Device for reducing distortion of end edges of glass sheets

Abstract

The present invention relates to a device for reducing the end edge distortion of a glass sheet in a tempering process, the device comprising a roller carriage arranged in a roller track, the roller carriage moving the glass sheet following a glass tempering furnace, wherein the roller carriage is between two driving rollers in the roller track, the roller carriage comprising a plurality of freely rotatable independent rollers, the plurality of freely rotatable independent rollers supporting the glass sheet when the glass sheet moves from the tempering furnace to a quenching unit. The present invention also relates to a method for reducing the end edge distortion of a glass sheet in a glass tempering process, and a system comprising the device of the present invention.

Description

Technical Field

[0001] The invention relates to a method for thermally strengthening or tempering a glass sheet, wherein the glass sheet is heated to the tempering temperature and the actual tempering is carried out by blowing cooling air onto both surfaces of the glass sheet moving at the desired conveying speed, wherein the glass is further supported after leaving the tempering furnace before the tempering, and to a roller comprising a freely rotating roller which is installed in a tempering furnace for glass sheets. Background Art

[0002] Tempering furnaces for glass sheets are generally known and used, in which the glass sheets are moved in rotation in one direction or back and forth on ceramic rollers and are conveyed from the ceramic rollers on roller tracks at the tempering temperature to a quenching unit located at the rear of the furnace, where they are quenched by air jets. In the art, furnaces provided with roller tracks are referred to as roller hearth furnaces, for example. Typical furnace temperatures are about 700° C., and the temperature of the air used for cooling is generally about the same as the air temperature outdoors or in the factory hall. The cooling air is supplied by fans or compressors. In furnaces and quenching units based on air support technology, the glass sheets are floating while being supported by a thin air bed and are in contact with conveyor track rollers or other transport elements only along one of their side edges. Glass sheet tempering machines based on air support technology are significantly less common than tempering machines provided with roller tracks. Furnaces based on air support technology are referred to as air support furnaces, for example, in the art.

[0003] A typical tempering temperature (i.e. the temperature of the glass from the furnace to the quenching unit) for a 4 mm thick glass sheet is 640°C. The glass tempering temperature can be slightly reduced as the glass thickness increases. An increase in the tempering temperature enables tempering of progressively thinner glass and reduces the cooling capacity required for quenching. On the other hand, simply increasing the tempering temperature from 640°C to 670°C creates a significantly higher degree of strengthening or tempering on a 4 mm thick glass, i.e. an increase in compressive stresses at the glass surface. For example, for a thin glass of 2 mm thickness, the tempering temperature must be increased to at least 660°C for successful tempering. Both reducing the thickness of the glass and increasing the tempering temperature increase the problem of end edge distortion, which is solved by the present invention.

[0004] The glass obtained in the tempering process is excellent in its flatness and optical properties. It typically has a glass surface compressive stress of 1-4 MPa. The goal in the tempering process is to provide an increased glass sheet with sufficient strength while compromising the flatness and optical properties of the glass sheet as little as possible. In addition to strength, another desired quality of tempered glass is safety in breaking. Non-tempered glass breaks into large pieces that are a cutting hazard. Tempered glass breaks into almost harmless fragments.

[0005] The compressive stress (intensity or degree of tempering) established in the tempering of the glass surface depends on the temperature distribution of the glass in the thickness direction, because the glass is cooled through the typical transition temperature range for glass (about 600→500°C). Thinner glass requires greater cooling capacity to obtain the same above-mentioned temperature difference. For example, the target of a 4 mm thick glass sheet in tempering is a surface compression of about 100 MPa, whereby the center of the glass thickness has a tensile stress of about 46 MPa. This type of glass sheet breaks into fragments that meet the requirements of safety glass standards. When tempering so-called FRG glass (fire-resistant glass), the target is significantly higher surface compressive stress. FRG tempering will be successful when the cooling capacity in the quenching unit is significantly increased relative to tempering. The target of so-called heat-strengthened glass is not to achieve safe breaking characteristics, or to achieve strength as high as tempered glass (enough for surface compression of about 50 MPa). Heat strengthening will be successful when the cooling capacity of the air jet in the quenching unit is significantly reduced relative to tempering. The present invention solves the problem of end edge distortion in glass tempering (also including heat strengthening). The above tempering temperatures also apply as examples in thermal strengthening, i.e., the tempering temperatures also refer to thermal strengthening temperatures. If the tempering temperature remains constant, the end edge distortion problem is not very dependent on whether the glass seeks a compressive surface tension of 50, 100 MPa or even more.

