Grease Properties Research Articles

Effect of Polysoap on the Physical and Tribological Properties of Soybean Oil‐Based Grease

AbstractSoybean oil (SBO)‐based grease, containing polysoaps synthesized from polymeric epoxidized soybean oil (PESO), were investigated. Greases were prepared using a mixture of lithium soap and triethanolammonium polysoap. Grease properties investigated were hardness, using the cone penetration procedure (ASTM D217); oxidation stability, using the pressurized differential scanning calorimetry (PDSC) method (ASTM D‐5483); and friction and wear, using a four‐ball tribometer (ASTM D‐2266). Penetration data showed that grease formulated in the presence of polysoap was harder than that without polysoap, and this was attributed to the cross‐linking in the polysoap structure, which was expected to provide higher resistance to deformation. The PDSC results indicated that the onset temperature of grease formulated with 3.8 and 7.3 wt% polysoap increased by 8 and 12°C, respectively, compared to grease without polysoap. The coefficient of friction of grease formulated with polysoap was much lower (0.015) than grease without polysoap (0.034).

Novel Tribological Behavior of Hybrid MWCNTs/MLNGPs as an Additive on Lithium Grease

The goal of this paper is to investigate tribological characteristics of nanographene platelets and hybridized nanocomposite of multiwalled carbon nanotubes (MWCNTs)/multilayer nanographene platelets (MLNGPs)/lithium based-grease. Characterization is done through high resolution transmission electron microscopy (TEM) and X-ray diffraction. While grease properties were tested using Falex four-ball testing machine. Scanning electron microscopy (SEM) and energy dispersive X-ray diffraction (EDX) were utilized to characterize the lubrication mechanism and the worn surface. The results showed that 1% of MLNGPs is the optimum concentration. Wear scar diameter (WSD) was reduced by 66%, friction coefficient was reduced by 91%, while maximum nonseizer load was increased by 90 kg over ordinary lithium grease. Hybrid MWCNTs\MLNGPs were studied, and the optimum ratio of MLNGPs to MWCNTs was found to be 4:1.

Film Thickness Model for Grease-Lubricated Bearing Seals with an Axial Contacting Lip

A theoretical model is presented to predict the oil film thickness in an axial sealing contact based on grease properties and operating conditions. It is assumed that a small amount of grease will form an oil reservoir on the rotating part and slowly supply oil to the sealing contact. The oil bleed model from a previous study is implemented and oil loss due to centrifugal forces and the seal pumping action are taken into account. The results show that, depending on the operating conditions, an oil film is present in the sealing contact for a certain period of time. The oil film thickness decreases in time due to the decreasing oil supply from the grease reservoir and oil loss from the contact due to centrifugal forces. Seal pumping has only a small effect and the seal material and geometry are therefore not important for the predicted time until the mixed lubrication regime is reached. This time depends on the oil viscosity, rotational speed, and seal contact radius and scales with the η /(n2·ds) parameter. The volumetric size of the grease reservoir also has a large impact on maintaining the film thickness in time.

Basic Study of Grease Rheology and Correlation with Grease Properties

Basic Study of Grease Rheology and Correlation with Grease Properties

Impact of polyurea structure on grease properties

AbstractThe thickener structure of polyurea grease has a crucial effect on its properties. Therefore, it is very important to study the relationship between a thickener structure and physical and performance properties. In this study, polyurea greases were synthesised, having a different number of urea groups in per polyurea thickener molecule. Properties such as dropping point, penetration, oil separation, shear stability and four‐ball wear and extreme pressure (EP) were evaluated. The result shows that properties of polyurea grease vary with the number of urea group per polyurea molecule. Based on molecular theory, the mechanisms explaining these effects are briefly discussed. Copyright © 2010 John Wiley & Sons, Ltd.

Analysis of a grease-lubricated contact from an energy point of view

A number of grease lubricated contacts are working under mixed friction conditions. In this paper, we try to model the grease-lubricated contact considering the density distribution within the grease film. A proposal is presented to quantify the friction energy for the fluid friction part by using experimental work. The friction leads to a process of structural degradation (rheological wear) of the lubricating grease. This process is analysed and some new parameters are defined. A proposal for quantifying the irreversible change of the grease properties is made. All this work is done from an energetical point of view and is supported by experimental work.

Bearing performance limits with grease lubrication: the interaction of bearing design, operating conditions and grease properties

The majority of rolling element bearings in use today are lubricated by grease. Grease is a two-phase lubricant with complex rheological properties and poses severe challenges for the prediction for lubricating performance. Grease lubricated contacts are liable to starvation and as a result the film thickness is reduced, which can result in surface damage or premature bearing failure. It is important to know when starvation occurs and the effect of grease type, bearing design and operation on lubrication replenishment. The influence of bearing design and operation in controlling lubricant supply to the contact zone is examined in this paper. The aim is to develop a starvation parameter capable of predicting the operating limits for a particular bearing/grease system.A number of bearing design parameters are examined in the paper; these include cage design, ball spin and bearing size. Ball spin and cage effects can be efficient mechanisms for maintaining the lubricant supply to the track. Increased bearing size, line contact geometries and high load result in reduced lubricant replenishment of the contact. Using this analysis it will be possible to establish operating limits for families of bearings.

