Knowledge

Welcome to our knowledge centre. Here you can find a selection of resources and articles on our products and industries we are involved with.

Paper

On the Film Forming and Friction Behaviour of Greases in Rolling/Sliding Contacts

The film forming and friction properties of nine greases covering different thickener types, viscosities and NLGI grades have been investigated. …

The film forming and friction properties of nine greases covering different thickener types, viscosities and NLGI grades have been investigated. Film thickness results are in agreement with previous work that all greases form a thicker film than the base oil counterpart at low speeds, suggesting that lambda ratio and kappa of greases can be much higher than their corresponding oils. The base oil viscosity appears to govern the grease film thickness at low speeds by a direct relationship for polyurea greases whereas by an inverse relationship for lithium and calcium complex greases. Grease friction results indicate that the shape of grease friction curves can differ quite significantly from that of oils. Possible underlying mechanisms that govern friction properties are discussed.

View abstract

Paper

Rheological and Film Forming Behavior of the Developed Nanocomposite Greases Under Elastohydrodynamics Lubrication Regime

Performance of grease lubricated point contact under elastohydrodynamics lubrication (EHL) regime is critical in many engineering applications. The present work …

Performance of grease lubricated point contact under elastohydrodynamics lubrication (EHL) regime is critical in many engineering applications. The present work deals with the evaluation of rheological, film forming characteristics and elastic recovery of newly developed nanocomposite greases. The nanocomposite greases are formulated by dispersing different nano-additives to bare grease (BG). The nano-additives include reduced graphene oxide (rGO) nanosheets, CaCO3 and α-Al2O3 nanoparticles. The microstructure evaluation of the nano-additives and different greases is done using high-resolution transmission electron microscopy (HRTEM). Estimation of the rheological parameters (storage and loss moduli) is done using rotational rheometer. The film forming behavior is recorded using elastohydrodynamic (EHD) rig for range of speed at different temperatures and constant load. The results indicate that change in microstructure due to nano-additive incorporation improves the responses of different greases. Based on rheological response, CaCO3 doped grease seems better but rGO doped grease is able to bear high shear stresses. Further, based on film forming characteristics and reflow or recovery behavior, rGO doped grease is better. The rGO-based grease registers approximately 90% elastic recovery followed by 75% for CaCO3-based grease, 65% for BG and 10% for α-Al2O3-doped grease.

View abstract

Paper

Elastohydrodynamic Lubricant Flow with Nanoparticle Tracking

Lubricants operating in elastohydrodynamic (EHD) contacts exhibit local variations in rheological properties when the contact pressure rises. Direct evidence of …

Lubricants operating in elastohydrodynamic (EHD) contacts exhibit local variations in rheological properties when the contact pressure rises. Direct evidence of this behaviour has only been obtained by examining through-thickness velocity profiles U(z) of lubricants in a contact using luminescence-based imaging velocimetry. In the present study, nanoparticles (NPs) are added to polybutene (PB) as tracers to investigate the effect of pressure on the flow of PB in an EHD contact. By tracking NPs in the contact, particle velocity distributions f(U) under various pressures are obtained and found to be pressure dependent. Results show quantitatively that f(U) and U(z) are correlated and thus confirm that U(z) of PB changes from Couette flow to partial plug flow above a critical pressure. This confirmation highlights the complexity of lubricant rheology in a high pressure contact.

View abstract

Paper

Effect of Over Rolling Frequency on the Film Formation in Grease Lubricated EHD Contacts under Starved Conditions

The service life of rolling bearings is significantly affected by the lubricating film formation in elastohydrodynamic (EHD) contacts. Grease lubricated …

The service life of rolling bearings is significantly affected by the lubricating film formation in elastohydrodynamic (EHD) contacts. Grease lubricated EHD contacts show a film thickness decay from a characteristic rotational speed, which is referred to as starvation. Thus, the film thickness of grease lubricated contacts differs from that of oil lubricated contacts. However, the base oil properties under fully flooded conditions are commonly assumed to estimate the operating lifetime of grease lubricated bearings, which are usually not fully flooded. Hence, this assumption results in an overestimation of the film thickness for rotational speeds in the range of starvation, which can lead to uncertainties in the bearing design. At high rotational speeds, i.e., high over rolling frequencies, starvation is likely to occur, due to insufficient lubricant supply by replenishment behind the rolling element. Therefore, the focus of this contribution is to investigate the effect of over rolling frequency, and thus replenishment time, on the lubricating film formation in starved, grease lubricated EHD contacts. The film thickness measurements were performed on a ball-on-disc tribometer, which was extended by adding a second ball specimen in front of the measuring ball. By varying the angular distance between the two contacts, the lubricant displacement can be controlled, such that the effect of replenishment time on the film formation can be determined. These investigations should help to establish an advanced understanding of the mechanisms of grease lubrication, and encourage future work with a focus on developing a method to predict the film formation in grease lubricated EHD contacts.