[0006] Generally, end edge distortion refers to the downwardly deflected shape of the end of the glass.

[0007] During the heating process, when the ends of the glass begin to creep downward, end edge distortion begins to form. Since the glass is heated to a temperature of more than 500°C in the furnace, the ends creep, wherein the mechanical material properties of the glass begin to change relatively sharply. At the same time, the glass begins to change from elastic to plastic. The deformation of the glass reverses more weakly with the increase of plasticity. If the glass is uniformly supported in the furnace, the distortion and creep of the ends of the glass will not occur. However, the glass support points (lines) in the roller hearth furnace are only located at the roller spacing interval (usually 7 to 14 cm). In the air-supported furnace, the overpressured air bed (relative to the pressure in the space of the furnace) supports the edge of the glass to a weaker extent than the rest of the glass area because the static overpressure of the air bed supporting the glass is lower on the edge of the glass. Glass that is deflected at the end of the glass in the furnace will not straighten itself in the quenching, which solidifies the glass into its final elastic shape within a few seconds. The end edge distortion typically starts at about 70-200 mm from the end of the glass, depending on, for example, the thickness of the glass and the type of tempering machine.

[0008] Figure 1A way for measuring the end edge distortion of glass according to standard EN12150-1 is shown. Therein, the top surface of the glass is the opposite surface with respect to the direction of the end edge distortion. The glass is placed on the measuring plane so that the end of the glass extends slightly beyond 50 mm of the plane. A 300-400 mm long ruler is placed on top of the end of the glass so that the dial in the other end of the ruler is exactly at the end of the glass to be measured. The reading of the dial is the end edge distortion of the glass. According to the above standard, for example, the allowable end edge distortion of 4 mm thick glass is 0.4 mm. In practice, the requirements of tempered glass producers regarding end edge distortion are slightly stricter than the standard. The better quality value of the glass is a competitive advantage for tempering machine manufacturers and, further, for producers of tempered glass.

[0009] The problem of end edge distortion arises partly during the transfer from the tempering furnace to the quenching unit, because the glass is at its hottest state at this time. During the transfer, the glass is supported by rollers that move it, between which there is inevitably a gap of about 10 cm in length. Since the bearings at the ends of these rollers, the gears required for the drive by the rollers and other components have dimensions significantly larger than the diameter of the rollers, the rollers cannot be close to each other. On the other hand, the measuring beam of the temperature sensor that measures the temperature of the glass also requires space, which limits the reduction of the distance between the end of the furnace and the start of the quench cooler. Due to material durability and energy consumption, there must be a certain distance between the hot furnace and the start of the quench cooler.

[0010] In publication FI20175608, the discussed end edge distortion problem is solved by blasting compressed air as an initial blast on the top surface of the leading and trailing edges of the glass sheet to reduce the end edge distortion of the leading and trailing edges of the glass sheet. This solution requires relatively complex blasting equipment and precise information about the position of the ends of the moving glass sheet relative to the blasting equipment. Summary of the invention

[0011] The object of the present invention is a method and a device by means of which a tempered glass sheet can be made straighter at its front and rear end edges. In other words, the object of the present invention is to improve the quality of glass by reducing the end edge distortion of the glass (measured, for example, according to standard EN12150-1). In particular, the object of the present invention is to reduce the end edge distortion of glass requiring a tempering temperature of more than 650°C and / or those having a thickness of less than 3.5 mm.

[0012] The object is achieved by a method for reducing the end edge distortion of a glass sheet in a glass tempering process, wherein a glass sheet (G) is heated to a tempering temperature and the actual quenching is performed by blowing cooling air onto both surfaces of the glass sheet moving at a desired conveying speed (TV), wherein after heating and before the glass sheet is conveyed to the quenching, the glass sheet is supported on non-driven rollers, the end edge distortion of the glass sheet being prevented by the support of the non-driven rollers, and by a device for reducing the end edge distortion of a glass sheet in a glass tempering process, the device comprising a roller carriage arranged in a roller track, the roller carriage causing the glass sheet to follow the glass tempering furnace, wherein the roller carriage is between two driven rollers in the roller track, the roller carriage comprising a plurality of individual free-rotating rollers, the plurality of individual free-rotating rollers supporting the glass sheet when the glass sheet moves from the tempering furnace to the quenching unit, thereby preventing the end edge distortion of the glass sheet. The invention also relates to a system comprising a tempering furnace, a quenching unit and a device for reducing the end edge distortion of a glass sheet installed between the tempering furnace and the quenching unit.

