JPS5925734B2 - Glass plate heat treatment method - Google Patents

Description

[Detailed Description of the Invention] The present invention manufactures heat-treated glass that does not cause cracks to propagate even when a glass plate cracks, has sufficient wind pressure resistance, and does not crack due to heat, and is ideal for use in windows of high-rise buildings. It is about the method.

For example, in high-rise buildings, extra-thick glass plates of about 10 to 20 mm are used to improve the wind pressure resistance of window glass plates.

The disadvantage of using such extra-thick glass plates is that the weight increases significantly, and when thick heat-absorbing glass or colored goat glass plates are used, there is a particular risk of thermal cracking. The disadvantage is that it is expensive.

Although it is possible to use air-cooled tempered glass sheets to reduce weight and prevent heat cracking, air-cooled tempered glass sheets break into many small pieces when broken, so air-cooled tempered glass sheets are not used in high-rise buildings. It is undesirable to use glass panels because there is a risk that glass fragments may fall from the windows of high-rise buildings when they break.

For this reason, attempts have been made to prevent the cracks from propagating by adjusting the degree of reinforcement of the glass plate by so-called manual strengthening, but in devices that normally use air to cool the glass, natural cooling in the atmosphere without air ejection has been attempted. Even with this method, which has the lowest cooling capacity, when the glass thickness is 10% or more, the glass is strengthened by natural convection heat transfer, and it is not possible to manufacture glass with low stress that prevents self-propagation of cracks.

There is also a chemically strengthened glass sheet that has a high surface compressive stress and a low fragment number density as a type of tempered glass sheet, but this chemically strengthened glass sheet has a significant decrease in strength when scratched and is difficult to process during the strengthening treatment process. It is not suitable for practical use because it requires a long time.

First, the applicant has discovered that, unlike conventional tempered glass plates, even when a crack occurs in the glass plate, the crack does not propagate by itself.
The heat-treated glass has sufficient wind pressure strength and does not crack due to heat and is suitable for use in window glasses or spandrels of high-rise buildings, that is, heat-treated glass sheets with a thickness of 10 to 15 mm, and the central tensile stress σt of the heat-treated glass sheet is 85-20
0 kg/crIL, and the ratio σC/σt of the surface compressive stress σC and the central tensile stress σt is 1.5.
We proposed a heat-treated glass plate with a cross-sectional stress distribution in the range of ~2.0.

The present invention was obtained as a result of repeated research aimed at providing an industrial manufacturing method for such heat-treated glass plates. After heating the glass plate to 600°C to 660°C through the air, the glass plate is taken out from the heating furnace, and immediately after that, hot air of 50°C to 300°C is blown onto the surface of the glass plate to control the cooling rate of the glass plate. By cooling the glass plate slower than natural cooling to below the strain point temperature of the glass plate, the central tensile stress σt of the treated glass plate is 85 to 200 kMf.
More preferably, the surface compressive stress is 200 to 30, so that the ratio σC/σt of the surface compressive stress σC and the central tensile stress σt is in the range of 1.5 to 2.0.
The present invention relates to a method for heat treatment of a glass plate, characterized in that the heat treatment method is controlled to achieve 0 kg/l:yit.

Conventional ordinary tempered glass sheets are made by heating a glass sheet made of soda-lime glass to a softening point temperature range of 600 to 700 degrees Celsius, then immediately blowing air on both sides of the glass sheet to quickly cool and strengthen it. 1500 kg/ct
A surface compressive stress of it and a tensile stress of about 1/2 of the surface compressive stress are generated at the center in the cross-sectional direction, and the cross-sectional stress distribution is as shown in FIG.

When this tempered glass plate breaks, the cracks generated in the glass plate propagate by themselves, and the fracture density is uniquely determined by the magnitude of the central tensile stress, for example, 40 to 20.
0 pieces break into small pieces with a 15crrL angle.

Moreover, the semi-tempered glass plate has a surface compressive stress of 300 to 600 kg/i and 250 to 400 kg/cr? It has a central tensile stress σt of L and a ratio of σC/σt of less than 1.5, and its cross-sectional stress distribution is as shown in Figure 2. When this semi-strengthened glass plate breaks, fine Although it cannot be broken by fragments, the cracks that occur in the glass plate at the time of destruction propagate by themselves.
It extends to the edge of the glass plate.

