84 extending vertically downward from this 
power relaying means 83. A sprocket wheel 86 shown in FIG. 3 is fitted to 
this gear box. A shaft 72 of a sprocket wheel 70 incorporated within the 
header 21 projects out of the header 21 as shown in FIG. 6 and a sprocket 
wheel 87 is fitted to this projecting part 72a. A chain 88 shown in FIGS. 
2 and 3 is provided on this sprocket wheel 87 and the sprocket wheel 86 of 
the gear box 85. 
By the above, the motor 30 is a driving source not only for the glass sheet 
conveying chain 12 but also for the baffle member 74 moving chains 73 and 
the driving forces of both chains 12 and 73 are branched in the bearing 
part 40. In this case, the power transmitting system from the bearing part 
40 to the sprocket wheel 70 of the chain 73, that is, the driving device 
consisting of the chain 80, gear box 81, connecting rod 82, power relaying 
means 83, connecting rod 84, gear box 85, sprocket wheel 86, chain 88 and 
sprocket wheel 87, is so formed as to be able to run the chains 73, which 
are endless running belts, at the same speed and in the same direction as 
the glass sheet conveying chain 12 by the adjustment of the gear ratios or 
the sizes of the sprocket wheels. Therefore, when the chain 12 runs 
through the heating section and quenching section to convey the glass 
sheet 14, the chains 73 run as synchronized with the chain 12. 
While the glass sheet 14 heated in the heating furnace 10 moves through the 
quenching section under the conveying action of the chain 12, the baffle 
members 74 fitted to the chains 73 move in coincidence with the moving 
direction and moving speed of the glass sheet 14 and close the openings 
60a at the base ends of the upper air nozzles 60 in turn. The jetting of 
air out of the nozzle closed with the baffle member 74 stops but is 
continued out of the nozzle not closed, until such nozzle is closed. Air 
is intermittently jetted out of the respective nozzles 60 and stopped as 
synchronized with the movement of the glass sheet 14 through the quenching 
section. The air jetting nozzles 60 change in turn in coincidence with the 
moving speed and moving direction of the glass sheet 14. 
Thus, while the glass sheet 14 moves through the quenching section, the 
glass sheet is blown on the surface with air in the same portions from 
many upper air nozzles 60, arranged as fixed in this section, but is not 
blown in other portions with air so that portions rapidly cooled by air 
and portions uncooled may be made on the glass surface. The areas of these 
portions are determined by the flat shape and surface area of the baffle 
member 74. When the shape and surface area of the baffle member 74 are 
properly determined, the glass surface will be able to be partially 
quenched in respective narrow zones. When the glass sheet 14 is reduced in 
temperature to the normal temperature, the differentials of the residual 
strain will be set up between the rapidly cooled portions and the uncooled 
portions. 
As explained above, in the present embodiment, air is intermittently jetted 
out of the respective nozzles 60 and stopped as synchronized with the 
movement of the glass sheet 14. However, the intermittent air jet can be 
made also by such a program in which the air circuits of the respective 
nozzles are constituted by separate systems respectively so as to be set 
on and off in conformity with the movement of the glass sheet 14. 
As clearly shown in FIG. 5, each upper air nozzle 60, arranged as fixed to 
be directed downward on the lower plate 21a of the upper header 21, is 
provided at the tip side with a pipe member 61 projecting toward the glass 
surface and at the base side with a cylinder member 62 fitted to the lower 
plate 21a. The nozzle 60 is formed by fitting the pipe member 61 within 
the cylinder member 62. 
RESULTS OF EXPERIMENTS 
A quenching station 20 was provided adjacent to a heating furnace 10. As in 
FIG. 2, lower air nozzles 50 and upper air nozzles 60 were arranged as 
fixed in the quenching station 20. A plurality of baffle members 74 were 
fitted to chains 73 incorporated within the upper header 21. The baffle 
members 74 were 25 mm. wide, 490 mm. long and 0.5 mm. thick and were made 
of vinyl chloride. The baffle members 74 were moved at the same speed in 
the same direction as of a glass sheet 14 which was 460 mm. wide, 1060 mm. 
long and 4.1 mm. thick. The glass sheet 14 coming out of the heating 
furnace 10 was at a temperature of 650.degree. C. and a moving speed of 
16.0 m./min. The air pressure from the nozzles 50 and 60 was 750 mm. Aq. 
When the glass sheet thus quenched by blowing the glass surface with air in 
the same portions by using the baffle members 74 was purposely broken, the 
number of broken pieces per unit area of 5.times.5 cm. was 57 to 259. 4 
Glass sheets were broken and substantially no spline of a length exceeding 
6 cm. was produced. 
On the other hand, when a glass sheet quenched on the entire surface 
without using baffle members was purposely broken, the number of broken 
pieces per unit area of 5.times.5 cm. was 57 to 230. 4 Glass sheets were 
broken and 16 splines of a length exceeding 6 mm. were produced. 
As evident from the results of this experiment, it is found that the number 
of broken pieces in the case of using baffle members 74 was substantially 
the same as in the case of using no baffle members and both were within 
the required range of the standard; but that the splines were reduced by 
the present invention when the baffle members 74 were used. 
According to the present invention, if quenched portions and unquenched 
portions are alternately provided in each narrow zone on a glass surface 
so that the differentials of the residual strains may be set up on the 
glass surface, the generation of splines will be able to be prevented 
while keeping the number of broken pieces within the range of the standard 
.