1. A cold roll forming method for ultra-thin high-aluminum cover plate glass is characterized by comprising the following steps:

generating a compressive stress on the surface of the glass plate: firstly, generating stress on two surfaces of a glass plate so as to strengthen the two surfaces of the glass plate by utilizing compressive stress; and

bending the glass sheet: the glass plate is bent and deformed due to unbalanced compressive stress on two surfaces by thinning one surface of the glass plate.

2. The method for forming an ultra-thin high-alumina cover glass according to claim 1, wherein the step of generating a compressive stress on the surface of the glass sheet is one of chemical hardening which is a surface compressive stress generated by subjecting the glass sheet to ion exchange and physical hardening which is a surface thermal stress generated by rapidly cooling the glass sheet after heating the glass sheet.

3. The process for forming an ultra-thin high aluminum cover glass according to claim 1, wherein the step of bending the glass sheet is performed at a temperature that does not cause rapid dissipation of the compressive stress on the surface of the glass sheet.

4. The method for forming an ultra-thin high aluminum cover glass according to claim 3, wherein the step of thinning is performed at room temperature.

5. The method of claim 3, wherein the step of imparting compressive stress to the surface of the glass sheet is a step of imparting stress layers of a predetermined thickness to both surfaces of the glass sheet, and the step of bending the glass sheet is a step of controlling the bending deformation of the glass sheet by reducing the predetermined thickness of the glass sheet.

6. The method of forming an ultra-thin high aluminum cover glass as claimed in claim 5, wherein the thickness of the thinned glass is controlled to be not more than the depth of the compressive stress layer on the surface of the glass sheet being thinned.

7. The method of claim 6, wherein the bending deformation of the glass sheet is controlled by calculating a thinning pattern based on the desired shape and curvature of the glass sheet to control the position, area and thickness of the glass sheet.

8. The method of forming an ultra-thin high aluminum cover glass in accordance with claim 7, wherein the reduction in thickness is based on the measured depth of the chemically-stiffened ion exchange layer and the surface compressive stress σ_sTo calculate.

9. The method of claim 8, wherein the thinning pattern is calculated, the glass sheet is coated with a film according to the pattern, and the coated glass sheet is chemically thinned.

10. The method for forming an ultra-thin high aluminum cover glass according to claim 7, wherein the thinning position and area are formed in the same or different patterns, including symmetrical or asymmetrical dots, lines, grids, lattices, etc., and the curved shape of the glass plate includes symmetrical and asymmetrical shapes.

Background

Most of the currently marketed front windshields and skylights for vehicles are formed by using two physically-stiffened soda-lime glass plates and sandwiching a layer of Polyvinyl butyral (PVB) adhesive film therebetween, and these glasses can be designed in a planar or curved surface shape, but are often designed in a micro-curved surface shape according to the fluid mechanics of the appearance. It has been proved that, since it is difficult to temper glass having a thickness of 2.0mm or less by a physical tempering method, the strength of the glass after physical tempering, particularly the Compressive stress (σ) of the glass surface is to be achieved_s) The glass needs to be maintained at a thickness of more than 2mm, and the requirements and details regarding physical rigidity are well known in the art and are not described herein.

Since the glass windows have traditionally been glued with a PVB film using soda lime glassIf the weight reduction effect is achieved by reducing the thickness of the glass, and the mechanical performance of the glued glass window combination cannot be reduced, the glass window combination is limited by two factors of the strength of the soda lime glass and the requirement of physical rigidity on the thickness of the glass plate. In order to overcome the restriction factor, the soda-lime glass plate can be replaced by the high-alumina glass cover plate, the high-alumina silicate cover plate glass has higher strength than the traditional soda-lime glass due to high content of aluminum and silicon, the strength of the traditional soda-lime glass can be achieved by using a thinner thickness, and chemical stiffening can be performed by using a chemical ion exchange method, the chemical stiffening method can be applied to the high-alumina cover plate glass with any thickness, so that the limitation of the thickness of the glass plate is avoided, the surface strength of the chemically stiffened high-alumina glass plate can be 2-3 times that of the physically stiffened soda-lime glass plate, and the impact resistance of the surface of the glass can be greatly improved. Therefore, the use of high-alumina-calcium plate glass as a new material for vehicle windows has gradually become a technical development trend for light weight of vehicle glass. The high-alumina-calcium plate glass with proper thickness can be selected to partially or completely replace the prior vehicle soda-calcium glass, but the cost factor that the price of the high-alumina cover plate glass is higher than that of the traditional soda-calcium glass is considered, so that one of the two pieces of glass in the vehicle window is replaced by the high-alumina glass, the weight of the vehicle window glass can be reduced, the strength of the glass window can be maintained, the cost can be controlled within the acceptable range of an end user, and the method is a feasible stage lightweight process in the prior industry. The chemical tempering method is not limited by the thickness of the glass, so that the chemical tempering method can be used for strengthening the surface of the glass for the glass plate with the thickness of the high-aluminum cover plate glass of less than 2 mm. In general, the narrow sense of chemical toughening of glass refers to the ion exchange of potassium ions in a silicate glass containing sodium oxide with sodium ions in a potassium nitrate molten salt at a temperature of about 380-460 ℃ by ion exchange, wherein the volume of potassium ions is slightly larger than that of sodium ions, so that when potassium ions are substituted for sodium ions on the surface of the glass, as shown in fig. 1(a), a compressive stress layer is formed on the surface, and the Depth of the compressive stress layer is generally referred to as the Depth of the ion exchange layer (Depth of ion-exchange layer)Layer, DOL), resulting in a Compressive stress (σ) of the surface_s) The size of (b) is influenced by factors such as glass composition and ion exchange depth. The region between the compressive stress layers on the two outer surfaces of the glass sheet is the Central tension zone (σ)_c) When the surface of the glass is enhanced in resistance to external impact due to the compressive stress, the central area is weakened due to the generation of the tensile stress. Chemical toughening of glass in a broad sense means that any ion exchange method can be used to replace some metal ions on the surface of the glass, and the foreign ions newly placed on the surface of the glass are usually ions with the same charge valence but with a volume slightly larger than that of the original glass surface, and can diffuse into the glass in an ion exchange manner when sufficient kinetic energy is provided, so as to achieve the purpose of surface strengthening. Therefore, the exchange of potassium ions and sodium ions in potassium nitrate molten salt for glass containing sodium ions is only the most common glass chemical strengthening method in the industry, but not the only method, and other glass chemical strengthening methods performed in an ion exchange manner can be found in many references, and are not described again.

