Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B29/00—Reheating glass products for softening or fusing their surfaces; Fire-polishing; Fusing of margins
  • C03B29/04—Reheating glass products for softening or fusing their surfaces; Fire-polishing; Fusing of margins in a continuous way
  • C03B29/06—Reheating glass products for softening or fusing their surfaces; Fire-polishing; Fusing of margins in a continuous way with horizontal displacement of the products
  • C03B29/08—Glass sheets
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
  • F27B9/30—Details, accessories, or equipment peculiar to furnaces of these types
  • F27B9/36—Arrangements of heating devices
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
  • F27B9/30—Details, accessories, or equipment peculiar to furnaces of these types
  • F27B9/40—Arrangements of controlling or monitoring devices
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D21/00—Arrangements of monitoring devices; Arrangements of safety devices
  • F27D21/0014—Devices for monitoring temperature

Definitions

• the invention concerns an apparatus and method of controlled heating of glass sheets in a furnace, in particular for the tempering of the glass.
• the method according to the invention allows the control of the temperature on the whole surface of the glass sheet, apart from the particular cause of lack of thermal homogeneity and feed direction of the glass sheet.
• the patent EP 0564489 in the name of Tamglass Engineering Oy 1 filed on 20th of December 1991 describes a method for equalising the temperature profile of glass sheets in a furnace provided with rollers on which the glass sheets slide, wherein, in an already known way, the glass sheets are exposed to radiative, convective and conductive effects on both faces, and the upper surface of the glass sheets undergoes an intensified air convection at least at the beginning of the glass heating step, by means of air blowing-in pipes placed over the glasses.
• the patent EP 0564489 introduces the novelty that the air blowing-in pipes (that are transversal with respect to the feed direction of the glass) are controlled individually or in groups so as they are activated only in the zone wherein the glass sheets is present. For this reason, a longitudinal position sensor of the input glass sheet is present, as well as a calculator which calculates the glass position on the basis of the movement imposed to the last.
• the novelty introduced by the patent is that on the lower surface of the sheets the air is blown in by means of slanting jets directed towards the glass, which form an ingle of at least 5° with respect to an axis transversal to the glass; moreover, the air jets are oriented in the feed direction of the glass sheets and the nozzles of the air jets directed in such a way that their symmetry axis cuts through the surface of the lower face of the sheets beyond the median of the distance that separates the symmetry axis of two subsequent rollers.
• the upper heating elements and/or the lower heating elements are placed modularly in the two directions to cover the heating surface of the furnace and are individually controlled;
• each upper and/or lower heating element is continuously detected respectively by one or more corresponding upper and/or lower thermocouples in a zone that, when a glass sheet is travelling in front of the upper and/or lower heating element, is in the proximity of the glass sheet surface facing the relevant upper and/or lower heating element, - each upper and/or lower heating element is activated and regulated with respect to the heating power on the basis of said detected temperature value; so that each upper and/or lower heating element is activated only when a glass sheet travels in front of it and regulated with a power that is such as to obtain the desired heating of the zone covered by the same upper and/or lower heating element.
• the glass sheet heating relevant to each upper and/or lower module is additionally obtained by convection of air that is heated by the same heating element.
• each upper heating element is activated and regulated with respect to heating power on the basis of the value of the difference between the temperature detected by the said corresponding one or more upper thermocouples and a corresponding predefined nominal value.
• said predefined nominal value is equal for all the upper heating elements.
• each upper heating element is activated and regulated with respect to heating power on the basis of the time variation of said detected temperature value.
• each upper heating element is only activated with respect to heating power on the basis of the value of the temperature detected by said corresponding one or more upper thermocouple as above specified,
• upper master only one predefined upper heating element, called “upper master” is regulated with respect to heating power on the basis of the value of the temperature detected by said corresponding one or more upper thermocouples as above specified;
• each upper heating element except the "upper master" is regulated on the basis of the values of the temperatures detected by the said corresponding one or more upper thermocouples and said one or more thermocouples of the upper master.
• the lower heating elements are of the same type of, in the same number of, and are placed specularly to the upper heating elements to cover the heating surface of the furnace, and are individually controlled;
• each lower heating element is activated and regulated with respect to the heating power on the basis of the temperature value detected by the facing upper heating element; so that each lower heating element is activated only when a glass sheet travels above it and regulated with a power that is such as to obtain the desired heating of the zone covered by the same lower heating element.
• the lower heating elements are placed modularly in the two directions to cover the heating surface of the furnace and are individually controlled;
• the temperature value is continuously detected, by one or more corresponding lower thermocouples, in a zone that is in the proximity of the glass sheet surface facing the relevant lower heating element when the glass sheet is passing above the upper heating element,
