Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B25/00—Annealing glass products
  • C03B25/04—Annealing glass products in a continuous way
  • C03B25/06—Annealing glass products in a continuous way with horizontal displacement of the glass products
  • C03B25/08—Annealing glass products in a continuous way with horizontal displacement of the glass products of glass sheets
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
  • G01K1/00—Details of thermometers not specially adapted for particular types of thermometer
  • G01K1/14—Supports; Fastening devices; Arrangements for mounting thermometers in particular locations
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
  • G01K13/00—Thermometers specially adapted for specific purposes
  • G01K13/04—Thermometers specially adapted for specific purposes for measuring temperature of moving solid bodies
  • G01K13/06—Thermometers specially adapted for specific purposes for measuring temperature of moving solid bodies in linear movement

Definitions

• the present invention relates to an installation for measuring the surface temperatures of a glass ribbon in a flat glass annealing lehr.
• a flat glass annealing lehr is a tunnel kiln equipped with heating and cooling means for following a heat annealing and controlled cooling cycle with a glass ribbon. It consists of successive zones generally designated by AO, A, B, C, D, E and F, the zone AO being located on the ribbon entrance side.
• zones AO, A, B and C of the lehr the control of the cooling of the glass is obtained by radiative exchanges with cold parts, commonly called exchangers, or heating elements, whereas in zones D, E and F the cooling is performed by convection blown air. Zones AO to D are closed by insulated walls to better control the cooling of the glass.
• the drying rack is placed downstream of the tin bath for a production line according to the float process, or downstream of the melting and conditioning furnace for a laminated glass production line.
• the first critical phase of the annealing and cooling cycle of the flat glass strip is located in the areas of the lehr where the glass is in a viscoelastic state. Cooling induces thermal gradients and stresses on the surface and the core of the glass ribbon. To limit the creation of permanent stresses and allow their relaxation, the start of cooling is performed at a reduced rate to allow annealing of the glass. A level of permanent stress that is too high causes problems in the subsequent processing of the glass such as cutting.
• the second critical phase of the cooling cycle begins, where the goal is to cool the glass quickly to limit the length of the lehr. Since the glass is now in the solid state, thermal gradients during this cooling induce so-called temporary constraints. Temporary constraints excess in the width or thickness of the ribbon will break the glass. It is therefore important to finely control the longitudinal thermal profile, transverse and in the thickness of the glass ribbon.
• the temperature measuring devices installed on the prior art devices lead in practice to much larger errors.
• the generally available measuring means do not allow the temperature measurement of the critical points that are the edges, also called edges, of the ribbon.
• the measurement of the temperature at the same point on the upper face and the lower face of the ribbon is generally not available.
• thermocouples are traditionally vaulted and suspended above the ribbon. Lower thermocouples are attached to a bar between the ribbon support rolls. These thermocouples placed in rigid tubes are adjustable but often remain several centimeters from the glass. The positions of the thermocouples are always located at the end of the closed zones for radiative cooling (A 1 B 1 C). Thermocouples are not placed in the convective zones (D and F) because of the measurement disturbance that convection causes in these zones. Five thermocouples are generally implanted on the upper face over the width of the ribbon and three thermocouples on the lower face. These thermocouples being placed several centimeters from the ribbon, they receive the radiation emitted by the ribbon but are cooled by the exchangers. As a result, they do not make it possible to correctly measure the temperature of the glass ribbon.
• pyrometers are vaulted at a few points along the length of the lehr and aim at the upper surface of the ribbon.
• the emissivity of these pyrometers is not always controlled by the operators, which leads to measurement errors.
• Pyrometric scanners are vaulted and aim at the full width of the ribbon through a slot in the vault of the closed sections.
• the position of the measurement is obligatorily at the end of the zone because of the obstacle represented by the heat exchange tubes present in the radiative zones.
• thermocouple and pyrometry should, within the limit of their measurement accuracy, give comparable results. In fact, there are divergent values between the measurements made by thermocouple and pyrometry.
• thermocouples and pyrometers In areas with low cooling, the values measured by thermocouples and pyrometers are quite close. This is explained by the measurement environment which is almost isothermal. When the cooling increases, a large measurement error appears which can reach 100 0 C. Thermocouples are heated by the tape but also cooled by the cooling devices. In cabinets without pyrometers or scanners, this measurement difference is taken into account by applying a correction factor to correct the temperature delivered by the thermocouples and thus estimate the true temperature of the ribbon. However, this approach is unsatisfactory because it does not achieve the required accuracy on the temperature measurement.
• a second example of this divergence relates to the temperature measured over the width of the ribbon in a radiative zone B2 of a lehr.