Although the high-alumina cover glass can obtain high surface strength by chemical stiffening, the surface strength generated by the surface compressive stress is mainly determined by controlling the external ion concentration, temperature and time during ion exchange, taking potassium and sodium ion exchange as an example, when the temperature is about 420 ℃ and the reaction time is about 4-5 hours, the surface compressive stress of about 750-900MPa (the high-alumina glass of different brands has slight difference due to different glass components) can be obtained, the surface compressive stress is caused by the distribution of potassium ions in the glass, at this time, if the chemically-strengthened glass is heated for the second time and the temperature is higher than the ion exchange temperature, the potassium ions in the glass can be given enough kinetic energy and cause the potassium ions to continuously diffuse into the glass, so the original potassium ion concentration distribution can be destroyed and the potassium ion concentration on the glass surface can be reduced, resulting in a reduction of the surface compressive stress, i.e. the glass surface is weakened. In addition, not only is the strengthened glass sheet not suitable for reheating, but the tensile stress in the central region weakens the strength in the central region, so that the strengthened glass sheet is more likely to be chipped or damaged when subjected to cutting and other machining processes again than before being strengthened. The same situation also occurs in the case of a physically stiffened glass pane, so that, in the production of a glass window, both a chemically stiffened high-alumina glass pane and a physically stiffened soda-lime glass pane require a first geometric processing, i.e. processes relating to the dimensions and the glass curvature, such as cutting, drilling, polishing and shape bending, to be carried out, and then a respective strengthening process, followed by a gluing process and finally all surface finishing processes.

As can be seen from the above description, when two pieces of semi-finished glass after a plurality of previous processes are to be glued, considerable resources are already invested in the whole process and considerable manufacturing costs are incurred, and when the gluing process is found that the shapes or curved surfaces cannot be tightly sealed, considerable cost loss is incurred, and the reworking of the strengthened glass is extremely difficult as mentioned above. At present, the problem of non-sealing when the strengthened high-alumina glass and the soda-lime glass are bonded really occurs in the industry, most of reasons are caused by high-alumina cover plate glass, and the main reason of the non-sealing is that the bending degree of the two pieces of glass is not consistent. Generally, the thickness of soda-lime glass plate is more than 2mm, the softening point temperature of the soda-lime glass plate is low, about 580-620 ℃ (different from manufacturer type), the soda-lime glass plate can be precisely processed, the production yield is high, but the high-aluminum cover plate glass is thin, the thickness is mostly less than 1.8mm, the softening point temperature is as high as about 900 ℃, the high-aluminum glass plate cannot be subjected to a hot bending process synchronously with the soda-lime glass plate in a furnace, even if the high-aluminum cover plate glass is subjected to the hot bending independently, the thin plate glass heated at high temperature is easy to cause that the bending degree of the glass is not in place due to uneven temperature distribution, surface ripples or wrinkles caused by uneven heat conduction, thermal stress of corners caused by incomplete slow cooling, and defects caused by two factors of high temperature and the thin plate. The above problem is a major difficulty that the use of high-alumina sheet glass for the lightweight automotive glass is currently hindered.