In addition, chemically strengthened glass plates have a weight of 1000 kg/i to 3000 kg/i
This chemically strengthened glass sheet has a surface compressive stress of 10 to 60 kg/i and a central tensile stress of 9/d, and its cross-sectional stress distribution is as shown in Figure 3. Since the layer is thin, the impact strength when scratched is significantly reduced.

On the other hand, the heat-treated glass plate manufactured according to the present invention has a central tensile stress controlled to be low between 85 and 200 kg/-, more preferably 100 and 150 kg/crj, and a surface compressive stress σC and a central The ratio σC/σt to tensile stress σt is controlled within the range of 1.5 to 2.0, and the surface compressive stress is also 127 to 400 kg/cI.
? L is suppressed to a low range, more preferably 200 to 300 kg/d, and the cross-sectional stress distribution is as shown in Figure 4, so that when a crack occurs in this heat-treated glass plate, the fracture line will not move on its own. No, it cannot be broken by small pieces.

Moreover, this heat-treated glass plate has a thickness of 10 mm or more and 15 mm.
It has the following properties and has a surface compressive stress of 127 to 400 kg/i, more preferably 200 to 300 kg/crrt, so the wind pressure strength is more than twice that of raw board of the same thickness, which is sufficient for practical use. Yes, and there is no heat cracking.

For example, when the plate thickness is 121 nm, the central tensile stress σt is 250 nm.
ky/i, surface compressive stress σc is 380 kg/cyyt
When a heat-treated glass plate with (σC/σt=ts2) cracks because the central tensile stress is too high, the crack propagates on its own and the fragments become finer, resulting in the fracture shown in Figure 5. This is undesirable because it creates a pattern and increases the risk of debris falling from the window.

Also, the plate thickness is 15 mm and the central tensile stress σt is 275 ky/
ffl, surface compressive stress σC is 450 kg/cr? The same applies to the glass plate of i (ie, ac/at=1.64).

On the other hand, the fracture patterns of the heat-treated glass plates produced according to the present invention, for example, the samples of Examples 1 to 4, are as shown in Figures 6 to 9, respectively, and when cracks occur in the glass plates, the cracks occur automatically. This prevents the breakage lines 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/ctyt or more, particularly preferably 20 kg/ctyt.
Since it has a surface compressive stress higher than 0 kg/i,
There is little risk of thermal cracking, and it also has sufficient wind pressure resistance.

In addition, when a glass plate breaks, the self-propagation of the crack is suppressed so that the fracture line (crack) does not extend from one side of the glass to the other, so there is a risk of broken pieces of the glass plate falling from the window. Although it is preferable to have a small number of broken lines (cracks) extending from one side of the glass plate to the other, there is actually no danger of broken pieces falling from the window into the ground, so this type of breakage of about one line is not recommended. The presence of lines (cracks) is acceptable as a fracture pattern in the heat treated glass produced according to the present invention.

For example, Figures 7 and 8 are examples of this permissible.

Next, a specific example of the method for manufacturing a heat-treated glass plate of the present invention will be described.

FIG. 10 shows a specific example of the apparatus used for producing the heat-treated glass plate of the present invention, and in the figure, 1 is the glass plate to be heat-treated, 2 is the roller hearth, and 3 is the glass plate. A conveying roll for the plate, 4 a heating device for the glass plate, and 5 a hot air outlet.

The glass plate 1 to be heat treated is conveyed horizontally by the conveyor roll 2 in the roller hearth 2, or is slid horizontally until the temperature is sufficient to strengthen the glass plate.
For example, it is heated to 600-660°C.

The glass plate 1 taken out from the roller hearth 1 is
The hot air outlet is moved between vertically opposed hot air outlets, from which hot air of 50°C to 300°C is blown onto the glass plate surface, and after the temperature of the glass plate has decreased to 200 to 450°C, the hot air outlet is It is taken out and made into a tempered glass plate product with a predetermined stress value and stress distribution.

