ADVERTISEMENT FEATURE 43
Nord-Lock has outstanding quality and consequently
it normally can be reused. The result is reduced life cycle cost (LCC).
Lubricate the bolt
Nord-Lock provides safe locking in both dry and lubricated conditions. However, lubricating a bolted joint will increase the durability and safety of the application. Lubricating bolted joints is an effective method
of reducing friction, which in turn reduces torsion stress and preload deviation. Minimising friction will significantly improve
the joint’s performance characteristics and thereby making control over the clamp load possible. It is especially beneficial for applications with large and/or long bolts. An appropriate lubricant can also minimise the effect of galling in stainless steel bolts. Since Nord-Lock washers utilise tension instead of friction to secure the fasteners, the locking function will not be compromised by lubrication.
T
he following illustrates the importance of lubricating bolted joints. One customer manufacturing hedge trimmers had experienced
bolt failure when four high-grade M12 bolts holding a hydraulic motor broke from fatigue. The engineers thought they had taken all safety measures available by using a nylon inserted nut, thread adhesive and Nord-Lock washers. Looking at the torque figure, it was suspected that
Fig. 4. Reducing friction with lubrication improves the performance characteristics of the fasteners.
yield strength was utilised in the bolts due to too much friction from the nut and the adhesive – the preload was too low resulting in unwanted movement in the joint. As the applied torque could not be tripled, the design was revised. By replacing the adhesive with thread grease
in combination with Nord-Lock, the problem was solved. The company’s new recommendations for
torque have been set from laboratory tests done by Nord-Lock using calibrated torque transmitters and load cells.
In-house testing
Nord-Lock’s in-house testing laboratories perform a wide range of tests every year either for internal studies or on behalf of the company's customers. It has been found that Nord-Lock’s lubricant, GTP600, provides all the benefits you would expect from a good lubricant even during long-term use in harsh environments. GTP600 is a graphite paste of high
purity which outperforms any conventional lubricant in laboratory tests. When tightening bolts and nuts, using
GTP600 will ensure low and uniform friction conditions, making it possible to utilise the bolts’ full capacity. GTP600 helps optimise the performance and increases the cost efficiency of bolted joints.
The compound is environmentally friendly, complying
the clamp load was too low so the torque/load ratio was measured. Using the specified torque value supplied by the customer, it was determined that only 25 per cent of the
with EINECS (EU) and TSCA (US) regulations. Joints lubricated with GTP600 can be easily
dismantled after years of service in corrosive environments.
Thread friction
Minimising thread friction with lubrication and at the same time safely secure a joint may seem like an impossible equation for design engineers who are used to traditional locking methods. Systems that rely on friction in their attempts to
secure bolted joints do not manage well in harsh applications when faced with vibration and dynamic loads.
The use of these systems is the single most common
reason why the full capacity of the bolted joints is not utilised. It is also one of the causes for bolt fatigue failures in demanding applications. The resulting lower friction in lubricated joints
secured with Nord-Lock will ensure safely locked fasteners at the highest possible preload level. n
Enter 43 or ✔ at
www.engineerlive.com/ede Fig. 5. The compound of GTP600 is anti-seize.
Harlen Seow is with Nord-Lock International AB, Malmö, Sweden.
www.nord-lock.com
www.engineerlive.com
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