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GB/T 5267 consists of the following parts under the general title Fasteners:
——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 is Part 2 of GB/T 5276.
This part is developed in accordance with the rules given in GB/T 1.1-2009.
This part replaces GB/T 5267.2-2002 Fasteners－Non-electrolytically applied zinc flake coatings, and the following main technical changes have been made with respect to GB/T 5267.2-2002:
——zinc flake coatings are added (see 4.1.4.2 and A.1.2);
——the coating terms and definitions specified in GB/T 3099.3 are cited (see Clause 2);
——"Depending on the zinc flake coating system, the curing temperatures may be up to 350℃. The curing temperature shall not be above the tempering temperature of fasteners” is added (see 4.3);
——the specifications for avoiding internal hydrogen embrittlement are added (see 4.4);
——“The neutral salt spray test shall be carried out on fasteners alone, not sooner than 24h after coating in the “as-coated” condition, i.e. before sorting, packaging and/or assembling” is specified (see 5.2 and 5.3);
——the coating performance items and test methods, such as thickness and weight determination, torque/tension relationship and hexavalent chromium determination, are added (see 5.3, 7.3, 7.7, 7.8 and A.2);
——the bulk handling, automatic processes, storage and transport are added (see 5.4 and A.4);
——the requirements for applicability of tests are modified (see Clause 8; Clause 8 of Edition 2002);
——the requirements of coating designation and labeling are modified (see Clause 9; Clause 9 of Edition 2002);
——the design aspects and assembly of coated fasteners as well as control of the corrosion resistance of the cabinet for neutral salt spray test for coated fasteners are added (see Annex A and Annex C);
——the detailed specifications for coating thickness and thread clearance for ISO metric screw threads are rearranged as Annex B (see Annex B; Annex A of Edition 2002).
This part has been redrafted and modified in relation to ISO 10683: 2014 Fasteners - Non-electrolytically applied zinc flake coatings (English version).
The main technical differences with respect to ISO 10683: 2014 are as follows:
——for normative references, international standards are replaced with Chinese standards (Clause 2), and GB/T 90.3 (4.3), GB/T 5782 (B.6.1), GB/T 5783 (B.6.2) and GB/T 1237 (5.1) are added to meet Chinese standards for fasteners;
——the curing temperatures may be up to 350℃ instead of 320℃ to meet the curing temperature requirements of main products in China;
——the coating thickness and cohesion are important factors to measure coating performance. Tests on coating thickness and/or coating weight or adhesion/cohesion are added as tests mandatory for each lot (8.2).
This part was proposed by China Machinery Industry Federation.
This part is under the jurisdiction of the 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 part.
The previous edition of this part is as follows:
——GB/T 5267.2-2002.
Fasteners - Non-electrolytically applied zinc flake coatings
1 Scope
This part of GB/T 5267 specifies requirements for non-electrolytically applied zinc flake coatings for steel fasteners. It applies to coatings:
——with or without hexavalent chromium;
——with or without top coat;
——with or without lubricant (integral lubricant and/or subsequently added lubricant).
Note: National regulations for the restriction or prohibition of certain chemical elements shall be taken into account in the countries or regions concerned.
It applies 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.
Note: Coatings in accordance with this part are especially used for high strength fasteners (≥1,000MPa) to avoid risk of internal hydrogen embrittlement (see 4.4).
Information for design and assembly of coated fasteners is given in Annex A.
This part does not specify requirements for such fastener properties as weldability or paintability. It does not apply to mechanically applied zinc coatings.
2 Normative references
The following referenced documents are indispensable for the application of this standard. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 90.1 Fasteners - Acceptance inspection (GB/T 90.1-2002, idt ISO 3269: 2000)
GB/T 90.3 Fasteners - Quality assurance system (GB/T 90.3-2010, ISO 16426: 2002, IDT)
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 5782 Hexagon head bolts (GB/T 5782-2016, ISO 4014: 2011, MOD)
GB/T 5783 Hexagon head bolts - Full thread (GB/T 5783-2016, ISO 4017: 2011, MOD)
GB/T 6462 Metallic and oxide coatings - Measurement of coating thickness - Microscopical method (GB/T 6462-2005, ISO 1463: 2003, IDT)
GB/T 9789 Metallic and other non-organic coatings - Sulfur dioxide test with general condensation of moisture (GB/T 9789-2008, ISO 6988: 985, IDT)
GB/T 10125 Corrosion tests in artificial atmospheres - Salt spray tests (GB/T 10125-2012, ISO 9227: 2006, IDT)
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
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 coatings
Non-electrolytically applied zinc flake coatings are produced by applying a 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 may or may not 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 or flat fasteners from sticking together (e.g. washers, clips, fasteners with washer, flanged nuts).
An additional top coat may be applied to increase corrosion resistance and/or to achieve specific properties (e.g. torque/tension properties, chemical resistance, appearance, color, electrical insulation/conductivity, see A.2).
4.2 Composition of zinc flake coating
There are four basic zinc flake coating systems as shown in Figure 1.
Keys:
1——only base coat;
2——base coat + lubricant;
3——base coat + top coat;
4——base coat + top coat + lubricant.
Figure 1 Basic zinc flake coating systems
Base coat and top coat may be with integral lubricant, 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.
Depending on the zinc flake coating system, the curing temperatures may be up to 350℃. The curing temperature shall not be above the tempering temperature of 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 also A.1.3 for other possible factors.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 General characteristics of the coating
5 Corrosion resistance and testing
6 Dimensional requirements and testing
7 Mechanical and physical properties and testing
8 Applicability of tests
9 Designation
10 Ordering requirements
Annex A (Informative) Design and assembly of coated fasteners
Annex B (Informative) Coating thickness and thread clearance for ISO metric screw threads
Annex C (Informative) Control of the corrosion resistance of the cabinet for neutral salt spray test for coated fasteners
