Paints and varnishes are often used to protect a variety of substrates.When the paints and varnishes are hardened,a dry film is formed on the substrate surface.Unsuitable thickness can easily lead to premature failure of protection.Therefore,it is necessary to use vanish and paint thickness gauge to ensure the standard thickness.Below we will briefly introduce several methods for measuring the thickness of paints and varnishes. And the thickness gauges that use these measuring methods.
The gravimetric method is to measure the difference in mass between the unpainted substrate and the brushed substrate by means of a balance.And then divide the mass difference by the surface area and density of the dry film to calculate the dry film thickness.The dry film thickness obtained by this method is the average value of the entire dry film area and it is required to ensure that the back surface of the substrate is clean when painting.Otherwise it is easy to affect the precision due to the paint film which is mistakenly brushed on the back surface.
1)The thickness of the dry film can be measured by a micrometer or a dial gauge, calculated by the difference between the total thickness of the substrate and the film minus the substrate thickness.
2)The depth gauge or surface profile scanner can directly measure the paint film thickness,that is,the difference in height between the dry film surface and the exposed substrate surface.
The above four varnish and paint thickness gauges require the film to have sufficient hardness, otherwise it is easy to affect the reading due to the indentation of the paint film when the instrument is measured.
The optical method mainly uses a drill or a knife to cut the coating at a certain angle to obtain a bevel cut.Then uses a microscope to measure the distance after the cut bevel is projected onto the substrate surface.Then the film thickness is calculated by a trigonometric function.This method is suitable for a good distinction between the coating and the substrate.And the substrate may be drilled or cut.
The radiation method uses a radioisotope as a radiation source to determine the paint film thickness by the interaction between the ionizing radiation and the paint film coating.
The photo thermal method measures the film thickness by calculating the time difference between the hot wave or the ultrasonic wave.
The sonic method measures the paint film thickness by the time it takes for the ultrasonic pulse to pass through the paint film. The color vanish and paint thickness gauges using this method mainly include an ultrasonic thickness gauge.
1)Magnetic thickness gauge
The varnish and paint thickness gauges using the magnetic attraction method contain magnets.The dry film thickness is calculated by measuring the attractive force between the magnet and the substrate.
2)Magnetic flux thickness gauge
The varnish and paint thickness gauges using the magnetic flux thickness measurement method contain magnets.And the instrument is placed close to the paint film.Then the instrument is lifted and away from the paint film in a direction perpendicular to the coating surface.And the paint film thickness can be moved. The force required for the instrument (magnet) is calculated.
3)Induced magnetic thickness gauge
The induced magnetic thickness gauge contains an electromagnet inside.And the electromagnetic field in the instrument changes when it contacts the ferromagnetic substrate.Then the paint film thickness is determined.
4)Eddy current thickness gauge
The eddy current thickness gauge contains an electromagnet inside.A eddy current is generated when the conductive substrate is measured.The paint film thickness is measured by detecting a change in the magnetic field caused by the eddy current.
In addition to the above four principles of thickness gauges,there are also some varnish and paint thickness gauges that use both the magnetic thickness measurement method and the eddy current thickness measurement method.For example, QNix and Linshang coating thickness gauges.As shown in the above figure, such an instrument can automatically switch the measurement mode when measuring different substrates,which is more convenient to use.
The above is all the methods and principles of measuring paints and varnishes thickness,as well as some professional varnish and paint thickness gauges.If you need to know more about them,please refer to the“national standard GBT13452.2-2008 paint and varnish film measurement standard of the thickness.”