[0001] This invention relates to a method of toughening a glass sheet, and can be used to
produce flat or curved sheets of thermally toughened glass to be used as motor vehicle
side or rear windows.
[0002] In most countries there are official regulations specifying the fracture requirements
for toughened glass sheets which are to be used as side or rear windows for motor
vehicles.
[0003] Typically such regulations specify that the toughened glass sheets shall be fractured
by localised impact at a defined position on the glass sheets, two particular positions
being at the geometrical centre of the glass sheet and at a position adjacent the
edge of the sheet. It is then required that areas of the fractured glass sheet should
be selected where the particle count is a minimum and where the particle count is
a maximum and limitations are placed on the minimum and maximum particle counts permissible
in such areas. The minimum particle count permissible determines the maximum size
of particles resulting from fracture so as to limit the danger of laceration by larger
particles subsequent to fracture of the glass sheet in an accident. The maximum particle
count permissible determines the minimum fineness of particles resulting from accidental
fracture of the glass sheet so as to limit the danger of ingestion of fine glass particles.
At present motor vehicle side and rear windows are made from glass of about 4.0 mm
to 6.0 mm thickness and can be uniformly toughened so as to meet official fracture
requirements.
[0004] For example glass sheets of thickness 4 mm and above meet the proposed E.E.C. standard
referred to below if uniformly toughened to have a central tensile stress in the range
55 MN/m
2 to 59 MN/m
2. However in the interest of reducing weight there is now a trend towards the use of
thinner glass in motor vehicles, e.g. of about 3.0 mm thickness, glass of thickness
in the range 2.5 mm to 3.5 mm being of particular interest.
[0005] In the draft standard under discussion by the European Economic Community (E.E.C.)
it is required that the number of particles in any 5 cm x 5 cm square traced on the
fractured glass, excluding a 3 cm wide band around the edge of the glass sheet and
a circular area of 7.5 cm radius around the point from which fracture is initiated,
should be 50 at the minimum and 300 at the maximum.
[0006] The proposed E.E.C. standard also has the requirement that the fractured glass shall
not contain any elongated particles with jagged ends of more than 6 cm in length,
such particles being referred to as "splines".
[0007] British Standard No. BS 5282 entitled "ROAD VEHICLE SAFETY GLASS" is less restrictive
that the proposed E.E.C. standard in that it specifies for glass less than 4 mm in
thickness a minimum particle count of 40 in a 5 cm x 5 cm square may be permitted
and the maximum permitted particle count in a 5 cm x 5 cm square may be 400. The British
Standard also basically prohibits the presence of splines of more than 6 cm in length
in the fractured test glass. The British Standard also requires that no splines are
to be present in the fractured glass sheet..
[0008] It had been found difficult to toughen thinner glass sheets to meet the official
fracture requirements, this difficulty being particularly evident in a size greater
than about 1100 mm x 500 mm this is about the size of the smallest vehicle rear window
in current production. Many vehicle side windows are also of about this size or greater.
[0009] In German Offenlegungsschrift No. 2709105 published 15th September, 1977, there is
described and claimed a solution to the problem based on the discovery that glass
sheets of the kind used as motor vehicle side or rear windows which are from 2.5 mm
to 3.5 mm thick, particularly sheets 3 mm thick, could be toughened in a way which
meets official fracture requirements such as the proposed E.E.C standard, by quenching
a distribution of regions of the glass sheet at a maximum rate so that interspersed
regions of the glass sheet are simultaneously quenched at a minimum rate, regulating
the maximum quenching rate and the size and spacing of the regions of the glass sheet
which are quenched at the maximum rate such that an average central tensile stress
is produced in the glass sheet within a range from a maximum of 62 MN/m
2 for all thicknesses of glass from 2.5 mm to 3.5 mm to a minimum of 56.5 MN/m
2 for 2.5 mm thick glass varying inversely with thickness down to the minimum of 53
MN/
M2 for 3.5 mm thick glass, and such that there is produced in the glass sheet a distribution
of areas in which the principal stresses acting in the plane of the glass sheet are
unequal, the principal stress difference in at least some of said areas being at a
maximum in the range 8 MNfm
2 to 25 MN/m
2, the major principal stresses in adjacent areas in which the principal stress difference
is a maximum being in different directions and the distance between the centres of
such adjacent areas being in the range 15 mm to 30 mm.
