Andy Lovatt, Mechanical Design Engineer, BAE Systems Land (UK)

Matrix Engineering can deliver this course in North America, further information, including contact details are available on the Matrix website.

Training Course in North America on Bolting Technology for Engineers and Designers

The course content includes:

Introduction to Threaded Fasteners

• Know the meaning of thread terminology.
• Learn when it is appropriate to use a fine rather than a coarse thread.
• Be aware of the principal bolt and nut strength property classes and how they should be specified.
• How to match the nut strength to that of the bolt so that thread stripping problems are prevented.
• Find out why bolt tensile fracture is preferable to the threads stripping.
• Learn what the proof load is and why it is used.
• Be able to identify the meaning of the markings on bolt heads and nuts.
• Learn about the thread stress area and how it is derived and used.
• Be able to calculate the tensile strength of a threaded fastener.
• Understand how a pre-tensioned bolted joint sustains an applied load.

• Learn why there can be such a significant variation in the preload (tension in the bolt) and the consequences of this.
• How the torque is distributed between the threads and the nut face when free spinning and torque prevailing fasteners are used.
• Why preload is so crucial in a bolted joint.
• How preload variation can be accounted for at the design stage.
• The effect of the tightening method on the preload variation sustained by a fastener.

• What is galling and what types of materials tend to be affected?
• Examples of fastener threads that have galled, sectioned and x-ray photos.
• Four ways that galling can be eliminated.

Methods of Tightening Threaded Fasteners

Have an understanding of the principles behind each of the following tightening methods:

• Torque controlled tightening.
• Torque-angle controlled tightening.
• Yield controlled tightening.
• Bolt stretch method.
• Heat tightening.
• The use of load indicating methods.
• The use of ultrasonics to determine bolt loading.

• Learn the differences between a manufacturing and design quality defect.
• Be able to identify whether a failure is due to a fault in the design specification or is manufacturing related.
• Learn the 5 main design related failure modes of threaded fasteners and bolted joints.
• Have knowledge of the critical importance of a fastener's clamp force in ensuring a joint's structural integrity.
• Why the joint design normally prevents bolt overloading.
• Learn about fatigue and where failures normally occur on a threaded fastener.
• Why bearing stress can be crucial in ensuring a reliable joint.
• Learn about the nature of internal and external thread stripping failures.
  

Have an overview of the research completed over the last 50 years into establishing the cause of self-loosening of threaded fasteners.
Appreciate the forces that are acting on the threads that tend to self loosen a fastener.

• Why fine threads can resist loosening better than coarse threads. The inclined plane analogy.
• Learn about the work completed by Goodier and Sweeney into loosening due to variable axial loading.
• The work completed by ESNA and the theory of shock induced loosening and resonance within fasteners.
• The MIL-STD 1312-7 vibration test for fasteners.
• Junker’s theory on self-loosening of fasteners and why fasteners self-loosen.
• The Junkers/transverse vibration test for fasteners.
• The influence that vibration amplitude has on the fastener self-loosening rate.
• Preload decay curves and the effectiveness of various fastener types in resisting vibrational loosening.
• The findings of Haviland and Kerley and how fasteners can come loose as a result of bending, shock or impact and differential thermal expansion.
• Conclusions from the research and how loosening can be prevented.

• What is meant by a tightening torque?
• Units used to measure torque.
• What are the consequences of not applying sufficient torque to a bolt.
• How torque is absorbed by a nut/bolt assembly.
• The torque-tension graph.
• The relationship between the tightening torque and the resulting bolt preload (tension).
• The factors which affect the torque-tension relationship.
• The nut factor method of determining the correct tightening torque.
• Example calculation of how to determine the correct tightening torque.
• Scatter in the bolt preload resulting from friction variations.
• Determining the bolt preload (tension) resulting from a tightening torque.
• Prevailing torque fasteners (such as those containing a nylon insert) and how they affect the torque distribution and the correct torque to use.

Load Sensing Fasteners

• The use of strain gauged bolts.
• The use of load cells.
• The use of Rotabolts™.
• The use of Smartbolts™.
• The use of direct tension indicators (load indicating washers).
• Squirter™ direct tension indicators.
• Tension control bolts.

Hydraulic Tensioning of Threaded Fasteners

• The principles behind hydraulic tensioning.
• The number of tensioners that are used to tighten a joint – 100%, 50%, 33% and 25% tensioning methods.
• The effect of elastic recovery on the tension induced into a bolt.
• The use of hydraulic nuts and the sequence used to tighten them.
• The use of oil filled nuts.
• The use of rubber filled nuts.

• The problems of tightening multi-bolt assemblies.
• Elastic interaction or bolt cross-talk.
• The use of a tightening sequence.
• The single pass tightening sequence.
• Tightening sequences for non-circular bolt patterns.
• Tests completed to verify tightening sequences.
• The two pass tightening sequence.
• The use of multiple tightening tools.
• Bolt cross talk and hydraulic tensioning.
• Methods that can be used to check the tightening sequence.
• The solder plug method.
• The use of pressure sensitive films.
• Establishing a tightening procedure.
• Examples of tightening sequences for circular joints consisting from 4 to 32 bolts are given in the handbook together with an example tightening procedure.
  

A training course handbook is provided that contains background information to the material presented in the course, together with appendices containing tables of thread size details, fastener material strengths and a glossary detailing the key terms used in bolting technology.

  This training course is also available now, online. Click for details.