GB2477094A

GB2477094A - A method of making toughened glass plate with the appearance of hand-made glass

Info

Publication number: GB2477094A
Application number: GB1000877A
Authority: GB
Inventors: Steven David Collins
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-01-20
Filing date: 2010-01-20
Publication date: 2011-07-27
Anticipated expiration: 2030-01-20
Also published as: GB201000877D0; GB2477094B

Abstract

A glass plate is distorted and toughened by heating the glass plate which is in contact with a distorting surface to a softening temperature, thereby distorting the surface of the glass plate and then toughening the glass plate. The distorting surface can be formed from silica particles of diameter 0.5-6 mm or from a textured surface. Toughening can be by cooling the glass after it has been heated to a temperature above its annealing temperature (e.g. to a temperature of 600-750 °C). Preferably the plate is annealed at a temperature of 540-550 °C for 15-60 minutes between the distorting and toughening steps. Glass plate produced by this process has an appearance which mimics antique hand-made glass but has the strength and safety benefits of toughened float glass.

Description

Process for Manufacturing Glass [0001] This invention relates to processes for manufacturing glass having an appearance which mimics that of historic hand-made glass but has strength and safety benefits similar to those of toughened float glass. The invention also relates to such glass itself and products containing it.

BACKGROUND

[0002] Traditionally, window glass was made by cutting a pane of glass from a large disc or rondel of crown glass, or by cutting open and then flattening a large blown cylinder of glass.

Nowadays, however, float glass is commonly used in windows. Float glass is a pane of glass made by floating molten glass on a bed of molten metal.

[0003] Window glass manufactured by traditional processes looks very different to modern window glass. Traditional window glass does not have a uniform thickness and has an uneven surface, whereas modern glass has a uniform thickness and a very even surface.

[0004] When viewed from the building front, a building having modern float glass windows looks very different compared to a building having traditional glass windows. Traditional glass distorts the reflected and transmitted images and thus imparts character to the building.

Modern float glass does not distort the reflected and transmitted images and therefore appears featureless when compared to traditional glass. Accordingly, it is desirable to use glass manufactured by traditional processes in some buildings for aesthetic and conservation reasons.

[0005] There are various problems with glass manufactured by traditional processes. For example, this type of glass is very expensive to manufacture when compared to the costs of manufacturing float glass. Additionally, in many countries, traditional glass does not meet the modern strict building regulations for safety.

[0006] It is possible to reduce the cost of producing traditional-looking glass, i.e. glass which appears to be produced by traditional processes, by kiln-distorting' float glass. The kiln-distortion process is well known and typically involves laying a pane of glass on a distorting surface and heating the glass to allow the glass to soften and become distorted. The distorting surface is often a layer of aggregate, e.g. sand on a floor or other horizontal surface of a kiln.

[0007] Toughened window glass is float glass that has been subjected to a controlled thermal process in which the glass is first heated and then rapidly cooled. The toughening process creates balanced internal stresses which increase the strength of the glass.

Toughened glass will usually shatter into small fragments instead of sharp shards when broken. These combined properties make glass safer for window applications because toughened glass is less likely to cause severe injury when broken.

[0008] Toughened glass is usually made from annealed glass via a thermal tempering process. The toughening process is well known to those in the art, as is the process for annealing glass. Typically, the toughening process involves placing the glass onto a roller table and then annealing it in a kiln or furnace. The annealing process comprises heating the glass in the kiln or furnace to a temperature above its annealing point and rapidly cooling the glass. Normally, the glass is heated to about 720°C and the glass is rapidly cooled with forced air drafts. Toughened glass cannot be re-worked once toughened. Therefore, cutting or pressing to shape must be conducted before toughening the glass.

[0009] The toughening process cannot be applied to glass made by traditionally manufactured processes because of the uneven surface and non-uniform thickness of the glass. Thus, the safety properties of toughened glass cannot be imparted to glass made by traditional processes.

[0010] It would therefore be desirable to provide a process for the manufacture of glass visually reminiscent of traditional-looking glass and having the qualitative benefits of toughened glass. It would also be desirable to provide toughened glass having a textured surface.

BRIEF SUMMARY OF THE DISCLOSURE

[0011] In accordance with the present invention there is provided a process for heat-distorting a plate of glass characterised in that the process further comprises toughening the distorted glass plate.

