GB2163599A - Insertion unit of an immersion thermocouple element - Google Patents

Abstract

An expendable insertion unit of an immersion thermocouple has thermocouple wires 13 inside a U- shaped quartz tube 21 which emerge from the limbs of the U for connection to wires of similar thermoelectric properties. In order to facilitate these connections, elastomeric bushes 31 are used which have bores with larger diameter portions and reduced diameter portions. The larger diameter portions are pushed onto the ends of the quartz tube, and within the reduced diameter portions the thermocouple wires and the wires to which they are to be connected are pressed into contact with one another by the resilience of the material of the bushes. <IMAGE>

Description

SPECIFICATION Insertion unit of an immersion thermocouple element This invention relates to an expendable insertion unit of an immersion thermocouple element, in particular for steel melting, consisting of a ceramic cylindrical shaped part, which is able to be inserted coaxially to the outer sleeve of a measuring lance, an insulating tube of quartz, which is bent in a U-shape, is able to be attached by its shanks to the head of the shaped part on the melt side and which is protected by a cap, in which the insulating tube receives the soldered junction of the thermocouple wires representing the temperature sensor which, emerging from the shanks of the insulating tube, are connected with equalizing wires and a contact carrier provided at the base of the shaped part, which receives the equalizing wires and is able to be inserted into a contact bush for the transfer of electrical signals.

Expendable insertion units for thermocouple elements have gained in use world-wide in the measurement of melting bath temperature, particulariy for steel melting. Owing to the fact that the immersion thermocouple elements are used only once, there is a high consumption of precious metals, and namely platinum and platinum rhodium. In order to keep the precious metal wires short, thermo immersion sensors are used, which have an equalizing wire, preferably of copper, in the insertion unit between the insulating tube and the contact piece.

From German Patent Specification No. 15 73 233 an insertion unit for an immersion thermocouple element is known, in which equalizing wires are provided, which are weided or soldered to the thermocouple wires projecting from the shanks of the insulating tube. In this known measuring head, the lower part of the shanks of the insulating tube, the part of the thermocouple wire projecting out of the insulating tube, the equalizing wire, the welded or soldered junction of the said wires and a part of the contact piece are embedded in cement. Between the wires and the cement a material is provided which is intended to insulate the wires electrically, whereby the cement has no contact with the wires at any point.

This arrangement of an insertion unit for an immersion thermocouple element has the disadvantage that on contacting the thermocouple wires with the equalizing wire, welding or soldering defects can occur, which falsify the measurement. It is technically difficult to intimately join metals with such differing chemical and physical properties, such as here for example platinum or platinum rhodium with copper. The difficulties of connecting the wires is further intensified by the small wire thickness, usually hitherto in the case of the equalizing wires of approximately 0.6 mm and in the case of the thermocouple wires of approximately 0.2 mm.

A disadvantage in the melt-connection methods for the abovementioned wires is also the change in the structure of the material with an undesired effect on the transfer of the measured value.

A further disadvantage of the known measuring head is the insulating of the wires, which is costly in terms of fitting, from the exit of the wire out of the shank of the insulating tube up to entry into the contact piece.

In this instance it is not guaranteed that porosities arise on the contact surface between the front of the insulating tube and the side of the contact pipe facing the insulating tube, which enable a penetration of humidity out of the cement into the insulating cover. The result would be a falsification of the measured value brought about by the formation of galvanic elements.

An insertion unit for immersion thermocouple elements is in fact known from German Patent Specification No. 15 39 299, which consists of a ceramic cylindrical shaped part, which is able to be inserted coaxially to the outer sleeve of a measuring lance, and has an insulating tube, which receives the temperature sensor, and also has a contact carrier, which is able to be inserted into a contact bush. In this known insertion unit, however, the thermocouple wires are passed through a sleeveshaped contact carrier and, in the case of one thermocouple wire bent approximately in the centre and in the case of the other thermocouple wire bent at the top of the sleeveshaped contact carrier, and returned for a sufficient portion to pass on contact. The sleeve-shaped contact carrier is able to be inserted into a contact bush.This contact bush has contact rings, which rest on the respective thermocouple wires.

A disadvantage of this insertion unit is the high consumption of precious metal wire by the length of thermocouple wires which is required from the soldered joint of the thermocouple element up to the contact carrier.

