Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1981-01-07
1984-05-29
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
324243, 324262, G01N 2772, G01R 3312
Patent
active
044517874
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method and an apparatus for detecting discontinuities in materials. Particularly, the invention relates to detecting, by electrical means, such discontinuities as cracks, slag inclusions and similar discontinuities in metallic materials, which chiefly exist in the form of a material web.
Within the industry, the detection of discontinuities in materials is of great importance in the quality control of the materials. In this respect, the materials are scanned by a probe which is sensitive to these discontinuities and reacts to discontinuous changes or jumps in the properties of the material. Then the probe emits a signal. This signal can be processed in different ways, and can, for example, be presented on a display or by a recorder. The signal can also be analysed by a computer in order to make a closer investigation of the discontinuities. Very often the problem is to investigate metallic materials wherein these are scanned by means of a probe which is sensitive to discontinuities in the electromagnetic properties of the material. These electromagnetic discontinuities are produced by the discontinuities of the material when for instance eddy currents are induced in the material or when a magnetic field is applied to the material. However, the invention is not limited to either metallic materials or to electromagnetic detection of the discontinuities.
Thus the invention can, as an example, also be applied for investigation of non-metallic materials by means of ultra-sound and a detector sensitive to ultra-sound, or by reflected laser light.
In modern quality control, it is often necessary tht the testing of the material is continuous in which case the material very often is continuously transported as a web. During this transportation, the material is continuously scanned by one or more probes. In order to accurately detect small discontinuities, it is necessary that the probe cover only a small area in each moment, and in order to cover a larger piece of material, the probe is moved over the material. Alternatively a large number of probes can be used, but practical difficulties limit this number.
In order to increase the sensitivity when using a differential measuring process, and in order to get a signal in a suitable frequency interval, one always wants to move the probe in that direction where the discontinuity has its least extension. Then the probe detects the most pronounced change and this leads to an increased sensitivity. It is easily realized that if the probe is moved along an elongated discontinuity, no pronounced change in the input signal of the probe will be received and this discontinuity could be undetected under unfortunate conditions.
In order to get an efficient scanning of the material when it is continuously moved as a web, one very often wants to move the probe perpendicularly to the moving direction of this web. For example, this is a commonly used method when examining tubes which have an orientation of the discontinuities preferentially in the direction of the axis of the tube. In these cases, the probe rotates around the tube while the tube is moved along the direction of its axis.
If the discontinuities are randomly distributed in the material and have no preferential direction, it is necessary to scan the material in at least two different directions by means of two or more probes in order to detect safely all the discontinuities. One way of achieving this is to let two probes perform an oscillatory movement above the surface of the material perpendicularly to each other. Thus, above the web of the matrial, two probes could oscillate in two directions which each has an angle of 45 degrees to the travel direction of the material and perpendicularly to each other. This procedure is usable at low scanning speeds but with an increased speed, the frequency of oscillation becomes too high in order to completely cover the surface of the material. Mechanically, this solution is also too complicated as the forces of inertia become too high at the turning po
REFERENCES:
patent: 3431774 (1969-03-01), Dory
patent: 3611120 (1971-10-01), Forstor
patent: 4041379 (1977-08-01), Karlsson
Bergstrand Karl-Gunnar
Bergstrand Kvalitetskontroll AB
Snow Walter E.
Strecker Gerard R.
LandOfFree
Method and apparatus to detect randomly distributed discontinuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus to detect randomly distributed discontinuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus to detect randomly distributed discontinuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1400273