[0013] Preferred embodiments of the invention are disclosed in the dependent claims.In the claims, tempering generally refers to a significant strengthening of the glass based on heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Shows how to measure the end edge distortion of glass according to standard EN12150-1;

[0015] Figure 2 The system of the present invention is shown, the system comprising an air support furnace, a quenching unit and a device installed between the air support furnace and the quenching unit to reduce end edge distortion;

[0016] Figure 3 The system of the present invention is shown, the system comprising a roller hearth furnace, a quenching unit and a device installed between the roller hearth furnace and the quenching unit to reduce end edge distortion;

[0017] Figure 4 The device of the present invention is shown between two drive rollers;

[0018] Figure 5 The device of the present invention is shown. DETAILED DESCRIPTION

[0019] The system according to the present invention comprises a tempering furnace 1 and a quenching unit 2, and a device installed between the tempering furnace 1 and the quenching unit 2 to reduce the end edge distortion. The tempering furnace 1 can be a roller hearth furnace or an air-supported furnace. The tempering furnace 1 heats the glass to a tempering temperature of about 620-700° C., and the quenching unit 2 is usually supported by rollers.

[0020] like Figure 2 As shown, the tempering furnace 1 and the quenching unit 2 are arranged one after another in the stated order in the traveling direction (x direction) of the glass sheet G. The rollers 4 ( Figure 3 ) with its conveying elements forms a conveying track for the glass sheet. In the conveying track between the end of the furnace and the blast box 6 of the first quenching unit, there are usually at least two driving rollers. The glass sheet G to be heated is driven continuously in one direction at a constant speed in the furnace 1 or driven back and forth during the duration of the heating cycle. After being heated to the tempering temperature, the glass sheet G advances from the furnace to the quenching unit 2 at a conveying speed TV. Depending on the thickness of the glass sheet, the conveying speed TV is usually 200-1000 mm / s. When the end of the glass sheet comes out of the furnace, the end of the glass sheet is placed on a device for reducing the distortion of the end edge (a roller bracket 5 for reducing the distortion of the end edge). Between the tempering furnace 1 and the cooling unit 2, there is advantageously a temperature scanner 9 to monitor the temperature of the glass sheet G. In the cooling unit, the glass sheet is cooled by blowing cold air from the blast box 6 through the blast opening 14 onto the surface of the glass sheet. When the roller blocks the air that has hit the bottom surface of the glass, the flow obstacle 7 blocks the exit path of the air that hits the top surface of the glass, so that the glass remains connected to the roller.

[0021] The device for reducing the end edge distortion comprises a so-called roller carriage 5, which includes a free-rotating roller 10, which supports the glass sheet G when the glass sheet G moves from the tempering furnace 1 to the quenching device 2, thereby preventing the end edge of the glass sheet G from being distorted. Unlike the drive roller 4, the roller carriage 5 is not driven and is therefore a non-driven roller. The roller carriage 5 includes a row of adjacent free-rotating rollers 10, each of which can have its own bearing, or a structure similar to the bearing that realizes an easy and free-rotating structure. For example, instead of an actual bearing, the shaft passing through the roller can be supported by the end of the shaft to a U-shaped support, for example, at the U-shaped support, the roller is rotated by its shaft, that is, the end of the shaft gently rubs the bottom of the U. In this way, the rollers rotate freely independently of each other. The roller 10 is light, and the roller-specific bearing or other arrangement ensures that the roller 10 rotates easily. When the glass sheet hits the roller 10, the roller 10 rotates and supports the glass sheet, in other words, the end of the glass sheet rests on the roller 10, thereby reducing the end edge distortion. Furthermore, other deformations caused by supporting the hot, creeping glass sheet (eg, roller corrugation) may be reduced.