View abstract

Paper

EHD Friction Properties of ISO VG 320 Gear Oils with Smooth and Rough Surfaces

The elastohydrodynamic (EHD) friction properties of seven ISO VG 320 gear oils including three polyalphaolefins (PAOs), three polyglycols (PG) and …

The elastohydrodynamic (EHD) friction properties of seven ISO VG 320 gear oils including three polyalphaolefins (PAOs), three polyglycols (PG) and a mineral oil have been investigated in rolling/sliding conditions at six different temperatures and three roughnesses. Film thickness, Stribeck and traction curves have been generated using a ball-on-disc tribometer. Film thickness results are in agreement with previous work that it is primarily controlled by pressure-viscosity coefficient and viscosity of lubricants. The results with smooth surface show that all oils experience significant shear heating leading to friction reduction at higher strain rates or lambda ratios but only PGs reach limiting friction whereas mineral oil and PAOs do not. Friction curves obtained at different temperatures and roughnesses enable simulating an extensive range of lubrication regimes and allow isothermal friction correction for shear heating. Stribeck curves with rough surfaces show an increase in friction in the lambda range of 0.5–3.5, where asperity separation varies from partial to full–indicating that roughness effects can be expected even under full film condition. This increase in friction is attributed to formation of a micro-EHD region, and is seen only with mineral oil and PAOs whereas not with PGs. The results also highlight how EHD friction properties of different family of fluids could be influenced by roughness effects, and the possible mechanisms are discussed.

View abstract

Paper

Evaluation of Tribological Properties of Graphene Oxide Dispersed Paraffin Oil

This research study investigates the tribological behavior of ODA Graphene nano particles as lubricant additives in mineral based paraffin oil. …

This research study investigates the tribological behavior of ODA Graphene nano particles as lubricant additives in mineral based paraffin oil. All tests are performed under varying load and 0.2% w/w concentration of nano particles in lubricating oil using ball and disc configuration and four-ball testers. Experimental results state that small percentage of ODA Graphene is improving the friction, anti-wear properties and dynamic viscosity. Coefficient of friction in EHD and boundary regime is decreased by 75% and 61.8% respectively. The results are validated by using the Raman Spectroscopy of worn steel ball to confirm the presence of ODA graphene nano particles.

View abstract

Paper

Drop-on-Demand Printing as Novel Method of Oil Supply in Elastohydrodynamic Lubrication

The feasibility of drop-on-demand printing as a novel method for oil supply in elastohydrodynamic lubrication was tested for a single …

The feasibility of drop-on-demand printing as a novel method for oil supply in elastohydrodynamic lubrication was tested for a single ball-on-disk contact to allow precise lubrication control at a minimal level of lubricant. It is shown that it is feasible to jet droplets of 3.3 pL for an oil of 46 mPa s viscosity at a controlled frequency which, for the conditions considered, results in droplets on the surface with a radius significantly smaller than the Hertzian contact radius. Experimental results of the film thickness evolution over time are presented from dry contact to fully flooded contact with different supply frequencies and a total oil usage of approximately 40 nL. By means of numerical simulation, the details of droplet ingestion into the contact are illustrated. It is shown that the central film thickness over time can accurately be predicted. The theoretical and experimental results provide a very strong incentive for further investigation of drop-on-demand printing as method to achieve optimal (re)lubrication at minimum level in the realistic setting of a rolling bearing.

View abstract

Paper

Composition Containing Heterocyclic Compounds and a Method of Lubricating an Internal Combustion Engine

The present invention relates to a lubricating composition containing (a) an oil of lubricating viscosity; and(b) a compound selected from …

The present invention relates to a lubricating composition containing (a) an oil of lubricating viscosity; and(b) a compound selected from the group consisting of: (i) an ester-containing heterocycle; (ii) an amide-containing heterocycle; and (iii) a pyrimidine, wherein the ester-containing heterocycle and the amide-containing heterocycle have a hydrocarbyl group containing 6 to 40 carbon atoms. The invention further provides for a method of supplying an internal combustion engine with the lubricating composition.

View abstract

Paper

Simulation and Prediction of Wear Using Finite Element Analysis with Experimental Validation

Recently, developments in automotive industries have increased competition. So, the design and development of new products have become more time …

Recently, developments in automotive industries have increased competition. So, the design and development of new products have become more time sensitive. But an equally important aspect is the durability and reliability of new products. Currently, the reliability of products is tested and examined using traditional laboratory methods. In this traditional approach, the products are tested until failure, which is usually a costly and time consuming process. Additionally, this approach increases the time from design to market. Reducing the testing duration of new products will reduce the product development cost and time to market. Therefore there is an increase in employing Accelerate Life Test (ALT) methods by many companies. ALT is the method of testing a product sample by applying more severe environmental conditions than normal conditions. Although cost and time can be reduced by this method, the method is insufficient in many cases because it often does not accurately determine the root cause of potential failures. Consequently, this need has given rise to the development of prediction models to enable a better understanding of product reliability. According to many studies, the main reason for the failure of mechanical components is the loss of material on the surfaces, in other words, wear. Previous research efforts have created a platform for wear simulation by combining Finite Element Analysis (FEA) with mathematical wear equations. This research is focused on reducing the wear simulation time by using an axisymmetric model and developing a mathematical equation in which the wear on the contacting surfaces in relative motion can be calculated by simulating the wear on only one surface in contact. This approach should make the FEA model more time and cost efficient. In this research, a critical factor (wear rate) is determined from experimental data, i.e., wear tests. Based on these results, the local wear is firstly calculated and then integrated over the sliding distance. Then, a series of FEA simulations are done in a loop by updating the wear coefficient and load conditions. Finally, the simulation results and mathematically calculated results from a derived equation are compared with experimental results. The simulation results show a reasonably good agreement with the experimental results. Moreover, the simulation model gives more details like the distribution of contact pressure and the spreading of stress at the contact surfaces.

View abstract