Electricity: measuring and testing – Magnetic – Magnetic test structure elements
Reexamination Certificate
2000-12-21
2002-07-30
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetic test structure elements
C324S240000, C324S261000, C269S087300, C269S2540CS
Reexamination Certificate
active
06426622
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to eddy current inspection and more particularly to fixtures for facilitating the use of hand held eddy current inspection probes.
Eddy current inspection is a commonly used technique for nondestructively detecting discontinuities or flaws in the surface of items made of electrically conductive material, including many gas turbine engine components. Eddy current inspection techniques are based on the principle of electromagnetic. induction in which eddy currents are induced within the component under inspection by application of alternating magnetic fields. Known eddy current probes include absolute probes, which contain a single inductive coil, and differential probes, which have a drive coil and a sense coil. In the case of a differential probe, eddy currents are induced in the component under inspection when the probe is moved into proximity with the component by alternating magnetic fields created in the drive coil. The eddy currents produce a secondary magnetic field that is detected by the sense coil, which converts the secondary magnetic field into an electrical signal that may be recorded and/or displayed for analysis. As the eddy current probe is passed over the component, the presence of cracks and other discontinuities or deformations in the component will produce changes in the magnitude of the induced eddy current as compared to the magnitude of the induced eddy current in areas that do not have such anomalies. This results in corresponding variations in the magnitude of the signal output by the sense coil. Hence, the output signal, specifically the amplitude of the output signal variations, is an indication of the condition of the component. An eddy current machine operator may then detect and size flaws by monitoring and analyzing the output signals.
Rotor blades are used in the compressor and turbine sections of gas turbine engines for interacting with the gas stream flow of the engine. Rotor blades typically include a shank having a dovetail for mounting the blade to a rotor disk and an airfoil that extends radially outwardly from the shank and into the gas stream. The airfoil includes a pressure side and a suction side joined together at a leading edge and at a trailing edge. Rotor blades are ordinarily formed as a one-piece casting of a suitable superalloy, such as a nickel-based superalloy, which has acceptable strength at the elevated temperatures of operation in the gas turbine engine.
During engine operation, the leading and trailing can be susceptible fatigue cracking because of the high temperatures and pressures to which the blades are exposed. Furthermore, the trailing edges can experience cracking during the blade manufacturing process because they are very thin compared to the rest of the airfoil. Thus, it is common to frequently subject rotor blade leading and trailing edges to eddy current inspection before and after service.
This is typically accomplished with a hand held eddy current probe, wherein an operator moves the probe by hand along the leading or trailing edge of the rotor blade airfoil. However, this can often be a difficult procedure to perform because of probe normalization and “lift-off” variables. In other words, it is difficult for a human operator to maintain the probe at the proper angle and in constant contact while moving the probe over the surface being inspected. If either probe angle is altered or lift-off occurs, then the inspection integrity can become compromised. Accordingly, it would be desirable to have a means for maintaining probe angle and contact during eddy current inspections.
BRIEF SUMMARY OF THE INVENTION
The above-mentioned need is met by the present invention, which provides a fixture for use with eddy current inspection probes. The fixture includes a fixture body having a hole formed in one side thereof for receiving a probe and a V-groove formed in another side thereof for receiving a workpiece surface. A clamp arm is pivotally mounted to the fixture body, and a spring is disposed between the clamp arm and the fixture body. The spring biases one end of the clamp arm towards the fixture body so that a workpiece can be clamped between the clamp arm and the fixture body.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.
REFERENCES:
patent: 2893275 (1959-07-01), Lindemann
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patent: 4066949 (1978-01-01), Condrac
patent: 4638602 (1987-01-01), Cavalieri
patent: 4644274 (1987-02-01), Casarcia
patent: 4757258 (1988-07-01), Kelly, Jr. et al.
patent: 4906926 (1990-03-01), Rogacki et al.
patent: 4986771 (1991-01-01), Braswell
patent: 5847350 (1998-12-01), Dorrel et al.
Givens Glenn D.
O'Connell James P.
Traxler Joseph A.
Atwood Pierce
General Electric Company
Kinder Darrell
Lefkowitz Edward
Ramaswamy V. G.
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