EUROLAB laboratory provides testing and compliance services within the scope of EN 14399-6 standard. This part of the EN 14399 standard, together with EN 14399-1 and EN 14399-2, specifies hardened and tempered chamfered flat washers intended for large series hexagonal high-strength structural bolts and nuts bolting assemblies with thread sizes M12 to M36.
According to this standard, washers are not designed for use in direct contact with oversized or slotted holes.
This document on structural bolting reflects the situation in Europe where there are two technical solutions to achieve the required ductility of bolt/nut/washer assemblies. These solutions consist of two different systems (HR and HV) of bolt/nut/washer assemblies, Both systems are proven and are the responsibility of the experts using structural bolting, whether they use one or the other.
However, preventing mixing of components of both systems is important to the performance of the assembly. Therefore, bolts and nuts for both systems are standardized in a single part of this European Standard and the marking of components of the same system is uniform.
Preloaded bolt-on assemblies are very sensitive to manufacturing and lubrication variations. It is therefore important that the bolting kits are supplied by a manufacturer who is always responsible for the functionality of the bolting kits. For the same reason, it is important that the coating of bolting assemblies be under the control of a single manufacturer.
Besides the mechanical properties of the components, the functionality of the bolting assemblies requires that the specified preload be achieved if the bolting assemblies are tightened with an appropriate procedure. For this purpose, a test method has been established for the preload suitability of the bolting kits, which will show whether the functionality of the bolting kits is met.
It should be noted that compared to ISO 272, the widths between the flats (wide series) for M12 and M20 have been changed to 22 mm and 32 mm, respectively. These changes are justified for the following reasons.
Under special conditions of structural bolting, compressive stresses under the bolt head or nut for M12 sizes can be very large on flat surfaces of 21 mm, especially if the washer is eccentrically attached to the bolt axis.
For size M20, a flat width of 34 mm is very difficult to produce. The switch to 32 mm is primarily due to economy, but it should also be noted that the flat width of 32 mm is already common practice in Europe.
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