In the present invention, in order to obtain predetermined surface compressive stress, central tensile stress, and cross-sectional stress distribution,
Heating the glass plate to a temperature of 50 to 300°C, blowing hot air to a temperature of 200 to 450°C
The combination of these conditions is important.

Although the method for manufacturing the heat-treated glass plate of the present invention described above uses a roller hearth, the method is not limited to this method. Alternatively, the heated glass plate may be heated in a heating furnace while being suspended from a hanger while being transported, and the heated glass plate may be heat treated immediately after it comes out of the outlet of the heating furnace. It can be manufactured similarly.

In addition, when obtaining a tempered glass plate using the gas hearth shown in Figure 10, there is a method in which the air is heated in a roller hearth furnace using a heat exchanger, or the gas is heated in the middle of the air blowing duct leading to the hot air outlet. It is practically preferable to obtain hot air by heating the air with a burner or an electric heater.

Example A soda-lime glass plate was heat-treated using the above-mentioned apparatus under the conditions shown in Table 1, and the resulting heat-treated glass plate had a central tensile stress σt1 surface compressive stress σc1 σC/σt,
Allowable load indicating wind pressure resistance (probability of failure 1/1000 or less)
The results of the thermal cracking test (temperature difference between the central part and the peripheral part of the glass plate until thermal cracking) are also shown in Table 1.

5 to 9 show the fracture patterns obtained when the fracture tests specified in JISR3206 6-5 were conducted on the heat treated glass plates of Examples 1 to 4 and the heat treated glass plates of Comparative Example 1.

By the method of the present invention, the central tensile stress σt is 85 to 200.
The reason why a heat-treated glass plate can be obtained in which the ratio of the surface compressive stress σC to the central tensile stress σC/σt is in the range of 1.5 to 2.0 is thought to be as follows. .

Generally, the residual stress generated when a softened glass plate is cooled and strengthened is based on the following theoretical formula.

Cooling capacity: Q Glass plate temperature: θ Specific heat: C Density: ρ Cooling time: t Glass plate thermal expansion coefficient: α Poisson ratio Elastic modulus: E Thermal conductivity is second Glass plate thickness: h (How heat is transferred inside the glass) equation) Solving this The central tensile stress σt is becomes.

Here, the cooling capacity of natural cooling is usually about K = 1.1'C/sec.

From the relationship of Q=2.5X10'k Kqal/m2h, when the plate thickness is 10m/m, a t =1511y/ff11
2 m/m ” σt=181 tt15m/m
tt σt = 226 // However, in the case of natural cooling, the glass plate warps because it is not possible to control the difference in cooling capacity on both sides of the glass plate.

In order to adjust this, the cooling capacity on one side is set to k>1.1, so in practice, for glass plates longer than long, σt<200k
g/Cr? It has become industrially impossible to achieve L.

The present invention makes it possible to control the value of k by using hot air and adjust it within the range of σt=85 to 200 kg/crit.

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,
Linearly polarized light A, which has been passed through a polarizer 13, a lens 14, and an aperture 15 using a He-Ne laser 12 as a light source, is incident perpendicularly to the end face.

Let y and z be the directions parallel and perpendicular to the surface of the glass plate 11, respectively, and let X be the incident direction.

The direction of vibration of the incident light is set at 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, and has an axis at an angle of 45° with the y-z axis as shown in Figure 12. The polarization changes as follows: ellipse → circle → ellipse → straight line (perpendicular to the incident light) → ellipse → circle → ellipse → straight line, and with a phase difference of 360°, the vibration direction returns to the same linear polarization 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 a direction of 45° with respect to the y and z axes in the -z plane, it appears as dots for each wavelength, as shown in FIG. 13B or FIG. 14.

Since the scattering of the float glass plate is very small, the scattered light to be observed is weak.

For this purpose, a night vision device with a built-in micro-channel image intensifier is used to project a dot pattern of scattered light onto the monitor television 1T through the high-sensitivity television camera 16.

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 determined using the photoelastic constant.