• each lower heating element is activated and regulated with respect to the heating power on the basis of said detected temperature value; so that each lower heating element is activated only when a glass sheet travels above it and regulated with a power that is such as to obtain the desired heating of the zone covered by the same lower heating element.
• each lower heating element is activated and regulated with respect to heating power on the basis of the value of the difference between the temperature detected by said corresponding one or more lower thermocouples and a corresponding predefined nominal value.
• said predefined nominal value is equal for all the lower heating elements.
• each lower heating element is activated and regulated with respect to heating power on the basis of the time variation of said detected temperature value.
• each lower heating element is activated and regulated with respect to heating power on the basis of the time variation of said detected temperature value.
• each lower heating element is only activated with respect to heating power on the basis of the value of the temperature detected by said corresponding one or more lower thermocouples (260) as above specified, - only one predefined lower heating element, called “lower master” is regulated with respect to heating power on the basis of the value of the temperature detected by said corresponding one or more lower thermocouples as above specified; each lower heating element, except the "lower master", being regulated on the basis of value of the difference between the temperature value detected by said corresponding one or more lower thermocouples and the temperature value detected by said one or more thermocouples of the lower master.
• each lower heating element and each upper heating element is activated and regulated with respect to heating power on the basis of a combination of the temperature values detected in the proximity of the two glass surfaces so that the lower heating element and the upper heating element are activated only when a glass sheet travels in front of them and are regulated with such a power that one obtains the desired heating of the zone covered by the same lower heating element and upper heating element.
• the temperature value for each upper and/or lower heating element is obtained by the combination of the values detected by more upper and/or lower thermocouples.
• an apparatus for the control of the temperature profile of glass sheets in a furnace provided with transport rollers and comprised in a horizontal heating plant, in particular for glass tempering such an apparatus comprising lower heating elements and upper heating elements for the heating of the glass sheets along their horizontal path inside the furnace, characterised in that: the upper heating elements and/or the upper heating elements are a plurality of elements individually controllable and modularly disposed on a plane in the two principal directions so as to substantially cover the useful surface for the heating of glass sheets; each upper and/or lower heating element is respectively provided with one or more corresponding upper and/or lower thermocouples which protrudes from the same element and gets near to the zone of sliding of the glass sheets, there are comprised in the apparatus means for the activation and the power regulation of said upper and/or lower heating elements, each upper and/or lower heating element being activated and regulated, according to the method subject-matter of the invention, with respect to heating power on the basis of the temperature value respectively detected by said corresponding upper and/or lower thermo
• each upper and/or lower heating element further comprises means for the convection of air heated by the same heating element.
• each upper heating element comprises means for the blowing-in of the heated air on said glass sheets, said means comprising or being constituted by an input pipe of compressed air, a coil, disposed on an upper plane but near to said upper and/or lower heating elements, for the heating of the compressed air, and nozzles for the sending of the same air on the surface of the glass sheet.
• the compressed air feeding to said input pipe is regulated by suitable frequency flow rate regulators.
• suitable frequency flow rate regulators Preferably according to the invention, only one thermocouple for each upper and/or lower heating element is used, that respectively protrudes from the central region of the surface of each upper and/or lower heating element.
• the lower heating elements are constituted by air blowing-in pipes disposed transversely to the feeding direction of the glass sheets.
• - figure 1 shows a view of an embodiment of the apparatus according to the invention
• - figure 2 shows a detail of an embodiment of the apparatus according to the invention
• FIG. 3 shows a further view of an embodiment of the apparatus according to the invention
• - figure 4 shows an embodiment of the apparatus according to the invention.
• heating module will be used both to indicate the whole heating module of the glass sheets, to be included in the whole of the furnace for glass, and a single heating module which is arranged to heat only a zone of the glass sheet. The difference will be evident thanks to the context.
• the compressed air enters through the input duct 110 and passes through a horizontal coil 120, which contacts the ceramic material 140 which supports resistances 150. In such a way, the air is pre-heated.
• the ceramic material is shaped so as to leave uncovered the part of the resistances 150 turned to the glass sheet and rollers (not shown).
• the so pre-heated air is made flowing out in the direction of the glass sheets through the nozzles 130, in the particular embodiment illustrated six nozzles per module.
• the nozzles 130 in the particular embodiment illustrated six nozzles per module.
• one shows from above the composition of the upper modules 100. Only four of them are illustrated for the sake of simplicity.
• the coils 120 are visible.
• Each module is therefore powered and heated independently from the other modules. It is here to be specified that the modularity of the heating is on the two direction of the surface to be heated, therefore both horizontally and transversely at least two modules are present.
