Showing papers on "Grease published in 2016"

Effect of Thickener Particle Geometry and Concentration on the Grease EHL Film Thickness at Medium Speeds

Abstract: The aim of this paper was to understand the parameters influencing the grease film thickness in a rolling elastohydrodynamically lubricated contact under fully flooded conditions at medium speeds. Film thickness measurements were taken under pure rolling for six commercial greases and their bled oils. The grease film thickness was found to be higher than corresponding bled oil, suggesting the presence of thickener in the contact. No rheological properties (characterized by steady and dynamic shear) showed any direct relation to the film thickness of the studied greases. AFM measurements of the thickener microstructure, from which the dimensional properties of the thickener particles (fibers/platelets/spheres) were estimated, showed that the relative increase in the film thickness due to entrainment of the thickener was proportional to the ratio of thickener volume fraction to the size of the fibers/platelets/spheres. Hence, with the same concentration, smaller thickener particles lead to the generation of thicker films than larger thickener particles. Next, this relation was used to establish the percentage of the thickener particles passing through the contact. Depending on the grease type, between about 1 and 70 % of the thickener particles were found to travel through the contact.

The Field-Dependent Rheological Properties of Magnetorheological Grease Based on Carbonyl-Iron-Particles

Abstract: This paper presents dynamic viscoelastic properties of magnetorheological (MR) grease under variation of magnetic fields and magnetic particle fractions. The tests to discern the field-dependent properties are undertaken using both rotational and oscillatory shear rheometers. As a first step, the MR grease is developed by dispersing the carbonyl iron (CI) particles into grease medium with a mechanical stirrer. Experimental data are obtained by changing the magnetic field from 0 to 0.7 T at room temperature of 25 °C. It is found that a strong Payne effect limits the linear viscoelastic region of MR grease at strains above 0.1%. The results exhibit a high dynamic yield stress which is equivalent to Bingham plastic rheological model, and show relatively good MR effect at high shear rate of 2000 s-1. In addition, high dispersion of the magnetic particles and good thermal properties are proven. The results presented in this work directly indicate that MR grease is a smart material candidate that could be widely applicable to various fields including vibration control.

Ionic Grease Lubricants: Protic [Triethanolamine][Oleic Acid] and Aprotic [Choline][Oleic Acid].

Abstract: Ionic liquid lubricants or lubricant additives have been studied intensively over past decades. However, ionic grease serving as lubricant has rarely been investigated so far. In this work, novel protic [triethanolamine][oleic acid] and aprotic [choline][oleic acid] ionic greases are successfully synthesized. These ionic greases can be directly used as lubricants without adding thickeners or other additives. Their distinct thermal and rheological properties are investigated and are well-correlated to their tribological properties. It is revealed that aprotic ionic grease shows superior temperature- and pressure-tolerant lubrication properties over those of protic ionic grease. The lubrication mechanism is studied, and it reveals that strong physical adsorption of ionic grease onto friction surface plays a dominating role for promoted lubrication instead of tribo-chemical film formation.

Tribological behaviour of calcium grease containing carbon nanotubes additives

Abstract: Purpose The purpose of this paper is to fabricate composite nanogrease for tribological applications. Multi-walled carbon nanotubes (MWCNTs) with a size 10 nm average diameter and 5 μm in length were used as additives to calcium grease. Design/methodology/approach The tribological four-ball machine was used to evaluate calcium grease with carbon nanotubes (CNTs) as an additive. The interaction between CNT and calcium grease (nanogrease) were studied by transmission electron microscopy and X-ray diffraction. Findings MWCNTs composite nanogrease was manufactured for tribological applications. The effectiveness of the fabricated grease in improving the tribological performance at different concentrations and under different loads was tested. The results are summarized as follows. CNT nanoparticle additive dispersed in calcium grease significantly improve its anti-wear performance, reducing friction, increasing load-carrying capacity and extreme pressure (EP) property. The friction is reduced by about 50 per cent, the wear scar diameter (WSD) decreased to 32 per cent and the EP properties increases about 38 per cent, with only 3 wt.%. The modified grease with CNTs additives of 3 wt.% showed the most favorable results. Energy dispersive x-ray (EDX) analysis shows that C was present on the worn scar surface, with atomic concentration of about 22 per cent. The presence of C suggests that a lubricating film is likely formed because of the presence of CNTs and very likely prevented the steel-to-steel direct contact. Originality/value The results indicated that a 3 wt.% of MWCNT nanogrease is an excellent antiwear, with EP and low friction coefficient. It was also found that the friction coefficient was reduced to about 50 per cent, the WSD decreased by about 32 per cent and the EP properties increased about 38 per cent. The mating surfaces were investigated with scanning electron microscopy and EDX. The results show that a boundary film mainly composed of CNTs, Cr and Fe was formed on the rubbed surfaces.