[0010] In carrying out the method of the above mentioned patent application quenching was
effected by directing quenching jets at the glass sheet, and imparting a vertical
oscillation or a circular oscillation to the quenching jets to produce the required
distribution of regions of the glass sheet quenched at a maximum rate. The quenching
could also be effected by directing stationary quenching jets at the glass sheet to
produce the required distribution of regions of the glass sheet quenched at a maximum
rate.
[0011] We have now discovered that a distribution of areas of highly and lesser toughened
glass can be produced by a method in which flow of gas towards a moving hot glass
sheet is pulsed so as to subject adjacent areas of the glass to different rates of
heat transfer from the glass.
[0012] According to the invention there is provided a method of toughening a glass sheet
in which the glass sheet is advanced through a quenching station where the sheet is
subjected to quenching gas flow, characterised in that the quenching gas flow is at
least one localised gas flow which is pulsed at a repetition frequency related to
the speed of advance of the glass through the quenching station to induce in the glass
a distribution of regions of more highly toughened glass interspersed with regions
of lesser toughened glass.
[0013] In one embodiment of the invention the glass sheet is advanced between flows of quenching
gas at the quenching station to produce overall toughening of the glass, and said
at least one localised gas flow is superimposed on said flows of quenching gas.
[0014] The invention may be applied to a glass sheet which is being advanced horizontally
either on a roller conveyor or on a gaseous support. From this aspect the invention
provided a method characterised in that the glass sheet which is advancing horizontally
between said flows of quenching gas is subjected to a plurality of said localised
gas flows by directing towards at least one face of the glass, as it passes through
the quenching station, gas jets which are spaced apart in a row transversely to the
direction of advance of the glass, and pulsing said gas flows to produce said distribution
of regions of more highly toughened glass interspersed with regions of lesser toughened
glass in which distribution there are areas in which the principal stresses acting
in the plane of the glass sheet are unequal.
[0015] In one embodiment of the invention the advancing glass is subjected to an array of
gas jets which are spaced apart in rows transversely of the direction of advance of
the glass with the rows spaced apart in the direction of advance, and the gas jets
are pulsed at a rate related to the speed of advance of the glass so that localised
areas of the glass are subjected to accumulative chilling by successive pulsed jets.
[0016] In one embodiment of the invention the sheet of glass is advanced horizontally on
a gaseous support through the quenching station, and said at least one gas jet is
directed towards the upper face of the sheet at the quenching station.
[0017] The gas jets thus superimposed localised chilling of the upper surface of the glass
on the generalised chilling effected by the chilling air flows over both faces of
the glass.
[0018] In an alternative embodiment of the invention the sheet of glass is advanced horizontally
on rollers through the quenching station, and said at least one gas jet is directed
towards at least one face of the sheet at the quenching station.
[0019] The invention also comprehends a toughened glass sheet for use as a side or rear
window for a motor vehicle produced by the method of the invention.
[0020] In order that the invention may be more clearly understood some embodiments thereof
will now be described, by way of example, with reference to the accompanying drawings,
in which:-
Figure 1 illustrates the fracture pattern of a differentially toughened glass sheet
suitable for a side or rear window of a motor vehicle produced by the method of the
invention,
Figure 2 is a side elevation partly in section of apparatus for carrying out the invention
in which the glass sheet to be differentially toughened is transported on a gaseous
support as it is heated and quenched,
Figure 3 is a sectional elevation of the quenching station forming part of the apparatus
of Figure 2,
Figure 4 is an underneath view of the upper part of the quenching station on line
IV-IV of Figure 3,
Figure 5 is a detailed view of part of the quenching station of Figures 3 and 4,
Figure 6 is a schematic diagram showing one way of pulsing gas supplies to the quenching
station,
Figure 7 illustrates another way of pulsing gas supplies to the quenching station,
Figure 8 is a view similar to Figure 2 of apparatus for carrying out the method of
the invention including means for bending the hot glass sheet prior to the advance
of that sheet . through the quenching station, and
Figure 9 illustrates the toughening of a glass sheet by the method of the invention
while the sheet is supported on a roller conveyor.
[0021] Figure 1 illustrates the fracture pattern of a toughened glass sheet suitable for
use as the side window or rear window of a motor vehicle produced by the method of
the invention. The glass sheet has a distribution, in rectangular array, of localised
areas 1 of more highly toughened glass in the glass sheet interspersed with areas
2 of lesser toughened glass. Areas 3 of the glass have a medium toughening stress
and in each of the areas 3 the principal stresses are unequal with the major principal
stress acting in the direction indicated by the arrows 4.
