JPH0345526A - Heat treatment of glass plate - Google Patents

Abstract

PURPOSE:To easily obtain a glass plate excellent in resistance to wind pressure and thermal crack by cooling a glass plate under specified cooling conditions depended on its thickness to control the enhancing stress generated. CONSTITUTION:Firstly, a glass plate 5-12mm thick is heated to 570-660 deg.C. Sec ond, air is blown on the surface of the glass plate heated to bring the cooling heat transfer coefficient to 40-60Kcal/m<2>h deg.C, thus cooling the plate to its strain point temperature or lower. Third, said glass plate is further cooled while the heat transfer coefficient is gradually increased to 100-120Kcal/m<2>h deg.C. Thence, the glass plate is further cooled with its heat transfer coefficient kept invariant so that its central tensile stress sigmat fall between 85 and 200kg/cm<2> and the ratio sigmac/sigmat between 1.5 and 3 (where sigmac is surface compressive stress).

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is suitable for use in windows of high-rise buildings, which prevents cracks from propagating even when a glass plate cracks, has sufficient wind pressure resistance, and does not crack due to heat. The present invention relates to a method for producing optimal heat-treated glass.

[Prior Art] In high-rise buildings, extra-thick glass plates of about 10 mm to 20 mm are used in order to improve the wind pressure resistance of window glass plates. Using extra-thick glass plates like this has the disadvantage of significantly increasing weight, and when thick heat-absorbing glass or colored coated glass plates are used, there is a particularly high risk of thermal cracking. There is a drawback. It is also possible to use air-cooled tempered glass sheets to reduce weight and prevent heat cracking, but air-cooled tempered glass sheets break into many small pieces when broken, so air-cooled tempered glass sheets are not recommended for high-rise buildings. This is undesirable, as there is a risk that glass fragments may fall from the windows of high-rise buildings when they break.

A glass plate made of soda lime has a softening point temperature range of 600~
Conventional tempered glass sheets, which are heated to 60°C and then immediately quenched and strengthened by blowing air on both sides of the glass sheet, have a surface compressive stress of 1000 kg/cm'' to 1500 kg/cm2 and a center of the cross-sectional direction. A tensile stress that is 1/2 of the surface compressive stress is generated in the area, and the cross-sectional stress distribution is as shown in Figure 1.When this tempered glass plate breaks, the cracks that have occurred in the glass plate It runs on its own and breaks into small pieces with a crushing density that is uniquely determined by the magnitude of the central tensile stress, for example, 40 to 200 pieces of 15 cm square.Also, so-called early-strengthened glass plates, in which the degree of reinforcement of the glass plate is adjusted, It has a surface compressive stress σc of 300 to 600 kg/cm2, a central tensile stress σt of 250 to 400 kg/cm, and a ratio of σc/σt of less than 1.5, and its cross-sectional stress distribution is as shown in Figure 2. Therefore, when this early-strengthened glass plate is broken, although it does not break into small pieces, the cracks that occur in the glass plate at the time of breakage propagate by themselves and extend to the edges of the glass plate.

In addition, chemically strengthened glass plates have a weight of 1000 kg/cm” ~ 3
000 kg/am” surface compressive stress and 1 (1 to 60 kg
/ca+", and its stress distribution is shown in Figure 3. Although some pieces have a small number of fragments when crushed, this chemically strengthened glass sheet has a surface compressive stress layer. Since it is thin, it has the disadvantage that the impact strength when scratched is significantly reduced, and the reinforcing treatment process requires a long time, so it is not suitable for practical use.

[Problem to be solved by the invention] In order to solve the problems that occur when conventional tempered glass is used as window glass for high-rise buildings, etc., it is necessary to solve the problems that occur when the conventional tempered glass is used as window glass for high-rise buildings. Not running,
Heat-treated glass that has sufficient wind pressure resistance and does not crack due to heat, making it ideal for use in high-rise building window glass or swandrels.
That is, the heat-treated glass plate has a thickness of 5 to 12 mm, and the central tensile stress σt of the heat-treated glass plate is 85 kg/cm2.
~200 kg/cm', and the ratio σC/σ1 of the surface compressive stress σゎ and the central tensile stress σt is 1.
．． Heat-treated glass sheets have been proposed with cross-sectional stress distributions in the range of 5 to 3.0.

