10th ELGI Annual General Meeting, Dublin, 10-12 May 1998

Citation

Margaroni, D. (1998), "10th ELGI Annual General Meeting, Dublin, 10-12 May 1998", Industrial Lubrication and Tribology, Vol. 50 No. 5. https://doi.org/10.1108/ilt.1998.01850eab.003

10th ELGI Annual General Meeting, Dublin, 10-12 May 1998

10th ELGI Annual General Meeting, Dublin, 10-12 May 1998-06-11

Keywords: ELGI, Lubricants

The rate of growth of the European Lubricating Grease Institute (ELGI) has been impressive since its inception in May 1989. ELGI is an independent, self-governing institute, financed solely by members with the objective of promoting interest and development in grease and grease-related issues such as packaging. Of all classes of lubricants, for some reason grease has always commanded a degree of interest far beyond that which would be expected considering its market share and relative importance in the marketplace.This is no doubt due to the fact that the manufacture of grease is so dependent on process conditions, the properties of the final product being governed as much, if not more by, the manufacturing conditions rather than the composition and properties of the ingredients, unlike the majority of other lubricants. Even so, the often quoted "black art" tag applied to grease manufacture is strongly refuted by grease technologists; grease structure responding in a predictable way to variations in physical processing conditions in a situation where the process is under proper control. With some 200 delegates at this event, it is becoming more and more of a problem for the organisers to accommodate all guests, speakers, etc. on the same premises as well as providing a suitable conference venue. Some 23 countries were represented, making this a truly international event rather than merely a European one, with representatives from Canada, China, the USA, Saudi Arabia, South Africa in addition to those from most of the European countries.

Following a board meeting on the Sunday, the event started in earnest on 11 Monday with a general welcome from the current president, Terry Dicken of Global Lubricants. Then followed a short business meeting, during which new committee members were voted in and the treasurer's report was presented. The new and past chairmen along with Art Polishuk and Graham Gow gave a brief presentation on the first ten years of ELGI, outlining the various stages of the initial establishment of the institute, before the various presentations commenced.

What's the Po.in't?

Graham Gow (Axel Christiernsson IC)

This was a light-hearted presentation, although with serious messages, on what the author considered to be the current deplorable state of thinking in terms of grease development, quoting extracts from historical articles supposedly looking to the future, and highlighting how little had changed in the meantime. He made much reference to the functional word "Po" as crystallising the concept of lateral thinking, which provided opportunities rather than limitations. Quoting from the works of Edward de Bono, Po is an escape from the yes/no system, is a-rational not antirational, is a fantasy device, is a repatterning and insight tool, introduces the discontinuity function and is the laxative of language. He then applied the concept of such lateral thinking to grease. As examples the speaker quoted the use of mixtures of base fluids as opposed to a single component, including blends of paraffin and naphthenic oils to achieve the right solubility parameters for optimum structure control. Mineral oils could be mixed with synthetics, but more interestingly, the mixtures of fluids normally considered to be incompatible were considered, e.g. mineral oils and perfluoroethers, the inherent structure of the grease imparting a solid character which prevented the separation on incompatible fluid components.

He also queried the concept that grease was habitually regarded as a "thickened oil", whereas, in certain circumstances involving highly loaded contacts or combined rolling and sliding mechanisms, where the soap was the active lubricating ingredient, the grease would be more correctly described as a "thinned soap". Thus the sponge theory of grease lubrication, where separated oil is supposed to act as the lubricant, with the soap merely imparting the structure to the grease, is definitely questionable. If one now assumes that the function of the oil is to thin the soap lubricant, then there is no need for lubricity in the oil, or base fluid, since it is acting merely as a carrier for the solid lubricant. In the case of high temperature applications which would normally restrict the use of hydrocarbons, the diluent would ideally evaporate off, leaving the solid lubricant behind to perform its function. Even the use of a water carrier could be envisaged for use in environmentally sensitive situations.