[0022] Areas 5 of the glass also have a medium toughening stress and have unequal principal
stresses with the major principal stress acting in the direction indicated by the
arrows 6. The major principal stress 6 in each area 5 acts in a direction substantially
perpendicular to the direction of the major principal stress 4 in each of the areas
3.
[0023] Normal toughening stresses are produced in each of the areas 1, 2, 3 and 5, of the
glass sheet to an extent which is dependant on the rate of quenching of those areas.
A high central tensile stress which is of equal magnitude in all directions in the
plane of the glass sheet is produced in the more highly toughened areas 1, a low central
tensile stress is produced in the lesser toughened areas 2, and compensating compressive
stresses are produced in both surfaces of the glass sheet.
[0024] The medium toughening stresses produced in the areas 3 and 5 of the glass sheet are
a combination of the normal toughening stresses of equal magnitude in all directions
in the plane of the glass sheet, and additional area stresses produced in the areas
3 and 5 due to the different rates at which the adjacent areas 1 and 2 are cooled
and contract. These area stresses are not of equal magnitude in all directions in
the plane of the glass sheet. The central tensile stress in the areas 3 and 5 of the
glass sheet due to the combined effect of the normal toughening stresses and the area
stresses can be resolved into unequal principal stresses in the plane of the glass
sheet namely a major principal tensile stress and a minor principal tensile stress
acting at right angles to the major principal tensile stress.
[0025] As shown by the arrows 6 in the areas 5 the major principal tensile stress 6 acts
in a direction perpendicular to the direction of the major principal tensile stress
4 in the areas 3.
[0026] The size of the particles produced in a fractured glass sheet depends on the degree
of toughening of the glass and in general the fineness of the particles increases
with the degree of toughening. Hence the particles of relatively small size are produced
in the more highly toughened areas 1, in the lesser toughened areas 2 larger particles
are produced, and in the areas 3 and 5 having a medium toughening stress particles
of medium size are produced. This distribution of small, larger and medium sized particles
is produced over the whole surface of the fractured glass sheet, and there are no
splines in the fracture. The requirements of the proposed E.E.C. standard and of British
Standard No. BS 5282 with regard to minimum and maximum particle sizes are met when
the glass is toughened to the degree described in German Offlengungsschrift No. 2709105,
referred to above.
[0027] When a toughened glass sheet is fractured the cracks tend to run substantially perpendicular
to the direction of major prinicipal stress in the glass. This is illustrated in Figure
1 where the cracks tend to run perpendicular to the direction of the major principal
stresses 4 and 6 in the areas 3 and 5 and are directed towards the more highly toughened
areas 1 where particles of smaller size are produced. Since the major principal stresses
in adjacent areas 3 and 5 are perpendicular to one another, a wavy type of fracture
pattern results in which the size of the areas 3 and 5 limits the maximum length of
the particles which can be produced. Hence the fracture pattern does not include elongated
particles, or splines, of the kind which are found in the customary radial type of
fracture pattern produced in a conventional uniformly toughened glass sheet.
[0028] The glass sheet having such a stress distribution is produced according to the invention
by subjecting at least one face of the glass sheet to pulsed localised gas flows for
a predetermined time during its advance between quenching gas flows of a more generalised
nature such as are used in the conventional toughening of a glass sheet. The effect
of a localised gas flows is to induce in the toughened glass the rectangular distribution
of regions of more highly toughened glass interspersed with regions of lesser toughened
glass just described with reference to Figure 1.
[0029] Apparatus as shown in Figure 2 may be employed for transporting glass sheets on a
gaseous support through a heating station to a quenching station. Flat sheets of glass
7 which are cut to the required shape for use as a side or rear window of a vehicle
are fed in sequence on to asbestos covered conveyor rollers 8 at the loading end of
the apparatus. The rollers 8 have collars 9 of slightly larger diameter than the major
surfaces of the rollers and the glass sheets ride on the collars 9. The rollers 8
are inclined at a slight angle to the horizontal, for example an angle of about 5°.
