GB2088056A - Disposable sampling and temperature sensing unit - Google Patents

Abstract

A disposable unit for sampling and sensing the temperature of a metal melt in which the unit is immersed comprises an elongate, tubular housing (1) at the leading end of which is mounted a sampling mould (2) having an inlet passage (5) opening at the leading end of the housing. A thermocouple (16) is mounted on a side of the housing 1 from which side the thermocouple projects in use into the metal melt. Lead wires (23A, 23B, 25A, 25B, 29A, 29B, 30A, 30B) from the thermocouple extent into and through the housing (1) away from the sampling mould (2). The arrangement is such that the temperature sensed, in use, by the thermocouple (16) is substantially unaffected by the surface of the housing (1). <IMAGE>

Description

SPECIFICATION Disposable sampling and temperature sensing unit In the past, when it has been desired to extract a sample and measure the temperature of a metal melt, such as molten iron or molten steel, individual sampling and temperature sensing devices have been immersed separately into the melt. With the advent of hardware permitting testing to be carried out automatically, it became desirable to provide a unit having both sampling and temperature sensing components. Such unit is illustrated in British Patent Specification No.

1,158,537. In this unit, a thermocouple is provided at the leading end of a tubular housing, while entry to a cylindrical sampling chamber in the housing is provided by an opening in one side of the housing. A second thermocouple for measuring the liquidus arrest temperature of the metal melt in the sampling chamber is also provided, the two thermocouples being arranged back to back. The unit which is used in practice and which is based on that shown in the earlier Patent Specification has a different contact arrangement. The lead wires from the thermocouples terminate in contacts on the outer surface of the housing member and connect, in use, with corresponding contacts on the inside surface of a circular tube through which the unit is pushed.Clearly, in order to permit the unit to be pushed through the circular tube, there cannot be any parts on the unit housing projecting outwardly.

A number of problems have arisen when using this unit. The sampling chamber provided in the housing is mainly for the purpose of obtaining the liquidus arrest temperature and, although it is suggested that the solidified sample may be extracted by sawing through the housing, the sample obtained is not usually of good quality. It is desirable to obtain samples which are uniformly deoxidized, cavity free, and of the required shape which is usually non-cylindrical. With this earlier side entry unit, particularly where the housing is formed by a cardboard tube, bubbles or boils can form on the surface of the tube and are carried into the sampling chamber by the metal melt causing cavities to be formed when the melt solidifies.Although a degree of bubbles may be overlooked in a sample which is only to be used to determine liquidus arrest temperature, this is not so when a sample is required for separate analysis.

A further problem arises in this earlier unit in that although the juxtaposition of the two thermocouples provides a convenient arrangement, lead wires from the thermocouples have to extend past the sampling chamber and they are thus subjected to heat conducted outwardly from the sample through the sampling chamber wall and inwardly, from the metal melt surrounding the unit, through the housing.

Consequently, wall dimensions have to be considerably increased to protect adequately the thermocouple lead wires and this is prohibitively expensive.

Another significant difficulty which is encountered with the earlier unit is that of the different sampling chamber entry arrangements which are required for different metal melts for example deoxidized steel, oxygen rich steel, or iron. In the example illustrated in British Patent Specification No. 1,158,537 it is suggested that aluminium wire should be placed in the sampling chamber where the molten metal is steel.

However, this arrangement is inefficient for deoxidizing a metal melt.

Another unit which specifically deals with side entry into a sampling mould is described in British Patent Specification No. 1,150,149. This construction also suffers from the disadvantages of side entry as outiined above. In some of the examples disclosed in this specification, an attempt is made to incorporate a thermocouple which is supported within the unit housing and protrudes slightly through the side opening. It is clear from looking at the drawings that the thermocouple is positioned almost flush with the housing surface and in any case the metal whose temperature is to be measured will be subjected to the chilling effect of the cardboard housing and the turbulent effect due to metal melt passing through the side opening producing gas bubbles and causing the sensed temperature to oscillate preventing the true bath temperature to be measured.Furthermore, the method of mounting the thermocouple from within the housing is ciearly unwieldy and it is apparent that the thermocouple will be subjected to large stresses due to the force applied by metal melt passing into the sampling chamber.

In accordance with the present invention, a disposable unit for sampling and sensing the temperature of a metal melt in which the unit is immersed comprises an elongate, tubular housing at the leading end of which is mounted a sampling mould having an inlet passage opening at the leading end of the housing; and a temperature sensing device mounted on a side of the housing from which side the device projects in use into the metal melt, lead wires from the device extending into and through the housing away from the sampling mould, the arrangement being such that the temperature sensed, in use, by the temperature sensing device is substantially unaffected by the housing surface.

