FI60695C - FOERFARANDE FOER VAERMEHAERDNING AV EN GLASSKIVA - Google Patents

Description

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JgfiA lBJ (11) UTLAGGNINCSSKRIFT 60 695 C (45) Patent granted 10 03 1932 ifiÄjS Patent seddelat ', (51) K ».ik.3 / im.a.3 C 03 B 27/00 FINLAND - FINLAND (21) P · * · "** '·» · »·" »» »· -PMMtmUninc T62U68 (22) HtktmiipUvi - Antettntnpdif 27-08.76 (23) Alkuptlvt — Giftifhtadtg 27-08.76 (41) Tullut lulklMktl - Bllvlt offvntllg 01.03.7

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Patent and registration authorities in the Netherlands and the United Kingdom public · 30.11. Ö1 (32) (33) (31) Requested request — B ^ Ird prlorltet 29-08.75 29.08.75, 10.06.76 England-England (GB) 35769/75, 35770/75, 2H123 / 76 (71) Pilkington Brothers Limited , Prescot Road, St. Helens, Merseyside WA10 3TT, England-England (GB) (72) Raymond Peter Cross, Preston, Lancashire, Derek Edward Thomas,

Chester, Cheshire, England-England (GB) (7) +) 0y Roister Ah (5) 4) Method for thermal tempering of glass sheets - Förfarande för värme-härdning av en glasskiva

The invention relates to the heat treatment of glass, and in particular to the thermal tempering of glass objects, e.g. flat glass or bent glass sheets. Such tempered glass panes may be used as such as a motor vehicle windscreen or as part of a motor vehicle laminated windscreen, motor vehicle side or rear windows, or used in the construction of windscreen structures for aircraft or locomotives, or in the construction of windows for ships or architectural purposes. The method according to the invention can also be used to thermally temper other glass objects, such as pressed or blown glass objects.

The final tensile strength of the glass article can be increased by a heat-tempering process in which the glass is heated to a temperature approaching the softening point of the glass, after which the glass surfaces are rapidly cooled from center to surface to develop temperature gradients through the glass thickness. These temperature gradients are maintained when the glass is cooled through its deformation point.

As a result, compressive stresses are created in the surface layers of the glass sheet and tensile stresses compensating in the central core of the glass sheet thickness.

This thermal tempering is generally carried out using cooling air directed uniformly to both surfaces of the glass sheet, however, it is difficult to achieve a high degree of tempering with air currents, especially when tempering glass sheets with a thickness of 3 mm or less. Attempts to increase the degree of tempering of the glass sheet by increasing the flow rate of the cooling air can cause loss of optical quality of the glass surfaces and distortion of the shape of the glass sheet due to the pushing thrust caused by the cooling air.

According to another method of heat tempering, a glass sheet having a temperature close to its softening point is quenched in a coolant. This method can be used to generate high stresses. Glass plates must be cleaned after quenching.

Thermal tempering of a glass sheet has also been proposed to be performed by a method in which a hot glass sheet is immersed in a substantially free-bubbling fluidized bed of solid particles, e.g. sand. To date, this method has not been applied on a commercial scale.

When trying to use such a fluidization layer for heat tempering of glass, the main problem has been found to be high in glass sheets; tendency to rupture when treated in the fluidized bed. In a free-bubbling fluidized bed, the rupture of a quenched glass sheet is thought to be caused by disintegrating tensile stresses at the leading edge of the glass sheet due to uneven cooling as the conductive edge moves to the particulate layer in the bubbling or aggregative fluidizing state.

The loss of glass sheets due to breakage is a particularly serious problem in the case of trying to temper thin glass sheets with a thickness of e.g. 2.3 to 4.0 mm at a high stress value, and the losses have been of such a magnitude that the method could not be accepted in the commercial production of tempered glass sheets. e.g. for use in car windshields. The rupture problem also occurs to a lesser but still commercially significant extent when trying to harden thicker sheets with a thickness of up to 8 mm.

The free-bubbling layer in the aggregate fluidization state has also been found to damage the 3,60695 hot glass sheets embedded in this layer. This is due to the irregular forces exerted on the glass in the free-bubbling layer. This can cause both variations in the overall shape and more local surface damage. The above-mentioned deformations occur mainly in connection with thinner glass sheets with a thickness of e.g.

2-3 mm. Deformations, in turn, can cause lamination difficulties, and surface damage can degrade optical quality to such an extent that it is unacceptable when glass is used as a window or as a component of a laminated window.

The invention is based on the finding that the use of a gas fluidized bed in a calm, evenly expanded fluidized state caused by particle fluidization surprisingly causes suitable stresses to develop in glass sheets that are suddenly cooled in such a layer and can significantly reduce losses of glass so as to achieve a commercially acceptable yield.

