Knowledge

Conventionally, carboxylic acid salts are widely applied as anti-wear additives for water–glycol (W/G) hydraulic fluids. Here, Mini-Traction Machine (MTM) was employed to evaluate the friction properties of four carboxylates in W/G fluid. The results indicate that undecylenate salt (CN-3) exhibits the best antifriction capability and the friction coefficient nearly remains stable when its concentration increases from 3 wt% to 6 wt%. However, ball-on-disc tribology tests show that CN-3 as a single lubricant additive cause poor lubrication under severe condition like a high load of 125 N. Fortunately, the combination of CN-3 and a water soluble heterocyclic compound (COMB) lead to the outstanding antiwear and friction-reducing properties. The possible reason is ascribed to the formation of more stable tribofilm containing FeS2 and carbon structures according to XPS analysis of the worn surfaces. Furthermore, a vane pump test was conducted to confirm the results of the simulating tests. The W/G hydraulic fluid formulation based on COMB as the antiwear package performs well in the pump test, giving rise to only slight pump wear loss. The results of the pump test and the simulating test are consistent with each other. Meanwhile, the W/G hydraulic fluid possesses excellent other physic-chemical properties and meets the specification of ISO 12922 requirement.

Food oral processing is a study of mastication that involves food-saliva interaction. Instrumental approaches have improved sensorial attributes like texture by stimulating the oral environment for the past years. However, a thorough estimation of oral food processing is still an open research topic with persisting challenges. This review summarizes the role of tribology as a novel oral processing tool for the sensory evaluation of foods. The paper further covered state of the art on instrumentation, working principles, the efficiency of the tribometer, and its application in dairy and non-dairy foods. Moreover, sincere attempts have been made to classify the research gap and challenges in oral food processing using tribometer.

Lubricant additives that reduce wear by forming protective tribofilms on sliding surfaces are crucial to maintaining the efficient and reliable operation of many engineering systems. The most important of these additives, zinc dialkyldithiophosphate (ZDDP), has been in use for almost a century; however, several aspects of the physicochemical mechanisms through which it reduces wear remain unclear. While changes to the molecular structure of ZDDP are known to affect tribofilm formation and antiwear performance, the underlying mechanisms are not well understood. Here, we show using macroscale tribometer experiments under well-defined temperature and stress conditions, how the ZDDP tribofilm formation rate on steel from nonpolar base oils can be controlled by tailoring the additive’s alkyl substituents. Our results suggest that the chain-length, branching and presence of cycloaliphatic groups can affect the packing density, steric hindrance, and stress transmission, leading to large differences in the temperature- and stress-dependencies of the tribofilm formation rate.

General reductions in lubricant viscosities in many machine components mean that the role of lubricant additives in forming tribofilms has become increasingly important to provide adequate surface protection against scuffing. However, the relationship between scuffing and the formation and removal of tribofilms has not been systematically demonstrated. In this study a step-sliding speed scuffing test based on contra-rotation using MTM-SLIM and ETM-SLIM has been employed to observe concurrently tribofilm thickness and the onset of scuffing. The initial sliding speed used was found to significantly affect scuffing performance since it determines the extent to which a tribofilm can form before critical sliding speed conditions are reached. Generally, additives that formed thicker tribofilms, especially ZDDPs and triphenyl phosphate, gave effective protection against scuffing, though their protective tribofilms were progressively removed at higher sliding speeds, eventually resulting in scuffing.

The wear rate of any lubricated contact is dependent on many factors, including, surface roughness, lubricant composition, environment, operating conditions, temperatures, etc. There are also many different wear mechanisms, often operating in parallel. Since wear in itself is not an intrinsic property of a system, different wear tests can give very different results.
Despite their popularity and widespread use, all wear bench test methods all have some shortcomings when used to investigate complex lubricant additive combinations. However sophisticated the test method, they are inevitably unable to directly mimic real lubricated contacts conditions of machine elements. Interpretation of different bench test results can be difficult and misleading conclusions can sometimes be drawn.
A new pure sliding wear test is described which can produce measurable wear within a reasonable period of time. The repeatability and merits of the test method is discussed.

One of the least expensive pathways to achieving improvements in vehicle fuel economy is through changes to engine lubricant viscosity and composition. Driven by ever more stringent emissions regulations, OEMs are therefore requiring engine oils to continue protecting engines at lower viscosities and reduced friction.
Different engine operating conditions represent a range of lubrication conditions, and to better understand the full impact of engine lubrication process, one must understand how oils perform in these conditions. In general, additives in lubricants help to provide the right balance of fuel economy while maintaining durability protection. The focus of the present study is on the hydrodynamic lubrication regime, and the rheological properties of oils were investigated and correlated to their fuel economy performance in different engines, Mercedes Benz OM 501 LA and Detroit Diesel DD13, and driving cycles, WHTC (World-Harmonized Transient Cycle) and modal.

The replacement of traditional mineral oil lubricants with water-based bio-compatible fluids has long been a desirable, if unrealised, ambition in many applications. This is particularly relevant in marine-based energy generation systems, where oil-based lubricants create a high risk of environmental pollution. The use of bio-lubricants has been explored in several previous studies, however no significant technological advances have been achieved. Most of the work has focused on traditional lubrication mechanisms, with bio-molecules being employed to form an adsorbed surface film which reduces friction. However, due to their inherent biological, thermal and/or oxidative instability, bio-molecules are unsuited to long-term industrial applications. The alternative approach is to use stable, bio-friendly molecules, designed to exploit the lubrication mechanisms found in nature. These mechanisms have evolved to be far more diverse than those found in traditional “mineral oil” tribology and are, as yet, poorly understood.

The effect of top of rail lubricant composition on adhesion has been investigated using a laboratory ball-on-disc tribometer. Rheological properties were analysed using viscosimeter and high pressure torsion device. As a base medium, a biodegradable ester oil with bentonite thickener was selected. Added particles for friction modification were aluminium oxide, zinc oxide, copper sulfide and solid lubricants molybdenum disulfide and graphite. The effect of these components in the base medium on adhesion was evaluated. It was found that the most dominant component was the solid particles for friction modification. Based on the results, top of rail lubricant substances were prepared and tested. The best performing substances provided the optimal level of adhesion. These substances also showed resilience to overdosing, which caused commercial products to provide very low adhesion conditions. The rheological investigation confirmed the very low adhesion is controlled by elastohydrodynamic regime while the stable values are a result of transition to boundary lubrication.

Electric vehicle motors in e-drivetrain are equipped with grease-lubricated bearings operating at both low and high speeds with frequent speed changes. The grease-bearing system must secure a long lifespan and low frictional torque to improve efficiency and sustainability. The present paper focuses on the influence of two types of thickener, lithium complex and polypropylene, on the grease lubrication performance under conditions typical for e-motors. The comparison of both thickeners is performed in terms of friction torque and energy consumption in eight long-duration experiments (337 hr). The results show that the polypropylene thickener provides 21.5% lower energy consumption compared to the lithium complex. Changes in grease rheology and degradation in the tests are analysed and correlated with the grease lubrication performance.