Types of Coating Thickness Gauge
The coating thickness gauge can non-destructively measure the thickness of non-magnetic coatings (such as aluminum, chromium, copper, enamel, rubber, paint, etc.) The thickness of a non-conductive coating (such as enamel, rubber, paint, plastic, etc.) on a metal substrate (such as copper, aluminum, zinc, tin, etc.). The coating thickness gauge has the characteristics of small measurement error, high reliability, good stability, and easy operation. It is an indispensable testing instrument for controlling and ensuring product quality. It is widely used in manufacturing, metal processing, chemical industry, Commodity inspection and other testing fields.
name
Ferrous/non-ferrous coating thickness gauges use magnetic sensors to measure non-ferromagnetic coatings and coatings on ferromagnetic metal substrates such as steel and iron, such as: paint, powder, plastic, rubber, synthetic materials, phosphating layer , chromium, zinc, lead, aluminum, tin, cadmium, porcelain, enamel, oxide layer, etc. Use eddy current sensors to measure enamel, rubber, paint, plastic layers, etc. on copper, aluminum, zinc, tin, etc. substrates. Widely used in manufacturing, metal processing, chemical industry, commodity inspection and other testing fields. Coating thickness gauge generally has the following five types according to the measurement principle:
Magnetic thickness measurement
It is suitable for measuring the thickness of the non-magnetic layer on the magnetically conductive material. The magnetically conductive material is generally: steel\iron\silver\nickel. This method has high measurement accuracy
Eddy Current Thickness Measurement
Applicable to the measurement of the thickness of non-conductive layers on conductive metals. This method is less accurate than the magnetic thickness measurement method
ultrasonic thickness measurement
At present, there is no such method in China to measure the thickness of the coating. Some foreign manufacturers have such instruments, which are suitable for the measurement of the thickness of multi-layer coatings or the occasions where the above two methods cannot be measured. But the general price is expensive and the measurement accuracy Not high either.
electrolytic thickness measurement
This method is different from the above three methods. It does not belong to non-destructive testing and needs to destroy the coating. Generally, the accuracy is not high. It is more troublesome to measure than other types
Radiographic Pachymetry
This kind of instrument is very expensive (generally above 100,000 RMB), and is suitable for some special occasions.
The most common method currently used in China
The first and second methods are the most commonly used in China at present. the
example 1
Iron-based coating thickness gauge dual-purpose coating thickness gauge 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:
* Copper, chromium, zinc, etc. electroplated layer or coating thickness of paint, coating, enamel, etc. on steel. the
* Thickness of anodized film on aluminum and magnesium materials. the
* Coating thickness on non-ferrous metal materials such as copper, aluminum, magnesium, zinc, etc. the
* The thickness of aluminum, copper, gold and other foil strips and paper and plastic films. the
*Thickness of thermal spray coating on various steel and non-ferrous metal materials. the
The instrument complies with national standards GB/T4956 and GB/T4957, and can be used for production inspection, acceptance inspection and quality supervision inspection. the
Instrument Features
* It adopts dual-function built-in probe 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. the
* Using the mobile phone menu function selection method, the operation is very simple. the
* The upper and lower limits can be set. When the measurement results exceed or meet the upper and lower limit values, the instrument will make a corresponding sound or flashing light to prompt. the
* Extremely high stability, usually can be used for a long time without calibration. the
The principle of conventional coating thickness gauge
The covering layer formed to protect and decorate the surface of materials, such as coating, plating, cladding, sticking, chemically formed film, etc., is called coating in relevant national and international standards. the
Coating thickness measurement has become an important part of quality inspection in processing industry and surface engineering, and it is an essential means for products to meet high quality standards. In order to make the products internationalized, there are clear requirements for the thickness of the cladding in my country's export commodities and foreign-related projects.
The measurement methods of coating thickness mainly include: wedge cutting method, optical section 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. Among these methods, the first five are destructive testing, the measurement methods are cumbersome and slow, and most of them are suitable for sampling inspection. the
X-ray and β-ray methods are non-contact and non-destructive measurements, but the devices are complicated and expensive, and the measurement range is small. Due to the radioactive source, users must comply with radiation protection regulations. X-ray method can measure extremely thin coating, double coating and alloy coating. The β-ray method is suitable for the measurement of the coating and the coating with the atomic number of the substrate greater than 3. The capacitance method is only used when measuring the thickness of the insulating coating of a thin conductor. With the increasing advancement of technology, especially after the introduction of microcomputer technology in recent years, thickness gauges using the magnetic method and eddy current method have taken a step forward in the direction of miniature, intelligent, multi-functional, high-precision, and practical. The measurement resolution has reached 0.1 microns, and the accuracy can reach 1%, which has been greatly improved. It has wide application range, wide measuring range, easy operation and low price, and is the most widely used thickness measuring instrument in industry and scientific research. the
The non-destructive method neither damages the coating nor the base material, and the detection speed is fast, so that a large amount of detection work can be carried out economically.
