The Experts: Sharing the load

Why does Nord-Lock supply a hardened washer with every Superbolt tensioner?

Each multi-jackbolt tensioner (MJT) is supplied with a hardened washer. This is needed because, on the one hand, it transfers the forces into the joint and, on the other hand, it protects the face against high loads.

During the tightening process a very high surface pressure is produced under the jackbolts. The hardened washer spreads the load over the full contact area and offers the jackbolts a hard and flat contact surface. This helps to ensure that the MJTs can be tightened accurately.
Soft surfaces tend to deform or settle. Thicker and larger washers are therefore used to keep the surface pressure as low as possible and to transfer the load optimally.

Washers that are not hardened would deform due to the high localized stresses under the jackbolts, and the pre-load could potentially be compromized. Joints where load is not distributed properly can loosen with potentially serious consequences. Thus, it is absolutely critical to use only genuine Superbolt hardened washers.

Note for maintenance: A hardened washer can be used in spite of wearing marks. Impressions of a few hundreds of a millimetre are normal and acceptable.