Mixtures of vegetable oils and di‐2‐ethylhexyl‐sebacate as lubricants

Lubricants based on vegetable oils are growing in popularity in various applications. Environmentally friendly, vegetable oils and their derivatives constitute alternatives to mineral‐based lubricants. Soybean oil, sunflower oil and rapeseed oil have better viscosity indices than mineral oils and even some synthetic oils, are biodegradable and have low production costs. However, vegetable oils have disadvantages, such as poor thermo‐oxidative stability due to the carbon–carbon double bonds and poor low‐temperature properties, which limit their use as lubricant base stocks. This study describes new base‐stock oils obtained from mixture of vegetable oils and di‐2‐ethylhexyl‐sebacate synthetic oil, which become lubricants when additives are introduced. These mixtures offer a large range of kinematic viscosities, while their pour points are under −33°C and their flash points over 240°C. The copper strip corrosion test result is 1a. The diameters of wear scars measured under four‐ball testing (40dyn) are less than 1mm. A differential scanning calorimetry study and a thermo‐gravimetric study under a nitrogen atmosphere for the mixed oils are reported. In the former study two‐endothermic processes were observed between −15°C and −50°C. In the thermo‐gravimetric analysis curve the weight loss is specific for each vegetable and synthetic oil component. From these studies a higher thermal stability was observed for vegetable oils than for ester oils, and it was concluded that the mixtures of vegetable and synthetic oils of diester type are physically homogeneous mixtures. The low production cost of lubricants based on vegetable oils makes them attractive alternatives for mineral oil based lubricants. Overall the mixtures of vegetable and ester oils can be competitive base oils for environmentally friendly lubricants. Copyright © 2006 John Wiley & Sons, Ltd.     

Performance comparisons of synthetic and mineral oil crankcase lubricant base stocks

The physical and performance characteristics of representative synthetic base stocks are compared with those of mineral oils. Comparisons of the base stocks alone and as fully formulated crankcase lubricants are presented. Bench test results and physical properties of unformulated synthetic and mineral oil base stocks are compared. The volatility characteristics of synthetic base stocks are superior to typical mineral oil base stocks. All the synthetic base stocks displayed greater viscosity indices than did mineral oils. Bench tests designed to measure thermal and oxidative stabilities are used to compare synthetic with mineral oil base stocks. Although synthetics appeared no more resistant to oxidation than did mineral oils, fewer sediments, deposits and fluid viscosity increases were observed with synthetic base stocks. No one type of synthetic base oil showed a distinct advantage in these evaluations. Fully formulated mineral oil-based lubricants are compared with commonly used synthetic-based lubricants containing identical additive treatments. The synthetic lubricants showed superior engine cleanliness, and resistance to viscosity increased in these tests, but were directionally less effective in wear prevention than mineral oil-based lubricants. Proper formulation or addition of an antiwear supplement overcame this deficiency. These comparisons demonstrated that synthetic base stocks are available with a wide range of physical properties. Available synthetic base stocks offer performance advantages at an increased cost over mineral oils, but proper formulation of the synthetic lubricant is necessary to ensure totally acceptable lubricant performance.     

Synthetic Lubricants in Hydrodynamic Journal Bearings: Experimental Results

Synthetic lubricants and additives have seen many major improvements in recent years. However, very little is known about the performance peculiarities of these new lubricants in actual machines. To fill this gap, a new full-scale hydro-dynamic journal bearing test rig has been constructed to evaluate the behavior of conventional and new bearing designs, synthetic lubricants and variations in operating parameters. This test rig’s bearing has diameter 180 mm with measuring capabilities including continuous film thickness and film pressure as well as temperature. The new machine was used to compare a number of synthetic lubricants to mineral based lubricants, finding that performance of the synthetic lubricants was superior to their mineral based counterparts of much higher viscosity grade. These tests showed that high viscosity index (VI) synthetic lubricants had higher viscosity in the region of maximum pressure and lower viscosity elsewhere in the bearing than similar mineral based lubricants. This reduction in viscosity in low pressure zones was found to produce a measurable reduction in friction and power loss in the bearing system. This paper provides comparative performance results of several formulations of current and future turbine oils from measurements of losses, oil film thickness, and temperature under a range of operating parameters. Lubricants tested include ISO VG68 and VG32 mineral based turbine oils (VG68 and VG32), ISO VG32 synthetic ester based oil (SE32), two ISO VG22 synthetic ester based oils (SE22 and SV22), and ISO VG15 synthetic ester based oil (SE15). It was found that SE32 and VG68 provided similar performance at lower speeds while SV22 provided similar performance to VG68 at the highest speed. Likewise, SE22 and SV22 provided similar performance to VG32 at low speeds while SE15 provided similar performance to VG32 at medium to higher speeds. Generally, the results demonstrate the potential for replacing mineral based lubricants with high performance synthetic lubricants of significantly lower viscosity grade without sacrificing bearing safety.     

