METHOD AND APPARATUS FOR TESTING WHEELS AND DEFECT DETECTION IN WHEELS

• US 3,812,708 A
• Filed: 11/17/1971
• Issued: 05/28/1974
• Est. Priority Date: 11/17/1971
• Status: Expired due to Term

• Current Assignee: Gerald Deg. Cowan, John Gerald Cowan, John Vincent Cowan
• Original Assignee: Gerald Deg. Cowan, John Gerald Cowan, John Vincent Cowan
• Inventors: Cowan, John Vincent, Cowan, Gerald DeG., Cowan, John Gerald
• Primary Examiner(s): Queisser, Richard C.
• Assistant Examiner(s): Korkosz, Arthur E.
• Application Number:
  US05/199,487
• Time in Patent Office: 923 Days
• Field of Search: 73/67.5,67.7,67.8,67.8S,67.9 246/169S
• US Class Current: 73/598
• CPC Class Codes: G01B 17/06 for measuring contours or curvatures
• CPC Class Codes: G01N 2291/0258 Structural degradation, e.g. fatigue of composites, ageing of oils
• CPC Class Codes: G01N 2291/02854 Length, thickness
• CPC Class Codes: G01N 2291/0422 Shear waves, transverse waves, horizontally polarised waves
• CPC Class Codes: G01N 2291/048 Transmission, i.e. analysed material between transmitter and receiver
• CPC Class Codes: G01N 2291/102 one emitter, one receiver
• CPC Class Codes: G01N 2291/2626 Wires, bars, rods
• CPC Class Codes: G01N 2291/2636 cylindrical from inside
• CPC Class Codes: G01N 2291/2696 Wheels, Gears, Bearings
• CPC Class Codes: G01N 29/041 on the surface of the material, e.g. using Lamb, Rayleigh or shear waves
• CPC Class Codes: G01N 29/043 in the interior, e.g. by shear waves
• CPC Class Codes: G01N 29/27 by moving the material relative to a stationary sensor
• CPC Class Codes: G01N 29/343 pulse waves, e.g. particular sequence of pulses, bursts

Abstract

Wheel testing apparatus according to the invention comprises at least one search unit positioned '"'"''"'"''"'"''"'"'in-track'"'"''"'"''"'"''"'"' replacing a portion of a rail so that the gauged wheels of a passing railroad train roll thereover. Each search unit has a thin vertical rail aligned with the gauge edge of the track for supporting each passing wheel adjacent to its flange, and thereby exposing the running surface of the wheel for testing in a zone which does not interfere with the wheel'"'"''"'"'s path. Each search unit has two ultrasonic transducers enclosed in a flexible fluid-filled boot and are positioned adjacent to the thin vertical rail in the test zone under the running surfaces of passing wheels, the fluid-filled boot providing good ultrasonic coupling therewith. The transducers are angled and opposed; ultrasonic energy pulses are refracted substantially tangent to the wheel and thereafter travel about the periphery of the wheel in opposite directions, depending on which transducer is pulsed. The pulse travels around the wheel and returns to the search unit, where a portion of the pulse is returned from the wheel to the second transducer confirming the presence of the pulse in the wheel and halting further pulsing of the first transducer. The returned pulse also is used to adjust the amplified gain of the output of the first transducer, which is monitored for echo pulses reflected from defects in the surface of the wheel. The travel time of pulses around the wheel is measured to indicate wheel size. A wear measurement is made by measuring the time interval between the time for the pulse to travel about the periphery of the running surface and the time for the pulse to travel about the larger diameter flange. Outputs from the electronic test circuit include a defect alarm signal, an excessive wear alarm signal, a wheel size indication, and a test certification signal. These outputs trigger pressurized color-coded paint sprays for marking the wheels if they are passing at low speed, or terminals for connection with automatic car identification systems for recording information relating to the wheels passing at either low or high speed.