The method according to the invention is mainly characterized in that the supply of fluidizing gas is adjusted so that the fluidizing gas flows evenly upwards over the entire upper surface of the film at a rate of 0.045-5.61 cm / s and the layer is in the space between incipient fluidization and maximum expansion through which the leading edge of the hot glass sheet enters the layer.

The fluidized bed of finely divided material in a calm, evenly expanded state of particulate fluidization used in the practice of the invention can be determined by the flow rate of gas flowing through the bed and the expanded height of the bed. A calm, uniformly expanded fluidization state of the particles exists between the time limit of the gas velocity representing the onset of fluidization, i.e., the gas free surface.

The upper limit of the flow rate of the fluidizing gas may slightly exceed the rate at which the Pacific surface of the first clearly identifiable bubble breaking, e.g., 5 mm in diameter, is detected. One or two such bubbles may be visible at this velocity of the gas.

4,60695

The higher gas velocity causes extensive bubbling in the bed, and when such bubbling is initiated, the height of the bed partially decreases.

It is believed that abrupt cooling of the sheet in the fluidized fluidized bed of the gas in a calm, uniformly expanded particulate fluidized state will not develop transient tensile stresses at the leading edge of the glass sheet penetrating the fluidizing bed to the extent of compromising the glass sheet.

The substantially bubble-free nature of the layer also ensures that the hot glass is not subjected to irregular forces that could cause fractures or deformation of the glass or superficial damage during sudden cooling.

It has previously been thought that in order to achieve a high heat transfer coefficient between the fluidization layer and the article embedded therein, the layer should preferably be kept in a free bubbling state so that rapid and continuous movement of particles can cause heat transfer between the article and the layer mass. It was thought that such heat transfer would not occur in a quiet layer where the particles move less. However, it has now been found that it is possible to achieve surprisingly high heat transfer coefficients between a hot glass article and a cooler layer formed in a calm, evenly expanded fluid state of finely divided material and having certain selected properties.

It has been found that the finely divided material in the uniform fluidized state is heat-mixed at hot glass surfaces when the hot glass sheet is quenched in the bed, and that the particles in the fluidized bed move faster and have more turbulence in the glass sheet surfaces than in the rest of the bed mass. This results in a high heat transfer from the glass surfaces. It is believed that the particles that heat up as they pass through the glass surfaces then move rapidly away from the glass sheet and transfer heat to the fluidizing air in the bed mass.

Other advantageous features of the invention are set out in claims 2-4.

The density of the particles and their average size are both important factors when judging the suitability of a finely divided material in a fluidized bed in which they are in a quiet, evenly expanded state when used in the process of the invention. A suitable finely divided material which can be brought into a uniformly expanded state by fluidizing air when the bed is operating at normal room temperature and climatic pressure is generally a material for which the numerical product of particle density and particle size does not exceed 220 when the density is pronounced 3 g / cm and particle size in size / μm.

The degree of tempering of the glass sheet achieved by the method according to the invention depends on the heat transfer coefficient between the finely divided material in the fluidization state and the hot glass sheet embedded therein. As already explained above, there is heat-induced mixing at hot glass surfaces, which causes heat to rapidly dissipate from these surfaces. The properties of the particles themselves also affect the magnitude of the heat transfer coefficient.

The invention will now be described in more detail with reference to some of its working examples and the accompanying drawings.

Figure 1 shows a schematic vertical section of an apparatus for carrying out the method according to the invention.

Figure 2 shows a detail of Figure 1 in section.

Fig. 3 is a graph illustrating the nature of a layer of particles introduced into a uniformly inflated fluidized fluid by a gas when this layer is used to practice the invention.

Figure 1 shows a vertical tempering furnace 1 with side walls 2 and a roof 3. The side walls 2 and the roof 3 are made of a conventional refractory material, and the bottom of the furnace is open so as to have an elongate opening 4 made in the base plate 5, which supports the oven 1. A movable shutter (not shown) is used in a known manner to close the opening 4. The glass sheet 6 to be bent and then heat-tempered is suspended in the oven 1 by means of pliers 7 which adhere to the upper edge of the plate 6 and remain closed in the usual manner by the weight of the glass sheet adhered between the pliers. The pliers 7 are suspended from a pliers rod 8, which in turn is suspended from a crane (not shown) running on vertical guide rails 9. These rails extend downwards from the oven to control the lowering and raising of the lifting bar 8. Two bending molds 10 and 11 are placed in the chamber 12 on each side of the path of the glass plate 6, and the chamber is heated by means of hot gas flowing from the channels 12a. The interior of the chamber 12 is the molds 10 and 11 are kept at the same temperature as the hot glass sheet 6 when this enters the chamber 12.

