The Calo tester, also known as a ball craterer or coating thickness tester, is a simple and inexpensive piece of equipment used to measure the thickness of coatings.

Coating A coating is a covering that is applied to the surface of an object, usually referred to as the substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquids, gases or solids e.g. Pow ...

s with thicknesses typically between 0.1 to 50

micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

s, such as

Physical Vapor Deposition Physical vapor deposition (PVD), sometimes called physical vapor transport (PVT), describes a variety of vacuum deposition methods which can be used to produce thin films and coatings on substrates including metals, ceramics, glass, and polym ...

(PVD) coatings or Chemical Vapor Deposition (CVD) coatings, are used in many industries to improve the surface properties of tools and components. The Calo tester is also used to measure the amount of coating

wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in ...

after a wear test carried out using a Pin-on-Disc Tester. The Calo tester consists of a holder for the surface to be tested and a steel

sphere A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is th ...

of known

diameter In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid fo ...

that is rotated against the surface by a rotating shaft connected to a motor whilst

diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, ...

paste is applied to the contact area. The sphere is rotated for a short period of time (less than 20 seconds for a 0.1 to 5 micrometre thickness) but due to the

abrasive An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflec ...

nature of the diamond paste this is sufficient time to wear a crater through thin coatings. Calo tester kaloMAX II BAQ

Calculating coating thickness using the Calo tester

optical microscope The optical microscope, also referred to as a light microscope, is a type of microscope that commonly uses visible light and a system of lenses to generate magnified images of small objects. Optical microscopes are the oldest design of microsc ...

is used to take two measurements across the crater after the Calo test and the coating thickness is calculated using a simple geometrical equation.

t = \fracd

Where t = coating thickness, d = diameter of the sphere x = difference between the radius of the crater and radius of the part of the crater at the bottom of the coating x+y = diameter of the crater

References

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External links

www.pvd-coatings.co.uk on Coasting Thickness Tester

Determination of layer thickness with a spherical cap grinder (Calotest)
Industrial processes Measuring instruments