With this arrangement the problems of side entry into a sampling chamber are overcome by providing the entry to the sampling chamber in the leading end of the housing. The sampling mould may comprise a conventional two part mould which is removably mounted in the leading end of the housing to enable it to be simply and easily removed to obtain the solidified sample.

Furthermore, the different sampling chamber entry arrangement can be easily accommodated by push fitting appropriate elements into the leading end of the housing.

We have always considered that it would be difficult to sense the temperature of the metal melt adjacent a side of the housing due to the effects of the housing surface on the temperature sensed as will happen with the construction shown in Specification No. 1,150,149. In order to overcome this affect, we considered that it would be necessary to space the sensitive part of the device a large distance from the housing surface.

We have found, however, surprisingly that this is not the case. In fact, we have found that the sensitive part of the device need be spaced only a few tens of millimetres from the housing surface to be substantially unaffected by the surface. A distance of at least 20mm, preferably substantially 25mm and in particular 30mm is advantageous.

Alternatively, or additionally, a flange part of the temperature sensing device may extend over the adjacent surface of the side of the housing through which the device projects. This prevents boils and bubbles forming in the housing surface adjacent the device. The relative dimensions of the flange part diameter and the distance of the sensitive part of the device from the housing surface may be mutually altered. For example, the sensitive part of the device may be spaced a relatively large distance from the housing surface while a small diameter flange is provided or alternatively, a large diameter flange and a smaller spacing may be chosen. The precise dimensions depend to a certain extent on the type of melt in which the unit is to be immersed but a particularly convenient device has a flange part diameter of substantially 37mm.This may be accompanied by a spacing of 30mm. Furthermore, where for example the housing is made of cardboard or the like, anti-boil material comprising for example sand, refractory cement, fibrous ceramic or asbestos may be provided on the surface of the housing adjacent the temperature sensing device.

The temperature sensing device may comprise a conventional thermocouple having a body with a flange diameter of, for example, 28mm with the thermocouple junction spaced 1 8mm from the flange. In this case, the spacing of the thermocouple junction from the housing surface may be adjusted by inserting refractory material e.g. cement or sand to mount the device to the housing between the flange and the housing.

The use of conventional thermocouples and sampling moulds simplifies considerably the construction of the disposable unit.

Preferably, the temperature sensing device is spaced apart from the sample mould in the direction away from the leading end of the housing and thus the lead wires are subject only to the effect of gases heated, in use, by the metal melt and being emitted from vent holes in the sampling mould or expanding from around the sampling mould. Preferably, a refractory shield is provided in the housing between the sampling mould and the parts of the temperature sensing device located in the housing. The shield may comprise an element of insulating material, for example ceramic, sand, plastic, metal or cardboard, which provides a socket for a lance and supports electrical contacts connected to the temperature sensing device for connection, in use, to a lance.Thus, the lead wires from the temperature sensing device may extend through the refractory element from the temperature sensing device to the electrical contacts. It is particularly convenient if a part of the outer surface of the element is fluted to allow hot gases to pass by the element and along the length of the housing. Thus, the lead wires do not need to pass beside the sampling mould and so are not subjected to direct heat from the mould.

This unit is much slimmer and cheaper than the earlier side entry sampling chamber units and, as is apparent, the lead wires from the temperature sensing device can be brought simply and in a short distance to a lance socket position within the housing.

Two examples of a unit constructed in accordance with the present invention are illustrated in the accompanying drawings, in which: Figure 1 is a longitudinal section of one example with some parts cut away; Figure 2 is a part sectional view of a second example; and, Figure 3 is a perspective view of the refractory element of the Figure 2 example.

The disposable unit illustrated in Figure 1 comprises a cardboard tube 1 having an outer diameter of typically 60mm. The leading end of the cardboard tube 1 supports a sampling mould 2. The mould 2 is of conventional form having two steel half moulds 2A, 2B held together by means of a clip 3. The mould 2 is mounted in the tube 1 by means of a sand insert 4 having a central bore 5 in which a spigot 6 of the mould is received. A silica tube 7 is mounted in the spigot 6 of the mould 2 and passes through the bore 5 from which it slightly projects. A conventional slag cap 8 for preventing the entry of slag into the silica tube 7 during insertion of the unit into a metal melt is force fitted onto a further cap 9.The cap 9 has a deoxidant plug 1 0 and is also push fitted onto a cap 11 having an aperture 1 2 and defining the conventional mixing chamber arrangement.

