NL7905983A - METHOD AND APPARATUS FOR THERMAL TREATMENT OF GLASS - Google Patents

Description

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Pilkington Brothers Limited in St. Helens, Merseyside, Great Britain

Method and device for the thermal treatment of glass.

The invention relates to the thermal treatment of glass, and more particularly to the thermal hardening of flat glass or curved glass plates, for example single-use glass plates as a windscreen for motor vehicles or as part of a layered windscreen for motor vehicles, a side window or rear window for a motor vehicle or for use in making windshield assemblies for aircraft and railway locomotives.

In Dutch patent application no. 76.09 ^ 88 in applicant's name discloses a method of heat treating glass objects by heating each glass object to a temperature above its shape change point, and quenching the glass objects one at a time in a gas fluidized bed particulate material, which is placed in a quiescent, steadily expanded state of particle fluxization by the control of distribution of the fluidizing gas in the particulate material at a gas flow rate through the particulate material between the velocity corresponding to initial fluidization, and the velocity corresponding to the maximum expansion of the particulate material.

This state of fluidization of the bed is such that agitation of the fluxed particulate material is caused on the hot dipped surfaces of the glass as it cools in the fluxized bed, but with temporary tensile stresses generated in the surface of the hot glass when the leading edge thereof first contacts the fluidized bed are not so severe as to endanger the glass. Derhalke the 790 5 9 83 werkwijze i 2 process has a high yield.

The degree of curing of a glass plate immersed in such a fluidized bed depends on the degree of heat transfer between the fluidized particulate material and the hot plate immersed therein, and on the rapid transfer of hot particles away from the vicinity of the glass plate with a simultaneous rapid supply of cooler particles from the fluidized bed body to near the glass plate.

The movement of the particles near the glass surfaces is faster than the movement of the particles in the main mass of the bed due to the rapid agitation of the fluidized particulate material, which is caused on the hot immersed surfaces of the glass as due to heating of the particulate material through the glass, which continues as the glass cools in the fluidized bed.

Stirring of the particulate material at the glass surfaces is greatly enhanced when using a selected particulate material, which has latent gas-generating properties, so that gas evolves rapidly from the particulate material when heated. near the glass surfaces.

It has now been found that there are three factors that predominate in controlling the thermal curing of glass in a gas fluidized particulate material, and in particular controlling the degree of curing of the hot glass plate upon contacting it. with a gas fluidized particulate material.

These factors are the following: 1. The gas-generating properties of the particulate material.

2. The thermal power per unit volume of the particulate material at minimum fluidization. This is derived from the specific heat of the material, measured at 50 ° C and the density of the material of the bed, measured at a minimum fluidization of the material.

3. The "fluidity" of the particulate material, as defined below, which is the sum of four point ratings, which are assigned to the material by determining four properties of the liquid particulate material 790 5 9 83 The term "fluidity", as used herein, has this meaning.

The four properties of a liquid particulate material and the method of assigning point ratings are described in the article "Evaluating Flow Properties of Solids" by Ralp L. Carr

Jr., Chemical Ehgineering Volume 72, Number 2, January 18, 19 $ 5 and are the following: ........ 100 (P-A) * 1. Compressibility * -p-? where P = packed mass density 10 and A e aerated mass density.

2. Natural slope: this is the angle in degrees between the horizontal and the slope of a pile of the particulate material deposited from a point above the horizontal until an equal angle is measured.

15 3. Spatula Angle: A spatula is inserted horizontally into the bottom of a mass of the dry particulate material and lifted straight up out of the material.

An average value of the angle in degrees from the side of the heap of material on the spatula relative to the horizontal is the spatula angle, 1 *. Grain size distribution (referred to in the aforementioned article as the regularity coefficient):

This has been described in the aforementioned article as the numerical value obtained by dividing the width of the sieve opening (ie grain size) through which sieve opening 60? of the particulate material passes through the width of the screen opening, which allows just 10JC of the particulate material to pass through.

All of the grain size distribution values referred to in the specification were measured in a known manner by a method using a Coulter counter to determine the particle diameters that match retained cumulative weight percentages of bQ% and 90 ?, corresponding to widths of sieve openings, 35 just 60? and just 10? passage of the particulate material.

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The numerical values of compressibility, natural slope and spatula angle were measured using a device designed especially for use in determining the "Flowability" of powders.

In principle, the fluidity of a particulate material is related to factors such as the average grain size, the grain size distribution and the shape of the grains, which is sometimes referred to as the angularity of the grain, ie whether they have a rounded or angular shape . The value of the fluidity 10 increases as the average grain size increases, as the grain size distribution narrows and the angularity of the grains decreases.

The thermal power per unit volume at minimum fluidization is dependent on the specific heat of the material 15 and the density of the fluidized bed at minimum fluidization, which density increases as the grain size distribution narrows.

A high value of the curing stress is produced in glass when it is subtracted in a fluidized bed, with an optimum fluidity. Certain materials that produce required cure strains are commercially available. Other commercially available materials can be adapted to produce the required curing stresses by sieving the material to change the average grain size and grain size distribution thereof.

However, there is a difficulty in that there is a limit to the degree to which the degree of curing stress generated in the glass can be controlled by changing the fluidity of commercially available materials. Materials that have the required fluidity cannot be commercially available. The production of a large amount of material, which has the required fluidity, may include screening a large amount of particulate material.

Moreover, when using a single material, the only way to adjust the thermal power of the fluidized bed is to narrow the grain size distribution, so there is no way to adjust the thermal power independent of the 790 5 9 83 ♦ * 5 change the fluidity, which is produced by narrowing the grain size distribution.

It has now been found that a particulate material can be produced with optimum gas generating properties, thermal power and fluidity for the production of required curing stresses in a glass article by using a mixture of particulate materials, each of which contributes to the optimum properties of the mixture. By choosing particulate materials and the proportions in which they are mixed, the gas fluidized particulate material can be custom-adjusted to provide required curing stresses over a wide range.

In accordance with the invention, there is provided a method of thermally treating glass, wherein glass is heated to a predetermined temperature and contacted with a gas fluidized particulate material, which method is characterized by using a particulate material which comprising a mixture of a number of selected particulate materials, further selecting at least one of the particulate materials to have gas-generating properties upon heating through the hot glass, and mixing the materials in selected predetermined proportions, giving the gas-fluidized mixture of particulate materials a thermal power and a fluidity so that a required thermal treatment of the glass is achieved.

The method can be characterized by mixing the materials in selected, predetermined ratios, so that required curing stresses are generated in the glass as it cools in the gas fluidized particulate from a temperature above its shape change point.

The invention further provides for selecting as the gas-generating particulate material a material capable of generating between k% and 31% of its own weight of gas upon heating to a constant temperature at 800 ° C, and mixing of the particulate materials in predetermined proportions, giving the mixture a thermal power per unit volume and at minimum fluidization in the range of 1.02-1.73 MJ / m ^ C and a fluidity in the range of 60 to 86.

790 5 9 83

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When thermally curing a sheet of sodium carbonate-calcium oxide-silica glass having a thickness in the range of 2-2.5 mm by heating it to a temperature in the range of 610-680 ° C, the mixture being quenched in a In a regularly expanded state of particulate fluidization, the method is characterized by assembling the particulate material to cause a tensile stress in the center in the range of 35-57 MPa.