The issue of grease additives was subjected to the same process of lateral thinking. Although grease additives are habitually oil-soluble, it was argued that additives of lower solubility, i.e. higher polarity, would compete more effectively with more migration and adhesion to the metal surface, since conventional oil-soluble additives of low polarity are displaced by the highly polar soap. Also, instead of adding substances to the grease, certain additives could work more effectively if they were not contained within the grease but outside it! A "striped" grease was envisaged where the anti-corrosion additives, being on the outside of the grease mass, would be immediately available for use.

A further fruitful field for lateral thinking is the area of grease manufacture, since the basic methodology has remained unchanged for some 20-30 years. Various modifications to the generally accepted procedures were suggested, such as homogenising and filtering during the middle of the process instead of at the end, this could improve control of fibre size along with yield and rheological properties.

The packaging of grease was then considered. The use of circular drums was challenged in view of the wasted space. Triangular cross-sectioned packages have been successfully used for other products, with consequent savings in space, resulting in more efficient vehicle loading and a significant reduction in journeys.

Finally, the testing of grease was described as "pathetic" in that we are still using test methods which are outdated, unreliable and completely and utterly irrelevant. The penetration test, in particular, was singled out as a prime example of the unwillingness of grease technologists to consider a more appropriate test. While its usefulness as a simple production control test was acknowledged, the test is completely inappropriate to assess the complex rheological behaviour of grease.

A brief review of calcium greases

Arthur T. Polishuk (Grease Technology)

The applicability of the traditional calcium soap grease is severely limited by its limited temperature range, the drop point being some 93ºC. Later developments involved the manufacture of anhydrous calcium greases with fatty acids instead of whole fats. In the absence of the glycerine normally liberated when whole fats, as opposed to fatty acids, are saponified, melting points increased to some 135ºC. Use of 12-hydroxystearic acid in place of animal fatty acids improved the melting point still further to some 148ºC for anhydrous calcium greases.

It had already been established that the addition of calcium acetate could impart extreme pressure properties to greases, and it was suggested that the acetate could be directly incorporated into the soap, with the di-valent Ca being a natural candidate for the soap base. Further investigation showed that when two dissimilar acids were attached to the di-valent calcium ion, (such as a long chain C₁₈ stearic acid, and a short chain C₂ acetic acid), they formed a soap with a dramatically increased dropping point of over 260ºC. Further work confirmed that the greater the proportion of acetate incorporated into the molecule, the greater the extreme pressure load capability (see Table III).

This grease had a major drawback, however, in that its behaviour was not reversible in that when the grease was heated, it would not revert back to its original consistency but would harden on cooling. With successive periods of heating, the grease would progressively harden to such an extent that it would cause seizure in a bearing. The greater the degree of incorporation of acetate, the greater this hardening characteristic. The grease was subsequently identified by x-ray diffraction studies as being a true "complex" grease rather than a mixed soap base grease in that both stearate and acetate were combined with an individual calcium ion.

However, further progress in the development of calcium greases resulted in the much more successful calcium sulphonate grease, with a dropping point of around 260ºC initially, but increasing to in excess of 300ºC in the case of a complex borate modified overbased complex calcium sulphonate grease. The grease performed well in humid and wet environments at high temperatures, and had good corrosion resistance, together with good extreme pressure and anti-wear characteristics, and represents the current state-of-the-art in calcium greases.

The compositions of the various greases were shown, and the manufacturing process of the borate over-based calcium complex grease was described in detail.

Combined experimental/numerical approach to generate insight in gear pitting

Per-Olof Larsson and Roland Larsson (Lulea University)

The authors described how the results of a combined experimental/numerical approach could be used to generate an insight into how different lubricant properties could be used as a design tool. It is essential that when designing a new mechanical system, the design of the lubrication system must also be considered in order to optimise operating efficiency and longevity. In order to do this, the various critical parameters, such as viscosity, pressure-viscosity coefficient, thermal properties, density, limiting shear stress, temperature-viscosity coefficient, thermal conductivity, specific heat, etc., of the potential lubricants must first be evaluated. The measurement of some of these properties and their influence were discussed. Tests such as the jumping ball apparatus and a modified split-Hopkinson pressure bar apparatus were described and their application in the measurement of limiting shear stress and the dilatation-pressure relationships of lubricants, including greases, were described. The assessment of true elastohydrodynamic (EHL) behaviour is still generally only applied to model problems, and has yet to find wide application in industry.