Through patent search, as mentioned in U.S. Pat. No. 10,237,184B2, a glass plate with a thickness of not more than 0.3mm is strengthened in a bending mode in a strengthening furnace, and is glued to another hard plate after being strengthened, and the strengthened bent glass is flattened, so as to achieve the enhancement effect on a single glass surface, after the curved surface strengthened glass is forcedly flattened, the original convex surface can be extruded to form new pressure stress, thereby having the effect of surface re-strengthening, but the other surface (the original concave surface) can be opened, the surface pressure stress can be reduced, this side is chosen to be attached to the rigid sheet, so that a glued glass with a stronger outer surface can be formed, although it is also mentioned that the two sides of the glass sheet have different compressive stresses, but its purpose is not to bend the glass and it is not applied to thinning the glass surface and its described technique is limited to glass thicknesses not exceeding 0.3 mm. Furthermore, as described in U.S. Pat. No. 9,302,937B2, the inner and outer glass surfaces of the flat glass and the tubular glass are strengthened under different conditions to generate different surface compressive stresses, the compressive stress on one of the glass surfaces is reduced to reduce the tensile stress in the central region of the glass, and then the glass is laminated to form a sandwich structure to achieve the purpose of strengthening the laminated glass, and simultaneously suppress the micro-bending of the glass due to uneven stress, i.e., the bending defect of the glass due to uneven stress is regarded as a defect, and the patent does not mention the possibility of controlling the bending of the glass by thinning the glass surface. Further, as in U.S. patent publication nos.: 2018/0370852A1 describes a method of bending glass using stress differential between opposite sides of a glass sheet by high energy physical metal ion implantation on one surface of the glass sheet using ion implantation (ion-implantation) and ion exchange on the glass sheet in a chemical tempering furnace, wherein the metal ion implanted side of the glass sheet has a reduced ion exchange rate, resulting in a difference in compressive stress between the opposite sides of the glass sheet, thereby deforming and bending the glass sheet during tempering, which method has the disadvantages that (1) ion implantation is a relatively expensive process and is not suitable for machining large windows, such as windows; (2) the temperature of the chemical strengthening furnace is as high as more than 400 ℃, the bending shape formed at high temperature is more difficult to operate than the normal temperature, and the shape at high temperature and the like are changed due to the temperature difference when the temperature is reduced to the normal temperature. Also, this patent application does not mention a simple method of thinning the glass surface that can be operated at ambient temperature.

Disclosure of Invention

The invention mainly aims to provide a cold roll forming method for ultrathin high-aluminum cover plate glass, which can bend the high-aluminum cover plate glass on the premise of not heating the glass, is simple and easy to use, has low cost and is suitable for batch production and application.

In order to achieve the above purpose, the present invention provides a method for cold roll forming ultra-thin high aluminum cover plate glass, comprising the following steps: generating a compressive stress on the surface of the glass plate: firstly, generating compressive stress on two surfaces of a glass plate to strengthen the two surfaces of the glass plate by utilizing the compressive stress; bending the glass sheet: the glass plate is bent and deformed due to unbalanced compressive stress on two surfaces by thinning one surface of the glass plate.

Alternatively, in the step of generating the compressive stress on the surface of the glass sheet, the method of generating the compressive stress on the surface of the glass sheet is one of chemical stiffening which is a surface compressive stress generated by subjecting the glass sheet to ion exchange, and physical stiffening which is a surface thermal stress generated by rapidly cooling the glass sheet after heating.

Alternatively, the step of bending the glass sheet is performed at a temperature that does not cause the compressive stress on the surface of the glass sheet to rapidly disappear.

Optionally, the step of thinning is performed at ambient temperature.

Optionally, the step of generating compressive stress on the surface of the glass plate is to generate stress layers with a predetermined thickness on two surfaces of the glass plate, and the step of bending the glass plate is to control the bending deformation of the glass plate by reducing the predetermined thickness of the glass plate.

Optionally, the thickness of the thinning is controlled to be not more than the depth of the compressive stress layer of the surface of the glass sheet being thinned.

Optionally, the method of controlling the bending deformation of the glass plate is to control the position, area and thickness of the thinned surface of the glass plate according to the thinning pattern calculated by the required shape and bending degree of the glass plate.

Optionally, the reduced thickness is based on the measured chemically stiffened ion exchange layer depth DOL and the surface compressive stress σ_sTo calculate.

Optionally, after the thinning pattern is calculated, the surface of the glass plate is coated with a film according to the pattern, and then the coated glass plate is chemically thinned.

Alternatively, the thinned locations and areas are implemented in the same or different patterns, including symmetrical or asymmetrical dots, lines, grids, lattices, etc., and the resulting curved shape of the glass sheet includes symmetrical and asymmetrical shapes.

Drawings

FIG. 1a shows σ when Δ h is 0_s、σ_cAnd a schematic diagram of DOL and glass sheet thickness h and mathematical relationships thereof.

FIG. 1b is σ at Δ h < DOL_s、σ_cDOL and glass sheet thickness h.

FIG. 2 is a schematic diagram illustrating the bending moment and shape of a glass sheet when the entire sheet is uniformly stressed.

FIG. 3 is a graph illustrating σ when DOL < Δ h < (h-DOL)_s、σ_cDOL and glass sheet thickness h.

