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This document is developed in accordance with the rules given in GB/T 1.1-2020 Directives for standardization—Part 1: Rules for the structure and drafting of standardizing documents.
This document is Part 2 of GB/T 5267. The following parts of GB/T 5267 have been published.
——GB/T 5267.1 Fasteners—Electroplated coatings;
——GB/T 5267.2 Fasteners—Non-electrolytically applied zinc flake coatings;
——GB/T 5267.3 Fasteners—Hot dip galvanized coatings;
——GB/T 5267.4 Passivation of corrosion-resistant stainless—steel fasteners.
This document replaces GB/T 5267.2-2017 Fasteners—Non-electrolytically applied zinc flake coatings. In addition to structural adjustments and editorial changes, the following main technical changes have been made with respect to GB/T 5267.2-2017:
a) The maximum curing temperature is modified from 350°C to 320°C (see 4.3 hereof; 4.3 of Edition 2017);
b) The hardness limit that shall not be subjected to acid cleaning is modified from 385 HV to 390 HV (see 4.4 hereof; 4.4 of Edition 2017);
c) The maximum torque requirement when the nominal thread diameter is 3 mm is added (see Table 2 hereof);
d) The maximum clearance of tolerance position e in the last column of Table B.2 is deleted (see Table B.2 of Edition 2017);
e) Annex C is modified (see Annex C hereof; Annex C of Edition 2017);
f) Annex D is added, giving the complete NH4NO3 rapid corrosion test method and evaluation requirements (see Annex D).
This document is modified in relation to ISO 10683: 2018 Fasteners—Non-electrolytically applied zinc flake coatings.
The technical differences with respect to ISO 10683: 2018 and their justifications are as follows:
——ISO 1891-2 is replaced by the normative reference GB/T 3099.3 to adapt the technical conditions of China (see Clause 3);
——ISO 9227 is replaced by the normative reference GB/T 10125 to adapt the technical conditions of China (see 5.2);
——ISO 6988 is replaced by the normative reference GB/T 9789 to adapt the technical conditions of China (see 5.3);
——ISO 1502 is replaced by the normative reference GB/T 3934 to adapt the technical conditions of China (see 6.2.2);
——ISO 1463 is replaced by the normative reference GB/T 6462 to adapt the technical conditions of China (see 7.3);
——ISO 16047 is replaced by the normative reference GB/T 16823.3 to adapt the technical conditions of China (see 7.7);
——ISO 8991 is replaced by the normative reference GB/T 1237 to adapt the technical conditions of China (see 9.1).
——The following editorial changes have been made to this document:
——The standard title is modified to Fasteners—Non-electrolytically applied zinc flake coatings;
——The normative international documents are replaced by Chinese documents;
——The note in 5.2 is moved to 5.1;
——The content "see Clause 10, g) and h)" in 7.1 is modified to "see Clause 10, h)";
——Informative Annex D is added, giving a complete NH4NO3 rapid corrosion test method and evaluation requirements, so as to quickly evaluate the corrosion resistance of non-electrolytically applied zinc flake coatings;
————The contents of "Bibliography" are modified.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The issuing body of this document shall not be held responsible for identifying any or all such patent rights.
This document was proposed by the China Machinery Industry Federation.
This document is under the jurisdiction of National Technical Committee on Fasteners of Standardization Administration of China (SAC/TC 85).
The National Technical Committee on Fasteners of Standardization Administration of China is in charge of the interpretation of this document.
The previous editions of this document and documents replaced by this document are as follows:
——This document was issued in 2002 for the first time and was revised in 2017 for the first time.
——This edition is the second revision.
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Introduction
The coating is an important link in the production of fasteners. According to the function of coating, the requirements for corrosion resistance, decoration and functionality of fasteners may be achieved. When selecting coating for threaded fasteners, it is necessary not only to realize various functions, but also to meet the requirements of thread engagement.
GB/T 5267 aims to standardize the technical requirements for the coating of fastener, and provide a standard basis for coating suppliers, coaters, fastener manufacturers, distributors and end users to organize production, sales and product quality acceptance inspection. It is to be composed of 5 parts:
——GB/T 5267.1 Fasteners—Electroplated coatings (ISO 4042);
——GB/T 5267.2 Fasteners—Non-electrolytically applied zinc flake coatings (ISO 10683);
——GB/T 5267.3 Fasteners—Hot dip galvanized coatings (ISO 10684);
——GB/T 5267.4 Passivation of corrosion-resistant stainless-steel fasteners (ISO 16048);
——Coatings of fasteners—Thermal diffusion zincification (expected to be Part 5 of GB/T 5267).
GB/T 5267 has transformed 4 independent international standards for coatings of fasteners. On this basis, it is planned to independently develop the surface treatment standards for thermal diffusion zincification for easy use.
Fasteners—Non-electrolytically applied zinc flake coatings
1 Scope
This document specifies requirements for non-electrolytically applied zinc flake coating for steel fasteners.
It is applicable to coatings:
——with or without hexavalent chromium;
——with or without top coat;
——with or without lubricant (integral lubricant and/or additional lubricant).
It is applicable to bolts, screws, studs and nuts with ISO metric thread, to fasteners with non-ISO metric thread, and to non-threaded fasteners such as washers, pins, clips, etc.
This document does not specify requirements for such fastener properties as weldability or paintability. It is not applicable to mechanically applied zinc coatings.
Note: Coatings in accordance with this document are especially used for high strength fasteners (≥ 1,000 MPa) to avoid risk of internal hydrogen embrittlement (see 4.4).