Rheology and thermal conductivity of calcium grease containing multi-walled carbon nanotube

Abstract: Recently, nanofluids attract considerable interest for enhanced rheological behavior and thermal performance. The aim of this research is to study the influence of additives Multi-Walled Carbon Nanotubes (MWCNTs) on the rheological behavior and its structure, thermal conductivity, and the influence of shear thinning rate on oil separation at different temperatures for calcium grease. Various concentrations of MWCNTs (0.5, 1, 2, 3, and 4%) have been added to the grease to obtain the best percentages that improve the properties of nanofluid. The microstructure of MWCNTs and nanofluid were examined by X-ray diffraction (XRD), Transmission Electron Microscope (TEM), and Scanning Electron Microscope (SEM). These experimental investigations were evaluated with a Brookfield programmable Rheometer DV-III ULTRA. The results indicated that the optimum concentration of MWCNTs was 3%, and the dropping point increasing about 11%. The rheological behaviors of the nanofluids show that the grease with various con...

AFM and SEM Assessment of Lubricating Grease Microstructures: Influence of Sample Preparation Protocol, Frictional Working Conditions and Composition

Abstract: The microstructure of lubricating greases greatly conditions their in-service performance. In that sense, optimal testing protocols are required in order to accomplish their correct morphological characterization. This study explores and compares the suitability of atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques for imaging six different commercial metallic soap-based greases and two novel biopolymer-based formulations. Pros and cons of both techniques and the effect of sample preparation protocol were analysed. The results revealed a wide variety of morphological characteristics depending on composition. Thus, the four anhydrous calcium-based greases demonstrated two clearly distinct microstructures (fibrous and granular) determined by the type of base oil employed. With regard to the lithium complex greases, the typically reported microstructure characterized by well-defined entangled and fibrous network was observed in both AFM and SEM techniques. As for the two biopolymer-based greases, fibre networks were also encountered. Besides this, selected greases were subjected to different tribological tests, and the effect of high-shear frictional working treatments on their microstructure was also analysed. As a result of the friction and internal wear, the AFM results evidenced microstructural changes which depended on grease composition. Overall, the combined use of AFM and SEM techniques was demonstrated to be a powerful approach to microstructurally characterize lubricating greases.

Impact of Water on the Rheology of Lubricating Greases

Abstract: The operational life of bearings is often determined by the performance of the lubricating grease. The consistency of the grease prevents it from leaking out of the bearing and provides good sealing properties. The possible ingress of water into the bearing will have a considerable impact not only on this consistency but also on the lubricating ability of the grease. There are numerous applications where water ingress may occur, such as in the steel, food, pulp, and paper industries. Some greases are less sensitive to water than others. No specific guidelines are available to select the proper grease for bearings subjected to water ingress. The goal of the article is to contribute to the development of such guidelines for greases subjected to water ingress by studying the impact of water on grease rheology. Fully formulated, commercially available greases with the most common thickeners and base oils are used as model greases. It will be shown that water strongly influences rheological properties such as zero-shear viscosity, yield stress, and storage modulus. Calcium sulfonate greases were found to become stiffer after absorbing a considerable amount of water, leading to an increase in zero-shear viscosity and yield stress. However, lithium, lithium complex, and polyurea greases were found to soften, with appreciable changes in measured rheological properties

On Monitoring Physical and Chemical Degradation and Life Estimation Models for Lubricating Greases

Abstract: Degradation mechanisms for lubricating grease are categorized and described. An extensive survey of the available empirical and analytical grease life estimation models including degradation monitoring standards and methods are presented. A summary of the important contributions on grease degradation is presented.