[0012] In accordance with the present invention there is further provided a process for heat-texturing a plate of glass characterised in that the process further comprises toughening the textured glass plate.

[0013] The invention includes a kiln-distorted, toughened glass plate. The invention includes a kiln-textured, toughened glass plate.

[0014] The invention also provides a glass plate having the characteristics of toughened glass and having multiple distortions (deviations from flatness) in its surface to distort reflected and transmitted images.

[0015] In accordance with another aspect of the invention there is provided a toughened glass plate having image distorting characteristics reminiscent of a traditional glass plate.

[0016] In accordance with the invention there is further provided a double-glazed window unit comprising a pane of glass obtainable by the process of the present invention. Glass obtainable by the process of the invention has a textured and/or distorted surface (non-smooth surface) and may have image distorting characteristics which render the glass reminiscent of a traditional glass plate.

[0017] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0018] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any process or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any process or process so disclosed.

[0019] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Embodiments of the invention are further described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a cross-section of a kiln including a plurality of particle and a pane of glass resting on the particles.

Figure 2 is a cross-section of a pane of glass prior to the distortion process.

Figure 3 is a cross-section of a pane of distorted glass after the distortion process.

Figure 4 is a plan view of a pane of distorted glass.

DETAILED DESCRIPTION

[0021] This patent specification describes processes which involve heating glass. The glass is heated in a suitable heating apparatus, customarily referred to as a kiln or furnace. This specification makes no distinction between the terms kiln' and furnace', but, for convenience, uses the word kiln' to refer to all apparatuses for heating the glass plate to the high temperatures required by the described processes. Thus, whenever the word kiln' is used herein, it includes reference to apparatus which the skilled person would prefer to describe as a furnace.

[0022] Embodiments of the invention involve the use of an aggregate. By the term aggregate' is meant construction aggregate, including sand, crushed stone, gravel, slag or recycled crushed concrete.

[0023] According to a first aspect, the invention provides a process for heat-distorting a plate of glass characterised in that the process further comprises toughening the distorted glass plate. The glass plate is normally float glass, however this is not a technical requirement of the process which merely serves to transform a flat glass, however manufactured, to a distorted and toughened glass.

[0024] The processing of glass is very well understood and has been undertaken for many years. Accordingly, the skilled person will require no instruction as to how to perform the invention just described. However, for avoidance of doubt the following detailed description is offered.

[0025] Therefore, the invention includes a process for heat-distorting a glass plate which comprises contacting a surface of the glass plate with a distorting surface. The process then comprises heating the glass plate to a softening temperature and allowing the glass to soften while in contact with the distorting surface. The process then comprises toughening the distorted glass plate.

[0026] In an embodiment, the distorting surface is a plurality of particles and the contacting comprises resting the glass on the plurality of particles. This is illustrated by way of example in figure 1. Thus, a plurality of particles may be randomly scattered on a floor or shelf of a kiln, or more generally on any internal substantially horizontal surface, and the glass pane rested on top of the particles. As previously described, the kiln is then heated to soften the glass so that it becomes distorted by the weight of the glass on the distorting surface. The invention therefore enables a simple and economical method of distorting the glass. The random scattering of the particles will result in the glass being randomly distorted. Thus, no two panes of glass resulting from this process need have the same distortion pattern. Of course the process is not limited to random scattering of particles and regular scattering is included in the scope of the invention.

[0027] The plurality of particles comprises a particulate material able to withstand the elevated softening temperature of the glass, for example it may consist of silica particles. By being able to withstand the elevated softening temperature' it is meant that the particles do not themselves lose shape or stick to the glass surface when subjected to the elevated softening temperature. In an embodiment, the plurality of particles is an aggregate.

Aggregates are readily available materials and are able to withstand the temperatures required to distort the glass. For example, the aggregate may be sand.

[0028] The particle size is dependent on the level of distortion desired and on the thickness of the glass to be distorted. In an embodiment, each particle, e.g. sand particle has an average diameter of from 0.5 mm to 4 mm. Typically, a particle having a diameter smaller than 0.5 mm would be too small to achieve distortion reminiscent of a traditional glass plate in a pane of glass having a thickness of more than 1 mm. Nonetheless, a particle having a diameter of smaller than 0.5 mm provide distortion in the form of texturing of the surface of the surface of a pane of glass having a thickness of more than 1 mm. A particle having a diameter larger than 4 mm may be used depending on the thickness of the glass. Typically, a particle having a diameter larger than 4 mm would too large to distort a pane of 3 or 4 mm glass. In a preferred embodiment, each particle has an average diameter of from 1 mm to 3 mm.