FIG. 4 is a schematic diagram illustrating bending moments and bending shapes formed when a glass sheet is subjected to a non-uniform stress distribution.

Fig. 5 is a graph illustrating graphs generated for various patterns.

Detailed Description

The present invention is further described with reference to the following drawings and specific examples so that those skilled in the art can better understand the present invention and can practice the present invention, but the examples are not intended to limit the present invention.

The cold roll forming method of the ultra-thin high-aluminum cover plate glass of a preferred embodiment of the invention can finish the stable bending of the glass on the premise of not heating the glass, and the principle is that the glass has surface compressive stress after being strengthened, when the stress on two surfaces of the glass is in a balanced state, the glass can maintain the original shape when being hardened, namely, if the glass is a plane when being strengthened, the glass is still the plane after being strengthened; if the surface is curved during strengthening, the surface is still curved after strengthening. At this time, if one side of the strengthened glass plate is thinned, that is, the surface of the glass plate is removed by a thickness, generally speaking, the thickness is only several micrometers to several tens of micrometers, the surface compressive stress of the slightly thinned glass surface is also reduced, so that the stress on the two sides of the glass plate is unbalanced, the glass plate is protruded toward the surface with large stress, that is, the glass plate is formed into a bow shape, the bow shape is toward the direction with large surface compressive stress, and the stress is changed by the thinning thickness, so that the overall bending shape of the glass plate can be controlled by adjusting the thinning position, area, thickness and other factors. Conversely, if the strengthened glass sheet is itself in a regular curved shape, such as a bowed shape, the glass sheet can be returned to a planar shape by thinning the glass surface of the raised surfaces.

Specifically, the first step of the present invention is to generate a compressive stress on the surface of the glass sheet: the method is mainly characterized in that compressive stress is generated on two surfaces of a glass plate to strengthen the two surfaces of the glass plate by utilizing the compressive stress. The method comprises the steps of selecting proper high-alumina cover plate glass, cutting and cracking the high-alumina cover plate glass according to the preset thickness and size, and trimming the edge of the cracked glass to avoid edge breakage, corner breakage and microcracks as much as possible. Cleaning the cut glass plate, drying and then rigidizing the glass plate to generate pressure stress on the surface of the glass plate, wherein the rigidizing mode can be chemical rigidizing or physical rigidizing, in the embodiment, the chemical rigidizing is used for generating surface pressure stress on the two surfaces of the glass plate through ion exchange, the stress layer with the preset thickness is provided, the chemical rigidizing temperature can be set to be 380-470 ℃, the rigidizing time is generally more than 4 hours according to actual needs and also according to the DOL (direction of arrival) of the actual needs, and potassium nitrate adhered to the surface of the glass plate is cleaned after the chemical rigidizing.

When the general chemical toughening method is used for the traditional soda-lime glass plate, the DOL is mostly half mediumBetween 12 and 20 μm, corresponding to σ_sApproximately 450-600MPa, because σ_sIs also affected by the glass composition, so even if the same DOL is used, the obtained sigma is different for different glass brands and models_sWill also be different. Similarly, when the chemical tempering method is applied to the commercial production of the high-aluminosilicate cover glass, the DOL of the glass is mostly between 25 and 40 μm and sigma is 0.7mm thick glass_sApproximately between 650 and 1000 MPa. The glass plate after chemical toughening can greatly improve the capacity of resisting external impact by about 10-15 times, which is far better than that after physical toughening by 2-3 times.

The second step of the invention is to bend the glass sheet: under the temperature (including but not limited to normal temperature) that will not cause the pressure stress on the glass plate surface to disappear, one surface of the glass plate is thinned to make the glass plate generate bending deformation due to unbalanced pressure stress on two surfaces, the thinning pattern and the thinning depth are calculated according to the required glass plate shape and the glass plate curvature designed in advance to control the thinning position, area and thickness of the glass plate surface, the thinning thickness is based on the measured depth DOL of the chemically stiffened ion exchange layer and the surface pressure stress sigma_sThe chemical thinning process is controlled to be not more than the depth of the compressive stress layer on the surface of the glass plate to be thinned, the glass plate is coated (coated with the acid-resistant film) according to the pattern after the thinning pattern is calculated, and then the coated glass plate is chemically thinned, wherein the chemical thinning process is a technique known in the industry, as long as the glass surface which is not coated with the acid-resistant film can be uniformly removed in an etching manner, a uniform thinning effect is obtained, and the glass surface is kept flat and smooth, can be used for performing the glass thinning process, and the chemical thinning solution used can be any acid solution known in the industry. In addition, the glass may be thinned by any method of thinning the surface of the glass by a frosting method, a lapping and polishing method, a laser ablation method, a hot acid bath method, or the like, and the method may be applied to the so-called glass thinning.

