3rd Quarter 2012Electrical switching & drive systems & components
The Nord-Lock bolt securing system uses tension instead of friction to ensure that joints holding sub-assemblies together remain secure. Bolts on pumps need to be easily removable during maintenance procedures, but must resist the loosening effects of vibrations and dynamic loads. Bolts that are locked conventionally by friction in the thread tend to lose most of their preload through vibrations, while those locked by the tension of this system present a minor loss of preload which is caused mainly by settlement in the thread. Even after moderate tightening, the bolt is safely locked when using Nord-Lock.
It has become increasingly important to have good control of the torque-clamp load relationship when tightening a joint. To optimise the design of the joint and utilise as much of the capacity of each dimension as possible, it is important to know the required tightening torque. Nord-Lock washers, which are installed in pairs, cam face to cam face, have cams on one side, with a greater rise than the pitch of the bolt. When the bolt and/or nut is tightened, the radial teeth on the opposite side grip and seat the mating surfaces. The teeth also lock the washers in place, allowing movement only across the face of the cams. The resulting tension makes the bolt self-locking.
These washers can be used on standard grade, as well as high grade bolts and there is no need for adhesives to lock the stud bolt. This system is designed for use in tapped and counter-bored holes and for larger holes or on soft materials, a flange nut or bolt should be used in combination with Nord-lock washers with a larger outer diameter.
Advantages of this reusable system include maximum safety when locking fasteners, easy assembly and disassembly, positive locking at low or high preload levels and minimum surface marring or scratching. This system, which has the same temperature characteristics as a standard bolt or nut, resists loosening caused by vibration and dynamic loads. The locking function is not lost by lubrication.
A method for testing the security of a bolted joint is the Junker-vibration test where the preload (bolt tension) is measured by a load cell and vibrating motions are generated radically through the bolt.
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