[0029] When the distorting surface comprises a plurality of particles, it is particularly important that, when the glass is removed from the kiln, it is removed as carefully as possible.

Careless removal of the glass from the kiln could result in the glass being scratched on removal of the glass from the kiln. Additionally, when the glass is removed from the kiln, it may be necessary to clean the surface of the glass to remove any particles remaining on the surface of the glass. This is important to prevent the surface of the glass from being scratched by the particles rubbing the glass.

[0030] In an embodiment, the distorting surface comprises a textured surface and the contacting comprises resting the glass on the textured surface. The textured surface may be a sheet, e.g. of metal, having protrusions on the surface, the protrusions being from 0.5 mm to 4 mm in height. A benefit of using a textured surface rather than a plurality of particles as the distorting surface is that it is not necessary to clean the surface of the glass after the glass is removed from the kiln.

[0031] In some embodiments, the glass is inserted into a cold kiln for softening, not into a pre-heated kiln. This allows the glass to be heated more gradually and can help prevent damage to the glass.

[0032] In an embodiment, the softening temperature is from 550°C to 750°C. The temperature chosen for softening will depend on a number of factors, including the desired length of the softening period, the thickness of the glass and the level of distortion desired. In an embodiment, the softening temperature is from 600°C to 700°C.

[0033] In an embodiment, the heating of glass to a softening temperature includes increasing the temperature of the kiln at a rate of from 100°C per 1 minute to 100°C per 2 hours. The rate of temperature increase can be limited by, inter a/ia, the type of kiln employed because some kilns are able to heat up quicker than others. For example, the rate at which an electric kiln can heat up will be different to the rate at which a gas fired kiln can heat up. Also, the desired rate of temperature increase may depend on the thickness of the glass being distorted. In an embodiment, for 4 mm thick glass, the heating includes increasing the temperature at a rate of 100°C per 30 minutes.

[0034] In an embodiment, the glass is maintained at the softening temperature for a period of from 30 seconds to 60 minutes. In an embodiment, the glass is maintained at the softening temperature for 1 minute. In other words, the kiln may be maintained at the softening temperature for a desired period of time. This is not essential and in an alternative embodiment, as soon as the temperature of the glass reaches a target softening temperature, the kiln is turned off.

[0035] In an embodiment, the process includes the step of annealing the glass after step (ii) and prior to step (iii). The annealing step is not essential, but is preferred since it further strengthens the glass. Not meaning to be bound by theory, it is thought that the act of distorting the glass (by heating the glass to a softening temperature) weakens the glass by altering the internal structure of the glass. The act of annealing the glass is then thought to strengthen the glass by altering the internal structure of the glass and thereby returning the internal structure of the glass to its structure prior to distorting. In an embodiment, after step (ii), the kiln is cooled to an annealing temperature and the glass is allowed to anneal. In an alternative embodiment, after step (ii), the kiln is first cooled to ambient temperature and subsequently reheated to an annealing temperature. The reheating to an annealing temperature of the glass may be conducted in the same kiln or a different kiln in which step (ii) was carried out. In either of the above embodiments, the kiln in which the glass is annealed may be held at the annealing temperature for a period of from 15 minutes to 1 hour. The period for which the glass is held at the annealing temperature is dependent on the thickness of the glass. In either of the above embodiments, the annealing temperature for most common thicknesses of float glass is from 400°C to 550°C, preferably from 540°C to 550°C. For example, the annealing temperature may be 545°C. The annealing temperature is also dependent on the thickness of the glass. For example, 4mm glass is suitably held at 545°C for approximately 30 minutes.

[0036] It will be recalled that, after the glass has been distorted and optionally annealed, the glass is then subjected to a toughening step. In some embodiments the glass is caused or allowed to cool, e.g. to ambient temperature, after being distorted (and optionally annealed) but before being toughened. This allows the toughening to be conducted at a different site to the site at which the glass was distorted and optionally annealed. In other embodiments, the glass is subjected to the toughening step directly after being distorted (and optionally annealed), i.e. the glass is toughened in the same kiln as the kiln in which the glass was distorted and optionally annealed.