For the production of windshield glass, the method 10 may be characterized by mixing the particulate materials in predetermined proportions, which give the mixture a fluidity in the range of 71-83, and a thermal power per unit volume at minimum fluidization. in the range of 1.09-1.38 MJ / m ^ K.

The gas-developing material can be γ-alumina.

The γ-aluminum oxide can be mixed with ct-aluminum oxide. The mixture can comprise between 7 and 86 wt.% Aluminum oxide.

Another way of carrying out the invention is characterized by cooling a hot glass plate in a gas-fluidized mixture of a gas-generating particulate material and at least one particulate metal oxide, the thermal capacity of which per unit volume and at minimum fluidization is in the range of 1.76-2.01 MJ / m K, and by mixing the particulate materials in predetermined proportions, giving the mixture a thermal power per unit volume at minimum fluidization in the range of 1.27-1 »76 MJ / m K 25 and a fluidity in the range of 71-82.

The particulate metal oxide may consist of spheres of iron oxide (α-FegO4). The mixture may comprise between 30 and 70% by weight of spherical iron oxide. Furthermore, the mixture may comprise between 70 and 30% by weight γ-alumina as a gas-developing material. According to another way of working out this aspect of the process, the mixture may comprise between 28 and 35% by weight spherical iron oxide, and between U5 and 56% by weight α-alumina, the remainder being γ-alumina as gas -developing material.

The particulate metal oxide may consist of Arkone 35 (ZrOg.SiOg). The mixture may comprise between 10 and 70% by weight & aluminum monohydrate 790 5 9 83% (7) of Al2O3, IHgO) as a gas-decomposing material, and between 90 and 30% zirconium.

In another embodiment, the gas-depleting particulate material is an aluminum silicate. The aluminum silicate 5 may be zeolite, with between 8 and 10 parts of zeolite being mixed with between 90 and 92 parts of 55 alumina to form the mixture.

The gas-desensitizing particulate material can be aluminum monohydrate (AlgOy IHgO).

Furthermore, in accordance with the invention, the mixture may comprise silicon carbide (Sic), mixed with a gas-deflecting particulate material. In one embodiment, the gas-sensitizing particulate material is aluminum monohydrate (Al 2. 1H 2 O), the mixture additionally comprising 17 parts aluminum monohydrate mixed with 83 parts silicon carbide.

In another way of carrying out the sprouting, the gas-depleting particulate material is aluminum trihydrate (A1203.3H20).

The mixture may include gas-decomposing particulate materials, aluminum trihydrate (Α1203 · 3Η20) and γ-aluminum-20 oxide in equal proportions.

In yet another way of practicing the invention, the gas-densifying particulate material is sodium bicarbonate (HaHCO3). The mixture can be formed by 10% by weight sodium bicarbonate mixed with 90% by weight α-alumina.

The invention also includes an apparatus for thermally treating glass, each apparatus comprising a container for a gas fluidized particulate material, gas supply means connected to the container for maintaining the fluidization state of the particulate material, and means for placing hot glass into the container 30, each device is characterized in that the container incorporates a gas-fluidized mixture of selected particulate materials, at least of which it has gas-decomposing properties when heated by the hot glass, forming particulate materials mixed in selected predetermined ratios which impart thermal power and fluidity to the gas-fluidized mixture to achieve a required thermal treatment of the glass.

The invention further includes thermally treated glass, for example, a thermally cured flat glass sheet produced by the present method.

The invention is further elucidated with reference to the drawing, in which: Fig. 1 schematically shows a fat section of the device for thermally curing glass plates with the present method, Fig. 2 shows a graph of the tensile stress in the center plotted against the proportions of the mixture of particulate materials, which mixture forms the gas-fluidized bed, showing the change of the voltage with the change of the proportions, Fig. 3 shows a graph similar to Fig. 2, with the change in the tensile stress in the middle with changes of the proportions in another mixture of particulate materials are shown, Fig. U shows a graph similar to Fig. 3, the change of the compressive stress at the surface in 2.3 mm glass with 20 shows a change in the composition of the gas-fluidized bed, FIG. 5 is an FIG. 3 shows a similar graph showing the tensile stress in the center as generated in 6 mm thick glass, FIG. 6 shows a graph similar to FIG. U showing the change of the compressive stress at the surface generated in 6 mm thick glass, Fig. 7 shows a graph similar to Fig. 3 for 12 mm glass, Fig. 8 shows a graph similar to Fig. b for 12 mm glass, and Figs. 9, 10 and 11 show a change showing the tensile stress at the center with the composition of the mixture of particulate materials in three other ways of carrying out the present method.

With reference to Fig. 1, a vertical curing oven 1 has side walls 2 and a roof 3. The side walls 2 and the roof 3 are made of the usual refractory material, with the bottom of the oven 7905983

Jf * 9 has an open mouth defined by an elongated opening U in a base plate 5 on which the oven 1 is carried. A sliding hatch, not shown, is provided to close the mouth in a known manner. A glass sheet to be bent and then thermally cured is suspended in the oven 1 by tongs T, which engage the upper edge area of the glass sheet 6. The tongs T are suspended on a tong bar 8, which is suspended on a conventional lifting tool , not shown, which runs along vertical guides 9, which extend down from the oven to guide the lowering and lifting of the tongs-rod.

A pair of bending dies 10 and 11 are arranged directly under the mouth U of the oven in a heated chamber 12, which is maintained at a temperature such that the dies are at the same temperature as the hot glass that they bend. The chamber 12 is heated by 15 hot gases supplied through ports 12a. When the dies are open, they are located on either side of the web of the glass plate 6. The die 10 is a solid partridge, mounted on a jack 13, and has a curved front face that defines the curvature that must be on the hot glass plate Be given. The mold 11 is an annular window mold, supported by 20 struts 1, mounted on a support plate 15, which is mounted on a jack 16. The curvature of the mold frame 11 corresponds to that of the plane of the partridge 10.

The restraints extend downwardly on either side of the bending dies to a fluidized bed container 17 particulate refractory in which the hot curved glass sheet is to be cooled by lowering the sheet into the bed.

The fluidized bed holder includes a top open rectangular tray 18 mounted to a scissor lift platform 19 * When platform 19 is in its elevated position, the top edge of tray 18 is just below the bending dies 10 and 11.

A microporous high pressure drop membrane 20 extends over the bottom of the tray 18.

The edges of the membrane 20 are secured between a flange 21 on the tray and a flange 22 on a pressure chamber 23, which forms the bottom 35 of the tray. The flanges and the edges of the membrane 20 are bolted together at 2b 79059 83 V «· 10 \. A gas inlet channel 25 is connected to the pressure chamber, whereby fluidizing air is supplied to the channel at a controlled high pressure. There is a high pressure drop of at least 60% of the pressure across the membrane 20, resulting in a regular distribution of the fluxizing air in the particulate material at a gas flow rate through the particulate material between the velocity corresponding to minimum fluidization, with the particles just suspended in the upwardly flowing air, and the velocity corresponding to the maximum expansion of the particulate material, maintaining dense-phase fluidization. The expanded bed is in a substantially bubble-free quiescent state of particle flux distribution with a horizontal quiescent surface through which the glass sheet enters the bed.

