Abstract:
A roller comprises a thermocouple delivering a voltage signal which is converted by converting mechanism carried by the roller into a stabilized signal whose magnitude is independent of the resistance of the output circuit. The stabilized signal is transmitted to the fixed part of the measuring circuit by a device comprising slip rings and fixed collectors. The converting mechanisms are disposed in a case of the roller and provided with an air cooling device. The air is channelled in the case by annular supports and frames carrying the converting mechanism. Application in the measurement of the temperature of flat products travelling through a continuous annealing furnace.

Description:
The present invention relates to a roller for supporting and/or driving flat products or sheets comprising one or more temperature sensors constituted by thermocouples. 
     In the course of the manufacture of the sheet, the state of the latter is monitored by carrying out various measurements, for example temperature measurements. 
     It is known to carry out these measurements by incorporating at least one thermocouple in a roller supporting or driving the sheet. 
     To transmit the signal directly from the thermocouple to a fixed measuring apparatus located outside the roller, it is not possible to employ systems comprising slip rings and collectors. Indeed, this signal delivered by the thermocouple is a voltage of low value, of the order of a millivolt, and if one tried to transmit this signal through a set of rings and collectors, the signal would be excessively disturbed by electric pollutants created by the environment and variations in resistance in the circuit due to imperfect contacts between the slip rings and the collectors. The resulting measurement would totally lack precision. 
     DISCUSSION OF THE RELATED ART 
     In order to solve this problem, it has already been proposed, for example in the document U.S. Pat. No. 3,824,857, to convert in the rotating part the millivolt signal issuing from the thermocouple into a signal modulated in frequency and to transmit this frequency-modulated signal to the fixed part through rotating transformers or radio wave. 
     However, these systems are sophisticated and expensive and are not completely protected against possible exterior disturbances of the signal. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to transmit to the fixed part of the measuring circuit a precise signal insensitive to electric pollutants, by employing simple and consequently inexpensive means. 
     The invention therefore provides for a roller for supporting and/or driving flat products or sheets including at least one thermocouple, characterized in that the roller comprises converting means constituted, for each thermocouple, by a converter converting the voltage signal delivered by the thermocouple into a stabilized current whose value is independent of the resistance of the circuit in which this current flows, and a set of slip rings and fixed collectors the rings of which are connected to the outputs of the converters. 
     With the device according to the invention, the signal recovered on the fixed collectors and transmitted to the measuring circuit which is fixed with respect to the roller, is a current signal of a plurality of milliamps whose value is independent of the disturbances produced by the rings-collectors system and precisely reflects the voltage signal delivered by the thermocouple. 
     According to other features of the invention: 
     a connector is interposed between each thermocouple and the associated converter; 
     the roller includes air cooling means for the converting means; 
     the converting means are disposed inside a case and said cooling means comprise a cooling air inlet port provided in the wall of the case, and annular supports and frames in the vicinity of the axis of which the converting means are fixed, which define a path for the circulation of the air in the case. 
     The invention is also applied to a roller comprising a hollow cylindrical body whose outer surface cooperates by contact with the sheet, and at least one thermocouple disposed inside the cylindrical body and having one end or hot junction disposed in the wall of the cylindrical body in the vicinity of the outer surface of the latter, characterized in that the thermocouple is removably passed through a guide tube which extends inside the hollow cylindrical body and has an end opening onto a blind hole in the wall of the cylindrical body constituting a cavity for the hot junction. 
     According to other features of this roller: 
     the end of the guide tube through which the hot junction extends is fixed to the inner surface of the cylindrical body by a connector whose first end or base is soldered to the inner surface of the cylindrical body and whose second end or spigot is soldered to the guide tube; 
     the characteristics of expansion of the material of the connector are substantially equivalent to those of the material of the cylindrical body; 
     the end of the guide tube through which the hot junction extends and the blind hole forming a cavity for the hot junction are substantially perpendicular to the wall of the hollow cylindrical body; 
     the guide tube is mounted with clearance, inside the roller, in supports and staples connected to the roller, and 
     sealing means seal off the gases contained in the hollow cylindrical body from the converting means. 
