Effects of Flow Properties of Lithium Soap Greases on Bearing Torque

This study describes the influence of flow properties of lithium soap greases on torque of small ball bearings. Three types of greases with different worked penetration were tested in this study. Their rheological properties are revealed by a cone plate type rheometer. Shear stresses under various shear rates are fitted with the Herschel-Bulkley equation. In addition, viscoelastic behaviors of the greases are measured by small amplitude oscillatory shear. The crossover stress that means the shear stress at G’=G” is obtained for the greases. Then, the bearing torque when three types of greases are used as a lubricant is measured. As the results, the grease with higher crossover stress shows the lower bearing torque regardless of that it has larger apparent viscosity. On the other hand, the grease with lower crossover stress shows the higher bearing torque regardless of that it has lower apparent viscosity. These results imply that the channeling state appears in the grease with higher crossover stress while the churning state appears in the grease with lower crossover stress.

MODIFICATION OF THE RECOVERED LOW- GRADE FAT TO FORMULATE ECO-FRIENDLY LUBRICANT GREASE

This study presents utilization of the inedible by-product fat of the municipal massacres to formulate bio-based lubricant grease. Inedible animal fat of acceptable quality has been recovered through the wet rendering process. The recovered fat was sterilized and bleached using 200 ppm chlorine dioxide solutions. The acceptable saponification and iodine values of the fat emphasize that it can be used in the chemical industry as an oleochemical resource. The fat was fractionalized into two fractions; stearic and oleic. The lithium soap of the stearic fraction was employed as a thickener and the oleic fraction has been adapted for use as base oil, depending on its proportion of combination compared to the thickener. It was found that the ideal composition of the formulated bio-grease is 15-20 % thickener to 85-80 % base oil. The performance testing shows that the formulated grease has NGLI ranges between 2- 3. The grease can be utilized as a lubricant agent in machinery and gears with an acceptable lubricating performance.

OPTIMIZATION OF LITHIUM SOAP-BASED GREASE TESTING METHODOLOGY BASED ON MEASUREMENTS REPEATABILITY

The purpose of the paper is to investigate the rheological properties of a lithium soap-based grease, using a Brookfield viscometer. An optimized methodology was proposed, applicable to the tested grease, which takes into account the possibility of reducing the testing time by analyzing the degree of measurements repeatability. Finally, the thermal variation of the rheological parameters (yield stress and viscosity) was obtained, in the temperature range 10...75 oC. The main result of the paper is the reducing of the testing time from 6 hours to 3 hours for one temperature, with the same precision of measurements, according to economical effects.

Lubrication properties of modified lard and rapeseed oil greases with sodium and lithium thickeners

Purpose – The purpose of this paper is to conduct research on the possibility of improving the tribological and utilization properties of lard and rapeseed oil bio-based greases by mixing it with ethanol and selection of thickener and modification with special biological additives. Design/methodology/approach – Rapeseed oil- and lard-based greases with sodium and lithium soap thickeners were mixed with either water or ethanol and modified with a special biological anti-wear additive. Tribological properties of modified lubricants evaluated on a four-ball machine. Findings – Rapeseed oil- and lard-based greases suspended in ethanol and modified with bio-additive have the same wear resistance as the industrial non-biological lubrication grease and much higher wear resistance as bio-based reference grease. The tribological efficiency of the additives is higher in greases of rapeseed oil and less efficient in lard-based greases. Oxidation and wear tests show that investigated bio-based greases have comparatively stable tribological properties also after their aging. Modified greases have sufficient consistence according penetration measurements and high thermal resistance according drop-point temperature measurements. All produced experimental greases pass within the category of the easily degradable materials. Originality/value – The greases mixed with the ethanol make possible to form more homogeneous and stable grease mixture. Modified bio-based greases have significantly higher wear resistance as bio-based reference grease, their lubrication properties are stable also after the aging and are categorized as easily degradable materials.

Influence of Grease Characteristics on Gear Friction Loss

In a previous study, we analyzed the mechanical loss factors of a small-sized geared motor comprising an induction motor and a parallel gear reducer. The load dependent loss is mainly caused by gear mesh friction, which is related to grease characteristics. This study investigates how the grease characteristics influence the friction loss of the gear mesh. The important grease characteristics are the cone penetration, kinematic viscosity, type of base oil, and type of thickener. The loss of gear mesh friction was evaluated in terms of the average friction coefficient between the gear teeth and was found to be unrelated to the cone penetration and kinematic viscosity of the base oil. The average friction coefficient of grease combined with lithium soap/poly urea and mineral base oil was 0.09–0.11; when combined with aluminum complex soap and synthetic base oil, the friction coefficient reduced to 0.07–0.08.

Grease thixotropy: evaluation of grease microstructure change due to shear and relaxation

Purpose – The thixotropy of lubricating grease thickened with lithium 12-hydroxystearate with mineral base oil was investigated. The thixotropy has a significant influence on the flow resistance and pressure drop in the structural components of lubrication systems, which is of major importance as today the latter are being centralized and automated. The paper aims to discuss these issues. Design/methodology/approach – Rheometer studies on thixotropy were carried out and the grease microstructure was visualized using atomic force microscopy (AFM). Total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was used to study the physicochemical interactions which indicate the disintegration and recovery of the grease microstructure. Findings – A qualitative assessment of the physicochemical interactions between lithium soap floccules was made and a theory of the self-ordering effect of lithium 12-hydroxystearate associated molecules during shearing and their aggregation and flocculation during relaxation has been proposed. Originality/value – Because of the complexity of the disintegration and recovery of the lubricating grease thickener microstructure, there is still limited physical understanding of the mechanism of this process. Therefore, the present research was undertaken to identify the phenomena involved.

Bearing torque characteristics of lithium soap greases with some synthetic base oils

This article describes the influence of rheological properties on the bearing torque characteristics of the lithium soap greases with five types of base oils. The greases used had different yield stress depending on the base oils even with the same thickener concentration. Measurement of bearing torque was conducted for a deep-groove radial ball bearing by using a bearing test apparatus. The bearings filled with greases initially exhibited high torque but showed gradual decrease in the torque with prolonged rotation, where the greases with higher yield stress showed larger normalized torque decrease. Observation of bearing after the rotation revealed a tendency that the greases with larger normalized torque decrease had been pushed aside in the raceway by channeling. This implied that the greases with higher yield stress tended to show channeling. On the other hand, the greases with lower yield stress circulated within the bearing by churning and showed smaller normalized torque decrease. These behaviors were explained in terms of the yield stress of the greases and the shear stress to entrain the greases into the contacts. Observation of grease structure was made with atomic force microscopy showed that the greases whose thickener network structure was distributed more densely had higher yield stress.