The membrane 20 may comprise a steel plate, which has a regular distribution of holes, and a number of layers of strong, micro-porous paper, which is placed on the plate. For example, fifteen sheets of paper can be used. The membrane is completed by a woven wire mesh superimposed on the paper layers, for example, stainless steel 20 A glass waste collection basket may be located near the membrane 20 and is designed to allow the regular flow of flux-dispersing gas upward from the diaphragm.

The restraints 9 extend downwardly to a position below the bending dies, and terminate in the region of the top edge of the tray. A fixed frame 27 is mounted in the tray To, and has upwardly bent legs 28 at its bottom for receiving the bottom edge of a glass sheet immersed in the fluidized bed when the tongue bar is lowered beyond the bending dies by the hoist.

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To load a glass plate into the device, the scissor lift table 19 is lowered, with the tongues bar in its lower position at the bottom of the straps, the glass sheet to be bent and hardened to be loaded on the layers 7.

The hoist then brings the suspended glass plate up into the oven 1, which is kept at a temperature of, for example, 850 ° C, so that the glass plate is quickly heated to a temperature close to its shape change point, for example in the range of 610-680 ° C.

When the glass plate has regularly reached the required temperature, the hatch closing the mouth U is opened, and the hot glass plate 5 is lowered by the hoisting vehicle into the position between the open bending dies 10 and 11. The jacks 13 and 16 are operated, and the dies are closed to bend the plate to a desired curvature. When the required curvature is given to the plate, for example to be able to use the plate as a part of a laminated windshield for a motor vehicle, the dies are opened, and the hot curved glass plate is quickly lowered into the fluidized bed in the bin 18 , which has been moved upward to the quench position for raising the scissor lift off el 19 while heating the glass plate in oven 1. The fluidized bed is maintained at a temperature between 30 ° C and 150 ° C by a vessel cooling jacket attached to the flat longer walls of the bin 18.

The fluidized bed 17 is formed by a gas-fluidized particulate material, which is a mixture in predetermined proportions of a number of particulate materials, at least 20 of which have gas-developing properties, and can evolve gas when the fluidized material is in contact with the hot glass.

An appropriate gaseous-desiccating particulate material can develop between U, 0 - 31% of its own gas weight when heated to a constant weight at 800 ° C, suitable materials being ήτ-alumi-25 nium oxide (γ-ΑΙ ^ Ο ^), which is porous and contains water adsorbed in its pores, furthermore aluminum silicates, which are porous and which contain water adsorbed in their pores, aluminum hydrates, such as aluminum trihydrate (AlgO2. SHGO), which contain crystal water, and aluminum monohydrate (AlgO2.

IH0) which contains crystal water, and is porous, water also being adsorbed in the pores, and materials which generate gases other than water vapor, for example sodium trimicarbonate (NaHCO2).

To produce required curing stresses in the glass, the components of the mixture of particulate materials are mixed in predetermined proportions, which give the mixture a fluidity of 60-86, and a thermal power per unit volume at 79059 83. 3 «... Λ 12 minimum fluidization in the" range of 1.02-1.75 MJ / m K,

Other "ingredients of the mixture which are mixed with the gas-generating particulate material are particulate materials which are inert in the sense that substantially no gas is evolved from the material" upon heating thereof. Examples are α-alumina (o-AlgO ^), zircon (ZrOg.SiOg), silicon carbode and spheres of iron oxide (a-Fe ^).

These particulate materials have a dense, non-porous shape, and have been chosen for a fluidity and a thermal power different from that of the gas-developing particulate material, so that depending on the ratio of the dense, non-porous material used they act to change the fluidity and thermal power of the mixture of particulate materials to such an extent that a required degree of cure stress is produced in the glass.

It is believed that when a hot glass plate is quenched in a gas fluidized bed of such particulate mixture, the rapid development and expansion of the gas generated from the gas-developing particulate material as a result of heating thereof near the glass surfaces, the local stirring strengthens the mixture, sharing islet materials on the glass surfaces in a manner similar to the boiling of a liquid, with the result that stirred layers of gas and particulate matter spread over the glass surfaces flow when the glass is cooled in the fluidized bed.

By mixing the ingredients of the mixture in predetermined proportions, there is an optimum heat transfer away from the yeast surfaces in the mass of the bed, generating the stresses to be generated in the glass, with continuous scattering taking place from the heat to the more distant portions of the bed, which heat is extracted from the glass by agitating the fluidized particulate material located directly around the glass plate.

The water-cooled jacket 29 keeps the more distant parts of the bed cool, so that they actually act as a 7905983% 13% heat trap. Vigorous stirring of the particulate material on the glass plates continues well after the glass has cooled to below its form spring point, ensuring that the temperature gradients from the center to the surface are initially generated in the glass when gradients are generated in the glass. this is contained in the fluidized bed, are maintained as the glass cools by its shape-change point, with the required curing stresses then developed during further cooling of the glass while still immersed in the bed.

The bottom edge of the hot glass plate is regularly cooled as the bottom edge enters the horizontally quiescent surface of the expanded fluidized bed. Substantially the same tensile stresses are generated in different areas of the surface of the edge of the glass plate, so that little breakage occurs. During the lowering of the bottom edge of the glass into the bed, each portion of the bottom edge always comes into contact with fluidized material, which is in a quiet, regularly expanded state of particulate fluidization, which regularly treats the bottom edge regardless of the flow of particulate material, which can be generated on the hot glass surfaces by gas evolution from the gas-generating component of the mixture, substantially prevents breakage, as well as the resulting difficulties of handling glass fragments in the bed. This, together with the prevention of losses of glass plates due to shape change of the glass plates and / or damage to the surface quality thereof, ensures a commercially attractive yield of hardened glass plates.

Some examples of application of the invention with selected mixtures of particulate matter are now given. In each of these examples, the numerical value of the product of the granular

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in g / cm and the average grain size in µm of each of the components of the mixture, less than 220. This is a criterion useful for determining on a particular particulate material suitable for fluidization in a quiet, regular expanded state of particle fluidization when working with air at ambient conditions of usual temperature and pressure. A mixture of the particular particulate materials can then be in a calm, regularly expanded state 7 * 05983 *

Ut of particle fluidization, are fluidized.

EXAMPLE I

The fluidized bed 17 consisted of a mixture of γ-alumina as the gas-developing particulate material, and 5 α-alumina.

The γ-alumina used was a microporous material with pores with diameters in the range 2.7-4.9 nm, and 20-40 $ free pore space. The pores contained adsorbed water, which was released as a gas when the material was heated.

10 7 The γ-alumina used had the following properties: average grain size = 119 µm grain size distribution - 2.34 ^ fluidity = 90.25 water content (weight loss at = 4.3 $ a 800 ° C}

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thermal power per unit volume * 1.09 MJ / m K

at minimum fluidization

The α-aluminum oxide used was a dense, non-porous shape with the following properties: average grain size * 30'-ym grain size distribution = 1.22 fluidity = 70 3

25 thermal power per unit volume = 1.3 MJ / mK

at minimum fluidization

Investigations were conducted with mixture f-alumina and α-alumina mixed in predetermined proportions. Glass with a sodium carbonate-calcium oxide-silica oxide composition and 2.3 mm thick were cut, the edges of the cut plates being finished by rounding them using a fine diamond grit wheel. Each plate was heated to 660 ° C in the oven 1 prior to bending and quenching in the fluidized mixture, which was in a quiescent, regularly expanded state of particle fluidization.