The mold 10 is a fixed male mold mounted on the impact piston 13 and having a curved front surface which determines the curvature to be applied to the hot glass sheet. The mold 11 is a ring-shaped female mold supported by supports 14 mounted on a backing plate mounted on the percussion piston 16. The curvature of the mold frame 11 corresponds to the curvature of the surface of the male mold 10.

The guide rails 9 extend downwards through the chamber 12 on both sides of the bending molds towards the container of the layer 17 to be fluidized. This layer is a fine refractory material where the hot bent glass sheet must be cooled. The fluidized bed tank is an open-ended rectangular tank 18 mounted on a scissor crane platform 19.

When the platform 19 is in its raised position, the upper edge of the container 18 is just below the bending molds 10 and 11.

The microporous membrane 20, which will be explained in more detail on the basis of Figure 2, extends across the bottom of the container 18. The edges of the membrane 20 are fixed between the flange 21 of the tank and the flange 22 of the collecting chamber 23 forming the bottom of the tank. These flanges and the edges of the plate 20 are bolted together as shown in 24. The gas inlet line 25 is connected to the collecting chamber 23, and the fluidizing air is supplied to this line 25 under a regulated pressure. The structure of the membrane is such that the fluidizing air flows evenly into the fluidized bed through this entire base to keep the bed in a calm, uniformly expanded fluidizing state formed by the particles.

The finely divided refractory material in the container 18 is maintained in a calm, evenly expanded fluidized state through a porous membrane 20 by an evenly distributed upward air flow. The swollen layer is essentially bubble-free in a quiet state, and there are no areas in the layer that are not in a fluidized state.

Figure 2 shows a preferred structure of a microporous film described in UK Patent Application No. 24124/76. This film has a steel plate 26 with regularly spaced holes 27. Holes for bolts 24 are drilled in the edges of the plate. The seal 7 6 O 6 9 5 28 is located between the lower surface of the edges of the plate and the flange 22 of the collecting chamber.

A plurality of layers 29 of strong microporous paper are laid on the plate 26. For example, fifteen sheets of paper can be used. The film is supplemented with a woven wire mesh 30, e.g. a stainless steel mesh laid on top of the paper. The upper seal 31 is located between the wire mesh 30 and the tank flange 21.

Near the plate 20 there may be a basket for collecting cullet, and this basket is designed so as not to interfere with the smooth flow of fluidizing air upwards through the membrane.

According to Fig. 1, the guide rails 9 extend downwards to a point below the bending molds and end in the region of the upper edge of the container 18. A fixed frame 32 is mounted on the container 18, and at the bottom of this frame there are upwardly directed legs 33 for receiving the lower edge of the glass sheet when this glass sheet is lowered into the fluidized bed by lowering the clamp rod 8 by means of a crane past the bending molds.

With the scissor crane table 19 lowered and the pliers 7 and the pliers bar 8 in their lowest position below the guides 9, a cold glass plate is loaded on the pliers, which must be bent and tempered. The crane then lifts the suspended glass sheet into the furnace 1, which is maintained, for example, at 850 ° C when tempering soda-lime-silica glass. The glass sheet is rapidly heated to a temperature close to its softening point, for example in the range 610-680 ° C.

When the glass sheet has reached the desired uniform temperature, a shutter is opened which closes the opening 4, and the hot glass sheet is lowered by means of a crane between the open bending molds 10 and 11. The intermediate levers 13 and 16 are actuated and the molds are closed to bend the plate. Once the sheet has the desired curvature, the molds are opened and the hot bent glass sheet is quickly lowered into the fluidized bed in the tank 18, which is lowered to the cooling position by the scissor crane table 19 while the glass sheet was heated in the oven 1.

In the manufacture of high quality laminated glass products that include heat-tempered glass sheets in the fluidized bed by cooling, optical quality has been found to improve when the first air cooling is applied to the glass sheet surfaces just before the glass is immersed in the fluidized bed. This can be done by placing hollow blow frames just above the top of the tank 18, which direct cooling air onto the surfaces of the bent glass sheet as this sheet leaves between the bending molds and enters the fluidized bed 60695.

This initial surface cooling "modifies" the surfaces of the glass sheet so as to avoid the slight variations in these surfaces which have sometimes been observed and which may result from the mixing of the finely divided material in the fluidized state by heat at the glass surfaces. However, such surface cooling should only be used if glass is used to make laminates of high optical quality.

