CA2871239C

CA2871239C - Method for manufacturing tempered vacuum glass

Info

Publication number: CA2871239C
Application number: CA2871239A
Authority: CA
Inventors: Hui Wang; Zhiwu Xu; Shan Hua; Chengwei Lui
Original assignee: Hui Wang; Zhiwu Xu; Shan Hua; Chengwei Lui; Qingdao Hengda Glass Technology Co. Ltd.; Chen, Yandi
Current assignee: Qingdao Hengda Glass Tech Co Ltd
Priority date: 2013-11-11
Filing date: 2014-11-07
Publication date: 2017-05-16
Anticipated expiration: 2034-11-07
Also published as: CN103588387B; CA2871239A1; CN103588387A; WO2015066956A1

Abstract

The present invention provides a method for manufacturing tempered vacuum glass, including five steps of manufacturing supporting points, over-tempering plate glass, bonding, sealing and evacuating. The above manufacturing method can reduce the spontaneous breakage rate of the tempered vacuum glass while maintaining its toughening degree.

Description

TITLE
METHOD FOR MANUFACTURING TEMPERED VACUUM GLASS
FIELD OF THE INVENTION
The present invention relates to the field of manufacturing of vacuum glass, more particularly, to a method for manufacturing tempered vacuum glass.
BACKGROUND
Vacuum glass is made of two sheets of plate glass, in which all the edges of the two sheets of plate glass are enclosed and the gap between the two sheets is evacuated into vacuum and pumping holes are sealed. Since the two sheets of plate glass that constitute the vacuum glass are thin, supporting points are usually provided between the two sheets of plate glass to support the glass against the outside atmospheric pressure in order to make the pressures from the outside and inside meet each other, which operate in a similar manner as heat insulation in vacuum bottles.
If vacuum glass is applied as windows or glass walls of skyscrapers, the two sheets of glass constituting the vacuum glass need to meet requirements as safety glass.
Tempered glass is a representative kind of safety glass thanks to its excellent mechanical properties, which are better than those of ordinary common glass, such as in impact resistance, wind load resistance and bending resistance. Therefore, theoretically, if tempered glass is applied as the two plate glasses constituting the vacuum glass, the safety of the tempered vacuum glass thus formed is much better than the one manufactured from ordinary plate glasses.

However, for various reasons, tempered glass is more likely to have spontaneous breakage. Research shows that, especially when the surface stress > 52MPa, the probability of "spontaneous breakage" caused by the impurities inside the tempered glass is increased greatly, and thus, normally, a heat soak test (HST) is required for tempered glass, that is, homogenizing. The HST heats the tempered glass up to 290 C I0 C and keeps the temperature for a certain time to facilitate quick crystal phase transformation of nickel sulfide in the tempered glass, and any affected tempered glass artificially breaks beforehand in the homogenizing furnace, rather than experiencing spontaneous breakage 3.0 after use. In this manner, the occurrence of spontaneous breakage in use after installation is reduced.
However, actually, the tempered glass is heated again in the HST, and in the process of manufacturing vacuum glass, the sealing step therein also would heat the tempered glass again. Due to limitations of the inherent properties of the tempered glass itself, being heated again will inevitably cause the decrease of the surface stress of the tempered glass, which may have a negative effect on the mechanical properties of the tempered vacuum glass, such as impact resistance, wind load resistance and bending resistance.
SUMMARY OF THE INVENTION
In order to address the above problem, the present invention provides a method for manufacturing tempered vacuum glass, to decrease the probability of "spontaneous breakage" in the tempered vacuum glass while maintaining the surface stress of the tempered vacuum glass.

2 The present invention provides a method for manufacturing tempered vacuum glass, comprising the steps of:
1) manufacturing supporting points: through screen printing, print heat-resistant glass glaze containing no lead or cadmium uniformly and dispersedly onto a surface of a plate glass to form supporting points having a designed height and area;
2) over-tempering the plate glasses: transfer plate glasses for manufacturing the tempered vacuum glass into a continuous tempering furnace for being subject to over-tempering process so as to form over-tempered glasses;

3) bonding: bond an over-tempered glass that has no supporting point printed, onto a surface of the over-tempered glass, wherein said surface is printed with the supporting points; and wherein, one of the two bonded over-tempered glasses is provided with pumping holes;

