Nord-Lock Ltd

Room 9, Main Building
Aspire Business Centre
Ordanance Road
Tidworth
Wiltshire
SP9 7QD
UK

T: 01980 847129
F: 01980 847674
E: Click here to email Nord-Lock Ltd

VISIT OUR WEBSITE:
www.nord-lock.com

NORD-LOCK produces a bolt securing system that does not use any traditional technique to secure the fastener, and yet offers a safe locking system. NORD-LOCK utilises tension instead of friction to secure a bolted joint. The proven wedge locking method meeting DIN 25201 is superior to any traditional method. The washer cam angle a is greater than the thread angle b. In addition, there are radial teeth on the opposite side. The washers are installed in pairs, cam face to cam face. When the bolt and/or nut is tightened the teeth grip and seat the mating surfaces. The NORD-LOCK  washers are locked in place, allowing movement only across the face of the cams. Any loosening attempt of the bolt/nut to rotate loose is blocked by the wedge-locking effect of the cams. When un-tightening, sliding always occurs between the cam faces of the washers thereby avoiding scoring of the mating surface.

Clamp load
When faced with a problem joint, it is not surprising that the design engineer will not have an answer when asked about the clamp load. Calculations must be based on the existing conditions and these are very vague. If all the parameters are not exact the torque calculation will be unreliable. Examples of these parameters are:

• Thread condition;
• Hardness of the mating surfaces;
• Extra friction from a "locking" fastener;
• Type of mating material (steel, aluminium, etc.);
• Adhesive on the thread;
• Type of bolt head (flanged, regular or serrated);
• Surface coating of the bolt;

Control over the clamp load in a bolted joint is vital. To achieve that the friction on the bolt should be low which in turn will result in a minimum of clamp load deviation.

Failure
Some of the many reasons for machine failure due to bolts coming loose or breaking are:

• In principle, the bolt is designed to hold due to its own friction in the thread and under the head. This works during static conditions but not when there are high dynamic forces. Especially transverse dynamic loads are dangerous;
• The thread pitch can be compared with a down hill slope where thread slip occurs;
• The clamping length could be too short so that any motion in the bolt will result in a severe loss of tension;
• When re-using bolts without lubrication, the friction can be very high, resulting in a very low clamp load;
• Re-using bolts initially locked with adhesives with higher friction and a very low clamp load as a result;
• Loss of clamp load due to bearing surface being too small leading to fatigue failures;

Various studies have been done in NORD-LOCK's test laboratory on torque/load ratios and vibration tests on specific joints. During regular testing of customer's applications, it has been noticed that illogical measures have been taken with the purpose of achieving higher bolt security. It often happens that a high-grade bolt is chosen for a joint that has had bolt failures with a standard 8.8 bolt. Unfortunately, the surface treatment on high-grade bolts compared with normal electro zinc-plated may change the friction conditions which should be taken into consideration when calculating the torque figures. In addition, there is a risk of over-loading the base material of the joint. Even with a higher torque value, the clamp load may be too low due to the higher friction. The joint becomes more expensive but not safer.

Downloads from Nord-Lock Ltd

• Nord-Lock Technical Brochure

Full category listing for Nord-Lock Ltd

• Fasteners
• Health & Safety
• Health & Safety Equipment
• Maintenance Products
• Steel