Bolt security is essential for optimum safety in all industries, particularly in the railway sector, where demands on rail lines and train components are under increasing pressure, as trains and railway networks become more sophisticated.
That’s according to Wean Marais, National Product Manager – Nord-Lock Group, Fasteners Division, BMG, who said bolt loosening anywhere on railway infrastructure and rolling stock can be costly and even fatal if a train is in motion.
“It is critical to ensure that the selected bolt securing product holds firmly, despite a train’s high-speed travel when carriages are under constant vibration and strain,” he said.
“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.”
He said the Nord-Lock X series ensures there is no bolt loosening in safety-critical areas of railway bogies, coupling devices, brake systems, rail dampers and housings. “These robust washers provide maximum security for critical bolted joints that are exposed to bolt loosening and slacking – ensuring they remain secure, no matter how fast the train is travelling.
“The Nord-Lock bolt securing system improves personal safety, reduces the risk of lost production or material damage due to bolt failure and also lowers maintenance requirements.”
Marais cited the example of BMG customer, Wam Metals, a manufacturer and supplier of non-ferrous and ferrous components, which works closely with the rail freight sector, servicing local and international markets.
“The solution to previous problems of the loosening of bolts was to replace locking plates with Stainless Steel Nord-Lock washers,” he said.
“We recommend the use of NLX10, NL10ss and NL12ss on various components, including signal bonds, contact splices and rail and mast bonds. The use of Nord-Lock washers on the contact splices means there is no need to re-tighten components at a later stage, which means fewer hook-up incidents, reduced maintenance requirements and minimal downtime.”
He said extensive testing indicated that X-series washers had performed to required specifications in arduous conditions, with no slip occurring. To date, no incidents have been reported regarding hook-ups caused by contact splices that are fitted with Nord-Lock washers.
“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, added Marais, prevents spontaneous bolt loosening and is enhanced by an integrated spring-effect that compensates for the loss of preload due to slackening.
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.