GB2167326A - A device for taking a sample of molten metal - Google Patents

Abstract

The device 10 comprises a chamber 30 in a sampling cavity 14, for taking a sample of molten metal by dipping the device into the metal. A body 12 has an open-ended bore 24 which enables the device to be engaged over the protective tube 22 of an immersion thermocouple 16 comprising a temperature sensing element 18 mounted on a lance 20. <IMAGE>

Description

SPECIFICATION A device for taking a sample of molten metal The present invention relates to devices for taking samples of molten metal. Samples of molten metal are taken as a matter of routine during the production of metals such as steel, and are then analysed to monitor the production process.

A sample of metal is often taken at the same time as a measurement is made of the temperature of the molten steel. More often, temperature measurement is carried out alone, using an immersion thermocouple of the type herein defined as comprising a disposable thermocouple unit mounted in the end of a protective tube. The disposable thermocouple unit is commonly called a tip and the tube is typically a cardboard tube sheathing a lance which has electrical contacts making connection with contacts on the disposable tip.

Wires within the lance convey signals from the thermocouple to apparatus for displaying and/or recording the signals. Cardboard tubes are commonly supplied with a thermocouple tip already in position, and in order to make a temperature measurement, a user simply places the protective cardboard tube over the lance, and then, holding the lance, dips the tip into the steel. The cardboard tube chars on contact with the steel, but does not burn, because of the low concentration of oxygen in the steel. After the measurement has been made, the tube and the tip, which is destroyed by the measurement, are taken off the lance and discarded.

About 75% of the uses of the lance are for temperature measurement alone. When simultaneous sampling and temperature measurement are required, an alternative tip is used, comprising a thermocouple and a small sampling chamber. When the tip is dipped into the steel, a small sample is collected in the sampling chamber while the thermocouple measures the temperature.

A third type of tip is known, which has a sampling chamber, but no thermocouple. This type is only occasionally used, because a temperature measurement is usually required when a sample is taken.

Tips comprising a sampling vessel as well as a thermocouple are naturally more expensive than tips comprising a thermocouple alone. Although the user should select a tip with a chamber when and only when a sample is required, and a cheaper thermocouple tip when only a temperature measurement is required, it is found in practice that many users select the more expensive type of tip on every occasion, for convenience, and to avoid the need to have a supply of more than one type of tip readily available. This results in unnecessary expense through the wastage of tips having thermocouples and sampling chambers being used for temperature sensing only.

The present invention seeks to overcome this problem by encouraging the user to take a sample only when one is required, and to use tips having only a thermocouple on all other occasions.

The present invention provides a device for taking a sample of molten metal, comprising a body for dipping into the metal, and a sampling cavity in the body, wherein the body has a portion shaped to engage over the protective tube of an immersion thermocouple of the type hereinbefore defined, thereby to mount the device on the protective tube.

A user of the lance is provided with a supply of thermocouple tips (usually already mounted in the ends of protective tubes) and a supply of devices according to the invention, and because preparing the lance for taking a sample and a temperature reading requires an extra operation to preparing it for temperature measurement alone, namely engaging the device over the protective tube of the lance, a user will tend not to sample the steel unless sampling is actually required.

When cardboard tubes are supplied with a thermocouple tip already in position, it is envisaged that the device could be used, when only a sample is required, by slipping it over a tube which has already been used, and whose thermocouple tip has therefore been destroyed, if the tube is not too badly charred.

Alternatively, the device could be slipped over a new tube without a thermocouple tip.

Preferably, the shaped portion has an openended bore through the body, for receiving the protective tube, so that the device may be conveniently slipped over the tube on the lance after a temperature tip has been fitted.

In this case, means are preferably provided to prevent the body slipping off the protective tube after mounting. These means may be barbs within the bore and positioned to engage the cardboard tube around the lance.

Two embodiments of an accessory according to the invention will now be described by way of example with reference to the accompanying drawings in which: Fig 1 is a section through one embodiment of the invention, shown in position on an immersion thermocouple; and Fig 2 is a section through a second embodiment also shown in position on an immersion thermocouple.

Referring to Fig 1, the device 10, shown in section, comprises a body 12 for dipping into molten metal. The body 12 has a sampling cavity 14 for collecting a sample of molten metal. The body 12 has a portion shaped to engage over the protective tube 15 of an immersion thermocouple of the type defined above.

The immersion thermocouple 16 comprises a thermocouple in a temperature measuring tip 18 which is mounted at the end of a lance 20. Electrical contacts for the thermocouple are provided but are not shown. The lance 20 is surrounded by a cardboard tube 15 for protection from the molten steel. The tip 18 may be mounted directly on the lance, or may be mounted in the end of the tube which in turn sheathes the lance. In the latter case, not shown in the drawings, the tip may be held in the tube by a solvent adhesive, and the cardboard tube may project beyond the end of the lance, so that the tip is spaced from the end of the lance.

The body 12 has a cylindrical bore 24, open at both ends, in which the lance 20 and cardboard tube 15 are located. The bore 24 enables the accessory to be slipped over the protective tube 15 when a sample of the steel is required. A spring steel collar 26 has barbs 28 projecting both inwardly and outwardly.

