EP1647791A1 - Contactless temperature measuring device for melting furnaces - Google Patents

Abstract

A contactless melting oven crucible (2) temperature measurement unit has a pyrometer (5) with sensor (6) using optics aimed at part of the crucible by a sample glass (18) connected to the upper end of a tube extending (22) into the oven melt zone (11).

Description

The invention relates to a device for non-contact measurement of the temperature of a melting in a crucible in a melting furnace, in particular the investment casting technique, by means of a pyrometer, which has an optical system and at least one visually connected to the optics sensor, the optics by a Sight glass can be aligned on at least a portion of the crucible.

Such contactless temperature measuring systems for the precise determination of the temperature of a melt in a melting furnace of the investment casting technique, in particular dental technology, are known, for example, from EP 1 440 750 A1.

Fig. 1 shows such a known device 1 for carrying out a melting and casting process of investment casting technique, as used in particular in the dental technology of dental laboratories. The device has a crucible 2 for receiving (not shown) melt and a Heating device 3 for heating the melt in the crucible 2 located on. Below the crucible 2 and the heater 3 is a mold 4, in which liquid melted material can be poured from the crucible 2, for example, to produce dental bridges, dental crowns or other products of investment casting.

To give the melt from the crucible 2 in the mold 4, one half of the two-part crucible 2 is raised, so that in the lower region of the crucible, an opening is formed, from which the melt can pour into the mold 4.

During such a casting process, the particular current temperature of the melt is of particular interest for many products, in particular products of investment casting technology. This temperature is measured without contact by means of a pyrometer 5. The pyrometer 5 has a working in the infrared region sensor 6, which is connected via an optical waveguide 7 with an optical system 8. The sensor 6 is coupled via optoelectronic components to electronics 9 of the pyrometer 5, which converts optical signals or light signals into electrical signals, from which the radiation power detected by the sensor 6 can then be converted into a temperature value. The optics 8 is housed within a hinged folding panel 10, which allows insight into the interior 11 of the melting device 1 (melting space). In order to protect the pyrometer optics 8, in particular from excessive heat, a melting chamber window 12 is provided, which separates the melting chamber 11 from the pyrometer optics 8.

It has been found that in the melting of some alloys to measurement inaccuracies, since the melting chamber window 12 is polluted by flue gases. Volatile metal components with a low boiling point, such as zinc, as well as fumes of molten powder are responsible for deposits on the melting chamber window 12. Although these deposits can be easily removed on a regular basis, some users tend to disregard the intended cleaning intervals. This then has erroneous measurement results and ultimately a detrimental effect on the quality of the manufactured products.

The invention is therefore based on the problem of reducing such impurities.

The invention solves this problem in a device of the type mentioned in that the device comprises a tube which adjoins the sight glass in the region of its upper end, extends into a melting chamber of the melting furnace and can be aligned in the direction of the crucible.

The invention is based on the finding that smoke particles are carried by the hot melt by convection to the top of the melting chamber, where they precipitate. However, so that the smoke particles do not precipitate on the viewing window of the pyrometer optics, it is advantageous to prevent this convection in the region of this viewing window, but at least to minimize significantly.

The invention has also recognized that by means of a long tube with the smallest possible internal cross section, an air flow within the tube can be almost completely avoided. By preventing such an air flow, the supply of smoke particles in the region of the sight glass of the pyrometer optics is prevented, so that the sight glass remains largely unaffected by smoke particles before the pyrometer optics.

Another advantage of the tube is that there is much less smoke in the field of view of the sensor, since the tube does not fill or only very little with smoke. Since such smoke or the corresponding flue gases can affect the view of the pyrometer sensor on the melt, a reduction of the smoke in the optical path from the melt to the pyrometer optics is particularly advantageous.

By the measures according to the invention, the temperature measurement can be significantly improved with an optically operating pyrometer.

Particularly preferably, the upper end of the tube is sealed gas-tight by means of the sight glass, while the lower end of the tube is open. A gas-tight seal of the upper tube end prevents any convection flow within the tube, even at the bottom open tube end. A downwardly open pipe end is advantageous because a precipitation surface for smoke particles would likewise form at a possible termination by means of a further glass body at the lower end of the pipe.

In a further preferred embodiment, the cross-sectional area of the tube is substantially as large as the cross-sectional area of the measuring spot of the pyrometer. This achieves the lowest possible pipe cross-section. This is advantageous because it allows very little smoke to enter the space inside the pipe.

