42 ADVERTISEMENT FEATURE
Focus on fasteners and security
How well a design functions is often a direct result of, among other things, how well the fasteners perform. A design will not be better than its weakest link. Harlen Seow reports.
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n a typical design institute or department, a lot of time and effort is invested in the functionality of mechanical designs. The fasteners incorporated in the designs normally receive
scant attention from engineers. The amount of planning, capital and investment that
goes into projects can easily make the little things seem insignificant. Bolts and nuts are looked upon as trivial hardware
but if the fasteners allow a joint to fail, serious consequences may follow. This is especially true when the joints are subjected to dynamic loads. Traditional bolt securing methods are generally based
on friction, which means that the bolt/nut is prevented from turning loose by friction in the bolt thread and the joint. This will work in static conditions but not when there are dynamic forces involved. In such a case the fasteners will turn loose leading
to severe loss of tension and eventually fatigue failure in the joint. Expensive warranty claims, down time and maintenance costs may result..
Reliable locking function
Nord-Lock has developed a securing system that makes fasteners self-locking. The method is based on a pair of washers that provide a wedge-locking action meeting DIN 25201 – a method using tension instead of friction to secure a bolted joint. On one side the washers have cams with an angle α
Fig. 1. Traditional bolt locking methods are based on friction.
greater than the rise of the bolt thread β. In addition, there are radial teeth on the opposing
washer sides. The washers come pre-assembled in pairs cam face
to cam face. When the bolt and/or nut is tightened, the teeth grip and seat the mating surfaces. The washer pair 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. Nord-Lock has, over the past two decades, developed
into a global product, used widely for solving bolt securing problems in industries such as railway, transportation, heavy machinery, offshore, marine, power generation and forestry. Since using Nord-Lock will ensure quick assembly/ disassembly, maintenance time can be reduced to a minimum.
Fig. 2. Nord-Lock use geometry to make bolts self locking.
Fig. 3. The washers come pre-assembled in pairs.
www.engineerlive.com
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