Three different analyses were performed, the first examining the transient EHL analysis of a spur gear using liquid lubricants based on a mineral oil, a polyalphaolefin (PAO) and a PAO-based grease. The second analysis showed the influence of the pressure-density relation on sub-surface stresses, the third duplicating the first spur gear analysis, but this time taking gear tooth flexibility into account. Figures showing how the load, mean velocity, curvature and amount of sliding are assumed to vary along the line of action were shown. Other figures shown included the variation in minimum film thickness along the line of action, the friction coefficient vs. position along the line of action, the pressure distribution and film thickness profile in pure rolling situations, the sub-surface stress, the loading on gear teeth when taking into account tooth flexibility, and finally the comparison between mineral and PAO oils in maximum contact pressure. The situation for greases was more complex due to the influence of thickener type, base oil type and thickener concentration, also due to the "memory" effect shown by greases. The general conclusions were:

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  PAO based Li-Ca complex greases had low EHL friction.

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  Mineral oil based Li-12-OH greases had high friction.

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  EHL frictions and y-values were higher for mineral based oils than for PAOs.

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  EHL frictions and y-values were lower for greases than for their base oils.

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  If base oil viscosity increases, the EHL friction and y-value decrease.

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  Low EHL friction and y-values, as in greases, results in high gear efficiencies.

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  High lubricant compressibility is an advantage in reducing surface fatigue, as in gear pitting.

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  Effects of soap thickener entering the contact zone need to be further investigated.

Role and progress of SAE AMS-M Aerospace Committee

Terry Dicken (Global Lubricants)

At the Budapest ELGI AGM in 1994, the major problem in aviation industry grease specifications was highlighted by representatives from KLM during the Grease Training Course. Some 102 different greases were currently being specified by different airlines, also there was a great deal of overlap between the various specifications, some of which were 20-30 years old, used in low severity applications, and were considerably dated in terms of grease technology. A similar situation had existed in the USA, but at the 1996 SAE meeting in San Diego, a new AMS-M committee was formed to investigate the standardisation of aviation greases, since the airline operators were anxious to try to resolve this situation. The committee had the support of all the major air-frame manufacturers, and four specifications were subsequently identified which would meet 95 per cent of the requirements. It was now the intention that these specifications would be finalised and put to ballot to become industry standards.

Environmental criteria for lubricating greases

Ulf Duus (Project Ren Smõrja in Gõteborg)

A national investigation into environmental issues in Sweden had revealed that, although positive steps had been taken in reducing emissions, less was known about products and their effects on the environment. Of particular concern were those products which were disseminated into the environment such as the lubricants associated with forestry harvesting.

In 1992, the Gothenburg Council started the Clean Lubrication Project in consultation with the Swedish National Chemicals Inspectorate to encourage the development of environmentally adapted hydraulic fluids. As a consequence, a new Swedish standard in November 1996 set new limits for acceptability criteria for hydraulic fluids, of which some 40,000 tonnes were estimated to leak from forestry machines such as excavators, trucks, cranes, dredgers, etc. Two standards were defined, the "A"-level which represented the ultimate "wish-list", and the "B" level ­ which represented the minimum standards which were considered acceptable. The same philosophy had now been directed towards lubricant grease products where the greater part was likely to end up in the environment. Although no technical specifications or guidelines were set, it was intended that the criteria should be looked on as a "health/environmental" bar.

Condition monitoring of grease lubricated rolling bearings

B.Williamson (Shell)

For bearing wear tests, the onset of wear can occur at any point in the test duration and, unless the wear process is catastrophic, will remain undetected until the end of the test rating. Bearing life can be related to lubricant performance in terms of the EHD film thickness generated in the inlet region of the EHD contact between the ball or roller and the bearing raceway.

