This standard specifies the method for non-destructive measurement of the thickness of non-conductive coatings on non-magnetic base metals using an eddy current thickness gauge. This method is suitable for measuring the thickness of most anodized films; but it is not suitable for all conversion films, and some conversion films are too thin to be measured by this method. GB/T 4957-2003 Eddy current method for measuring the thickness of non-conductive coatings on non-magnetic base metals GB/T4957-2003 Standard download decompression password: www.bzxz.net
This standard specifies the method for non-destructive measurement of the thickness of non-conductive coatings on non-magnetic base metals using an eddy current thickness gauge. This method is suitable for measuring the thickness of most anodized films; but it is not suitable for all conversion films, and some conversion films are too thin to be measured by this method.

GB/T 4957—2003/ISO 2360,19B2 This standard adopts [ISO 2360:1982 Measurement of thickness of non-conductive coating on non-bacterial substrate metal
Turbulence method
(English version).
This standard replaces [ISO 2360:1982 Measurement of thickness of non-conductive coating on non-bacterial substrate metal
Turbulence method
(English version).
This standard replaces [ISO 2360:1982] 4957—1982 Measurement of thickness of non-conductive coating on non-bacterial substrate metal
Turbulence method
This standard is based on [ISO 2360:1982] and makes the following editorial changes: 1) "This standard" replaces "this international standard"; 2) The wording of the international standard is eliminated; 3) The national standards that adopt the international standard are cited; 4) Regulatory reference documents are added; 5) This standard is issued by China Machinery Industry Corporation. The Federation proposed: The technical committee for standardization of the gold-plated bottom coating ... 236:19B2 Eddy current method for measuring the thickness of non-conductive overlying layers on non-magnetic substrate metals
This standard specifies a method for measuring the thickness of non-conductive overlying layers on non-magnetic substrate metals using an eddy current thickness gauge. This method is suitable for measuring the thickness of most anodic oxide films; however, it is not suitable for some conversion films, which cannot be measured by this method because they are too thick (see Chapter 1). This method can theoretically measure the thickness of overlying layers on magnetic substrate metals, but it is not recommended. In this case, the flammability method specified in GB/T4956 is used for measurement. 2 Normative references
The clauses in the following documents become the clauses of this standard through reference in this standard. For any document with a specified date, all subsequent revisions (excluding errors) or sub-editions shall not be applicable to this standard. However, the parties who reach an agreement based on this standard shall study whether the latest versions of these documents can be used. For any referenced document without a specified date, the latest version shall apply to this standard. BT4056 Determination of thickness of non-magnetic layer on magnetic body (1S02178, 1982, IDT) 3 Application principle | |tt||The high electromagnetic field generated by the probe of the current measuring device will produce a current in the body under the probe. The blur and phase of the current are functions of the thickness of the non-conductive layer between the conductive probe and the probe. 4. Element Affecting Measurement Accuracy
The following factors may affect the accuracy of the measurement of the thickness of the cover layer 4.1 The uncertainty of the measurement of the cover layer
is inherent in the method. The uncertainty of the measurement of the cover layer is (to be precise) a constant value, related to the measurement of the subject, and at least U.5J11 for each single measurement. For overburden thickness greater than 25 m, the uncertainty of the measurement is equal to the product of the constant value of the overburden thickness. If the overburden thickness is equal to or less than 5 m, the average value of several readings should be taken: for overburden thickness less than 3 m, the measurement can reach the required accuracy. 4.2 Electrical properties of base metal
The measurement with eddy current instrument will be greatly affected by the conductivity of the base metal. The conductivity of the metal is related to the composition and heat treatment of the material. The influence of the conductivity on the conductivity varies significantly with the make and model of the instrument. 4.3 Different properties of base metal
Each instrument has a sample temperature of the base metal. Due to this thickness, the temperature measuring box is not affected by the increase of the base metal. Since the critical thickness depends on both the test frequency and the conductivity of the substrate metal, the critical value should be determined by experiment unless the manufacturer has specified it. For a certain test frequency, the higher the conductivity of the substrate metal, the smaller its critical thickness. For a certain substrate metal, the higher the test frequency, the smaller the critical thickness. 4.4 Edge Image Effect Eddy current instruments are very sensitive to irregularities on the sample surface. Therefore, measurements at edges or inner corners are not acceptable unless the instrument is specified in GD/T 4957—2003/ISO 236;1982 The instrument has been calibrated for this type of measurement. bzxz.net
4.5 The effect of the curvature of the specimen on the measurement. The effect of curvature varies greatly with instrument make and type, but is always more pronounced with greater curvature. Therefore, measurements on curved specimens will not be reliable unless the instrument has been specially calibrated for this type of measurement.
