Session: CT-04-02 Assembly of Bolted Joints - 2

Paper Number: 101616

101616 - Some Tribological Insights Into Threaded Fastener Friction and Lubrication 

In torque tightening, the precision and variability of fastener tension is greatly influenced by the friction at the fastener interfaces. Complementary experimental analyses have been performed to investigate different aspects of friction and lubrication mechanisms in threaded fasteners. The changes to fastener surfaces during assembly were found to correlate closely with the frictional behaviour. After assembly, changes in the roughness and skewness of the nut face and thread surfaces varied between fastener material and lubricant combinations. The main causes of variation were the removal of surface peaks, embedding/adhesion of solid lubricant materials, and removal of original oxide layers.

Different friction mechanisms were observed with different lubricant technologies: Metal-containing, non-metal and MoS₂ lubricants showed distinct behaviours. The lubricating material also changed significantly during assembly, which affected subsequent reassemblies. In particular, the alignment and burnishing of MoS₂ and the plastic deformation of metal powders generated a greater reduction in friction coefficient when reassembled.

A multivariate statistical analysis was performed on a broad range of fastener materials and lubricant combinations: This identified some key material, physical and tribological parameters that inform the precision of fastener tension in torque tightening. Again, distinct parameters affected the friction coefficient of metal-containing, non-metal and MoS₂ lubricants, confirming the distinct friction mechanisms of these lubricant technologies in fastener interfaces.

Presenting Author: Christopher Dyson ROCOL, A Division of ITW Limited

Presenting Author Biography: Chris Dyson first encountered tribology during his Mechanical Engineering studies at the University of Leeds. After graduating, he was fortunate to have opportunity to do a PhD in engine tribology, supervised by Prof Martin Priest, finishing in 2011. He then worked jointly with the University of Leeds and ROCOL, collaboratively researching and developing high temperature lubricants for polymer-steel contacts as part of a Knowledge Transfer Partnership (KTP). Since this project finished in 2013, Chris has continued to work for ROCOL, a specialist lubricant manufacturer in Leeds, UK, keeping collaborative links with the Universities of Leeds and Bradford.

Authors:

Christopher Dyson ROCOL, A Division of ITW Limited
Martin Priest University of Bradford
Malcolm Fox Faculty of Engineering and Informatics, University of Bradford
William A Hopkins ROCOL, A Division of ITW Limited