A lack of permanence shouldn’t mean a lack of security. While, unlike welds, fasteners generally are not permanent, their hardware joins two or more objects together, and this affixing is crucial to the fabrication of numerous products across the expanse of industries. It’s no surprise that standards and fasteners exist in harmony, but standardization efforts for fasteners extend far beyond that of fastener shapes and sizes. Standards also need to consider the physical and chemical means by which a fastener can undergo detrimental change.
ISO 4042:2018 – Fasteners – Electroplated Coating Systems does this, since it details specifications for electroplated coatings and coating systems on steel fasteners. Electroplating is the process of plating one metal onto another through hydrolysis, and it’s often necessary for fasteners because they, whether in the form of bolts, screws, nuts, or studs, are composed of steel. Steel is a vastly useful iron alloy, but, without the right metals or chemicals to bond, mix, or otherwise join, change, or react with, steel parts can corrode.
The oxidation of these components can disastrously degrade fasteners. Fortunately, zinc and zinc alloy coating systems (including zinc, zinc-nickel, zinc-iron) and cadmium can provide corrosion protection, as well as other functional properties. ISO 4042:2018 specifies these types of coating systems.
In general, ISO 4042:2018 applies to zinc and zinc alloy electroplated coatings with or without conversion coating, sealant, top coat, and lubricant. It applies to bolts, screws, nuts, and studs with ISO metric thread, fasteners with non-ISO metric thread, and non-threaded fasteners like washers, pins, clips, and rivets. The standard also specifies guidelines and recommendations to minimize the risk of hydrogen embrittlement.
While it does not specify other electroplated coatings and coating systems (like tin, tin-zinc, copper-tin, copper-silver, copper, silver, copper-zinc, nickel, nickel-chromium, copper-nickel, copper-nickel-chromium), ISO 4042:2018 does include their specifications only for dimensions related to fasteners with ISO metric threads.
For those who have made use of the ISO 4042:2018 international standard in the past, these details might seem a little foreign. This is because ISO 4042:2018 revises the 1999 edition of the same standard thoroughly. The logic behind this complete revision was to take into account new developments related to hexavalent chromium free passivations, the application of sealants and top coats, specifications for functional properties, and results of research work to minimize the risk of hydrogen embrittlement.
As such, the changes made to ISO 4042:2018 are as follows:
- The standard now applies to all fasteners, including self-tapping and thread forming screws, washers, rivets, clips, etc.
- New focus on coatings designed for corrosion protection of fasteners.
- The standard now applies to electroplated coating systems with or without additional layers (conversion coating, sealant, top coat, lubricant).
- New specification of minimum corrosion resistance (white corrosion and red rust).
- Inclusion of up-to-date knowledge about hydrogen embrittlement and prevention measures.
- Added definitions specified in ISO 1891-2:2014 – Fasteners – Terminology – Part 2: Vocabulary And Definitions For Coatings.
- Added a sulfur dioxide test (Kesternich) and calibrated a neutral salt spray test for testing corrosion.
- Added gaugeability and assemblability guidelines.
- Added adequate test methods for thickness determination and deleted batch average thickness.
- New designation system for all coating systems.
- The standard now specifies mechanical and physical properties and related test methods.
- Expanded information about design aspects and assembly of coated fasteners.
- Expanded information regarding coating thickness and thread clearance for ISO metric screw threads.
- Expanded information about the evaluation of cabinet corrosivity for the neutral salt spray test.
ISO 4042:2018 – Fasteners – Electroplated Coating Systems is available on the ANSI Webstore.