Grease composition for constant velocity joint

Abstract: To provide the grease composition for the constant velocity joint that has both durability and abnormal noise resistance characteristics.SOLUTION: The grease composition for the constant velocity joint having outer race surface roughness Ra less than 0.80 μm comprises a diurea compound represented by R-NHCONH-CH-p-CH-CH-p-NHCONH-R(formula 1), poly-α-olefin with a kinematic viscosity at 40°C of 1000 mm/s or more to less than 1500 mm/s, a mixed base oil including other base oils, copper dithiocarbamate, and molybdenum dithiocarbamate, wherein the mixed base oil has a kinematic viscosity at 40°C of 180 mm/s or more to less than 400 mm/s, and the mixed base oil contains 15 mass% or more to less than 40 mass% of poly-α-olefin based on a total mass of the mixed base oil.SELECTED DRAWING: Figure 1

Impact of Water on EHL Film Thickness of Lubricating Greases in Rolling Point Contacts

Abstract: This paper investigates the influence of water on the EHL film thickness of six commercial lubricating greases under fully flooded and starved conditions. Although grease can absorb large quantities of water, separation occurs due to pressure and shear, leading to free water. This does not have an impact on the film thickness under fully flooded conditions. However, water does have an effect on the film thickness under starved conditions where the differences are related to the change in oil bleed. In the presence of water, an increase in oil bleed was found for lithium, lithium complex and polyurea grease. These greases showed a reduction in the levels of starvation and, therefore, thicker films. Water contamination led to lower oil bleed for calcium sulfonate complex greases, which led to an increase in starvation, and therefore, thinner films compared to their uncontaminated counterparts.

Film Forming Behavior of Greases Under Starved and Fully Flooded EHL Conditions

Abstract: Improving knowledge on the film forming behavior of greases is essential to be able to develop efficient greases. This article examines how operating conditions (e.g., temperature, lubrication condition [fully flooded/starved]) and base oil viscosity influence the film forming properties of greases by comparing the behavior of two lithium-based greases and their respective base oils in rolling point contact. It is found that the onset and degree of starvation is controlled by speed (u) × viscosity (ν)/load (W) factor (uν/W) and temperature and that low uν/W values promote entrainment of thickener into contact. Thus, grease with low base oil viscosity shows significant thickener entrainment in the low speed region compared to the one with high base oil viscosity, which leads to the formation of thickener-rich viscous material during extended running with the low base oil viscosity grease. The results suggest that the shape of the film thickness versus speed curve is viscosity and uν/W range depende...

Conductive capacity and tribological properties of several carbon materials in conductive greases

Abstract: Purpose The purpose of this paper is to synthesize a new kind of conductive grease which possesses a prominent conductive capacity and good tribological properties. Design/methodology/approach A two-step method was used to prepare complex lithium-based grease. Ketjen black (KB), acetylene black (AB) and carbon black (CB) were characterized by transmission electron microscope and used as lubricant additives to prepare conductive greases. Conductive capacity was evaluated by a conductivity meter, a surface volume resistivity meter and a circuit resistance meter. Tribological properties were investigated by a reciprocating friction and wear tester (MFT-R4000). The worn surfaces were analyzed by a scanning electron microscope, Raman spectroscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscope. Findings The conductive grease prepared with KB has a prominent conductive capacity at room temperature, 100°C and 150°C. Further, this conductive grease also possesses better tribological properties than AB and KB greases. When the concentration of KB is 1.8 Wt.%, the coefficient of friction and wear width reduced by 11 and 14 per cent, respectively. Originality/value This work is a new application of nanometer KB as a lubricant additive in grease, which provides a direction for preparing conductive grease. The conductivity and tribology experiments have been carried out though the variation of experiment conductions.

Effects of Electrostatic Discharges on Bearing Grease Dielectric Strength and Composition

Abstract: Bearing faults may significantly reduce the useful life of electric machines. With the advent of modern fast-switching frequency converters, electric currents induced by the high-frequency common-mode voltage of these converters have been recognized as additional, sometimes severe, contributors to bearing degradation. The degradation is understood to progress both by damaging the bearing surfaces and by altering the chemical composition of the lubrication greases, which can lead to ineffective lubrication and reduction in permissible mechanical bearing load. This paper studies the effect of grease degradation due to discharge currents on the grease dielectric strength and chemical composition of several greases typically used with electric drives. From this, conclusions on the grease selection for variable-speed drive applications are drawn.