Influence of load and lubricants on EHD film thickness and rolling-contact fatigue lives of AISI 52100 steel balls

This work has evaluated the influence of load and type of lubricant on the thickness of the elastohydrodynamic (EHD) film and the rolling-contact fatigue lives of AISI 52100 steel balls. The lubricants studied have various viscosities and included two mineral oils and five synthetic oils from three families. Firstly, the central film thickness was determined in order to predict the lubrication regime. The stress—number of cycles fatigue curves were then calculated by means of Weibull plots, and the fatigue mechanism was evaluated. The test machine used for the analysis was a Seta-Shell 1980 four-ball EP lubricant tester. The 12.7 mm diameter test balls were made from a single batch of carbon-vacuum-deoxidised AISI 52100 steel with hardness RC65. Elastohydrodynamic film thickness estimation was carried out using pressure—viscosity coefficients (a). In this study, to calculate (X), a new interferometric technique, ultrathin film interferometry, was employed to measure the film thickness. A practical method was developed for evaluating EHD, mixed film, and solid lubrication processes. Micrographic mapping and energy dispersive spectroscopy (EDS) were used to analyse the rolling track of the test balls.     

Vegetable oil derivatives: environment‐friendly lubricants and fuels

A critical appraisal is made of the applications of vegetable oils, the fatty esters complex and synthetic esters as rapidly biodegradable and non‐toxic lubricants and fuels in the developed countries of America, Europe and Asia. The criteria employed for assessing the toxicity and biodegradability of the various fluids and limits set by various state and regional organizations are reviewed. The properties of vegetable oils, fatty esters, chemically modified esters and synthetic esters relevant for performance as lubricants in various applications such as hydraulic oils, refrigeration oils, chainsaw lubricants, metalworking fluids, engine oils, two‐stroke oils, mould release lubricants, greases, gear and transmission oils vis‐à‐vis conventional mineral oils and greases for corresponding applications are compared. The advantages, such as high lubricity, viscosity–temperature relationship, low lubricant consumption, energy efficiency combined with public health, safety and environmental contamination, more than offset the disadvantages of initial costs in most of these applications. It has been suggested that modified and stabilized oils of wasteland and forest origin and other non‐edible oils and their chemically modified derivatives can be produced at relatively cheaper cost than similar oils marketed in the developed world and can be introduced in India with immense environmental and performance benefits, particularly in applications involving high environmental contamination safety and public health. When blended with highly refined diesel fuels, methyl esters can work as highly efficient environment‐friendly fuels particularly for applications in passenger transport, light commercial vehicles and generators. Copyright © 2006 John Wiley & Sons, Ltd.     

Metalworking emulsions from industrial vegetable oils

In the present work, an attempt has been made to develop the indigenous formulation for metalworking lubricants by replacing mineral oils partially with non‐edible industrial oils like rapeseed and karanja oil. Metalworking formulations consist of vegetable oil, mineral oil, an emulsifier and commercial additives for better performance. Non‐edible vegetable oils such as karanja and rapeseeds are renewable, biodegradable and cheaper than synthetic fluids. The constituent vegetable oils and mineral oils were evaluated for physico‐chemical characteristics and blended as per the saponification value and viscosity requirements of the reference oils. The so formulated oils are taken as 5% oil‐in‐water emulsion and tested for lubricity, load bearing capacity, particle size distribution, wear test, weld load test and plate‐out test. Performance of all formulated oils was compared with that of the reference oils, and optimized to meet the market requirements. Copyright © 2008 John Wiley & Sons, Ltd.     

Biodegradability of lubricant base stocks and fully formulated products

Increasing awareness of the environmental impact of consumer and industrial products has produced a demand for lubricants that biodegrade. There is a number of biodegradation tests that can be used on lubricants, although not all are always appropriate, as this paper explains. The CEC test is among the best known and is in use for both conventional and synthetic oils. There will, in future, be a greater movement to biodegradable oils in Europe, perhaps extending to all oils.     