• the difference between pyrometers and thermocouples is of the order of 20 ° C. in this zone. Pyrometers may indicate an increase in ribbon temperature from left to right while thermocouples will indicate the opposite!
• thermocouples The measurement of the temperature of the glass ribbon in the lehr with thermocouples according to the state of the art is not satisfactory, the measurement obtained being disturbed by the radiation to the walls of the lehr, chillers and rollers , and convective cooling of convective zones. This disturbance persists even if the thermocouple is in slight mechanical contact with the glass.
• the object of the invention is, above all, to solve this problem and to allow an improved measurement of the surface temperature of the glass ribbon.
• it comprises a subassembly placed on one of the two faces of the glass ribbon that is flush with the surface of the glass ribbon, and creates a thermally insulated space on the side of the ribbon surface where the subset is located. It comprises at least one temperature measuring member placed in the thermally insulated space,
• the means for correcting the measurement error may consist of a thermal calculation means taking into account the radiation loss through the ribbon to correct the temperature measurement error of the thermally insulated space.
• the means for correcting the measurement error may be constituted by a second subassembly situated on the side of the ribbon opposite the first subassembly, flush with the surface of the ribbon, and creating an isothermal space.
• the subassemblies create an isothermal space on both sides of the glass ribbon by a thermal and optical insulation, . and it comprises at least one temperature measuring member placed in at least one of the isothermal spaces and supported by at least one of the subassemblies, the other subassembly constituting the means for correcting the error measurement.
• the isothermal space around each member for measuring the temperature of the ribbon is advantageously designed so as to limit thermal losses by conduction, radiation and convection.
• This isothermal space can be made in the form of a hollow in the face of a sheet of insulation which is flush with the surface of the glass ribbon.
• the two subassemblies respectively placed on either side of the glass ribbon are preferably substantially symmetrical with respect to the glass ribbon so as not to generate a temperature difference between the two faces of the ribbon.
• the installation advantageously comprises several temperature measuring members arranged at several points in a direction parallel to the width of the glass ribbon in order to determine the temperature profile over the width of the ribbon.
• At least one temperature measuring member is arranged on each of the faces of the ribbon, so that the measurement can be performed on both sides of the ribbon at a point or at several points in a direction parallel to the width of the ribbon of glass , to determine the profile of the temperature difference between the two sides of the ribbon.
• the distance between the measurement points located in a direction parallel to the width of the ribbon is smaller at the edges of the ribbon than in the central zone, so that more measuring points are available on the ribs than in the central zone. center of the ribbon.
• the temperature measuring device may, for example, be a thermocouple or a thermistor.
• the temperature measuring member is placed near the surface of the glass ribbon, without being in contact therewith.
• the organ the temperature measurement is placed within one centimeter of the surface of the glass ribbon, without being in contact therewith.
• the thermal and optical insulation that is flush with the surface of the glass ribbon can be made of a flexible material with a low coefficient of friction.
• the thermal and optical insulation is advantageously constituted by a sheet of mineral wool or glass wool.
• the installation according to the invention comprises mechanical protection members against deterioration caused by the breaking of the glass ribbon.
• These protection devices can be fixed relative to the lehr. They can also be removable as are the curtains used in the cabinets to limit convection.
• the installation according to the invention also comprises means for limiting air convection between the ribbon and the temperature measuring member.
• the invention also relates to a flat glass annealing lehr, characterized in that it is equipped with at least one installation for measuring the temperature of the glass ribbon as defined above.
• the invention also relates to a method for driving a flat glass annealing lehr, characterized in that a continuous measurement of the surface temperature of the glass ribbon is performed by an installation
• the means for correcting the measurement error may consist of a thermal calculation means taking into account the radiation loss through the ribbon to correct the temperature measurement error of the thermally insulated space.
• the means for correcting the measurement error may be constituted by a second subassembly situated on the side of the ribbon opposite the first subassembly, flush with the surface of the ribbon, and creating an isothermal space.
• the method for driving a flat glass annealing lehr is then characterized in that the continuous measurement of the surface temperature of a glass ribbon is carried out by an installation which comprises two subassemblies respectively placed on each side. and other glass ribbon and facing, each subset of which is flush with the surface of the glass ribbon, with an isothermal space formed around each member for measuring the temperature of the ribbon with a thermal and optical insulation, and is used to automatically adjust the operating parameters of the outrigger via a control loop.
• a combination of the lehr control system and the temperature measuring equipment is advantageously provided to allow the operating parameters of the lehr to be adjusted rapidly so that the level total stress remains below a determined value to prevent breakage of the glass or ribbon deformations perpendicular to the plane of the ribbon and the permanent stress level remains below a given value for subsequent processing of the glass.