[0037] The action of toughening the glass may be achieved by exposing the distorted glass to a toughening temperature and subjecting it to accelerated cooling to below the annealing temperature. In the event that the annealing is omitted, then the exposure to the toughening temperature may be the same action as the heating of the glass to a softening temperature; in other words, when the heated glass has become distorted it is directly subjected to accelerated cooling to toughen it. Alternatively, the glass may be allowed to cool more slowly after completion of the distorting process and subsequently reheated to a toughening temperature prior to application of accelerated cooling. In those processes in which the distorted glass is annealed, therefore, it must be increased to the toughening temperature after completion of the annealing process (bearing in mind that the annealing temperature is lower than the toughening temperature), irrespective of whether the glass cools after the annealing or is directly raised to the toughening temperature.

[0038] In an embodiment, the glass is heated to a temperature of from 550°C to 750°C during the toughening step before being cooled. In an embodiment, the toughening temperature is from 600°C to 700°C. In an embodiment, the glass is heated to a temperature of 720°C during the toughening step before being cooled.

[0039] In an embodiment, the thickness of the glass plate is from 1 mm to 6 mm. In an embodiment, the thickness of the glass plate is from 1 mm to 4 mm. Preferably the glass plate is either 3 mm glass or 4 mm glass.

[0040] The glass obtainable by the above described process is novel and forms an aspect of the invention. The invention therefore includes a kiln-distorted, toughened glass plate, and also includes a glass plate having the characteristics of toughened glass and having multiple distortions (deviations from flatness) in its surface to distort reflected and transmitted images.

The multiple distortions in the surface of the glass may also be described as texturing' and therefore the surface of the glass may also be described as a textured' surface.

[0041] In an embodiment, substantially the entire area of the plate, optionally excluding a marginal area, is occupied by the distortions. In an embodiment, the plate includes multiple contiguous distortions. In other words, the plate does not include any significant flat areas (float glass-like areas) in the area occupied by the distortions. The distortions may also be described as surface depressions and surface protrusions, and/or as raised and lowered areas.

[0042] It will be appreciated from the above description that the present invention provides amongst other things a toughened glass plate having image distorting characteristics reminiscent of a traditional glass plate. The invention also provides a toughened glass plate having a textured surface.

[0043] The invention further includes glass-containing products comprising a glass of the invention, e.g. a double-glazed unit comprising a pane of glass obtainable by the process of the present invention.