     The invention also provides an annealing furnace for the continuous treatment of flat products or sheets employing at least one roller according to the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the invention will now be described hereinafter with reference to the accompanying drawings in which: 
     FIG. 1 is a partial diagrammatic longitudinal sectional view of a sheet-driving roller; 
     FIG. 2 is a detail sectional view of the part of FIG. 1 delimited by dot-dash lines and designated by the reference numeral 2; 
     FIG. 3 is a detail view of FIG. 1 showing a first support of a guide tube; 
     FIG. 4 is a sectional view taken on line 4--4 of FIG. 3; 
     FIG. 5 is a detail view of FIG. 1 showing a second support of the guide tube; 
     FIG. 6 is a sectional view taken on line 6--6 of FIG. 5; 
     FIG. 7 is a cross-sectional view of the guide tube disposed in a staple; 
     FIG. 8 is a cross-sectional view of the guide tube disposed in a support and a staple; and, 
     FIG. 9 a partial longitudinal sectional view of an electromechanical device disposed at one end of the roller. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a sheet-driving roller 10 employed in an annealing furnace of a continuous treatment installation. This roller 10 comprises a hollow cylindrical body 12 including a straight cylinder 14 having opposite ends respectively closed by two plugs 16 defining a neck. Owing to the symmetry arrangement, only one of the plugs 16 is shown, namely that placed at the right end of the cylinder 14 as viewed in FIG. 1. The cylinder 14 has, in the presently-described embodiment, a length of 1,800 mm, a diameter of 600 mm and a wall 20 mm thick. The outer surface of the wall of the cylinder cooperates with the sheet by contact. The plugs 16 are respectively welded to each end of the cylinder 14 in the region of their largest diameter and comprise a shaft 18 which is mounted in the end of the respective plug 16 in the region of the smallest diameter of the plug. The plugs 16 extend through a wall 20 defining the enclosure of the furnace. The bearings carrying the shafts 18 and the means for controlling and driving the roller are located outside the furnace and are not shown in the Figures. Ports 22 extending in a direction roughly perpendicular to the walls of each plug put the interior of the hollow cylinder 12 in communication with the atmosphere of the furnace for homogenizing the hot gases in the roller 10 and in the furnace. 
     The shaft 18 shown in FIG. 1 is stepped and defines cylindrical portions whose diameters decrease in the direction of the free end of the shaft. The free end of the shaft includes a stepped axial bore 24 and an electromechanical device which is shown in FIG. 9 and will be described hereinafter. 
     Extending through the shaft 18 on the axis of the latter is a conduit 26 in which is partly disposed a guide tube 28 adapted to receive a temperature sensor, namely a thermocouple. The guide tube 28 extends from the stepped bore 24 of the shaft 18 to the wall of the cylindrical body 12 where it is fixed roughly in the region of the median transverse plane 30 of the roller shown in dot-dash lines in FIG. 1. In the presently-described embodiment, the guide tube 28 is of stainless steel. It has a diameter of 6 mm and its wall has a thickness of 1 mm. The means for positioning the guide tube inside the cylindrical body 12 will be described in more detail hereinafter. 
     FIG. 2 shows how the end of the guide tube 28 is fixed to be perpendicular to the wall of the cylindrical body 12 by a connector 32. This connector has a generally cylindrical shape and consists of two cylindrical portions 34, 36, one of which is of large diameter and is termed a base 34 welded to the inner surface of the cylindrical body 12, whereas the other is of small diameter and is termed a spigot 36 which is welded to the guide tube 28. The connector 32 is preferably composed of a material having the same coefficient of expansion as the wall of the cylindrical body 12 so as to optimize the strength of the fixing of this connector to the wall of the cylindrical body 12 and avoid in this wall the creation of stresses which would otherwise result from differential expansions. 
     The end of the guide tube 28 extends through the connector 32 and opens onto a blind hole 38 provided in the wall of the cylindrical body 12 in a position perpendicular to this wall. In the illustrated embodiment, the inner end of the blind hole 38 is at 3 mm from the outer surface of the cylindrical body 12. However, this distance may be reduced to 1 mm by employing an apparatus capable of precisely measuring thickness for the machining of the blind hole. With reference to FIG. 2, it can be seen that the upper end of the blind hole 38 has an inside diameter adapted to receive the end of the guide tube 28, and the lower end of the blind hole has a smaller inside diameter less than the diameter of the guide tube 28 and is adapted to receive the end of a thermocouple 39 constituting the hot junction. A shoulder 40 which constitutes the boundary between the two parts of the blind hole 38 whose inside diameters are different has a rounded shape to facilitate placing the end of the thermocouple in position in the inner end of the blind hole 38 and avoid initiating any fracture. 
     FIGS. 3 to 8 show in more detail the mounting of the guide tube inside the roller 10. FIG. 3 shows how the guide tube 28 is positioned in the cylindrical body 12 by means of a first support 42 in the form of a plate. This support 42 is disposed in a longitudinal plane of the hollow cylindrical body 12 and is fixed by a longitudinal edge to the inner surface of the hollow cylindrical body 12. A groove 44 is provided in the free edge of the support 42. The section of the groove 44 is shown in FIG. 4. The width and depth of the groove 44 are adapted to receive the guide tube 28 with clearance. The contour of the edge of the support 42 in which the groove 44 is provided defines curved shapes which give predetermined orientations to the guide tube 28. Thus, as viewed in FIG. 3, the end of the guide tube extends out of the groove 44 on the left side of the support 42 in a direction perpendicular to the wall of the cylindrical body 12. Likewise, the guide tube 28 extends out of the groove 44 on the right side of the support 42 in a direction roughly parallel to the wall of the cylindrical body 12. 
