Michael R Peck

US Patent:

56660510, Sep 9, 1997

Filed:

Oct 4, 1995

Appl. No.:

8/539241

Inventors:

Warren R. Junker - Monroeville PA
Lee W. Burtner - Elizabeth Twp., Allegheny County PA
Michael G. Peck - Greensburg PA
Richard J. Makar - Greensburg PA
David A. Chizmar - Export PA

Assignee:

Thermo King Corporation - Minneapolis MN

International Classification:

G01R 3312
G01N 2772
G01B 724

US Classification:

324209

Abstract:

Both a system and method are provided for mapping the magnitude of residual compressive stresses over the surface of a ferromagnetic machine component, such as a valve ring of the type used in refrigeration compressors. The system includes an eddy current probe having a detection coil for emanating a fluctuating electromagnetic field that shallowly penetrates the surface of the valve ring or other ferromagnetic component, a probe circuit connected to the coil for both conducting a high frequency alternating electric current through the coil and detecting changes in the impedance in the coil, and a scanning mechanism having a turntable for supporting and rotating the component. A support arm positions the coil of the eddy current over a central portion of the valve ring while the ring is rotated by the turntable and changes in coil impedance are detected by the probe circuit. A microprocessor converts the fluctuations in the impedance detected by the eddy current probe circuit into residual stress values, and correlates these values with regular positions on the valve ring in order to generate a map of the residual surface stresses over the ring.