GB/T 39130-2020 English PDF (GBT39130-2020)
GB/T 39130-2020 English PDF (GBT39130-2020)
GB/T 39130-2020: Measuring method for adhesion of zinc coating for galvanized products
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
Measuring method for adhesion of zinc coating for
ISSUED ON: OCTOBER 11, 2020
IMPLEMENTED ON: MAY 01, 2021
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Terms and definitions ... 4
4 Samples ... 5
5 Bending test ... 6
6 Test report ... 11
Appendix A (Normative) 180° bending test grade evaluation ... 12
Appendix B (Normative) V-shaped bending test grade evaluation ... 14
Appendix C (Informative) Evaluation of coating adhesion by impact method ... 16 Measuring method for adhesion of zinc coating for
This Standard specifies the terms and definitions, samples, bending tests, and test reports of measuring methods for coating adhesion of zinc coatings for galvanized products, zinc-iron alloys, zinc-aluminum alloys, and aluminum-zinc alloy products. This Standard applies to the coating adhesion test of galvanized, zinc-iron alloy, zinc- aluminum alloy and aluminum-zinc alloy coated steel sheets (steel strips) with a thickness of 0.1 mm ~ 3.0 mm.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies to this document. For undated references, the latest edition (including any amendment) applies to this document.
GB/T 2975, Steel and steel products - Location and preparation of samples and test pieces for mechanical testing
3 Terms and definitions
The following terms and definitions are applicable to this document.
Phenomenon of granular or powdery matter formed due to internal failure of the zinc- iron alloy coating.
The magnitude of the reflective power of normal incident light.
Note: Calculated in percentage (%).
3.3 Powder width in tape
The width of the ribbon-shaped powder spread on the tape during the powdering test. Note: in millimeters (mm).
4.1 General requirements
During the test, square or rectangular samples shall be used. The cutting position, direction and quantity of sample blanks shall be in accordance with the requirements of GB/T 2975 or related product standards.
Both sides of the double-sided-coated product shall be sampled for testing; if one sample is enough for the double-sided test, only one sample shall be taken. The sample shall be flat without deformation; the edges shall be free from burrs; the surface shall be clean and free of oil and corrosion.
Before the test, any hammering, impact or cold or hot processing shall not be performed on the sample.
The samples shall be free from transverse burrs, scars or scratches on the edge that would affect the test results.
The test shall be carried out within the temperature range of 10 °C ~ 35 °C. When there are strict requirements on temperature control, the temperature shall be controlled within (23±5) °C. In case of dispute, the sample to be tested shall be placed in an environment where the temperature is (23±2) °C and the humidity is 50%±5% for at least 24 h before testing.
4.2 Sample size
The sample size is shown in Figure 1.
a – sample thickness;
D – bending indenter diameter;
lv – V-shaped groove side length;
r – indenter rounding radius;
α – die angle;
F – applied force.
Figure 2 – Schematic diagram of bending device
Note: The lower die in Figure 2b) generally has arcs or notches.
The schematic symbols of the bending device are shown in Table 1.
5.2.2 Bending device
The test device consists of a press and a support with sufficient hardness, which can provide sufficient pressure to ensure that the sample is bent and formed. The contact surfaces of the bending indenter and support with the sample shall be flat. When using a flat-pressing bending device, the side length of the indenter shall not be less than the width of the sample; when using a V-shaped bending device, the width of the bending indenter and the support shall not be less than the width of the sample. The bending indenter shall have sufficient rigidity, and there shall be no deformation during the test.
5.3 Test methods
5.3.1 180° bending test
Firstly, preliminarily bend the sample; then, place the sample between the parallel platens in the flat-pressing bending device [Figure 2a)]. The built-in spacer can be added or not during the test, and the thickness of the spacer is equal to the diameter of the specified bending indenter, which is usually an integer multiple of the thickness of the sample. Unless otherwise specified in the product standard, built-in spacers are 18.104.22.168 Reflectance method
Use a reflectometer to measure the reflectivity of the powder (powdering and peeling of the coating) adhered to the tape. The probe of the reflectance meter shall be rectangular. The recommended spot test area is 12 mm × 7 mm. It can be used after being calibrated by a standard white board. The standard reflectance of the standard white board shall be within (85±5) %, and the fluctuation shall not exceed ±1%. The reflectivity of the test white board shall be 80% ~ 95%; the color shall be uniform; the uniformity of reflectivity of the whole white board shall be within ±1%; there shall be no obvious cracks, impurities, bubbles and other defects.