In addition, as a manufacturing method for such a heat-treated glass plate, a glass plate is passed through a heating furnace and heated to 600 to 660°C, and then the glass plate is taken out from the heating furnace, and then air is immediately blown onto the surface of the glass plate to heat the glass plate. It is known to slow down the cooling rate to 1/3 to 1/4 of that of ordinary air-cooled tempered glass to cool the glass plate to below its strain point temperature. However, in this manufacturing method, the cooling rate of the glass plate is slow, so the cooling time is about 2 to 3 times that of ordinary tempered glass, so the productivity is low and it is not suitable for mass production. there were.

The present invention is a heat treatment method that is thinner than conventional extra-thickness glass sheets for window glass of high-rise buildings, etc., does not allow cracks to propagate, does not cause thermal cracking, has no practical problems, and can be mass-produced. Its purpose is to provide a method for manufacturing glass.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and it is possible to heat a glass plate having a thickness of 5 mm to 12+ nm at 570°C to
A heating process of heating the glass to 660°C, and then taking out the glass from the heating furnace, immediately blowing wind on the glass surface to increase the cooling heat transfer coefficient of the glass plate surface to 40 to 60 kcal/
An initial cooling process in which the glass plate is cooled down to the strain point temperature or less as m''h'C, then a transition process in which the glass plate is cooled while gradually increasing the cooling heat transfer coefficient, and the cooling heat transfer coefficient is 100~
When the temperature reaches 120 kcal/m2h"c, a secondary cooling process is carried out to cool the glass plate while maintaining the cooling heat transfer coefficient, and the central tensile stress σt of the treated glass plate is 85
~200 kg/cm'', and the ratio σC/σt of the surface compressive stress σc and the central tensile stress σt is 1.5.
The present invention provides a method for heat treatment of a glass plate, which is characterized in that the heat treatment is controlled to be in the range of .about.3.0.

The heat-treated glass plate of the present invention has a central tensile stress σt of 8
Controlled low between 5 and 200 kg/cm,
and the ratio σ of the surface compressive stress σc and the central tensile stress σt
e/σt is controlled in the range of 1.5 to 3.0, and the surface compressive stress is kept low in the range of 127 to 600 kg/cm'', more preferably 250 to 350 kg/cm'', as shown in Figure 4. Since the cross-sectional stress distribution is uniform, when a crack occurs in this heat-treated glass plate, the fracture line does not propagate on its own, and it does not break into small pieces. Moreover, this heat-treated glass plate has a thickness of 51III+ or more and 12 mm or less, and has a weight of 127 to 600 kg/cm, more preferably 2
Since it has a surface compressive stress of 50 to 350 kg/c-, the wind pressure strength is more than twice that of a raw board of the same thickness, which is sufficient for practical use, and it does not suffer from thermal cracking.

For example, when the plate thickness is 6ffII11, the central tensile stress σt is 2
50kg/cm”, surface compressive stress σc is 500kg/C
m” (σc/σt=2), if the central tensile stress is too high and the glass plate cracks,
As the crack propagates on its own, the fragments become finer and the 9th
This results in a crushing pattern as shown in the figure, which is undesirable because there is a high risk that the crushed pieces will fall out of the window. Also, the board thickness is 8mm
, the central tensile stress σt is 300 kg/cm" and the surface compressive stress σc is 580 kg/am" (i.e. a Jσ-1-9
The same applies to the glass plate 3).

On the other hand, the fracture patterns of the heat-treated glass plates manufactured by the present invention, for example, the samples of Examples 1 to 3, are as shown in Figs. This prevents the breakage line from entering from one end of the glass plate to the other, and prevents broken pieces of the glass plate from falling from the window. In addition, the surface compressive stress required to prevent thermal cracking and wind pressure fracture is 127 kg/am” or more, particularly preferably 200 kg.
Since it has a higher surface compressive stress than /c-, there is less risk of thermal cracking and also has sufficient wind pressure resistance.

In addition, when a glass plate breaks, the risk of falling fragments of the window glass plate is reduced if the self-propagation of the crack is suppressed and the fracture line (crack) does not extend from one side of the glass to the other. Although it is preferable, even if there is about one fracture line (cracks) extending from one side of the glass plate to the other, the risk of falling fragments from the window is actually reduced by one.
The presence of cracks is acceptable as a fracture pattern in the heat-treated glass produced according to the present invention. For example, Figure 7.8 is an example of this being allowed.

