Electricity: measuring and testing – Magnetic – Current through test material forms test magnetic field
Reexamination Certificate
1999-06-14
2001-04-10
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Current through test material forms test magnetic field
C324S248000, C505S846000
Reexamination Certificate
active
06215303
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to reliability, and more specifically this invention permits monitoring of the structural and geometrical integrity of electrically-conducting wires during the manufacturing process, or it may be utilized to inspect the integrity of wires at any time after manufacture. Unlike many other inspection techniques which assess only defects observable on the surface, this invention provides instantaneous information on defect structures within the interior of the wires, as well as on the surface. Given this unique diagnostic ability, it is possible to improve quality control and to avoid manufacturing down-time and waste. For wire already produced, this invention provides an inspection technique for verifying the integrity of the wire prior to its use in a given application. Although this invention pertains most simply to any conductor with a circular cross section, it applies equally well to any long length of conductor with arbitrary cross section and composition, regardless of whether the conductor is referred to as a wire, tape, cable or some other designation. For the case of wires with composite internal structure, this invention permits one to validate the uniformity of the internal structure and to detect deviant features.
The following patents are examples of prior art, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 5,729,135 Mar. 17, 1998 Kugai and Hyogo
U.S. Pat. No. 5,572,123 Nov. 5, 1996 Wikswo, Jr., et al.
U.S. Pat. No. 5,109,196 Apr. 28, 1992 Wikswo, Jr., et al.
U.S. Pat. No. 4,982,158 Jan. 1, 1991 Nakata et al.
U.S. Pat. No. 5,610,517 Mar. 11, 1997 Ma et al.
It is common in the manufacture of vast lengths of conducting wires to start with a large-diameter, relatively small-length volume of the conducting (generally metallic) material and to pull it through a succession of dyes, each time reducing the diameter and increasing the length of the material. This process can introduce strain in the wire and small geometrical asymmetries of defect structures dependent on the condition of the dye and the forces applied. Additionally, the initial bulk material may have contained a variety of impurity substances or small inclusive volumes of material whose physical properties differ significantly from that of their surroundings. As wire is drawn down to smaller and smaller diameters, their material anomalies can have a profound effect on the drawing process. For example, an inclusive impurity volume although small, becomes a relatively larger hazard as the diameter of the host material is decreased, possibly resulting in a high probability of wire rupture during the drawing process. When such an event occurs, the process must be discontinued and the ruptured wire removed before resuming the operation. The waste wire material and manufacturing down-time are costly consequences of the inability to monitor on-line the structural integrity of the wires being produced. Sometimes the rupture can result from surface irregularities. While there are various techniques capable of detecting surface irregularities on the wire, none of these is capable of reliably detecting internal defects. occasionally, the surface defects are responsible for wire rupture, bit in many instances, the vast majority of ruptures (e.g., over 80% for aluminum wire with 0.1% of embedded silicon inclusions) occur due to included impurities.
SUMMARY OF THE INVENTION
The key element of this invention is a superconducting (SQUID) magnetic field sensor which is used to detect small magnetic anomalies produced by alternating electrical current, provided by a constant-current power supply. The SQUID is shielded from undesirable environmental signals by a superconducting, open-ended cylindrical shield or by a cylindrical magnetically-shielded container with a suitably-sized hole in its bottom plate. Alternately, a SQUID gradiometer configuration may be used to cancel undesirable environmental magnetic signals. The signal generated by the magnet field produced by the current in the wire and detected by the SQUID is transmitted from the cryogenic region in the dewar by an electrical cable to flux-locked-loop circuitry located just outside the dewar. The rectified output signal from this circuitry is carried to one input of a lock-in amplifier, with the other input coming from the constant-current AC power supply. The output of the lock-in amplifier is correlated with information on the motion of the wire in a data storage unit and can be printed upon demand in the form of a graph of magnetic signal versus distance along the wire. The current passes through the wire under test, while the wire itself passes through a fairly tight-fitting guide at a given speed under the SQUID sensor. A drive motor may be used to power a take-up reel, and the wire either originates from a supply reel or as a result of being drawn through a die. Although, in principle, this form of defect detection can employ a direct electrical current, the invention is most sensitive when phase-sensitive detection via a lock-in amplifier is utilized in conjunction with a low-frequency alternating current. Typically, a frequency range of 100 to 2,000 Hz is used, although not at a frequency which is an integer multiple of the prevailing input line frequency, i.e., 60 Hz in the USA and 50 Hz in most other countries. The electrical current may be applied most simply by providing pressure contact points and along the wire on both sides of the wire.
It is an object to permit monitoring of the structural and geometrical integrity of electrically-conducting wires during the manufacturing process, or to inspect the integrity of wires at any time after manufacture.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the pertinent art from the following detailed description of a preferred embodiment of the invention and the related drawings.
REFERENCES:
patent: 4982158 (1991-01-01), Nakata et al.
Tralshawala Nilesh
Weinstock Harold
Auton William G.
Snow Walter E.
The United States of America as represented by the Secretary of
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