Quickly stick the tape to the test white board; move it at a constant speed along the length of the tape; find the area with the smallest powder reflectivity on the tape; measure this area several times; record the minimum value. During measurement, the distance between the probe of the reflectance meter and the measuring surface shall not exceed 5 mm, and the probe shall be as perpendicular to the measuring surface as possible. For the convenience of observation, the angle between the probe and the measuring surface shall not exceed 5°.
At the same time, when the sample thickness a is not greater than 1.0 mm, the long axis direction of the light spot of the reflectance meter probe shall be parallel to the peeling length direction of the tape; when the sample thickness a is greater than 1.0 mm, the long axis direction of the light spot of the reflectance meter probe shall be perpendicular to the peeling length direction of the tape, as shown in Figure 4.
Evaluation of coating adhesion by impact method
This Appendix – giving the principle, device, sample, test conditions, result calculation and test report for evaluating the adhesion of the coating by the ball impact test method and the double cup test method – applies to the measurement of the coating adhesion of galvanized and zinc-iron alloy coated steel sheets (steel strips) with a thickness of 0.1 mm ~ 3.0 mm.
C.2 Test device
The test device shall be composed of base, stamp die, moulding-die, punch and other parts. Stamp dies, moulding-dies and punches shall have sufficient rigidity; the Vickers hardness of the working surface shall be at least 750HV30, and there shall be no deformation or rotation during the test.
The stamp dies and moulding-dies shall be quenched and the surface in contact with the sample shall be polished. The diameter of the moulding-die hole shall be larger than the spherical diameter of the punch; the fillet radius inside the moulding-die shall be (0.65±0.1) mm.
The end of the punch is hemispherical and polished; the diameter of the sphere shall be (20.00±2) mm; the deviation between the center of the spherical part and the axis of the stamp die and moulding-die shall not exceed 0.1 mm. The distance between the initial position of the punch and the moulding-die shall not be less than 10 mm. The test device shall be able to set single or double strokes, and the stroke display scale shall be 0.1 mm or higher.
The test device shall have sufficient constant clamping force to ensure clamping of the sample.
C.3 Test methods
C.3.1 General requirements
Unless otherwise specified in the agreement, the general pure zinc coating is evaluated by the ball impact test method, and the alloyed coating is evaluated by the double cup test method.
C.3.2 Ball impact test method
Fix the sample between the stamp die and the moulding-die, and make the hemispherical top of the punch contact with the sample, making the punch at zero position. Adjust the position of the sample so that the intersection of the central axis of the punch and the sample is not less than 35 mm from each side of the sample. Turn on the testing machine; push the hemispherical top of the punch to the sample at a constant speed; generally, control the punch speed within (0.2±0.1) mm/s, until the specified depth or the sample hits the neck and critically ruptures.
C.3.3 Double cup test method
Set the first stroke (generally 8.9 mm); insert the sample between the die and the pad die; face the test surface to the pad die to complete the first stamping. Reset the punch; after taking out the sample and turning it over 180°, make the punched protrusion downward. Insert the sample between the die and the pad die; ensure that the raised part is located in the center of the pad die; set the second stroke (usually 6.3 mm); complete the stamping of the second stroke.
The stamping speed shall be controlled within (3±1) mm/s; the distance between the measuring parts on both sides and the edge of the steel plate width shall be about 80 mm.
Note: It is recommended to apply a small amount of lubricating oil on the non- observation surface of the sample to avoid damage to the punch.
C.4 Measurement and result evaluation
C.4.1 Ball impact test method – tape method
Use a tape with a peeling strength of (11±1)N/25 mm to stick it tightly on the embossed part; tear off the tape, and observe whether there is cracking or peeling of the coating on the surface of the sample; refer to Table C.1 for rating; report the test results at the highest grade among a group of samples.
If the critical fracture of the neck of the impact sample is used for punching, it can also be expressed by the maximum stroke when the coating does not peel off.