Influence of Glycol Molecular Configuration on Friction

Boundary or mixed friction studies on a wide range of synthetic lubricants and mineral oils demonstrated that ethylene glycol gave higher static friction and much lower kinetic friction than did other lubricants tested. To investigate this unusual properly of ethylene glycol, poly-hydroxy alcohols of various molecular configurations were evaluated. The results indicate, that kinetic friction increases and static friction decreases as either the number of atoms between primary hydroxyl groups increases or primary hydroxyl groups are replaced with secondary hydroxyl groups. Surface coatings containing oxidation products of the glycols are believed to be responsible for the observed friction characteristics.     

A potential biodegradable lubricant from castor biodiesel esters

Worldwide, 12 million tonnes per year of lubricants are disposed of in the environment through leakages, exhausted gas, incorrect disposal, water–oil emulsions and so on. Some are resistant to biodegradation, representing an environmental threat. One solution to modify this situation is the replacement of mineral oils by biodegradable synthetic lubricants. Esters, whose chemical structures are similar to natural triglycerides, are excellent substitutes for mineral oils. Castor oil contains around 90% ricinoleic acid, and as a result, castor oil has a higher viscosity and a lower viscosity index, compared with other vegetable oils. This work was based on the production of biodegradable lubricant base fluids from castor biodiesel esters, using various chemical catalysts to yield products with interesting properties, such as high viscosity index and good oxidation stability, compared with mineral oils. This route to lubricants is safer, more economical and more efficient. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthetics versus vegetable oils: Applications,options, and performance

Environmental concerns have brought forward vegetable oils as alternatives to more expensive synthetic lubricant base stocks, in moderate operating conditions. The contents of various acids, such as oleic and linoleum, can be changed by selective breeding to produce more desirable lubricating properties and less oxidation vulnerability. Different tests are needed for such lubricants, and the Baader test has been modified to show the ageing stability of rapeseed oil raffinate, TMP trioleate, dioctyl adipate, and HOSO. Such oils can also be modified with additive packages.     

Gear Lubrication in Inert Gas Atmospheres

An investigation was made of the effect of inert gas atmospheres on the gear load-carrying capacity of lubricants. The experiments were performed in two types of gear test machines, using case-hardened AMS-6260 steel test gears. It was found that two mineral oils (a solvent-extracted turbine oil base stock and a USP grade white mineral oil), as well as the same oils fortified with different extreme-pressure additives, all exhibited a decided increase in load-carrying capacity when the gears were operated in an atmosphere of nitrogen or argon instead of air. On the other hand, the response of synthetic lubricants was not found to be necessarily similar. In fact, only one of the six synthetic fluids tested showed any significant increase in load-carrying capacity when the gears were operated in a nitrogen atmosphere.     

Use of lubricants during cold rolling of aluminium

Natural and synthetic lubricants specially formulated for cold rolling of aluminium were evaluated in terms of their ability to lower mill loads. The use of additives was also studied. Roll separating forces and roll torques were monitored. No significant differences between natural and synthetic oils were observed. The ability to maintain lubricant action was found to be lowest when synthetic esters were present, either in the base oil or as an additive.     

Development and testing of nano particulate lubricant for worm gear application

Bio-degradable lubricants are an attractive alternative for the mineral based and synthetic based lubricants. Bio-degradable lubricants are environmental-friendly and non-toxic. The present study deals with the tribological investigation of bio-degradable nano lubricants for worm gear applications. Nano additives like CuO and TiO₂ were used. Bio-degradable oils like palm oil and sunflower oil were used as base oils. The nano lubricants were prepared by adding two nano additives and two bio-degradable oils each of 0.1 % and 0.2 % weight composition. Friction and wear characteristics were tested on pin-on-disc tribometer under varying load conditions. Extreme pressure tests for nano lubricants were carried out using four ball tester. The wear surface obtained was analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy. From the tests conducted, it was found that the addition of nano additives in biodegradable oils reduced the friction co-efficient and wear rate to a considerable extent.

     

Fuel economy of multigrade gear lubricants

A light‐duty axle efficiency test for evaluating gear lubricants for their fuel economy performance is described. Data collected for an internal reference oil highlight the repeatability of the test with different axles. Comparisons between single‐grade SAE 90 and multigrade gear lubricants were made under a variety of pinion torques and speeds to simulate highway and city driving conditions. Lubricant rheology and its importance in maintaining film strength for adequate bearing and gear lubrication for optimum torque efficiency and axle temperature are discussed.     