On pushing the contact carrier into the contact bush, considerable friction occurs between the contact rings of the contact bush and the thermocouple wires. In a disadvantageous manner, relatively thick thermocouple wires with sufficient tensile strength have to be used.

A disadvantage in this known insertion unit is also the costly construction of the contact bush, which to pass on contact has rings with the length of the bent-over end of the thermocouple wire.

The invention is based on the problems of minimizing the material consumption of precious metal in an expendable insertion unit of a thermocouple element, to create thereby a connection of the thermocouple wires forming the thermocouple element with the equalizing wires, which is simple to provide, does not alter the base material, but is secure in terms of contact, and which makes it possible to use precious metal as the thermocouple wire which is extremely thin and as short as possible.

According to the invention, in the vicinity of each shank foot of the insulating tube a tubular sleeve is provided, which consists of resilient material, in the sleeve inner bore the respective thermocouple wire and the equalizing wire are arranged paraxially, and the diameter of the sleeve inner bore and the equalizing wire are of a size such that, through the restoring forces of the resilient sleeves the thermocouple wires are pressed against the equalizing wire making contact.

In the preferred form of the insertion unit of an immersion thermocouple element according to the invention, the thermocouple wires have a diameter of 0.05 mm and only project out for a short distance on the shanks of the insulating tube. The respective end of a thermocouple wire is carried through the inner bore in a sleeve and laid around on the side of the sleeve facing from the insulating tube. In this way the precious metal wires are kept short.

Precious metal wires can be used which are up to a diameter size of 0.03 mm. In this way, advantageously, the consumption of platinum and rhodium is reduced. The recovery of the precious metal, at the present time, is too costly.

Through the small diameter of the thermocouple wire, in addition advantageously a short measurement period can be achieved in which to determine the temperature. The measurement times are reduced by one to two seconds. This represents approximately a third of the present measurement time. Here the wear on various parts of the measuring lance, for example the outer tube, is too reduced.

As the period of immersion of the parts into the melt is shorter, these can therefore be designed with thinner walls and accordingly with a greater saving on material.

The use of the insertion unit according to the invention with the sleeve as connection point of the thermo-wire and equalizing wire permits the assembly work to be largely mechanized. It is of considerable advantage here that a reliable connection point for the transfer of measurement signals is produced through the simply assembled and easily controllable connection point.

In a preferred embodiment of the invention unit, the sleeve is held by the contact piece, when in turn is detachably connected with the lance. The sleeve and contact piece are made from the same material, e.g. PVC which is unaffected by changes in temperature. The fashioning and connection of the sleeve and contact piece are designed such that the wires do not have any contact with the refractory material which is introduced into the shaped part. This, in turn, has the advantage that no humidity can reach the wires, having a negative effect on the measured values through the formation of galvanic elements.

The sleeve is of rubber elastic material and its internal diameter, in comparison with the external diameter of the equalizing wire, is equal in size or somewhat smaller. On fitting, the equalizing wire, the tip of which does not have an edge which damages the rubber elastic material, is introduced into the internal bore of the sleeve, which is intended for the connection of thermocouple wire and equalizing wire, over the entire length of the bore.

Thereby the precious metal wire which is likewise located in the internal bore is pressed on one side into the internal surface of the sleeve and on the other side to a sufficient extent into the external surface of the equalizing wire.

The restoring forces of the rubber elastic material of the sleeve are designed such that the equalizing wire may be comfortably introduced into the internal bore. The contact pressures are thereby so strong that a sufficent physical contact exists between the thermocouple wire and the equalizing wire.

Owing to the short length of the sleeve, during the introduction of the equalizing wire, slight frictional forces occur only briefly between the equalizing wire and the thermocouple wire. A tearing of the thermo wire does not occur here.

The construction of the connection point is kept very simple and consists exclusively of the sleeve, which is able to be produced at favourable cost because of its simple form, the equalizing wire, which is unworked with the exception of the breaking of the edges, and the thermo-wire, which merely has to be cut off after placing into the sleeve.

Dependent upon assembly, it may be necessary to couple the end of the equalizing wire facing the melt by means of a compression device. In this case, a short piece of the equalizing wire, as described above, is connected with the thermo-wire. The part of this small piece projecting out of the sleeve is formed in a quiver shape. During the final assembly of the probe, the remaining part of the equalizing wire can be inserted into the 'quiver' and can be connected securely in terms of contact by squeezing the 'quiver' together.