Charge–Discharge and Thermal–Electrical Characteristics of GdBCO Coils Wound With Various Types of Grease as an Insulation Material

Abstract: This paper reports the charge-discharge and thermal-electrical characteristics of GdBCO single-pancake coils employing various types of grease, such as N-grease (N coil), Si-based grease (Si coil), and vacuum grease (V coil), as an insulation material to ameliorate the charging-discharging delay observed in no-insulation (NI) coils. The charge-discharge test results confirmed that the use of grease as an insulation material can effectively reduce leakage current because the turn-to-turn grease layers serve as an effective insulation material. In sudden discharge tests, the time constant values of coils wound with N-grease, Si-based grease, and vacuum grease were drastically lower than those of the NI coil. In the over-current test at 1.5 Ic, the maximum voltages of N and Si coils were 3.8 times lower than that of the V coil, indicating that the thermal and electrical stabilities of N and Si coils were considerably enhanced. Moreover, the heat dissipating test results indicated that the peak temperature of the Si coil was lower than those of other coils because the Si-based grease acted as the most effective heat dissipater in the event of local hot spot generation in the coil. In conclusion, among the various types of grease tested in this study, Si-based grease may be the most effective turn-to-turn insulator for the development of highly stable second-generation (2G) HTS magnets with ameliorated charging-discharging delay of NI coil.

Prevention of Electrical Pitting on Rolling Bearings by Electrically Conductive Grease

Abstract: This paper describes a fundamental study of the preventive measures against electrical pitting on rolling bearings by using electrically conductive lubricating grease. In order to evaluate the ability to prevent the electrical pitting on rolling bearings of several types of grease into which conductive nanometer-scaled carbon particles, or "nanocarbon" particles, have been dispersed, bearing rotation tests were conducted when an electric current was turned on. It was concluded that the electrically conductive grease has the ability to prevent electrical pitting, or "ridge marks", if the electric current density at the points of rolling contact is lowered.

Yield Stress and Low-Temperature Start-Up Torque of Lubricating Greases

Abstract: A comprehensive study of the yield stress and start-up torque for six commonly used rolling bearing greases is presented. Both parameters were found to depend exponentially on temperature where the exponent changes below a low-temperature “break point.” This break point was found to be related to the pourpoint of the base oil, although the start-up torques of the greases were an order higher in magnitude than that of their corresponding bled oils. The start-up torque is mostly used to measure the low-temperature limit of a grease. It was found here that this temperature is much lower than the break point. The start-up torque criterion is measured using a particular bearing type and conditions. The low-temperature break point for the yield stress is a more universal grease parameter that gives useful information about the behavior of a grease at low temperatures and can be used as one of the guidelines for grease selection for low-temperature applications

Recycling of Waste Water Collected from Automobile Service Station

Abstract: This paper compares the effectiveness of chemical and physical methods in treating the wash water collected from automobile service stations. Wash water was collected from two service stations in the city of Bangalore, and the effluent was characterised for different parameters such as pH, turbidity, conductivity, total solids, oil and grease, COD (chemical oxygen demand), BOD (biological oxygen demand), chlorides, sulphate and total hardness. For chemical treatment, alum was used and locally available natural materials such as saw dust and sugarcane bagasse were used for physical treatment. Alum at different concentrations was agitated with the effluent for a prescribed contact period which led to the formation of flocs. The filtered samples were tested for COD and oil & grease. in the form of filter columns of three different heights. The percentage reduction in COD and oil and grease was correlated with the depth and type of filter media. A comparison of physical and chemical methods of treatment revealed that natural materials are effective in removing oil & grease and COD from the automobile effluent and hence provide a viable solution because of its eco-friendliness. From the experimental studies it is observed that in physical treatment, the sorption capacity of any material is dependent on its porosity, surface area and height of filter bed.

A review on graphite and hybrid nano-materials as lubricant additives

Abstract: The paper presents a review on use of nano-particles as lubricant additives. Nanoparticles have a strong potential to improve the lubrication property of grease when they are used as additives. Nano-grease has several advantages such as improved frictional behaviour, high load bearing capacity and reduced wear, as compared to base oil grease. Current advancements, limitations and challenges in use of nano-grease as a lubricant are discussed. Although, nanogrease has shown outstanding results, more research is required in this field for the commercialization of technology related to nano-grease.