4) sealing: apply lead-free low-melting glass powder to all the edges of the gap between the two bonded over-tempered glasses, and thereafter, transfer the glasses into an edge-sealing furnace to melt the lead-free low-melting glass powder by low temperature heating, so as to seal the gap between the two bonded over-tempered glasses; in the heating process of low temperature heating, the two over-tempered glasses are transformed into tempered glasses;
and

5) evacuating: bake and pump the sealed gap between the two tempered glasses using an evacuating device to form tempered vacuum glass and finally, seal the pumping holes on the tempered vacuum glass.
The present invention has the following advantages:

1) To decrease of the occurrence of "spontaneous breakage" of the tempered vacuum glass, while maintaining the surface stress of the tempered vacuum glass.
2) Supporting points are processed through screen printing, which can improve the production rate and the automation level, and can be used for mass production, and wherein the thickness of the vacuum layer is easy to adjust.
3) The application of the lead-free glass powder allows the final product to be eco-friendly and non-toxic, whose low melting temperature also allows low energy consumption and high efficiency of the production.
4) The application of evaporable getter can effectively improve the service life of the product and the transparency of the glass.
In order to achieve the above and related goals, one or more aspects of the present invention comprise the features described in the detailed description and specified in the claims hereinafter. The following description and the attached drawings illustrate some exemplified aspects of the present invention. However, these aspects only represent some of the various ways in which the present invention can be implemented.
Additionally, the present invention is intended to include all these aspects and their equivalents.
BRIEF DESCRIPTION OF THE DRAWINGS
Other goals and results of the present invention can become more clear and comprehensible with reference to the detailed description with respect to the drawings and the claims with a more complete understanding for the present invention.
In the drawings:
Figure 1 is a flowchart schematic for the manufacturing of tempered vacuum glass according to embodiments of the present invention;

Figure 2 is a structural schematic of the tempered vacuum glass according to embodiments of the present invention;
Figure 3 is a sectional view taken along A-A line of Figure 2;
Figure 4 is an enlarged view of a part of Figure 3;
Figure 5 is a sectional view taken along B-B line of Figure 4;
The referential numbers include: 1-sealing edge, 2-supporting point, 3-gap, 4-plate glass, 5-pumping hole, 6-evaporable getter, 7-plate glass, and 8-sealing hole.
Throughout these drawings, the same numerals indicate similar or corresponding features or functions.
DETAILED DESCRIPTION OF THE DRAWINGS
In the following description, for the purpose of illustration, numerous specific details are set forth to provide a complete understanding for the one or more embodiments. However, apparently, these embodiments may also be implemented without these specific details.
zo It should be understood that, plate glass itself becomes tempered glass or over-tempered glass after tempering or over-tempering, respectively. In fact, plate glass, tempered glass and over-tempered glass are names used to indicate the same sheet of glass in different processes. Therefore, for convenience of illustration, plate glass, tempered glass and over-tempered glass are indicated by the same referential numeral in the following description of the present invention, and the term "tempered glass" may collectively refer to glass after being subject to tempering or over-tempering.

Figure 1 illustrates a flowchart for a manufacturing method of tempered vacuum glass according to the present invention, and Figures 2-5 illustrate the structure of the tempered vacuum glass according to embodiments of the present invention.
As illustrated in Figures 1-5, the present invention provides a method for manufacturing tempered vacuum glass, including the following steps:
S110: Manufacturing supporting_points.
Print or dispense supporting points onto a surface of a plate glass 7 and cure the surface including the supporting points. Particularly, heat-resistant glass glaze containing no lead or cadmium is printed uniformly and dispersedly onto the surface of the plate glass through a screen printing process, to form supporting points of a designed height and area.
In manufacturing supporting points, supporting points 2 are manufactured on the surface of at least one plate glass, and the heat-resistant glass glaze containing no lead or cadmium is printed uniformly and dispersedly on the upper surface of the plate glass 7 to form the supporting points 2.
Preferably, the heat-resistant glass glaze can resist a temperature of 580 C
or more and has a color near to the glass body and a good transmittance of light.
The supporting point in the prior art usually uses metal support, which has good heat conductivity and is significantly visible and easily movable. In the present invention, inorganic non-metal materials (such as ceramic, glass, ink or others) are used as the supporting points and have a low conductivity of heat. Through spraying, dispensing,