In a further preferred embodiment, the length of the tube is dimensioned such that the lower tube end is below a portion of the melting space, which fills with smoke when a predetermined amount of melt is melted in the furnace. As hot gases rise, first the upper part of the melting chamber is filled with smoke, as far as smoke particles can reach this upper space by convection. In the region of the tube, however, such convection does not take place or only to a very small extent, so that no or only very few smoke particles can enter the interior of the tube, in particular if the smoke particles can move into other areas of the melting space. The longer the pipe is, that is, the lower the lower end of the pipe, the larger the space that can be filled with smoke particles from the hot melt.

In a particular embodiment, the tube length is dimensioned such that the lower tube end terminates in the region of the upper edge of the crucible or the melt. By this measure one reaches a particularly long Pipe length with particularly low contamination properties for the sight glass of the pyrometer optics.

Fig. 1

eine Vorrichtung zur berührungslosen Messung der Temperatur eines sich in einem Schmelztiegel befindenden Schmelzguts in einem Schmelzofen gemäß dem Stand der Technik;

Fig. 2

eine Vorrichtung zur berührungslosen Messung der Temperatur eines sich in einem Schmelztiegel befindenden Schmelzguts in einem Schmelzofen gemäß einem Ausführungsbeispiel der Erfindung in einer vereinfachten Darstellung;

Fig.3

eine Schnittansicht eines ersten Ausführungsbeispiels einer erfindungsgemäßen Vorrichtung;

Fig. 4

eine Schnittansicht eines zweiten Ausführungsbeispiels einer erfindungsgemäßen Vorrichtung;

Fig. 5

eine perspektivische Explosionsansicht des in Fig. 4 gezeigten Ausführungsbeispiels;

Fig. 6

eine Überwurfmutter zur Verwendung in einem der in den Fig. 3 bis 5 gezeigten Ausführungsbeispiele;

Fig. 7

ein Schauglas zur Verwendung in einem der in den Fig. 3 bis 5 gezeigten Ausführungsbeispiele;

Fig. 8

ein Rohrstück zur Verwendung in einem der in den Fig. 3 bis 5 gezeigten Ausführungsbeispiele,

Fig. 9

eine Schauglasplatte zur Verwendung in einem der in den Fig. 3 bis 5 gezeigten Ausführungsbeispielen und

Fig. 10

eine Schnittansicht einer Schauglasplatte samt Befestigungsanordnung zur Verwendung in dem in Figur 2 gezeigten Ausführungsbeispiel.

Further particular embodiments will become apparent from the dependent claims and from the illustrated with reference to the accompanying drawings embodiments. In the drawings show:

Fig. 1

a device for the non-contact measurement of the temperature of a melt in a crucible in a melting furnace according to the prior art;

Fig. 2

a device for non-contact measurement of the temperature of a melting in a crucible in a melting furnace according to an embodiment of the invention in a simplified representation;

Figure 3

a sectional view of a first embodiment of a device according to the invention;

Fig. 4

a sectional view of a second embodiment of a device according to the invention;

Fig. 5

an exploded perspective view of the embodiment shown in Figure 4;

Fig. 6

a cap nut for use in one of the embodiments shown in Figures 3 to 5;

Fig. 7

a sight glass for use in any of the embodiments shown in Figs. 3 to 5;

Fig. 8

a tube piece for use in one of the embodiments shown in FIGS. 3 to 5,

Fig. 9

a sight glass plate for use in one of the embodiments shown in FIGS. 3 to 5, and

Fig. 10

a sectional view of a sight glass plate including mounting arrangement for use in the embodiment shown in Figure 2.

FIG. 2 shows a device 1 for non-contact measurement of the temperature of a melt within a melting furnace, which largely corresponds to the device 1 shown at the outset with reference to FIG. To avoid repetition, reference is made to the features explained there, unless otherwise stated below. In that regard, in Fig. 2, the same reference numerals have been used as in Fig. 1. In particular, reference is made to the explanations to those mentioned by the reference numerals 1 to 11 elements of FIG.

However, the following is further supplemented: the right half of the crucible 2 is mechanically coupled for the purpose of opening the crucible with an actuator 13 which is capable of the right (or in an alternative, not shown embodiment, the left, front or rear) Half of the crucible 2 to raise and lower. The actuating device 13 is connected to a control device 14 in such a way that the control device 14 can automatically initiate the opening of the crucible and thus the casting process.