Influence of Carbon Nanotubes on Conductive Capacity and Tribological Characteristics of Poly(ethylene Glycol-Ran-Propylene Glycol) Monobutyl Ether as Base Oil of Grease

Abstract: Carbon black (CB) and three kinds of carbon nanotubes (CNTs) including multiwalled CNTs (MWCNTs), carboxyl multiwalled CNTs (CMWCNTs), and single-walled CNTs (SWCNTs) were doped as conductive additives in poly(ethylene glycol-ran-propylene glycol) monobutyl ether (denoted as PAG) to afford conductive greases in the presence of polytetrafluoroethylene (PTFE) as the thickener and acetone as the polar dispersant. The effects of the conductive additives on the conductive capacity and tribological characteristics of the PAG grease were investigated, and the tribological action mechanisms of the conductive additives were analyzed in relation to worn surface analyses by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Results indicate that the SWCNTs can reduce the volume resistivity of the base grease by over 10,000 times. In the meantime, the CB and the three kinds of CNTs as conductive additives can improve the tribological characteristics of the base grease to some extent, and the CNTs are advantageous over the CB in improving the friction-reducing and antiwear abilities of the base grease. The reason lies in that CNTs with a small size and a large specific surface area can be easily adsorbed on sliding steel surfaces to form a surface protective film.

Influence of Grease on High-Pressure Gas Tightness by Metal-to-Metal Seals of Premium Threaded Connections

Abstract: A premium threaded connection for oil country tubular goods (OCTG) has a metal-to-metal seal portion to ensure its gas tightness under high pressure and high temperature. The metal surfaces are coated with grease and then integrated by rotary sliding. Despite several studies, the gas tightness mechanism of the metal-to-metal seal has not yet been clarified. In this study, as the first step to clarify the mechanism, we evaluated how grease affects the gas tightness by fundamental tests considering rotary sliding and grease degradation due to high temperature. Our results showed that grease is mandatory for the gas tightness of the metal-to-metal seals and the gas tightness is affected by both types of base oils and solid additives of grease. The seals coated with the grease composed of mineral oil had better gas tightness than those coated with that composed of plant oil, even after degradation due to high temperature. In addition, grease containing soft metal particles had better gas tightness than grease containing hard inorganic particles because the extended soft metal particles adhering to the rough parts of the seal surfaces reduced the size of the leakage paths.

Shield tail sealing grease and preparation method thereof

Abstract: The invention discloses shield tail sealing grease and a preparation method thereof. The shield tail sealing grease for tunnel construction tunneling equipment namely a shield tunneling machine consists of the following components: 15-30% of base oil, 10-20% of lubricating grease, 2-8% of a tackifier, 1-5% of an adhesion promoter, 5-10% of fibers, and 30-50% of a flour filler. The shield tail sealing grease is mainly formed by the combination of the base oil, the lubricating grease, the fibers and the filler, particularly the adhesion promoter is added, and the adhesion and the stability of a product are enhanced by the interaction force between the adhesion promoter and the surface of a base material; the product is stable in performance, avoids phenomena of segregation and sun crack when exposed in the air for a long time, does not generate sag and flow when encountering heat, and can still keep a relatively good pumping performance at a low temperature; and the shield tail sealing grease has relatively high impermeability, is convenient to operate and easy to pump, has excellent adhesion and certain corrosion resistance to metals, has outstanding water-stop and lubricating effects, and is easily biodegradable, environment-friendly and nontoxic.

Graphene based composite grease for elastohydrodynamic lubricated point contact

Abstract: This paper present tribological and dynamic evaluation of reduced graphene oxide (rGO) sheets as an additive in lithium grease. Highly dispersion mixing method is used to mix rGO in commercial lithium grease to prepare composite grease. Tribological contact under investigation is established by ball-on-disc configuration. Friction, noise and vibration responses are recorded for the point contact lubricated with composite grease and base lithium grease in rolling and sliding- induced-rolling conditions. Relative speed of disc with the speed of ball is varied in order to get sliding-induced-rolling contact. Observations are performed at different nornal loads and fixed speed in elastohydrodynamic lubrication (EHL) regime. Results show existence of an optimum concentration (0.4% w/w) of rGO in commercial lithium grease. Friction, noise and vibration are recorded minimum for concentration of 0.4% w/w of rGO in commercial lithium grease. Reduction in friction coefficient is recorded up to 30% and 20% for rolling contact and sliding-induced-rolling contact respectively at optimum concentration of rGO in lithium grease. The lamellar structure of rGO in base grease controls the lubricity of concentrated point contact.