UK section of STLE Spring technical seminar

Citation

(2001), "UK section of STLE Spring technical seminar", Industrial Lubrication and Tribology, Vol. 53 No. 5. https://doi.org/10.1108/ilt.2001.01853eab.003

UK section of STLE Spring technical seminar

UK section of STLE Spring technical seminarKeywords: STLE, Seminar

In March this year the Society of Tribologists and Lubrication Engineers, UK Section, used their first technical seminar of the year to explore the increasingly important area of micro pitting.

Three papers were presented to members. The first covered work done at Cardiff School of Engineering in Cardiff University on the effect of roughness on elastohydrodynamic lubricant films when gear teeth are in contact. Researchers have looked at the EHL situation in real gears where the surface roughness is the same order of magnitude as the lubricant film. Under these conditions the standard pressure distribution through the contact area is significantly different to the smooth surface theory. In fact the lubricant film can generate higher than expected pressures but over a broader area and unlike smooth surfaces the peak pressures are lower than in the dry condition. The work done also showed that it was possible to obtain local lubricant cavitation and local surface contact depending on the relative positioning of the asperities as they travelled through the contact area. The investigators suggested that their findings might provide some insight into the so far unproven causes of micro pitting.

Members then heard about work done by Castrol on overcoming micro pitting. The pitting in question could be represented by pits 5 to 10 microns long and 5 microns deep. It was clear from the presentation that micro pitting can progress to a stage after which no further damage will occur but unfortunately in many cases it can produce catastrophic failures of the surface or loss of gear teeth. Often it seems that machinery prone to this type of failure is simply not inspected often enough or that the cause of failure is incorrectly diagnosed. It seems that although the use of the correct lubricant has a role to play it is far more important to get the engineering right at the design stage. Contaminants can act as precursors to micro pitting but good housekeeping and preventative maintenance should eliminate this problem. However, the work done by Castrol has shown that the correct type of base oil with a complementary additive treatment can provide an improved micro pitting resistance.

A number of bodies in UK have collaborated in work presented to the meeting by DERA (part of the British Ministry of Defence). The process of micro pitting was described and its complex roots explained by the many factors that can instigate and influence its development. The group had carried out some work using the FZG machine to compare the micro pitting resistance of different oils. It was found that the best measurement of micro pitting is profile loss but that it may be difficult to relate laboratory performance predictions to the real world.

Micro pitting is a subject that has received very little coverage in recent years although it is clear that many mechanical failures may well have been instigated by micro pitting. STLE's UK Section is to be congratulated on promoting this meeting, which provoked considerable discussion amongst members. "Industrial Lubrication & Tribology" would welcome contributions or comments from readers around the world working on micro pitting.