Alternatively, however, the casting process can also be brought about by tilting an integrally formed crucible. For this purpose, an actuating device is also provided, which, however, can cause a tilting movement of the crucible. Such an actuating device is also connected to the control device 14.

The controller 14 further controls a generator (not shown) which supplies the heater 3 with electric power.

The temperature determined by means of the pyrometer 5 is fed to the control device 14, which controls or regulates the melting and casting process as a function of the determined temperature. The control device 14 has an input unit 15 for the input of melting material identification parameters and other input variables and process variables. Further, the controller 14 has a display 16 for displaying data or process data input to the user.

The melting chamber 11 is formed as a pressure chamber. Before and during a casting process, this pressure chamber 11 is evacuated so that a vacuum is created within the pressure chamber 11. Such a vacuum during a casting operation is advantageous because the oxide formation is reduced due to the reduced oxygen content. After the melt has been placed in the mold 4, however, an overpressure is generated within the chamber 11 in order to press the melt into all areas of the mold 4. For this purpose, the chamber 11 is connected to a vacuum / overpressure pump (not shown), which together with the control device 14 can set the underpressure or overpressure in the chamber 11.

In the device 1 explained above, the sensor 6 was coupled with an optical system in the region of the melting chamber 11 with the interposition of an optical waveguide 7. This arrangement can also be used in connection with embodiments according to the invention. Alternatively, according to the invention, the sensor 6 can also be arranged directly without interposition of an optical waveguide 7 in the immediate vicinity of the melting chamber 11, in particular if no mobility between the optics and the sensor is required.

Unlike the apparatus shown in Fig. 1 is located within the melting chamber 11 directed from above the bottom of the crucible 2 pipe section 17, which adjoins a sight glass 18 and by means of a Nut (eg hex nut) 19 is attached to a sight glass plate 20. The sight glass plate 20 is, for example, directly or indirectly connected to an upper, preferably hinged housing wall GW of the melting chamber, for example by means of a screwed connection piece 42 fastened to the housing wall GW, to which the sight glass plate 20 is screwed by means of a lock nut 21. Details of the mounting of the sight glass panel will be explained below. Alternatively, other closure possibilities of the sight glass panel 20 are provided on the upper housing wall GW of the melting space 11.

Above the sight glass 18, the likewise hinged folding panel 10 connects, which in turn has one or more tinted sight glasses through which the optics 8 extends. This hinged cover 10 is attached to one of the upper housing wall GW of the chamber 11 associated, substantially horizontally oriented metal panel BB.

The lower tube end 22 is arranged so deep that it lies below a portion 23 of the melting chamber 11, which fills with smoke 24 when a predetermined amount of molten material has been melted in the furnace. In this way, the optical path between the pyrometer optics 8 and the lower tube end 22 and thus substantially also the melt substantially free of smoke, which otherwise could adversely affect the measurement of the temperature of the melt.

The sight glass plate 20 serves to additional visual control of the events within the furnace. However, thanks to the automation of the melting and casting process, which is aided by the invention, visual inspection is dispensed with, so that in one alternative embodiment the sight glass plate 20 can be replaced by a simple, non-transparent plate.

The tube piece 17 extends through the sight glass plate 20, which has for this purpose a bore or recess with a pipe section 17 corresponding cross-section. Alternatively, however, the pipe section 17 of The underside of the sight glass plate 20 beginning to extend downwards and, for example, be glued on this underside. The optical path from the pyrometer optics 8 to the melt would then pass through the sight glass plate 20.

Fig. 3 shows the central part, by means of which the pyrometer optics (not shown) via the pipe section 17 with the melting chamber 11 is optically connected. The pipe section 17 extends through a bore or recess through the sight glass plate 20. The pipe section 17 has in the region of its upper end a circumferential projecting portion 25 with an outer diameter which is greater than the diameter of the underlying pipe section, through the Sight glass plate 20 passes.

This lower tube section has an external thread 26, on which the nut 19 can be screwed, which with the interposition of, for. two, plate springs 28, the pipe section 17 with its upper circumferential projecting portion 25 in a recess 29 of the sight glass 20 draws. For sealing is located between the circumferential projecting portion 25 and the recess 29, a sealing ring 30th

In the region of the upper tube end 31 above the peripheral projecting portion 25 is a section with an external thread 32 for screwing a union nut 33. In the region of the upper tube end 31, the tube piece 17 in the interior of the tube has a relation to the underlying inner tube section enlarged cross-section, which serves to receive the sight glass 18. This sight glass has a substantially equal cross-sectional area, so that a seal from the interior of the melting chamber 11 is achieved to the environment. By tightening the nut 33, the sight glass 18 is pressed in the interior of the upper end portion 31 against a sealing ring 34, which in turn is supported on a projection 35 in the interior of the pipe section 17.

