Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1983-07-07
1984-02-21
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
33169F, G01B 710, G01R 3312
Patent
active
044332904
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The field of the invention is electricity, measuring and testing wherein a layer or layered material thickness is measured using a magnetic field to test the material. The present invention is particularly concerned with the measurement of the thickness of nonmagnetic coatings or layers on magnetic base materials.
BACKGROUND ART
The state of the art of measuring the thickness of nonmagnetic coatings on a magnetic base using a magnetic field may be ascertained by reference to U.S. Pat. Nos. 2,469,476; 2,625,585; 2,903,645; 3,521,160 and 3,699,487, the disclosures of which are incorporated herein by reference.
U.S. Pat. No. 2,469,476 of Sellers discloses an instrument for measuring the thickness of nonmagnetic coatings on a ferrous base and the patent also discloses that it is possible to use the instrument for measuring the irregularities in the surface of a machined ferrous material. According to this patent an adjustable bar magnet bridge is pivoted between the legs of a U-shaped magnet. The limbs of the U-shaped magnet are placed on the surface to be measured. The pivoted bar magnet has an indicator attached thereto and is spring biased so that changes in the magnetic flux of the U-shaped magnet indicate the layer thickness or roughness.
The magnetic measuring gauge disclosed in U.S. Pat. No. 2,625,585 makes use of the principle that forces necessary to disengage a magnet from a workpiece vary in inverse proportion to the thickness of the nonmagnetic plating or coating disposed upon the magnetic base surface. U.S. Pat. No. 2,903,645 makes use of this same principle but in a more complex instrument.
U.S. Pat. No. 3,521,160 is representative of a series of patents of Nix et al which show magnetic thickness gauges using a magnet mounted on the end of a balanced rotatable arm to which a dial is coupled over a spring. The dial is turned until the increasing tension of the spring breaks the magnetic contact and the thickness is read directly from the dial.
Steingroever discloses in U.S. Pat. No. 3,699,487 magnets of anisotropic materials for use in the magnetic thickness gauges.
According to these magnetic thickness gauges of the prior art, the magnet is placed on a coated steel surface and pulled off by a spring. The force required to pull the spring off of the surface is indicated on a scale and expressed in coating thickness. The spring force and the magnetic force are of an uncomplimentary or non-linear nature and produce a logarithmic scale. As time goes on, the magnet either loses or gains magnetism and the spring is subject to fatigue and temperature variations. To obtain a fair degree of accuracy, each prior art gauge has to be individually calibrated and requires an elaborate set-up which is very time consuming. These so-called "pull-off gauges" are calibrated to a mild steel plate. As soon as the coated steel surface is of a rough nature or the substrate is of a different steel than that to which the gauge is calibrated, the readings of these gauges become relative.
OBJECTS AND BRIEF DISCLOSURE OF INVENTION
Having in mind the limitations of the prior art, it is an object of the present invention to provide a coating thickness and surface roughness comparator which avoids the uncomplimentary or non-linear reaction between magnetic force and spring force.
This object is accomplished in the present invention by using the principle of magnetic force versus friction.
In a particular embodiment of the comparator of the present invention, the comparator has the following elements:
(a) a permanent rod magnet or a rod having equal magnets at each end;
(b) a ferromagnetic rod approximately parallel to the permanent rod magnet or the rod having equal magnets at each end;
(c) nonmagnetic slides or spacers preventing contact between the rod magnet and the ferromagnetic rod; and
(d) an indicator of the middle of the rod magnet.
The comparator is used for making measurements by placing a first or reference pole of the rod magnet in contact with a reference ferromagnetic base material. The sec
REFERENCES:
patent: 2469476 (1949-05-01), Sellers
patent: 2507529 (1950-05-01), Lipson
patent: 2625585 (1953-01-01), Krouse
patent: 2749505 (1956-06-01), McNary
patent: 2903645 (1959-09-01), Wright
patent: 3521160 (1970-07-01), Nix
patent: 3699487 (1972-10-01), Steingroever
patent: 3761804 (1973-09-01), Steingroever
DeFelsko Corporation
Strecker Gerard R.
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