A novel application of an electrical condition monitoring technique had been devised which was based on both capacitive and resistive methods, and which could predict lubricant and bearing failure before the end of the test rating. Normally, the major problem when endeavouring to predict grease performance is that greases possess unique rheological properties that change with changes in shear stress and shear rate in a non-linear manner, i.e. the grease is non-Newtonian. The changes in grease rheology can be both reversible and irreversible in nature.

The rolling element bearing can be considered as a composite electrical capacitor; the EHD lubricant film acting as the dielectric insulator. An apparatus, marketed commercially by SKF (Lubcheck Mk.II) has been devised which applies a small oscillating voltage across the bearing. Under conditions of satisfactory lubrication, i.e. a "thick" EHD film, there is no metallic contact between the rolling elements and the bearing raceways. Under these conditions, the lubricant film thickness is directly proportional to the magnitude of the output voltage. At the onset of bearing wear, there is occasional metallic contact since the bearing surface asperities are frequently touching when wear is taking place. At this point, the output voltage will begin to show variations.

The technique had been applied to monitor the grease lubricant performance in a standard SKF R2F bearing test machine using commercial NLGI Grade 3 grease.

In practice, using this technique during a test run, it was possible to establish that the first sign of grease/bearing distress occurred at 140hrs, although the temperature only began to rise from the set point of 130ºC at 160hrs, the bearing finally failing by seizure at 186hrs.

Mineral oil and the environment

Nicole Barral (Nynas Naphthenics)

The composition and manufacturing processes of the different categories of base oils were first presented, together with their regulatory status and labelling requirements. The various health effects, including acute toxicity, local effects, skin delipidising, sensitisation, chronic toxicity/long term effects, mutagenicity, carconigenicity and teratogenicity were then covered. The various methods of determining polycyclic aromatics (PCA) were discussed, including high pressure liquid chromatography with anthracene or naphthalene as a marker, gas chromatography/mass spectroscopy, IP 346, and individual analyses for specific compounds known to be dangerous e.g. benzo × pyrene.

The environmental aspects were then covered in more detail. The mobility of a substance is usually determined by its solubility in water. However, any potential risk relating to the mobility of a substance must also take into account the toxicity and the biodegradability. A substance with relatively low toxicity and high degradability will become rapidly diluted in the environment. At the same time, a substance which does not degrade readily and is toxic is much more harmful than one which is persistent but non-toxic.

The bioaccumulation of a substance reflects the increase in concentration in living beings with time. DDT and PCBs are familiar examples. A substance bioaccumulates when it dissolves more easily in fat than in water, with the result that it accumulates in the fatty tissue of the animal instead of being absorbed by the blood and disposed of by the liver and kidneys. Bioaccumulation is measured in log Pow (the logarithm of the distribution constant between ocatanol and water, with a high value indication a high potential to bioaccumulate. Substances found in mineral oils have a relatively high log Pow (3.9 × 6). The risk will then depend on the toxicity of the substance, i.e. the PAC content.

The ecotoxicity of a substance is concerned with the effects on aquatic organisms, soil organisms, flora and land animals. Other factors could include the effects on the ozone layer, greenhouse gas potential, effects on waste water processing, etc. In the case of mineral oils there is a clear relation between PAC and ecotoxicity. Ecotoxicity measurements usually involve examining the effects upon aquatic life. Studies have shown that well-refined oils do not have any toxic properties capable of posing a long-term threat to aquatic organisms and that LC50 values exceed 1,000mg/litre. Therefore, in spite of the relatively high Pow values, chronic toxicity studies have confirmed that well refined mineral oils do not represent a long-term danger to the aquatic environment.

