Selection and Influencing Factors of Coating Thickness Gauge
Users can choose different thickness gauges according to the needs of measurement. Magnetic thickness gauges and eddy current thickness gauges generally measure thicknesses of 0-5 mm. These types of instruments are divided into probe and host integrated type, probe and host separated type, the former Easy to operate, the latter is suitable for measuring non-planar shapes. Thicker dense materials should be measured with an ultrasonic thickness gauge, and the measured thickness can reach 0.7-250 mm. The electrolytic thickness gauge is suitable for measuring the thickness of gold, silver and other metals plated on very thin wires.
Dual-purpose
The instrument is produced in Germany. It combines the functions of magnetic thickness gauge and eddy current thickness gauge. It can be used to measure the thickness of coatings on ferrous and non-ferrous metal substrates. like:
The thickness of copper, chromium, zinc and other electroplating layers on steel or coating thickness of paints, coatings, enamels, etc.
The thickness of the anodized film on aluminum and magnesium materials.
Coating thickness on non-ferrous metal materials such as copper, aluminum, magnesium, and zinc.
The thickness of aluminum, copper, gold and other foil strips, paper and plastic films.
Thickness of thermal spray coating on various steel and non-ferrous metal materials.
The instrument conforms to the national standards GB/T4956 and GB/T4957, and can be used for production inspection, acceptance inspection and quality supervision inspection.
Instrument Features
The dual-function built-in probe is used to automatically identify ferrous or non-ferrous matrix materials, and select the corresponding measurement method for measurement.
The ergonomically designed dual-display structure can read measurement data at any measurement position.
Using the mobile phone menu-type function selection method, the operation is very simple.
The upper and lower limit values can be set. When the measurement result exceeds or meets the upper and lower limit values, the instrument will issue a corresponding sound or flashing light prompt.
Stability*, usually long-term use without calibration.
Technical Specifications
Range: 0～2000μm,
Power supply: Two AA batteries
The standard configuration
Regular
The covering layer formed on the surface protection and decoration of materials, such as coating, plating, coating, sticking layer, chemically generated film, etc., is called coating in relevant countries and standards.
The coating thickness measurement has become an important part of the quality inspection of the processing industry and surface engineering, and it is the best means for the products to reach the superior quality standards. In order to make products into products, my country's export commodities and foreign-related projects have clear requirements for the thickness of the cladding.
The measurement methods of coating thickness mainly include: wedge cutting method, optical interception method, electrolysis method, thickness difference measurement method, weighing method, X-ray fluorescence method, β-ray backscattering method, capacitance method, magnetic measurement method and eddy current measurement. law, etc. The first five of these methods are destructive testing, the measurement methods are cumbersome and the speed is slow, and they are mostly suitable for sampling inspection.
The X-ray and beta-ray methods are non-contact and non-destructive measurements, but the devices are complex and expensive, and the measurement range is small. Due to the presence of radioactive sources, users must comply with radiation protection regulations. X-ray method can measure ultra-thin coating, double coating and alloy coating. The β-ray method is suitable for the measurement of coatings and substrates with atomic numbers greater than 3. The capacitance method is only used when measuring the thickness of insulating coatings of thin conductors.
With the increasing advancement of technology, especially after the introduction of microcomputer technology in recent years, the thickness gauge using magnetic method and eddy current method has taken a step forward in the direction of miniaturization, intelligence, multi-function, high precision and practicality. The resolution of the measurement has reached 0.1 micron, and the accuracy can reach 1%, which has been greatly improved. It has a wide range of applications, wide measuring range, easy operation and low price, and is the most widely used thickness measuring instrument in industry and scientific research.
The non-destructive method neither damages the coating nor the substrate, the detection speed is fast, and a large number of detection work can be carried out economically.
Influencing factors
(a) Magnetic properties of base metal
The thickness measurement by magnetic method is affected by the magnetic change of the base metal (in practical applications, the change of the low carbon steel's magnetic properties can be considered to be slight). The standard sheet is used to calibrate the instrument; it can also be calibrated with the test piece to be coated.
(b) Electrical properties of base metal
The conductivity of the base metal has an influence on the measurement, and the conductivity of the base metal is related to its material composition and heat treatment method. The instrument is calibrated using a standard that has the same properties as the base metal of the test piece.
(c) Base metal thickness
Every instrument has a critical thickness of the base metal. Above this thickness, the measurement is not affected by the thickness of the base metal. The critical thickness value of this instrument is shown in Attached Table 1.
(d) Edge effects
This instrument is sensitive to abrupt changes in the surface shape of the specimen. It is therefore unreliable to measure near the edge of the specimen or at the inner corner.
(e) Curvature
The curvature of the test piece affects the measurement. This effect always increases significantly as the radius of curvature decreases. Therefore, measurements on the surface of a curved specimen are unreliable.
(f) Deformation of the specimen
The probe deforms soft-covered specimens, so reliable data is obtained on these specimens.
(g) Surface roughness
The surface roughness of the base metal and cover layer affects the measurement. The roughness increases, the influence increases. Rough surfaces will cause systematic and accidental errors, and the number of measurements should be increased at different positions for each measurement to overcome such accidental errors. If the base metal is rough, it is also necessary to take several positions on the uncoated base metal specimen with similar roughness to calibrate the zero point of the instrument; zero.
(h) Magnetic field
The strong magnetic field generated by various electrical equipment around will seriously interfere with the thickness measurement by magnetic method.
(i) Adhering substances
The instrument is sensitive to the adhering substances that prevent the probe from being in close contact with the surface of the covering layer. Therefore, the adhering substances must be removed to ensure direct contact between the probe and the surface of the test piece.
(j) Probe pressure
The amount of pressure applied by the probe placed on the test piece will affect the measurement reading, so keep the pressure constant.
(k) Orientation of the probe
The placement of the probe affects the measurement. During the measurement, the probe should be kept perpendicular to the surface of the specimen.
Rules to be followed
(a) Base metal properties
For the magnetic method, the magnetism and surface roughness of the base metal of the standard sheet should be similar to the magnetism and surface roughness of the base metal of the test piece.
For the eddy current method, the electrical properties of the base metal of the standard sheet should be similar to those of the base metal of the test piece.
(b) Base metal thickness
Check whether the base metal thickness exceeds the critical thickness, if not, use one of the methods in 3.3 to calibrate.
(c) Edge effects
Measurements should not be made in close proximity to sudden changes in the specimen, such as edges, holes and internal corners.
(d) Curvature
Measurements shall not be made on the curved surface of the test piece.
(e) Number of readings
Usually, several readings must be taken within each measurement area because each reading of the instrument is not exactly the same. Local differences in overlay thickness also require multiple measurements within any given area, especially when the surface is rough.
(f) Surface cleanliness
Before measurement, remove any adhering substances on the surface, such as dust, grease and corrosion products, but do not remove any covering substances
