JP4397197B2 - Manufacturing method of heat strengthened glass - Google Patents

Description

  The present invention relates to a method for producing a so-called heat strengthened glass manufactured by an air cooling method, particularly a heat strengthened glass having a thickness of 2.5 mm or less.

  From the viewpoint of resource saving and energy saving, tempered glass has been made thinner and strengthened, and chemical strengthening method and physical strengthening method are mainly used for this purpose. The chemical tempering method is a method of applying a compressive stress to the glass surface using ion exchange, crystallization, a difference in thermal expansion coefficient, and the like, and the tempered glass by the method is called chemical tempered glass. The chemical strengthening method is suitable for strengthening a thin plate having a thickness of 3 mm or less, particularly 2 mm or less, but since the thickness of the compressive stress layer of the chemically strengthened glass is thin, a problem of scratching strength is likely to occur. There is a disadvantage that the place of use is limited.

  On the other hand, the tempered glass by a physical strengthening method is manufactured by quenching from the surface the glass heated to the softening point vicinity so that it may be called the heat strengthened glass. In the case of heat strengthened glass, it has an advantage that it has a compressive stress layer of about 1/6 of the plate thickness and hardly causes a problem of scratching strength. As a manufacturing method of heat strengthened glass, so-called air-cooled tempering method using air as a cooling medium for rapid cooling is often used for production cost and safety reasons. The manufactured heat-tempered glass is also called air-cooled tempered glass. It is.

  A heat-strengthened glass is manufactured by utilizing the temperature difference and viscous flow in the glass after heating in a furnace. For this reason, it is known that when the degree of strengthening of the heat strengthened glass is increased, the following two methods are mainly used. One is to increase the glass temperature at the start of cooling as much as possible, and the other is to increase the temperature difference in the glass between the surface layer and the inner layer during cooling.

  By increasing the glass temperature at the start of cooling, the degree of strengthening can be increased, and a thin tempered glass can also be produced. Moreover, the glass breakage during manufacture can be reduced. However, if the glass temperature is too high, the glass is deformed and a fatal problem that a predetermined shape cannot be obtained occurs. For this reason, when the degree of strengthening of the thin plate tempered glass is increased, there is a limit only by the method of increasing the glass temperature.

  On the other hand, increasing the temperature difference in the glass between the surface layer and the inner layer at the time of cooling can be explained by, for example, the concept of increasing the biot number. The biot number is a dimensionless number expressed by (heat transfer coefficient x plate thickness / thermal conductivity). By increasing the bior number, the degree of strengthening of the glass can be increased. That is, it is possible to increase the degree of strengthening of the glass by increasing the heat transfer coefficient, increasing the plate thickness, and decreasing the thermal conductivity. However, when reducing the thickness of the tempered glass, that is, when producing a thin tempered glass, the thermal conductivity of the glass is generally constant. I have to make it bigger. For this reason, when thinning glass, a method for increasing the heat transfer coefficient is the main countermeasure.

In cooling using a nozzle, between the heat transfer coefficient and the cooling conditions,
(H · r _n ) /λ=0.286Re ^0.625
Re = (V _g · r _n ) / ν
V _g = 6.63 V _n · d / Z
Etc. have been experimentally derived (see, for example, Non-Patent Document 1). Here, h is the heat transfer coefficient, lambda is the thermal conductivity of air, [nu is the kinematic viscosity of air, Re is Reynolds number, r _n is the distance between nozzles, d is the nozzle diameter in the nozzle exit, V _n is the nozzle exit , V _g is the flow velocity on the glass surface, and Z is the nozzle-glass distance. Although the above numerical values are established when Z / d is larger than 8, as is apparent from the form of the above equation, as a general method for increasing the heat transfer coefficient, the ejection speed from the nozzle is set as follows. It is effective to increase (increase the ejection pressure from the nozzle), increase the nozzle diameter, increase the number of nozzles, reduce the distance between the glass and the nozzle tip, and increase the energy when the cooling medium collides. Has been.

