BMG’s range of Nord-Lock bolt securing systems includes the X-series washers, designed for optimum bolt security, even in the most demanding operating conditions.
These bolt securing washers have been developed to safely secure bolted joints exposed to severe vibration and dynamic loads. The wedge-effect design of this series prevents spontaneous bolt loosening and an integrated spring effect of the system compensates for the loss of preload due to slackening.
“There are two main reasons why bolted joints normally fail – spontaneous bolt loosening and slackening,” says Maryna Werner, business unit manager, Fasteners, BMG. “Bolted joints in heavy industries are constantly subjected to external forces, which results in spontaneous loosening, due to vibration and dynamic loads. With the development of new materials and techniques – such as corrosion resistance composites – slackening is a common problem that results from settlement and relaxation.”
Each washer pair has cams on one side and radial teeth on the opposite side to secure the bolted joint with tension, rather than friction. The conical shape of these washers creates an elastic reserve in the bolted joint to compensate for the loss of preload and prevents slackening.
Advances in polymers and sandwich composite technology have the advantage of strength to weight ratio and corrosion resistant properties that make applications lighter, without losing strength. But these materials are softer than metal materials previously used and make slackening an additional challenge. The multifunctional wedge-locking concept of the X-series combats these problems.
Surface treatments, which are common for corrosion protection, can also lead to slackening as the bolt sinks into the treated surface after tightening. Even a thin millimetre surface would normally put bolts at risk, but with the compensating spring of X-series, slackening is prevented.
The combined tension and spring action of X-series washers combats the effects of surface treatments, thermal cycling and vibration.
The Nord-Lock X-series washers, which is quick and easy to install and remove with standard tools, has been certified by quality and safety by TŰV, a leading international institute in quality and safety certification.
All bolted joints have a functional preload range in which the joint is safe. Serious problems start as soon as the preload falls outside the functional range. If the preload is too high, yielding occurs. If it is too low, there is separation or sliding between the parts.
Independent tests show this series performs better than conventional washers when compensating slackening in static conditions and in preventing rotation of the fastener when the joint is exposed to vibration in the dynamic phase. These are the only washers currently available that can secure bolts from both critical loosening factors – spontaneous loosening and slackening – at once.