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BMG’s Nord-Lock wedge-locking washers safely secure bolted joints in the railways sector

BMG’s Nord-Lock bolt securing system is based on advanced wedge-locking technology, designed to safely secure bolted joints that are exposed to severe vibration and dynamic loads in extreme conditions – including the railways industry.

Nord-Lock wedge-locking washers ensure there is no bolt loosening in safety-critical areas of railway bogies, coupling devices, brake systems, rail dampers and housings. This bolt securing system improves personal safety, reduces the risk of lost production or material damage due to bolt failure and also lowers maintenance requirements.


“The two reasons why bolted joints normally fail, are spontaneous bolt loosening and slackening,” says Maryna Werner, business unit manager, Fasteners, BMG. “Bolted joints in heavy industries like the railways sector, 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 in modern engineering – for example, corrosion-resistant composites – the problem of slackening is a challenging consequence of settlement and relaxation.

“The multi-functional design of the Nord-Lock X-series offers the highest security against spontaneous bolt loosening and slackening – even at the highest levels of vibration caused by rail traffic, which normally put bolted joints at risk. This wedge-locking construction prevents spontaneous bolt loosening and is enhanced by an integrated spring-effect that compensates for the loss of preload due to slackening.”

Nord-Lock washers are being used by many rail companies globally to replace conventional locking-wire mechanisms on wheel sets, providing maximum bolt security. With previous bolt systems, vibrations cause bolts to loosen, resulting in significant safety concerns.

The Nord-Lock X-series, which is quick and easy to install and remove with standard tools, has been certified for quality and safety by TŰV, a leading international institute in quality and safety certification.

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.

On tightening the fastener, the washers flatten and the serrations engage the contact surfaces. Since the cam angle ‘α’ is greater than the thread pitch ‘β’, the wedge-locking effect will prevent any rotation of the fastener. Directly after tightening, the joint settles and the fastener sinks into the surface material. The washers immediately deflect and the spring-effect counteracts the slackening movement of the bolt, thereby preventing loss of preload of the joint.

These multiple functions continuously act on the bolted joint to maintain preload and prevent spontaneous bolt loosening, providing an effective solution for vibration, dynamic loads, settlement and relaxation.

BMG offers a technical advisory service to determine the dimensions and load conditions of existing or required bolted joints. Current tightening methods are evaluated and bolt preloads, for absolute reliability and durability, are calculated by the highly-skilled team.


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