4.6 Surface roughness
The surface topography of the base and the object has an effect on the measurement. The surface can cause both systematic errors and accidental errors. Making multiple measurements at different locations can reduce the residual errors. If the base contains metallic debris, it is also necessary to calibrate the instrument zero at several locations on the base metal specimen. If not For substrates with suitable end-traces, use a small amount of solvent from the substrate to remove the heavy layers on the test piece. 4. Remove external dust
The probe of the eddy current instrument must be in close contact with the surface of the sample. The receiver is very sensitive to foreign matter such as the probe being in close contact with the surface of the test piece. The smoothness of the front end of the probe should be checked. 4.8 Probe pressure
The pressure applied by the probe to the sample affects the instrument's test data. Therefore, the pressure should be kept constant. This can be achieved with the help of a suitable pressure gauge.
4.9 Probe placement
The tilt of the probe will change the instrument's response. Therefore, the probe should always be in close contact with the test surface at the measuring point. This can be achieved with the help of a suitable pressure gauge. 4.10 Deformation of the Specimen
The probe can deform soft or thin specimens. The desired measurements on such specimens may be impossible or may only be made with special probes or fixtures: 4.11 Accuracy of the Probe
Since large changes in temperature will affect the contact of the probe, the probe should be brushed with the probe under conditions approximately the same as those used for the calibration. 5. Calibration of the Receiver
5.1 Description
Before use, each instrument should be calibrated with suitable calibration standards in accordance with the instructions for use with the test instrument, paying due attention to the considerations in Chapter 4 and the procedures in Chapter 6. 5.2 Calibration Standards
Calibration standards of known thickness may be used. 5.2.1 Calibration Standards
5.2.1.1 Calibration standards are usually made of plastic and are easier to obtain on curved surfaces than standards with coatings. 5.2.1.2 To avoid measurement errors, the foil must be in contact with the substrate. If possible, avoid using flexible foils. Standards are prone to compression and must be replaced frequently. 5.2.2 Thermal Standards
Standards with coatings should be made of a non-conductive coating of known thickness that is uniformly bonded to the substrate. 5.3 Calibration Standards
5.3.1 The substrate of the calibration standard should have electrical properties similar to those of the test specimen. It is recommended that the readings obtained from the base metal of the calibration standard without any layer be compared with the readings obtained from the test base metal to confirm the applicability of the calibration standard. 5.3.2 If the base metal thickness exceeds the critical thickness defined in 1.2, the pre-coating sequence measurement is not affected by the base metal thickness. If it does not exceed the critical thickness, the base metal thickness of the calibration can be as close as possible to the base metal thickness of the calibration. If this is not possible, a sufficiently thick metal mesh with the same electrical properties should be used to support the calibration standard or test base metal to ensure that the reading is not affected by the base metal thickness! However, if there are problems on both sides of the base metal, or there is any gap between the base metal and the backing metal, this method cannot be used. 5.3. If the test layer is curved and cannot be calibrated in a flat manner, the curvature of the adjusted standard piece or the curvature of the base foil should be the same as the curvature of the sample to be tested. 6 Measurement procedure
6.1 Speed ​​
Operate an instrument according to the manufacturer's instructions, giving corresponding attention to the requirements listed in Chapter 4. Each time the instrument is put into use, and every certain period of time during use (at least once an hour), the calibration of the instrument should be checked on site to ensure normal performance of the instrument. The following precautions must be observed.
6.2 Base metal thickness
Is the base metal thickness above the critical thickness? If not, use the method described in 5.3.2. If it is ensured that the instrument has been calibrated with a standard specimen of the same order and electrical performance as the sample, 6.3. Reverse Efficiency
Do not make measurements near the edges, pores, inside corners, etc. of the specimen unless the validity of the calibration made for these measurements has been verified.
6.4. Curvature
Do not make measurements on the curved surface of the specimen unless the validity of the calibration made for such measurements has been verified. 6.5. Reverse Efficiency of the Number
Because of the positive fluctuation of the position, it is necessary to collect several numbers at each measuring position. Local differences in the degree of lamination may also require multiple measurements on any given surface, especially when the surfaces are similar. 6.6. Surface Cleanliness
Before measurement, any foreign matter such as dust, grease and corrosion products should be removed from the specimen surface, but any intermediate coating materials should not be removed.
7. Accuracy Requirements
The instrument and its calibration and operation should be such that the overburden thickness can be measured to within 10 % of the actual accuracy. If measuring an overburden depth of less than 5 m, it is advisable to take the average of several readings. This accuracy may not be achieved for overburden thicknesses less than 3 m. In order to assess the effect of the test, a simple method should be used, i.e. a clean sample with two fixed points in front of it, as follows: place the probe on the sample at a distance of 5 m from the surface, and move the probe gradually to the point indicated in the diagram. The position of the probe when the test effect occurs, the distance between the average effect and the measured voltage, may be difficult to use directly. If the probe is used for other purposes, then only the instrument should be specially calibrated. If more is required, please consult the manufacturer's instructions.
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