In addition, the pressure stress difference generated by the two outer surfaces of the glass plate can be an evenly distributed stress difference or an uneven stress difference, the former can cause the symmetrical deformation Bending of the glass plate, the latter can cause the asymmetrical deformation Bending, and by controlling the factors such as the position and the area of the thinned area of the glass surface, the thinned thickness and the like, the Bending moment (Bending moment) of each position of the glass plate can be controlled, and further the Bending degree (curvature) of the glass plate at each position can be controlled. And after thinning, cleaning the glass plate, measuring the thickness, the shape and the bending rate, managing the quality, and connecting with a subsequent gluing process.

Therefore, the invention provides a method for bending and forming high-aluminum cover plate glass without raising the temperature, aiming at the technical problem that high-aluminum sheet glass is not easy to be bent and formed, namely, the high-aluminum cover plate glass is firstly subjected to ion exchange and reaches the expected chemical strengthening effect, and then the method of local chemical thinning is used at normal temperature, so that the two outer surfaces of the glass substrate have different compressive stresses, and the natural bending result of the glass along with the stress distribution is achieved by utilizing the principle of the stress difference.

In other words, the manufacturing method can be regarded as a stress cold bending method, the curved surface forming method of the high-aluminum cover plate glass using stress cold bending can be suitable for appearance protection of automobile instrument display, car windows, panoramic skylights, display protection cover plates and other consumer electronic products, particularly for occasions where the high-aluminum cover plate glass is not suitable for high-temperature softening forming, the glass bending process can be directly completed at room temperature without a mould, and various defects caused in the glass hot bending forming process can be avoided. Moreover, compared with the hot bending forming process, the equipment and operation of the stress cold bending process are relatively simple, the cost is low, the product reproducibility is high, and the competitive advantage is achieved. Furthermore, the stress cold bending process can be applied not only to chemically strengthened high-alumina cover glass, but also to other chemically strengthened and physically strengthened glass, including soda-lime glass plates, based on the same principle and method.

The principle of the stress cold bending process of the manufacturing method of the invention is explained in detail as follows:

the symbols in the formula illustrate:

t is the temperature;

t is time;

k is the thermal conductivity;

rho is density;

C_pspecific heat;

x is the coordinate value of the thickness direction of the glass plate;

y is the coordinate value of the length direction of the glass plate;

r is curvature radius;

k is glass thermal diffusivity (K is K/rho. C)_p)；

h is the thickness of the glass plate;

d is ion diffusion coefficient;

c, ion concentration;

b, Lattice expansion constant (Lattice dimension constant);

σ_ssurface compressive stress (Surface compressive stress) of the glass Surface;

σ_ctensile stress (Central tension stress) in the Central region of the glass;

v. Poisson's ratio.

As shown in fig. 1a and 1b, when the thickness of the glass is t, after potassium ions in the potassium nitrate molten salt exchange sodium ions on the surface and inside of the glass through chemical rigidization, the volume of the potassium ions is slightly larger than that of the sodium ions, so that the potassium ions generate a squeezing effect on the surface of the glass, and simultaneously, a compressive stress σ is generated on the surface of the glass_s(Surface compressive stress) and a corresponding tensile stress σ is generated in the central portion of the glass_c(Central tension stress). At this time, if the ion exchange depth is DOL, the following formula can be obtained according to the stress balance principle:

when the glass surface has compressive stress, the central region also has tensile stress, and at this time, the sigma_sCan cause strengthening of the glass surface, but σ_cWill weaken the impact resistance of the central zone of the glassThe hitting ability.

Chemical strengthening of high-alumina cover glass mainly uses ion exchange to exchange metal ions on the glass surface with larger metal ions in the external molten salt, and the exchanged ions usually have the same electric valence, for example, potassium ions in molten potassium nitrate are used to replace sodium ions on the glass surface at a temperature of about 390 ℃ to 470 ℃. The volume of potassium ions is slightly larger than that of sodium ions, so that the surface of the glass generates compressive stress due to the volume effect, and simultaneously generates tensile stress at the central part of the glass correspondingly. Compressive stress on the glass surface may improve the ability of the glass surface to resist external impacts, but tensile stress in the central region of the glass may weaken the impact resistance in the center of the glass.

When external ions are diffused into the glass through the surface of the glass at a sufficient temperature, the diffusion behavior can be expressed by Fick's diffusion law:

the Boundary condition (Boundary condition) is

C＝C₁When is coming into contact with(Right surface of glass plate)

C＝C₂When is coming into contact with(left surface of glass plate)

Initial conditions (Initial conditions) are

C＝C₀When t is 0 and C₀＜C₁，C₀＜C₂

After the ion exchange process, if the concentrations of the external ions on the left and right sides of the glass plate are the same, that is C₁＝C₂According to the diffusion law, the concentration distribution of the foreign ions in the right half of the glass can be expressed as follows:

the Error function (Error function) is defined here as:

and satisfy erf (0) ═ 0, erf (1) ═ 0.8427

Similarly, the foreign ion concentration profile of the left half of the glass sheet can be expressed as follows:

since C (x) is a function of x, the average concentration C_avCan be obtained by C (x) integration of the whole thickness of the plate, i.e. forIntegration, the results are as follows:

here, the number of the first and second electrodes,

at this time, the stress distribution from the left to the right with respect to the thickness of the glass sheet can be expressed by the following equation:

here, B is a Lattice expansion constant (Lattice dimension constant).