Claims

CLAIMS1. A process for heat-distorting and/or heat-texturing a plate of glass characterised in that the process further comprises toughening the distorted and/or textured glass plate.
2. A process of claim 1 comprising: (i) contacting a surface of the glass plate with a distorting surface; then (ii) heating the glass plate to a softening temperature and allowing the glass to soften while in contact with the distorting surface; and then (iii) toughening the glass plate.
3. A process of claim 2, wherein the distorting surface comprises a plurality of particles and wherein the contacting comprises resting the glass on the plurality of particles.
4. A process of claim 3, wherein the plurality of particles are silica particles.
5. A process of claim 3 or claim 4, wherein the plurality of particles have a diameter of from 0.5 mm to 6 mm, and optionally a diameter of from 1 mm to 3 mm.
6. A process of claim 2, wherein the distorting surface comprises a textured surface and wherein the contacting comprises resting the glass on the textured surface.
7. A process of any of claims 2 to 6, wherein the softening temperature is from 550°C to 750°C.
8. A process of any of claims 2 to 7, wherein the heating includes increasing the temperature at a rate of from 100°C per 1 minute to 100°C per 2 hours.
9. A process of claim 8, wherein the heating includes increasing the temperature at a rate of 100°C per 30 minutes.
10. A process of any of claims 2 to 9, wherein the glass is maintained at a softening temperature for a period of from 30 seconds to 60 minutes, optionally 1 minute.
11. A process of any of claims 2 to 10, further comprising annealing the glass plate after step (ii) and prior to step (iii).
12. A process of claim 11, wherein glass plate is annealed at a temperature of from 540 to 550° C, optionally 545° C.
13. A process of claim 11 or 12, wherein the glass is annealed by maintaining the glass plate at the annealing temperature for a period of from 15 minutes to 1 hour, optionally 15 minutes.
14. A process of any preceding claim, wherein the step of toughening the glass involves heating the glass to a temperature above its annealing temperature or maintaining the glass at a temperature above its annealing temperature, and then immediately cooling the glass to a temperature below its annealing temperature.
15. A process of claim 14, wherein the glass is toughened by heating to a temperature of from 600 to 750°C or maintaining the glass at a temperature of from 600 to 750°C, and then immediately cooling to a temperature below 540°C.
16. A process of claim 15, wherein the glass is toughened by heating to 720°C or maintaining the glass at a temperature of 720°C, and then immediately cooling to a temperature below 540°C.
17. A process of any preceding claim, wherein the thickness of the glass plate is from 0.5 mm to 4 mm, and optionally from 1 mm to 3 mm.
18. A process of any preceding claim, wherein the glass plate is a float glass plate.
19. A kiln-distorted and/or kiln-textured, toughened glass plate.
20. A glass plate having the characteristics of toughened glass and having multiple distortions (deviations from flatness) in its surface to distort reflected and transmitted images.
21. A toughened glass plate having image distorting characteristics reminiscent of a traditional glass plate.
22. A double-glazed window unit comprising a pane of glass obtainable by a process of any of claims ito 17.
23. A process for making distorted and/or textured, toughened glass substantially as hereinbefore described.
24. A kiln-distorted and/or kiln-textured, toughened glass plate substantially as hereinbefore described.Amendments to the claims have been filed as follows:CLAIMS1. A process for manufacturing a toughened glass plate having image distorting characteristics reminiscent of a traditional glass plate comprising: (i) resting the glass plate on a plurality of particles; then (ii) heating the glass plate to a softening temperature and allowing the glass to soften while in contact with the plurality of particles; and then (iii) toughening the glass plate.2. A process of claim 1, wherein the plurality of particles are silica particles.3. A process of claim 1 or claim 2, wherein the plurality of particles have a diameter of from 0.5 mm to 6 mm, and optionally a diameter of from 1 mm to 3 mm.4. A process of any of claims 1 to 3, wherein the softening temperature is from 550°C to 750°C.5. A process of any of claims 1 to 4, wherein the heating includes increasing the temperature at a rate of from 100°C per 1 minute to 100°C per 2 hours.Q 6. A process of claim 5, wherein the heating includes increasing the temperature at a rate of 100°C per 30 minutes.7. A process of any of claims 1 to 6, wherein the glass is maintained at a softening Q temperature for a period of from 30 seconds to 60 minutes, optionally 1 minute.8. A process of any of claims 1 to 7, further comprising annealing the glass plate after step (ii) and prior to step (iii).9. A process of claim 8, wherein glass plate is annealed at a temperature of from 540 to 550° C, optionally 545° C. 10. A process of claim 8 or 9, wherein the glass is annealed by maintaining the glass plate at the annealing temperature for a period of from 15 minutes to 1 hour, optionally 15 minutes.11. A process of any preceding claim, wherein the step of toughening the glass involves heating the glass to a temperature above its annealing temperature or maintaining the glass at a temperature above its annealing temperature, and then immediately cooling the glass to a temperature below its annealing temperature.12. A process of claim 11, wherein the glass is toughened by heating to a temperature of from 600 to 750°C or maintaining the glass at a temperature of from 600 to 750°C, and then immediately cooling to a temperature below 540°C.13. A process of claim 12, wherein the glass is toughened by heating to 720°C or maintaining the glass at a temperature of 720°C, and then immediately cooling to a temperature below 540°C.14. A process of any preceding claim, wherein the thickness of the glass plate is from 0.5 mm to 4 mm, and optionally from 1 mm to 3 mm.15. A process of any preceding claim, wherein the glass plate is a float glass plate.16. A toughened glass plate having image distorting characteristics reminiscent of a traditional glass plate.17. A double-glazed window unit comprising a pane of glass obtainable by a process of any of claims 1 to 15.18. A process for making distorted and/or textured, toughened glass having image distorting characteristics reminiscent of a traditional glass plate substantially as hereinbefore described.19. A kiln-distorted and/or kiln-textured, toughened glass plate having image distorting characteristics reminiscent of a traditional glass plate substantially as hereinbefore described. Co