NORD-LOCK - Wedge Effect Self-Locking Bolts for Rail Subassemblies

It is vital that joints holding subassemblies together remain secure. Bolts need to be easily removable during maintenance, but resist loosening effects of vibrations and dynamic loads.

NORD-LOCK AB has developed a securing system that makes the bolt self-locking. Their product is a pair of washers that provide a wedge-locking action meeting DIN 25 201 - a unique method using tension instead of friction. On one side the washers have cams with a rise greater than the pitch of the bolt. In addition, there are radial teeth on the opposing washer sides.

NORD-LOCK WASHER

The washers come pre-assembled in pairs, cam face on cam face. When the bolt and/or nut is tightened, the teeth grip and seat the mating surfaces. The NORD-LOCK washer is locked in place, allowing movement only across the face of the cams. Any attempt from the bolt/nut to rotate loose is blocked by the wedge effect of the cams making the bolt/nut self-locking (Picture 2).

NORD-LOCK BOLT SECURING SYSTEM

The NORD-LOCK bolt securing system has been on the market since 1982. The company performs torque-load ratio tests for most kind of joints and runs Junker tests for bolt size M3 to M27. In a Junker test according to DIN 65151, the joint is subjected to transverse movements while the tension is measured continuously by a load cell.

Picture 3 shows bolt tension during vibration testing of some common fasteners. The tension will drop completely for non-secured nuts, while most of the tension will be lost for nuts with added friction to the thread. Even a tab washer may open during a Junker vibration test.

All vibration tests with NORD-LOCK show a positive result. Some of the initial tension is lost due to normal settlements. The locking function proves itself when the nut is untightened with a wrench and a clear increase of tension is registered.

REGULAR SERVICE AND MAINTENANCE

For machinery that requires regular service and maintenance, NORD-LOCK is the optimum solution. Bolted joints secured with NORD-LOCK are easy to untighten with general tools, mounting elements can easily be lubricated prior to reassembly and the fasteners are reusable.

Since NORD-LOCK washers do not rely on friction, lubrication has no negative impact on their locking effect. Upon assembly it is recommended to lubricate in order to reduce friction. With less friction, less torque is required to obtain the desired preload. In addition, the spread in preload will be minimized through more controlled friction.

The washers are available in hardened steel with modern coatings and stainless steel. Dimensions range from M3 to M130 for standard plated / high-grade and from M3 to M80 for stainless steel bolts.

NORD-LOCK WASHERS FOR RAIL RETARDER SYSTEMS

Ultra Dynamics in the United Kingdom, a manufacturer of rail retarder systems used in marshalling yards worldwide, has chosen NORD-LOCK washers as their standard fastener due to the retarders being exposed to high / low frequency vibrations, shock loads, pressure loads and daily temperature changes.

The washers have been proven to solve loosening problems on rails, switches, signal systems, car connections, seat fixings, etc. in Europe and in the USA.

The NORD-LOCK washer is not just a 'problem solver', but also a guarantee that new problems will not appear. A system that makes assembly easy, provides maximum safety, and allows easy service has great advantages.

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