Fasteners - Non-electrolytically applied zinc flake coating systems (ISO 10683:2018); German version EN ISO 10683:2018

Standard Overview and Technology Evolution

DIN EN ISO 10683:2018 replaces the 2014 version and sets comprehensive technical requirements for non-electrolytic zinc flake coating systems for steel fasteners. The standard applies to coating systems containing or not containing chromium (VI), with or without a sealing layer, and with or without a lubricant (integrated or post-applied). The standard covers metric ISO threaded fasteners, non-metric ISO threaded fasteners, and non-threaded fasteners (such as washers, pins, clamps, etc.).

Coating System Classification and Structure

Zinc flake coating systems are manufactured by applying a zinc flake dispersion (usually with aluminum flakes) to the surface of steel fasteners and forming an intermetallic bond through heat treatment (baking). The system forms a sufficiently conductive inorganic surface coating to ensure cathodic protection. The standard defines four basic coating structures:

Key technical requirements

Corrosion protection performance

The standard requires that the corrosion resistance of the coating system be evaluated through the neutral salt spray test (NSS). The test time is determined according to the required protection level:

For outdoor applications, ISO 6988 sulphur dioxide humid condensation test, the minimum number of cycles shall be determined by negotiation between the supplier and the buyer.

Thread compatibility and assemblability

The coating thickness has an important influence on thread fit, and the standard stipulates strict dimensional requirements:

• The external thread shall not exceed the zero line (basic dimension) after coating
• The internal thread shall not be lower than the zero line after coating
• Use the through gauge specified in ISO 1502 for inspection, the external thread is the h tolerance zone, and the internal thread is the H tolerance zone
• The maximum allowable screw-in torque is calculated as 0.001d³Nm (d is the thread diameter)

Mechanical performance protection

The coating process shall not affect the mechanical and physical properties of the fastener:

• The baking temperature shall not exceed the tempering temperature of the quenched and tempered fastener
• The hardness exceeds 390 Fasteners of HV or strength grade 12.9 and above shall not be pickled
• The coating process shall avoid the risk of hydrogen embrittlement (IHE)

Testing and quality control

Process control test

The standard requires comprehensive process control testing, including:

Customer required tests

Additional tests available upon customer request:

• Sulfur dioxide test (outdoor application)
• Torque/preload relationship test
• Ductility test
• Cathodic protection test
• Chromium (VI) content test

Marking and ordering requirements

The standard specifies a detailed coating marking system in accordance with ISO 8991 requires the coating identification to be added after the fastener identification:

Identification format: flZn/[Corrosion resistance time]/[Chromium content]/[Sealing layer type]/[Lubricant type]/[Friction coefficient range]

Example: flZn/480/nc/Tn/L/C0.17 - Indicates zinc flake coating, 480-hour corrosion resistance, chromium (VI)-free, sealant without integrated lubricant, additional lubricant, coefficient of friction 0.17

Implementation Recommendations and Application Guide

Coating System Selection

The following factors should be considered when selecting a coating system:

• Corrosiveness of the service environment
• Assembly torque requirements
• Compatibility with joining materials
• Temperature tolerance requirements
• Electrical insulation/conductivity requirements

Special Fastener Considerations

Special considerations are required for certain types of fasteners:

Storage and handling

The storage and handling of coated fasteners should pay attention to:

• Avoid direct contact with water or other liquids
• Prevent condensation and dust contamination
• Maintain a dry and ventilated storage environment
• Avoid mechanical damage and wear

Technical evolution of the standard and major changes

Compared with the 2014 edition, the major technical changes in the 2018 edition include:

• Updated normative references
• Removed the restriction on external thread collar in paragraph 2 of 6.2.2
• Deleted the maximum clearance column for the position of the e tolerance zone in Table B.2
• Completely revised Appendix C (Salt spray test chamber corrosion evaluation)

These changes reflect technological progress and the accumulation of practical experience, especially the improvement of coating performance testing and evaluation methods.

Compliance and Certification Requirements

Manufacturers need to establish a comprehensive quality assurance system to ensure that the coating process meets standard requirements:

• Establish process control procedures and records
• Regularly calibrate test equipment
• Conduct personnel training and qualification
• Maintain traceable production records
• Perform regular internal audits and third-party certification