FIG. 10 shows a specific example used for manufacturing the heat-treated glass plate of the present invention, and in the figure,
1 is a glass plate of 5~l O++u++ thickness to be heat treated;
2 is a roller hearth, 3 is a conveyor roll for a glass plate, 4 is a heating device for a glass plate, 5 is a wind outlet provided vertically facing each other, and 6 is a cooling furnace surface coating surface provided vertically facing each other. show. Only one wind outlet 5 may be provided as shown in Fig. 10, and the cooling heat transfer coefficient of the glass plate surface may be controlled by controlling the strength of the wind from the wind outlet 5 using a program or the like. Alternatively, two or more air outlets may be provided to vary the air volume. The glass plate 1 to be heat treated is heated to a temperature sufficient to strengthen the glass plate, for example, 570° C. to 6° C., while being horizontally conveyed or slid horizontally in a roller hearth 2 by a conveying roll 3.
Heated to 60°C. (Heating process) The glass plate 1 taken out from the roller hearth 2 is moved between vertically opposed wind suction ports, and air is blown onto the glass plate surface from the wind suction ports to transfer cooling heat to the glass plate surface. Rate is 40-60
kcal/m"h"c, and the temperature of the glass plate is below the strain point (520°C for normal soda lime glass).
℃ or lower, preferably 480℃ or lower).

(Initial cooling process) At this time, the optimum cooling heat transfer coefficient is 6
Approximately 60kca1/m2h℃, 8mm for a mm thick glass plate
Approximately 50kcal/m2h'c, 10mm with thick glass plate
It is approximately 40kcal/m"h'C for a thick glass plate.

Also, at this time, the temperature of the air being blown should be between 50℃ and 400℃.
If the hot air is
By using nAg, the heat transfer coefficient of the glass plate surface is 4
It can be controlled to be 0 to 60 kcal/m2h'c.

Furthermore, in this case, if the air outlet or the cooling furnace wall is made of mirror-finished 5US304 or the like with an emissivity of 0.1 or less and cooling by radiation is suppressed, it will be easier to control the cooling heat transfer coefficient of the glass plate surface. preferable.

Once the temperature of the glass plate has fallen below the strain point in this way, cooling is then carried out while gradually increasing the cooling capacity, that is, usually while gradually increasing the cooling heat transfer coefficient of the surface of the glass plate. (Transition process) If the rate of gradual increase is too large, it may cause damage to the glass plate, and if it is too small, the effect of the present invention in improving productivity will be small. It is preferable to set it within a certain range.

Specifically, for a 6mm thick glass plate, 2 to 4 kca
l/m2h"c 5 For an 8 mm thick glass plate, it is preferably 1 to 3 kcal/m"h@c 5 For a 10 mm thick glass plate, it is preferably 0, 5 to 2, 5 kcal/m2hC s.

The cooling heat transfer coefficient of the glass plate surface is 100 to 120 kcal
/m"h"Cs, cooling is performed thereafter while maintaining that heat transfer coefficient. (Secondary Cooling Step) As can be easily understood from the above, the time required for the transition step depends on the thickness of the glass plate, but is approximately 20 to 40 seconds.

Figure 16 shows the changes in the cooling heat transfer coefficient of a typical glass plate surface for each glass plate thickness. Here, the horizontal axis represents time, and the vertical axis represents cooling heat transfer coefficient.

When the surface is cooled by increasing the cooling heat transfer coefficient, one cycle of heat treatment can be performed in about 240 seconds to 420 seconds. This is a time of about %~H compared to the conventional heat treatment method, and it can be seen that by employing the glass plate heat treatment method according to the present invention, it is possible to significantly improve productivity.

Thereafter, the glass plate is taken out from the air outlet and is made into a tempered glass plate product having a predetermined stress value and stress distribution.

The heat-treated glass plate of the present invention is manufactured using a roller hearth as described above, but this method is not limited to this method.The glass plate is heated while being conveyed horizontally using a gas hearth, and the glass plate is heated from the outlet of the gas hearth. A method of heat-treating the heated glass plate immediately after it comes out, or a method of heating the glass plate in a heating furnace while hanging it from a hanger and transporting it, and then heat-treating the heated glass plate immediately after it comes out of the outlet of the heating furnace. It can also be manufactured in the same way.