Information for design and assembly of coated fasteners is given in Annex A.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 1237 Designation system for fasteners (GB/T 1237-2000, eqv ISO 8991: 1986)
GB/T 3099.3 Terminology of fasteners—Coatings (GB/T 3099.3-2017, ISO 1891-2: 2014, MOD)
GB/T 3934 Specification of gauges for general purpose screw threads (GB/T 3934-2003, ISO 1502: 1996, MOD)
GB/T 6462 Metallic and oxide coatings—Measurement of coating thickness—Microscopical method (GB/T 6462-2005, ISO 1463: 2003, IDT)
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GB/T 9789 Metallic and other non-organic coatings—Sulfur dioxide test with general condensation of moisture (GB/T 9789-2008, ISO 6988: 1985, IDT)
GB/T 10125 Corrosion tests in artificial atmospheres—Salt spray tests (GB/T 10125-2021, ISO 9227: 2017, MOD)
GB/T 16823.3 Fasteners—Torque/clamp force testing (GB/T 16823.3-2010, ISO 16047: 2005, IDT)
ISO 3613: 2010 Metallic and other inorganic coatings—Chromate conversion coatings on zinc, cadmium, aluminium-zinc alloys and zinc-aluminium alloys—Test methods
Note: GB/T 9791-2008 Chromate conversion coatings on zinc, cadmium, aluminium-zinc alloys and zinc-aluminium alloys—Test methods (ISO 3613: 2000, MOD).
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 3099.3 apply.
4 General characteristics of the coating
4.1 Zinc flake coating system
Zinc flake coating systems are produced by applying zinc flake dispersion to the surface of a steel fastener, usually with the addition of aluminium flakes, in a suitable medium. Under the influence of heat curing, a bonding amongst flakes and also between flakes and substrate is generated, thus forming an inorganic surface coating sufficiently electrically conducting to ensure cathodic protection. The coating system can contain hexavalent chromium, Cr(VI).
Special techniques shall be necessary to avoid excessive or insufficient coating thickness.
Special techniques shall be necessary to prevent lightweight and/or flat fasteners from sticking together (e.g. washers, clips, fasteners with washer, flanged nuts).
An additional top coat can be applied to increase corrosion resistance and/or to achieve specific properties (e.g. torque/clamp force properties, chemical resistance, aspect, color, electrical insulation/conductivity, see A.2).
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4.2 Composition of the systems
There are four basic zinc flake coating systems, as shown in Figure 1.
Figure 1 Basic zinc flake coating systems
Base coat and top coat may be with self-lubricating, see detailed possible combinations in A.1.2.
4.3 Mechanical and physical properties and curing
The coating process shall not adversely influence the mechanical and physical properties of the fasteners.
Note: Distributors who coat non-coated fasteners are considered as alteration distributors in accordance with GB/T 3099.4.
Depending on the zinc flake coating system, the curing temperatures may be up to 320°C. The curing temperature shall not be above the tempering temperature of quenched and tempered fasteners.
Warning: The curing process (especially with higher temperature and/or longer duration) may affect the fatigue limit of fasteners with thread rolled after heat treatment. See A.1.3 for other possible effects of curing.
Foreword i
Introduction iv
1 Scope
2 Normative references
3 Terms and definitions
4 General characteristics of the coating
4.1 Zinc flake coating system
4.2 Composition of the systems
4.3 Mechanical and physical properties and curing
4.4 Avoidance of internal hydrogen embrittlement
4.5 Coating systems and coating processes
5 Corrosion resistance and testing
5.1 General
5.2 Neutral salt spray test
5.3 Sulfur dioxide test (Kesternich test)
5.4 Bulk handling, automatic processes such as feeding and/or sorting, storage and transport
6 Dimensional requirements and testing
6.1 General
6.2 Fasteners with ISO metric thread
6.3 Other fasteners
7 Mechanical and physical properties and testing
7.1 Appearance
7.2 Corrosion resistance related to temperature
7.3 Test methods for thickness or coating weight determination
7.4 Ductility
7.5 Adhesion/cohesion
7.6 Sacrificial cathodic protection
7.7 Torque/clamp force relationship
7.8 Determination of hexavalent chromium
8 Applicability of tests
8.1 General
8.2 Mandatory test for each lot
8.3 Tests for in-process control
8.4 Tests to be conducted when specified by the user
9 Designation
9.1 Designation of zinc flake coating systems
9.2 Designation of zinc flake coating systems for labelling
10 Ordering requirements
Annex A (Informative) Design and assembly of coated fasteners
A.1 Design
A.2 Functional properties
A.3 Particular issues related to fasteners and coating processes
A.4 Storage of coated fasteners
Annex B (Informative) Coating thickness and thread clearance for ISO metric screw threads
B.1 General
B.2 Geometrical relationship between coating thickness and pitch diameter
B.3 Variability of coating thickness
B.4 Clearance for coating thickness
B.6 Examples of application
Annex C (Informative) Coating systems tested in accordance with GB/T 10125—Evaluation of cabinet corrosion resistance for the neutral salt spray test
C.1 Introduction
C.2 Purpose
C.3 Frequency
C.4 Operating conditions
C.5 Corrosivity results
C.6 Example of report format for annual control and monthly monitoring of the cabinet
Annex D (Informative) Ammonium nitrate rapid corrosion test
D.1 Preparation of 20% ammonium nitrate solution
D.2 Test methods
D.3 Judgment criteria
D.4 Description
Bibliography
