AP589A

AP589A - Sensor array for measuring temperature

Info

Publication number: AP589A
Application number: APAP/P/1995/000761A
Authority: AP
Inventors: Paul Clement Verstreken; Jozef Theodoor Aegten
Original assignee: Heraeus Electro Nite Int
Priority date: 1994-09-21
Filing date: 1995-08-24
Publication date: 1997-04-30
Also published as: NO953121D0; KR100205976B1; MX9504019A; IS1911B; CA2158719A1; IS4296A; HU216038B; GR3032241T3; RU2128826C1; NO319570B1; US5752772A; RO117766B1; PL179107B1; CA2158719C; HUT72941A; NO953121L; EP0703026A1; NZ280049A; HU9502744D0; KR960011396A

Abstract

The invention relates to a

Description

TO* SENSOR ARRAY FOR MEASURING TEMPERATURES

Abstract: The invention relates to a sensor array for measuring temperatures of mellOts, comprising a vessel which includes at least one strip or wire-shaped support member and an aperture on its upper side and a thermoelement provided in the vessel. In order to provide a sensor array by means of which the liquidus temperature of cryolite melts can be determined accurately, the vessel is made of metal. The invention also relates to a temperature measuring means comprising such a sensor array, in which the at least one support means on its side facing away from the vessel is mounted in a sleeve and the sleeve is releasably connected to a holding means. However, it is also possible for the sleeve to be permanently connected to the holding means. Furthermore, the invention palates to a process for measuring the liquidus temperature of cryolite melts in a vessel which during cooling of the cryolite melt is vibrated.

(56) Documents died: DE-A-2225766

INVENTORS CONTINUED

2. JOZEF THEODOOR AE6TEN Hamonterweg 25 B-395O Bocholt BELGIUM

AP.00539

Rcf:\bomeMDWub\beneia.n· 15.06.95

Sensor Array for Measuring Temperatures

The invention relates to a sensor array for measuring temperatures of melts, comprising a vessel which includes at least one strip or wire-shaped support member and an aperture on its upper side and a thermoelement provided in the vessel. The invention also relates to a temperature measuring means and a process for measuring the liquedus temperature of cryolite melts.

Such sensor arrays are used, for example for determining the liquidus temperature of melts wherein, the cooling curve of the melt charged into the vessel is determined. From the liquidus temperature it is possible to derive informations concerning the composition of the melt. A known apparatus of the type set out in the introduction for determining the liquidus measurement of cryolite melts comprises a graphite crucible for taking samples in which a thermoelement is provided. The graphite crucible is fitted to a mounting by means of a metal rod. The graphite crucible is dipped into the cryolith melt for sampling and after having attained thermal equilibrium is withdrawn from the , melt containing a melt volume of about 3 cnP. Thereafter, the cooling curve is θ recorded and therefrom the liquidus temperature is determined. The data obtained by means of this measuring apparatus for the liquidus temperature are subject to a fluctuation of several degrees and are accordingly very inaccurate so that the measuring results cannot be used reliably in practice.

Another apparatus for temperature measurements is known from US 3,643,509. By means of the apparatus there described it is possible to perform liquidus measurements in steel. For this purpose a thermoelement is accommodated in a small U-shaped silica tube inside a vessel made of silica.

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The vessel is fitted in a conventional manner to the tip of a measuring head and comprises some lateral inlet apertures for the steel melt. This apparatus is employed after its immersion into the steel melt for measuring the bath temperature and after its withdrawal from the steel melt for measuring the liquidus temperature. However, such arrays are not suitable for melts having, for example, a low melting heat and poor thermal conductivity as is the case with cryolite melts.

A need exists to provide a sensor array of the type referred to in the introduction by means of which the accurate measurement of the liquidus temperature is possible in the case of cryolite melts and which can nevertheless be manufactured at reasonable cost. It is furthermore an object of the invention to provide a temperature measuring means and a process for measuring the liquidus temperature of cryolite melts by means of which measuring results are attainable which are reproducible with a high degree of accuracy.

The invention provides a sensor array as described in the introduction, wherein the vessel is made of metal and the at least one support member is rigidly connected to a vibrator. Such a vessel has a relatively low thermal capacity and a high thermal conductivity so that the vessel can withdraw only a very small amount of heat from the cryolite melt. For this purpose it is advantageous if the vessel has a wall thickness of less than 0,5 mm, in particular less than 0,2 mm and that preferably copper is employed as the material for the vessel.