The sheets 7 are fed in sequence by the rollers 8 through an inlet 10 into a heating
furnace comprising a tunnel structure including a roof 11 and side walls 12. The sheets
7 are conveyed through the first part of the heating furnace on further asbestos covered
rollers 8 and are then conveyed through the remaining length of the furnace on a gaseous
support generated by a base bed structure. The bed structure comprises a base plate
13 which is a flat plate of heat-resistant stainless steel and which forms the roof
of an exhaust chamber indicated at 14. The plate 13 is uniformly apertured for the
passage of hot gases from outlet apertures 15, Figure 3. Each of the apertures 15
for the passage of hot gases upwardly through the base plate 13 is defined by the
bore of a supply tube 16 which is fitted into a hole in the base plate. The tops of
the tubes 16 are flush with the top surface of the base plate 13 and the tubes 16
extend downwardly from the base plate 13 and are located at their lower ends in holes
in a floor 17 of the exhaust chamber 14. Hot gases are supplied through ducts 18,
Figure 1 to plenum chambers 19. The floor 17 of the exhaust chamber 14 forms the roof
of one of the plenum chambers 19.
[0030] The base plate 13 is also formed with equally interspersed exhaust openings 20 communicating
with the exhaust chamber 14. Outlet apertures, not shown, in the walls of the exhaust
chamber 14 allow gases to escape either to atmosphere or for collection and recirculation.
[0031] The upper face of the base plate 13 is an accurately flat surface formed to receive
in intimate engagement the lower face of a series of removable blocks 21 which are
machined from heat-resistant stainless steel with their lower faces machined flat
so that they can be slid into the apparatus from one side into gas- tight engagement
with the upper surface of the base plate 13. The blocks 21 each have gas escape apertures
22 communicating with the outlet apertures 15 and gas exhaust apertures 23 communicating
with the exhaust openings 20. Hot gases supplied through the ducts 18 into the plenum
chamber 19 proceed upwardly through the tubes 16 and the apertures 22 in the block
21 and escape and expand above the upper surface of the block 21 to create a gaseous
support under the advancing glass sheets 7.
[0032] Gas is continually released from the apertures 22 into the gaseous support for each
glass sheet and simultaneously gas escapes from the gaseous support through the exhaust
apertures 23 into the exhaust chamber 14 and thence to the outlet apertures.
[0033] The upper surfaces of the blocks 21 are transversely tilted so as to lie at the same
small angle to the horizontal, for example 5°, as the conveyor rollers 8. The upper
surfaces of the collars 9 on the conveyor rollers 8 are slightly higher than the level
of the upper surface of the first block 21 so that as soon as each glass sheet 7 becomes
completely and uniformly supported on the gaseous support it tends to slide down the
transverse incline until it is in engagement with rotating discs 24 mounted alongside
the blocks 21 on vertical spindles (not shown) which extend upwardly from drive motors
(not shown) arranged outside the furnace. The drive motors drive the discs at a controlled
speed commensurate with the rate of advance of the glass sheets on to the gaseous
support by the rollers 8. The collars 9 may be arranged so that if the sheets are
already touching the collars then they will be in a position to be driven by the edge
discs 24 without any substantial movement of the sheets down the transversely sloping
upper surface of the first block 21.
[0034] The glass sheets are, as shown in Figure 2, placed on the conveyor rollers end-to-end
so that a succession of flat glass sheets 7 are advanced into the furnace by the driving
action of the conveyor rollers.
[0035] As the glass sheets advance over the rollers 8 in the first part of the furnace and
then subsequently over the blocks 21 on the gaseous support created by the presence
of the sheets over the blocks they become heated by the hot gases of the support and
by radiant heat from heaters 26 mounted in the roof structure over the path of travel
of the glass sheets.
[0036] The edge discs 24 maintain the registration of the glass sheets in the furnace and
also provide drive to cause the forward movement of the sheets. However, some of the
discs 24 may be free running and act as rotatable guides.
[0037] In the apparatus of Figure 2 there are three sections to the furnace which are of
identical construction. The construction of the last section is illustrated in Figure
3, and by the time each glass sheet 7 reaches the end of the furnace the glass is
at a temperature of the order of 630°C to 670°C for soda-lime-silica glass suitable
for the thermal toughening of the glass by subjecting the glass to quenching gas flows,
usually flows of air at ambient temperature.
[0038] The advance of the hot glass sheets continues to a quenching station which is indicated
generally at 27 in Figure 3. At the quenching station the glass sheets are supported
on a gaseous support generated above a bed of identical construction to the bed in
the furnace except that the bed is supplied with chilling air at ambient temperature.
The presence of each glass sheet advancing into the quenching station 27 from the
furnace generates a gaseous cushion between the sheet and the upper surface of the
bed which provides both the required support for the sheet and a flow of chilling
air against the bottom surface of the glass sheet. The advance of the glass sheet
is continued by means of rotating discs, not shown.
