Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1995-11-08
1998-05-05
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
324225, 324235, 324242, G01N 2783
Patent
active
057479887
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/JP95/01254 filed Jun. 22, 1995.
FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for flaw detection in which an object material having magnetic properties is magnetized and leakage fluxes generated due to a flaw, which are detected to indicate a flaw of the object material, and a sensor for detecting leakage fluxes generated due to a flaw of a magnetized object material having magnetic properties.
DESCRIPTION OF RELATED ART
A method for detecting a flaw in an object material having magnetic properties by magnetizing the object material and using leakage magnetic fluxes generated due to a flaw such as a surface flaw or an internal flaw is well known.
FIG. 1 is a side view showing a model of a conventional leakage flux flaw detection apparatus of a rotary type, and FIG. 2 is a diagram showing a model partially enlarged from FIG,1. A couple of feeders 81, 81 each including a pair of upper and lower guide rolls are arranged in predetermined spaced relationship with each other in a transportation area to hold and transport a solid-cylindrical or tubular object material P having ferromagnetic properties in the direction indicated by an arrow. The feeders 81, 81 have an annular rotary head 71 arranged therebetween in such a manner that the object material P is adapted to pass through the rotary head 71. The rotary head 71 has mounted thereon a pair of electromagnet poles 72, 72 in predetermined spaced relationship with each other along the peripheral direction of the rotary head 71 for magnetizing the object material P. A sensor 73 such as a flux-sensing element or a search coil for detecting the changes of magnetic flux density due to a flaw is mounted at substantially the center between the electromagnet poles 72, 72.
The rotary head 71 is mounted coaxially with the center axis of an annular rotary unit 80 on the input side of the object material P for driving the rotary head 71. The output signal of the sensor 73 of the rotary head 71 is applied to a flaw signal analyzer 82 through the rotary unit 80. A marking unit 83 for marking the position of any flaw detected is arranged on the output side of the rotary unit 80. This marking unit 83 attaches an appropriate mark on the surface of the object material P in response to a command from the flaw signal analyzer 82.
In this apparatus, the rotary head 71 is rotated by the rotary unit 80 while the object material P is fed in the direction of the arrow by means of the feeders 81, 81. The object material P fitted in the rotary head 71 is magnetized in the peripheral direction of the object material P by electromagnet poles 72, 72, the leakage fluxes due to a flaw K are detected by a sensor 73, and the output signal of the sensor 73 is applied to the flaw signal analyzer 82. When the output signal level supplied from the sensor 73 is not less than a predetermined value, the flaw signal analyzer 82 applies a command to the marking unit 83 and causes the marking unit 83 to attach a mark along the periphery of a corresponding portion of the object material P. As a result, the object material P is searched for flaws along the whole periphery and the whole length thereof.
The conventional apparatus in which an object material is magnetized by a pair of magnet poles, however, poses the problem that the detection sensitivity is lowered in the case where the direction of a flaw occurring in the object material is approximate to the direction of magnetization of the magnet poles.
FIG. 3 is a graph showing the relation between the direction of a flaw and the sensor output. The abscissa represents a tilt angle .theta. with respect to the center axis of the object material, and the ordinate gives the sensor output expressed as a relative value when a flaw occurs in the direction of the center axis (i.e., .theta.=0.degree.). As seen from FIG. 3, the sensor output is strongest when the flaw lies in the direction of the center axis of the object material (.theta.=0.degree.), and steadily decreases with the incre
REFERENCES:
patent: 2031469 (1936-02-01), Drake
patent: 4477776 (1984-10-01), Spierer
patent: 4495465 (1985-01-01), Tomaiuolo et al.
patent: 4538108 (1985-08-01), Huschelrath et al.
Strecker Gerard R.
Sumitomo Metal Industires Limited
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