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Prevention of fastener loosening, part 3

In the first two instalments in this series on the prevention of fastener loosening, we talked about methods of chemical thread-locking before starting to look at some of the mechanical methods in common used, of which there are many. As mentioned before, axial thread interference is occasionally used, mainly as a way to improve the distribution of load between threads, but it has the happy coincidence of introducing some extra friction into the relationship, which is useful when trying to...

Prevention of fastener loosening, part 2

In last month’s article on this subject, the main topic of discussion was chemical threadlocking methods, but there is a little more to be said on this before looking at mechanical methods. The anaerobic liquid threadlocking compounds, while being easy to use, have their own problems. As suggested in the previous article, they have an inconsistent effect on the torque-angle relationship, so while we might be reassured that the bolt won’t unwind, we can’t be entirely sure...

Prevention of fastener loosening part 1

Threaded fasteners are an unavoidable part of building any engine. When we want to harness the energy contained in fuels, liberating this energy via a rapid series of small explosions, we need to be sure our engine assembly stays in one piece. The forces involved, and the rapid accumulation of damaging stress cycles, means we place great demands on bolted joints, and we need to know they are not going to come loose, as the consequences can be financially costly. The best way to ensure that...

Fatigue-resistant threadforms

The term ‘fatigue resistant’ might be a little misleading, as it is not a quality that is in black and white but shades of grey, and any component can be made to fail through fatigue by subjecting it to a high enough level of cyclic stress. However, when it comes to fasteners, there are some design features, material choices and manufacturing methods that we can use to improve fatigue strength. Many of these have been covered in previous RET-Monitor articles in this channel. One...

Using springs

When considering a bolted joint, and when explaining how it works under load to a novice engineer, it is often helpful to consider the components as springs. The joint and the bolt ‘share’ any imposed loads depending on coefficients that are functions of the components’ stiffness, as is the case with nested helical springs. It does not take a huge leap of imagination to look at the actual applications of helical springs as fasteners. There are applications where the imposed...