GB/T 18684-2002 English PDF (GB/T18684-2002)

GB/T 18684-2002: Specifications of zinc/chromate coating
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GB/T 18684-2002
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 25.220.20
A 29
Specifications of Zinc/Chromate coatings
Issued on March 10, 2002 Implemented on August 1, 2002
Issued by. General Administration of Quality Supervision, Inspection and
Quarantine of the People's Republic of China
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Normative References ... 4 
3 Definition ... 4 
4 Classification ... 4 
5 Documents that are required to be supplied to supplier ... 5 
6 Technical requirements ... 5 
7 Sampling ... 6 
8 Test methods ... 7 
Appendix A ... 9 
Appendix B ... 11 
Foreword
Appendix A and B in this Standard are informative.
This Standard was proposed by the China Machinery Industry Federation.
This Standard shall be under the jurisdiction of the China Standardization Technology
Committee of Metallic and Non-metallic Coatings.
The responsible drafting organizations of this Standard. Wuhan Research Institute of
Materials Protection, and Nanjing Hongguang Parachute Equipment Factory.
The participating drafting organizations of this Standard. Wuhan Yongtaihe Metal
Anticorrosion Technology Co., Ltd., and Beijing Yongtaihe Metal Anticorrosion Technology
Co., Ltd.
The main drafters of this Standard. Wu Yong, Xue Zhongyou, Zhang Weiming, Li Chunyan
and Zhang Hongwei.
Specifications of Zinc/Chromate coatings
1 Scope
This Standard specifies the technical requirements and test methods of zinc/chromate
coatings of steel parts and components.
2 Normative References
The following normative documents contain the provisions which, through reference in this
text, constitute the provisions of this Standard. For the dated reference, the subsequent
amendments (excluding corrigendum) or revisions of these publications do not apply.
However, the parties who reach an agreement based on this Standard are encouraged to
use the latest edition of these documents. For undated references, the latest edition of the
normative document referred to applies.
GB/T 5270-1985 Metallic Coatings on Metallic Substrates - Electrodeposited and
Chemically Deposited Coatings - Review of methods available for testing adhesion (eqv
ISO 2819.1980)
GB/T 6462 Metallic and oxide coatings - Measurement of Coating Thickness -
Microscopical method (eqv ISO 1463)
GB/T 10125-1997 Corrosion Tests in Artificial Atmospheres - Salt Spray Tests (SS) (eqv
ISO 9227.1990)
3 Definition
The following definition is applicable to this Standard.
Zinc/Chromate coatings
Using water-based zinc/chromate coatings to dip-coat, brush-coat or spray onto the
surface of steel parts or components, then it is baked to form into the inorganic
anticorrosion coating of which the main ingredients are the flake zinc and zinc
chromate.
4 Classification
The zinc/chromate coatings are divided into 4 classes shown in Table 1 according to the
6.2 Coating quantity and coating thickness
The coating quantity and coating thickness of different classes shall not be lower than the
requirements specified in Table 1.
6.3 Adhesion strength
The coating must not be peeled off and bottom-exposed, after conducting adhesion
strength test for coating according to the method in 8.3. However, it is allow that the
adhesive tape is color-change and and is adhered with zinc and aluminum dust granules.
6.4 Salt spray corrosive resistance property
For different class of coating, after conducting salt spray test, the time of appearing red
rust shall not be lower than the requirements specified in Table 2.
Table 2 The test requirements of salt spray corrosive resistance
Coating class 1 2 3 4
Time of appearing red rust /h 120 240 480 1000
6.5 Water resistant test property
For class 3 and 4 coatings, after it is conducted for water resistant test according to the
requirements of 8.5, the coating must not be peeled off from the matrix or bottom-exposed.
For class 1 and 2 coatings, it is exempted from water resistant test.
6.6 Moist-heat proof property
For class 3 and 4 coatings, after it is conducted for moist-heat resistant test according to
the requirements of 8.6, red-rust must no appear in 240h. For class 1 and 2 coatings, it is
exempted from moist-heat resistant test.
7 Sampling
7.1 In the same batch of products, it is required to randomly sample 3 samples for each
test for experiment. If any sample among which is nonconformance after testing, then it is
required to randomly sample another 3 samples to conduct the same test one more time.