The construction described above also serves as a burst protection for the protection of the sight glass plate 20, since the disc springs 28 in conjunction with the sealing ring 30 form a pressure relief valve: Once inside the melting chamber 11 has formed a certain pressure, the pipe section 17 is pressed axially outward, ie in the illustration in Fig. 3, the pipe section 17 is lifted upwards. The plate springs 28 are compressed and at the same time the sealing ring 30 relaxed. When a certain limit pressure is reached, the sealing ring 30 no longer or no longer completely seals the pipe section 17 against the sight glass plate 20, so that the overpressure in the melting chamber 17 can escape to the outside. As soon as the pressure has fallen below the limit again, due to the restoring force of the disk springs 28, the sealing ring 30 will again seal the pipe section 17 against the sight glass plate 20, so that the melting chamber 11 is sealed against the environment. The construction of the pipe section 17 in conjunction with the disc springs 28 and the sealing ring 30 in this way allows a simple overpressure control, which limits the pressure in the melting chamber 11 to a maximum allowable pressure. This limit value of the overpressure, at which the overpressure escapes, is set by the choice of the disc springs 28 and in particular by the number of springs 28 and by the bias generated by the nut 19.

FIG. 4 shows a further exemplary embodiment which largely corresponds to the exemplary embodiment shown in FIG. 3. For identical components, therefore, the same reference numerals have been used. Concerning. these same components will be referred to the above explanations. However, the following differences are pointed out: The disk springs 28 according to FIG. 3 are replaced by a further sealing ring 36. By attaching this sealing ring 36 in the interior of the melting space, the sealing ring 30 shown in FIG. 3 can be dispensed with.

At the lower end of the tube are in this embodiment, two axially extending slots. These serve to fix the pipe section 17 when tightening the nut 19 or the union nut 33rd

Fig. 5 shows an exploded view of the embodiment shown in Fig. 4. In this respect, reference is made to the above explanations.

Fig. 6 shows the union nut 33 in a partial sectional view. At the outer edge, this union nut 33 has a knurling 37. Inside, the union nut 33 has an internal thread 38.

Fig. 7 shows the sight glass 18 in a detailed detailed view. This sight glass 18 is cylindrical. It is preferably made of silicate glass, in particular borosilicate glass.

Fig. 8 shows the pipe section 17 in a detailed detailed view. The individual sections of the pipe section 17 have already been explained in connection with FIGS. 2-4, so that reference is made to these explanations. In addition, it should be noted that the pipe section around its longitudinal axis i.w. is formed rotationally symmetrical, which brings significant advantages in the creation of the thread 26 and 32, but also facilitates the processing of the individual sections of the pipe section 17, since the pipe section 17 can be rotated.

Fig. 9 shows the sight glass panel 20 in a more detailed detail view, also in a partial sectional view. The sight glass plate 20 has a bore 39, which is followed at the top by a bore 40 with a larger diameter. The transition between the two holes 39 and 40 forms the aforementioned circumferential projecting portion 25. The sight glass plate 20 is preferably also made of silicate glass, in particular borosilicate glass formed.

The holes 39 and 40 are arranged either centrally or off-center in the preferably point or rotationally symmetrical sight glass plate 20. An eccentric arrangement is advantageous because in this way the optics 8 of the sensor together with the pipe section 17 are not positioned at a fixed location must be, but on a predetermined path, in particular circular path, can be variably arranged.

The construction described allows for easy assembly and disassembly of the sight glass 18, so that the sight glass 18 can be easily cleaned or replaced.

FIG. 10 shows an arrangement 41 for fastening the sight glass plate 20 to the upper housing wall GW of the chamber 11. This arrangement has the mounting boss 42 already mentioned in connection with FIG. 2, which has an outer shoulder 43, which projects into a corresponding bore or recess ., A - preferably circular - hole in the housing wall GW of the device 1 can be added. The mounting boss 42 is screwed or welded in the region of paragraph 43 with the housing GW.

