METHOD FOR DETERMINING THE NEUTRAL TEMPERATURE IN LONG-STRETCHED WORKPIECES

Abstract

The invention pertains to a method for respectively determining the neutral temperature or the stressfree state in a rail section (1), wherein an ultrasonic signal is coupled into a representative volume of the rail profile perpendicular to its longitudinal direction, wherein the volume is subjected to stresses in the longitudinal direction of the rail section (1), wherein the stresses are measured, wherein an ultrasonic signal influenced by these stresses is decoupled, wherein a function describing the functional dependence of the decoupled ultrasonic signal on the introduced stress is determined, and wherein the stressfree state is determined based on the course of this function.

Claims

1. A method for respectively determining the neutral temperature or the stressfree state of an elongate workpiece, wherein a test section of said workpiece is subjected to longitudinal stress in a defined fashion, and wherein the state of stress in the test section is determined and used as the basis for determining the stressfree state, characterized in that a signal, which is influenced by the value of the longitudinal stress, or a sequence of these signals is coupled into a representative volume of the workpiece cross section, in that longitudinal stresses are introduced into the test section of the workpiece, in that a signal decoupled from the representative volume is evaluated, in that a function describing the functional dependence of a parameter of the decoupled signal on the respective longitudinal stress is determined, and in that the stressfree state is determined based on the course of this function with consideration of the temperature during the measurement.

2. The method according to claim 1, characterized in that a magnetic signal or a sequence of magnetic signals is coupled into the representative volume of the workpiece, in that the magnetic signal decoupled from the representative volume is evaluated, in that a function (21) describing the functional dependence of a parameter of the decoupled magnetic signal on the respective longitudinal stress is determined, and in that the stressfree state is determined based on the course of this function (21).

3. The method according to claim 2, characterized in that the evaluation is carried out based on the determination of the deviation between an externally excited magnetic field and a magnetization in the representative volume induced thereby.

4. The method according to claim 2, characterized in that at least one transmitter coil (13) and one receiver coil (14) are used for the magnetic signal and assigned to the representative volume.

5. The method according to claim 4, characterized in that the transmitter coil (13) and the receiver coil (14) are arranged in such a way that their axes extend at an angle of 90° to one another and that angles of 45° to the longitudinal axis of the workpiece.

6. The method according to claim 5, characterized in that the transmitter coil (13) and the receiver coil (14) are respectively incorporated into magnetic circuits (15, 16), in which one element is formed by part of the workpiece.

7. The method according to claim 1, characterized in that an ultrasonic signal or a sequence of ultrasonic signals is coupled into the representative volume of the workpiece, in that an ultrasonic signal decoupled from the representative volume is evaluated, in that a function (10) describing the functional dependence of a parameter of the decoupled ultrasonic signal on the respective longitudinal stress is determined, and that the stressfree state is determined based on the course of this function (10).

8. The method according to claim 1, characterized in that a workpiece section located between a transmitter (7) and a receiver (8), which is arranged opposite of said transmitter transverse to a longitudinal workpiece direction, is used as representative volume.

9. The method according to claim 1, characterized in that ultrasonic signals in the form of transverse waves are used in the representative volume, and in that the valuation of a decoupled signal is carried out with consideration of the polarizing angles of the transmitter (7) and the receiver (8) relative to a longitudinal axis of the workpiece.

10. The method according to claim 9, characterized in that the determination of the neutral temperature is carried out with fixed polarizing angles.

11. The method according to claim 9, characterized in that the determination of the neutral temperature is carried out with polarizing angles, which can be varied within an angular range between 0° and 90°.

12. The method according to claim 3 characterized in that at least one transmitter coil (13) and one receiver coil (14) are used for the magnetic signal and assigned to the representative volume.

13. The method according to claim 12, characterized in that the transmitter coil (13) and the receiver coil (14) are arranged in such a way that their axes extend at an angle of 90° to one another and that angles of 45° to the longitudinal axis of the workpiece.

14. The method according to claim 12, characterized in that the transmitter coil (13) and the receiver coil (14) are respectively incorporated into magnetic circuits (15, 16), in which one element is formed by part of the workpiece.

