X-ray or gamma ray systems or devices – Specific application – Fluorescence
Reexamination Certificate
2000-08-10
2003-10-07
Dunn, Drew A. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Fluorescence
C378S042000
Reexamination Certificate
active
06631177
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device for measurement of the thickness of a first layer, comprising one or more sublayers, on a second layer of a metal sheet by X-ray fluorescence analysis, and a method of use therefor. In particular, the device comprises means defining a specimen plane for supporting the metal sheet, and further comprises means for generating and directing a beam of polychromatic primary X-rays. The beam is able to penetrate into the first and second layers for converting primary X-rays into chemical element specific fluorescent X-rays by means of absorption of the primary X-rays and re-emission of the fluorescent X-rays by the chemical element. The device further comprises means for detecting element specific fluorescent X-rays and determining an intensity thereof.
2. Description of Related Art
An X-ray device is known from U.S. Pat. No. 2,711,480. In the known device, the beam of primary X-rays is directed at an arbitrary angle on a sheet material, and relative to the beam of primary X-rays the detection means are aligned at an arbitrary angle to receive fluorescent radiation that emanates in all directions from the sheet. The known device is applicable in a method to determine the thickness of a layer of material on a chemically different base material, by measuring the attenuation of fluorescent radiation of the most abundant element comprised in the base material in passing through the layer.
However, in many cases it is not possible to use the fluorescence of the most abundant element, in particular when dealing with metal sheets comprising layers of alloys with mutually very similar compositions. Within the scope of this description, the term “cladding” is used to denote the first layer, and the term “clad layer” is used to indicate a sublayer.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a device for measurement of cladding thickness, which is capable of using fluorescence signals from elements that are present in a layer in low concentration for the thickness determination.
It is a further object of the invention to provide a device that is capable of measuring both the cladding thickness, as well as the thickness of the full metal sheet, with improved accuracy and reduced measurement time, so that the cladding thickness can be expressed as a fraction of the total metal sheet thickness.
It is a further object of the invention to provide a device for measurement of cladding thickness and metal sheet thickness with improved ease of operation, and reduced probability for operator mistakes.
It is a further object to provide a device that is suitable for use in a production environment.
It is a further object to provide a method of using the device.
According to the invention, one or more of these objects is achieved by providing a device in which the means for detection have been placed at an angle with respect to the primary beam of X-rays in dependence of the chemical element from which the fluorescent X-rays are to be detected. This achieves an improvement of the efficiency of detection, and the measurement time is reduced accordingly. Hence, a device is provided in which alloys with a low concentration of fluorescent elements can now be analysed, for determining the thickness of a cladding. In the scope of the present description, the term “detection channel” will be used to denote means for detection that have been placed to selectively receive fluorescent x-rays specific for one chemical element.
The invention is based on the finding that the fluorescent radiation emanates from a metal sheet under an exit angle that is characteristic of the wavelength of the emitted fluorescent X-rays inside a host material complex. When properly excited, chemical elements are able to emit fluorescent X-rays with a spectrum of wavelengths that is characteristic for each fluorescent element. Hence, by placing the means for detection to receive fluorescent X-rays that emanate from the surface of the metal sheet under a specific exit angle, an element selective fraction of the X-rays that emanate from the metal sheet is detected. Thus the detection means receive a pre-selection of fluorescent X-rays, in favour of the fluorescent X-rays that carry the relevant information to be quantified.
In a preferred embodiment, the device comprises at least two different detection channels placed at an angle to receive fluorescent X-rays from different chemical elements. Herewith a device is provided with high flexibility in its ability to measure a variety of types of metal sheets. Additionally, the device is flexible in its ability to take into account multiple signals of fluorescent X-rays converted in different elements. The device can thus select a signal that provides the most advantageous measurement in a given operation of thickness measurement. A further advantage of the device according to this embodiment is that for each chemical element from which fluorescence is detected it is possible to measure the thickness of an additional (sub-)layer in the metal sheet.
In a preferred embodiment, the means for directing the beam of primary X-rays has been placed such that the beam of primary X-rays is directed substantially perpendicular to the specimen plane. Herewith it is achieved that primary X-rays penetrate as deep as possible into the metal sheet to be converted into fluorescent X-rays. This geometry offers the most space along the specimen plane for additional detection channels over the full azimuthal range.
In an embodiment of the invention, the means for directing a beam of primary X-rays and the means for detecting element-specific fluorescent X-rays are integrated into one measuring unit. Herewith a single measuring unit is obtained that can be moved across for instance a large metal sheet, to analyse the metal sheet in several locations. Amongst other ways to guide the motion of the integrated unit, it is particularly advantageous to provide a set of rail members for this purpose.
In an embodiment of the invention the device comprises means for pressing the measuring unit toward the specimen plane. Accordingly, during operation of this embodiment of this device, the measuring unit can be pressed against the surface of the metal sheet under investigation. This embodiment assures that the angle of incidence and exit of X-rays with respect to the surface of the metal sheet is well defined and constant. Moreover, a close contact is achieved between the metal sheet and the means for supporting the metal sheet. As a consequence, the device with pressing means is capable of performing measurements with higher accuracy than without pressing means.
Preferably, the means for pressing is pneumatic means for pressing. A high degree of control of the pressing force is obtained using a pneumatic system. Another advantage is that a quick change is made possible between a state of pressing the unit against a body and a state of release. This enables a quick succession of measurements to be made on different areas of the sheet under investigation.
In an embodiment of the invention, the device comprises means for storing an identifying label and a corresponding standard result for a plurality of standard metal sheets, and means for processing and comparing a measurement of at least one fluorescent X-ray intensity to the standard to find the identifying label of the standard metal sheet that best matches the measurement. Such a device is capable of executing metal sheet identification. In this embodiment, the appropriate materials parameters such as layer composition can now be available for extracting the correct values for the thickness of the metal sheet and/or a cladding. By preference, intensities of a plurality of detectors are compared to corresponding standard intensities. The device can then find the best matching metal sheet identification label using the combined intensities. In many practical situations the chemistry of the layers in which the fluorescent X-rays have been converted varies from metal
Ghaziary Hormoz
Haszler Alfred Johann Peter
Corus Aluminium Walzprodukte GmbH
Dunn Drew A.
Kiknadze Irakli
Stevens Davis Miller & Mosher LLP
LandOfFree
Device for measurement of metal sheet thickness and clad... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for measurement of metal sheet thickness and clad..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for measurement of metal sheet thickness and clad... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3165311