Precision instrument oils

Precision instrument mechanisms require highly specialized oils. These stringent requirements limit the choice of lubricants to synthetic types only. In this paper the physico-chemical and peformance characteristics of a watch oil developed by the authors have been discussed to show how it meets the basic requirements of watch oils, and compares favourably with widely accepted watch oils. Where the test methods and test limits are at variance with the specification IS: 1088–1975 for watch and clock oils, commentary is given and suitable recommendations for modifying IS: 1088–1975 are made.     

Ester base stocks

Natural esters contained in animal fats such as sperm oil, lard oil or in vegetable oils like rapeseed and castor oil have been the main lubricants from antiquity until the early 19th century. By 1890, petroleum oils had almost completely displaced natural oils. However, fatty products were still used as ‘oiliness agents’ to reduce friction and wear in bearings and gears lubricated by petroleum products. About 1937, Dr Herman Zorn of IG Farben Industrie in Germany began an intensive search for lubricants having the lubricating properties of natural oils, such as castor oil, while eliminating the tendency of these natural products to gel at low temperatures and to form gums and lacquers when used in engine operation. This paper describes the properties, types and applications of esters, as a main group of synthetic lubricants developed during the last four decades.     

Assessing friction characteristics of liquid lubricants

A reduction in friction in tribological contacts will lead to reduced energy requirements. It is therefore important to be able to measure the frictional characteristics of various liquid lubricants. Current laboratory tests measure friction, but the test rigs invariably induce wear between the mating contacts. A new test rig, the wire‐on‐capstan rig, is presented which measures friction without inducing wear between the wire and the rotating capstan. All seven lubricants tested (three without additives and four proprietary hydraulic oils) exhibit a reducing coefficient of friction with increasing temperature. Temperatures ranged from 25°C to 100°C. The mineral‐based oil showed the lowest friction coefficient and the three synthetic ester based oils produced the highest friction coefficient over the complete temperature range. Future testing will extend the range of operating conditions and product types. Copyright © 2006 John Wiley & Sons, Ltd.     

Influence of lubricant on gear failures — test methods and application to gearboxes in practice

Base oil type, oil viscosity, and additive type and content have a strong influence on typical gear failures. As it is not possible to quantify the influence of a lubricant on load‐carrying capacity simply from a knowledge of the physical or chemical oil data, many test methods have been developed for the evaluation of mechanical—technological lubricant properties. Simple low‐cost bench test methods often show poor correlation with practice. From both experience and systematic investigation, it can be seen that testing of gear lubricants can be performed adequately only in gear test rigs using specified test gear geometry. The standard FZG back‐to‐back gear test rig has been developed over many years and improved for different types of gear failure simulation. The standard FZG oil test A/8.3/90 is widely used for the evaluation of the scuffing properties of industrial gear oils. Automotive gear oils of GL4 level can be tested in the step test A10/16.6R/90, and axle oils of GL5 level in the shock test S‐A10/16.6R/90. For slow‐speed regimes, the C/0.05/90:120/12 wear test can be used. The influence of lubricants on the micropitting performance of gears can be evaluated in the GF‐C/8.3/90 micropitting test. Different pitting tests are available, as single‐stage (PT‐C/9:10/90) or load spectrum (PT‐C/LLS:HLS/90) tests. The aim of this paper is to describe the influence of the lubricant on the different failure modes in gears, how to quantify this effect in adequate test methods, and how to introduce the results of such tests as determining values of the lubricant into load‐carrying capacity rating methods.     

Characterization of the Lubricating Action of Oils Under Boundary Lubrication Conditions

Polyalphaolefin (PAO) and polypropylene glycol (PPG)-based lubricants as well as mineral oils were tested to characterize their wear reducing performance under boundary lubrication conditions, using the ISO 7148 test method, which was originally developed for the characterization of bearing materials.

This test method has practical value with respect to developing lubricants for use in sliding contacts, such as occur in worm gear drives. It is found that the wear reducing action of PAO-based lubricants is significantly better than that of mineral oils. PPG fluids perform equally well or slightly better than PA Os. Provided that viscosities are in line and additives are compatible, contamination of PAOs with mineral oils has no or only marginal effect on wear reduction.     

Synthetic lubricating greases for the food industry

The requirements of lubricating greases in the deep-freezing industries, that lubricants do not undergo degradation of their lubricating properties, and the need for non-aromatic and non-toxic/non-carcinogenic lubricants in food production, are discussed. Experimental data on the applicability of synthetic oils as bases for synthetic greases, are presented.