GB/T 1720-2020 English PDF (GBT1720-2020)

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GB/T 1720-2020: Circle-drawing test of coating films
GB/T 1720-2020
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 87.040
G 50
Replacing GB/T 1720-1979
Circle-drawing test of coating films
ISSUED ON: NOVEMBER 19, 2020
IMPLEMENTED ON: OCTOBER 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 ... 5 
2 Normative references ... 5 
3 Principle ... 5 
4 Instruments and apparatuses ... 6 
5 Sample ... 8 
6 Test panel ... 8 
7 Test procedure ... 9 
8 Expression of results ... 9 
9 Test report ... 10 
Foreword
This Standard was drafted in accordance with the rules given in GB/T 1.1-2009.
This Standard replaces GB/T 1720-1979, “Method of test for adhesion of paint
films”. Compared with GB/T 1720-1979, the main technical changes, except
editorial changes, are as follows:
-- Change the standard name to "Circle-drawing test of coating films";
-- Add Scope, Normative references, Principle, Sample, Test panel, Test
report (see Chapter 1, Chapter 2, Chapter 3, Chapter 5, Chapter 6, and
Chapter 9);
-- Modify requirements for the equipment (see 4.1; Chapter 1 of version
1979);
-- Add the schematic diagram of the circle-drawing tester of electric coating
films and the dimension figure of the rotating needle (see Figure 2, Figure
3);
-- Add regulations for the rotating needle (see 4.2);
-- Modify the test procedures (see Chapter 7, Chapter 2 of version 1979);
-- Modify requirements for the test panel (see Chapter 6; Chapter 1 of version
1979);
-- Modify the expression of results (see Chapter 8; Chapter 3 of version 1979);
This Standard was proposed by China Petroleum and Chemical Industry
Federation.
This Standard shall be under the jurisdiction of National Technical Committee 5
on Paints and Pigments of Standardization Administration of China (SAC/TC 5).
The drafting organizations of this Standard: Heilongjiang Institute of Quality
Supervision and Inspection, Biuged Laboratory Instruments (Guangzhou) Co.,
Ltd., Guangzhou Research Institute of Synthetic Materials, Avic Biam New
Materials Technology Engineering Co., Ltd., Zhejiang Yu Tong New Materials
Co., Ltd., Qingdao Air++ New Materials Co., Ltd., Shenzhen Grandland High-
tech New Material Co., Ltd., CNOOC Changzhou Paint and Coatings Industry
Research Institute Co., Ltd., Qingdao Xingguo Paint Co., Ltd., Ningbo Xin'an
Dope Co., Ltd., Dongguan Taiho Paint Products Co., Ltd., China Academy of
Building Research, Pushen Testing Instruments (Shanghai) Co., Ltd., Jiangnan
Circle-drawing test of coating films
1 Scope
This Standard specifies a test method to evaluate the peeling degree of the
coating film from the substrate, when the overlapping cycloid diagram
penetrates the coating film to the substrate.
This Standard applies to the determination of circle-drawing test of a single flat
coating film on a hard substrate.
The performance that is measured by this experimental test method not only
depends on the adhesion of the coating to the substrate, but also on various
other factors; so, this test method cannot be regarded as a method for
measuring adhesion.
2 Normative references
The following documents are indispensable for the application of this document.
For dated references, only the dated version applies to this document. For
undated references, the latest edition (including all amendments) applies to this
document.
GB/T 3186, Paints, varnishes and raw materials for paints and varnishes -
Sampling
GB/T 9271, Paints and varnishes standard panels for testing
GB/T 9278, Temperatures and humidity for conditioning and testing of paint
specimens
GB/T 13452.2, Paints and varnishes - Determination of film thickness
GB/T 20777, Paints and varnishes - Examination and preparation of samples
for testing
GB/T 37356, Paints and varnishes - Lighting and procedure for visual
assessments of coatings
3 Principle
Fix the test panel on a test-bed that can be moved forward and backward; while
moving the test-bed, the rotating needle in a circular motion penetrates the
7 Test procedure
7.1 Test number of times
Perform three tests in parallel.
7.2 Test environment
Unless otherwise agreed, the test shall be performed under the conditions that
are specified in GB/T 9278.
7.3 Inspection of circle-drawing diameter
7.3.1 Check the rotating needle tip (4.2); if it is not sharp, replace it.
7.3.2 Install an uncoated tinplate on the test-bed; draw circles according to
normal operation; use a vernier caliper to measure the diameter of the circle,
which shall be (10.5 ± 0.1) mm. When it does not match, adjust it in time. The
user is recommended to regularly check the circle-drawing diameter according
to the usage of the instrument.
7.4 Test
7.4.1 Check the sharpness of the rotating needle tip according to 7.3.1. It is
recommended to replace the rotating needle regularly according to the usage
frequency that is recommended by the supplier.
7.4.2 Fix the test panel on the test-bed with the coated surface facing up, so
that the tip of the rotating needle touches the coating film. If the substrate is not
exposed due to scratches, add weights from small to large.
7.4.3 Shake the handle evenly in a clockwise direction; control the speed within
the range of 80 r/min ~ 100 r/min. If an electric circle-drawing tester of coating
films is used, the rotation speed is usually set to 80 r/min.
7.4.4 When the drawn cycloid scratch reaches the standard drawing length (7.5
± 0.5) cm, stop the test; take out the test panel; use the soft brush (4.4) to
remove the paint chips on the scratch.
7.4.5 Observe the upper side of the scratch under natural or artificial sunlight
as specified in GB/T 37356; use a 4x magnifier (4.3) to observe if necessary.
8 Expression of results
Mark seven positions, namely 1, 2, 3, 4, 5, 6, and 7, in turn on the upper side
of the cycloid scratch, which are divided into 7 grades, where grade 1 is the