The outwardly projecting barbs are cemented to the body 12. The inwardly projecting barbs engage the cardboard tube 15 to prevent the device 10 slipping off the tube 20 during use.

A sampling chamber 30 is located in the sampling cavity 14 and has a mouth 32 through which a sample of molten metal may flow into the chamber 30 when the device 10 is dipped into the metal. The mouth 32 is covered by a steel cap 34 before use. The cap 34 is held in position by refractory cement, and melts on contact with the molten steel. Vent holes 36 are provided through the walls of the chamber 30 to allow air inside the chamber to be displaced by molten metal entering through the mouth 32. A strip of deoxident material 38, preferably aluminium, is provided in the chamber.

The chamber 30 is made in two identical halves held together by a mild steel retaining clip 40. The mouth 42 of the cavity 14 is plugged with a cork stopper 44 made of pure, high density cork, and fixed in the mouth 42 by an adhesive such as COREFIX No 9 waterbased adhesive manufactured by FOSECO. The chamber 30 has a neck 46 which extends through a bore 48 in the body 12, so that its mouth 32 is adjacent the thermocouple tip of a lance on which the device 10 is mounted.

The bore 48 is sealed around the neck 46 by magnesium oxide refractory cement. The neck 46 is not integral with the two halves forming the body of the chamber 30. During manufacture, the neck 46 is bonded to one of the halves by epoxy resin, to facilitate assembly of the chamber. Gaps around the neck 46, between the neck 46 and the halves of the chamber 30, act as additional vent holes.

After sampling, the chamber 30 is removed from the cavity 14 by smashing the body 12, and is opened by removing the clip 40 and parting the two halves forming the chamber.

The sample of metal in the chamber is then removed and taken for analysis.

The body 12 is made of a refractory material, for instance a ceramic material containing alumino-silicate fibres. The body 12 provides thermal insulation between the chamber 30 and the environment outside, so that the interior of the chamber remains relatively cool, and molten metal entering the chamber quickly solidifies.

The second embodiment of the device 10, shown in Fig 2, differs from that shown in Fig 1 in the layout of the sampling cavity 14 and in the means for providing barbs for securing the accessory to the cardboard tube 15. The same numerals are used in Figs 1 and 2 for equivalent features, and only the differences between the embodiments is described below.

The cavity 14 has only one mouth 50, which opens adjacent the end of the bore 24 at which the thermocouple tip 18 is located when the device is mounted on a lance 16.

The chamber 30, which is the same as the chamber shown in Fig 1, is placed in the cavity 14 so that its neck 48 projects out of the mouth 50. The cavity 14 around the chamber 30 is filled with a filler material such as resin bonded sand, which holds the chamber in position in the cavity. The chamber 30 is further secured in the cavity 14 by brads 51 (thin, flat nails) projecting through the body 12 and into the walls of the chamber neck 48. The brads are inserted during manufacture, using a pneumatic gun.

The chamber 30 is removed from the body 12 shown in Fig 2 by smashing the body.

In the embodiment of Fig 2, barbs 28 are provided on a sleeve 52 rather than on a collar. That is, the sleeve 52 is cylindrical and has an axial length considerably longer than the collar 26 of Fig 1. Naturally, the sleeve 52 can be used with the embodiment of Fig 1, and the collar 26 of Fig 1 can be used with the embodiment of Fig 2. The axial length of the collar or sleeve can be chosen according to the security required in holding the device on a lance, since more barbs can be provided on a longer collar.

The body 12 may be made entirely of resin bonded sand, cast around the chamber 30 to hold the chamber in position.

Claims (12)

1. A device for taking a sample of molten metal, comprising a body for dipping into the metal, and a sampling cavity in the body wherein the body has a portion shaped to engage over the protective tube of an immersion thermocouple of the type hereinbefore defined, thereby to mount the device on the protective tube.

2. A device according to claim 1, wherein the shaped portion has an open-ended bore through the body, for receiving the protective tube.

3. A device according to claim 2, having means for preventing the body slipping off the protective tube after mounting.

4. A device according to claim 3, wherein the means for preventing the device slipping off comprise barbs within the bore and positioned to engage the protective sleeve.

5. A device according to claim 4, wherein the barbs are provided on a sleeve or collar fixed in the bore.

6. A device according to any preceding claim, comprising a sampling chamber mounted in the sampling cavity and into which molten metal flows when the device is dipped into the metal.

7. A device according to claim 6, wherein the body is formed around the chamber by casting.

8. A device according to claim 6, wherein the cavity has a main region with a mouth allowing a chamber to be put into the cavity, and a narrower bore extending between the main region and the outside of the body, the chamber having a main housing located in the main region and a neck between the main housing and the chamber mouth, the neck being located in the bore.

9. A device according to claim 8, insofar as it is dependent on claim 2, wherein the outer end of the cavity bore is adjacent one end of the tube receiving bore.

10. A device according to claim 6, wherein the cavity is a single-ended bore in the body, and the chamber has a main housing within the cavity and a neck between the main housing and the chamber mouth, the neck projecting out of the cavity mouth.

11. A device according to claim 10, insofar as it is dependent on claim 2, wherein the chamber mouth is adjacent one end of the tube-receiving bore.

12. A device substantially as described above with reference to Fig 1 or Fig 2 of the accompanying drawings.