Claims

1. The method of inspecting a body for defects in a curved peripheral surface thereof forming an uninflected closed curve comprising the steps of:

A. coupling a zone of the curved surface with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the body;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of ultrasonic energy pulses projected by the transducer being inclined with respect to a tangent plane of the zone at an angle whereby low frequency ultrasonic energy delivered to the body along the sonic axis enters the body, penetrates to a substantial depth therein, and is refracted substantially tangent to the curved surface; and

whereby the energy which penetrates the body to a substantial depth travels along a path near to and converging toward the curved surface and having a progressively increasing radius of curvature, and thereby migrates toward the curved surface thereof, as it travels along said path;

C. pulsing the first ultrasonic transducer to produce a low frequency ultrasonic energy pulse; and

D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the curved surface and refracted out of the body at the coupled zone to impinge on the first ultrasonic transducer.

2. switch the output of the second transducer to the defect signal detector, and

3. The method of inspecting a body for defects in a curved peripheral surface thereof as described in claim 2 wherein the closed path curved peripheral surface comprises an ellipse.

4. The method of inspecting a wheel for defects in the peripheral surface thereof comprising the steps of:

A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially parallel to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle whereby ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface;

C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof along a path adjacent to and converging toward the surface with a progressively increasing radius of curvature; and

D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium.

5. The method of inspecting a wheel for defects in the peripheral surface thereof comprising the steps of:

A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially parallel to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface, migrating convergingly toward said surface;

C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof adjacent to the surface; and

D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium, wherein the ultrasonic energy pulse has a frequency of below 1, 000 kiloHertz, the ultrasonic energy pulse thereby initially penetrating to a substantial depth in the wheel, and thereafter gradually migrating toward the surface of the wheel as it travels thereabout.

6. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 5, wherein the ultrasonic pulse has a frequency of 400 kiloHertz.

7. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 4, wherein the method is performed with apparatus positioned adjacent to a wheel supporting surface and:

E. rolling the wheel onto the apparatus to establish ultrasonic coupling therewith.

8. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 7, wherein the wheel is a railroad wheel, and wherein the method is performed with apparatus positioned in a gap between two rail segments comprising from a portion of a railroad track.

9. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 4, wherein monitoring the first ultrasonic transducer for echo pulses is performed for a predetermined time interval.

10. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 4 and further comprising the steps of:

E. positioning a second ultrasonic transducer in the coupling medium with the sonic axis of the second transducer substantially parallel to the plane of the wheel and inclined with respect to the plane tangent to the coupled zone at an angle substantially corresponding and opposite to the angle of the sonic axis of the first transducer wherein ultrasonic energy entering the coupled zone from within the wheel is refracted out of the wheel through the coupling medium to impinge upon the second transducer; and

, F. monitoring for through-transmission pulses received by the second transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel by the first transducer and peripheral travel of the ultrasonic energy pulse about the periphery of the wheel.

11. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 10, and further comprising the step of:

G. measuring the time interval during which the ultrasonic energy pulse passes about the periphery of the wheel, and indicating the wheel size therefrom.

12. The method of inspecting a wheel for defects in the peripheral surface thereof comprising the steps of:

A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially paralleL to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface;

C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof adjacent to the surface, migrating convergingly toward said surface;

D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium;

E. positioning a second ultrasonic transducer in the coupling medium with the sonic axis of the second transducer substantially parallel to the plane of the wheel and inclined with respect to the plane tangent to the coupled zone at an angle substantially corresponding and opposite to the angle of the sonic axis of the first transducer wherein ultrasonic energy entering the coupled zone from within the wheel is refracted out of the wheel through the coupling medium to impinge upon the second transducer;

F. monitoring for through-transmission pulses received by the second transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel by the first transducer and peripheral travel of the ultrasonic energy pulse about the periphery of the wheel;

G. measuring the strength of the through-transmission pulses received by the second transducer; and

H. adjusting the gain of the amplified output of the first transducer as a function of the strength of the through transmission pulses received by the second transducer, wherein monitoring of the first transducer for defect echo pulses is more efficiently accomplished.

13. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 12 wherein the gain of the amplified output of the first transducer is adjusted as a function of the strength of the largest through-transmission pulse received by the second transducer.