From this, the compressive stress σ of the glass on both surfaces can be estimated_sAnd is located at the pressureCentral tensile stress sigma between stress zones_c：

From the stress distribution curves in the equations (8) and (9), a left-right symmetrical form is shown, when the ions with larger external volume diffuse into the glass, the surface concentration distribution and the surface compressive stress show a consistent trend, i.e. the compressive stress generated by the region with higher concentration is larger. At this time, if one of the surfaces of the glass sheet is thinned, i.e., one layer of the surface is removed, if one layer of glass is removed from the right side S1 glass surface and the thickness is Δ h, the thickness in the right half of fig. 1b is reduced by Δ h, but the ion concentration profile of the remaining glass is the same as before and is not redistributed due to the thinned surface. However, the stress distribution curve is reduced due to the compressive stress at the left half, and the stress distribution of the thinned glass plate must be readjusted in the x-axis (thickness) direction, so that the overall compressive stress and the overall tensile force are balanced again.

According to equation (3), if the thickness of the right half decreases from the surface by Δ h, the foreign ion concentration at the right surface will be:

after finishing, the following can be obtained:

at this time, at the position x, the stress value can be calculated by equation (8):

therefore, the compressive stress of the left side and the right side of the glass plate is unequal, the compressive stress difference is generated, the glass plate can be bent, the compressive stress of the left side is not thinned to be large, the edges of the two ends of the glass plate can be pressed to the right, and the phenomenon can be expressed by the following expression:

substituting equation (10) into equation (12) yields the mathematical relationship between Δ σ and Δ h.

Secondly, for the thin plate with four unfixed sides, the deformation occurs when a uniform compressive stress is applied, and because of the stress relationship, as shown in fig. 2, the Bending moment (Bending moment) M is:

in the above formula, w is the uniform compressive stress acting on the thin plate, and L is the plate length; here, w represents the stress difference between the left and right surfaces of the thin plate, and therefore w can be regarded as Δ σ, that is, w is Δ σ.

The bow formed by the sheet bending resulting from such a two-sided stress imbalance described above is also applicable to the high alumina glass sheets discussed herein. The arch height δ can be expressed here by the following formula:

where L is the length of the long side of the glass sheet and R is the Radius of curvature of the bow (Radius of curvature). The R value is closely related to the mechanical properties of the glass sheet material and can be expressed by the following formula:

substituting the formula (13) into the formula (15), and obtaining the formula (16) after arrangement as follows:

substituting the delta sigma in the formula (12) into the formula (16) to obtain the product

If the formulas (16) and (17) are respectively substituted into the formula (14), the final product can be obtained

In the above formula the minus sign indicates that the bow is convex to the left,the items represent the material factor and the material factor,representing the geometric factor of the glass sheet, C₁-C′_xRepresenting the difference in compressive stress due to the difference in the concentration of foreign ions on both sides.

From the formula (18), when C'_x→C₁Shi Gao delta → 0, and vice versa, when C'_xThe maximum value delta appears at the arch height delta → 0_max. Similarly, an increase in plate length L or a decrease in plate height h will result in an increase in bow height δ.

For high-aluminum cover plate glass with the same material, length, width, shape and thickness, the formula (18) can be simplified into

Constant in the above formula

As shown in fig. 3, when Δ h ═ DOL, the ion exchange layer on the right side of the glass sheet has been completely removed, at which time C is present_x' 0, results in_x' 0, results in Δ σ_sThis is the maximum difference in compressive stress between the two glass surfaces. Thus, if the right glass continues to be thinned, Δ h > DOL, while the central tensile stress layer of the glass is directly exposed to the right surface. When the tensile stress area is continuously thinned, the stress area is reduced because of sigma_sThe maximum value of the compressive stress is reached, the Bending moment (Bending moment) of the glass plate cannot be continuously improved, but the thickness of the tensile stress area is gradually reduced along with the increase of delta h in the tensile stress area, and the tensile stress sigma can be obtained according to the formula (1) and after rearrangement_cThe thickness h-delta h and sigma of the thinned glass plate_s(compressive stress on the left side of the glass):

this formula applies to (h-DOL) > Δ h > DOL (21)

DOL, h, σ for a particular glass sample_sAre all fixed, σ h increases (continuing to thin the glass), σ_cWill continue to increase until Δ h → (h-DOL), at which point σ continues to increase_c→ infinity means that during the continued thinning of the glass, the central tensile stress will increase all the way and provide a new impetus for the bending of the glass sheet until such tensile stress exceeds the material failure strength of the glass causing the pullout to break or fracture.