From the known technology, for example, the glass temperature in the plate width direction is adjusted with exhaust air used for rapid cooling (see, for example, Patent Document 1), or the use of a tapered nozzle is used (see, for example, Patent Document 2). In addition, a first group nozzle for injecting blower air and a second nozzle group for injecting compressed air (for example, see Patent Document 3), or devised to follow a curved plate glass whose shape changes (for example, Patent Document) 4), the idea of limiting the width of the belt-like region, the maximum principal stress difference, the average surface compressive stress, and the like (for example, see Patent Document 5). Further, the present applicant has also shown a heat strengthening method by using a shock tube (see, for example, Patent Document 6).
Japanese Patent Laid-Open No. 2001-48561 Japanese Patent Publication No. 6-76223 JP 2001-26434 A JP 7-29164 A JP 11-199257 A JP-A-62-158128 R. Gardon and J. Cobonpue, Heat Transfer between a Flat Plate and Jets of Air Impinging on It, Int.Develop Heat Transfer, ASME (1962), pp454-460.

  In the case of producing a heat-tempered glass having a thickness of 2.5 mm or less, particularly a thin-sheet tempered glass having a thickness of 2.3 mm or less, the conventional method of increasing the glass temperature during tempering and / or the method of obtaining a large heat transfer coefficient, Therefore, it can not be said that the manufacturing method is established, and therefore the desired heat-tempered glass cannot be obtained. In particular, this tendency is remarkable in the case of thin heat strengthened glass.

  In other words, methods for increasing the heat transfer coefficient include increasing the ejection speed from the nozzle (increasing the ejection pressure from the nozzle), increasing the nozzle diameter, increasing the number of nozzles, and the distance between the glass and the nozzle tip. It is effective to reduce the cooling energy and increase the collision energy of the cooling medium.However, if the method of increasing the ejection speed from the nozzle or reducing the distance from the glass is used, the nozzle ejection trace is attached to the glass. , Optical problems occur. Also, the method of increasing the nozzle diameter or increasing the number of nozzles increases the cross-sectional area occupied by the nozzles, so the air flow after collision with the glass cannot be managed well, resulting in a large heat transfer coefficient. Can't get. Furthermore, it is not realistic to use a cooling medium other than air in terms of production cost. There is a limit to the high glass temperature at the start of cooling.

  The method disclosed in JP-A-2001-48561 cannot secure a sufficient glass temperature. In addition, even the methods disclosed in Japanese Patent Publication No. 6-76223 and Japanese Patent Application Laid-Open No. 2001-26434 cannot obtain a large heat transfer coefficient. Even with the technique disclosed in Japanese Patent Laid-Open No. 7-29164, the above-mentioned thin sheet tempered glass cannot be obtained, and in some cases, the degree of strengthening may even decrease. The methods disclosed in Japanese Patent Application Laid-Open No. 11-199257 and Japanese Patent Application Laid-Open No. 62-158128 are difficult to apply directly to heat strengthened glass having a large degree of curvature.

  As a result of detailed examination of the flow of air ejected from a nozzle used when manufacturing tempered glass, the present invention has found a fact to be partially corrected in the conventional heat transfer concept. The relationship between the jet flow ejected from the nozzle and the heat transfer coefficient is not as simple as it has been said in the past, but it is a complex behavior that is affected by the length and inner diameter of the nozzle, the pressure of the jet, and its fluctuation range. By discovering this fact and using it, it was possible to produce a thin tempered glass having a thickness of 2.0 to 2.5 mm, which has been considered difficult until now. The present invention is effective when manufacturing thin plate tempered glass and super tempered glass, but it is also possible to efficiently manufacture general tempered glass.

In the present invention, when producing a heat strengthened glass having a thickness of 2.5 mm or less by blowing a collision jet ejected from a cooling nozzle onto a glass plate, the pressure fluctuation width ΔP of the collision jet is 0.1 MPa or more and 0.5 MPa or less. A value k obtained by multiplying the pressure P of the impinging jet and the pressure fluctuation width ΔP is 0.02 (MPa) ² or more and 0.5 (MPa) ² or less .

  Moreover, the pressure P of an impinging jet is the manufacturing method of said heat strengthened glass which exists in 0.1 MPa or more and 0.8 MPa or less.

  Moreover, it is the manufacturing method of said heat-strengthened glass in which the diameter d of the nozzle for cooling is φ1 mm to φ8 mm and the nozzle length L is 10 mm to 400 mm.