[Function] By the method of the present invention, the central tensile stress σt is 85 to 200.
kg/cm” and its surface compressive stress σc
and the central tensile stress σt, the ratio σc/σt is 1.5 to 3.0
The reason for obtaining heat-treated glass in the range of
It can be considered as follows.

When a softened glass plate is rapidly cooled, the temperature distribution in the cross-sectional direction of the glass plate reaches a steady state after passing through a certain transition state. Normally, the temperature at the center of the glass plate is the solidification temperature (560 to 57
The temperature distribution (difference in temperature between the surface and the center) when passing through the glass plate (0°C) determines the degree of reinforcement of the glass plate, that is, the central tensile stress and the surface compressive stress.

The method of the present invention focuses on controlling the temperature distribution when this softened glass plate is solidified. That is, once the thickness of the glass plate is determined, the temperature distribution in the cross section of the glass plate is uniquely determined by the cooling conditions, so the strengthening stress that occurs is controlled by controlling the cooling conditions.

[Example] Using the above-mentioned apparatus, a normal soda-lime glass plate (
Strain point: 511°C, softening point: 740°C) was heat treated under the conditions shown in Table 1, and the heat treatment conditions, central tensile stress σ, surface compressive stress σc, σJσ1, and wind pressure resistance of the resulting heat-treated glass plate are shown. Allowable load (probability of failure 1/1000 or less),
Thermal cracking test results (temperature difference between the center and periphery of the glass plate until thermal cracking), the time required for - treatment cycles, etc. are shown in Table 1 as Examples 1 to 3 and Comparative Examples 1 to 4. Ta. In addition, the fracture patterns when the destructive test specified in JISR3206 6-5 was conducted on the heat-treated glass plates of Examples 1 to 3 and the heat-treated glass plates of Comparative Examples 1 to 3 were 5 to 8.
As shown in the figure.

By comparing Examples 1 to 3 in Table 1 with Comparative Examples 1 to 3, it can be seen that according to the heat treatment method for glass plates according to the present invention, glass plates showing almost the same crushing pattern as the conventional method can be obtained in an extremely short treatment cycle. It can be seen that it can be obtained by

The surface compressive stress of the glass plates in the above Examples and Comparative Examples was measured using a Toshiba air-cooled tempered glass surface stress meter FSM-30, and the central tensile stress was measured as follows.

・Measurement of central tensile stress Hold the glass sample 11 horizontally as shown in Figure 11,
A He-Ne laser 12 is installed perpendicular to the end face, and a polarizer 1 is used as a light source.
3. Linearly polarized light A that has passed through a lens 14 and an aperture 15 is incident. The directions parallel and perpendicular to the surface of the glass plate 11 are respectively y,
z, and the incident direction is X.

The vibration direction of the incident light is set to form an angle of 45@ with respect to each axis in the y-z plane.

Linearly polarized light A incident from the end surface of the glass plate produces a phase difference due to the principal stress difference in the y-z plane inherent in the glass,
As shown in Figure 12, an ellipse with its axis at an angle of 45° with the y-z axis - one circle, one ellipse, one straight line (orthogonal to the incident light) - an ellipse N circles - an ellipse -
The linear and polarized light changes, and returns to linearly polarized light with a phase difference of 360° and the same vibration direction as the original incident light.

This polarized light is scattered within the glass and is oriented at right angles to the optical axis.
- When observed from the direction of 45 degrees with the y and z axes in the z plane,
As shown in FIG. 13B or FIG. 14, each wavelength looks like a dot.

Since the scattering of the float glass plate is very small, the scattered light to be observed is weak. For this reason, micro
Using a night vision device with a built-in channel image intensifier, monitor TV through a high-sensitivity TV camera 16. A dot pattern of scattered light is projected onto 17. In combination with the position analyzer 18, the length can be read in real time.

Since one dot corresponds to a phase difference of 360° (one wavelength), by measuring this actual length, the principal stress difference can be calculated from the photoelastic constant.

From the principal stress difference Δσ obtained here, the central part σt is determined by the following formula.