The fluidized bed is maintained at a suitable temperature to generate the desired central tensile stress in the glass, e.g., 30 to 150 ° C, by using water cooling jackets 30 near the long walls of the reservoirs 18, and adjusting the temperature of the fluidized air supplied to the collection chamber 23. These sheaths 34 absorb heat which is transferred through the layer from the hot glass sheet.

The lower edge of the hot glass sheet cools evenly along its entire length as it protrudes into the horizontal pad surface of the expanded fluidized bed, so there is no chance of developing different high tensile stresses in different areas of the glass edge surface, which could lead to breakage. As the bottom edge falls into the layer, this edge always contacts the fluidizing material, which is in a calm, evenly expanded fluidization state, and this uniform treatment of the bottom, independent of the upward flow of particulate material that may develop at hot glass surfaces as soon as they enter the fluidization layer, widely prevents breakage. resulting from the handling of la-sisal fragments in the floor. This, together with the fact that losses due to deformation of the glass sheets and / or damage to the surface quality are avoided, ensures profitable production of tempered glass on a commercial scale.

Local mixing of the fluidized bed under the action of heat occurs near hot glass surfaces, possibly because the gas expands rapidly in a manner similar to that of a liquid boiling. Stirring ensures that sufficient heat is transferred away from the glass surfaces to the mass of the fluidized bed, since heat transfer coefficients between the bed and the glass sheet in the range of 0.003 to 0.002 cal / cm 2 / ° C are achieved. The heat transfer clearly continues even after the glass has cooled below its deformation point, so that there is sufficient certainty that the temperature gradients acting on the surface towards the center are maintained when the glass cools through its deformation point 9 60695 and that the tempering stresses then develop still sunk on the floor.

The mixing of the material in the fluidized state at the glass surfaces causes currents in the layer mass which continuously transfer to the distant parts of the layer the heat which, due to the thermal mixing, is transferred from the glass to the layer in the area immediately surrounding the glass sheet. The heat-receiving water cooling jackets 34 keep these distant portions of the bed cool.

The plate presses on the legs 33 of the frame 32 at the end of its lowering movement, whereby the pliers 8 are released. The glass sheet is then rested on the frame 32 as it cools in the fluidized bed. The glass sheet remains in this fluidized bed until it has cooled sufficiently to be processed, and the tank 18 is lowered by lowering the scissor crane platform to expose the fixed frame 32 and the tempered glass sheet supported by it, which glass sheet is then removed to further cool to room temperature.

Figure 3 illustrates the nature of the Pacific uniform fluidization state of the fluidized bed formed by the particles. This figure plots the pressure in the collection chamber as a function of the height of the bed in the tank 18 using N-alumina particles as described in Example 2 below, and the tank size and fluidization conditions described in this Example 2, and the bed temperature is 80 ° C.

When the pressure in the collecting chamber reached 2 15 kN / m, the layer began to expand, whereby the velocity of the fluidizing air flowing through the layer is sufficient to start the initial fluidization state. That is, at this lower gas velocity limit, the β-alumina particles are just suspended in the upwardly flowing air. Due to this large pressure drop in the membrane, the velocity of the gas flowing upwards through the finely divided material can be readily adjusted so as to control the still fluidization of the J maintained.

In this way, the velocity of the gas can be readily adjusted by adjusting the accumulating pressure prevailing in the chamber 23, and when this pressure increases, no sudden or discontinuous change in the state of the bed occurs. Instead, the calm, evenly expanded state of the bed is maintained as shown in Figure 3 when the aggregate pressure is increased to about 25 kN / m, and the bed expands to a height of about 102 cm in the tank.

With this aggregation pressure, it can be seen that the first clearly identifiable bubbles, e.g. about 5 mm in diameter, break through the surface of the Pacific bed, and this rate of fluidization air can be considered as the minimum bubbling rate.

Due to the use of the large pressure drop in the membrane 20, it has been found that this minimum bubbling rate is not necessarily the gas rate that develops the maximum expansion of the bed, so further adjusting the collection chamber pressure to 27 kN / m gave a maximum bed height of 105 cm . Increasing the pressure in the collection chamber to this value of 27 kN / m 2, several small bubbles were observed to break through the surface of the layer, but these small random bubbles were not so significant as to adversely affect the layer's ability to cool hot glass sheets, especially thick glass sheets.

2

As the pressure in the collection chamber was increased above 27 kN / m, permanent bubbling of the bed was observed, and it was found that the bed tended to descend to a height less than its maximum height of 105 ohms. The layer in this state was not suitable for tempering hot glass sheets.