Measuring Principles and Instruments
Measuring Principle of Magnetic Attraction and Thickness Gauge
*The suction force between the magnet (probe) and the magnetic steel is proportional to the distance between the two, and this distance is the thickness of the cladding. Using this principle to make a thickness gauge, as long as the difference between the magnetic permeability of the coating and the base material is large enough, it can be measured. In view of the fact that most industrial products are stamped and formed by structural steel and hot-rolled cold-rolled steel plates, magnetic thickness gauges are the most widely used. The basic structure of the thickness gauge is composed of magnetic steel, relay spring, scale and self-stop mechanism. After the magnetic steel is attracted to the measured object, the measuring spring is gradually elongated thereafter, and the pulling force is gradually increased. When the pulling force is just greater than the suction force, the thickness of the coating can be obtained by recording the pulling force at the moment when the magnetic steel is detached. Newer products can automate this recording process. Different models have different ranges and applicable occasions. This instrument is characterized by easy operation, durability, no power supply, no need for calibration before measurement, and low price. It is very suitable for on-site quality control in workshops.
Measuring principle of magnetic induction
When the principle of magnetic induction is used, the thickness of the coating is measured by the magnitude of the magnetic flux flowing from the probe through the non-ferromagnetic coating into the ferromagnetic substrate. The size of the corresponding magnetoresistance can also be measured to indicate the thickness of the coating. The thicker the coating, the greater the reluctance and the smaller the flux. The thickness gauge using the principle of magnetic induction can in principle have the thickness of the non-magnetic coating on the magnetic substrate. Generally, the magnetic permeability of the substrate is required to be above 500. If the cladding material is also magnetic, a sufficiently large difference in permeability from the base material is required (eg nickel plating on steel). When the probe with the coil wound on the soft core is placed on the sample to be tested, the instrument will automatically output the test current or test signal. Early products used a pointer gauge to measure the magnitude of the induced electromotive force, and the instrument amplified the signal to indicate the coating thickness. In recent years, circuit design has introduced new technologies such as frequency stabilization, phase locking, and temperature compensation, and uses magnetic resistance to modulate measurement signals. The designed integrated circuit is also used, and the microcomputer is introduced, so that the measurement accuracy and reproducibility have been greatly improved (almost an order of magnitude). The modern magnetic induction thickness gauge has a resolution of 0.1um, an allowable error of 1%, and a range of 10mm. The magnetic principle thickness gauge can be used to measure the paint layer on the steel surface, porcelain, enamel protective layer, plastic, rubber coating, various non-ferrous metal plating layers including nickel chromium, and various anti-corrosion coatings for chemical oil industry .
Eddy current measurement principle
The high-frequency AC signal generates an electromagnetic field in the probe coil, and when the probe is close to the conductor, an eddy current is formed in it. The closer the probe is to the conductive substrate, the greater the eddy current and the greater the reflection impedance. This amount of feedback characterizes the distance between the probe and the conductive substrate, that is, the thickness of the non-conductive coating on the conductive substrate. Since these probes specialize in measuring the thickness of coatings on non-ferromagnetic metal substrates, they are often referred to as non-magnetic probes. Non-magnetic probes use high-frequency materials as coil cores, such as platinum-nickel alloys or other new materials. Compared with the principle of magnetic induction, the main difference is that the probe is different, the frequency of the signal is different, the size and scale relationship of the signal are different. Like the magnetic induction thickness gauge, the eddy current thickness gauge has also reached a high level of resolution of 0.1um, allowable error of 1%, and range of 10mm. The thickness gauge using the principle of eddy current can in principle measure the non-conductive coating on all electrical conductors, such as the surface of aerospace vehicles, vehicles, household appliances, aluminum alloy doors and windows, and other aluminum products. Anodized film. The cladding material has a certain conductivity, which can also be measured by calibration, but the ratio of the two conductivity is required to be at least 3-5 times different (such as chrome plating on copper). Although the steel substrate is also an electrical conductor, it is more suitable to use the magnetic principle for this kind of task