Improvement of CIATIM-201 Grease Properties for Use under Severe Conditions using Suitable Additives

Improvement of CIATIM-201 Grease Properties for Use under Severe Conditions using Suitable Additives

Characteristics and potential applications of a novel shock absorbing elastomeric composite for enhanced crashworthiness

The impact absorbing properties of a novel class of devices comprising stout, flexible, high tensile stiffness bags filled with a blend of small elastomeric capsules and a matrix liquid are described. The devices combine the elastic impact absorbing properties of elastomeric closed cell foams with the hydraulic pressure equalisation and viscous damping properties of liquids. The capsules can take many forms, including beads of expanded foams, bubble packing and air filled, open ended tubes. The matrix liquid, which may be a Newtonian liquid or a grease, contributes lubrication, viscous damping and pressure equalisation properties. The impact absorbing characteristics of the devices are less dependent on the shape of the contact face of the impacting body, compared with elastomeric foam impact absorbers, but uniaxial stiffness decreases, as the size of impact face of the device, relative to the impact zone, increases. Problems of package leakage and weight are addressed. The novel impact absorbing properties of the devices suggest that they could have a wide range of crash protection applications, including the design of pedestrian friendly vehicle front ends, to meet pending European legislative requirements.

Thin-film grease lubrication

One of the most important examples of the thin-film regime is in the grease lubrication of rolling element bearings. Grease lubrication is not usually considered in this context and yet there is considerable evidence that many bearings operate under starved conditions where the film thickness drops to a fraction of the fully flooded value. Thus it is the mechanisms of lubricant supply and film formation in the starved regime that are important in ensuring the successful operation of a bearing. The aim of this paper, therefore, was to explore grease lubrication from a thin-film perspective and to examine the many factors that could influence starved film formation. Much of the current understanding in this area is derived from studies of starved fluid film lubrication and this provides a convenient starting point for the discussion. Grease lubrication is considered as a replenishment problem and recent experimental work is presented illustrating some of the aspects discussed in the text. The effect of grease properties, bearing operation and design on film formation is examined. Grease lubrication in the thin-film regime is a complex problem. It includes aspects of non-Newtonian rheology, surface chemistry, capillary flow and starved elastohydrodynamic lubrication (EHL). All of these aspects need to be resolved in any future model that will be capable of explaining and predicting grease lubricating behaviour in bearings.

Physical and chemical mechanisms of influence of Cu‐containing additives on grease properties

AbstractThe mechanisms governing the influence of copper additives (powders, oxides, organic and inorganic salts, complex compounds) on tribological, rheological and basic physical properties of greases with various thickeners (lithium, complex lithium, complex aluminium and polyurea) are discussed. The copper plating effect was found to occur only under EP conditions. The physical and chemical patterns of copper‐containing grease additives under antiwear and extreme pressure conditions are discussed together with rational application alternatives in friction couples of equipment and machinery.

Application of calorimetry and thin-layer chromatography in investigation of lubricating greases

whole. Standard methods cannot be used to determine the changes in the physiochemical properties of greases under frictional conditions, mainly because of the need for large samples in such analyses. In order to solve this problem, micro methods have been developed for the evaluation of grease properties, using modern analytical equipment. Here we are reporting on a feasibility study of using differential scanning calorimetry (DSC) and thin-layer chromatography (TLC) to investigate changes in the properties and composition of greases in the process of friction. We have used DSC to determine the thermooxidative stability, thermodynamic stability, and phase transitions of the original and used greases. The thermooxidative stability was rated according to the nominal temperature for initial oxidation tio , the induction period I, and the oxidation rate v. The value of tio was determined from a calorimetric curve

Compatibility of lubricating greases

This article reports on a study of grease serviceability in actual mechanisms. Investigates the formation of grease mixtures during relubrication of the component and subsequent operation. Finds that the mechanical stability of the mixtures varied for the most part in proportion to the ratio of greases. Points out that the nature of the thickening agent is the predominant factor in determining grease properties and compatibility. Examines model systems obtained by thickening a given oil with the various thickening agents that are most widely used in commercial production.

The properties of elastohydrodynamic grease films

The results of investigations of elastohydrodynamic grease films are reported. The elastic deformation of the rolling elements and changes in the grease properties due to pressure were considered. The theoretical results were confirmed by optical interference measurements of the film thickness. A formula for the film thickness as a function of the rheological grease parameters is given. The effects of breakdown of the grease structure and of starvation conditions on the film thickness are discussed.