6 printing or other coating processes, the supporting points are directly joined together with the glass and hardly move, and the inorganic non-metal materials used are transparent or semi-transparent, which provides a good visual effect.
After printing the supporting points 2, curing is required for the printed supporting points. Particularly, the plate glass 7 formed with supporting points 2 is naturally dried in the air or baked in a baking oven to form supporting points having a designed height and area. Typically, the supporting points 2 can be fixed onto the plate glass 7 only if naturally dried in the air for one hour or more or dried in the baking oven at a temperature of approximately 120 C for about 15 minutes.
S120: Over-tempering the plate glass The plate glass 7 used for manufacturing tempered vacuum glass is transferred into a continuous tempering furnace for the over-tempering process to form the over-tempered glass.
The specific details of the over-tempering process are set forth below.
zo A. The phase of starting heating From room-temperature atmosphere, the plate glass 7 is transferred into the tempering furnace for heating. Since glass is not a good conductor for heat, the inner layer has a relatively low temperature and the outer layers have a relatively high temperature, causing the outer layers to expand while the inner layer does not. Thus, compressive stress is temporarily formed in the outer layer because its expansion is limited by the surface of the inner layer, and sterile stress is formed in the inner layer.

7 Since glass has good compression strength, the glass does not break, even being subject to quick heating.
However, it should be noted that, once the plate glass 7 is transferred into the furnace, stress is formed between the inner and outer layers of the glass because of the temperature difference between the inner and outer layers. Therefore, suitably for thick glass, the heating process should be a little slower and the heating temperature should be a little lower; otherwise, the plate glass 7 would break in the tempering furnace because of a too big temperature difference between the inner and outer layers.
B. The phase of continuing heating The plate glass 7 goes on being heated. The temperature difference between the inner and outer layers of the plate glass 7 continues to decrease. When both the inner and outer layers reach the tempering temperature, the heating stops.
It should be noted that, the heating time for heating the plate glass 7 should be controlled to be within approximately 150 to 250 seconds, and the tempering temperature should be controlled to be within approximately 690 C to 720 C.
zo C. The phase of starting quenching In the tempering furnace, the plate glass 7 is blown by the air grid. In this way, the temperature of the surface layer drops lower than the temperature of the central layer, and the surface layer starts to shrink but the central layer does not; therefore, the shrinkage of the surface layer is limited by the central layer, and sterile stress is formed temporarily in the surface layer and compressive stress is formed in the central layer.

D. The phase of continuing quenching The inner and outer layers of the plate glass 7 are being further quenched, and the surface layer of the plate glass 7 has been hardened (its temperature is lowered below 500 C) and has stopped shrinking. At this time, the inner layer starts to cool and shrink while the hardened surface layer limits the shrinkage of the inner layer. As a result, compressive stress is formed in the surface layer and sterile stress is formed in the inner layer.
E. Continuing quenching The temperatures of the inner and outer layers of the plate glass 7 are further lowered. At this time, the temperature of the inner layer is lowered to about 500 C and its shrinkage accelerates, and the compressive stress of the outer layer and the sterile stress of the inner layer have been substantially formed. Meanwhile, the central layer is still relatively soft and more or less in a state of viscous flow, and is still not in the desired final stress state.
F. Over-tempering completed At this time, the inner and outer layers of the plate glass 7 have been totally tempered, the temperature difference between the inner and outer layers has narrowed, and the desired final stress of the plate glass 7 (that is, the compressive stress in the outer layer (surface layer) and the sterile stress in the inner layer)has formed.
Because the subsequent process requires manual work, the plate glass 7 is air-cooled between approximately 200 and 500 seconds to a temperature below 50 C and above room temperature. Here, room temperature means the temperature of the glass at which a person can hold the plate glass for a relatively long time, usually 25 C 5 C.
In order to lower the spontaneous breakage rate of the over-tempered glass, the over-tempered glass is required to be transferred into a homogenizing furnace for a heat soak test (HST). The heat soak test for tempered glass is especially important because the tempered glass is more likely to experience spontaneous breakage.
Particularly, the tempered glass 7 including supporting points 2 is transferred into the homogenizing furnace for the heat soak test. Through convection heating in the homogenizing furnace, hot air flows parallel to the surface of the tempered glass 7 without impediments caused by breakage of the tempered glass, wherein the heat soak test includes three phases of temperature rising, temperature keeping and cooling.
The phase of temperature rising starts at atmospheric temperature (where the over-tempered glass 7 is) and ends when the surface temperature of the tempered glass 7 reaches a temperature of about 280 C. The temperature in the furnace may rise over 300 C, and the temperature of the surface of the glass should be kept below 320 C, and the time in which the surface temperature of the glass is over 300 C should be reduced to as short as possible.
The phase of temperature keeping starts at the time when the surface temperature of the tempered glass 7 reaches 280 C, and lasts at least two hours.
Throughout the phase of temperature keeping, the surface temperature of the glass should be kept within 290 C
+ 10 C.
After the phase of temperature keeping is completed, the phase of cooling starts.