An example of one embodiment of the invention is shown in the drawings, in which: Figure 1 shows a section through an insertion unit of an immersion thermocouple element, Figure 2 shows a section through the sleeve.

The description of the insertion unit corresponds in its chonology to the sequence of assembly.

In the insulating tube 21, which is designed in a U-shape, is the soldered junction 11 forming the thermocouple element. The thermocouple wires projecting out of the insulating tube 21 at the shank foot 22, the platinum wire 12 and the platinum-rhodium wire 13, are threaded into the sleeve inner bore 32 of the resilient elastomeric sleeve 31 and bent around at the front face 36.

The sleeve 31 is pushed onto the respective shank foot 22 up to the base surface 33 of the widening, whereby the widening 34 surrounds the insulating tube 21.

In the opposite direction to the thermocouple wire 12, 13, the equalizing wire 14, which is of a material having the same thermoelectric properties as the thermocouple wire 12, 13, is introduced into the sleeve inner bore 32.

To facilitate the introduction of the wire and to avoid damaging the thermo-wire 12, 13, the equalizing wire 14 has a reduced edge on one face, preferably in the form of a truncated cone.

The sleeve 31 is provided at its bore orifices with chamfers 35 which are likewise intended to facilitate the introduction of elements into the bores.

The equalizing wire 14 is introduced into channels of the contact piece 41 and the sleeves 31 which are placed onto the insulating tube 21 are placed in recesses 42 of the contact piece.

The contact piece 41 is then pushed coaxially into the shaped part 24 with the insulating tube 21. The interior space 25 of the shaped part 24 which remains free, which therefore is not filled by the contact piece 41, the sleeve 31 and the insulating tube 21, is filled with fireproof material.

In a recess 26 arranged on the side of the shaped part 24 facing the melt, the open end of the cap 23 is placed, which surrounds the insulating tube 21 as a protection.

The insertion unit 20 is now ready to be installed and can be inserted into the outer tube 51 of the measuring lance 50, whereby the contact carrier 41 is able to be engaged in a bush 52.

Claims (10)

1. Expendable insertion unit of an immersion thermocouple element, in particular for steel melting, consisting of a refractory cylindrical shaped part, to be inserted coaxially into the outer sleeve of a measuring lance, an insulating tube, which is bent in a U-shape, to be attached by its shanks to the head of the shaped part on the melt side, and which is protected by a cap, in which the insulating tube receives the soldered junction of the thermocouple wires representing the temperature sensor which, emerging out of the shanks of the insulating tube, are connected with equalizing wires, and a contact carrier provided at the base of the shaped part, which receives the equalizing wires and is inserted into a contact bush for the transfer of electrical signals, and wherein in the vicinity of each shank foot of the insulating tube a tubular sleeve is provided, which consists of resilient material, in the sleeve inner bore the respective thermocouple wire and the equalizing wire are arranged paraxially, and the diameter of the sleeve inner bore and the equalizing wire are of a size such that, through the restoring forces of the resilient sleeves the thermocouple wires are pressed against the equalizing wire making contact.

2. Insertion unit according to Claim 1, wherein the thermocouple wire has a diameter equal to or less than 0.06mm.

3. Insertion unit according to Claim 1, wherein the equalizing wire has a diameter equal to or less than 0.3mm.

4. Insertion unit according to Claim 3, wherein the equalizing wire has a reduced edge on the side which is able to be inserted into the sleeve.

5. Insertion unit according to Claim 1, wherein the sleeve inner bore has a stepshaped widening and the diameter of the widening is of a size which is equal to or smaller than the external diameter of the insulating tube.

6. Insertion unit according to Claim 5, wherein the sleeve is arranged so as to be placed up to the base surface of the widening onto the respective shank foot of the insulating tube.

7. Insertion unit according to Claims 1, 6 and 7, wherein the internal diameters have chamfers at the orifices of the sleeve.

8. Insertion unit according to one of Claims 1 to 7, wherein each sleeve is arranged so as to be inserted into a recess on the side of the contact carrier facing the melt.

9. Insertion unit according to Claim 8, wherein the part of the contact carrier facing the melt is arranged so as to be inserted in the shaped part.

10. Expendable insertion unit of an immersion thermocouple substantially as described with reference to the accompanying drawings.