Further discussion of the bending moment created in the tensile stressed region, if σ_c ⁰Tensile stress when Δ h is DOL, then

By substituting equations (13), (14) and (15), M, R, δ can be obtained:

in the above formulaThe items represent the material factor and the material factor,representing the geometric factor of the glass sheet,representing the increased tensile stress after the central region is thinned. As can be seen from the formula (24), whenHeight delta of time bow_c→ 0, indicates that the glass sheet was still maintained at its original δ height, i.e., the height caused by the compressive stress difference. On the contrary, whenHeight delta of time bow_cIncreases with increasing tensile stress until the glass breaks. Similarly, an increase in the plate length L or a decrease in the plate thickness h will cause an increase in the bow height δ.

For high-aluminum cover plate glass with the same material, length, width, shape and thickness, the formula (25) can be simplified into

Constant in the above formula

When the reduced thickness exceeds DOL, the bending moment acting on the glass sheet is composed of two parts, delta when delta h is less than or equal to DOL and delta when delta h is greater than DOL_c. If Φ represents the sum of the heights of the arches due to these two causes, then

It can be observed from equation (27) that the former is determined by the concentration of foreign ions in the compressive stress layer, and the latter is determined by the increase of the tensile stress in the central region. It should also be noted here that the concentration of the foreign ions in the compressive stress layer and the σ in the tensile stress layer_c ⁰All determined by the process conditions in ion exchange, the final resulting surface compressive stress σ_sThe depth DOL of the compressive stress layer, in addition to the material properties of the glass itself, especially Young's modulus and conifer ratio, is the main factor affecting the bending deformation of the stress, and of course, the geometrical factors of the glass, such as length and thickness, are also the basic factors for designing the bending process using this method.

For central tensile stress sigma_cAfter finishing, the formula can be expressed as follows:

1. when Δ h is equal to 0,

2. when the delta h is more than 0 and less than DOL,the central tensile stress in this interval decreases as Δ h increases.

3. When Δ h is equal to DOL,

4. when DOL < Δ h < (h-DOL),the tensile stress in the middle of the interval increases with the increase of deltah, the tensile stress increases the bending effect, and the bending effect generated by the original compressive stress is added, so that the bending moment obtained by adding the tensile stress and the bending effect enables the glass plate to be continuously bent until the glass is broken.

Furthermore, the above mathematical relationship still exists when the stress applied to the surface of the glass sheet becomes non-uniformly distributed, but differs in that the bending moment varies with different stress distributions, and thus different bending shapes are also created. For example, the case shown in fig. 4 is the simplest case of the non-uniform distribution of stress, in which stress is distributed in a non-uniform manner between the points B to C, thereby forming a bending moment biased to the right, and the bending shape and the arch height are changed accordingly. The situation in fig. 4 is that the long axis (long side) of the glass sheet is unevenly distributed, and if the short axis (wide side) is also unevenly distributed, the bending shape of the glass sheet is unevenly bent along the long and wide sides, and finally the bending shape of the entire glass sheet is determined by the balanced bending moment.

In the process implementation method, the non-uniform stress distribution can be realized by simply adopting local thinning of the glass plate, because the thinned position can generate stress difference and bending moment, the non-thinned position is still in a stress balance (no stress difference), and the thinning position and thickness of one surface or two surfaces of the glass plate are controlled, so that the bending shape of the glass plate, particularly the asymmetric bending shape, can be determined.

Several examples of the method of the invention and related parameters are as follows:

example 1:

the embodiment uses high-alumina cover glass of rainbow special glass, model Irico CG-01, and the thickness is 0.7 mm; potassium nitrate (purity more than 99%) is placed in a standardized forced furnace and is converted into chemicalThe strong temperature is 400 ℃, after chemical rigidization, DOL and sigma are measured by using FSM-6000LE surface stress meter manufactured by Japan steppe_s. The size of the glass test piece is 140mm x 70mm, all the glass test pieces are subjected to edge treatment and edge microcracks are eliminated as much as possible, and the glass pieces after being finished are cleaned and dried firstly and then are placed into a chemical strengthening furnace for chemical strengthening. The chemical rigidification time will depend on the desired DOL and can range from 4 hours to 48 hours.

Cleaning and drying the chemically-stiffened glass sample, and then performing DOL and sigma_sAnd (6) measuring. In this example, the ion exchange depth of the chemically toughened glass was 40 μm, the measured surface compressive stress was 858MPa, and the material parameters of CG-01 high-alumina cover glass are summarized in Table 1 and can be used to calculate and verify mathematical models and experimental results.

TABLE 1

One glass surface of a chemically-stiffened glass sample is covered by an acid-resistant film, the other glass surface of the chemically-stiffened glass sample is completely exposed and is etched in chemical liquid medicine, the main component of the chemical liquid medicine is mixed liquid of sulfuric acid and hydrofluoric acid, the concentration of the sulfuric acid is 5%, the concentration of the hydrofluoric acid is 2%, the chemically-stiffened glass sample is thinned in the chemical liquid medicine to a specified thickness, the sample can be subjected to chemical etching and thinning to measure the shape and the arch height, and for the glass plate sample with uniform stress distribution of the whole plate, the arch height can be used for calculating the curvature radius, so that the curvature of the glass is represented.

