As detailed in our October 2024 Technical Tip, oil varnishing is primarily caused by the oxidation of the lubricant which, at high temperatures in the presence of dissolved oxygen, causes the breakdown of the hydrocarbons in the base oil. This breakdown results in a degradation of the lubricating properties and accelerates the wear of components. […]

Oils are widely used in hydraulic systems, both as lubricants to reduce friction and to increase cooling capacities. An increase in the demands on the properties of the oil, and a move to more advanced base stock, which requires new additives, has led to an increase in varnishing problems associated with oil degradation. Most of […]

Tightening bolts is relatively easy to conduct in practice but attaining a specific preload and assessment of the preload achieved is a lot more difficult than what is typically believed. In previous tech tips we have discussed the need for using a device that can measure preload (such as Skidmore-Wilhelm machine) to calibrate the pretensioning […]

In a recent case of component failure, the importance of the assumed material properties was highlighted. Material property in this case refers to the fracture toughness of a metal, and its dependence on various parameters. Unfortunately fracture toughness of a metal is not a rigorous unchanging ‘property‘ of the material, such as its melting point, […]

Part 2 The first ‘Technical Tip on Double Nutting’ provided a description and methodology of the process and the mechanics of ‘double nutting’ – the process of adding a second (typically thicker) nut to a preloaded fastener to help prevent self-loosening.  The process has been fully described in this article which is available on our […]

Part 1 A commonly used method to prevent the self-loosening of bolted connections is the so-called ‘double-nut’ method, where two nuts are tightened onto a single threaded fastener. The jamming action associated with this practice, creates high frictional loads that resist relative movement of the nuts and provides a degree of resistance to self-loosening to […]

Part 2 As mentioned in our last technical tip the heat input associated with welding and cooling rates of the weld and adjacent parent material causes changes to the material microstructure, which is likely to have normally deleterious effects on local properties and physical performance – particularly as far as fatigue is concerned.  These microstructural […]

Part 1 Welding is arguably the most common, popular and successful method of joining metal components, and has virtually completely replaced older methods, such as riveting.  However, the welding process does affect the microstructure of the welded and adjacent material, which may have effects on local properties and physical performance, particularly as far as fatigue […]

This month’s Technical Tip considers an interesting failure arising effectively from a misunderstood load path. The failure in question involved a 1000 tonne 600mm diameter hydraulic cylinder after approximately 3 months in service. Owing to the large size of the cylinder, the piston had been threaded onto the rod and was screwed down against a […]

This Tech Tip follows closely from the previous one in which the importance of accurate evaluation of the stresses in engineering design was highlighted. The sentiments expressed in this previous Tech Tip, focussed on the importance of the reliable estimation of loads and theoretical analysis of stresses during design and comparison of these estimates, to […]