If there is any sample is still nonconformance, then this batch of products shall be deemed
as nonconformance.
7.2 For assembly OR part or component of which the mass of single-part exceeds 150 g,
it may cut a part of the workpiece as the sample for testing. In order to avoid the matrix of
bare steel at incision impacting the test result, it shall adopt coating, wax or adhesive tape
to protect the incision. For the part with complicated shape and difficult to determine its
surface area, it may adopt the same method to prepare the sample.
8 Test methods
8.1 Appearance
To inspect with the naked eye under the nature diffused light.
8.2 Coating and test
8.2.1 Dissolve weight method
For the sample of which the mass is large than 50 g, adopt balance of which the precision
is 1 mg to weigh its original mass W1 (mg). Place the sample into the water solution with
70°C~80°C 20% NaOH water solution; soak for 10 min; make the zinc/chromate coatings
dissolve fully. Take out the sample; wash in water adequately; dry immediately; then weigh
the mass W2 (mg) of sample of which the coating has been dissolved. Measure and
calculate the surface area S(dm2) of the workpiece; calculate the coating quantity Ws
(mg/dm2) according to the following formula.
The calculation method of coating surface area of general parts shall refer to Appendix A.
Note 1. If the mass of sample is less than 50g, it shall accumulate some samples to reach above the
mass of 50g, then conduct coating test.
Note. After the zinc/chromate coatings are dissolved in the solution of NaOH for 10 mins, it shall prolong
the soaking time, until the coating is fully dissolved.
8.2.2 Metallographic microscope method
Adopt metallographic microscope method to inspect the coating thickness according to
the requirements of GB/T 6462.
8.3 Adhesion Strength Test
Adopt adhesive tape test method to inspect the adhesive strength between zinc/chromate
coatings and matrix; the tape test shall be conducted according to the requirements of
Clause 1.4 in GB/T 270-1985.
8.4 Salt spray test
The salt spray test shall be conducted according to the requirements of Clause 3.2.1 in
GB/T 10125-1997.
8.5 Water resistant test
Soak the sample into de-ionized water of 40°C ±1°C; continuous soak for 240h; take out
the sample; dry at room temperature; then, conduct the adhesive strength test according
to the requirements of 8.3; the test result shall meet the requirements of 6.3. The adhesive
strength test shall be conducted within 2h after the samples are taken out from de-ionized
water.
8.6 Humid heat test
The humid heat test shall be conducted in humid heat test box; the humid heat test box
shall be able to adjust and control the temperature and humidity.
Set the temperature of humid heat test box at 40°C±2°C and relative humidity at 95%±3%;
hung the samples vertically in humid heat test box; the samples shall not be touched each
other. When the humid heat test box reaches the set temperature and humidity, start to
calculate the testing time. Continuously test for 48 h; then inspect once; inspect whether
the red rust appears on the samples. After 2 times of inspection, inspect once for each 72
h. After each inspection, the position of samples shall be exchanged. After 240 h, conduct
the last inspection.
Appendix B
(Informative)
The application and limit of zinc/chromate coatings
B.1 The application of zinc/chromate coatings
The zinc/chromate coatings is a kind of high anticorrosion coating; the production process
have no pollution to the environment basically. Compared with electro galvanizing, electro
tinning, hot galvanizing, the advantages and application of zinc/chromate coatings are as
follows.
B.1.1 Better corrosion-resisting property
The corrosion-resisting property of zinc/chromate coatings is better than those of electro-
galvanizing, electro-tinning and hot galvanizing; it can be used for the fastener with higher
anticorrosion requirements or used at the severe corrosive condition (such as oceanic
atmosphere, industry atmosphere and moist heat atmosphere, as well as the elasticity
part and other parts and components of steel, aluminium and other alloy.
B.1.2 Be able to be used to multifold parts
The zinc/chromate coatings can be used for the surface protection of multifold of steel,
...
GB/T 18684-2002
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 25.220.20
A 29
Specifications of Zinc/Chromate coatings
Issued on March 10, 2002 Implemented on August 1, 2002
Issued by. General Administration of Quality Supervision, Inspection and
Quarantine of the People's Republic of China
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Normative References ... 4 
3 Definition ... 4 
4 Classification ... 4 
5 Documents that are required to be supplied to supplier ... 5 
6 Technical requirements ... 5 
7 Sampling ... 6 
8 Test methods ... 7 
Appendix A ... 9 
Appendix B ... 11 
Foreword
Appendix A and B in this Standard are informative.
