GB2109114A

GB2109114A - Metallurgical furnace

Info

Publication number: GB2109114A
Application number: GB08230179A
Authority: GB
Inventors: Siegfried Rohmann
Original assignee: Westofen GmbH
Current assignee: Westofen GmbH
Priority date: 1981-10-24
Filing date: 1982-10-22
Publication date: 1983-05-25
Also published as: IT8249342A0; DE3142241A1; CH657917A5; SE8206013D0; IT1148424B; SE8206013L; ES8307049A1; NL8203984A; BE894756A; ES516751A0; FR2515341A1; DK464282A

Abstract

A metallurgical furnace 2 includes an electrode 6 which extends into its interior 1 and produces a short circuit current when it contacts the melt 3 in the furnace. A motor 11 is arranged to move the electrode vertically. A sensor 12 senses the angular position of the motor. In use, the electrode is moved downwardly until it contacts the melt. The appropriate one of a plurality of lamps (S1 to S6) determined by the sensor 12 is then turned on to indicate the melt level and the electrode is moved up a short distance to protect it from the melt. After a predetermined time the procedure is repeated. <IMAGE>

Description

SPECIFICATION Metallurgical furnace The invention relates to a metallurgical furnace and is concerned with such furnaces including a device for indicating the melt level within it of the type including an electrode extending within it and arranged to produce a short-circuit current when it contacts the metal melt. A furnace with such an electrode is described in German Patent No. 2022989 which is concerned with a dosing device.

Molten metal rising in a delivery tube under the action of pressurised air contacts two electrodes and the short circuit which occurs is used as a control signal. The device disclosed in this prior patent is, however, not arranged to indicate the level of the melt in the furnace.

It is desirable in a furnace for a metal melt to be able to indicate the melt level at any time at a point outside the furnace and accordingly it is an object of the present invention to provide a furnace including a device which automatically indicates the level of the melt within it and variations thereof.

In accordance with the present invention there is provided a metallurgical furnace into the interior of which an electrode extends, the electrode being connected in an electrical circuit through which, in use, an indicating current flows when the electrode contacts the surface of a melt in the furnace and being connected to a motor to be. moved vertically by the latter, the furnace including a sensor arranged to sense the angular position of the motor, control means to rotate the motor to move the electrode into contact with the surface of the melt at predetermined time intervals and to reverse the direction of rotation of the motor when the indicating current begins to flow to move the electrode upwards a predetermined distance and indicator means connected to the sensor.

Thus, in use, the electrode is repeatedly moved into contact with the melt surface. As soon as it touches the latter an indication of the melt level is produced which is derived from the angular position of the motor. On contact with the melt the direction of rotation of the motor is reversed so that the electrode rises up away from the melt with the result that the electrode is not continuously subjected to the melt. The operating personnel can thus read off from an indicator to what level the furnace is full. Of particular interest are the limiting cases in which the furnace is full or requires refilling and these states may be separately indicated.

The furnace preferably includes means to vary the time interval at which the motor is rotated to move the electrode downwards.

One embodiment includes first and second timing elements connected to the control means, the first of which is arranged to be operative when the furnace is being filled and the other second of which is arranged to be operative when the furnace is not being filled, the first timing element being set at a shorter time than the second and both timing elements being arranged to initiate rotation of the motor to move the electrode downwards after the time determined by them has elapsed after the electrode has been moved by the predetermined distance. Thus during the refilling process a rapidly repeated measurement adapted to the rapid rising of the melt level occurs. When a rapid change of the melt level is not to be expected, the measurement is effected correspondingly less frequently.

Preferably the indicator means is of visual type whose output changes in discreet steps to indicate the melt level in the furnace and which is arranged so that its output does not alter when the electrode is moved upwar.ds by the predetermined distance.

Further features and details of the invention will be apparent from the following description of one specific embodiment which is given by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic elevation of a metallurgical furnace in accordance with the invention; and Figure 2 is a side view of the furnace of Fig. 1.

The furnace 2 defines an interior space 1 which contains an aluminium melt 3 and communicates in a gas-tight manner with a drive box 4. An electrode 6 is movably guided in an electrically insulated manner through an opening 5 extending between the drive box 4 and the interior space 1. The electrode 6 is mechanically suspended on a rope 7 which extends over a guide roller 8 and thence to a winding pulley 9 to which it is secured.

The winding pulley 9 is mounted on a shaft 10 which may be rotated by an electric motor 11 via an appropriate speed reduction gear 1 3. An angular sensor 12, such as a cam disc with switches associated with the cams, is connected to the shaft 10.

The electrode 6 is arranged to be movable over a distance H which is as large as or a little larger than the height difference between the melt levels V, when the furnace is full, and L, when the furnace is empty. In this specific embodiment, the winding pulley 9 is so dimensioned that its periphery is slightly longer than the distance H. Thus, less than one revolution of the winding pulley 9 is necessary to move the electrode 6 over the distance H.

The electrode 6 is electrically connected to a cable 14. The electrode 6 and the cable 14 can be unipolar when the electrical circuit is to be completed via the aluminium melt 3.

Alternatively the electrode 6 and the cable 1 4 can be of two-pole construction.

The electrode 6 is connected to an electrical control circuit 1 5 by means of the cable 1 4.