The mounting boss 42 also has an external thread 44, which is screwed to the nut 21. The groove nut 21 has an inwardly directed projection 46, which is designed such that it covers the sight glass plate 20 at the edge. The groove nut 21 is screwed over the external thread 44 of the screw 42, so that the sight glass plate 20 is pressed against an inner shoulder 47 of the screw 42 and thus fixed. To protect the sight glass panel 20, between the projection 46 and the outer edge of the sight glass panel 20 is a seal, e.g. Flat gasket 48. Furthermore, located between the opposite edge of the sight glass plate 20 and the shoulder 47 of the screw 42, a further sealing ring, in particular a silicone O-ring 49. Both seals 48, 49 serve the sight glass plate 20 on the one hand to protect against damage and on the other To seal the interior 11 of the furnace against the environment.

In Fig. 10, the bore 39, 40 is not shown through the sight glass plate for the sake of simplicity of illustration.

The construction according to the invention achieves a highly effective smoke deflector, which protects the sensitive pyrometer arrangement, in particular its appearance, from messure-distorting dirt deposits, in particular smoke particles. Thanks to the invention, the maintenance of temperature measuring systems on melting and casting devices of investment casting technology, in particular dental technology, can be significantly reduced and at the same time the quality of the measurement results are upheld.

The above arrangement has been described with reference to a closed melting and casting system. However, it is also conceivable to apply the idea according to the invention of further developing a temperature measuring sensor by attaching a pipe for smoke rejection in other melting processes, since the essential idea, namely the inhibition of a convection-induced flow of dirt particles in the region of the viewing window of the sensor, already by the attachment of a tube to the sensor is achieved when the tube is directed onto the melt from above.

Claims (12)

Device for non-contact measurement of the temperature of a melt in a crucible (2) in a melting furnace, in particular the investment casting technique, by means of a pyrometer (5), optics (8) and at least one optically related to the optics (8) Sensor (6), wherein the optical system (8) through a sight glass (18) on at least a portion of the crucible (2) is alignable,
marked by
a tube (17) which adjoins the sight glass (18) in the region of its upper end (31), extends into a melting chamber (11) of the melting furnace and can be aligned in the direction of the crucible (2). Device according to claim 1,
characterized in that
the upper tube end (31) is sealed gas-tight by means of the sight glass (18) and the lower tube end (22) is open. Apparatus according to claim 1 or 2,
characterized in that
the tube cross-sectional area substantially corresponds to the cross-sectional area of the measuring spot of the pyrometer (5). Device according to one of the preceding claims,
characterized in that
the tube length is dimensioned such that the lower tube end (22) lies below a portion (23) of the melting space (11) which fills with smoke (24) when a predetermined amount of melting material has been melted in the melting furnace. Device according to one of the preceding claims,
characterized in that
the tube length is dimensioned such that the lower tube end (22) ends in the region of the upper edge of the crucible (2) or the melt. Device according to one of the preceding claims,
characterized in that
the tube (17) extends through a plate (20), in particular sight glass plate. Device according to one of the preceding claims,
characterized in that
the tube (17) in the region of its upper end (31) has a circumferential projecting portion (25) with an outer diameter which is greater than the diameter of the underlying tube portion. Device according to one of the preceding claims,
characterized in that
the tube (17) above the circumferential projecting portion (25) has a portion mifeinem external thread (32) for receiving a union nut (33) and that the tube (17) in the upper end portion (22) in the tube interior over the underlying inner tube section enlarged section for receiving the sight glass (18) with substantially the same cross section, wherein the sight glass (18) by means of the union nut (33) in the interior of the upper end portion (22) can be fastened. Device according to one of the preceding claims,
characterized in that
the plate (20), in particular sight glass plate, a bore (39, 40) for the passage of the tube (17). Device according to claim 9,
characterized in that
the plate (20) formed point or rotationally symmetrical and the bore (39, 40) for the passage of the tube (17) through the plate (20) outside the center of this plate (20) is arranged. Device according to one of claims 7 to 10,
characterized in that the circumferential projecting portion (25) is inserted into a recess (29) of the sight glass (20), wherein between the projecting portion (25) and the recess (29) is a seal (30), and
in that the tube (17) has a threaded lower portion (26) for receiving a nut (19) by which the projecting portion (25) is biased against a biasing force of one or more disc springs (28) interposed between the nut (19 ) and the sight glass plate (20) are arranged in the recess (19) with simultaneous sealing of a gap between the projecting portion (25) and recess (29) is pulled. Device according to claim 11,
characterized in that by means of the nut (19) and / or the at least one disc spring (28), a maximum allowable pressure in the melting chamber (11) is adjustable, above which sealed by the seal (30) at pressures below this maximum allowable pressure gap is opened to limit the overpressure to the maximum permissible overpressure.

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