This Standard was proposed by the China Machinery Industry Federation.
This Standard shall be under the jurisdiction of the China Standardization Technology
Committee of Metallic and Non-metallic Coatings.
The responsible drafting organizations of this Standard. Wuhan Research Institute of
Materials Protection, and Nanjing Hongguang Parachute Equipment Factory.
The participating drafting organizations of this Standard. Wuhan Yongtaihe Metal
Anticorrosion Technology Co., Ltd., and Beijing Yongtaihe Metal Anticorrosion Technology
Co., Ltd.
The main drafters of this Standard. Wu Yong, Xue Zhongyou, Zhang Weiming, Li Chunyan
and Zhang Hongwei.
Specifications of Zinc/Chromate coatings
1 Scope
This Standard specifies the technical requirements and test methods of zinc/chromate
coatings of steel parts and components.
2 Normative References
The following normative documents contain the provisions which, through reference in this
text, constitute the provisions of this Standard. For the dated reference, the subsequent
amendments (excluding corrigendum) or revisions of these publications do not apply.
However, the parties who reach an agreement based on this Standard are encouraged to
use the latest edition of these documents. For undated references, the latest edition of the
normative document referred to applies.
GB/T 5270-1985 Metallic Coatings on Metallic Substrates - Electrodeposited and
Chemically Deposited Coatings - Review of methods available for testing adhesion (eqv
ISO 2819.1980)
GB/T 6462 Metallic and oxide coatings - Measurement of Coating Thickness -
Microscopical method (eqv ISO 1463)
GB/T 10125-1997 Corrosion Tests in Artificial Atmospheres - Salt Spray Tests (SS) (eqv
ISO 9227.1990)
3 Definition
The following definition is applicable to this Standard.
Zinc/Chromate coatings
Using water-based zinc/chromate coatings to dip-coat, brush-coat or spray onto the
surface of steel parts or components, then it is baked to form into the inorganic
anticorrosion coating of which the main ingredients are the flake zinc and zinc
chromate.
4 Classification
The zinc/chromate coatings are divided into 4 classes shown in Table 1 according to the
6.2 Coating quantity and coating thickness
The coating quantity and coating thickness of different classes shall not be lower than the
requirements specified in Table 1.
6.3 Adhesion strength
The coating must not be peeled off and bottom-exposed, after conducting adhesion
strength test for coating according to the method in 8.3. However, it is allow that the
adhesive tape is color-change and and is adhered with zinc and aluminum dust granules.
6.4 Salt spray corrosive resistance property
For different class of coating, after conducting salt spray test, the time of appearing red
rust shall not be lower than the requirements specified in Table 2.
Table 2 The test requirements of salt spray corrosive resistance
Coating class 1 2 3 4
Time of appearing red rust /h 120 240 480 1000
6.5 Water resistant test property
For class 3 and 4 coatings, after it is conducted for water resistant test according to the
requirements of 8.5, the coating must not be peeled off from the matrix or bottom-exposed.
For class 1 and 2 coatings, it is exempted from water resistant test.
6.6 Moist-heat proof property
For class 3 and 4 coatings, after it is conducted for moist-heat resistant test according to
the requirements of 8.6, red-rust must no appear in 240h. For class 1 and 2 coatings, it is
exempted from moist-heat resistant test.
7 Sampling
7.1 In the same batch of products, it is required to randomly sample 3 samples for each
test for experiment. If any sample among which is nonconformance after testing, then it is
required to randomly sample another 3 samples to conduct the same test one more time.
If there is any sample is still nonconformance, then this batch of products shall be deemed
as nonconformance.
7.2 For assembly OR part or component of which the mass of single-part exceeds 150 g,
it may cut a part of the workpiece as the sample for testing. In order to avoid the matrix of
bare steel at incision impacting the test result, it shall adopt coating, wax or adhesive tape
to protect the incision. For the part with complicated shape and difficult to determine its
surface area, it may adopt the same method to prepare the sample.
8 Test methods
8.1 Appearance
To inspect with...