In the phase of cooling, the temperature of the tempered glass 7 is lowered to the atmospheric temperature. The phase of cooling can be considered as finished when the temperature inside the furnace is lowered to approximately 70 C. During the phase of cooling, the rate of temperature falling should be controlled to minimize breakage of glass caused by thermal stress.
Generally speaking, the surface stress of the tempered glass without being subject to HST is over 90 MPa, and the stress of the tempered glass subject to HST in the prior art is considerably lower than 90 MPa. In contrast, in the present invention, because of the over-tempering process, the surface stress of the formed over-tempered glass is between 110 MPa and 130 MPa. Thus, after being subject to HST of the present invention, although the surface stress is somewhat decreased, the associated tempering parameters of the over-tempered glass are still slightly higher than common tempered glass, which can meet requirements of being heated again in the subsequent sealing process.
S130: Bonding After the supporting points are made, bond the over-tempered glass that has no supporting points printed, onto the surface printed with supporting points of the over-tempered glass printed with supporting points; wherein one of the two bonded over-tempered glasses is provided with pumping holes, for evacuating the sealed gap after the sealing.
Particularly, for example, cover the side formed with supporting points 2 of the over-tempered glass 7 including the supporting points, with the over-tempered glass 4 having pumping holes 5.

In order to improve the transparency and vacuum property of the tempered vacuum glass, in one particular embodiment of the present invention, at least one piece of evaporable getter 6 is provided inside the corner(s) of the two bonded tempered glasses.
The evaporable getter is barium-aluminum getter, which not only has a good absorption rate but also can improve the transparency of the glass.
S140: Sealing Apply lead-free low-melting glass powder to all the edges of the gap of the two bonded over-tempered glasses, and then transfer the glasses into the edge-sealing furnace and heat them at a relatively low temperature to melt the lead-free low-melting glass powder, to seal the gap between the two bonded over-tempered glasses.
Particularly, for example, coat all the edges of the gap of the two bonded over-tempered glasses and the areas about the pumping holes with lead-free low-melting glass powder, and then transfer the glasses into the edge-sealing furnace for heating to seal the edge 1 and hole 8. The heating temperature is preferably between approximately 355 C and 380 C, and the heat sealing time is preferably about 2 hours in the continuous furnace, or about 24 hours in the single-unit furnace.
The tempered glass 4 including pumping holes is also manufactured through the above process. As to difference of property between the two tempered glasses, usually, the tempered glass provided with pumping holes 5 is cheaper than the other of the two, and the pumping holes 5 of the tempered glass 4 are usually inserted with glass pumping tubes (not shown in the drawings).

Wherein, the main composition of the lead-free low-melting glass powder is about 80 weight percent of arsenic oxide, and the rest includes about 10 weight percent of zinc oxide, about 5 weight percent of boron oxide, about 3 weight percent of aluminum oxide, about 2 weight percent of magnesium oxide and others, and manganese and/or cobalt is added as additives (about 0.1 to 1 weight percent with respect to the total weight). The glass powder is manufactured by conventional process, and whose expansion coefficient is 81x10-7, and whose lowest melting temperature is 353 C.
At the same time, during the process of heating at a relatively low temperature, since the surface stress of the over-tempered glass is lowered for being heated again, the over-tempered glass is transformed into tempered glass.
S150: Evacuating Bake and pump the sealed gap between the two tempered glasses using an evacuating device to form the tempered vacuum glass and seal the pumping holes on the glass.
Particularly, use the evacuating device to bake and pump the gap 3 of the tempered glasses which have been bonded together in the edge-sealing furnace, and then seal the pumping holes 5 in the glass 4 by planar heat-sealing process. The sealing surface of the sealed pumping holes 5 is lower than the external surface of the plate glass 4.
In the prior art, the sealing part of glass tubes looks like a "tail" on the outer side surface of a vacuum flask. For convenience of melting of glass tubes and bonding with the plate glass, almost all the glass tubes are higher than the surface of the plate glass by about 1 centimeter, and then a metal protection cap is added on it for protection.