Effects on the yield stress of lithium grease from the adsorption of surfactants on fillers

Various materials classed as additives or fillers may be added to greases to improve their service properties; these two types of materials differ greatly in their effects on the grease structure [i]. The desirable effects of the added materials are generally accompanied by undesirable side effects on the grease structure and properties. Most of the additives used to improve the lubricity and protective properties of greases are highly surface-active substances, and when used at the working concentrations, they soften the greases to an extent that cannot be tolerated [2, 3]. This same sort of softening occurs when greases are oxidized under the conditions of service and storage, as a result of the formation and accumulation of oxygen-containing surfactants, primarily acids and alcohols [4]. An effective method for improving the functional effects of additives and eliminating the undesirable side effects is the joint use of additives and fillers in the optimal ratio. The favorable results to be obtained by the use of such combinations are apparently due to adsorption of the additives on the surface of the filler particles. The presence of fillers also prevents any extreme softening of the greases when they are oxidized [5]. This effect can probably be attributed to adsorption of the oxidation products on the filler particle surface, so that the oxidation products have much less effect on the grease structure, and thus there is no sharp change in ~he properties of the grease when it is oxidized. In order to confirm this hypothesis, we investigated the adsorption of surfactants on fillers (graphite, mica, and MoS~--20-40 ~m fractions); the surfactants included certain individual straight-chain fatty acids and alcohols (Cs-C16) and certain additives that are widely used in greases--Khlor~f-40, KINKh-2, and DF-II.* The heat of adsorption, which is a measure of the energy of surfactant molecule interaction with a solid surface, was used to judge the adsorption activity of the fillers. The heats of adsorption of the alcohols, acids, and additives were determined by means of flow microcalorimetry on solutions in heptane, simulating the hydrocarbon dispersion medium in a grease. The microcalorimeter was of the type described by Groszek [6]. The tests were performed at room temperature, with a 0.2-g sample of the filler as the adsorbent. The heptane flow rate was chosen within the range of 1-2.2 ml/min, depending on the adsorption process kinetics. The content of surfactant in the solvent was in the range from I0 -s to I0 -6 M, the additives being supplied in the form of 10% solutions and the alcohols and acids in the form of 0.25 M solutions. The integral heat of adsorption of the acids and alcohols on the fillers depends on the number of carbon atoms in the surfactant molecule (Fig. i). For all of the surfactants investigated, the heat of adsorption varies only slightly as the chain length is increased up to C12. Further increases in the molecular weight of the surfactant lead to increases in the heat of adsorption on MoS= and particularly on graphite. For the mica, these changes are very minor. The adsorptivity of the graphite and MoS= for the acids is somewhat greater than for the alcohols. The mica differs from the other two fillers in that the heats of adsorption of alcohols on the mica surface are greater than those of the acids. The most likely explanation is that these surfactants are adsorbed on the mica mainly by the polar part of the molecule, and chemisorption influences the heat of adsorption. On the surface

Dependence of grease properties on state of surface of silicon dioxide modified with n-butanol

Dependence of grease properties on state of surface of silicon dioxide modified with n-butanol

Application of IR spectroscopy in studying grease composition and properties (review)

Application of IR spectroscopy in studying grease composition and properties (review)

Continuous process lithium grease production

1. It has been shown that grease made on a continuous process plant with a lithium stearate content of 8% by weight (optimum water content of the initial dispersion and free alkali content of 0.04% NaOH) can meet the GOST standard requirements for grease TsIATIM-201 containing 12% soap. 2. The significant influence of free alkali content on the structure and properties of lithium greases is confirmed. The major grease properties are highly dependent on excess alkali content. The optimum excess alkali content for lithium greases is 0.04 to 0.05% NaOH. 3. The beneficial effect of water specially introduced into the initial dispersion on the structure and properties of greases was established. When the water content of the dispersion is increased to 20% by weight there is an improvement in grease properties associated with improved thickening power of the lithium soap. 4. Increase in soap content (from 6 to 13%) of greases produced on the continuous process plant with different water contents of initial feed corresponds to the previously established changes in rheological and physicochemical properties as function of the dispersed phase content.

Investigation of Lubricants for Power Circuit Breakers

Abstract This paper describes a technique for the selection of proper lubricants for power circuit breakers. The circuit breaker is described briefly, and its lubrication requirements for dependable operation are discussed. The laboratory methods set up to determine the performance of the grease best suited for this application are outlined. Results of the laboratory test data are shown and evaluated with reference to circuit-breaker requirements. Properties of some typical greases are compared with their performance for this particular application. Because performance depends not only upon grease properties, but also upon the process of manufacture, the greases tested are referred to only in code. Life tests on actual circuit breakers have checked laboratory results. Therefore it is concluded that tests may be set up to determine the suitability of a lubricant for any particular application and especially for power circuit breakers.