In order to assess the overall environmental impact of a product it is necessary to perform a life-cycle analysis (LCA). In LCAs it is the system which is referred to, not the product, i.e. one studies not "a litre of process oil for rubber production", but "the amount of oil needed to achieve a certain plasticising effect in a certain amount of rubber". In order for an LCA to be meaningful, it should involve some kind of comparison between two different systems or between different parts of one and the same system, and in some numerical form which can be readily totalled. This involved some type of standardisation system, of which there are currently a number, although ideally there should be just one standardised approach. The Swedish Environmental Priority Strategies (EPS) in product design system is based on how much people in the OECD countries are prepared to pay in order to preserve a number of qualities in the environment, such as biodiversity, human health, the productive capacity of ecosystems, etc.

When evaluating the LCA of a Nynas oil, it was interesting to note that a major contributor to the total of the Environmental Load Units (ELU) was the hydrotreatment process. However, the alternative solvent refining process would result in a lower yield of product (0.5 as opposed to 0.8) and the generation of ecotoxic waste.

The total emissions involved in the oil production process were found to be as shown in Table IV.

This total of 0.6ELU/kg of oil is only relevant when viewed in relation to other products, i.e. alternative products for the same function and products with other functions relating to the same end product.

It must be stressed, however, the LCA determination is a relatively recent concept and the methods are gradually being refined.

Lubricant film development in ball and roller bearings

R.Karbacher (FAG)

To date, the evaluation of the lubricating condition in grease-lubricated rolling bearings has been exclusively based on base oil viscosity, which is assumed to be the same as with oil lubrication. The amount and type of thickener, the consistency, and the interactions with base oil and additives are not taken into account. The test rig can measure lubricating film thicknesses in bearings by varying and monitoring section height and electrical resistance. Results show that film thickness decreases with time, and also that any decrease below the value of the base oil depends on base oil viscosity and temperature. Lubricants deficiency in the rolling contact area, and thus a reduced film thickness, is only found if the temperature is too low. With identical thickener systems, there is a definite correlation between base oil viscosity and temperature. A further point was that different grease compositions do not behave in the same way in different bearing types (point and line contact); occasionally they may even display a contrary behaviour. The results concluded that test rig studies do necessarily allow conclusions to be drawn about the grease behaviour in certain bearing types.

Lubricating greases, correlation between composition and rheology

Philippe Vergne (Laboratoire de Mécanique des Contacts, Institut Européen de Tribologie, France)

Grease behaviour under working conditions is still not well understood. In this exercise, nine different greases were studied, both when freshly made and also after ageing at elevated temperature. Variables were the base oil viscosity, and the thickener nature and concentration. Three different procedures were used to observe the greases, i.e. stress sweeps to determine the yield stress and stationary flow properties, creep tests to quantify the transient behaviour in terms of elastic moduli and critical strain, and oscillatory experiments to evaluate the "linear viscoelastic" region. The conclusions may be summarised as shown in Table V.

A novel extreme pressure/antiwear additive

Dr James P. King, Desilube Technology, Inc.

With the reduction in use of chlorinated and heavy organometallic EP additives, there is need for a new generation of environmentally acceptable, biodegradable, non-hazardous, high performance, light coloured extreme pressure additives. A novel inorganic sulphur-phosphorus extreme pressure additive system (ISPEPA) has been developed by Desilube which would appear to fulfil many of the requirements, and is based on a two-component, synergistic blend of phosphate and a thiosulphate formed as a stable suspension in base fluid. The additive also meets the USDA H1 requirements for incidental food contact applications.

The additive has been evaluated by the four-ball EP and wear test, in addition to corrosion-resisting properties, in a variety of greases with various thickener-fluid combinations. Thickeners included lithium soap, lithium complex, aluminium complex, organoclay and polyurea. Base fluids included conventional mineral oil, white mineral oil, vegetable oils, trimethylol propane trioleate ester and its vegetable oil blends, polyalphaolefin. Performance of the additive was improved in many cases by the presence of molybdenum disulphide, which appeared to have a synergistic effect. In general, the EP performance was significantly improved by the presence of the additive, although the use of additional anti-wear agents was required in certain cases to achieve satisfactory anti-wear performance.

