US 5,862,199 A · Method and apparatus for measuring thickness of paint layers on substrates using backscattering of x-rays

Abstract

The present invention provides a method and apparatus for nondestructive, in situ measuring thicknesses of layers on substrates. The method and device uses a probe including a radioactive source in a source holder and a photodetector mounted behind the source for detection of backscattered photons. In one aspect the method is used to measure the thickness of paint deposited onto metal substrates. The source holder and photodetector array forms a cylindrically symmetric probe for producing an axially symmetric beam of primary photons. A source containing radioactive .sup.109 Cd producing high energy photons of energy 22 and 25 keV is spaced from the painted surface so the photons impinge on the painted substrate. The intensity of photons backscattered by Compton scattering in the paint layer is proportional to the mass density of the paint to give a direct measurement of the paint thickness. The photons penetrating through to the substrate are absorbed within the substrate.

Claims19

Dependent claims

A method for measuring thickness of a coating comprising elements of low atomic numbers such as, but not limited to paint formed on a surface of a metal substrate such as aluminum, titanium, iron, galvanized iron, copper, and alloys and equivalents thereof, the method comprising the steps of:

providing a radioactive source in a source holder, the radioactive source being selected to produce primary photons having energies in the range from about 14 keV to about 25 keV, sufficiently high so that Compton scattering from the paint coating is enhanced over Compton and Rayleigh scattering from the metal substrate but low enough to contrast between photoelectric absorption in the paint coating and the metal substrate;
positioning said source holder in opposing relation to a surface of a paint- coated metal substrate and measuring a total intensity of backscattered secondary photons from the paint-coated metal substrate;
and
determining the thickness of the paint coating from the total intensity of backscattered photons.

1 more element

A method for controlled application of paint to a surface of a metal substrate such as aluminum and its alloys, titanium and its alloys, iron and iron alloys including galvanized iron, copper and its alloys, and equivalents thereof, the method comprising the steps of:

a) providing an x-ray source in a source holder, the x-ray source being selected to produce primary photons having energies in the range from about 14 keV to about 25 keV, sufficiently high to provide dominance of Compton scattering from the paint coating over Compton and Rayleigh scattering from the metal substrate but low enough to provide sufficient contrast between photoelectric absorption in the paint coating and the metal substrate;
b) applying paint to said surface and positioning said holder in opposing relation to the surface of the metal substrate being painted and measuring a total intensity of backscattered secondary photons from the paint-coated metal substrate;
and
c) processing said intensity of backscattered secondary photons and calculating therefrom a thickness of the paint coating, comparing said thickness to a preselected paint thickness and if the thickness of the paint coating is less than said preselected paint thickness repeat step b) otherwise terminate applying paint to said surface.

1 more element

Dependencies are inferred from the claim text.

Method and apparatus for measuring thickness of paint layers on substrates using backscattering of x-rays

Life of this patent

Method and apparatus for measuring thickness of paint layers on substrates using backscattering of x-rays

Life of this patent

Abstract

Claims19