[0022] In a system comprising a tempering furnace 1 and a quenching unit 2, the distribution of the drive rollers 4 cannot be short enough to prevent the end edges from twisting, because space is required for the bearings 12 at the ends of the rollers 4 and for the gears of the roller drive 13. The roller drive 13 comprises gears, chains and motors at the ends of the rollers, which together are large. Usually, a temperature sensor 9 is additionally installed between the furnace 1 and the cooling unit 2 to monitor the process. The scanner 9 provides information with the help of which the tempering process and the cooling process can be monitored. The scanner also requires some space between the furnace 1 and the cooling unit 2. The third reason why space is required between the furnace 1 and the cooling unit 2 is to prevent quenching air from entering the furnace. If the furnace 1 and the quenching unit 2 are too close to each other, quenching air enters the furnace, thereby interfering with the tempering process.

[0023] The glass is supported by the rollers at their highest points. The roller gap is the distance between the highest points of the rollers in the direction of movement x of the glass, which is equal to the distance between the center points of the axes of rotation of the rollers in the same direction x. According to a preferred embodiment, the free-rotating roller carriage 5 shortens the roller gap by half. It is therefore advantageous to shorten it from about 10 cm to about 5 cm, from 6-14 cm to 3-7 cm. The roller carriage 5 is positioned in the roller track in the section between the tempering furnace and the first blower box of the quenching unit.

[0024] Figure 3 An embodiment of the system of the invention is shown which, in addition to the last or rear drive roller 4 of the tempering furnace 1, has a driven upper roller 8 which, together with the drive roller, can be said to form a nip roller. The upper roller 8 does not have to be in contact with the glass G, or at least it does not have to press the glass against the lower roller 4 to any significant extent. The upper roller 8 is arranged directly above the drive roller 4 after the tempering furnace, outside the tempering furnace, advantageously so that the axes of the two rollers are vertically in line. The end edge distortion of the glass sheet is further reduced by the combined action of the upper roller 8 with the roller bracket 5, and in addition, the upper roller 8 effectively prevents the cooling air from entering the furnace. The upper roller 8 is advantageously at least partially covered by a thermally insulating fiber cloth or fiber tape, such as a Kevlar tape.

[0025] Figure 4 A section of the roller track between the tempering furnace and the quench cooler is shown, viewed from above. The figure shows only a portion of the length of the rollers and the blower box. A roller bracket 5 is mounted between the drive roller 4 behind the tempering furnace and the first drive roller of the quench unit. Figure 4 As shown, the bearings 12 of the drive rollers 4 take up space, resulting in the rollers 4 not being able to be brought close enough to each other to achieve the necessary reduction in end edge distortion by simply shortening the distance between the rollers 4 . Figure 4 Also shown is a blast box 6 with blast openings 14 from which blasts of air hitting the glass surface cool the glass very quickly to a temperature below that which favours increased end edge distortion.

[0026] Figure 5 The device of the invention for reducing the distortion of the end edges of a glass sheet is shown, in other words a freely rotating, therefore non-driven roller carriage 5. The roller carriage 5 comprises a plurality of rollers 10, which are at a distance S from each other and which are arranged individually to rotate freely. The spacing S between the sides of the rollers is 1-50 mm, and the width W of the rollers is 5-50 mm. The outer diameter of the rollers is advantageously 10-40 mm. The roller carriage has a metal body, advantageously a light metal body, and their surface is provided with a heat-resistant insulating fiber braid that does not scratch the glass, i.e. a fiber cloth, such as a Kevlar belt or sleeve. The metal is advantageously aluminum. The fiber cloth is wound on a disc so that contact between the metal body of the roller and the glass sheet is substantially prevented. Each roller 10 is attached to an elongated body 11. The length of the body 11 matches the width of the furnace so that the rollers 10 attached to the body 11 cover the width of the furnace, so that the glass is supported over the entire width of the furnace, regardless of the width of the glass sheet.

[0027] According to a preferred embodiment, the distance S between the two side faces of two individual rollers 10 ranges from approximately half the width W of the rollers 10 to the width W of three rollers 10 .

[0028] Roller 10 is advantageously cylindrical. The roller axis coincides with the cylinder axis. In this case, except for the end faces, the surface of the cylinder is provided with the fiber cloth.

[0029] The advantage of the roller carriage 5 in relation to the uniform rollers is that the individual rollers rotate more lightly. The individual rollers rotate significantly less lightly relative to longer rollers. Since the task of the non-driven rollers is to carry the glass while supporting it, it is necessary that the rollers rotate as lightly as possible so that the leading edge of the glass does not hit the rollers or slow down the movement of the glass. Slowdowns, stops or jerks in the movement of the glass will have a negative impact on the final product of the tempering process, such as the quality of the glass.