Further, the glass - and the distance between nozzles was set to Z, glass - a nozzle distance Z _n and the method of manufacturing a thermally tempered glass ratio Z / d is 3 to 10 with the cooling nozzle diameter d.

  It has become possible to stably produce a thin tempered glass having a thickness of 2.5 mm or less, which has been considered difficult until now.

  As shown in FIG. 1, the heat transfer coefficient and the collision pressure change due to the difference in the distance between the tip of the nozzle that blows out air and the collision surface of the glass surface, and the behaviors of both differ completely depending on the pressure in the chamber. That is, in the case of an underexpanded jet, even if the distance to the collision surface is shortened, it cannot be said that the heat transfer coefficient is necessarily improved, and there are cases where it is improved if the distance is increased. Moreover, even if the pressure in the chamber is increased, there may be an adverse effect depending on the distance to the collision surface of the glass surface.

  The present invention provides a thermally tempered glass having a pressure fluctuation width ΔP of the impact jet of 0.1 MPa or more and 0.5 MPa or less in the case of manufacturing the heat strengthened glass by spraying the impinging jet jetted from the cooling nozzle onto the glass plate. It is a manufacturing method.

  If the pressure fluctuation width ΔP of the collision jet is increased, the heat transfer coefficient increases. Therefore, the pressure fluctuation width ΔP of the collision jet is preferably set to 0.1 MPa or more. If the pressure fluctuation width ΔP of the impinging jet is made smaller than 0.1 MPa, a predetermined heat transfer coefficient cannot be obtained. Preferably, it is 0.2 MPa or more. On the other hand, if it exceeds 0.5 MPa, the stability with respect to the degree of strengthening decreases. Considering the above, the pressure fluctuation width ΔP of the impinging jet is preferably 0.1 MPa or more and 0.5 MPa or less.

A value k obtained by multiplying the pressure P of the impinging jet and the pressure fluctuation range ΔP is preferably 0.02 (MPa) ² or more and 0.5 (MPa) ² or less. If k is made smaller than 0.02 (MPa) ^2, a thin tempered glass having good quality cannot be produced as a result. Even if only the pressure P of the impinging jet is increased as in the conventional tempering concept, a large heat transfer coefficient cannot be obtained, but the optical quality as tempered glass deteriorates. A value k obtained by multiplying the pressure P of the impinging jet and the pressure fluctuation range ΔP is a large guide. On the other hand, when k exceeds 0.5 (MPa) ² , the stability of the tempered glass is lowered and the yield is also lowered. From the above, the value k multiplied by the pressure P of the impinging jet and the pressure fluctuation range ΔP is 0.02 (MPa) ² or more and 0.5 (MPa) ² or less. More preferably, it is 0.04 (MPa) ² or more and 0.2 (MPa) ² or less.

Note that the heat transfer coefficient to be applied differs depending on the thickness of the glass to be heat strengthened. The heat transfer coefficient required for 2.5 to 2.2 mm thickness is 1.0 to 1.3 kW / m ² K, 2.2 to 1.9 mm thickness, although it varies somewhat depending on the glass temperature at the start of cooling. the heat transfer coefficient required in the case of 1.1~1.4kW ^/ m 2 K, the heat transfer coefficient required in the case of 1.9~1.7mm thick 1.2~1.5kW / ^{m 2} K is there.

That is, the value k obtained by multiplying the pressure P of the impinging jet and the pressure fluctuation range ΔP is 0.01 to 0.02 (MPa) ² and 2.2 to 1 when the thickness is 2.5 to 2.2 mm. and 0.02 to 0.04 ^{(MPa) 2} in the case of .9mm thickness, in the case of 1.9~1.7mm thickness good results by a 0.04 to 0.08 ^{(MPa) 2} Can be obtained. The pressure fluctuation width ΔP of the impinging jet is 0.007 to 0.015 MPa when the thickness is 2.5 to 2.2 mm, and 0.010 to 0.00 when the thickness is 2.2 to 1.9 mm. In the case of 020 MPa and 1.9-1.7 mm thickness, it is preferable that it is 0.015-0.035 MPa.

  Moreover, it is preferable that the collision jet is an underexpanded jet. This is because the underexpanded jet is important for increasing the heat transfer coefficient.