Table I shows the properties of various 790 5 9 83 15 mixtures of these materials in the range of 30-90 wt% ct-aluminum oxide, and 70-10 wt% paluminium oxide, as well as the tensile stress in the in the middle, generated in the glass plates and the scaling thereof. For comparison, the tensile stress in the center, produced using only the α-alumina, and the γ-alumina is also included in Table I.

TABLE I

Weighted weed ages in the mixture.

10 α-alumina 0 # 30JC 50 # 70 # 90 # 100 # γ-alumina; 100 # 70 # 50 # 30 # 10 # 0 # flowability of mixture 90.25 81.5 75 7¼ 72.25 70 thermal power of mixture per unit volume at minimum fluidization (MJ / mTC) 1, 09 1.16 1.20 1.24 1.28 1.3 tensile stress in the middle (MPa) 41 43 49 49 47 32

Fig. 2 shows the change of the tensile stress in the center with the composition of the mixture.

The palumium oxide alone has a fluidity which is too high for the production of a maximum curing stress in the glass plates, in particular due to its large average grain size and the fact that the particles have a relatively smooth, non-angular shape . The addition of an amount of o-alumina, which has a lower fluidity than the paluminum because of the smaller average grain size of the α-alumina and the angularity of its individual particles, decreases the fluidity of the mixture.

The fluidity of the mixture decreases as the amount of α-aluminum-2q oxide in the mixture increases, with a simultaneous increase in the tensile stress produced in the center. A maximum tensile stress in the middle of 49 MPa is reached when the fluidity is set to the optimum value of 74, and the mixture contains about 70 parts by weight alumina and 30 parts by weight alumina.

The alumina has a higher thermal capacity. 790 5 9 83 16 than the ct alumina, where when the ratio of yy-alumina in the mixture is increased, there is a gradual increase in the thermal power of the mixture, which contributes to the increase of the voltage, which is reached.

Further addition of α-alumina in a ratio above 70 wt.% Increases thermal power / more, and maintains reasonable fluidity, but reduces the tensile stress in the center which is generated because a ratio of the gas-developing component , γ-alumina, has been reduced to a low level.

EXAMPLE II

The fluidized bed consisted of a mixture of γ-aluminum oxide as the gas-developing particulate material, and α-aluminum oxide.

The γ-aluminum oxide used was a microporous material 15 with a pore size ranging from 2.7 to U, 9 nm and 20-UO / S free pore space. The pores contained adsorbed water, which was released as a gas when the material was heated.

The ataluminum oxide used had the following properties: 20 average grain size = 6k ym grain size distribution * 1.88 fluidity = 8h water content (weight loss at 800 ° C) * b% thermal capacity per unit volume _

gtj at minimum fluidization. * 1.06 MJ / πι K

The aluminum alumina used was the same as in Example I.

Investigations were conducted with mixtures of γ-alumina and α-alumina mixed in predetermined ratios of 100¾ γ-alumina and 0% α-alumina to 0¾ γ-alumina and 100¾ α-alumina.

Table II shows the thermal power per unit volume at minimum fluidization and the fluidity of the mixtures used.

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TABLE II

Mixture Thermal power Fluidity

zew.% MJ / m ^ K

γ-g 1 iimin i urnoxi de g-alumina 5 100 Θ 1.05 8¾ 86 1¾ 1.09 82.75 61 39 1 * 15 T9

ItO 60 1.20 T6 22 T8 1.25 T3.25 10 T 93 1.29 T1 0 100 1.30 T0

Plates of glass with a sodium carbonate-calcium oxide-silicon nridg-bonding ngflling ~ 2.3 mm thick were then cut, the edges of the cut plates being finished by rounding them using a fine diamond grit wheel. Each plate was hung on the layers 7, and heated in the oven 1 before bending and quenching it. The results are shown in Figures 3 and U.

The X axis of each curve represents the composition of the mixture 20 in data 55. In each of Figs. 3 and U there are four curves, which show the tensile stress in the center (Fig. 3) and the compressive stress at the surface (Fig.

1t), which stresses have been generated in the 2.3 mm thick glass plates, which were heated to a temperature of 610 ° C, 630 ° C, 650 ° C and 670 ° C, and then quenched in the fluidized bed 17, in a quiescent, steadily expanded state of particle fluxization was maintained in the temperature range of 60-800C.

The curves show that it is preferable to use between about 7 wt. Si and about 86% by weight α-alumina mixed with γ-alumina. When the proportions of α-alumina in the mixture are increased, the tensile stress in the center and the compressive stress at the surface generated in the glass during its thermal curing increase to a maximum reached when the amount of α aluminum oxide is about 70-80 parts by weight of the mixture. Generally, the greatest stresses are generated when the amount of α-aluminum oxide is between 55-85%. of the mixture is present. A larger ratio of 7 S 0 5 9 83 ί 18 α-aluminum oxide in the mixture produces a decrease in the stresses generated.

Due to an appropriate choice of the ratios γ-aluminum oxide and α-alumina, the mixture has gas-developing properties, a thermal capacity per unit volume, minimum fluidization at 50 ° C and a fluidity, which remains consistently high values producing tensile stress in the center and compressive stress on the surface of the glass sheets with a thickness of 2.3 mm.

For example, when the glass is heated to 6T0 ° C and then quenched, a required tensile stress at the center can be in the range of ^ 2-1 * 9 MPa, and an associated compressive stress at the surface in the range of 83-103 MPa, are generated in the glass to select the predetermined ratios of γ-alumina and α-alumina in the mixture in the range of 7-86% by weight of γ-alumina and 93-1U by weight of 15 α-alumina.

EXAMPLE III

Plates of sodium carbonate-calcium oxide-silica glass 6 mm thick, were cut and edged, then heated and quenched in a fluidized bed ii a quiet, regularly expanded state of particle fluidization consisting of a mixture of the same particulate γ-alumina and α-alumina materials as described in Example II. Figures 5 and 6 are graphs similar to those of Figures 3 and 11, showing the results obtained for glass plates heated to temperatures of 610 ° C, 630 ° C, 650 ° C and 6T0 ° C, 25 and then quenched.

The results show that the required curing stresses in the glass can be generated as a function of the ratio of γ-alumina and α-alumina in the mixture. Maximum stresses are reached when the mixture contains about 65-95 wt% α-alumina. For example, when the glass is heated to 670 ° C and then quenched in a fluidized mixture of 22% w / w aluminum oxide and 78 wt. % alumina, the tensile stress in the center generated in the glass is 91 MPa, and the compressive stress at the surface is 216 MPa.

This high strength 6 mm thick glass is used in the manufacture of aircraft window assemblies and railway locomotives.

7905983 4 «1 9

Similar results are obtained when curing sheets of sodium carbonate-calcium oxide-silica glass 10 mm thick.

These glass sheets are used in the manufacture of aircraft window assemblies, which assemblies may include, for example, 2 sheets of tempered glass 5 mm thick and an outer sheet 3 mm thick. The plates are joined in layers with known synthetic resin intermediate layers.

