The Calotest provides quick, simple and inexpensive determination of coating thicknesses. A rotating sphere, with a known diameter (Ø ball) is pressed on the coating surface with a preselected load. Both the position of the sphere relative to the sample and the contact load are constant. Upon adding abrasive slurry to the contact zone, a depression with the shape of a spherical cap is abraded into both the coating and the substrate.
Optical inspection of the depression reveals the projected surfaces of the abraded coating and substrate sections. By measuring the parameters X and Y, the thickness of the coating D can be calcuted by a simple geometrical equation.
The Calowear system extends the Calotest principle by incorprating a force sensor, a revolution counter and an automated slurry dispenser. A steel ball rolls on the test sample and a slurry composed of water and SiC particles falls continuously onto the ball at the contact region. The slurry wears the substrate in a controlled manner and thus assures highly reproducible results.
The normal force between the sphere and the specimen is measured. The rotational motion of the sphere is also measured. The rotation of the sphere against the specimen in the presence of the abrasive slurry generates a wear crater. By comparing the geometry of the crater for different periods of wear time, the thickness of the coating and the wear rate of the coating and the substrate can be determined precisely.
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