14. The method of inspecting a wheel for defects in the peripheral surface thereof and further comprising the steps of:

A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially parallel to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface, migrating convergingly toward said surface;

C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof adjacent to the surface;

D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium;

E. positioning a second ultrasonic transducer in the coupling medium with the sonic axis of the second transducer substantially parallel to the plane of the wheel and inclined with respect to the plane tangent to the coupled zone at an angle substantially corresponding and opposite to the angle of the sonic axis of the first transducer wherein ultrasonic energy entering the coupled zone from within the wheel is refracted out of the wheel through the coupling medium to impinge upon the second transducer;

F. monitoring for through-transmission pulses received by the second transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel by the fist transducer and peripheral travel of the ultrasonic energy pulse about the periphery of the wheel;

G. pulsing the first ultrasonic transducer prior to coupling the wheel with the ultrasonic energy transmitting coupling medium, the pulse interval being larger than the time interval necessary for the pulse to travel about the periphery of the largest wheel to be tested; and

H. inhibiting further pulsing of the first ultrasonic transducer upon receipt of the first through transmission pulse by the second transducer.

15. The method of inspecting a wheel for defects and in the peripheral surface thereof comprising the steps of:

A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially parallel to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface, migrating convergingly toward said surface;

C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof adjacent to the surface;

D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium;

E. positioning a second ultrasonic transducer in the coupling medium with the sonic axis of the second transducer substantially parallel to the plane of the wheel and inclined with respect to the plane tangent to the coupled zone at an angle substantially corresponding and opposite to the angle of the sonic axis of the first transducer wherein ultrasonic energy entering the coupled zone from within the wheel is refracted out of the wheel through the coupling medium to impinge upon the second transducer;

F. monitoring for through-transmission pulses received by the second transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel by the first transducer and peripheral travel of the ultrasonic energy pulse about the periphery of the wheel;

G. subsequent to substantial attenuation of the ultrasonic energy pulse delivered to the wheel by the first transducer, pulsing the second transducer to produce a second ultrasonic energy pulse delivered to the wheel along the sonic axis of the second transducer and refracted tangential to the surface of the wheel wherein the second ultrasonic energy pulse travels about the periphery of the wheel in a second opposite direction; and

, H. monitoring for echo pulses received by the second ultrasonic transducer, the echo pulses comprising a portion of the second ultrasonic energy pulse reflected from a defect in the wheel.

16. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 15 and further comprising the step of:

I monitoring for through-transmission pulses received by the first transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel.

17. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 16 and further comprising the step of:

J. certifying that a complete test has been performed when through-transmission pulses have been received in both directions of travel by monitoring the second transducer for through transmission pulses and monitoring the first transducer for through-transmission pulses.

18. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 15 wherein the second transducer is pulsed in synchronism with an attenuated through-transmission pulse delivered from the wheel to the second transducer.

19. The method of inspecting a wheel for defects in the peripheral surface thereof comprising the steps of:

A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially parallel to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface, migrating convergingly toward said surface;

C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof adjacent to the surface;

D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium;

E. positioning a second ultrasonic transducer in the coupling medium with the sonic axis of the second transducer substantially parallel to the plane of the wheel and inclined with respect to the plane tangent to the coupled zone at an angle substantially corresponding and opposite to the angle of the sonic axis of the first transducer wherein ultrasonic energy entering the coupled zone from within the wheel is refracted out of the wheel through the coupling medium to impinge upon the second transducer;

F. monitoring for through-transmission pulses received by the second transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel by the first transducer and peripheral travel of the ultrasonic energy pulse about the periphery of the wheel;

G. pulsing the second transducer subsequent to a predetermined time interval following pulsing of the first transducer, to produce a second ultrasonic energy pulse delivered to the wheel along the sonic axis of the second transducer and refracted therein substantially tangential to the surface of the wheel wherein the second ultrasonic energy pulse travels about the periphery of the wheel in a second opposite direction; and

, H. monitoring for echo pulses received by the second ultrasonic transducer, the echo pulses comprising a portion of the second ultrasonic energy pulse reflected from a defect in the wheel.

20. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 18 wherein said predetermined time interval is sufficient for substantial attenuation of the ultrasonic energy pulse delivered to the wheel by the first transducer to occur.

21. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 18 wherein the second transducer is pulsed in synchronism with the first attenuated through-transmission pulse occurring after the prEdetermined interval of time.

22. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 16 wherein the method is performed by positioning the coupling medium adjacent to a wheel-supporting surface and further comprising the step of:

J. rolling the wheel over the coupling medium to establish ultrasonic coupling therewith for a time interval dependent upon the speed of the wheel.

23. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 22, wherein the first transducer is defined as the transducer facing the direction of approach of the wheel.

24. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 16 and further comprising the step of:

J. subsequent to substantial attenuation of the ultrasonic energy pulse delivered to the wheel by the second transducer, repeating all of the above steps for as long as the wheel is coupled with the transducers.

25. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 23 and further comprising the step of:

A. subsequent to substantial attenuation of the ultrasonic energy pulse delivered to the wheel by the second transducer, repeating all of the above steps for as long as the wheel is coupled with the transducers.

26. The method of inspecting a wheel for defects in the peripheral surface thereof comprising the steps of:

A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel;

B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially parallel to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface, migrating convergingly toward said surface;

C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof adjacent to the surface;

D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium; and

E. marking the wheel upon receipt of echo pulses at the first transducer.

27. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 17, and further comprising the step of:

K. marking the wheel upon certifying that a complete test has been performed.

28. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 23 and further comprising the steps of:

K. positioning a second ultrasonic energy-transmitting coupling medium adjacent to the wheel supporting surface and close to the first ultrasonic energy-transmitting coupling medium;

L. positioning a third ultrasonic transducer in the second coupling medium in an orientation similar to the orientation of the first ultrasonic transducer in the first coupling medium;

M. positioning a fourth transducer in the second coupling medium in an orientation similar to the orientation of the second ultrasonic transducer in the first coupling medium;

N. performing the step of rolling the wheel over the first coupling medium to establish ultrasonic coupling therewith for a time interval dependent upon the speed of the wheel by rolling the wheel over the coupling medium at a sufficiently high speed that ultrasonic coupling is Destroyed prior to receipt of a through-transmission pulse by the first transducer, and thereafter;

O. rolling the wheel over the second coupling medium to establish ultrasonic coupling therewith for a time interval dependent upon the speed of the wheel;

P. upon establishing ultrasonic coupling with the second coupling medium, pulsing the fourth transducer to produce an ultrasonic energy pulse delivered to the wheel along the sonic axis of the fourth transducer and refracted tangential to the surface of the wheel wherein the ultrasonic energy pulse travels about the periphery of the wheel in a second opposite direction; and

, Q. monitoring for echo pulses received by the fourth ultrasonic transducer, the echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel.

29. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 28 and further comprising the step of:

R. monitoring for through-transmission pulses received by the third transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel.

30. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 28 wherein the first and third transducers are operated in parallel and the second and fourth transducers are operated in parallel.

31. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 28 and further comprising the steps of:

R. pulsing the fourth ultrasonic transducer prior to establishing coupling between the wheel and the second coupling medium, the pulse interval being larger than the time necessary for the pulse to travel about the periphery of the largest wheel to be tested; and

S. inhibiting further pulsing of the fourth ultrasonic transducer upon receipt of the first through transmission pulse by the third transducer.

32. Apparatus for testing railroad wheels comprising:

A. a first rail segment comprising a portion of one rail of a railroad track;

B. a second rail segment positioned a spaced apart distance from the first rail segment and aligned therewith to comprise a second portion of the same rail of a railroad track; and

C. a thin vertical support rail

33. Apparatus for testing railroad wheels as defined in claim 32 and further comprising:

H. a second transducer positioned in the ultrasonic energy-transmitting medium with its sonic axis substantially parallel to the plane of the wheel and inclined with respect to the top surface of the rail at an angle substantially equal and opposed to the angle of inclination of the sonic axis of the first transducer; and

I. a through-transmission signal detector connected to the second transducer for detecting through-transmission pulses comprising a portion of the ultrasonic energy pulse produced by the first transducer, traveling about the periphery of the wheel in a first direction returning to the coupling medium, and refracted out of the wheel to impinge upon the second transducer.

