Electricity: measuring and testing – Magnetic – Fluid material examination
Reexamination Certificate
1999-09-07
2001-10-30
Metjahic, Safet (Department: 2862)
Electricity: measuring and testing
Magnetic
Fluid material examination
C324S232000, C324S214000
Reexamination Certificate
active
06310471
ABSTRACT:
This invention relates to a device and method for testing magnetic inspection particle materials and more particularly to a device having at least one predetermined magnetic stripe situated thereon to receive a magnetic inspection particle suspension in order to provide a method for determining the effectiveness of the particle suspension or system for use in testing.
BACKGROUND OF THE INVENTION
It is well known in the art that magnetic inspection particle systems are useful and important in industrial applications. The basic application of this system is for non-destructive testing of an item. This importance is clearly set forth in U.S. Pat. No. 4,812,249 relating to a test system by Isabelle Y. Duminy-Kovarik, incorporated herein by reference.
A major problem with the magnetic inspection particle system is a testing of the materials and particles themselves for their effectiveness. This test for effectiveness is critical. As parts are inserted into the suspension, and tested, the testing suspension of particles will lose some of its effectiveness. It is very critical to have the suspension be effective and be able to easily determine the effectiveness of that suspension by a simple test, in order to have each part tested efficiently.
A suspension for the purposes herein is deemed to include wet method materials borne in conditioned water or kerosene-type liquid, and dry-method materials applied directly to the test surface.
This action is critical because of the expensive nature of the suspension, and the expensive parts which are being tested. It is hypercritical that these parts be tested efficiently and effectively with an effective suspension. If such efficient or effective testing is not achieved, or if the suspension is not known to have failed or been found deficient in its effectiveness, a detective part may receive a false approval and be used in a dangerously unsuitable manner. This defective part can eventually lead to a failure of a system in which it is used.
In order to compensate for this depletion of the magnetic inspection particle fluid during a series of tests on various parts, it is known to use a piece or part with a known crack in it for testing purposes. This process or testing mechanism is difficult to reproduce from factory to factory or establishment to establishment because no two cracks are the same. Thus, a part with a predetermined crack may not be the same as a part with predetermined crack in another location. In this fashion, it is impossible to use this test to have an accurately reproducible test at various locations.
There is also a settling tube or bulb test. However, the settling tube test merely shows the number of particles in the suspension. It does not show the effectiveness of the particles or the brightness of the particles or the sensitivity of the particles. The settling bulb test merely shows the number of particles in the suspension. A repeatedly used fluid can lose brightness and sensitivity. The settling bulb test is also effected by dirt, scale and metal particles from the part itself being tested. The settling bulb test thus suffers from a number of inaccuracies, especially regarding actual particle performance.
Another test for use a magnetic inspection particle fluid is a ring test. This device is accomplished by a ketos ring or Tiede MTU#3 ring. These rings suffer from a similar problem in that the ring itself is not consistently reproducible. This factor greatly interferes with the desirability of providing the same test to the same fluid at a number of different sites.
Ketos Ring Discussion
Similar testing patterns are important to determine the similar quality of the parts. The ketos ring is made of tool steel, and is a flat disc like device having a plurality of apertures drilled at various radial distances from the circumference thereof. The degree of magnetization of the ring, combined with the differing qualities of the steel and the spacing of the apertures, can have an adverse effect on the test mechanism. The defects in the ketos ring are well discussed in a paper presented by Donald Hagemaier at the 1992 ATA NDT Forum in Cincinnati, Ohio, which paper is incorporated herein by reference.
The Ketos ring is a tool that is most commonly used as grading device for evaluating the sensitivity of MPI materials. It is described most accurately by Aerospace Standard AS5282. The Ketos ring is actually a disk made of SAE J438 steel, which is manufactured with properties as described within AS5282. The disk contains a centrally located aperture, which receives a conductive copper bar. Various currents of electricity are passed through that centrally located conductive copper bar in a controlled manner. These currents ultimately generate varying magnetic fields and gradients associated with each of several small apertures drilled at varying distances inside the circumference of the ring. The small apertures are placed in such a manner that their associated fields and gradients become weaker as they are further from the circumference.
Magnetic particles can be applied to the circumference of the ring as a current is passed through the central conductor. Particles are graded by the number of apertures that can be detected by displaying a formation of particles at the circumference above the aperture at given amperage. A more sensitive powder will show more apertures than a less sensitive powder.
AS5282 describes a procedure for evaluating the Ketos ring performance by means of a magnetic field measuring device that sense the residual fields associated with the apertures after the ring has been exposed to current of 1500 amps of direct current. While this use of residual fields may suffice for evaluating rings it does not represent the gradients used to grade particles as generated by the various currents.
The Ketos ring has been accepted as the standard tool for measuring particle performance for many years. Much of this acceptance has probably been due to the fact that, despite a variety of troublesome issues surrounding the ring, a suitable replacement had not been developed. The issuance of AS5282 in 1997 has provided a standardized means of evaluation and grading rings but many inherent (and quite possibly problematic) issues remain:
AS5282 evaluates the Ketos ring in a residual state of magnetization. The correlation between the residual state and the active magnetic state at which the ring is used has not been firmly established.
The values of the magnetic fields and gradients associated with the respective apertures in the active magnetic state are not described.
Consistency of the magnetic properties of the steel from which the rings are made.
Many rings in use in industry have probably not been certified to AS5282.
A ring is only compared to itself in the residual state. Consistency between rings is not addressed.
AS5282 calls out that 3-phase, full-wave, rectified alternating current be used for ketos ring evaluation. This type of current may not always be readily available, depending on the type of equipment used by a given inspector.
The magnetizing equipment providing the current must be in proper calibration. The equipment, and even the process of equipment calibration, can be subject to error and tolerance that can affect the performance of the Ketos ring.
The complete cleaning and processing of the ring can be a time-consuming procedure.
The cleanliness of the ring surface can affect observations.
MPI is almost always used as strictly a surface inspection technique of nondestructive testing (NDT). The Ketos ring requires the evaluation of subsurface discontinuities. Interpretation of these discontinuities, especially as they are further in from the circumference, can be very subjective and subject to inspector interpretation.
The position of the ring on its central conductor bar can affect the observations.
The direction and amount of flow of particles over the ring can affect the observations.
The ability or inability of wet-method solutions to flow evenly over the surface of the ring can affect the obs
Circle Systems, Inc.
Metjahic Safet
Perrone, Jr. Mathew R. P.
Zaveri Subhash
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