When immersing a cold device into a cryolite melt the latter solidifies immediately on the components having a low temperature, on attainment of an equilibrium state this solidified cryolite will, however, melt once again. This remelting takes place most rapidly in a thin-walled vessel having a high thermal conductivity, because on the one hand only a very small amount of heat is taken up by the vessel and furthermore the vessel, due to its high thermal conductivity, very rapidly heats up again.

AP.0058:

For an accurate measurement it is advantageous if the vessel has a corrugated surface. Thereby the surface area of the solidifying cryolite melt is increased.

The solidification after withdrawal of the sensor array from the melt takes place first in the region of this surface and then progresses uniformly into the interior of the melt.

It is advantageous if the thermoelement is accommodated in a silica tube, in particular in a silica tube closed at one end and which comprises a rion-oxidic protective coating. Such a thermoelement is resistant against the cryolite melt and can be made to have a small volume so that only very little heat dissipation takes place by virtue of the thermoelement. It is advantageous to form the protective coating of a heat resistant metal or a non-oxidic ceramic material in order to increase the resistance against the cryolite melt. For an accurate recording of the cooling curve, it is advantageous if the thermoelement is provided approximately in the centre of the vessel.

In order to ensure firm handling characteristics of the sensor array it is advantageous if the support member is formed of metal wires because these have high resistance against the cryolite melt. Moreover, it was found to be θ advantageous if the at least one carrier means is rigidly connected to a vibrator.

Furthermore, it may be advantageous if the inner surface of the vessel has a roughness exceeding 1,25 gm, preferably between 2,5 gm and 15 gm.

The invention also provides a temperature measuring means comprising a sensor array of the type described, wherein above the at least one support means on its side facing away from the vessel is mounted in a sleeve and that the sleeve is releasably connected to a holding means. However, it is also possible for the sleeve to be permanently connected to the holding means. Such an array ensures great mechanical strength and easy handling of the apparatus when carrying out measurements. It is advantageous to form the sleeve essentially of

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AP . Ο η 5 8 9 refractory material, because it is then possible to shorten the length of the support members, without the sleeve, during the dipping of the vessel into the melt, being destroyed by the heat rising up from the melt. The holding means may, for example, be provided in the form of a lance or cardboard tube as is conventional in metallurgy.

It is advantageous if the thermal element is mounted in the sleeve and is conductively connected to a conductor member of the sleeve and if the connector member is in contact with signal conductors of the mounting means. In that manner, the vessel for withdrawing the melt sample and the thermal element are combined in a unit which can be removed from the holding means and be replaced by a new unit after the measurement. The signal conductors which pass the electrical signal of the thermal element to a data processing unit may be accommodated inside the holding means and are thus protected against damage.

For achieving a homogeneous solidifying of the melt it is advantageous if the holding means is rigidly connected to a vibrator.

According to the invention, there is further provided a process for measuring the liquidustemperature of cryolite melts, wherein, during the measurement of the cooling curve of the cryolite melt in a vessel, such vessel is in a state of vibration. As a result, a homogeneous solidifying of the cryolite melt, starting from the vessel surface, is attained. Due to the vibration of the cryolite melts during the cooling, super cooling effects in the melt are avoided. The vibration frequency amounts to about 20 to 1000 Hz, preferably 150 to 400 Hz, and the vibration amplitude amounts to about 0,01 to 0,5 mm, preferably 0,08 to 0,15 mm.

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In the following the invention will be further explained by way of a working example with reference to a drawing. In the drawing there is shown in:

AP 00589

Figure 1 a schematic illustration of the sensor array,

Figure 2 a preferred embodiment of the vessel, and

Figure 3 a schematic illustration of the temperature measuring means including the holding means.

Figure 1 shows a sensor array in which, in a vessel 1 a thermal element 2 is accommodated. The vessel 1 is made of copper and has a wall thickness of 0,1 mm. The wires of the thermal element 2 are accommodated inside a small silica tube which is closed at its end projecting into the vessel 1. The small silica tube comprises a coating of metal or a non-oxidic ceramic material, for example T1B2, TiN or BN. This coating can be applied by flame spraying, plasma spraying or vapour coating. Immersion coating or a similar coating process are also possible.

The rotationally symmetrical vessel 1 is fitted to three support means 3 formed of metal wires. The support means 3 may, for example, be welded to the vessel

1. Steel, having a diameter of 1 mm, is used as the material for the support means 3. The vessel is shown in detail in Figure 2. In this context Figure 2a represents a side elevation of the vessel 1, having an aperture 4, in which a mounting means 3 is fitted. Figure 2b represents a plan view of the vessel 1; in the latter case the corrugated peripheral surface is clearly visible. The vessel 1 has an inner surface roughness of about 2,5 to 15 jum.

