SE436196B - Process and apparatus for regulating the temperature of a glass sheet in an oven containing several successive cells - Google Patents

Abstract

The invention is a procedure for regulating the temperature of a glass panel in an oven with little thermal inertia, wherein the glass panel is heated following a predetermined program while it is moved at a specific rate. The presence of the panel is checked together with its incremental forward movement upstream of at least one cell of the oven in order to correct thermal output regulation. The invention is also a device with a pyrometer (24) positioned between two cells in order to perform the check. The invention makes it possible to limit scrapping by correcting regulation in the event of varying transport rate or gaps following the glass panels.<IMAGE>

Description

In another method, each cell is fed with constant electrical power and the rate of advancement of the glass sheets through the furnace is corrected if the furnace temperature deviates from a reference weapon (DE As 1 sas 382). It is also known, although in an oven where the glass sheets are continuously moved in a horizontal position, to measure their temperature at the exit-from the oven by means of an optical pyrometer and to regulate their rate of advance in the oven as a function of the detected deviations at the exit from In the desired value (DE OS 2 7HB 301). In this method, the control of the control is ensured by means of a microprocessor. On the other hand, the use of thyristor units for power control is equally classic and is described in patent DD Ps 78 780. Several of these known systems work satisfactorily in series production where glass sheets of the same size and mass are moved through the furnace at a constant rate. An approximate equilibrium is then established in the energy balance of the furnace 20. 7 The massive construction of currently used furnaces in fact imparts to them good insulation and strong thermal inertia, which leads to good stability in the heating, which becomes insensitive to external disturbances; on the other hand, these furnaces are not able to satisfactorily compensate for rapid disturbances in the working conditions.

I Under the influence of the control system, their average temperature oscillates slightly, but with a frequency considerably below the rate of advance of the glass panes. It follows that even when the temperature measurements are carried out inside the oven, the modifications of the temperature do not affect the glass sheets during treatment, but only take effect later.

Special difficulties with the regulation therefore occur in the event of disturbances of the energy equilibrium, connected 35 'for example, with incidents in the rate of movement of the wagons, i.e. the regularity of the advance of the glass sheets.It may also happen that one or more sheets come loose and fall, so that the transport trolley during its cycle passes through the oven empty, or with a smaller number of glass sheets than anticipated.

If such a gap occurs in the transport system, it is not possible to regulate the heating effect in the furnace cells in such a way that the immediately following glass sheet is heated to a suitable temperature. In general, several defective glass sheets come out before the oven has regained its balance.

Conversely, furnaces with low thermal inertia allow a faster response, but are sensitive to external disturbances.

The object of the invention is to improve the function of through-furnaces with rapid thermal response intended for the treatment of glass sheets in order to limit as much as possible the rejection when varying the speed of the transport system and or unforeseen gaps in the number of boards carried by the transport trolleys. In particular, in the event of the absence of a plate in the transport system, the power control must react in such a way that the glass plate immediately following the door shows the desired temperature at the oven exit.

According to a first feature of the invention, the presence of the glass sheet is checked synchronously with the step-by-step advancement upstream of at least one cell in the furnace and the regulation of the electrical power of the following cells as a function of the signal thus obtained is corrected.

The result is a pre-emptive regulation, where the power applied to a cell is determined before the disc is in it. This has the particular consequence that in the event of an unintentional absence of a glass plate, the power delivered to the cell is reduced before the empty transport trolley arrives there and creates an imbalance in the temperature. The method according to the invention can be practiced by means of a sensor or a reflective optical barrier. whether at the time determined by the operating program a glass plate is about to enter the cell. g According to another feature, not only is the presence of the glass sheet checked between two cells, but also its temperature is measured by means of a radiation pyrometer and the heating effect is regulated during normal work. in the following cells as a function of the measured temperature. 7 In order to eliminate the influence of the furnace walls on the measurement made with the pyrometer, an optical pyrometer with a relatively narrow measuring range directed towards an opening in the opposite wall of the furnace is advantageously used for this measurement of the glass plate temperature.

The method can also be refined by simultaneously using several optical pyrometers located opposite superimposed zones in each cell to regulate the heat output in sectors corresponding to the positions of the pyrometers.

