ELEMENT TO MEASURE THE OXYGEN CONTENT OF MOLTEN METALS

Abstract

The invention relates to an oxygen detecting element comprising a coated pin and a method for measuring the oxygen content of a metal melt with an oxygen detecting element. The coated pin comprises an electrically conductive core, which is eccentrically arranged in a coating. The coating comprises at least a two-layered coating section with an inner coating layer comprising a reference material and an outer coating layer comprising an electrolyte material. The invention further relates to an immersion sensor comprising the oxygen detecting element and a method for measuring the oxygen content of a metal melt with such an oxygen detecting element.

Claims

1. An oxygen detecting element, comprising a coated pin, the coated pin comprising an electrically conductive core and a coating, wherein the coating comprises at least a two-layered coating section comprising (i) an inner coating which covers and is in direct contact with at least a part of the electrically conductive core and comprises a reference material, and (ii) an outer coating which covers and is in direct contact with at least a part of the inner coating and comprises an electrolyte material, characterized in that the electrically conductive core is arranged eccentrically in the coating.

2. An oxygen detecting element according to claim 1, wherein the cross-sectional shape of the coating perpendicular to a longitudinal axis of the conductive core has a round, oval or elliptical shape.

3. An oxygen detecting element according to claim 1, wherein the coating has a minimal thickness of at least 0.06 mm.

4. An oxygen detecting element according to claim 1, wherein the coating comprises two thicknesses along a major axis of the cross-sectional area of the coating, a smaller thickness T.sub.S and a maximal thickness T.sub.MAX, wherein T.sub.MAX is at least 5% larger than T.sub.S.

5. An oxygen detecting element according to claim 1, wherein the maximum cross sectional-area of the coated pin is in the range between 0.5 and 7 mm.sup.2,

6. An oxygen detecting element according to claim 1, wherein the coating comprises a three-layered main coating structure, which covers a main portion of the electrically conductive core.

7. An oxygen detecting element according to claim 6, wherein the coating comprises a third coating structure, which covers a third portion of the electrically conductive core.

8. An oxygen detecting element according to claim 1, wherein the electrically conductive core comprises a mounting portion located at a mounting end which is not coated.

9. An oxygen detecting element according to claim 1, wherein the electrically conductive core comprises a tapered section.

10. An oxygen detecting element according to claim 9, wherein the tapered section extends over at least 10% of the length of the electrically conductive core.

11. An immersion sensor comprising an oxygen detecting element according to claim 1.

12. A method for measuring the oxygen content of a metal melt with an oxygen detecting element according to claim 1.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0093] The following schematic drawings show aspects of the invention for improving the understanding of the invention in connection with some exemplary illustrations. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. Herein

[0094] FIG. 1 shows different geometries of tip-ends of electrically conductive cores;

[0095] FIG. 2 shows schematic cross-sections of electrically conductive cores suitable for the present invention;

[0096] FIG. 3 shows schematic longitudinal cross-sectional views of oxygen detecting elements according to the invention;

[0097] FIG. 4 shows schematic transverse cross-sectional views of oxygen detecting elements; and,

[0098] FIG. 5 shows schematic transverse cross-sectional views of the measuring zone of oxygen detecting elements.

DETAILED DESCRIPTION

[0099] FIG. 1 shows cross-sections of different geometries of tip-ends 2 of electrically conductive cores 1. The tip-ends 2 in FIGS. 1A-IC are essentially flat and dome-shaped to different extends. The tip-end 2 shown in FIG. 1A has sharp edges, wherein the edges in FIG. 1B and FIG. 1C are rounded, resulting in a round (i.e. dome-shaped) tip. The tip-end 2 in FIG. ID is needle shaped and ends in a sharp tip. The tip-end 2 shown in FIG. 1E has a flattened needle shape, also referred to as a frustoconical shape. The tip-end 2 illustrated in FIG. 1F comprises a dome-shaped needle tip.

[0100] FIG. 2 shows schematic longitudinal cross-sections of electrically conductive cores 1 suitable for the present invention. The core 1 of FIG. 2A is a wire without tapered ends. The pins 1 of FIGS. 2B-2D have different geometries with respect to a tapered section of conductive core 3, the length of this section (L.sub.TS) and the degree of tapering at their ends. It is also illustrated where the degree of tapering is to be found, indicated by the taper angle . The taper angle is determined by the angle between two tangents adjacent to the surface of the tapered section in the plane of the maximum cross-section of the tapered section along the longitudinal axis of the pin. These tangents are indicated by dashed lines. The cores 1 of FIG. 2B and FIG. 2C have a central symmetrical geometry. FIG. 2B shows a needle shaped conductive pin 1 with a tapered section 3 which only extends over a part of the length of the pin. The tapered section 3 of the conductive core 1 shown in FIG. 2C extends over the whole length on the pin 1. The conductive core 1 of FIG. 2D also has a tapered section 3 over its whole length, but the geometry is not central-symmetric.