34. Apparatus for testing railroad wheels as defined in claim 33 wherein the pulse generator is a synchronizing pulse generator set at a pulse interval greater than the time necessary for an ultrasonic energy pulse to travel about the periphery of the largest wheel to be tested, and wherein the output of the through-transmission signal detector controls the output of the synchronizing pulse generator to inhibit further pulsing upon receipt of the first through-transmission pulse, thereby permitting only one ultrasonic energy pulse to be delivered to the wheel.

35. Apparatus for testing railroad wheels as defined in claim 34 and further comprising:

J. a time delay connected to the output of the through-transmission signal detector and initiated by the first through-transmission signal to provide a time interval following the first through-transmission pulse selected to permit substantial attenuation of the first ultrasonic energy pulse in the wheel to occur, and connected to provide an output signal following the time interval at a time delay output terminal;

K. a plurality of switches responsive to the output signal of the time delay and connected to;

36. Apparatus for testing railroad wheels as defined in claim 35 wherein the switches are connected to

37. Apparatus for testing railroad wheels as defined in claim 35 and further comprising:

L. a third transducer positioned in the ultrasonic energy-transmitting medium in an orientatIon corresponding to the orientation of the first transducer, longitudinally spaced apart therefrom, and connected in parallel therewith;

M. a fourth transducer positioned in the ultrasonic coupling medium adjacent to the third transducer in an orientation similar to the second transducer, longitudinally spaced apart therefrom, and connected in parallel therewith, whereby if the wheel has passed by the first and second transducers toward the third and fourth transducers prior to reception of a through-transmission pulse of a second, opposite direction ultrasonic energy pulse, the output of the synchronizing pulse generator is not inhibited until a second ultrasonic energy pulse is delivered to the wheel by the fourth transducer and a through-transmission pulse is received at the third transducer.

38. Apparatus for testing railroad wheels as defined in claim 37 wherein the ultrasonic energy-transmitting medium has a first portion having the first and second transducers positioned therein and a second portion having the third and fourth transducers positioned therein, and wherein the second portion is positioned in a second test zone.

39. Apparatus for testing railroad wheels as defined in claim 35 and further comprising:

L. means connecting the output of the through-transmission signal detector to the synchronizing pulse generator for synchronizing the output thereof with through-transmission signals, whereby the second transducer is pulsed in synchronism with the attenuating through-transmission pulses.

40. Apparatus for testing railroad wheels as defined in claim 36 wherein the first and second transducers have a resonant frequency less than 1,000 kiloHertz.

41. Apparatus for testing railroad wheels as defined in claim 36 wherein the first and second transducers have a resonant frequency of 400 kiloHertz.

42. Apparatus for testing railroad wheels as defined in claim 35 and further comprising:

L. two wheel sensors positioned flanking the test zone connected to provide an output signal indicating the direction from which a railroad wheel is approaching the test zone.

43. Apparatus for testing railroad wheels as defined in claim 42 and further comprising:

K. a direction control switch interposed between the synchronizing pulse generator and the inputs to the first and second transducers, the direction control switch connecting the synchronizing pulse generator to first pulse the transducer which is the first to have its sonic axis coupled with the wheel in response to the output of the wheel sensing switches.

44. Apparatus for testing railroad wheels as defined in claim 43 wherein the sonic axes of the first and second transducers cross below the surface of the thin vertical support rail, and wherein the transducer facing the direction of approach of the wheel is first pulsed.

45. Apparatus for testing railroad wheels as defined in claim 35 and further comprising:

L. a pressurized paint spray having an output nozzle directed toward the wheel being tested and a valve controlling the release of paint therefrom; and

M. means for operating the valve responsive to a defect alarm signal, whereby a wheel having a defect is marked with paint.