EXAMPLE IV

Plates-sodium carbonate-calcium oxide-silicon oxide glass, 10 12 mm thick, were cut and edged at the edges, then heated and quenched in a fluidized bed formed by a mixture of γ-alumina and α-alumina in predetermined proportions in the same manner as described in Example II.

Results were obtained for glass plates heated 15 to 610 ° C, 630 ° C, 650 ° C and 670 ° C with a range of ratios, γ-alumina and α-alumina, the results being shown by the curves in the fig. 7 and 8.

Maximum stress values are measured when the fluidized mixture comprises about 65-85% by weight α-alumina. When a plate is heated to 6T0 ° C and quenched in a fluidized bed from a mixture of 22% by weight γ-alumina and 78% by weight o-alumina, the tensile stress in the center of the glass is 12k MPa, and the compressive stress at the surface 261 MPa.

Figures 7 and 8 show how a wide range of curing stress values can be generated in the glass, as required, by choosing the proportions of the components of the mixture of particulate materials according to the temperature at which the glass is heated before quenching.

The results shown in FIGS. 3-8 have in common that greater cure stresses are achieved when the ratio in the mixture of the component having the greater thermal power (α-alumina) is increased to a point where a further Increasing the ratio, reducing the ratio of the gas-developing component (γ-aluminum oxide) to an insufficient level.

35 'The range ratios of the gas-developing material 7905983 20 and the other ingredient or ingredients of the mixture ensures a fluidity of the mixture in the range of 60-86 which is such that the nature of the stirring is favorable is for cooling the glass at a rate that achieves the required stress values in the glass.

The cooling of the glass occurs due to the rapid stirring of the particulate material near the glass surface, which stirring is mainly due to the development of water vapor from the γ-alumina component of the mixture.

A larger ct-alumina ratio increases the heat extraction rate of the glass, and changes the fluidity of the mixture.

EXAMPLE V

The fluidized bed consisted of a mixture of γ-alumina as the gas-developing component, with a ratio of spheres of iron oxide (α-Fe 2 O 3) and one or two kinds of e-alumina.

The γ-alumina had the following properties: average grain size = 8H hm grain size distribution = 1.9 ^ fluidity = 87> 25 water content (weight loss at 800 ° C) = 6% thermal capacity per unit volume _

at minimum fluidization = 1.063 MJ / nrK

The iron oxide spheres had the following properties: average grain size = Hl Hm grain size distribution = 1.69 fluidity = 76.5 thermal capacity per unit volume

at minimum fluidization = 2.01 MJ / in K.

The first alumina was the oxide as used in Example 1. The second α-alumina had the following properties: average grain size - 2h Vm grain size distribution = 1.25 fluidity = 66 thermal power per unit volume

at minimum fluidization = 1.192 MJ / nrK

7905983 s * 21

Glass plates with a sodium carbonate-calcium oxide-silica oxide, 2.3 mm thick, were heated to 660 ° C and quenched in fluidized blends of the foregoing materials, which blends in a quiescent, smoothly expanded state of particles of flux distillation. found.

The properties of the blends and the resulting tensile stresses in the center produced in the glass plates were as shown in Table III5 Λ

TABLE III

10 Weight percentage in the mixture.

(1) (2) (3) (¾) (5) γ-aluminum oxide 70? $ 0% 30% 20% 16%

Iron oxide globules 30% 50% 70% 35? 28% a-alumina (l) - - - h5% 36% 15 a-alumina (2) - - - - 20? fluidity of mixture 82 79 78 7h 73.5 thermal power of mixture per unit volume at minimum 1.3 ^ 7 1.5¾ 1.726 1.502 1 .¾¾ fluidisation (MJ / m3K) tensile stress in the middle (MPa) ¾5 ¾9 50 57 53.0 20

Figure 9 shows the change in the tensile stress at the center with the composition of the mixtures (1), (2) and (3) from γ-alumina and ct-Fe 2 O 3 in Table III. The tensile stress in the center due to the use of only the γ-alumina and only the α-Fe_0_ were 25 23 M MPa and 32 MPa.

As in Example 1, the γ-alumina used in this example had a fluidity too high to produce a maximum cure stress in the glass plates. The iron oxide spheres had a lower fluidity than the γ-aluminum oxide, in particular due to its smaller average grain size. The addition of increasing amounts of globules of iron oxide to the γ ^ aluminum oxide in the blends (1), (2) and (3) of Table III had an increasing effect of decreasing the fluidity of the mixture by gradually decreasing the average grain size of the mixture when increasing the amount of globules of iron oxide in the mixture. As the flowability of the mixture decreases, an increase in the tensile stress in the center produced in the glass plates occurs. A maximum tensile stress in the middle of 50 MPa is reached when the mixture contains approximately 70 $ spheres of iron oxide and 30 $ γ aluminum oxide.

The fluidity of the spheres of iron oxide is not as low as that of the α-aluminum oxide used in Example I, because it has a larger average grain size and the particles are smoothly rounded compared to the angular particles of the α-alumina. Therefore, the iron oxide spheres are not as effective in reducing the fluidity of the mixture as the α-aluminum oxide of Example I.

The mixture (3) of the present example, which contains 70 wt.% Iron oxide spheres and 30 wt.% Γ aluminum oxide, and produces the maximum tensile stress in the middle of 50 MPa, has a fluidity of 78, which is higher than the optimum fluidity of 7 µ of the mixture 15 from 70 wt% α-alumina and 30 wt% γ-alumina, which produces a high tensile stress in the center in Example I.

However, the maximum tensile stress in the center produced by the mixture (3) in the present example is approximately the same as the maximum tensile stress in the middle produced by the mixture 20 of Example I. This is because although the fluidity of the mixture ( 3) is slightly higher than the optimum fluidity, producing maximum stress, the spheres of iron oxide used in the mixture (3) have significantly greater thermal power than the α-aluminum oxide used in Example I.

Because the fluidity of the mixture (3) was considered slightly too high, the mixture (¾) was then made, containing a ratio of α-alumina, as used in Example 1. This reduced the fluidity of the mixture to an optimum value of 71 *, which mixture produced a further increase in the tensile stress in the center to 57 MPa despite the decrease in thermal power.

The mixture (b) has the same optimum fluidity value, jb, as the mixture of Example 1, consisting of 30% alumina and 70% alumina, producing a maximum tensile strength in the center of 9 MPa. The fact that the mixture {b) produces a greater tensile strength in the center of 57 MPa is due to the larger 790 5 9 83 23

O

thermal power of the mixture (U), i.e. 1.502 MJ / m K compared to 1.2k MJ / m \ of the mixture of Example I.

The further reduction in fluidity due to the incorporation of an amount of a second aluminum aluminum into the mixture (5) produces a reduction in the thermal power of the mixture compared to the mixture (k) with an associated slight reduction in tensile strength in the center.

EXAMPLE VI

The fluidized bed consisted of a mixture of the gas-evolving particulate material, alumina monohydrate (Al 2 O 3 1H 2 O) and zirconium (ZrO 4 SiOg),

The aluminum monohydrate was in the form of Boehmite, which is a porous material containing 55 weight percent composite crystal water and 13 weight percent water in its pores. Adsorbed water released during quenching of the glass is primarily effective in providing the gas evolution which gives rise to the improved tearing of the particulate material near the glass surfaces.

