WHAT IS COATING?
In engineering, a coating is classified as a substance/material applied to the surface of another substance/material (often referred to as base material) to specifically enhance the properties of the surface for the purpose of increasing durability or decorating the product.
Several factors determine the type of coating to be applied to a material surface, including cost, the service life of the substrate product to which the coating is applied, and suitability.
Coatings are applied to surfaces according to specific standards, such as ISO, BS, ASTM, DIN, etc., In addition, the thickness of the applied coating is determined by its function and cost.
Typical coating thicknesses can range from a few nanometers (nm) to several millimeters (mm). For example, Titanium Zirconium (TiZr) coatings can range from 1nm to 5nm thick, while anodic films can range from 0.5μm to 150μm, and paint coatings can be up to several millimeters thick.
Coating thickness gauge Sanko Denshi SAMAC-Pro : used to measure paint thickness on vehicle substrate
CLASSIFICATION OF COATINGS BY BASE MATERIAL
Coatings are divided into two distinct categories: layers formed by reactions involving surface modification of the substrate material and layers deposited on the surface of the substrate material.
Coatings have different properties depending on the coating applied to the substrate.
The most common types of coatings applied to substrates are those applied in solution by ion reduction reaction and include coatings deposited by electrodeposition (chromium, gold, silver, etc.) or by electroless deposition (e.g. electroless nickel plating).
→ From there, we can classify the coating according to the properties of the substrate material, in order to choose the appropriate equipment to measure the coating thickness.
COATING ON MAGNETIC BASE MATERIALS (Iron, steel,...)
Will use the induction method (ELECTRO-MAGNETIC)
The magnetic induction method is a method specially used for coatings on ferromagnetic substrates.
A measuring coil measures the generated magnetic field. The resulting measurement signal is converted into a coating thickness value using a specific probe output function (usually manufacturer specific).
Coating thickness gauge Sanko Denshi SWT-9000 with Fe-2.5 probe (measurement range 0-2500um) to measure coatings on magnetic substrates
COATING ON NON-MAGNETIC BASE MATERIALS (Aluminum, copper,...)
Will use eddy current method
The eddy current coating measurement method is used to non-destructively measure the thickness of non-conductive coatings (paints, primers, anodized coatings, etc.) applied to non-magnetic metal substrates (aluminum, aluminum alloys, copper, etc.) or non-magnetic stainless substrates.
Coating thickness gauge KETT LH-373 with LHP-J probe (measurement range 0-1200um) to measure coatings on non-magnetic substrates
COMBINATION OF BOTH MAGNETIC INDUCTION AND EDDY CURRENT METHODS
Measurement of coating thickness on magnetic and non-magnetic substrate materials
Manufacturers of coating thickness measuring equipment will combine 2 methods to be able to integrate the probe inside the machine or separate probe to be able to simultaneously measure the coating thickness on magnetic material (ferromagnetic) and non-magnetic substrate material (aluminum, copper, etc.).
Coating thickness gauge KETT LZ-990 with built-in measuring head inside the machine (measuring range 0-2000um) measures coatings on magnetic and non-magnetic substrates with automatic switching
produces sound waves into a material to measure its thickness.
Ultrasonic methods generate sound waves into a material to measure its thickness. Although they are primarily used to measure wall thickness, such as that of oil or gas pipes (to detect corrosion on the inside diameter), they can also be used to measure the thickness of coatings.
Sound waves when introduced into a material surface will travel towards the opposite side of it. Any boundary that the wave passes through, such as the boundary between a coating and a substrate, results in a reflection of the signal back to the transducer that produced it. This is detected and internally, based on the speed of sound in the material, the thickness is calculated using a formula of distance, speed and time.
OLYMPUS 38DL-PLUS ultrasonic Thickness Measurements on Plastics, Metals, Composites, Glass, Rubber, Ceramics
XRF is based on the basic principle that when an energy source excites individual atoms, those atoms emit energy or wavelengths of light that are characteristic of the atom from which they are emitted. By analyzing the number of photons of each energy, samples can be separated into their constituent components and from this information, coating thickness and elemental composition can be calculated.
The ability of XRF to differentiate between different atoms makes it an extremely powerful technique for analyzing multiple layers (theoretically up to 24 with an SDD detector, and if the coating is thin enough to allow the signal to pass through), it can also be used to measure the thickness of coatings on alloy materials. XRF requires more training than tactile methods and readings tend to take longer than 5 seconds.
In the silicon wafer semiconductor industry, coatings tend to be stacked on top of each other and XRF is used to routinely measure 5 to 10 layers simultaneously. XRF is also capable of determining the composition of the coating (e.g. the ratio and thickness of the zinc-nickel coating) or even the percentage of phosphorus in the nickel-phosphorus layer.
X-ray fluorescence measuring device FISCHERSCOPE X-RAY XDAL-237 with programmable XY and Z-axis stages for automation. Thin coating measurement and material analysis.
CONCLUDE
These are just some of the methods used in industry to measure coating thickness.
Other techniques exist but are beyond the scope of this article. The techniques presented here are guidelines and the benefits/disadvantages of each technique are discussed.
Ultimately, it is important to contact a representative of the coating thickness gage manufacturer to discuss the solution that best suits your needs.
With many years of experience in the field of coating thickness measurement and testing in the precision mechanical, electronics and household appliances industries, Semiki engineers are trained, have installed, operated and instructed customers on the most suitable and effective operation, testing and application of coating thickness measuring equipment.
Maintenance and calibration:
► SEMIKI will provide a calibration certificate attached (optional)
► Please maintain and calibrate the device after using it for a certain period of time.
CONTACT:
SEMIKI Measuring Equipment Company Limited
Email: sales@semiki.com
Office phone: +84 28 2253 3522