A further development of the method according to the invention consists in measuring the temperature of the glass plate after its exit from the furnace by means of an optical pyrometer and also incorporating this measurement in the regulation of the heating effect in the furnace cells. It is particularly advantageous to introduce all the signals or measurement values coming from the different measuring means into a microprocessor which regulates the different sectors of the furnace or as a function of a predetermined program taking into account the entered given values. The method according to the invention leads to very good results, if for the construction of the furnace use fast-reacting heating elements as well as insulation materials with little thermal inertia. In particular, the heat modules marketed under the name "Fibrothal" can be used successfully, which are composed essentially of ceramic fibers with an active surface, the heating elements of which are fully or partially embedded, and whose insulating portion weighs only a fraction of the weight of the usual insulation materials. This leads to a low thermal inertia, which results in greatly reduced heating times and cooling times. Such heating elements with an insulation of small specific gravity and large insulating ability are thus particularly suitable for the construction of curing furnaces regulated according to the invention. The heating means need not be incorporated in the insulating mass but can be hung on a suitable support placed in front of the insulating body.

The control method according to the invention is explained in more detail in connection with a preferred embodiment thereof.

Figure 1 shows a schematic longitudinal section along the middle plane of a three-cell oven together with an enlargement of a detail.

Figure 2 shows a diagram of the control and measuring points as well as the treatment of the measured values when applying the method according to the invention.

"Figure 3 schematically shows the complete control circuit according to the invention. Although the example described relates to a three-cell oven, it is obvious that the method can also be applied to ovens with more or less than three cells. In large manufacturing plants they have use the ovens_us usually five, six or more cells.The procedure is of course applicable to these ovens, where it has the same advantages.

Figure 1 shows the essential parts of a three-cell oven in longitudinal section along the vertical central plane. The oven comprises a bottom 1 made of insulating material, wall elements 2 and 3 at the entrance of the oven and its outlet, which together form vertical gaps, vaulting element H, which likewise forms a gap, this to enable transport and passage of the discs, and side walls 5. The glass sheets & are hung in gripping pliers 9, which themselves are fixed in vertical frames These carriages, which are movable along a transport rail 13, placed above the furnace in the longitudinal direction, are moved by means of a mechanical mechanism (not shown) in a continuous manner, followed at a fixed rate and thus also the glass sheets are moved. 8..

The oven shown has three cells I, II, III. Each cell is occupied during normal operation of a glass plate.

The side walls of the cells consist of an assembly of wall elements 16 formed of plates of an insulating material of agglomerated ceramic fibers.

Heating means consisting of resistor 17, are incorporated in the insulating mass on its inner surface against the interior of the furnace; they emit energy through radiation. The wall of each cell is divided into three superimposed zones A, B and C, which extend over the entire length of the cell, enabling zoning zone in the same cell; An optical latch 20 is arranged in front of the oven entrance and an optical beam pyrometer is placed after the oven outlet.

Between cells I and II is a non-heated intermediate zone 22, where an opening 23 is occupied by the furnace wall. In front of this opening and on the opposite side of the oven there is a radiation pyrometer 24 (figure 3), the measuring zone of which is located opposite the opening 23, so that the temperature measurement is not influenced by the radiation from the oven wall. Similarly, in the unheated intermediate zone 25 between cells II and III, an opening has been provided through the furnace wall. Opposite this opening is on the other side of the furnace a pyrometer, the measuring zone of which faces the opening 261. The beam pyrometer 2a determines whether during the stepwise movement of the transport device a glass plate has really been transported from cell I to cell II and at the same time measures its temperature. at the time of entry into cell II. Similarly, the beam pyrometer 27 determines whether a carriage passing from cell II to cell III actually carries a glass plate, the temperature of which it measures at the moment it is introduced into cell III.