The aluminum monohydrate used had the following properties: 20 average grain size = 51 µm grain size distribution = 1.70 fluidity * 7Ö water content (weight loss at 800 ° C) * 28, h% thermal power per unit volume ^

at minimum fluxization = 1.18 MJ / πι K

The zircon, which is an inert, non-porous, zirconia ortho-silicate with a higher thexmic capacity than o-alumina, had the following properties: average grain size = 3 µm 30 grain size distribution = 1.73 fluidity = 67 thermal power per volume. unit _

at minimum fluxdization = 1.76 MJ / nrK

2.3 MM thick glass plates were heated to 660 ° C and quenched in mixtures of the aluminum monohydrate and zircon, such as 79059 83 2k *. Indicated in Table IV, which shows the properties of the mixtures and the tensile stress produced in the glass plates in the middle*

TABLE IV

5 Weight percentage in the mixture.

aluminum monohydrate? 100? 70? 50? 20? 10? 0? zircon 0? 30? 50? 80? 90? 100? fluidity of mixture. 78 75.5 7 * + 73 71 6? thermal power of mixture per unit volume 1.005 1.277 1. ^ 1 1.62 1.70 1.76 ^ at minimum fluidization (MJ / m%) tensile stress in the middle (MPa) 37 h2 U 1 + 6.5 39 23

Figure 10 shows the change in tensile strength in the center with the composition of the mixture.

Aluminum monohydrate gives good gas-developing properties and a lower fluidity value than the Y-aluminum oxides, as referred to in Examples I and V. However, the fluidity of the aluminum monohydrate is higher than the optimum fluidity, which has a maximum tensile stress produces in the center, the thermal power being relatively low. Zircon has a lower fluidity and a higher thermal capacity than the aluminum monohydrate, where when zircon is increased proportionally in the mixture, there is an increasing increase in the tensile stress in the center produced in the glass, due to both gradually reducing the fluidity as increasing the thermal capacity of the mixture.

The zircon has a high thermal capacity, which contributes significantly to increasing the tensile stress in the center, produced in the glass plates, in the same way as the ball of iron oxide, eg V. Because the zircon has a lower fluidity than the balls iron oxide, for example V, it is more effective in reducing the fluidity of the mixture, and therefore contributes more strongly in increasing the tensile stress in the center, brought about by the reduction of the fluidity value of the mixture. mixture.

790 5 9 83 25

The maximum tensile stress in the center of h6.5 MPa is "reached when the mixture contains about 20% aluminum monohydrate and 60% zircon, which mixture has a fluidity of up to a maximum value of 73.

A further addition of zircon to about 80 wt% increases the thermal power of the mixture, but results in a reduction of the tensile stress in the center due to a significant reduction in fluidity below the optimum value, and reducing the ratio of the gas-evolving component, aluminum monohydrate, to a less effective level.

EXAMPLE VII

The fluidized bed consisted of a mixture of α-alumina with equal proportions of four γ-aluminum oxides, denoted A. B, C and D in Table V, representing the properties of the γ-aluminum oxides.

TABLE V

_γ-aluminum oxides_

ABC D

20 average grain size (ym) 7O 61 57 72 grain size distribution 1.U7 1.67 1.66 1.65 fluidity 88.5 88 85 86 water content (% weight loss * at 800 ° C). 7777 thermal power of mixture per unit volume at minimum 1.16 1.16 1.12 1.12 fluidization (MJ / m3K)

The properties of the α-aluminum oxides were as follows: average grain size = 22 ym 30 grain size distribution = 1.69 fluidity = 63 thermal power per unit volume at minimum fluidization = 1.2b (MJ / πΓΚ)

Glass plates of sodium carbonate-calcium oxide-silicon oxide 35 composition with a thickness of 2.3 mm were heated to 66 ° C and 790 5 9 & 3

* V

f 26 - gaps in gas-fluidized mixtures of the foregoing materials, which mixtures were in a quiescent, regularly expanded state of particle fluidization.

The properties of the blends and the resulting center tensile stresses produced in glass plates were as shown in Table VI.

TABLE VI

Percentage of impregnation in the mixture.

Mixture of 4 γ-aluminum oxides. 100 # HO # 20 # 10 # Ó # 10 o-aluminum oxides 0 # 60 # 80 # 90 # 100 # liquidity of mixture. 87 70 67 65 63 thermal power of mixture per unit volume with minimum fluidization (MJ / m3K) 1.1¾ 1.20 1.22 1.23 1.2¾ tensile stress in the middle (MPa) 39 Ho 35 31 25 15

Figure 11 shows the change of the tensile stress in the center with the composition of the mixture.

The foregoing examples have shown how greater stresses can be produced by blends of a gas-developing particulate material with an inert material than can be produced using only the gas-developing particulate material. However, it may be desirable to produce lower voltage values than can be achieved using only the gas-developing particulate material.

According to the present example, this is achieved by using an o-alumina with a small average grain size and a relatively wide grain size distribution, resulting in a considerably lower fluidity than that of the α-aluminum oxides used in the previous examples .

The maximum tensile stress produced at the center was HO MPa using a mixture of Ho # γ alumina, and 60 # α alumina with a fluidity of T0. This is only minorly greater than the tensile stress at the center of 39 MPa produced using only the alumina.

35 Gradually adding more α-alumina to the 790 5 9 83

2T

Mixtures »rapidly reduces the fluidity of the mixtures to such low levels that the tensile stress in the center produced in the glass plates is less than that produced using only the γ-aluminum oxides.

EXAMPLE VIII

The fluidized bed consisted of a mixture of 9 wt. Zeolite, which is a porous crystalline aluminum silicate with water adsorbed in its pores, and 91 wt.% Alumina.

The zeolite had the following properties: 10 average grain size = 2k vm grain size distribution = 1 * fluidity = 51 water content (weight loss at 800 ° C) = 2055 thermal power per unit volume -

at minimum fluidization * 0.8 MJ / nrK

15

The α-aluminum oxide had the following properties: average grain size = 37 Um grain size distribution = 1.682 fluidity = 70 20 thermal power per unit volume ^ at minimum fluidization = 1.1 * MJ / πΓΚ

The thermal power per unit volume at minimum 3 fluidization of the mixture was 1.3 ** MJ / m K, the fluidity of the mixture being 60.

A 2.3 mm thick glass plate was heated to 660 ° C and quenched in the fluidized mixture, producing a tensile stress in the center of 1 * 1 MPa in the plate. By changing the chosen proportions of the ingredients of the mixture, a tensile stress in the center in the range of 25-1 * 1 MPa could be generated in the plate.

EXAMPLE IX

The mixture of particulate materials for fluidization comprised 20% by weight γ-alumina, and 1% by weight each of two α-alumina, which were readily available and used in place of a single, rarer α-alumina.

790 5 9 81 28

The properties of the α-alumina were as follows: average grain size = 57 µm grain size distribution = 1.66 fluidity = 85 5 water content (weight loss he 800 ° C) - 1% thermal power per unit volume,

at minimum fluidization * 1.18 MJ / nrK

The properties of the two α-aluminum oxides, A and B, were as shown in Table VII.