The support means 3 and the thermoelement 2 are fixed by means of cement 5 in a sleeve 6 made of a refractory material, for example, Kordierit. Inside the sleeve 6, the thermo wires of the thermoelement 2 are connected to contacts of the connecting member 7. The sleeve 6, as shown in Figure 3, is accommodated in the end of the holding means 8. There the contacts of the connecting members 7 are conductively connected to signal conductors which

ΛΡ . 0f)58 pass through the holding means 8 and can be connected by way of the lance 9 to electronic measuring and data processing circuitry connected downstream thereof. A vibrator 10 is rigidly connected to the holding means 8 and the lance

9, causing the vessel 1, including the cryolite melt to be measured, to vibrate during the recordal of the cooling curve.

The frequency of the vibrations may be selected within a very wide range, however, it is preferably between 150 and 400 Hz in order to avoid super cooling effects of the cooling melt. The amplitude of the vibrations amounts to about 0,08 to 0,15 mm.

The claims which follow are to be considered an integral part of the present disclosure. Reference numbers (directed to the drawings) shown in the claims reserve to facilitate the correlation of integers of the claims with illustrated _c features of the preferred embodiment(s), but are not intended to restrict in any c way the language of the claims to what is shown in the drawings, unless the contrary is clearly apparent from the context. o

Claims

Claims

1. Sensor array for measuring temperatures of molten materials, comprising a vessel which includes at least one strip or wire-shaped support member and an aperture on its upper side and a thermoelement provided in the vessel, wherein the vessel (1) is made of metal and at least one support member (3) is rigidly connected to a vibrator (10).
2. Sensor array according to claim 1, wherein the vessel (1) has a wall thickness of less than 0,5 mm.
3. Sensor array according to claim 2, wherein the wall thickness is less than 0,2 mm.
4. Sensor array according to any one of claims 1 to 3, wherein the vessel (1) is made of copper.
5. Sensor array according to any one of claims 1 to 4, wherein the vessel (1) has a corrugated surface.
6. Sensor array according to any one of claims 1 to 5, wherein the thermoelement (2) is accommodated in a silica tube having a non-oxidic protective coating.
7. Sensor array according to claim 6, wherein the thermoelement (2) is accommodated in a silica tube closed at one end.
8. Sensor array according to claim 6 or 7, wherein the protective coating is formed of a temperature resistant metal.
9. Sensor array according to claim 6 or 7, wherein the protective coating is formed of a non-oxidic ceramic material.

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AP.00509
10. Sensor array according to any one of claims 1 to 9, wherein the thermoelement (2) is arranged approximately in the centre of the vessel (1).
11. Sensor array according to any one of claims 1 to 10, wherein the support member (3) is formed of metal wires.
12. Sensor array according to any one of claims 1 to 11, wherein the vibrator (10) has a vibration frequency of 20 - 1000 Hz.
13. Sensor array according to any one of claims 1 to 10, wherein the inner surface of the vessel (1) has a roughness greater than 1,25 gm.
14. Sensor array according to claim 13, wherein the inner surface of the vessel (1) has a roughness between 2,5 gm and 15 gm.
15. Temperature measuring means including a sensor array according to any one of claims 1 to 14, wherein the at least one support member (3), on its side facing away from the vessel (1), is mounted in a sleeve (6) and the sleeve (6) is connected to a holding means (8).
16. Temperature measuring means according to claim 15, wherein the sleeve (6) is essentially made of ceramic material.
17. Temperature measuring means according to claim 15 or 16, wherein the thermoelement (2) is mounted in the sleeve (6) and is conductively connected to a connector member (7) of the sleeve (6) and that the connector member (7) is in contact with signal conductors of the holding means (8).

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AP 00589
18. Temperature measuring means according to any one of claims 15-to 17, wherein the holding means (8) is rigidly connected to a vibrator (10).
19. Process for measuring the liquidus temperature of cryolite melts in a vessel, wherein the cooling curve of the cryolite melt is measured, wherein a vessel (1), containing a sample of the cryolite melt is caused to vibrate during the cooling of the melt.
20. Process according to claim 19, wherein the vibration frequency amounts to 20 to 1000 Hz.
21. Process according to claim 20, wherein the vibration frequency amounts to 150 to 400 Hz.
22. Process according to claim 19, 20 or 22, wherein the vibration amplitude amounts to about 0,01 to 0,5 mm.
23. Process according to claim 22, wherein the vibration amplitude amounts v to 0,08 to 0,15 mm.

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2£ A sensor array as claimed in claim 1, substantially as hereinbefore described or exemplified.