Determination of the hardness of automotive coatings

 

The hardness of the coating is one of the important properties that characterize the mechanical strength of the coating. At present, the pendulum-type hardness measurement method is commonly used to determine the hardness of automobile coatings. Pendulum type hardness can be divided into two types, single pendulum type and double pendulum type. The measured value of the former is expressed in seconds, and the latter is expressed as a percentage relative to the hardness of the glass.

Single pendulum is also known as König and Berthatz pendulum hardness. Some large foreign automobile coating manufacturers mostly use these two kinds of hardness testers. The hardness indexes of their automobile coatings, especially topcoats, are mostly expressed by these two kinds of hardness, such as Masaf, Storack, Akzo, etc. The working principle of several kinds of pendulum damping tests is basically the same, that is, when the pendulum contacting the coating surface swings in a certain period, if the surface is softer, the swing amplitude of the pendulum rod decays faster, and vice versa. Generally, the Konelo hardness value is about half of the Berthaz hardness value. Because the structure, weight, size, swing period and amplitude of various pendulum rods are different, and the interaction between the pendulum rod and the coating also depends on the elasticity and viscoelasticity of the coating itself, the various pendulums The measurement results cannot establish the conversion relationship between each other, so when listing the coating pendulum hardness value in the product standard, the type of pendulum instrument used must be specified at the same time.

Double pendulum hardness tester is more commonly used in China. Its result is expressed as the ratio of the damping time of the swing amplitude attenuation within the specified swing range to the damping time of the swing amplitude attenuation on the glass plate in the same swing angle range. The glass value must be calibrated before the double pendulum hardness tester is actually measured.

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