  Further, the diameter d of the cooling nozzle is a method for producing the above heat-tempered glass having a diameter of 1 mm or more and 8 mm or less. When the diameter d of the cooling nozzle is less than φ1 mm, many nozzles are required to maintain the cooling ability, and thus management thereof becomes difficult. On the other hand, when the diameter d of the cooling nozzle exceeds φ8 mm, the cooling ability tends to decrease and it becomes difficult to perform uniform cooling. More preferably, it is φ2 mm or more and φ6 mm or less.

  The cooling nozzle is a long and narrow nozzle having a uniform inner diameter. However, the same applies to a nozzle whose inner diameter changes, such as a Laval nozzle, and it is important to combine nozzles having different diameters, that is, different heat fluxes. In the present invention, the diameter d of the cooling nozzle means the diameter at the nozzle outlet. The cooling nozzle-glass distance Z indicates the distance between the tip of the nozzle and the glass plate. The cooling nozzle is usually connected to a chamber called a blast head, and a compressor or a high-pressure blower is located upstream of the chamber.

  The cooling nozzle is usually connected to a chamber called a blast head, and a compressor or a high-pressure blower is located upstream of the chamber. The pressure P of the chamber connected to the cooling nozzle is preferably 0.1 MPa or more and 0.8 MPa or less. When the pressure P of the chamber connected to the cooling nozzle is less than 0.1 MPa, it is difficult to obtain a heat strengthened glass having a thickness of 2.5 mm or less. On the other hand, it is difficult to obtain a pressure exceeding 0.8 MPa with a general apparatus, resulting in a significant increase in cost. Preferably, it is 0.2 MPa or more and 0.75 MPa or less.

  As a method for obtaining the degree of strengthening of the heat strengthened glass, a method of estimating from a crushing test (JIS R3205) or a surface compressive stress (JIS R3222) has been widely proposed. In the crushing test, the number of crushing pieces in a 5 cm square is expressed as a fragment density. The higher the fragment density, the greater the degree of strengthening. In the case of general heat-strengthened glass, the fragment density needs to be between 40 and 400. If it exceeds 400, it falls outside the category of general heat-strengthened glass, but some may be used as super-tempered glass. The value of the surface compressive stress of the tempered glass is not limited, but in general, the tempered glass having a higher tempering degree has a larger value of the surface compressive stress.

  Hereinafter, description will be made based on examples.

When using a nozzle with an inner diameter d of 4 mm and a length L of 200 mm as shown in FIG. 2 and maintaining the distance Z between the tip of the nozzle and the copper plate for heat flux measurement assuming glass, the heat flux was determined. It was 180 kW / m ² . The pressure P of the collision jet at that time is 0.14 MPa, the pressure fluctuation width ΔP of the collision jet is 0.19 MPa, and the value k multiplied by the pressure P of the collision jet and the pressure fluctuation width ΔP is 0.0266. (MPa) ² . The chamber pressure was 0.3 MPa.

When glass sized 490 x 820 mm and 2.3 mm thick were air-cooled and tempered under these conditions, the fragment density (number / 25 cm ² ) was 243 at the maximum, 103.5 at the minimum, and the spline length was 33 mm at the maximum. We were satisfied with the specifications.

A nozzle having an inner diameter d of 4 mm and a length L of 200 mm as shown in FIG. 2, the distance Z between the nozzle tip and the glass was maintained at 16 mm, and a glass having a size of 230 × 450 mm and a thickness of 2.0 mm was subjected to air cooling strengthening treatment. . At this time, the pressure P of the collision jet is 0.30 MPa, the pressure fluctuation width ΔP of the collision jet is 0.22 MPa, and the value k obtained by multiplying the pressure P of the collision jet and the pressure fluctuation width ΔP is 0.0415. (MPa) ² . The chamber pressure was 0.65 MPa. Moreover, the measurement data of the pressure of a chamber pressure and a collision jet are shown in FIG.

As a result, the fragment density (number / 25 cm ² ) was 266.5 at the maximum, 133 at the minimum, and all splines were 28 mm or less, satisfying the specifications as a heat-tempered glass.

