GB/T 18684-2002 PDF English
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| GB/T 18684-2002 | English | 70 |
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Specifications of zinc/chromate coating
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GB/T 18684-2002: Specifications of zinc/chromate coating---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/GBT18684-2002
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
coating quantity and coating thickness.
5 Documents that are required to be supplied to supplier
a) Number of this Standard;
b) Required coating class of the workpiece to be coated;
c) The final heat-treatment temperature of the workpiece to be coated.
6 Technical requirements
6.1 Appearance
The basic color of zinc/chromate coatings shall be silver gray; it can also be other colors
by modifying, such as black, and so on. The zinc/chromate coatings shall be continuous,
without defects such as miss-coating, bubble, peel-off, crackle, mottle and impurity.
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.
6.5 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.
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.
8 Test methods
8.1 Appearance
To inspect with the naked eye under the nature diffused light.
8.2 Coating and test
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;
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.
Appendix A
(Informative)
Calculation method of coating surface area
A.1 Shim bolt (pole) nut
A.1.1 Flat shim
A.2 Workpiece of complicated shape
A.2.1 To calculate by resolving into simple sharp
To resolve the surface of workpiece of complicated shape into surfaces of several simple
shapes; the surface area of workpiece of complicated shape is equal to the sum of surface
areas of several simple shapes. For example.
Note. S is the surface area of workpiece of complicated shape. S1, S2, S3, S4, S5, S6 and S7 is the surface
area of 7 simple shapes of ①, ②, ③, ④, ⑤, ⑥ and ⑦ respectively in above figure.
A.2.2 To calculate in profile modeling of plotting paper
Take a piece of plotting paper od which the area is X (dm2) as standard paper; and weigh
its mass as b (g). In addition, take a piece of plotting paper to model for a surface of
coated workpiece. Then weigh the mass of profile modeling paper as a (g). Calculate the
area of profile modeling paper, that is, the surface area S (dm2) of coated workpiece,
according to the following formula.
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.1.4 Not producing hydrogen brittleness
For the steel workpiece of high strength of which the tensile strength Rm≥N/mm2, it will not
produce hydrogen brittleness when coating with zinc/chromate coatings. Adopting
zinc/chromate coatings to replace electro galvanizing, electro tinning for the protection of
the surface of these kinds of workpieces may avoid the hazard of hydrogen brittleness. In
addition, in order to avoid the hydrogen brittleness, the preliminary treatment shall also
adopt the processes such as solvent de-oiling, mechanical de-rusting which will not
produce hydrogen brittleness.
B.1.5 Good deep-coating property
Because of electrostatic shield effect, the sections such as deep-hole and slit of workpiece
AND inner wall are difficult to be electroplated with zinc/ chromate; therefore, the
aforesaid sections of workpieces can not be protected by adopting electroplate method.
However, zinc/chromate coatings may enter these sections of workpieces and form into
zinc/chromate coatings; therefore, the zinc/chromate coatings are very suitable to these
kinds of workpieces.
B.1.6 Good coatable property
zinc/chromate coatings have good coating property. It not only enriches the appearance
color of workpieces, but also further improves the corrosion-resisting property.
B.1.7 Not producing bimetallic corrosion with aluminium and its alloy
The zinc/chromate coatings will not produce bimetallic corrosion with aluminium and its
alloy; it can be used to the surface protection of steel workpieces which contact with
aluminium and its alloy.
......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
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