Each zone A, B and C. in each cell I, II and III, as shown schematically in Figure 3, is provided with thermocouples 30 to 38 positioned in such a way that the soldering point of each thermocouple is located in front of the radiating surface of the heating elements. and close to this. The thermocouples 30 to 38 provide a momentary measure of the temperature of the resistance heaters in each zone of the furnace cells. All the values determined by the measuring instruments, d, etc. the signal originating from the optical barrier ZÖ, the temperature values supplied by the pyrometers 2H, 27, 21 and the values given by the thermocouples 3Q-'38 are introduced into a microprocessor which, based on these input values, regulates the different heating zones of the cells as a function of a predetermined program. mm QUALITY- 10 15 20 30 35 i 0106276-2 7 The electrical power is delivered to each zone over a thyristor control circuit H0 (figure 3). The microprocess used for the control may be of a commercial type. for example, the CP 80 type from AEG, the 55 and 150 types from Siemens or the TSX 80 type from Télémécanique, so a more detailed description of the microprocessor components is superfluous; it is sufficient to indicate the functional form of the control device of a description of the various functions according to Figures 2 and 3.

To begin with, in connection with Figure 2, the principle for the interaction of the various measured variables and for the regulation is stated. The line 41 sends to the memory register H2 the rate that has been fixed for driving the transport wagons.

At the same time, the verification signals emitted by the optical reflection barrier 20 are recorded when a disk enters the detection zone of the barrier during the stepwise movement of the transport carriages. is located at the oven entrance. After reviewing the register, the corresponding signal is sent over lines H3, 44, H5 to the proportional integral controllers M6, f47, 48, where it is executed as follows: I If the optical barrier at the programmed time has not detected the presence of a glass plate, the level of the electrical power applied to cells I, II and III by the regulators 46 is lowered to a value determined by the program.

However, the reduction in power in each cell does not take place immediately, but with a delay corresponding to the time it takes for the carriage to reach this cell after the passage of the optical barrier.

If, on the other hand, the optical barrier 20 detects a glass plate in front of the furnace input, the regulators H6, H7 and 48 are actuated while transmitting lines # 3, HH and 45, so that in each cell for carrying out a normal heating program it is applied to normally at the intended time.

The thermocouples 30, 31 and 32 in the cell I control the controller H6 directly during the transmission of the line 50; acting on the heating element of the cell I of the cell I 10. In the same way, the thermocouples 33, 3H and 35 act directly through the line 51 on the regulator H7, which controls the power supplied to the heating element of the cell II, and the thermocouples 36, 37, 38 through the line 52 on the regulator 48, which supplies power to the cell III heating element .

To simplify the description, a single regulator 46, 47 and H8 are shown for each cell; it is a given that if zones A, B and C are regulated separately, a special regulator is required in each cell and in each zone.

The signal originating from the pyrometer 24 is transmitted partly, via line 55, to the counter_54, and partly through the line 57 to the proportional controller 58. In the counter 54, the presence of discs indicating the signals is counted. The values applied to each of the controllers 46, # 7 and 48 are determined as a function of the state of the counter, the connection of the register H2 making it possible to detect the absence of glass disk and cause the signals to advance and be transmitted in concordance with the rate of the furnace. . The measure transmitted by the proportional regulator 58 from the pyrometer 24 induces a proportional intervention in cells II and III during mediation of the regulators H7 and 48. In the immediately before the curing station, i.e. where applicable, after the elevation station, the beam pyrometer 21, is an overall control element. It once again measures the temperature in this critical range and acts through the proportional regulator 62 on each of the regulators H6, 47 and H8 in the three cells.

The use of the different center and control elements is also shown schematically in Figure 3. It can be seen that the counter SH, the register H2, the proportional controllers 58, 60, 62 and the proportional integral controllers 46, H7, -H8 are elements in the microprocessor, which as such can be controlled manually by line 6H or automatically by the optical latch 20, thermocouples 30 to 38 and the beam pyrometers 24, 27 and 21. Since the measured values are analog center and the microprocessor can process only numerical values, analog-to-digital converters 66, 68 arranged. Since not all values can be utilized co- 10 8106276-2 9. early, a cyclic switch 70 is connected to the converter 66, which sequentially and in the intended order transmits the measured values of the beam pyrometers. A cyclic switch 72 is connected in parallel with the Go converter, which periodically and in the intended order takes the measured values of each thermocouple.