Packaging working group

Mike Morris (Castrol)

This report summarised the activities of the ELGI Packaging Working Group. Grease packaging was being re-evaluated from the viewpoint of legislative requirements, customer acceptance, operational convenience, etc. Conical pails were being recommended for fill weights of up to 25kg for ease of storage of empty containers. Fill quantities of 180, 50, 5 and 1kg were being recommended. Cartridge capacities for the nominal 400g cartridges may be increased due to problems in filling when using the lower-density greases. Other work would include the standardisation of dimensions, lid design, implications of and compatibility with the Manual Handling Regulations, etc. with a view to completing the programme before the 1999 AGM.

Test Methods Working Group

J.Pohlen (Axel Christiernsson IC)

A summary of the activities of this group will appear in a future issue of Eurogrease.

Rheology Working Group

L.Hamnelid (Axel Christiernsson IC)

Two meetings had been held so far. More aggressive marketing of the group was required in order to stimulate interest. Current topics included round robin testing, the setting up of a training course, and the compilation of a database.

ISO ­ protocol for test method approval

Paula Watkins (ISO/TC 28 Secretariat)

The International Standards Organisation (ISO) is a worldwide federation of national standards bodies representing 127 countries. Each member body is the "most representative of standardisation in its country", e.g. the BSI in the UK. The ISO covers standardisation in all fields apart from electrical and electronic engineering, and brings together the interests of producers, users, governments and the scientific community, in the preparation of International Standards, some 11,258 to date. These standards cover guides, test methods, classifications, specifications and technical reports. The work of ISO is carried out by various Technical Committees (TCs) and Working Groups (WGs), the number of groups totalling some 2,850 and involving 30,000 individuals. The central Secretariat is based in Geneva, where staff can give advice on ISO procedures, draft ISO standards are edited and ISO standards are published. Each TC or WG has a secretariat, consisting of the Chairperson and the Secretary, and which is allocated to a national body. For petroleum products and lubricants, the relevant TC is ISO/TC 28, which progresses the standardisation of methods of measurement, sampling and test, terminology and specifications for petroleum, petroleum products, and non-petroleum based lubricants and hydraulic fluids. Industry participates by inputting its views on draft standards through national committees that mirror the ISO TCs and SCs. Standards are developed through a balloting process which consist of a number of stages, and are reviewed at intervals of not more than five years.

Balloting stages:

(1) Preliminary work.

(2) New work item proposal.

(3) Committee draft.

(4) Draft international standard.

(5) Final draft international standard.

(6) Published international standard.

(7) Review after a maximum of five years:

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  confirmed ­ again then reviewed after a maximum of five years;

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  withdrawn;

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  revised ­ committee draft, etc.

There is a parallel process which includes CEN, the European Standards organisation.

IP ­ protocol for test method approval

John Cliff (Axel Christiernsson IC)

The Institute of Petroleum (IP) has a very close relationship with the BSI, the British Standards Technical Committee responsible for Petroleum Test Methods (PTI/13) being fully integrated into the IP's Test Methods Standardisation Committee, with the IP currently providing the secretariat. IP provides the majority of the technical input into the development of CEN and ISO standards. In addition, some 92 IP standards have been accorded the status of British Standard and these BS 2000 parts are published by the IP. The IP also has strong links with the American Society for Testing and Materials (ASTM), and some 80 joint IP/ASTM standards have been published, these forming the basis of International Standards. The IP also has direct links with other European Test Methods groups, including the Association de Français de Normalisation (AFNOR) and the Deutsche Institute Normung (DIN).

Standard Methods are arranged in numerical order with a figure after the solidus indicating the year in which the method was adopted or last reviewed. Proposed Methods are methods that are published for information and comment and are given a pair of designation letters following the words IP proposed. The designation letters are given in the sequence AA and the methods arranged in alphabetical order, with a figure after the solidus indicating the year in which the proposed method was adopted. Proposed methods are retained for a period of three years unless the Standardisation Committee gives an extension.

ISO Methods are dual numbered with the IP numbering above. They are arranged in IP numbering sequence.

Withdrawal of a method includes a notice of withdrawal section. Two years notice of withdrawal is given prior to the withdrawal date.