• thermocouples 160 indicated in figure 2 serve to detect the temperature of the glass sheet (not shown) which passes through the furnace on the rollers 300. In such a way, one can heat each module 100 as a function of the glass temperature detected in the zone of the glass sheet corresponding to the area projected by the heating module 100. The thermocouples are used at the same time to detect the presence itself of the glass sheet.
• the glass sheet is to be heated and therefore it will be always at a temperature lower than the pre-defined nominal temperature for the module 100.
• one of the modules 100 can define one of the modules 100 as a master module, for example at the centre of the furnace (whole heating module). Only with respect to this master module, the heating power will be regulated during time on the basis of the temperature difference between the thermocouple and the predefined nominal temperature, whilst all the other modules 100 will refer to the temperature detected by the thermocouple of the master module in order to be able to regulate their heating power during time.
• the thermocouple of the master module will refer to the temperature detected by the thermocouple of the master module in order to be able to regulate their heating power during time.
• we can obtain a better equalisation of the temperature profile of the glass, and most of all a temporal progression of the rotation, which is more regular, rapid and accurate.
• thermocouple detects the temperature of the air, then, where there is the glass that absorbs heat, the air has a lower temperature, therefore the program, in order to follow the master zone, provides more power to the interested zone.
• the power of a module 100 (module X) which is not the master module is given by:
• P x is the power of the zone of module X T x is the temperature of the zone of module X Ts is the pre-defined nominal temperature
• P M is the power of the zone of master module T M is the temperature of the zone of master module
• This methodology with the master module can be applied also to the lower modules 200.
• the master can be chosen only among the upper modules or only among the lower modules.
• thermocouples 260 in the lower heating modules 200.
• the information coming from the lower thermocouple 260 can be used for the control of the lower heating modules 200, which can be even of different nature with respect to the upper ones 100, or this information can be combined with the information coming from the upper thermocouples 160 to steer the upper and/or lower modules so as to guarantee uniformity of heating of the glass sheets, or impress particular deformation to the same.
• the lower modules 200 can also be constituted by pipes that are transversal to the glass feed direction (and comprising suitable nozzles for the blowing of the preheated air), as in the prior art, or be identical to the upper ones 100 according to the invention.
• FIG 4 one illustrates the whole heating module 1000, together with the compressed air feeding system.
• a compressor 2000 generates the compressed air, which then passes through a plenum chamber 3000 and arrives to distribution valves
• the compressed air is directed towards one or more frequency low rate regulators 5000, which determines the quantity of air let in in the coils 120 and therefore sent to the glass sheets 500 through the nozzles 130, 230.
• the lower modules can be powered also by another known system, but the whole is particularly effective using the solution of the present invention applied to the lower modules as well.
• An electronic central unit (not shown) elaborates the data coming from the thermocouples and steers the heating for each single (lower and/or upper) module. It is here to be specified thet even only upper heating elements or lower heating elements can be utilised.
• the last case is particularly adapted to the treatment of low-emissivity glasses, i.e. glasses with a covering material only the upper side. Indeed, in such a case the covering material reflects the rays and heats too rapidly with respect to what happens for the opposide side of the glass sheet, and therefore is convenient to measure the temperature in the neighbourhoods of the lower side.
• the modularity of the lower heating elements can be particularly advantageous still in the low-emissivity glasses case, since in such a case the detection of the temperature can be more precise.
• thermocouple too near to the glass sheet surface would not be convenient, due to the fact that the covering layer can be of different thicknesses. Instead, one can position the lower thermocouple very close to the lower surface of the glass sheet, for example 8 mm close to it, and this allows a more precise detection of the temperature.
• thermocouple is positioned between the rollers and this allows precisely to get close to the glass surface as above specified.
• each lower and/or upper heating element can be provided by more thermocouples; indeed, the relevant temperature values can be combined and the combination can be utilised for the activation and/or regulation of the same element.
• the solution according to the present invention allows to go beyond, all in one go, the partial solution of the prior art, because it allows, by means of a different system, to control the heating of the glass on different zones of the same, and therefore to guarantee a uniformity of upper/lower, longitudinal/transversal heating of the glass sheet.
• Such a uniformity is not even remotely possible to reach by the devices of the prior art because of the relevant limited technical solutions which, if on one hand improve a heating mode, on the other hand introduce technical problems and limitations to the control of the heating.

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

Applications Claiming Priority (2)

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Cited By (2)

Citations (7)

• 2008
  • 2008-02-14 IT ITRM20080079 patent/ITRM20080079A1/it unknown
• 2009
  • 2009-02-09 WO PCT/IT2009/000046 patent/WO2009101648A1/en active Application Filing

Patent Citations (7)

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