15. The method according to claim 13, characterized in that the transmitter coil (13) and the receiver coil (14) are respectively incorporated into magnetic circuits (15, 16), in which one element is formed by part of the workpiece.

16. The method according to claim 7 characterized in that a workpiece section located between a transmitter (7) and a receiver (8), which is arranged opposite of said transmitter transverse to a longitudinal workpiece direction, is used as representative volume.

17. The method according to claim 7 characterized in that ultrasonic signals in the form of transverse waves are used in the representative volume, and in that the valuation of a decoupled signal is carried out with consideration of the polarizing angles of the transmitter (7) and the receiver (8) relative to a longitudinal axis of the workpiece.

18. The method according to claim 8 characterized in that ultrasonic signals in the form of transverse waves are used in the representative volume, and in that the valuation of a decoupled signal is carried out with consideration of the polarizing angles of the transmitter (7) and the receiver (8) relative to a longitudinal axis of the workpiece.

19. The method according to claim 17, characterized in that the determination of the neutral temperature is carried out with fixed polarizing angles.

20. The method according to claim 18, characterized in that the determination of the neutral temperature is carried out with fixed polarizing angles.

Description

[0024] The invention is described in greater detail below with reference to the attached drawings. In these drawings:

[0025] FIG. 1 shows a schematic representation of an inventive measuring arrangement that operates based on ultrasound;

[0026] FIG. 2 shows a schematic representation of a magnetic sensor configuration;

[0027] FIG. 3 shows a graphic representation for determining the stressfree state of the rail based on a transit time measurement with ultrasonic waves;

[0028] FIG. 4 shows a graphic representation for determining the stressfree state of the rail based on their magnetization;

[0029] FIG. 5-FIG. 11 show alternative arrangements of transmitter and receiver modules for coupling a magnetic field into the rail profile to be analyzed and for determining a response signal; and

[0030] FIG. 12 shows isolated partial representations of the magnetic sensor configuration according to FIG. 2.

[0031] In FIG. 1, the reference symbol 1 identifies a rail section that should be analyzed with respect to longitudinal stresses, particularly a neutral temperature, by utilizing the inventive method.

[0032] A device intended and designed for introducing longitudinal stresses into this rail section 1 in the direction of the arrows 2 is not illustrated in this figure. However, devices of this type are generally known such that a more detailed description of their design is unnecessary. These longitudinal stresses are uniformly introduced into the rail section 1 on both sides.

[0033] The reference symbol 3 identifies a device for measuring the introduced external longitudinal stress, which is connected to the rail section 1 by means of clamping jaws 4, 5.

[0034] Two exemplary embodiments of sensor arrangements 6 for determining the stressfree state are described below, namely an embodiment that is based on alternating magnetic fields in accordance with claim 2 and an embodiment that is based on ultrasonic waves in accordance with claim 7.

[0035] The reference symbol 7 identifies an ultrasonic transmitter that emits transverse wave packets with a center frequency of 1 MHz to 10 MHz in a defined polarizing direction relative to the longitudinal axis of the rail section 1, wherein these transverse wave packets propagate within a representative volume of the rail material perpendicular to its surface and are ultimately detected by an ultrasonic receiver 8. The volume of the rail material, which is thusly penetrated by ultrasonic waves, is defined by the positioning of the ultrasonic transmitter 7 and the ultrasonic receiver 8 and located within the rail section 1.

[0036] A device for measuring the rail temperature is not illustrated in this figure. However, such a measurement is only required once.

[0037] FIGS. 2-11 show potential positions of the ultrasonic transmitter 7 and the ultrasonic receiver 8 relative to a cross-sectional profile 9 of the rail section 1. In this respect, it is essential that the ultrasonic transmitter 7 and the ultrasonic receiver 8 are arranged in an opposing fashion. The receivers could basically also be provided on both sides of the representative volume. This would make it possible to also receive reflected signal components. Furthermore, the two receivers could also be designed for receiving differently polarized transverse waves.

[0038] According to the basic principle of the measurement, the signal detected by the ultrasonic receiver 8 is dependent on the angles between the longitudinal rail axis and the polarizing directions of the transmitter and the receiver, as well as on a longitudinal rail stress, but not dependent on a calibration and on material parameters. A non-linear correlation exists between the angle formed by the longitudinal rail axis and the polarizing directions and the amount of longitudinal stress in the rail section. In addition, the measurements are not influenced by an internal stress component due to the selection of a representative volume to be penetrated by ultrasonic waves, wherein the time period required for the measurement is limited to a few minutes depending on the measured stress range and the device used for introducing mechanical stresses into the rail section.