Additionally connected to the control circuit 1 5 are the electric motor 11, the angular position sensor 1 2, an indicator unit 1 6 which includes a plurality of signal lamps S1 to S8 and an accoustic signal transmitter A, and to a filling valve or flap (not shown) which controls the furnace inlet.

When the electrode 6 contacts the surface of the melt 3, an electrical circuit is completed by or through the melt and a short circuit current flows. The control circuit 1 5 is so arranged that when this occurs the direction of rotation of the motor 11 is reversed with the result that the electrode 6 is lifted above the melt surface. The duration of this reverse rotation of the motor is so determined by means of a timing element in the control circuit 1 5 that the electrode 6 is lifted by about 1 5 to 20 mm above the melt level. The motor and thus also the electrode then remain stationary for a period determined by one of two further timing elements in the control circuit 1 5 whereafter the motor is rotated in the original direction to move the electrode downwards again.The two further timing elements are set at different times and the one that is operative at any one time is determined by the position of the filling flap. Thus when the filling flap is open, the stopping time of the motor is shorter than the stopping time when the filling flap is closed. The stopping time of the timing element which is operative when the filling flap is open is for instance 10 seconds whilst that of the other timing element may be about 1 minute.

The control circuit 1 5 switches the motor 11 on after the operative timing element has timed out and lowers the electrode 6 towards the melt 3. At the same time the angular sensor 1 2 is also rotated and successively switches on the indicator lamps S1 and S6 in accordance with its angular position at any time. These lamps are arranged one above the other and symbolically represent the melt level at any time in the space 1 of the furnace 2.

The indicator lamp S7 produces an additional signal when the furnace 2 is almost empty, that is to say should be filled. The indicator lamp S8 produces a still further signal when the furnace 2 is empty. The accoustic indicator A produces an additional signal when the furnace 2 is full.

The mode of operation of the described measuring device is thus as follows: When the filling flap is closed the electrode 6 is lowered onto the melt surface at time intervals of, for instance, 1 minute. As soon as it contacts the melt surface the indicator lamp S1 to S6 corresponding to the height of the melt lights up and the electrode 6 is lifted up again away from the melt by reversing the direction of rotation of the motor 11 to protect the electrode against being damaged by the melt. The control circuit 1 5 is arranged so that as the electroce is raised the indicated filling level does not alter. After a predetermined time, e.g. 1 minute, set by one of the two further timing elements the procedure is repeated.

As the melt level gets progressively lower the indicator lamps S1 to S6 then light up successively. Shortly before reaching the empty state L of the furnace 2 the indicator lamp S7 additionally switches on. On reaching the empty state L the lamp S8 also switches on.

When filling the furnace 2 the filling flap is open with the consequence that the other of the two further timing elements which is set at shorter time, e.g. 10 seconds, is operative.

The melt level is thus measured very much more frequently. In the course of the refilling of the furnace 2 the lamp S6 and S1 will then turn on successively. When the furnace 2 is full the accoustic indicator A also switches on.

The adjustment of the time in which, or the distance by which, the electrode 6 is lifted up away from the melt level to protect it is determined having regard to the short time period in which the motor 11 lowers the electrode 6 into contact with the melt level that the electrode 6 cannot be overtaken by the melt level and thus submerged in the melt even when the latter is rising at the most rapid rate to be expected so that the electrode 6 is always lowered from above onto the melt.

Claims

1. A metallurgical furnace into the interior of which an electrode extends, the electrode being connected in an electrical circuit through which, in use, an indicating current flows when the electrode contacts the surface of a melt in the furnace and being connected to a motor to be moved vertically by the latter, the furnace including a sensor arranged to sense the angular position of the motor, control means to rotate the motor to move the electrode into contact with the surface of the melt at predetermined time intervals and to reverse the direction of rotation of the motor when the indicating current begins to flow to move the electrode upwards a predetermined distance and indicator means connected to the sensor.

2. A furnace as claimed in Claim 1 including means to vary the time interval at which the motor is rotated to move the electrode downwards.

3. A furnace as claimed in Claim 2 including first and secon timing elements connected to the control means, the first of which is arranged to be operative when the furnace is being filled and the second of which is arranged to be operative when the furnace is not being filled, the first timing element being set at a shorter time than the second and both timing elements being arranged to initiate rotation of the motor to move the electrode downwards after the time determined by them has elapsed after the electrode has been moved upwards by the predetermined distance.

4. A furnace as claimed in any one of the preceding claims in which the indicator means is of visual type whose output changes in discreet steps to indicate the melt level in the furnace and which is arranged so that its output does not alter when the electrode is moved upwards by the predetermined distance.

5. A furnace as claimed in Claim 4 in which the indicator means comprises a plurality of electric lamps which are switched on successively as the level of the melt in the furnace varies.

6. A furnace as claimed in any one of the preceding claims in which the electrode is suspended by a cable which passes over a winding pulley driven by the motor, the periphery of the pulley being longer than the distance between the full and empty levels of the furnace.

7. A furnace as claimed in Claim 6 in which the angular position sensor is situated on the axis of the winding pulley.

8. A metallurgical furnace substantially as specifically herein described with reference to the accompanying drawings.