10 TABLE VII

ct aluminum oxides _

A B

average grain size (ym) 38 2k grain size distribution 1.19 1.25 fluidity 75 66 theimetic efficiency of mixture per unit volume with minimum fluidization (MJ / m3ie) 1.1U 1.19 .4

The fluidity of the mixture was 73.5, and the thermal power per unit volume at minimum fluidization thereof was 1.25 MJ / m3K.

A 2.3 mm thick glass plate was heated to 66 ° C and quenched into the fluidized mixture, the tensile stress generated in the plate being U8 MPa in the center. By changing the selected relative ratios of the components of the mixture, a chosen tensile stress in the center in the range of 3 8-8 MPa could be generated in the plate.

EXAMPLE X: 30 The versatility of the present process is further demonstrated by measuring a mixture by mixing a number of gas-generating components and a number of inert components, all of which are available and relative. In order to produce a mixture, inexpensive materials are provided with gas-generating properties and optimum fluidity and thermal power 790 5 S 83 29 for hot producing required stresses in the glass, quenched in that mixture, rather than in a quiet, regularly expanded state of particle fluidization ".

In this example, the mixture contained 5 parts each of four 5 Y-aluminum oxides, A, B, C and D, the properties of which are shown in Table VIII.

TABLE VIII

Y-Aluminum Oxides_AB £ 10 Average Grain Size (Wm) 70 61 57 72 Grain Size Distribution 1.1 * 7 1.67 1.66 1.65 Fluidity 88.5 88 85 86 Water Content (% Weight Loss at 800 ° C) 7777 thermal power of mixture per unit volume at minimum fluidization (MJ / m%) 1.16 1.16 1.12 1.12

This total of 20 parts Y-alumina was mixed with 26.67 parts 3 each of three α-aluminum oxides, E, F and G, the properties of which are shown in Table IX.

TABLE IX

«Aluminum oxides_

E F G

average grain size (Pm) 38 30 2k 2 ^ grain size distribution 1.19 1.22 1.25 fluidity 75 70 66 thermal power of mixture per unit volume at minimum fluidization (MJ / m%) 1.38 1.3 1.19

The fluidity of the mixture was 7¾, and the 3 ° thermal power per unit volume at minimum fluidization thereof was 1.26 MJ / m ^ K.

A 2.3 mm thick glass plate was heated to 660 ° C and quenched in the fluidized mixture, the tensile stress generated in the plate being 1 * 9 MPa in the center. By changing the selected ratios of the Y-aluminum oxides, which make up 20% by weight of the mixture 35 or by changing the proportions of the "-aluminum oxides, which make up 790 5 9 83 3% w%" by weight. of the mixture or by changing the mutual ratios of the total γ-alumina to the total α-alumina in the mixture, a chosen tensile stress in the middle in the range of 32-1 * 9 MPa could be generated.

5. EXAMPLE XI

The fluidized particulate material consisted of 17 wt.% Of the aluminum monohydrate of Example VI, mixed with 83 wt.% Silicon carbide, having the following properties: average grain size * 1 * 0 µm 10 grain size distribution = 1.32 fluidity * 72.75 thermal power per unit volume -

at minimum fluidization. = 1.21 MJ / nTK

The fluidity of the mixture was 75% and the thermal power per unit volume at minimum fluidization thereof was 1.02 MJ / m3K.

A 2.3 mm thick glass plate was heated to 66 ° C and quenched into the fluidized mixture, the tensile stress generated in the center of the plate being 51 MPa. These materials provided the ability to generate a selected center tensile stress in a wide range, 32-51 MPa, by choosing the predetermined ratios of the blend components to adapt the fluidized blend to production. of the required voltage in the glass.

EXAMPLE XII

In a two-component mixture, both particulate materials can have gas-developing properties. A mixture was made from equal weight ratios of Y-alumina and aluminum tri-20 hydrate (AlgO2. SHgO). A portion of the crystal water of the aluminum trihydrate is released upon heating, which adds to the action of the water released from the pores of the Y alumina.

The properties of the Y-alumina were as follows: average grain size = 60 µm 35 grain size distribution s 1 »9 7 Ö 0 5 9 83 31 fluidity = 8¾ water content (weight loss at 800 ° C) = 8% thermal capacity per unit volume ^

at minimum fluxization = 1.05 MJ / m K

5 The properties of the aluminum trihydrate were as follows: average grain size = 86 Urn grain size distribution = 1, U2 fluidity = 86 10 water content (weight loss at 800 ° C) = 3b% thermal power per unit volume 2

at minimum fluidization * 1.5 ^ MJ / m K

The fluidity of the mixture was 85.25 and its thermal capacity per unit volume at minimum fluidization was 1.31 MJ / lA.

A 2.3 mm thick glass plate was heated to 660 ° C and quenched in the fluidized mixture, the tensile stress generated in the plate being at the center of MPa. A chosen tensile stress in the middle in the range of b2-b1 MPa could be generated in the glass plate by 2Φ proper selection of the mutual proportions of the two gas-developing materials.

EXAMPLE XIII

Gas-evolving particulate materials, which generate gases other than water vapor when heated, can be used, for example, sodium bicarbonate (NaïCO ^}, which releases both carbon dioxide and water. A mixture of 10 parts sodium bicarbonate, containing 0.6 Contains% colloidal silica to improve its fluidity, with 90 weight percent of the α-alumina A of Example IX being used.

The properties of the sodium bicarbonate / colloidal 2Q silicon oxide mixture were as follows: average grain size ~ = 70 V® grain size distribution = 1.98 fluidity = 75

HgO + COg content (weight loss at 800 ° C) * 31% thermal power per unit volume

^ at minimum fluidization. * 1, U1 MJ / nrK

790 59 & 3 »* 32

The fluidity of the fluidized mixture was 75%, its thermal capacity per unit volume at minimum fluidization being 1.38.

A 2.3 mm thick glass plate was heated to 66 ° C and then quenched in the fluidized mixture, the tensile stress generated in the plate being 53.5 MPa in the center. By properly selecting the proportions of the components of the mixture, a chosen tensile stress in the center in the range of 3 ^ -55 MPa could be generated in the glass plate.

In many of the examples, an indication of the stress generated in the glass by quenching in the fluidized mixture of particulate materials, given as stresses, is generated in a 2.3 mm thick plate of sodium carbonate-calcium oxide-silica glass, heated to 66o ° C and then quenched. In the same manner as described in Examples II, III and IV, other stresses can be achieved by changing the temperature to which the glass is heated, generating proportionally higher stresses in thicker glass.

The examples all illustrate how the choice of a ratio of a gas-developing particulate material, which can evolve between k% and bj% of its own weight of gas when heated to a constant weight at 800 ° C, is then selected. mixing that gas-developing maternal in predetermined proportions with other gas-developing particulate materials or with inert materials, can adjust the mixture to produce a desired fluidity in the range of 60-86, and a thermal power per volume unit at minimum fluidization in the range of 1.02-1.75 MJ / m K, which ensures that the glass plate quenched in the mixture is thermally cured to the desired degree, as indicated in the examples by the tensile stress in the center . As is common with thermally toughened glass, the ratio of the compressive stress at the surface to the tensile stress at the center is of the order of 2: 1, the generated compressive stress at the surface usually being about 2 times the said tensile stress at the center .