• the temperature measurements can be made according to the width of the glass ribbon and can be used for adjusting the heating distribution over the width of the ribbon and / or adjusting the cooling distribution over the width of the ribbon.
• a mathematical model of the operation of the lehr can be established and used to define the optimum setpoints to be applied to the lehr, according to the measurements made, in order to obtain the desired level of temperature and stress.
• the invention consists, apart from the arrangements described above, in a certain number of other arrangements which will be more explicitly discussed below with regard to embodiments described with reference to the accompanying drawings, but which are not in no way limiting. On these drawings:
• Fig.1 is a schematic longitudinal vertical section illustrating the principle of the installation for continuously measuring the surface temperature of the glass ribbon in a lehr according to the invention.
• Fig.2 is a schematic longitudinal vertical section of an exemplary embodiment of the installation of Fig.1.
• Fig.3 is a diagram of the temperature profile in the thickness of the glass ribbon, the temperature being plotted on the ordinate and the thickness being plotted on the abscissa.
• Fig. 4 and 5 are diagrams illustrating the optical thickness plotted on the ordinate as a function of the wavelength on the abscissa.
• FIG. 6 is a diagram with two curves, one for the optical thickness plotted on the ordinate on the left scale, and the other for the emission of the black body plotted on the ordinate on the right scale, in function of the wavelength on the abscissa.
• thermocouples are a schematic top view of an implantation of thermocouples according to the invention.
• thermocouple TC preferably jacketed and small diameter, the diameter generally being equal to or less than 2 mm.
• the measurement point of the thermocouple TC is maintained at a point in the isothermal space and advantageously in the immediate vicinity of the glass surface but avoiding any contact between the glass and the thermocouple TC.
• immediate proximity is meant a thermocouple whose point of measurement is at a short distance from this tape, for example of the order of 2 mm.
• thermocouple TC The absence of contact between the thermocouple TC and the glass G makes it possible to prevent heating of the thermocouple TC by the heat of the friction which would lead to an error by excess of the measured temperature.
• thermocouple TC To measure correctly with this TC thermocouple the temperature of the ribbon, a thermal equilibrium between the ribbon G and the thermocouple TC is imperative. To avoid heat losses of the thermocouple TC, an isothermal space 2 is created around the thermocouple using a flexible insulator 3 with a low coefficient of friction which is flush with the surface of the ribbon G. By "low friction coefficient insulation” an insulation is designated that can touch the glass scroll without degradation of the measuring device or the surface of the glass. The thermocouple TC is thus isolated against heat loss to the outside.
• Examples of flexible insulation that may be suitable include mineral wool or glass wool which are two simple and inexpensive insulating materials adapted to the device, capable of withstanding temperatures well above those prevailing in a drying rack.
• the use of a flexible insulator which is flush with the glass surface also makes it possible to avoid the flow of air between the surface of the ribbon G and the measuring device thus eliminating the convection cooling of the temperature measuring member. TC. This first part of the device makes it possible to get closer to the true temperature of the glass.
• the installation carried out according to the invention takes into account the semi-transparent property of the glass.
• an isothermal space is created close to a black body on one side of the glass, part of the heat of this isothermal space is still lost through the ribbon by radiation in the transparent spectral window of the glass.
• Additional insulation 4 of the opposite side of the ribbon G keeps the heat by returning the radiation to the space created by the glass and the thermocouple.
• the thermocouple TC thus reaches a temperature very close to that of the glass.
• the installation according to the invention is thus characterized in that the isothermal space 2 around the measuring member TC of the temperature of the glass is obtained by limiting the thermal losses by conduction, by radiation and by convection.
• the additional insulation 4 is advantageously made in the same way as the insulation 3, with a flexible insulator, for example a sheet of mineral wool or glass wool.
• thermocouple TC a thermocouple TC2 disposed in another isothermal space 5, in the form of a hollow in the insulation 4, so as to be in the immediate vicinity of the face of the ribbon opposite to that corresponding to the first thermocouple TC.
• the theoretical temperature profile in the thickness of the ribbon is assumed to be that shown in FIG. 3. It shows that the temperature of a glass sheet is not homogeneous during cooling, with surfaces colder than the heart. This is particularly true for a relatively thick glass, for example beyond 8mm thick. For a thinner glass, the temperature gradients in the glass during cooling remain limited.
• Figure 3 shows a difference of 5 ° C between the center (i.e., at half thickness) and the ribbon surface for 4 mm thick glass and a given cooling rate.
• the error induced by a measurement of the surface temperature with respect to the average temperature in the thickness is less than 2.5 ° C.
