CRUCIBLE INDUCTION FURNACE AND METHOD OF CHECKING STATUS THEREOF

Abstract

The functional condition of an induction crucible furnace is checked by first establishing a set-point parameter corresponding to an optimum functional condition of the induction crucible furnace and characterizing the vibratory behavior of same. Then, during normal operation of the furnace, an actual-value parameter of the vibratory behavior is determined. These two parameters are then compared and, if a magnitude of a difference therebetween exceeds a threshold, an alarm is generated.

Claims

1. A method of checking the functional condition of an induction crucible furnace, the method comprising the following steps: establishing a set-point parameter corresponding to an optimum functional condition of the induction crucible furnace and characterizing vibratory behavior thereof; determining an actual-value vibratory-behavior parameter in operation of the induction crucible furnace; and comparing the parameters, determining any difference therebetween, and deriving the functional condition of the furnace from a magnitude of the difference.

2. The method according to claim 1, wherein the set-point parameter is determined in a new condition of the induction crucible furnace under nominal conditions with regard to maintenance and operation.

3. The method according to claim 1, wherein the set-point parameter is provided and is measured during operation of the induction crucible furnace.

4. The method according to claim 1, further comprising the step of: generating an alarm signal or other message if the difference exceeds a predetermined threshold value.

5. The method according to claim 1, further comprising the step of: using as the point parameter a range characterizing the vibratory behavior.

6. The method according to claim 1, wherein the actual-value parameter is determined by a sound-level measurement and is compared with a corresponding set-point sound level value.

7. The method according to claim 1, wherein the actual-value parameter is determined by measurement of electromagnetic waves and is compared with a corresponding set-point value.

8. The method according to claim 1, wherein the actual-value parameter of the induction crucible furnace is measured with inductive and/or capacitive sensors and/or piezo sensors.

9. The method according to claim 1, wherein the actual-value parameter of the induction crucible furnace is determined by evaluation by frequency analysis.

10. The method according to claim 1, wherein the actual-value parameter of the induction crucible furnace is determined by a long-term observation continuously or in regular intervals.

11. The method according to claim 1, wherein the actual-value parameter of the induction crucible furnace is determined by trend observation.

12. The method according to claim 1, wherein the actual value parameter is determined with an induction crucible furnace with channel inductor.

13. An induction crucible furnace constructed for carrying out the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE INVENTION

[0026] In the following the invention is described in detail by embodiments in connection with the drawing.

[0027] FIG. 1 is a vertical section through an induction crucible furnace strongly schematically;

[0028] FIG. 2 shows the induction crucible furnace according to FIG. 1 with schematically indicated acoustic sensors for determining the vibratory behavior of the induction crucible coil of the induction crucible furnace;

[0029] FIG. 3 shows the furnace of FIG. 1 with vibration pick-ups on the housing and on the magnetic yoke; and

[0030] FIG. 4 is a schematic flow chart of the method of checking the functional condition of the induction crucible furnace.

SPECIFIC DESCRIPTION OF THE INVENTION

[0031] FIG. 1 shows strongly schematically an induction crucible furnace that has a crucible 1 intended for holding metal parts that have been melted in the furnace. The metal parts (scrap) and/or the melt are indicated at 5.

[0032] An induction coil 2 surrounds the crucible 1 and generates heat energy for melting the metal parts 5 in the crucible 1 with corresponding electrical excitation. A magnetic yoke 3 is associated with the induction coil 2. They are surrounded by a housing 4 that forms a suitable supporting structure for the induction crucible furnace.

[0033] Above it was described that the crucible furnace coil 2 is exposed to dynamic electromagnetic forces in the operation condition that contract the coil windings periodically axially and expand them radially. Furthermore, radial, outwardly directed forces are generated by heat expansion of the crucible 1. This, in the course of time, damages intermediate insulating layers between the coil windings so that the material thickness of the intermediate layers is reduced and a free space allowing movement of the coil windings results at these points. With corresponding freedom of movement of the coil winding, the movement of the windings generated by the electromagnetic forces becomes acoustically or otherwise sensible. Now, the inventive method uses the vibratory behavior of the furnace or of the coil in the condition of operation in order to come to conclusions with regard to the functional condition (wear condition).

[0034] FIG. 2 shows schematically a first embodiment of the inventive method according to which the acoustic performance of the furnace generated by vibrations of the coil windings is determined by suitable acoustic pick-ups 6. These acoustic pick-ups can be microphones. With them at least one acoustic parameter is measured and is sent to a controller (not shown) as electrical signals. The controller compares a signal value with a value of this parameter that has been measured in another condition of the furnace under nominal conditions with regard to maintenance and operation. Then the obtained difference of these values is used in order to make a diagnosis of the functional condition of the furnace. The greater the difference is, the greater is the wear of coil. If a certain level of the difference value is exceeded an alarm signal or another message can be given.

[0035] FIG. 3 shows an embodiment of the method according to which a vibration pick-up 7 is mounted on the housing 4 and a vibration pick-up 8 is on the magnetic yoke 3. Also in this case the determined signal values are sent to a controller as electrical signals compared with earlier determined standard signals that represent an optimum condition of the furnace. The functional condition of the furnace is derived from the difference of the corresponding values.

[0036] FIG. 4 shows a schematic flow chart of the inventive method. In step 10 at least one parameter characterizing the vibratory behavior of the furnace is determined in the novel condition of the furnace under nominal conditions. In step 11 a measurement of this parameter is carried out in the operational condition of the furnace. Both values of these parameters are compared with one another in step 12, and a corresponding difference value is calculated. Then, in step 13 it is checked if the determined difference value exceeds a level corresponding to a functional condition of the furnace without defects. If this value is exceeded in step 14, an alarm signal is given indicating a defect of the furnace.