The different thinning thicknesses delta h and the corresponding bending bow heights delta are measured and then arranged in a table 2, and the bow heights of the measuring sides under each thinning thickness and the bending radius R, the compressive stress difference delta sigma, the bow heights delta generated by the allocation of the compressive stress difference and the corresponding bending bow heights delta are respectively calculated according to the mathematical formula>Tensile stress after DOL σ_cAnd bow height delta caused by tensile stress_c. Table 2 shows that σ can be calculated from equation (1) when Δ h is 0_c10.74, the height of the arch is 0, and the glass plate is positionedIn a stress equilibrium state; when DOL is present>Δh>At 0, δ results from the difference in compressive stress, as in the second term in table 2; when Δ h is DOL, Δ σ is σ_sThe material factor can be calculated by using the formula (21)The value of (A) here calculated to be 4.8x10^{- 12}MPa^-1This numerical ratio is 2.58x10 calculated using the Young's modulus and Poisson's ratio in Table 1^-12 MPa^-1To be larger, it is expected that since the values in Table 1 are the states before ion exchange, when potassium ions are gradually diffused from the surface of the glass into the interior of the glass, the internal structure of the glass is strengthened due to the lattice expansion effect, and thus the material factor is slightly increased, as is the case with the surface hardness of the glass after chemical hardening. When Δ h>In DOL, σ can be calculated from the equations (21), (22) and (25)_c、Δσ_cAnd delta_cAnd calculating the residual compressive stress difference delta sigma and the corresponding delta.

TABLE 2

Example 2:

the glass plate samples used in this example were the same as in example 1, except that the ion exchange depth was different, DOL in example 2 was 67 μm, the measured surface compressive stress was 789MPa, and the material factor was obtained by the same sample preparation method and calculation method as in example 1Has a value of 6.99x10^-12MPa^-1. The results of the measurements and calculations are collated in Table 3:

TABLE 3

Example 3:

the glass plate samples used in this example were the same as in example 1, except that the ion exchange depth was different, DOL in example 3 was 92 μm, the measured surface compressive stress was 722MPa, and the material factor was obtained by the same sample preparation method and calculation method as in example 1Has a value of 8.83x10^-12MPa^-1. The results of the measurements and calculations are collated in Table 4:

TABLE 4

Example 4:

in this example, low-alumina glass manufactured by the Nanbo glass of Gallery, model No. NB3, having a thickness of 0.7mm, was used; potassium nitrate (purity more than 99%) is placed in a standardized strong furnace, the strengthening temperature is 400 ℃, and after chemical strengthening, a FSM-6000LE surface stress meter manufactured by Japan dogma is used for measuring DOL and sigma_s. The size of the glass sample is 140mm x 70mm, the glass sheets after being finished are cleaned and dried, and then are placed into a chemical strengthening furnace for chemical strengthening, and the material parameters are finished in table 5.

TABLE 5

DOL after chemical rigidization was 24.5 μm, the measured surface compressive stress was 666MPa, and the material factor was obtained by the same sample preparation method and calculation method as in example 1Has a value of 3.38x10^-12MPa^-1The calculated value of the factor of the glass material before chemical hardening using the parameters in Table 5 was 2.50X10^-12 MPa^-1The numerical value after the strengthening is slightly smaller according to the expectation. Measuring and measuring deviceThe results are summarized in Table 6:

TABLE 6

Example 5:

in the second step of the present invention, different thinning patterns can generate various curved shapes of the glass surface, and the formed stress is non-uniformly distributed on the glass surface, thereby affecting the final curved shape of the glass, which is shown in fig. 5 as a graph generated by various patterns, which is only an example but the stress cold bending technique is not limited to these patterns and curved shapes.

It should be noted that any one or more of the following methods can be used in the thinning process of the manufacturing method of the present invention, but not limited to the following methods, for example: chemical etching, frosting, lapping and polishing, laser ablation, ion impact thinning, hot acid bath, etc., and the molten salt used includes, but is not limited to, potassium nitrate, sodium nitrate, or other metal salts that can be co-melted with potassium nitrate. Secondly, the surface compressive stress of the two sides of the glass plate can be in an unbalanced or uneven state before thinning, including but not limited to that the tin side of the float glass can reduce the ion exchange rate when being chemically stiffened, so that the surface compressive stress of the tin side of the glass plate is smaller than that of the air side, at the moment, the glass with a bent shape can still be manufactured by thinning the glass surface by using a stress cold bending method, and the air side can also be properly thinned to eliminate the bending of the glass after being chemically stiffened.

In summary, the present invention provides a method for forming an ultra-thin high-alumina cover glass by cold bending, which comprises subjecting an ultra-thin high-alumina cover glass to chemical strengthening, and then using local chemical thinning to make two outer surfaces of the glass have different compressive stresses, and using the principle of the stress difference to achieve the natural bending of the glass along with the stress distribution, thereby avoiding high temperature heating, and directly completing the bending of the glass at room temperature without a hot bending mold Easy control, low production cost far lower than the high temperature softening and forming process of glass plate, and high practical value.

The above-mentioned embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.