The planar heat sealing process in the present invention is as follows:
At a position close to the corner of the outer planar surface of the tempered glass 4, a pumping hole 5 is drilled inward, which is composed of a small hole and a large hole.
First, the small hole is drilled through the thickness of the glass 4, which has the same diameter as the glass tube, and then a large hole is socket drilled based on the small hole, which is not drilled through the glass 4 but stopped at the 2/3 thickness of the glass 4.
The diameter of the large hole is slightly larger than the small hole. Then the glass tube is buried in the small hole with its end in the large hole. Finally, the sealed upper end surface of the pumping hole 5 (sealed hole 8, see in Figure 3) is lower than the upper planar surface of the glass 4.
The melting of the glass tube is done via customary technical means, which is omitted here for clearness of description of the embodiment.
In the prior art, the sealing of the glass tube is to heat seal the glass tube with focused infrared light, and its sealed glass tube projects above the surface of the glass, which needs a protection cap for protection, and this kind of sealing is more likely to break during the installation and transportation of the glass and the protection cap is quite visible. In contrast, the planar heat sealing in the present invention employs glass plate or metal plate of circle, square or other shapes to cover the sealing surface with no projections on the surface of the glass and provides a better visual effect.
And side edge hole sealing may also be applied. In this process, the pumping tubes are arranged on the side edge of the glass and thus hidden in the window frame after installation, which is advantageous in protection of the pumping tubes and visual effect.
It can be seen from the above description of the embodiments, for the two plate glasses which constitute the vacuum glass, each of them needs to be over-tempered before bonding. In the past, since the glass powder used for sealing has a high melting temperature of 450 C or above, if the vacuum glass is directly used for tempering, the tempering temperature is required to be higher than 600 C, which means the sealed glass powder may undesirably melt again at this high temperature, and if the single plates of glass 4 and 7 are tempered first one-by-one before bonding, the annealing temperature for the tempering is about 400 C, which means the glass having been tempered may anneal again when heat sealing is performed with the glass powder. This dilemma can be solved with the lead-free glass powder, having a low melting temperature of 350 C.
The toughening degree of the two tempered glasses 4 and 7 can be still kept after heat sealing with the lead-free low-melting glass powder.
The method for manufacturing tempered vacuum glass of the present invention has been illustrated in the form of examples in the above with reference to the attached drawings. However, it should be understood for those skilled in the art that, various modifications and improvements can be made in the method of manufacturing the tempered vacuum glass herein without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the appended claims hereafter.

Claims

WHAT IS CLAIMED IS:

1. A method for manufacturing a tempered vacuum glass, the method comprising the steps of:
1) through screen printing, printing a heat-resistant glass glaze containing no lead or cadmium that is uniformly dispersed onto a surface of a first plate glass to form supporting points having a designed height and area;
2) transferring the first plate glass for manufacturing the tempered vacuum glass into a continuous tempering furnace for over-tempering processing so as to form a first over-tempered plate glass, wherein a tempering time of the over-tempering processing is 150 - 250 seconds, a tempering temperature of the over-tempering processing is 690°C - 720°C, an air cooling time of the over-tempering processing is 200 - 500 seconds, a temperature for the air cooling of the over-tempering processing is 50°C - 25°C, and a surface stress of the first over-tempered plate glass is 110 MPa - 130 MPa; then transferring the first over-tempered plate glass into a homogenizing furnace for a heat soak test;
3) bonding a second over-tempered plate glass that has no supporting point printed thereon, onto a surface with the supporting points of the first over-tempered plate glass;
4) applying a lead-free low-melting glass powder to the edges of a gap between the two bonded over-tempered plate glasses, and thereafter transferring the two bonded over-tempered plate glasses into an edge-sealing furnace to melt the lead-free low-melting glass powder by heating at a temperature range between 355°C and 380°C, so as to seal the gap between the two bonded over-tempered plate glasses, wherein the two over-tempered plate glasses are transformed into tempered plate glasses by heating at the temperature range between 355°C and 380°C; and 5) baking and pumping the gap sealed between the two tempered plate glasses using an evacuating device to form the tempered vacuum glass and, sealing pumping holes on the tempered vacuum glass.

2. The method according to claim 1, wherein the step of bonding further comprises inserting at least one piece of an evaporable getter at one or more corners between the two bonded tempered plate glasses.

3. The method according to claim 2, wherein the evaporable getter is a barium-aluminum getter.

4. The method according to claim 3, wherein the step of evacuating further comprises sealing the pumping holes through planar heat sealing, and wherein a sealing surface of the pumping holes is below an external surface of the tempered vacuum glass.