• the measurement of the surface temperature is sufficiently representative of the average temperature of the ribbon with regard to the accuracy sought. The situation is different for a thick glass.
• the core temperature and the average temperature can be determined.
• the radiation exchanged between the surface of the ribbon and the walls of the lehr, for a ribbon at 380 0 C having an emissivity of 0.85 and a wall temperature of the lehr of 170 0 C, is 7 kW / m 2 on each face.
• the creation of an isothermal space for the measurement of the temperature with a fibrous insulation of thermal conductivity 0.06 W / mK, a thickness of 50mm limits the thermal losses to 0.24 kW / m 2 .
• Standard glass is opaque for wavelengths above 2.7 ⁇ m
• Figs. 4 and 5 show the optical spectrum of float glass for a thickness of 15mm and 4mm.
• Figures 4 and 5 show that the glass is transparent to 2.7 ⁇ m before becoming opaque beyond this wavelength.
• FIG. 6 shows the optical spectra of glass 4 mm thick (curve L1) and that of a blackbody at 38O 0 C (curve L2).
• the integral of the L2 curve of the black body between 0 and 2.7 ⁇ m represents a radiative flux of 0.36 kW / m 2 . It should be noted that for a temperature measured further upstream in the lehr, for example for a ribbon at 600 0 C, this flow would be even greater because of the shift of the curve of the black body.
• the installation made according to the invention comprises the second isothermal space 5 similar to the first to mutually cancel the losses in the optical window of the glass.
• Another method for eliminating the effect of the radiation loss through the ribbon is to correct the temperature measurement error with the aid of a thermal calculation means. This requires additional information on the optical properties of the glass and the radiation flux exchanged towards the opposite side of the ribbon.
• FIGS. 1 and 2 An example measuring installation made according to the invention is now described more specifically with reference to FIGS. 1 and 2.
• thermocouples TC, TC2 lined with a diameter of 1 mm for measuring the temperature of the two sides of the ribbon G; glass wool or mineral wool as insulation and a fixing system 6, 7. It should be noted that the measurement of the temperature in the isothermal space can be carried out by thermocouples or also by thermistors or other organs temperature measurement.
• the isothermal spaces 2, 5 have been shown only in Fig.1, but similar spaces may be provided in the device of Fig.2, although not shown.
• the glass wool 3 is flush with the ribbon about 10 cm in length in the direction of travel of the ribbon.
• the thickness M of the glass wool in the form of a sheet for example 50 mm, creates an isothermal space and avoids the convection of air between the ribbon and the glass wool.
• the thermocouple TC is positioned slightly downstream of the middle of the overlap zone, where the possible infiltrations of air are attenuated.
• the orientation of the thermocouple TC is preferably horizontal, parallel to the surface of the glass.
• thermocouple sheath CT is preferably upstream side. In this way, it avoids any risk of attachment of the tip on the surface of the glass.
• the design of the installation according to the invention is such that it does not disturb, or little, the annealing process of the glass.
• the realization is as follows.
• the installation consists of two subsets D1, D2 placed respectively on either side of the ribbon G, sufficiently symmetrical not to generate a temperature shift between the two sides of the ribbon.
• the subassemblies D1, D2 of the installation have a minimum length in the direction of travel of the tape to obtain the desired thermal and optical confinement. These confinements limit the cooling of the glass surface during its passage through the assembly. It is easily understood that the absence of a subset on one side of the ribbon would lead to a temperature shift between the two surfaces, the non-equipped side of a subassembly cooling normally.
• the length of the installation in the running direction of the ribbon is limited to that required to obtain the desired thermal and optical confinements so as to reduce the length over which the cooling of the glass is disturbed.
• the length L of the device is less than 200 mm.
• the thickness of the insulation is for example 50 mm.
• the installation must generate the least possible disturbance in the lehr. For this, it is important that its dimensions are reduced. Indeed, a too large dimension would lead to disrupting the convection flows in the drying room because of a restriction of the passage section, especially in the convective zones. It is advisable not to disturb the radiation exchanges in the radiative zones between the glass and the various walls of the drying room because of the significant obstacle to the radiation that would constitute a device too bulky.
• the thickness M of the insulator is limited according to the invention. Too little thickness of the insulation can lead to a significant temperature gradient between its two faces due to a greater heat loss. This loss will be all the stronger as the thermal conductivity of the insulation will be high. In order to maintain a good accuracy of the measurement of the temperature of the glass, the device according to the invention avoids this loss or takes it into account in order to correct the temperature of the measured glass.