[0039] In the quenching station there is a generalised flow of quenched gas contacting the
upper surface of the glass sheet which gas flow has a substantially identical chilling
effect on the upper surface of the glass as the chilling effect of the lower surface
by the gaseous support. The gas flows on the upper surface are generated from an upper
gas supply and exhaust equipment of identical construction to the base bed supplying
gas to and exhausting gas from the gaseous support.
[0040] As shown in Figure 3 the upper part of the quenching station comprises a plate 28
of asbestos-based, heat-resistant material which has gas supply apertures 29 and gas
exhaust apertures 30. These apertures are also shown in Figure 4. The plate 28 is
fixed to an apertured base plate 31 of a gas exhaust chamber 32. The matching surfaces
of the plates 28 and 31 are machined flat so as to be gas tight. The roof of the exhaust
chamber 32 is a plate 33 which also forms the base of a plenum chamber 34 to which
chilling air at ambient temperature is supplied. The chilling air passes through apertures
in the plate 33 and is conducted down tubes 35 extending through the exhaust chamber
32 the lower ends of which tubes are fixed in the base plate 31 of the exhaust chamber
and communicate with the gas supply apertures 29 in the plate 28. The gas exhaust
apertures in the plate 28 are aligned with exhaust apertures 36 in the plate 31 so
that gas can escape from above the glass sheet into the exhaust chamber 32 whose walls
have apertures so that the exhaust gases can be exhausted to atmosphere or collected
and recirculated.
[0041] In order to produce the stress distribution described with reference to Figure 1
the hot glass sheet which is being subjected to the generalised quenching gas flows
at the quenching station is also subjected to localised gas flows by subjecting the
upper surface of the glass to a rectangular array of gas jets which are spaced apart
in rows transversely of the direction of advance of the glass with rows spaced apart
in the direction of advance. The distribution of the gas supply apertures 29 and gas
support apertures 30 in the plate 28 is slightly inclined to the direction of advance
of the glass, as illustrated in Figure 4, in order to minimise any striping effect
which could otherwise be produced in the form of a polarisation pattern on the glass
surface. The array of gas jets is provided by an array of gas supply nozzles 37 which
are connected in rows to ducts 38 located in the exhaust chamber 32. The nozzles 37
extend downwardly through specially enlarged gas exhaust apertures 30 in the plate
28 as illustrated in Figures 3 and 4. One end of each of the ducts is connected to
an air supply manifold 39 located outside the exhaust chamber alongside the quenching
station.
[0042] In the embodiment illustrated there are four rows of nozzles 37 spaced apart at the
same pitch as the gas exhaust apertures 30 in the direction of advance of the glass
sheet. In Figure 3 the quenching air flows supplied from the gas release apertures
29 are illustrated by the arrows 40 and the localised gas jets directed at the upper
surface of the glass are illustrated by the arrows 41. The mounting of the ducts 38
with their nozzles 37 is illustrated in more detail in Figure 5.
[0043] Figure 6 illustrates regulation of the air supply to the manifold 39 and therefore
regulation of the gas jets. The manifold 39 is connected through a pressure regulator
42 to the outlet of a solenoid operated spool valve 43 of conventional design. Air
is supplied from an air supply 44 through a regulator 45 to an air receiver 46 which
is connected to the inlet of the spool valve 43. The air supply 44 is a supply of
compressed air.
[0044] The spool valve is controlled by an electronic timing unit 47 connected by control
lines indicated at 48 to the spool valve. There are two setting controls on the timing
unit 47. One of these 49 controls the frequency of opening the valve 43 to supply
pulses of compressed air on the manifold 39 to the nozzles 37. The control 50 controls
the length of each pulse of compressed air.
[0045] When each hot glass sheet is advancing through the generalised quenching which it
receives by the quenching gas flows adjacent both its surfaces at the quenching station,
it is also subjected to localised gas flows from the nozzles 37 for a predetermined
time. These gas flows are pulsed at a pulse repetition frequency and with a pulse
length related to the speed of advance of the glass through the quenching station.
The controls 49 and 50 of the timing unit 47 are set so that each increment of the
glass sheet passes from one row of nozzles 37 to the next row of nozzles 37 in the
time between pulses. That is, the localised regions of the glass which have received
more intense quenching by reason of the pulsed gas jets from the first row of nozzles
are beneath the second row of nozzles by the time the second pulse of compressed air
is supplied to the nozzles. These localised areas are therefore subjected to accumulative
chilling by the successive pulsed jets of gas. This localised quenching of the upper
surface of the glass superimposed on the general overall quenching which is being
achieved at the quenching station produces in the glass the distribution of regions
of more highly toughened glass interspersed with regions of lesser toughened glass
described with reference to Figure 1 and the resultant toughened glass sheet which
emerges from the quenching station on rollers 51 has the required stress pattern.