Principal stress difference △σ Tensile stress oy = Component of stress in the plane direction, i.e. central tensile stress σt σ: Component of stress in the thickness direction (σ2 fathom○) Luni Laser light wavelength (632.8 mm He-Ne laser) βλ:
Optical path difference (cm) corresponding to a 360° phase difference C: Photoelastic constant 2.63 m u /cm/kg/am'' (float plate) Note that the central tensile stress σt manufactured by the present invention is 85
~200kg/cm”, surface compressive stress σc is 127~6
00kg/cm”, more preferably 200 to 300kg
/cm", the above stress values of the heat-treated glass plate are the 15th
As shown in the figure, 4 points P on the periphery of the heat-treated glass plate and 1 point on the center.
It shows the average of the measured values at five points, including point Q, and is taken as an average value.

[Effects of the Invention] According to the present invention, the wind pressure strength is practically sufficient and there is no thermal cracking, and even if a crack enters the glass plate, the crack does not propagate on its own and does not break into small pieces. It is possible to provide heat-treated glass with high productivity. Even if this glass plate breaks, there is little risk that some or all of the pieces will fall off the window frame, and it is useful as a glass plate for construction of buildings, houses, etc. In particular, there is a demand for a glass plate that is free from the risk of glass fragments falling, and the heat-treated glass plate of the present invention is most suitable as a building glass plate for windows of high-rise buildings.

Among these, the heat-treated glass plate of the present invention is suitable for glass plates such as heat-absorbing glass plates, colored coated glass plates, and heat-reflecting glass plates used for windows or spandrels that have a high risk of thermal cracking. .

In addition, the glass plate according to the present invention has improved wind pressure strength and thermal cracking strength, and also has improved crack self-propagation prevention.
I＼ THA L Sho 1 Legged Lug Book 18-
−100 Highness board was used. Uesaka window glass sheets for mid-to-high-rise buildings can be replaced with 6 mm thick heat-treated glass sheets according to the present invention, and 12 mm thick conventional Uesaka window glass sheets can be replaced with 8+n+++ thick heat-treated glass sheets according to the present invention, thereby reducing the weight of the glass sheets. can be achieved.

[Brief explanation of drawings]

1 to 3 are stress distribution diagrams of a cross section in the thickness direction of a conventional tempered glass plate, and FIG. 4 is a stress distribution diagram of a cross section in the thickness direction of a heat-treated glass plate manufactured by the method of the present invention. Fig. 5 is a diagram of the crushing pattern of a glass plate according to a comparative example, Figs. 6 to 8 are schematic diagrams of a specific example of the apparatus of the present invention, and Fig. 11 is a diagram of an apparatus for measuring the central tensile stress of a glass plate. Schematic diagram, 1st
Figures 2 to 14 are explanatory diagrams showing the principle of measuring the central tensile stress of a glass plate, Figure 15 is an explanatory diagram showing stress measurement points, and Figure 16 is a glass plate during heat treatment of the glass plate according to the present invention. Surface A + n lungs 2 Kochi Itl Kojuki Laya 20H21 7Fl: Glass plate to be heat treated, 2: Roller hearth furnace, 3: Conveyance roll, 4 Heating device for glass plate, 5:
Wind outlet. 71 Sho f3 Agony 2 Threshold 74 Muddy 71-5 Yusen 7 Diagram contradictory diagram and b diagram! -8 Figure 0 Figure Sai) I'I Sai! 2 o'clock off 3 Kakisai/4) 'A Sai/Puogi procedural amendment October 4, 1999

Claims (1)

[Claims] (1) Glass plate with a thickness of 5 mm to 12 mm at 570°C
A heating process of heating the glass to 660°C, and then taking out the glass from the heating furnace, immediately blowing air onto the glass surface to increase the cooling heat transfer coefficient of the glass plate surface to 40 to 60 kcal.
/m^2h℃ to below the strain point temperature of the glass plate, followed by a transition process in which the glass plate is cooled while gradually increasing the cooling heat transfer coefficient, and the cooling heat transfer coefficient is 100~
When the temperature reaches 120kca1/m^2h℃, there is a secondary cooling process in which the glass plate is cooled while maintaining the cooling heat transfer coefficient, and the central tensile stress σt of the treated glass plate is 85
~200 kg/cm^2, and the ratio σc/σt of the surface compressive stress σc and the central tensile stress σt is 1.
A method for heat treatment of a glass plate, characterized in that the heat treatment is controlled to be in the range of 5 to 3.0.