Thus, in this example, the uniform calm and swollen state of the fluidized bed of α-alumina particles suitable for tempering hot glass sheets is represented by the area of the curve of Figure 3 between 15 and 27 kN / m 2 in the collection chamber. uniform escape stresses developed in the glass.

The effective heat transfer coefficient between the fluidization layer and the hot glass is determined by the properties of the fluidizing gas, usually air, the gas flow rate through the bed, the properties of the particles of refractory fine material, in the case of particles, especially that the particles have a cavity, that is, that they have a certain porous or hollow structure. The heat transfer coefficient is also determined by the temperatures of the glass and the layer, because in case the difference between these temperatures is small, there will be only slight mixing at the glass surface, so the effective heat transfer coefficient will be relatively small.

Other factors that affect the heat transfer coefficient include the specific heat of the particles and their average heat capacity. In all of the following examples, the numerical value of the particle density-1 den (g / cm) and the average particle size (pm) product is less than 220. This is a criterion that can be used to determine the suitability of a finely divided material, i.e. its ability to be uniformly uniform. swollen fluidization state when operating at normal ambient temperature and pressure.

The following are some examples of the tempering of glass sheets in the apparatus of Figures 1 and 2 and using a uniform calm expansion layer with glass sheet thicknesses in the range of 2.4 to 12 mm. In all Examples 1-11, the edges of the glass sheets are finished by rounding them with a fine diamond gravel disc.

Example 1

Porous X-alumina was used as a finely divided refractory material having the following average particle size (d): 64 particle size distribution 20 to 160 μm particle density d (δ) 2.2 g / cm 2 material density 3.97 "δ x d 141"

the specific heat of the material is 0.2 cal / g / ° C

heat capacity per unit volume of the layer * _

per minimum fluidization state of 0.21 cal / cnr / G

velocity of fluidizing air in the bed 0.5 ^ cm / s 6 0 6 9 5

The layer was kept at 40 ° C, whereby the degree of tempering of 2.3-12 mm thick glass sheets was as follows when the initial temperature of the glass was in the range of 610-670 ° C:

Initial heat of glass- Glass thickness Average space, central tensile stress (0) (mn / b2) 610 2.3 37 610 10 92 610 12 93.5 630 2.3 42.5 630 6 72.5 630 12 96 650 2.3 46 650 4 64 650 6 75.7 650 8 92.7 650 10 96 650 12 99 670 2.3 44 670 6 75 670_____10___100___

The effective heat transfer coefficient between the layer and the glass sheets ranged from 0.01 to 0.012 cal / cm 2 / ° C / sec.

Example 2

In a special production series using the same porous alumina as in Example-1, glass sheets with a thickness of 2.3 mm were tempered. These plates were then used as a component of a laminated windshield for automobiles.

The properties of ^ 6 alumina were as follows: 60695 13

Mean particle size (d) = 64 51m particle size distribution = 30 - 150 μm particle density (6) = 2.2 g / cm ^ material density = 3.9 g / cm "* δ xd = 141 fluidized bed tank size = 38 cm x 215 cm x 105 om deep collecting pressure * 24 kN / m2 pressure drop in the diaphragm = 15 kN / m.,.., 60% total pressure drop in the diaphragm = + „la fluidization air flow rate = 0.175 m / min.

fluid velocity in the bed = 0.36 cm / s

fluidized bed temperature s 60 ° C

glass temperature: upper edge = 650 ° C to 655 ° C

edge = 670 ° C - 675 ° C

central 2 o uniform tensile stress formed in the glass s 38MN / m * - 40MN / m *

The effective heat transfer coefficient between the layer and the glass sheets was in the range of 0.01 to 0.012 cal / cm / C / sec.

Example 3

In another production series, glass sheets intended to be used as components of aircraft laminated windshields, having thicknesses of 3 mm, 4 mm, 6 mm, 8 sun, and 10 mm, were tempered in a uniformly calm expanded fluidized state layer of β-alumina. The same porous} L »alumina as in Examples 1 and 2 was used.

Size of the tank containing the fluidized bed = 45 cm x 245 cm x 150 cm deep

O

collecting pressure = 30 kN / m pressure drop in the diaphragm = 19 * 5 kN / m2 pressure drop in the diaphragm = 65% of the collecting pressure flow rate of the fluidizing air = 0.34 m ^ / min.

fluid velocity in the bed = 0.51 cm / s

fluidized bed temperature = 60 ° C

glass temperature = 645 ° C to 650 ° C

111 6 0 6 9 5

The uniform central tensile stresses developed in the glass were as follows:

Thickness Central tensile stress 3.0 mm 48 MN / m2 4.0 mm 53 MN / m2 10.0 mm 80 MN / m2

The effective transmission between the layer and the glass panes

O Q

the coefficient ranged from 0.01 to 0.012 cal / cm / C / sec.