[0101] FIG. 3 shows schematic longitudinal cross-sectional views of oxygen detecting elements 4 according to the invention. The conductive wire 1 of FIG. 3A has a two-layered coating 5 with a reference material coating 6 and an electrolyte material coating 7. The end of a conductive pin 9 opposite the tip end 2 is not coated. Typically, this end is mounted in a suitable material, for example a refractory material, when the oxygen detecting element is mounted in a sensor assembly, it is therefore also referred to as the mounting end.

[0102] The coating layers which cover the conductive pin can be applied by means of a spray-process, e.g., plasma-spraying or flame-spraying, which produces a very uniform and dense coating. First, a reference material like chromium-chromium dioxide is applied to the conductive followed by a coating step with an electrolyte material like stabilized zirconium oxide.

[0103] The thicknesses of the different layers can be uniform along the length of the coated pin but they can also vary, especially when a spraying process as described is applied to manufacture the sensing element. These different layers may have the same thickness, depending on the demand and application of the oxygen detecting element, they may also vary in shape and thickness.

[0104] The electrically conductive core in FIG. 3B comprises a coating with two portions: a first portion, a tip coating structure 10 (CS-T) covering the tip portion of the pin 1 with a length L.sub.TP and a second portion, a main coating structure 11 (CS-M), covering the main portion of the pin 1 with a length L.sub.MP. The tip coating structure 10 and the tip end 2 provide the measuring zone of the sensor 4 when it is in use. The main coating structure 11 comprises a three-layered structure. Additional to the two layers on the tip coating structure (6, 7), it comprises a reference material layer 8, which extends between the reference material coating 6 and the electrolyte material coating 7.

[0105] In the displayed embodiment, the electrolyte material layer 7 and the reference material layer 6 extend over the whole length of the coating structure, while the refractory material layer 8 is only present over the length of the main portion L.sub.MP.

[0106] In the views of FIG. 3A and FIG. 3B the conductive pins are positioned eccentrically in the coating structures. For the sake of clarity, the views of FIG. 3C and FIG. 3D show the pin positioned centrally.

[0107] The needle-shaped conductive pin 1 as shown in FIG. 3 C also has a coating structure with two sections: the tip coating structure 10 (CS-T) covering the tip portion and the main coating structure 11 (CS-M), covering the main portion of the pin 1.

[0108] In comparison to the embodiment of FIG. 3C, the coating of the embodiment illustrated in FIG. 3D comprises an additional third coating structure 12 on a third portion of a needle-shaped conductive pin 1 with a length Lap. The third coating structure 12 comprises a two-layered structure of the refractory material layer 8 and the electrolyte material layer 7. The two layers essentially comprise the same thickness.

[0109] FIG. 4 shows schematic transverse cross-sectional views of oxygen detecting elements 4, i.c. in a plane perpendicular to the plane as shown in FIGS. 1-3. Shown is the structure of the whole coating 5 without any inner layer structure, however, the coating may comprise several layers. Indicated are the major axis D.sub.MJ and of the minor axis D.sub.MI of the cross-sectional area of the coatings 5 as well as the intersection point IP of these axis, the maximal thickness of the coating structure T.sub.MAX and the smaller thickness T.sub.S along the major axis.

[0110] The coating 5 of FIG. 4A has a circular shape. Accordingly, the length of the major axis D.sub.MJ and of the minor axis D.sub.MI of the cross-section are equal. The pin 1 is eccentrically positioned in the coating-the center of the pin 1 has an off-set to the intersection point IP. The coating in FIG. 4B has an elliptical shape and the length of the major axis D.sub.MJ and of the minor axis D.sub.MI differ.

[0111] FIG. 5 shows schematic transverse cross-sectional views of the measuring zone of oxygen detecting elements in the area of the tip coating structure with a round circular coating in FIG. 5A and an elliptical coating in FIG. 5B. The coatings have a two-layered structurea reference material coating 6 directly on the pin 1 and an electrolyte material coating 7 on top of the reference material coating.

REFERENCE SIGNS

[0112] 1 Conductive core [0113] 2 tip end of conductive core [0114] 3 tapered section of conductive core [0115] 4 oxygen detecting element [0116] 5 coating [0117] 6 reference material coating [0118] 7 electrolyte material coating [0119] 8 refractory material coating [0120] 9 mounting end of coated pin [0121] 10 tip coating structure (CS-T) [0122] 11 main coating structure (CS-M) [0123] 12 third coating structure (CS-3) [0124] L.sub.TS length of tapered section [0125] L.sub.TP length of tip portion [0126] L.sub.MP length of main portion [0127] L.sub.3P length of third portion [0128] IP intersection point [0129] D.sub.MJ major axis of coating [0130] D.sub.MI minor axis of coating [0131] T.sub.MAX maximal thickness of coating [0132] T.sub.S smaller thickness of coating [0133] D.sub.MJ-T major axis of tip coating structure [0134] D.sub.MI-T minor axis of tip coating structure [0135] T.sub.MAX-T maximal thickness of tip coating structure [0136] T.sub.S-T smaller thickness of tip coating structure [0137] Taper angle