[0046] Instead of the electronically controlled solenoid operated spool valve of Figure
6, the pulsing of the supply of compressed air to the manifold 39 may be achieved
by means of a rotary ball valve 52, Figure 7, driven from a variable speed motor drive
unit 53 which is connected to the rotary ball of the valve 52 through a coupling 54.
The relationship between pulse repetition frequency and pulse length cannot be varied
with a valve of this kind although the repetition frequency and pulse length can be
varied together by variation of the speed of the motor.
[0047] In one example of operation of the apparatus described with reference to Figures
2 to 7 the compressed air supply is at 690 kPa on line 44. The diameter of the bore
of each of the nozzles 37 is 4.8 mm and the nozzle spacing is at 38 mm square pitch.
The spacing of the ends of the nozzles from the upper surface of the glass supported
on the gas cushion at the quenching station is 6 mm to 12 mm.
[0048] The frequency and duration of the pulsing of the compressed air supply depends on
the length of the glass sheet and its speed. With a speed of travel of the glass of
190 mm/s there is one pulse every 0.2 seconds and a duration of each pulse is 0.1
seconds.
[0049] The product had an average central tensile stress of between 55 MN/m
2 to 62 MN/m
2 with a principal stress difference in at least some of the areas at a maximum between
6 MN/m
2 and 15 MN/m
2. One result achieved was 8.4 MN/
M2.
[0050] For a nozzle spacing of 38 mm square pitch, the distance between the centres of adjacent
areas in which the principal stress difference is a maximum and is in different directions
is 27 mm. Nozzle spacings in the range 22 mm to 42 mm square pitch result in the distance
between the centres of such adjacent areas being in the range 15 mm to 30 mm.
[0051] The method of the invention can be employed for the production of the required stress
pattern in bent glass sheets using apparatus illustrated in Figure 8 which apparatus
is described in more detail in United Kingdom Patent No. 1,190,373. After heating,
each glass sheet advances on to a transitional block 55 whose thickness along its
longitudinal centre line is the same as the thickness of the two blocks 21 but whose
upper face is machined as a series of flats of gradually increasing angle which result
in the upper surface of the block 55 having the desired final curved form of the glass
sheets. The glass advantages on to this transitional block and is heated to a temperature
such that it can sag downwardly to conform to the shape of the block. The block is
apertured to provide a gaseous support created beneath the hot deformable glass as
it glides over the block. This downward sagging increases progressively as the glass
sheet advances and the glass which is still hot and deformable moves from the block
55 onto a final part of the bed 56 whose cross section conforms to the now curved
shape of the glass sheet. The glass sheet advances over this curved section of the
bed to the quenching station the upper and lower part of which are also suitably curved
with a curved distribution of the nozzles 37 in order to provide the overall quenching
of the glass sheets simultaneously with the localised quenching by the gas jets from
the nozzles 37.
[0052] Figure 9 illustrates the toughening of a glass sheet 7 which is being advanced on
a roller conveyor comprising a series of horizontal rollers 57.
[0053] The conveyor carries the glass sheet through a heating furnace indicated at 58 at
a quenching station where the rollers carry the glass sheet between upper and lower
blowing boxes 58 and 59. The box 58 has an array of blowing nozzles 60 which point
downwardly toward the roller conveyor so as to direct generalised quenching gas flows
on to the upper surface of the glass sheet 7. The nozzles 60 are arranged at a slight
angle to the direction of advance of the glass sheet in the same way as the supply
and exhaust apertures in Figure 4.
[0054] Similarly the lower blowing box 59 has upwardly projecting blowing nozzles 61 which
are directed through the gaps between the rollers 57 and are also arranged at a slight
angle to the direction of advance of the glass sheet. The flows of quenching gas from
the nozzles 60 and 61 is supplemented by localised gas flows from a row of gas supply
nozzles 37 connected to a duct 38 and mounted between adjacent rows of upper nozzles
60. The nozzles 37 direct localised gas jets at the upper surface of the glass in
the same way as described with reference to Figures 3 and 4 and are pulsed as described
with reference to Figure 6 or Figure 7 so that the glass sheet emerging from the quenching
station on the roller conveyor has the required distribution of regions of more highly
toughened glass interspersed with regions of lesser toughened glass.