Example 4

As a fine refractory material, a porous ground alumina-silicate material was used, each particle of which contained 13% by weight of alumina and 86% by weight of silica. The properties of the ground material were as follows: Particle size distribution = maximum particle size of 150 μm (d) = 60 μm particle density (6) = 1.22 g / cm ^ material density = 2.3 g / cva? 6 = d = 73

specific heat of the material = 0.38 cal / g ° C

heat capacity per unit volume of the floor

in the fluidization state = 0.19 cal / cnr ° C

the velocity of the fluidizing air in layer 1 0.21 cm / s

The layer was kept at 40 ° C, at which point the degrees of hardening of 2.3-10 mm thick glass sheets were as follows:

Initial temperature of glass Thickness of glass Average tensile stress C (MN / m2) 650 2.3 30.8 650 4 44 650 6 62.3 650 8 73 650 10 79

The effective heat transfer coefficient between the layer and the glass sheets ranged from 0.007 to 0.009 cal / cm 2 / 0C / sec.

f. » 60695 15

Example 5 A different form of ground alumina-silicate material was used. Each particle was porous and contained 29% by weight alumina and 69% by weight silica. The properties of this porous powder were as follows:

Particle size distribution = up to 150 pm particle size distribution = 75 μη particle density (δ) = 1.21 g / cm ^ δ x d = 91

* T

material density = 2.3 g / cnr

specific heat of the material = 0.2 cal / g ° C

heat capacity layer volume _

per unit in minimum fluidization mode = 0.11 cal / cnr ° C

fluidization air velocity in the bed = 0.33 cm / s

The layer was maintained at 40 ° C, and the initial glass temperature ranged from 610 to 670 ° C, whereby the following degrees of tempering were achieved with 2.3 to 10 mm thick glass sheets:

Initial glass thickness Glass thickness Average temperature (° C) central tensile stress (MN / m *) 610 6 51 610 10 74 630 2.3 31.3 630 6 33 650 2.3 33.7 650 4 48.3 650 6 56 650 8 71.3

650 10 8A

670 2.3 32 670 6 50 670 10 81.5 16 60695

The effective heat transfer coefficient between the layer and the glass sheets ranged from 0.007 to 0.01 cal / cm 2 / ° C / sec.

Example 6 nFillite "powder, which were hollow glass spheres made from pulverized fuel ash from power boilers, was selected so that the properties were as follows:

Particle size distribution = 20 to 160 μm average particle size (d) = 77 μm particle density (6) = 0.38 g / cm ^ δ x d = 29 material density = 2.6 g / cm ^

specific heat of the material = 0.18 cal / g ° C

heat capacity of the bed volume,

per unit minimum fluid state = 0.05 cal / cnrC

air fluidization rate in the "Fillite" layer = 0.11 cm / s In this fluidization layer, the degree of tempering achieved by thermally toughened glass sheets can be described by the average central tensile stress measured 40 ° C, the following results: 60695 17

Initial heat of glass - Glass thickness Average central state (Oc) (m) tensile stress (^, / ,, 2)

610 10 AO

610 12 A1 630 6 30 630 12 45 650 4 4 22.4 650 6 32 650 8 37 650 10 39 630 12 48.5 670 6 35 670 10 50

The effective heat transfer coefficient between the layer and the glass sheets ranged from 0.003 to 0.004 cal / cm 2 / ° C / sec.

Example 7 A second grade of "Fillite®" material with the following characteristics was used:

Mean particle size (d) = 120 μm particle density (δ) s 0.38 g / cm 2 material density = 2.6 g / cm 2 δ x d = 45

characteristic flap of the material = 0.18 cal / g ° C

heat capacity per unit volume *

per unit in the minimum fluidization state = 0.06 oal / om- 'C

velocity of fluidizing air in the bed = 0.27 cm / s 18 6 0 6 9 5

With the initial temperatures of the glass sheets in the range of 630-670 ° C and the layer temperature of about 40 ° C, the following stresses developed in the glass sheets 6-10 mm thick:

Initial heat of glass - Glass thickness Average central space (° c) tensile stress (MN / m2) 630 6 /, 2 630 ö 4 9 630 6 45.5 650 8 51 • 650 10 63

670 6 VJ

670 8 53

The effective heat transfer between the layer and the glass

Q Q

the coefficient ranged from 0.005 to 0.06 oal / cm / C / sec.