     Shown in FIG. 5 is a second support 46 for the guide tube 28, in the form of a plate which is contained, as the foregoing plate, in a longitudinal plane of the cylindrical body 12. This support 46 is fixed by an edge to the inner surface of the plug 16 of the cylindrical body 12. As for the previously-described support 44, a groove 48 is provided in the free edge of the support 46. The section of the groove 48 is shown in FIG. 6. The contour of the edge of the support 46 defines curved shapes whereby predetermined orientations may be given to the guide tube 28 which is received in the groove 48 without clearance. Thus, with reference to FIG. 5, although the guide tube 28 is not shown in this Figure, it will be understood that, on the left side of the support 46, the guide tube 28 extends out of the groove 48 and is roughly parallel to the wall of the cylindrical body 12, and, on the right side of the support 46, the guide tube 28 extends out of the groove 48 and is roughly on the axis of the conduit 26 of the shaft 18. 
     As already seen in FIG. 1, the guide tube 28 extends between the two supports 42, 46 alongside the wall of the cylindrical body 12. FIG. 7 shows one of the staples 50, termed short-branch staples, maintaining the guide tube 28 against the wall of the cylindrical body 12 between the two supports 42, 46. These staples 50 are fixed to the inner surface of the wall of the cylindrical body 12 by welding. The guide tube 28 is maintained closely between the staple 50 and the inner surface of the wall of the cylindrical body 12. 
     Shown in FIG. 8 is one of the staples 52, termed long-branch staples, disposed in a transverse position with respect to the groove 44 of the support 42. Long-branch staples 52 are also disposed on the support 46 in a manner similar to that shown in FIG. 8. It can be seen that, in distinction to the short-branch staples 50 shown in FIG. 7, the long-branch staples 52 maintain the guide tube 28 in the groove 44 with clearance. The guide tube 28 is therefore maintained with clearance between the walls of the grooves 44, 48 and the staples 52 to permit small displacements of the guide tube due to its expansion. 
     The thermocouple is disposed inside the roller 10 by passing it through the guide tube 28 when the roller has been placed in position in the furnace. However, the machining of the blind hole 38 where the hot junction of the thermocouple is received, and the fixing of the guide tube 28 inside the cylindrical body 12 must be carried out before fixing together the various elements constituting the roller 10, in particular the straight cylinder 14, the end plugs 16 and the shafts 18. 
     Only a single guide tube 28 is shown in the roller 10 in the Figures. However, it will be clear that other guide tubes 28 for thermocouples may also be placed in a similar manner in the roller 10. Preferably, three thermocouples are placed in the roller 10 and disposed respectively in three guide tubes 28. This permits dynamically balancing the roller 10 which is driven in rotation. The hot junctions of the thermocouples are for example disposed in the median transverse plane of the roller 10. However, they may also be disposed at any point of the wall of the roller. 
     When the roller 10 has been placed in position in the furnace, the thermocouple is passed through the guide tube 28 at the end of the latter which opens onto the stepped bore 24 of the shaft 18. The body of the thermocouple is urged so as to place the hot junction in position at the inner end of the blind hole 38 of the wall of the roller, at the other end of the guide tube 28. 
     FIG. 9 shows the end of the shaft 18 on which there is fixed an electromechanical device 54 connected to the thermocouple. The device 54 is disposed inside a case 56 fixed by screws 58 to a cover 60 connected to a fixed bearing (not shown) carrying the shaft 18. The end of this shaft 18 extends through the cover 60 in the region of an axial opening 62 in this cover. A wearing ring 64 is fitted on the end of the shaft 18 in the region of the opening 62 of the cover 60. A lip sealing element 65 provides a seal between the wearing ring 64 and the cover 60. 
     FIG. 9 shows a single guide tube 28 extending out of the conduit 26 in the stepped bore 24 and a single thermocouple 39 disposed in the guide tube 28. The thermocouple 39 is for example of the Chromel Alumel type. As already mentioned, preferably three thermocouples and therefore three guide tubes 28 are provided in the roller 10. They are assembled in a manner similar to that described hereinbefore. 