[0055] Alternatively or in addition localised gas jets may be directed against the lower
surface of the glass sheet by gas supply nozzles 37 directed upwardly through the
gaps between the rollers 57. When localised gas jets are directed against both the
upper and lower surfaces of the glass sheets these are arranged to act on opposed
regions of the two surfaces of the sheets. _
[0056] Such a toughening pattern may not be produced over the whole of the glass sheet.
Part only of the sheet may be subjected to the pulsed localised gas jets by providing
nozzles 37 only over the path of the part of the sheet to be specially toughened.
Only one nozzle may be employed to produce in a strip-shaped region of the sheet a
linear distribution of areas of more highly toughened glass interspersed with regions
of lesser toughened glass.
[0057] The toughening produced by the pulsed localised gas jets need not be superimposed
on a generalised toughening but may be employed alone when the glass sheet is advanced
on a roller conveyor or while suspended vertically from an overhead conveyor or while
carried in a near-vertical. position on a movable carriage. Because of the quenching
action of the spill of gas over the glass surface between the gas jets impinging on
the glass, there is a degree of lesser toughening of the regions of the glass which
lie between the regions of more highly toughened glass produced by the pulsed gas
jets. This may be affective over the whole of the sheet or over part only of the sheet
with the rest of the sheet untoughened.
1. A method of toughening a glass sheet in which the glass sheet is advanced through
a quenching station where the sheet is subjected to quenching gas flow, characterised
in that the quenching gas flow is at least one localised gas flow which is pulsed
at a repetition frequency related to the speed of advance of the glass through the
quenching station to induce in the glass a distribution of regions of more highly
toughened glass interspersed with regions of lesser toughened glass.
2. A method according to Claim 1, in which the glass sheet is advanced between flows
of quenching gas at the quenching station to produce overall toughening of the glass,
characterised in that said at least one localised gas flow is superimposed on said
flows of quenching gas. '
3. A method according to Claim 2, characterised in that the glass sheet which is advancing
horizontally between said flows of quenching gas is subjected to a plurality of said
localised gas flows by directing towards at least one face of the glass, as it passes
through the quenching station, gas jets which are spaced apart in a row transversely
to the direction of advance of the glass, and pulsing said gas flows to produce said
distribution of regions of more highly and lesser toughened glass in which distribution
there are areas in which the principal stresses acting in the plane of the glass sheet
are unequal.
4. A method according to Claim 3, characterised by pulsing an array of gas jets which
are spaced apart in rows transversely of the direction of advance of the glass with
the rows spaced apart in the direction of advance, which pulsing is at a rate related
to the speed of advance of the glass so that localised areas of the glass are subjected
to accumulative chilling by successive pulsed jets.
5. A method according to any of Claims 1 to 4, characterised in that said at least
one localised gas flow is directed towards the upper face of the glass sheet which
is advancing horizontally through the quenching station on a gaseous support.
6. A method according to any one of Claims 1 to 4, characterised in that said at least
one localised gas flow is directed towards at least one face of the glass sheet which
is advancing horizontally through the quenching station on rollers.
7. A toughened glass sheet for use as a side or rear window for a motor vehicle, produced
by a method according to any one of Claims 1 to 6.
1. Procédé de trempe de feuille de verre selon lequel la feuille de verre avance à
travers un poste de trempe où elle est soumise à l'action d'un courant de gaz de trempe,
caractérisé en ce que le courant de gaz de trempe est constitué par au moins un courant
gazeux localisé qui est pulsé à une fréquence de répétition liée à la vitesse d'avance
du verre à travers le poste de trempe, ceci pour établir dans le verre une distribution
de régions à degré de trempe relativement accusé entremêlées avec des régions à degré
de trempe moindre.
2. Procédé selon la revendication 1, selon lequel la feuille le de verre avance, au
poste de trempe, entre des courants de gaz de trempe destinés à assurer une trempe
d'ensemble du verre, caractérisé en ce que le ou chaque courant gazeux localisé précité
est superposé aux dits courants de gaz de trempe.