As shown in FIG. 3, a nozzle having an inner diameter D of 8 mm on the inlet side, an inner diameter d of 4 mm on the outlet side, and a length L of 200 mm, the distance Z between the tip of the nozzle and the glass is kept at 30 mm, and the dimensions are 540 × 1150 mm and 2 A glass of 5 mm thickness was tempered. The pressure P of the collision jet at that time is 0.16 MPa, the pressure fluctuation width ΔP of the collision jet is 0.16 MPa, and the value k obtained by multiplying the pressure of the collision jet and the pressure fluctuation width is 0.0256 (MPa). ² . The chamber pressure was 0.3 MPa.

  As a result, the fragment density was 652 at the maximum, 350 at the minimum, and the spline length was 30 mm or less at the longest, satisfying the level of tempered glass called high tempering degree. For reference, the specification of normal tempered glass is exceeded, but this specification of glass is used in part as super tempered glass.

A nozzle having an inner diameter d of 2 mm and a length L of 200 mm as shown in FIG. 2, the distance Z between the nozzle tip and the glass was maintained at 10 mm, and the glass having a size of 300 × 300 mm and a thickness of 2.0 mm was subjected to air cooling strengthening treatment. . The pressure P of the collision jet at that time is 0.12 MPa, the pressure fluctuation width ΔP of the collision jet is 0.31 MPa, and the value k multiplied by the pressure P of the collision jet and the pressure fluctuation width ΔP is 0.0385. (MPa) ² . The chamber pressure was 0.65 MPa.

As a result, the fragment density (number / 25 cm ² ) was 188 at the maximum, 97 at the minimum, and all splines were 29 mm or less, satisfying the specifications as tempered glass.

A nozzle having an inner diameter d of 8 mm and a length L of 200 mm as shown in FIG. 2, the distance Z between the tip of the nozzle and the glass was kept at 40 mm, and a glass having a size of 670 × 1200 mm and a thickness of 2.3 mm was subjected to air cooling strengthening treatment. . The pressure P of the collision jet at that time is 0.18 MPa, the pressure fluctuation width ΔP of the collision jet is 0.17 MPa, and the value k obtained by multiplying the pressure P of the collision jet and the pressure fluctuation width ΔP is 0.031. (MPa) ² . The chamber pressure was 0.65 MPa.

As a result, the fragment density (number / 25 cm ² ) was 377.5 at the maximum, 189.5 at the minimum, and the spline was 30 mm or less at the longest, which satisfied the specification as tempered glass.

(Comparative Example 1) Using a nozzle having an inner diameter d of 4 mm and a length L of 200 mm as shown in FIG. 2, the distance Z between the tip of the nozzle and the heat flux measuring copper plate assuming glass is kept at 20 mm, and the heat flux Was found to be 130 kW / m ² . The pressure P of the collision jet at that time is 0.14 MPa, the pressure fluctuation width ΔP of the collision jet is 0.11 MPa, and the value k multiplied by the pressure P of the collision jet and the pressure fluctuation width ΔP is 0.015. (MPa) ² . The chamber pressure at that time was 0.3 MPa.

When glass tempered with a size of 490 x 820 mm and 2.0 mm thick under these conditions, the fragment density (number / 25 cm ² ) is 29 at the maximum, 7 at the minimum, and the maximum fragment area is about 17 cm ² . Since the maximum was 83, the minimum was 27, and the maximum fragment area was about 5 cm ² , the specification as tempered glass could not be satisfied.

(Comparative Example 2) A nozzle having an inner diameter d of 4 mm and a length L of 200 mm as shown in FIG. 2, the distance between the nozzle tip and the glass being 4.0 mm, a size of 230 × 450 mm and a 2.3 mm thick glass Reinforced processing. The pressure P of the collision jet at that time is 0.23 MPa, the pressure fluctuation width ΔP of the collision jet is 0.04 MPa, and the value k obtained by multiplying the pressure of the collision jet and the pressure fluctuation width is 0.0092 (MPa). ² . The chamber pressure at this time is 0.65 MPa. FIG. 5 shows measurement data of the chamber pressure and the pressure of the impinging jet at this time. It can be seen that the pressure fluctuation width is small compared to FIG.

As a result, the maximum fragment density (number / 25 cm ² ) was 53, but the minimum was 11, and the maximum fragment area was about 12 cm ^2, so that the specification as tempered glass could not be satisfied.