By applying the present method, curing conditions can be easily repeated »allowing 790 5 9 83« * 33 to use a wide range of particulate materials, where available, and to use blends of cheaper and more readily available particulate materials instead of rarer and more expensive single components of the mixture, so that operating costs are reduced.

By an appropriate choice of the particulate materials and of the proportions in which they are. be mixed, it is further possible in Glass selected to reproduce greater cure stresses than the stresses, which can be achieved by using only one of the components of the mixture.

Certain of the above-described particulate materials are commercially available with an appropriate average grain size, grain size distribution, fluidity and thermal power.

When these properties of the required material, for example Y-alumina, are not present in commercially available materials, sieves are used to produce purified particulate materials having the required properties for mixing with other ingredients for the producing a mixture which, upon fluidization, generates the required curing stresses in the glass.

The fluidized mixtures of Examples I-IV and XIII have been found to be particularly suitable for the thermal curing of glass sheets for the manufacture of automotive laminated windshields. The fluidity of such mixtures is in the range of 71-83, the gas content thereof expressed in weight loss on heating to an equal weight at 800 ° C is in the range of k% -31%, where the thermal power thereof is volume unit at minimum fluidization is in the range of 1.09-1.38 MJ / m ^ K.

Selecting the proportions of the components of the mixture is possible to produce lower stresses in the glass than those produced by the gas-developing component alone.

This is illustrated by example VII.

It is clear that changes and improvements can be made without departing from the scope of the invention.

790 5 9 83

Claims (24)

A method of thermally treating glass which is heated to a predetermined temperature and contacted with a gas fluidized particulate material, characterized in that the particulate material comprises a mixture of a number of selected particulate materials, at least one of which has been selected with gas-developing properties upon heating through the hot glass, the materials being mixed in selected predetermined proportions to give the gas-fluxized mixture of particulate materials of such thermal power and fluidity, as follows, that a required thermal treatment of the glass is achieved. 2. A method according to claim t, characterized in that the materials are mixed in such chosen predetermined proportions, that required hardening stresses are generated in a glass plate when it cools in the gas-fluidized particulate material from a temperature above its shape-change point. 3. A method according to claim 2, characterized in that as the gas-developing particulate material, a material is chosen which can develop between h% and 31% of its own weight of gas when heated to a constant weight at 800 ° C. wherein the particulate materials are mixed in predetermined proportions which impart to the mixture a thermal power per unit volume at minimum fluidization in the range of 1.02-1.73 Mtf / m K, and a fluidity in 25 the range of 60-86. The method of claim 3 for thermally curing a sheet of sodium carbonate-calcium oxide-silica glass having a thickness in the range of 2-2.5 mm, wherein the glass sheet is heated to a temperature in the range of 610-680 ° C , and the mixture is held in a quiescent, steadily expanded state of particle fluidization, characterized in that the particulate material is formed to generate a tensile stress in the center in the range of 35-57 MPa. 5. Process according to claim 3 or k, characterized in that the particulate materials are mixed in predetermined proportions, which give the mixture a fluidity in the range of 71-83, and a thermal power per unit volume at minimum fluidization in the range of 1.9-1 »38 MJ / m ^ K. 6. A method according to any one of the preceding claims, characterized in that the gas-densifying particulate material consists of γ-aluminum oxide. Method according to claim 6, characterized in that the V-alumina is mixed with α-alumina. 8. Process according to claim 6, characterized in that the mixture comprises between 7-86% by weight γ-aluminum oxide and between 93-1k% by weight ct-aluminum oxide. Method according to claim 3 or 4, characterized in that a hot glass plate is quenched in a gas-fluidized mixture of a gas-developing particulate material and at least a particulate metal oxide, the thermal capacity of which is per volume. unit at minimum fluidization is in the range of 1.76-2.01 MJ / m K, which particulate materials are mixed in predetermined proportions, which give the mixture a thermal power per unit volume at minimum fluidization in the range of 1 , 27-1.76 MJ / m2 and a fluidity 20 in the range of 71-82. 10. Process according to claim 9, characterized in that the particulate metal oxide consists of spheres of iron oxide («-Fe ^^}. Process according to claim 10, characterized in that the mixture comprises between 30-70% by weight spheres of iron oxide. A method according to claim 11, characterized in that the mixture is between 70-30 wt.% V-alumina as the gas-developing material. Process according to claim 11, characterized in that the mixture comprises between 28-35% by weight spheres of iron oxide and between 1 * 5-56% by weight of α-aluminum oxide, the balance consisting of γ-aluminum oxide as the gas -developing material. lh. Process according to claim 9, characterized in that the particulate metal oxide consists of zircon (ZrO ^. SiO ^). The method of claim 1¾. characterized in that the mixture comprises between 10-70% by weight aluminum monohydrate (Al 2 O 2. 1H 2 O) as the 790 5 9 83 I * gas-developing material, and between 90-30% by weight zircon. . A method according to any one of claims 1-4, characterized in that the gas-developing particulate material is an aluminum silicate. i 5 1T. Process according to claim 16, characterized in that the aluminum silicate consists of zeolite, of which 8-10% by weight is mixed with 90-92% by weight α-alumina to form the mixture. 18. Process according to any one of claims 1-4, characterized in that the gas-generating particulate material consists of aluminum monohydrate (ΑΙ ^ Ο ^. ΙΗ ,, Ο). A method according to any one of claims 1-4, characterized in that the mixture comprises silicon carbide (SiC) mixed with a gas-developing particulate material. 20. A method according to claim 19, characterized in that the gas-developing particulate material consists of aluminum monohydrate (Al 2 O 2. 1H 2 O), the mixture comprising 17% by weight aluminum monohydrate, mixed with 83 wt. jS silicon carbide. 21. A method according to any one of claims 1-4, characterized in that the gas-developing particulate material consists of aluminum trihydrate (AlgO2 HgO). Process according to any one of claims 1 to 4, characterized in that the mixture comprises two gas-developing particulate materials, namely aluminum trihydrate (Al 2 O 3 .3 ^ 0) and V alumina in equal proportions. 23. A method according to any one of claims 1-5, characterized in that the gas-developing particulate material consists of sodium bicarbonate (NaHCO4). 24. Process according to claim 23, characterized in that 10% by weight sodium bicarbonate is mixed with 90% by weight α-alumina to form the mixture. 25. Apparatus for thermally treating glass by the method of claim 1, which apparatus includes a container for the gas fluidized particulate material, of a gas supply means, connected to the container by maintaining the state of fluidization of the particulate material, and of means 790 5 9 83 + 37 for placing hot glass in the container, characterized in that the container receives a gas-fluidized mixture of selected particulate materials, at least one of which has gas-developing properties when heated by the hot glass, which particulate materials are mixed in selected predetermined proportions to impart to the gas-fluidized mixture such thermal power and fluidity that a required thermal treatment of the glass is achieved ". 26. Heat-treated glass produced by the process of any one of claims 1-2U. 27. Thermally hardened flat glass plate produced by the method according to any one of claims 1-2¾. 28. Method substantially as described in the description and shown in the drawing. 7 9 0 5 9 83