Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-08-16
2001-05-29
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S001820, C073S632000, C310S334000
Reexamination Certificate
active
06237419
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the design of ultrasonic transducers used for inspection of solid objects with curved surfaces. Specifically, the inspection utilizes the immersion technique. In this technique, an object is placed in liquid to improve coupling of the ultrasonic wave energy into the part. Ultrasonic energy focused beneath the surface of the inspected object is also addressed, improving sensitivity of inspection in that region.
When an ultrasonic inspection is performed, a transducer is calibrated on a flat surface with the same material to be inspected. A set of inspection parameters, such as gain, operating frequency and water-path, are set and calibrated to the flat-top block. The inspection parameters are used to inspect production hardware. In many cases, the same parameters are used to inspect through curved entry surfaces.
Passing the sound beam through a convex surface decreases the effective sensitivity. However, for a concave surface, the sensitivity of the sound beam increases and then starts to sharply decrease after a certain depth. The effect of a curved surface on inspection sensitivity is very complex. It is difficult to compensate for curved surface effect and keep the same sensitivities as for the flat entry surface.
Many governing agencies and product specifications require that attention be paid to entry surface effects. It is also often required that a curved specimen be used to qualify the inspection process. However, procedure time and cost. and degree of surface curvature variations within a single region make compliance difficult.
It would be desirable then to have a transducer capable of inspecting a part with any curved direction of entry surface.
BRIEF SUMMARY OF THE INVENTION
Mathematical calculation shows that convex surfaces, not just concave, need compensation to get inspection results like a flat surface. However, concave surfaces present complications in that intensity of the sound beam increases then sharply decreases after a certain depth. Hence, a saddle shaped aspherical transducer with a curved element is calculated. The transducer is particularly suited for inspecting a part with a doubly curved entry surface. The aspherical transducers make ultrasonic inspection possible on highly curved parts, by compensating for the entry surface of the part.
An ultrasonic inspection element and method of fabrication are provided for ultrasonic inspection. Specifically, a method is provided for determining the radii of an aspherical transducer. First, various points on a transducer surface are located. These points include where a ray starts, passes through a water medium and a water-metal boundary, and runs into a desired focal point in the material to be inspected. Next, the points are fitted onto a cylindrical surface for ease of transducer fabrication.
Accordingly, the present invention provides an effective technique for performing ultrasonic inspection, particularly of curved entry surface parts.
REFERENCES:
patent: 4276779 (1981-07-01), Davis, Jr.
patent: 4395652 (1983-07-01), Nakanishi et al.
patent: 4726231 (1988-02-01), Tretout et al.
patent: 4888746 (1989-12-01), Wurster et al.
patent: 5003516 (1991-03-01), Sato et al.
patent: 5640961 (1997-06-01), Verdonk
Bantz Walter J.
Ingram Douglas E.
Klaassen Richard E.
Suh Ui W.
General Electric Company
Gressel Gerry S.
Hess Andrew C.
Williams Hezron
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