(Comparative Example 3) Nozzle 2 having an inlet-side inner diameter D of 8 mm, an outlet-side inner diameter d of 4 mm, and a length L of 200 mm as shown in FIG. 3 , and maintaining the distance between the nozzle tip and glass at 10 mm, A 2.5 mm thick glass at 540 × 1150 mm was subjected to air cooling strengthening treatment. The pressure P of the collision jet at that time is 0.16 MPa, the pressure fluctuation width ΔP of the collision jet is 0.038 MPa, and the value k multiplied by the pressure of the collision jet and the pressure fluctuation width ΔP is 0.0068 ( MPa) ² . The chamber pressure at this time was 0.3 MPa.

As a result, the maximum fragment density (number / 25 cm ² ) of 65 was obtained, but the minimum was 30 and the specification as tempered glass could not be satisfied.

(Comparative Example 4)
As shown in FIG. 2, a nozzle having an inner diameter d of 0.5 mm and a length L of 430 mm, and the pressure P of the impinging jet was set to 0.9 MPa. It was not at a usable level.

(Comparative Example 5)
As shown in FIG. 2, a nozzle having an inner diameter d of 10 mm and a length of L5 mm and a collision jet pressure P of 0.05 MPa. Even a glass of 2.7 mm has a fragment density of 20 or less and satisfies the JIS standard. Heat tempered glass that could not be obtained.

  The cooling start temperature when producing the heat strengthened glass was 680 ° C. In addition, although the concept of heat transfer has been described using a heat transfer coefficient, since the heat transfer coefficient measurement was performed using a heat flux sensor HFM7EL manufactured by Vatell, the heat transfer coefficient was expressed in this example. . The heat transfer coefficient can be obtained by dividing the heat flux by the temperature of the cooling medium (underexpanded jet in the present invention).

  The pressure of the impinging jet was measured with a pressure sensor PGM-10KC manufactured by Kyowa Denki. In addition, it confirmed by the visualization method by a double exposure holography interferometer method that the jet itself in an Example was an underexpanded jet.

  As shown in the above results, it cannot be said that the high heat transfer coefficient from reducing the nozzle-to-glass distance due to the high jet pressure from the nozzle, and stable tempered glass thinner than 2.5 mm It was extremely difficult to manufacture. However, by using the conditions of the present invention, it became possible to produce a thin sheet tempered glass, and the production yield was stable.

It is a conceptual diagram which shows the change of the heat transfer coefficient in an underexpanded jet. It is a conceptual diagram which shows the nozzle shape of Example 1, 2, 4, 5 and Comparative Examples 1, 2, 4, and 5, (a) is a side view, (b) is a front view. It is a conceptual diagram which shows the nozzle shape of Example 3 and Comparative Example 3, (a) is a side view, (b) is a front view. It is a measured value which shows the chamber pressure shown in Example 2, and the pressure change of a collision jet. It is a measured value which shows the pressure change of the chamber pressure shown in the comparative example 2, and a collision jet.

Explanation of symbols

1 Nozzle for cooling 2 Nozzle for cooling L Length of nozzle d Inner diameter of nozzle (outlet side)
D Inner diameter on the inlet side of the nozzle

Claims (4)

In the case of producing a heat strengthened glass having a thickness of 2.5 mm or less by blowing an impinging jet from a cooling nozzle onto a glass plate, the pressure fluctuation width ΔP of the impinging jet is 0.1 MPa to 0.5 MPa , A method for producing thermally tempered glass, wherein a value k obtained by multiplying the pressure P and the pressure fluctuation range ΔP is 0.02 (MPa) ² or more and 0.5 (MPa) ² or less . The method for producing thermally tempered glass according to claim 1, wherein the pressure P of the impinging jet is 0.1 MPa or more and 0.8 MPa or less. Method for producing a thermally tempered glass according to claim 1 or 2 diameter d is φ8mm less and a nozzle length L or φ1mm cooling nozzle is characterized in that in 10mm or 400mm or less. Glass - the distance between the nozzle when the Z, glass - in any one of claims 1 to 3, characterized in that the ratio Z / d of the distance between nozzles Z and the cooling nozzle diameter d is 3 to 10 The manufacturing method of the heat-strengthened glass of description.

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