By the proportional integral controllers 46, H7, H8 via the digital-to-analog converter 7H and the cyclic switch 76, the thyristor controllers summarized under the designation 40 are controlled, which supply each heating zone A, B, C in the three cells I, II, III below. individual regulation of the heating effect.

Claims (16)

ås fl oszvs-2 det L - ”'irl att 10 15 20 25 30 ö5 _10. IN PATENT CLAIMS A method of controlling the temperature of a glass sheet in a multi-successive cell comprising a rapid thermal reaction furnace, in which the sheet in the vertical position is moved from one cell to a next one at a fixed rate, to be heated to bending and / or or curing temperature, while the heating effect of each cell is regulated to a fixed level according to a predetermined program as a function of the wall temperature of that cell, it is felt and felt. checks the presence of the glass plate synchronously with the stepwise advancement upstream of at least one cell in the cell to obtain a signal, sun indicates the position of the glass plate in relation to the cell, and corrects the regulation of the electrical power of the following cells sm function of the received the signal. A method according to claim 1, characterized in that the presence of the glass plate is checked before entering the first furnace cell. IN A method according to claim 1 or 2; k ä n n e- t e c k n a t 'that the presence of the glass plate is controlled in a zone separating two furnace cells. I _ 4. A method according to claim 3, characterized in that the control is carried out by measuring the temperature of the glass plate by means of a beam pyrometer, which measurement is also used for regulating the heating effect in the following cells. 5. A method according to claim 4, characterized in that a beam pyrometer is used with a relatively narrow measuring range located opposite an opening in the opposite wall of the furnace. _ _ 6. »G. Presence according to any one of claims 3 to 5, characterized in that the presence of glašàiwæl is controlled at least in the intermediate portion between the first and the second cell during any measurement {of its temperature, 7. A method according to any one of claims H - 6, characterized in that the temperature of the glass sheet is measured in several vertically superimposed zones by means of several beam pyrometers arranged one above the other and in that the heating plate is measured in several vertically superimposed zones. The effect in the following cells is regulated separately in zones corresponding to the positions of the pyrometers as a function of the measured temperatures. ' IN Method according to one of Claims 1 to 7, characterized in that the control of the power in the cells located downstream of the cell following the measuring instrument is ensured by means of a memory register which in the control produces a delay corresponding to the time it takes for the glass plate to reach this cell. Method according to one of Claims 1 to 2, characterized in that the pulses emitted by the measuring instruments are compared with theoretical signals for the operating rate of the furnace, the heating program for all the cells being modified in the event of a deviation in the actual operating rate. , t «e1. in case of malfunction of the transport device. Method according to one of Claims 1 to 9, characterized in that the temperature of the glass plate is again measured at the outlet of the furnace by means of a beam pyrometer, this measurement serving as a parameter for the total regulation of the heat output of the furnace. _j 11. A method according to claim 10, characterized in that when the glass sheet is cured after bending at the outlet of the furnace its temperature is measured before entering the curing station, i.e. after the raising. Method according to one of Claims 1 to 11, characterized in that the signals emitted by the various measuring instruments are input to a microprocessor programmed for heating the furnace; 13. A method according to claim 12, characterized in that the temperature control program pours a count on the total passage of glass sheets, the registered power at the time of starting the oven being higher than during normal operation to compensate for the heat losses in contact with cold parts. j1N. A method according to any one of claims 1-13, 14. L o n n e t e c k a a t of the use of a furnace provided with rapidly reacting electric heating elements and with insulating materials of high insulating ability and weak thermal inertia. 15. A method according to claim 1, characterized by the use of heating elements incorporated entirely el =. partly in the surface of an insulating plate composed essentially of ceramic fibers with a specific gravity of about zoo kg / m3. '' Device for carrying out the method according to one of the preceding claims in a multi-cell vertical furnace (I, II, III) designed with low thermal inertia provided with a heating regulator served by temperature measurement signals emitted by thermocouples (30} .. 38 ) placed in the different cells in the middle of the heating element (16), characterized in that at least one optical pyrometer (2H) is placed in a space separating two cells and is connected to the controller for correcting the control f