From the principal stress difference Δσ found here, the central tensile stress σy is determined by the following formula.

Principal stress difference △σ σy: Component of stress in the plane direction, i.e. central tensile stress σ2: Component of stress in the thickness direction (σZki0) λ: Laser light wavelength (632,8 m p -He-Ne laser) lλ: 360 Optical path difference (crIl) corresponding to a phase difference of ° C: Photoelastic constant 2.63 mμ/crIL/kg/i (
Note that the center tensile stress σt manufactured by the present invention is 85
~200kg/d1 Surface compressive stress σc is 127~600
kg/cIIL1, more preferably 200-300 kg
The above stress values of the heat-treated glass plate /i are the four points P at the periphery and one point Q at the center of the heat-treated glass plate, as shown in Figure 15.
It shows the average of the measured values at five points, and is taken as an average value.

As described above, according to the present invention, the wind pressure strength is sufficient for practical use, there is no thermal cracking, and furthermore, even if a crack enters the glass plate, the crack does not propagate by itself and does not break into small pieces. Heat treated glass can be provided.

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, the heat-treated glass sheet produced by the method of the present invention is ideal for use as a window glass sheet for medium-to-high-rise buildings, which requires a glass sheet that is free from the risk of falling glass fragments.

The heat-treated glass sheet manufactured by the present invention is particularly suitable for glass sheets such as heat-absorbing glass sheets, colored coated glass sheets, and heat-reflecting glass sheets used for windows or spandrels that have a high risk of thermal cracking. It is.

In addition, the glass plate manufactured according to the present invention has improved wind pressure strength and thermal cracking strength, and also prevents self-propagation of cracks. The glass plate can be replaced with a 12 mm thick heat-treated glass plate manufactured according to the present invention, and the weight of the glass plate can be reduced.

[Brief explanation of the drawing]

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 a crushing pattern of a glass plate according to a comparative example, FIGS. 6 to 9 are diagrams of a crushing pattern of a heat-treated glass plate manufactured by the method of the present invention, and FIG. 10 is a diagram of a crushing pattern of a glass plate according to a comparative example. A schematic diagram according to one specific example; FIG. 11 is a schematic diagram of an apparatus for measuring the central tensile stress of a glass plate; FIGS. 12 to 14 are explanatory diagrams showing the principle of measuring the central tensile stress of a glass plate; FIG. 15 is an explanatory diagram showing stress measurement points. 1: Glass plate to be heat treated, 2: Roller hearth, 3:
Conveyance roll, 4: Glass plate heating device, 5: Hot air outlet.

Claims (1)

[Scope of Claims] 1. After passing a glass plate with a thickness of 10 mm to 15 mm through a heating furnace and heating it to 600°C to 660°C, the glass plate is taken out from the heating furnace, and immediately thereafter, the surface of the glass plate is heated at 50°C. By blowing hot air at ~300°C, the cooling rate of the glass plate is slower than that of natural cooling in the atmosphere, and the glass plate is cooled to below the strain point temperature of the glass plate, so that the central tensile stress σt of this treated glass plate is 85~ 200 kg/CIj, and the ratio of the surface compressive stress σC to the central tensile stress σt, σC/σt, is controlled to be in the range of 1.5 to 2.0. Method. 2 A glass plate with a thickness of 10mm to 151n11L is heated at 600°C to 66°C while horizontally conveying it in a roller hearth furnace.
After heating to 0°C, it is taken out horizontally from the roller hearth furnace, placed between opposing blowholes, and heated to a temperature of 50°C to 30°C.
2. The method for heat treatment of a glass plate according to claim 1, wherein the glass plate is cooled to a temperature below the strain point of the glass plate by blowing out hot air at 0°C. 3 Heated by a heat exchanger in a roller hearth furnace 5
3. The method for heat treating a glass plate according to claim 2, wherein hot air at 0°C to 300°C is blown onto both sides of the glass plate taken out horizontally from a roller hearth furnace. 4. The method for heat treating a glass plate according to claim 1, characterized in that the cooling air is heated to 50°C to 300°C by burning a gas burner in the middle of a duct passing through the blower to produce hot air.