• the thermal losses on the thickness of the insulator are suppressed by the addition of a heating device on the face 3a, 4a of the insulation 3, 4 opposite to that ribbon, for example an electrical resistance, so as to maintain the same temperature on both sides of the insulator 3, or 4.
• the taking into account of the losses is carried out by the calculation of the thermal losses in the insulator 3, 4 taking into account its thermal conductivity, the temperature measured in the hot face by the organ measurement TC, TC2 provided in the installation and that measured in cold face 3a, 4a of the insulation by the addition of at least one temperature measuring member, for example a thermocouple.
• the temperature of the glass measured by the installation is then corrected to take into account the influence of thermal losses in the thickness of the insulation.
• the loss losses are taken into account by calculating the thermal losses in the insulator by taking into account its thermal conductivity from the temperature measured in the hot face by the measurement TC, TC2 provided in the installation and estimating the cold face 3a, 4a of the insulation from the ambient temperature of the lehr to the location where the installation is located. The temperature of the glass measured by the installation is then corrected to take into account the influence of thermal losses in the thickness of the insulation.
• thermocouples calibrated.
• the space between two support rollers R1, R2 of the ribbon G makes it possible to install a bar 7 with several thermocouples TC2 along the width of the ribbon.
• a U-shaped bar 7 makes it possible to hold the fibrous isolate 4 and to fix the thermocouples TC2.
• An adjustment means (not shown) of the bar 7 in height makes it possible to adjust the device close to the glass. The position behind a roller protects the system against falling glass when the ribbon breaks.
• the upper device is suspended from a bar 6 which laterally crosses the space on the ribbon G.
• the flexible sheet 3 of a suitable length allows to cover a small length of the surface of the ribbon.
• This sheet 3 is composed of a flexible fabric with a lower face which makes it possible to fix flexible TC thermocouples.
• a thin fiberglass fabric is used in which TC thermocouples are integrated.
• On this fabric is placed a sheet of a fiberglass insulation of thickness M about 50mm.
• the diameter of the thermocouples is small, about 1mm, to ensure their flexibility.
• the contact zone 8 of the ply 3 is adjusted to the area covered by the lower insulator 4.
• the upper ply 3 can without any problem follow changes in the thickness of the ribbon G, provided that the overlap with the lower insulator remains correct. .
• thermocouples Implantation of thermocouples on the width of the ribbon
• the greatest temperature variations over the width of the ribbon are near the edges, especially if there is a difference in thickness between the edges or banks 9, 10 and the central portion 11 of the ribbon G.
• TC thermocouples In order to be able to trace the edge temperature profile which is typically 150mm wide for a thick ribbon, at least three TC thermocouples are needed. The distance between two of these successive TC thermocouples will therefore be about 3cm (30mm). Since the position of the edge typically varies by 300mm depending on the ribbon width produced, in this example, the implantation of ten TC thermocouples is performed on both sides of the ribbon. The number ten corresponds to the quotient of 300mm by 30mm.
• the total number of TC thermocouples per bar 6; 7 will be for example twenty six.
• Figure 7 shows an example of location of the thermocouples along the width of the ribbon.
• the information delivered by the measuring equipment can be used by the operators of the installation to manually adjust the operating parameters of the lehr.
• the temperature measurements can be displayed for the information of the operator of the lehr, for example in the form of curves showing the temperature profile over the width of the ribbon, so that to allow him to confirm the setting of the heating and cooling distributions operated on the lehr. It is also possible to record these values, especially for monitoring the quality of the product.
• the information delivered by the measuring equipment is used by an installation control system to automatically adjust the operating parameters of the lehr, via one or more control loops, by in particular for adjusting the heating and cooling of the glass in the running direction of the ribbon and its perpendicular direction.
• the regulation loop can be advantageously completed by a physical model of the annealing of the glass which, from the measurements made in one section of the lehr, allows the calculation of the instructions of the different zones upstream and downstream of the measurement section. , for heating and cooling the glass ribbon at each step of the glass annealing process.
• the physical model can advantageously exploit the temperature measurements delivered by the measurement equipment to estimate the stress levels in the glass and define their distributions in the ribbon width, thickness or length.

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• Physics & Mathematics (AREA)
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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Re-Forming, After-Treatment, Cutting And Transporting Of Glass Products (AREA)

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• 2006
  • 2006-06-27 FR FR0605769A patent/FR2902878B1/fr active Active
• 2007
  • 2007-06-25 CN CN2007800241909A patent/CN101479580B/zh active Active
  • 2007-06-25 WO PCT/FR2007/001047 patent/WO2008000939A1/fr active Application Filing
  • 2007-06-25 RU RU2009102544/28A patent/RU2447414C2/ru not_active IP Right Cessation
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