     As already seen in FIG. 1, the conduit 26 puts the interior of the hollow cylinder 12 in communication with the stepped bore 24. Consequently, the hot gases which are inside the cylindrical body 12 can reach the stepped bore 24 via the conduit 26. Sealing means 67 seal off the electromechanical device 54 from the hot gases contained in the furnace and the roller 10. These sealing means 67 comprise an annular spacer member 68 disposed in the stepped bore 24, an O-ring seal 70 located between the inner end of the stepped bore 24 and a first end of the spacer member 68, and a sealing disc 72 disposed between the second end of the spacer member 68 and a clamping nut 74 screwed in the stepped bore 24. The thermocouple 39 is passed through an adjustable connector 76 extending through the sealing disc 72. The thermocouple 39 is jammed in the connector 76 which thus maintains it in a position extending into the guide tube 28. 
     The electromechanical device 54 will now be described. This device comprises an assembly of annular supports 78, 79, 80 which are in juxtaposed relation and fixed to the shaft 18 by screws. The supports 78, 79 close to the shaft 18 respectively comprise two complementary elements 82, 84 of a miniature connector 85, for example of the type manufactured by the first. Thermo Electric under the reference CNN-21 200.KX. The connector element 82 is connected to the thermocouple 39. The connector element 84 is connected to means for converting the signal delivered by the thermocouple, namely a converter 86. The function of the converter 86 will be subsequently explained. It can be seen in FIG. 9 that the electromechanical device 54 includes two other identical converters 86 for two other thermocouples, the electric connecting wires and the corresponding connectors of which have not been shown. The three converters 86 are respectively disposed on annular frames 87, 88, 89 fixed to the support 79 by screws. The converters 86 are placed on the axis of the annular frames. 
     The output of the converters 86 is connected to a device 90 comprising slip rings 91 and collectors or brushes 92 of known type. The rings 91 are fixed to the support 80 which is secured to the shaft 18. The collectors 92, only one of which is shown in FIG. 9, are fixed to a support 94 carried by ball bearings 96 arranged between the support 94 and the ring support 80. The collector support 94 is prevented from rotating by a screw 98 which is screwed into the latter and has a stem portion extending through an oblong slot 100 in the case 56. This slot 100 allows the fixing screw 98 to travel in a direction parallel to the axis of the roller 10 as a result of expansion of the latter. 
     The converters 86 convert the voltage signals (0 to 18 mV) delivered by the thermocouples, before their transmission through the ring and collector device 90, into stabilized currents whose magnitude is solely dependent on the magnitudes of said voltages and are consequently independent of any variations in resistance (line resistances or contact resistances) of the output circuits of the converters. In the presently-described embodiment, the outputs of the converters deliver a current of between 4 and 20 mA linearly corresponding to temperatures of 0° to 1,000° C. In this way, the output current of the converters is insensitive to electric pollutants created by the contacts between the rings and the collectors. The ring-collector devices may consequently be of ordinary construction with no necessity to use an assembly of sophisticated and consequently costly collectors. Precise temperature measurements are in this way obtained. Further, the outputs of the converters at 4 to 20 mA are standardized and consequently data delivered by the thermocouples can be sent to a standard system receiving and processing numerical data for regulating the furnace. The measured signal can be directly utilized at the output of the set of collectors or can be sent through a single telephone line, with no other electronic processing, to a plurality of receivers, if need be, and at a great distance. 
     Owing to the use of the connector 85 connected to each thermocouple 39, the assembly comprising the converters 86 and the ring and collector device 90 is easily dismantled without having to move the thermocouples 39 relative to the roller 10. 
     The means for cooling the electromechanical device 54, in particular the converters 86 whose operation requires moderate temperatures, will now be described. A port 102 provided in the case 56 in the vicinity of the end of the shaft 18 provides a cooling air inlet. The air is brought to this air inlet port 102 by a supply device of known type (not shown in the drawing). In the case 56, the air is channelled by an annular sealing element 104 disposed between the support 78 and the case 56, to a radial duct 106 provided in the connector support 78. The annular shapes of the supports 78, 79, 80 and the converter frames 87, 88, 89 ensure a circulation of cooling air in a substantially axial path in the case 56. The cooling of the converters 86 optimized by throughway axially extending passages 108 provided in the converters. 
     To replace a thermocouple, it is sufficient to dismantle the case 56 and the electromechanical device 54, then extract the thermocouple by pulling on the latter at the connector 76. Another thermocouple can be placed in position by passing the latter through the connector 76 and through the guide tube 28 one end of which is in the vicinity of the connector 76. 
     Further, the converting means may be incorporated in any type of roller which carries or drives the sheet during a sheet manufacturing process. These rollers may be disposed in some place other than the annealing furnace, for example upstream or downstream of the latter with respect to the direction of travel of the flat product in the product manufacturing process.