[0030] The second advantage of the roller carriage is that it has good adjustability due to the single roller. Each roller can be adjusted independently in the vertical direction (y direction), that is, the height position of the highest point is set to be adjustable specifically for the roller. The adjustment range in the vertical direction is advantageously at least 5 mm. Adjustment allows the support line of the roller carriage to be adjusted. Adjustment is required because the roller diameter varies due to the tolerance of its components and the body 11 is not completely straight. Adjustment allows the support line to be straightened regardless of changes in the size of the roller carriage. When the glass comes out of the furnace, it may be slightly bent in the lateral direction (relative to the lateral direction of the glass movement, i.e., the z direction) and is therefore not completely straight. Especially in the case of an air-supported furnace, the shape of the end edge of the glass sheet after heating and tempering makes the corner lower than the central area. In this case, the roller can be adjusted to be higher in the central area than on the side, thereby ensuring that the roller supports the glass sheet over the entire width of the glass sheet.

[0031] The position of the rollers can also be adjusted individually in the z-direction, approximately within a distance S, i.e. the position of the rollers can be adjusted roller-specifically in a horizontal direction transverse to the movement of the glass. By adjusting in this direction, the rollers can be moved to precisely support the side edges of the glass. The adjustment range in the z-direction is advantageously the distance between the two side faces of the roller minus 10 mm.

[0032] The invention described above is not limited to the embodiments described but can be varied in many ways within the scope of protection of the claims.

Claims

1. A device for reducing the distortion of the end edge of a glass sheet during a tempering process, the device comprising a roller bracket, the roller bracket being arranged on a roller track, the roller bracket enabling the glass sheet to move following the movement of a glass tempering furnace, characterized in that: the roller carriage being between two drive rollers in the roller track, the roller carriage comprising a plurality of individual free-rotating rollers that support the glass sheet as it moves from the tempering furnace to a quenching unit; Wherein the roller carriage is non-driven.

2. The device according to claim 1, characterized in that Free-spinning roller carriages cut the gap between rollers in half.

3. The device according to claim 2, characterized in that The free-spinning roller carriage reduces the gap between rollers from 6-14 cm to 3-7 cm.

4. The device according to any one of claims 1 to 3, characterized in that The height position of the highest point of the roller is set to be roller-specifically adjustable.

5. The device according to any one of claims 1 to 3, characterized in that The position of the rollers can be adjusted roller-specifically in a horizontal direction transverse to the movement of the glass.

6. The device according to any one of claims 1 to 3, characterized in that The rollers are of light metal.

7. The device according to any one of claims 1 to 3, characterized in that The contact surface of the roller with the glass is at least partially covered by the fiber weave.

8. The device according to any one of claims 1 to 3, characterized in that The distance between the two sides of the roller is 1-50 mm, and the width of the roller is 5-50 mm.

9. The device according to any one of claims 1 to 3, characterized in that The distance between the two side faces of the roller on the roller bracket is 0.5-3 times the width of the roller.

10. The device according to any one of claims 1 to 3, characterized in that The outer diameter of the roller is 10-40 mm.

11. A system for reducing end edge distortion of a glass sheet in a glass tempering process, the system comprising a tempering furnace, a quenching unit and a roller track, the tempering furnace being used for glass, the roller track moving the glass after the tempering furnace, characterized in that: In the roller track, there is a roller carriage between two drive rollers, the roller carriage including a plurality of individual free-rotating rollers that support the glass sheet as it moves from the tempering furnace to the quenching unit; Wherein the roller carriage is non-driven.

12. The system according to claim 11, further comprising, in addition to the last drive roller in the tempering furnace, an upper roller, which together with the drive roller forms a nip roller.

13. A method for reducing end edge distortion of a glass sheet during a glass tempering process, wherein: The glass sheet is heated to a tempering temperature and the actual quenching is carried out by blowing cooling air onto both surfaces of the glass sheet, wherein, after heating and before the glass sheet is conveyed to the quenching, the glass sheet is supported on a roller carriage comprising a row of adjacent individual free-rotating rollers, the end edges of the glass sheet being prevented from twisting by the support of the carriage; wherein the roller carriage is non-driven.

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