Example 8

Hollow carbon spheres, known as "Carbospheres", were used as a fine refractory material and had the following properties:

Particle size distribution = 5-150 μm average particle size (d) s 48 pm particle density (δ) = 0.5 g / om ^ 6 x d = 14.4 material density s 2.3 g / om ^

specific heat of the material = 0.123 cal / g ° C

heat capacity of the layer volume.

per unit in minimum fluid state = 0.02 cal / cm '> ° C

velocity of fluidizing air in the bed * 0 * 33 cm / s 19 60695

In the fluidized bed at a temperature of about 40 ° C, the degrees of tempering of the cooled glass sheets were as follows:

Initial heat of glass- Thickness of glass Average tensile stress of the means (° C) (mm) (MN / m2) 610 10 44 630 6 34 650 4? -6.3 630 6 32.7 650 8 40 650 10 45 670 6 36 670 10 46

The effective heat transfer coefficient between the layer and the glass sheets ranged from 0.0035 to 0.004 cal / cm 2 / ° C / sec.

Example 9

Porous ground nickel having the following properties was used as a fine refractory material:

Average particle size (d) = 5) »particle density (6) * 2.35 g / cm ^ material density = 8.9 g / cm ^ δ z d = 12

specific heat of the material = 0.106 cal / g ° C

heat capacity of the bed volume,

per unit at minimum fluidization = 0.37 cal / cmJ ° C

fluidization air velocity in the bed = 0.045 cm / s

Glass plates ranging in thickness from 2.3 to 6 mm and having a temperature of 650 ° C were quenched in a dormant layer of this porous nickel powder, which was maintained at a temperature of about 40 ° C. The degrees of hardening presented as the mean central tensile stress were as follows: 60695 20

Glass thickness Average central _ (mm) _ tensile stress (MN / m2) 2.3 77 3 95 6 115

The effective heat transfer coefficient between the layer and the glass sheets was 0.02 cal / cm 2 / ° C / sec.

Example 10

Non-porous ground α-alumina was used as the finely divided material. Different α-alumina materials with different average particle sizes were used. All of these materials had the following common features:

Particle density (δ) = 3.97 g / cm 2 material density = 3.97 g / cnr

specific heat of the material = 0.2 cal / g C

The α-alumina material was obtained sorted by particle size, and four different fluidization layers were formed: α-aluminum- Particle Particle Minimization-rFluidation · Nioxide medium size δ x temperature of the coil in the heating capacitance (cal) Λ speed layer (μ-) d <,, 3/0 ^ ity (Sal / im3 / <b)? 0 ks 23 92 5 X 10'9 0.32 1.02 B 29 116 10 X 10 “9 0.32 1.62 C 45 180 38 X 10 ~ 9 0.32 3.90 D 54 216 66 X 10 "9 0.32 5.61 In these fluidized layers, glass sheets with thicknesses ranging from 2.3 to 12 sub were quenched at a temperature of 40 ° C. The initial plates of the glass sheets ranged from 610 to 670 °. C, and the degree of hardening of the sheets is characterized by an average central tensile stress in the range of 42 to 104 MN / m.

n 60695

The effective heat transfer coefficient between the layer and the glass sheets ranged from 0.0062 to 0.0086 cal / cm 2 / ° C / sec.

Example 11

A layer of small solid glass hems known as MBallotini ,, was brought to a fluidization state. The properties of the layer were as follows:

Particle size distribution = 0 to 75 μm average particle size (d) = 58 μm * 7 particle density (6) = 2.5 g / cm δ x d = 145 heat capacity per unit volume of bed with minimum fluidization

in state = 0.34 cal / c ^ uC

fluidization air velocity in the bed = 0.041 cm / s

Glass plates having a thickness in the range of 2.3 to 10 mm were heated to an initial temperature of 630 to 670 ° C, and quenched in a fluidized bed maintained at about 40 ° C. The degrees of tempering of the glass sheets were as follows:

Initial heat of glass- Glass thickness Average mean (C) tensile stress (“) (MN / .2) 630 2.3 30 630 6 72 630 8 07

650 2.3 AO

650 6 7A.5 650 8 87 650 10 90 670 2.3 A3 670 6 80 670 8 90 '60695

The average effective heat transfer coefficient between the layer and the glass sheets was 0.011 cal / cm 2 / ° C / sec.

To illustrate the high yield of unbreakable and undistorted glass sheets obtained using the gas fluidized bed layer of the invention, which was in a calm, evenly expanded fluidized state, compared to the yield obtained using a layer in a bubbling fluidized state, several similar glass sheets were treated with x 30 cm and with thicknesses of 2 mm, 6 mm and 12 mm. The edges of the glass sheets had been finished by flattening these edges with a silica-carbode grinding wheel. Thus, a rougher finish of the edges was obtained than in the glass sheets according to Examples 1-11, which were finished with a diamond gravel disc. Thanks to the invention, a higher yield was also achieved using this coarser and cheaper edge finish.