The particular arrangement of caps shown is that which would be used in the case of unkilled steel.

Other known inlet configurations would be used for sampling killed steel or liquid iron.

A bore 1 3 is provided in the side of the cardboard tube 1 at a position just past the end of the sampling mould 2 in a direction away from the leading end of the tube 1. A cylindrical, tubular portion 14 of a ceramic body part 1 5 of a conventional thermocouple 1 6 is push fitted into the bore 13. The ceramic body part 15 also has a flange portion 1 7 integral with the cylindrical portion 14 and having a central bore which, with the cylindrical, tubular portion 1 4 defines a bore 1 8. The flange portion 1 7 butts against the outer surface of the cardboard tube 1 and is cemented to the tube 1 as shown diagrammatically at 1 9.

A plastics plug 20 is bonded into the end of the cylindrical portion 14 of the body part 15 remote from the flange portion 1 7. The plug 20 has an integral extension 21 which carries a silica "U" tube 22 which contains and protects wires 23A, 23B which are connected at the bight portion of the "U" tube 22 to form a thermocouple junction 24. The wires 23A, 23B are connected to respective metal strips 25A, 25B which are supported by and extend through the plug 20.

The "U" tube 22, and the metal strips 25B are cemented in to the bore 1 8. A slag cap 26 is push fitted over the flange portion 1 7 of the ceramic body 1 5 to protect the thermocouple 1 6 from damage during insertion of the unit into the metal melt.

The outer diameter of the flange portion 1 7 is typically 37mm while the distance from the surface of the cardboard tube 1 to the thermocouple junction 24 is, in this case, typically 30mm. It has been found that this combination of flange width and thermocouple junction height ensures that the effect of boils forming on the surface of a cardboard tube on the temperature sensed is negligible.Other ways in which this may be achieved, or which may be used additionally to the flange portion 1 7 are: to coat the adjacent surface of the cardboard tube with anti-boil material such as sand, refractory cement, fibrous ceramic or asbestos; to increase the distance of the thermocouple junction 24 from the surface of the tube 1 by introducing cement between the flange portion 17 and the tube 1 to space the flange portion away from the tube 1; or to encircle the flange portion 1 7 with a ring of bonded sand.

Furthermore, by increasing the wall thickness of the silica tube 22, variations in the sensed temperature can be smoothed out.

An element 27 having an outer diameter substantially the same as the inner diameter of the tube 1 is positioned within the tube 1 so that a radially extending blind bore 28 in the element 27 is coaxial with the bore 13 in the cardboard tube 1. The element 27 may be made of ceramic, sand, plastics, metal, or cardboard. The cylindrical portion 14 of the ceramic body part 15 of the thermocouple protrudes in to the bore 28 and the protruding ends of the metal strips 25A, 258 are connected, via respective wires 29A, 298 to secondary metal contacts 30A,30B. The contacts 30A. 30B are supported substantially at right angles to the metal strips 25A, 25B in a plastics plug 31 which is mounted in an axial bore 32 in the element 27. The bore 32 opens into the bore 28.It has been found useful to introduce cement 33 into the bore 28 generally to solidify the assembly and this has been found additionally in practise to be useful since it prevents any heat or gases from affecting the wires 29A, 29B, and also prevents any gases which might find their way, in use, into the bore 28 from forcing the ceramic body 15 out of the bore 13. The plastics plug 31 has an integral spigot portion 34 which extends into a counterbore 35 in the element 27 which is coaxial with and communicates with the bore 32.

Metal contacts 30A. 30B, are supported in a conventional fashion by the spigot portion 34.

In order to enable air which has expanded due to the presence of hot metal melt in the sampling mould 2 and gases which have been emitted through vents in the sampling mould 2 to pass out of the unit during use, a part of the outer surface of the element 27 is fluted to provide one or more passages 36. For each passage 36, a communicating, radially extending groove 37 is provided in the end of the element 27 remote from the sampling mould 2.

A further cardboard tube 38 having an outer diameter smaller than the inner diameter of the cardboard tube 1 is mounted in the tube 1 and butts against the end of the element 27 remote from the mould 2.The cardboard tube 38 is held coaxial with the tube 1 by means of cylindrical spacers 39 and is cemented at 40 to the tube 1 and adjacent spacer 39. The inner diameter of the tube 38 is slightly larger than the outer diameter of a conventional lance and the diameter of the counterbore 35, which is generally the same as that of a conventional lance. The counterbore 35 has a taper 41 which at its widest part has a diameter substantially the same as the inner diameter of the cardboard tube 38.