[0039] The measurements can be carried out with fixed angles between the polarizing directions and the longitudinal rail axis. However, measurements with fixed angles, for example, of 0°, 45° or 90° or a pass through an angular range, for example, from 0° to 90° would also be conceivable.

[0040] FIG. 3 shows the respective determination of the neutral temperature or the stressfree state based on the analytical determination of the maximum of the function 10 illustrated in this figure, wherein the force introduced into the rail section is plotted on the abscissa 11. A parameter that is dependent on longitudinal stresses such as, e.g., a transit time shift between the transmitted and the received signal is plotted on the ordinate 12, but it would also be possible to use other parameter differences between these two signals. The maximum of the function 10 indicates the position of the stressfree state and therefore the neutral temperature.

[0041] A magnetic-inductive arrangement may also be used instead of an ultrasonic sensor 6. This measuring arrangement is based on the fact that nearly all magnetic properties of ferromagnetic materials are influenced by external mechanical stress. In this respect, we refer to FIGS. 2 and 12, in which functional elements corresponding to those in FIGS. 1 and 3-11 are identified by the same reference symbols.

[0042] The reference symbol 13 identifies a transmitter coil, the axis of which extends at an angle of 45° to the longitudinal rail axis of the rail section 1. This transmitter coil subjects the rail section 1 to a alternating magnetic field, by means of which a magnetization is induced in said rail section in response to this magnetic excitation, wherein the direction and intensity of this magnetization are influenced by the externally excited magnetic field, as well as by the mechanical stress, particularly the longitudinal stress, in the rail section.

[0043] The reference symbol 14 identifies a receiver coil, the axis of which extends at an angle of 90° to the axis of the transmitter coil 13.

[0044] The transmitter coil 13 and the receiver coil 14 are respectively incorporated into a magnetic circuit, which also includes the rail head of the cross-sectional profile of the rail section 1, such that a signal received by the receiver coil 14 is influenced by the rail head.

[0045] FIG. 12 shows two magnetic circuits 15, 16 that act as carriers of the transmitter coil 13 and the receiver coil 14 and respectively feature a gap 19, 20, which is designed for accommodating the rail head of the rail section 1 in order to complete these circuits. In the inserted state, the datum planes of the magnetic circuits extend at an angle of 45° to the longitudinal rail axis and at an angle of 90° to one another.

[0046] During the operation of this magnetic-inductive measuring arrangement, the signal decoupled by the receiver coil is evaluated, particularly with respect to deviations between the magnetization and the external magnetic field. The rail section is in the stressfree state when the magnetization and the external magnetic field coincide.

[0047] The evaluation of the signal received by means of the receiver coil 14 may take place in accordance with a mathematical model, the evaluation result of which is graphically illustrated in FIG. 3. The forces introduced into the rail section 1 are plotted on the abscissa 17 whereas the response signal of the receiver coil 14 is plotted on the ordinate 18. The sequence of determined measuring points describes a function 21, the minimum of which describes the position of the stressfree state and therefore the neutral temperature.

[0048] This variation of the method can also be carried out within a few minutes, wherein neither a calibration nor information on material parameters of the rail section 1 is required.

LIST OF REFERENCE SYMBOLS

[0049] 1 Rail section

[0050] 2 Arrows

[0051] 3 Device

[0052] 4 Clamping jaw

[0053] 5 Clamping jaw

[0054] 6 Sensor arrangement

[0055] 7 Ultrasonic transmitter

[0056] 8 Ultrasonic receiver

[0057] 9 Cross-sectional profile

[0058] 10 Function

[0059] 11 Abscissa

[0060] 12 Ordinate

[0061] 13 Transmitter coil

[0062] 14 Receiver coil

[0063] 15 Magnetic circuit

[0064] 16 Magnetic circuit

[0065] 17 Abscissa

[0066] 18 Ordinate

[0067] 19 Gap

[0068] 20 Gap

[0069] 21 Function