3. Procédé selon la revendication 2, caractérisé en ce que, pour soumettre la feuille
de verre, en cours d'avance horizontale entre lesdits courants de gaz de trempe, à
l'action de plusieurs desdits courants gazeux localisés, on dirige vers une face au
moins du verre pendant que celui-ci traverse le poste de trempe, des jets gazeux espacés
en rangée transversalement à la direction d'avance du verre, et en ce qu'on pulse
ces courants gazeux pour établir ladite distribution de régions à degrés de trempe
relativement accusé et moindre, cette distribution comportant des zones où les principales
contraintes agissant dans le plan de la feuille de verre sont inégales.
4. Procédé selon la revendication 3, caractérisé en ce que l'on pulse un ensemble
de jets gazeux qui sont espacés en rangées transversalement à la direction d'avance
du verre, les rangées étant espacées suivant la direction d'avance, la fréquence de
pulsation étant liée à la vitesse d'avance du verre de façon que certaines zones localisées
du verre subissent un refroidissement cumulatif sous l'action de jets pulsés successifs.
5. Procédé selon l'une quelconque des revendications 1 à 4, charactérisé en ce qu'au
moins un courant gazeux localisé est dirigé vers la face supérieure de la feuille
de verre, qui avance horizontalement à travers le poste de trempe sur un support gazeux.
6. Procédé selon l'une quelconque des revendications 1 à 4, charactérisé en ce que
le ou chaque courant gazeux localisé précité est dirigé vers une face au moins de
la feuille de verre, qui avance horizontalement à travers le poste de trempe sur des
rouleaux.
7. Feuille de verre trempé à utiliser comme glace latérale ou arrière pour véhicule
automobile, obtenue par un procédé selon l'une quelconque des revendications 1 à 6.
1. Verfahren zum Vorspannen einer Glasbahn, bei dem die Glasbahn durch eine Abschreckstation
vorgerückt wird, wo die Bahn einem Abschreckgasstrom ausgesetzt wird, dadurch gekannzeichnet,
daß der Abschreckgasstrom wenigstens ein örtlich begrenzter Gasstrom ist, der mit
einer von der Vorrückgeschwindigkeit des Glases durch die Abschreckstation abhängigen
Wiederholungsfrequenz pulsiert wird, um im Glas eine Verteilung von Zonen stärker
vorgespannten Glases mit eingesprengten Zonen geringer vorgespannten Glases zu erzeugen.
2. Verfahren nach Anspruch 1, bei dem die Glasbahn zwischen Abschreckgasströmen an
der Abschreckstation vorgerückt wird, un eine Gesamtvorspannung des Glases zu erzeugen,
dadurch gekennzeichnet, daß der wenigstens eine örtlich begrenzte Gasstrom den Abschreckgasströmen
überlagert wird.
3. Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß die Glasbahn, die horizontal
zwischen den Abschreckgasströmen vorrückt, einer Mehrzahl der örtlich begrenzten Gasströme
ausgesetzt wird, indem man auf wenigstens eine Fläche des Glases, wenn es durch die
Abschreckstation läuft, Gasstrahlen richtet, die in Abständen in einer Reihe quer
zur Vorrückrichtung des Glases vorgesehen sind, und die Gasströme pulsiert, um die
Verteilung von Zonen stärker und geringer vorgespannten Glases zu erzeugen, bei welcher
Verteilung Bereiche vorliegen, in denen die in der Ebene der Glasbahn wirkenden Hauptspannungen
ungleich sind.
4. Verfahren nach Anspruch 3, gekennzeichnet durch Pulsieren einer Gruppe von Gasstrahlen,
die in Abständen in Reihen quer zur Vorrückrichtung vorgesehen sind, wobei die Reihen
einen Abstand in der Vorrückrichtung aufweisen und das Pulsieren mit einer von der
Vorrückgeschwindigkeit des Glases abhängigen Frequenz derart erfolgt, daß begrenzte
Bereiche des Glases einer kumulativen Abkühlung durch aufeinanderfolgende pulsierte
Strahlen ausgesetzt werden.
5. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß wenigstens
ein örtlich begrenzter Gasstrom auf die Oberseite der Glasbahn gerichtet wird, die
horizontal durch die Abschreckstation auf einem gasförmigen Träger vorrückt.
6. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß wenigstens
ein örtlich begrenzter Gasstrom auf wenigstens eine Fläche der Glasbahn gerichtet
wird, die horizontal durch die Abschreckstation auf Rollen vorrückt.
7. Vorgespannte Glasscheibe zur Verwendung als Seiten- oder Hinterscheibe für ein
Motorfahrzeug, hergestellt durch ein Verfahren nach einem der Ansprüche 1 bis 6.