In use, a conventional lance 42 is inserted into the housing 38 and is pushed into the counterbore 35 until the contacts 30A, 30B are received in respective sockets in the lance. The unit is then plunged into the metal melt whereupon the respective slag caps 26, 8 will melt allowing the temperature of the metal melt to be sensed by the thermocouple 1 6 and simultaneously a sample of the metal melt to be taken by the mould 2. Any hot gases or air will pass through the passage or passages 36 and the respective grooves 37 and will then pass along the cylindrical passage 43 defined between the lance and the inner diameter of the cardboard tube 38 so that they can be extracted.

The disposable unit illustrated in Figures 2 and 3 is similar to that shown in Figure 1 and so the same reference numerals have been used for corresponding parts. The difference between the two examples is that the portion 14 and the element 27 of the first example have been replaced by a refractory element 44. The element 44 has a cylindrical body part 45 integral with a flange part 46. The plastics plug 31 is mounted in an axially extending bore 47 in the body part 45 and is arranged to connect with a conventional lance on insertion of the lance into the counterbore 35. The wires 23A,23B, extend from the silica "U" tube 22 into a cavity 48 in the body part 45 and are connected, as before, to wires 29A, 298 respectively which lead to the contacts supported by the plastics plug 31. The legs of the "U" tube 22 extend through respective holes 49 in the flange part 46 of the element 44 and through part of the body part 45 into the cavity 48.

The advantage of this element 44 is that the thermocouple 16 and the plastics plug 31 can be mounted into the element 44 and the cavity 48 can then be filled with refractory cement 50, before the element 44 is mounted in the cardboard tube 1.

Preferably, the body part 45 has a diameter of 30mm and since the internal diameter of the cardboard tube 1 is typically 40mm, no fluting is required around the surface of the element 44 to allow hot gases to pass down the carboard tube 1.

All that may be needed in this particular case, is the provision of a radially extending slot 51 to enable the gases to pass into and through the tube 38.

Claims (15)

1. A disposable unit for sampling and sensing the temperature of a metal melt in which the unit is immersed, the unit comprising an elongate, tubular housing at the leading end of which is mounted a sampling mould having an inlet passage opening at the leading end of the housing; and a temperature sensing device mounted on a side of the housing from which side the device projects in use into the metal melt, lead wires from the device extending into and through the housing away from the sampling mould, the arrangement being such that the temperature sensed, in use, by the temperature sensing device is substantially unaffected by the housing surface.

2. A unit according to claim 1 , wherein the sensitive part of the temperature sensing device is spaced at least 20mm from the adjacent outer surface of the housing.

3. A unit according to claim 2, wherein the sensitive part of the temperature sensing device is spaced substantially 25mm from the adjacent outer surface of the housing.

4. A unit according to claim 2, wherein the sensitive part of the temperature sensing device is spaced substantially 30mm from the adjacent outer surface of the housing.

5. A unit according to any of the preceding claims, wherein a flange part of the temperature sensing device extends over the adjacent surface of the side of the housing through which the device projects.

6. A unit according to claim 3, wherein the flange part has a diameter of substantially 37 mum.

7. A unit according to any of the preceding claims, wherein anti-boil material is provided on the exposed surface of the side of the housing adjacent the temperature sensing device.

8. A unit according to any of the preceding claims, wherein the housing is made of cardboard.

9. A unit according to any of the preceding claims wherein a refractory shield is provided in the housing between the sampling mould and the parts of the temperature sensing device located in the housing.

10. A unit according to claim 9, wherein the refractory shield comprises an element of refractory material which provides a socket for a lance and supports electrical contacts connected to the temperature sensing device for connection, in use, to a lance.

11. A unit accdrding to claim 9 or claim 10, wherein the shield is arranged to allow gases heated, in use, by metal melt to vent past the shield and through the housing.

12. A unit according to claim 10 or claim 11, when dependent on claim 10, wherein the element has a cylindrical body part within the housing, and an integral flange part exposed outside the housing, the temperature sensing device being supported by the element.

13. A unit according to claim 11 ,when dependent on claim 10, wherein at least a part of the outer surface of the refractory element is fluted to allow venting of hot gases to take place.

14. A unit according to claim 1 , substantially as described with reference to either of the examples shown in the accompanying drawing.

15. Apparatus for sampling and sensing the temperature of a metal melt, the apparatus comprising a unit in accordance with any of the preceding claims, and a lance extending into the housing to support the unit, a passage for gases heated, in use, by metal melt being provided between the lance and the housing.