Each plate was heated to the temperature mentioned below and thus immersed in the fluidized bed of porous α-alumina described in Example 1.

In these yield experiments, some hot glass sheets were immersed in a quiet fluidized bed as described in Example 1. Thereafter, a bubbling fluidization state of the bed was obtained by increasing the velocity of the fluidizing gas beyond the value at which maximum layer expansion developed, and as many hot glass sheets were bubbled.

The yield of unbroken glass panes of acceptable dimensions as a percentage of the total number of treated plates was as follows:

Glass thickness = 2 mm Output

Glass temperature ° C Calm layer Bubble layer 645 95% 52% 660 100% 80%

Glass thickness = 6 mm Output

Glass temperature ° C Calm layer Bubble layer 640 80% 40 <fo 645 100% 60%

Glass thickness = 12 mm Output

Glasses! temperature ° C Calm layer Bubble layer 635 80% 40% 645 loo% 75%? 3 6 0 6 9 5

Although the above results were obtained using square glass sheets of 30 cm x 30 cm, even lower yields with respect to breakage and distortion were obtained when treating large glass sheets, e.g. In contrast, the yields obtained when treating such large glass sheets in a calm fluidized bed were at least as good as those obtained according to the above examples.

The magnitude of the stresses developed in the glass decreases as the temperature of the layer increases, and at the limit, which may be about 300 ° C or higher, the stresses acting on the glass are such that the glass becomes annealed rather than tempered. Heating and / or cooling elements can be used near the side walls of the tank 16 to control the temperature of the fluidized bed. In all examples, the glass sheets were commercially available soda-lime glass sheets used in aircraft windshield panels, automotive windshields, ship windows and structural panels. · Glass of a different composition can be tempered or annealed in the same manner using the method of the invention. Objects other than glass sheets, e.g. compressed glass objects, such as insulators or line blanks or blown glass objects, can also be tempered or annealed by the method according to the invention.

The fluidization layer according to the invention can be used for other heat treatments of glass, e.g. to heat a relatively cold glass article before the next treatment step, whereby heat transfer from fluidizing material to glass embedded in the layer is facilitated without risk of glass damage even when the glass has reached a temperature below be damaged by the effects of irregular forces.

The invention can also be applied to the thermal tempering of glass sheets which have been heated and bent while supported in an almost vertical position, and the sheets have been made to travel along a horizontal path, as described in UK Patent Application No. 34,703 / 73 (Publication No. 1,442 .316). Using the apparatus described in this application, the bending molds are enclosed in a heated chamber which is tilted from an inclined position to a position in which the bent glass sheet is in a vertical position between the bending molds and can be lowered vertically into a resting fluidized bed of the type described above.

24 60695

According to another method in which the invention is applied, the glass sheet can be heated by immersing it in a fluidized bed having a temperature high enough to heat the glass to a pre-bending temperature. The sheet is bent after it has been removed from the hot layer, and then the bent sheet is hardened by immersing it in a fluidized bed having a fluidized bed of finely divided material in a uniformly expanded state as described above. The glass sheet can be supported with the same pair of pliers during heating, bending and tempering, whereby the pliers are mounted to be adjusted so that they can move and thus follow the bent shape of the glass. According to another arrangement, each glass sheet is suspended from non-adjustable forceps for heating and moved from the bottom to be supported during bending in the manner described in UK Patent No. 1,442c316, whereby a second group of forceps is attached to the bent glass sheet. then the glass is lowered into a resting fluidized bed for quenching.

Claims (4)

25 6 0 6 9 5 A method for thermally tempering a glass sheet, wherein a fluidizing gas is fed under the film so as to maintain above it a fluidized bed of particulate material having a particle diameter of less than 200 μm and a density of less than 9 g / cm and in which the hot glass sheet is tempered, that the supply of fluidizing gas is adjusted so that the fluidizing gas flows evenly upwards over the entire upper surface of the film at a rate of 0.045-5.61 cm / s and the layer is in the space between incipient fluidization and maximum expansion and has a horizontal calm surface . Process according to Claim 1, characterized in that the temperature of the bed is maintained at 30 to 150 ° C. A method according to claim 1 or 2, characterized in that the gas flow is controlled to maintain a quiet state of the fluidizing layer by generating a large pressure drop in the membrane through which the fluidizing gas flows into the bed. Method according to one of Claims 1 to 3, characterized in that the particulate material consists of particles having a density of 0.3 to 3.97 g / cm and an average size of 5 to 120 μτη.