New methods (which can originate from industry or panels, etc.) and major revisions to existing methods are normally undertaken by the appropriate "owning panel" with the approval of its parent sub-committee.

The new or revised method is then submitted to the Method Evaluation sub-committees Mathematical Analysis or Precision Evaluation for review.

A Test Methods Ballot form is used for method evaluation and can be used by other panels or sub-committees. Full documentary evidence of the approval process is maintained and retained at the IP.

ASTM ­ protocol for test method approval

David Slack (ASTM)

Subcommittee G (lubricating greases) currently has responsibility for 34 test methods, distributed among seven task groups, i.e. chemicals and general laboratory tests, consistency and rheology, physical tests, functional tests ­ tribology, functional tests ­ temperature, functional tests ­ contamination, and research techniques. When the need for the development or revision of a grease test method is identified, the item is assigned to a task group who then prepare a draft of the method for ballot.

Ballots are conducted at subcommittee and main committee level, the final method being published after all negatives have been resolved. All negatives are considered at subcommittee or main committee level, the voter being required to supply a clear explanation for a negative vote. Possible resolutions of negative votes are persuasive (two-thirds of voting members), withdrawn outright, withdrawn with editorial change, not persuasive, previously considered, or not related. International input on grease issues to the international Standards Organisation is provided by subcommittee G through the American Petroleum Institute and the American Standards Institute.

Optimising efficiency indices of constant-velocity joints with low-friction lubricants

Jens Richter (Volkswagen AG)

Earlier development had been successful in improving service life, reducing weight and optimising noise and vibration response in constant velocity (CV) joints. However, power losses in driveshafts/joints amount to some 1.3 per cent, and VW's target was now to reduce such losses by 0.3 per cent by the use of low-friction greases, with no reduction in the other performance parameters. Assuming that power losses are converted directly into heat energy, two types of joint (fixed joint and sliding joint) were lubricated with various lubricants and run under deflected conditions until a steady-state temperature was reached, whereupon the deflection angle and applied torque were suddenly and simultaneously reduced to zero. Since there would be no power loss under these conditions, the only heat that the joint radiates at this point is from the energy stored during the previous running phase with joint deflection. Statistical test planning and assessment test software were use to quantify the improvements in the efficiency index of the various test lubricants. Whilst the low-friction greases under test always displayed an improvement of at least 0.3 per cent over the reference lubricant, there were major individual discrepancies according to joint type. The efficiency improvements were then quantified under two different sets of running conditions, one using high deflection angles at low rotational speeds, the other using low deflection angles at high rotational speeds. Whilst low friction greases always showed a benefit in the first case, there was no benefit in the second case at torque levels of 400Nm or higher.

Evaluation of industrial bearing grease performance

Andy Kemble (NSK-RHP European Technology Centre)

The speaker described the various rigs involved used to test grease performance under working conditions.

For electric motors, which are commonly fitted with a single row deep groove radial ball bearing, the most important requirements are long life, ability to withstand prolonged high working temperatures, low drag torque and low noise. By using a general purpose 6305 test rig, the performances of a number of different grease types were evaluated. Large variations in working life were evident, the worst being a mineral oil/calcium complex grease (63 hours at 140ºC, the best being a synthetic fluid/polyurea grease (3,699 hours at 160ºC).

For furnace conveyor systems, the RHP Self-Lube bearings are advocated. The test rig used for this purpose evaluated the high temperature performance of the grease rather than that of the bearing. In this case, it was found that the higher degree of loading resulted in a significant change in the relative high temperature performances of the various greases.

In high-speed machine tools, angular contact ball bearings, arranged together in sets, are normally employed. Since oil/air lubrication is normally employed which can present practical problems in terms of drainage in certain applications. Greases can therefore be used in these circumstances, and the test rig devised in this instance reflected the load/temperature/rotational speeds encountered. It was difficult to determine the performances of the greases since their behaviour became unpredictable as they neared their ultimate speed capability. However, the PAO/ester-lithium special/complex greases gave the highest bearing speeds for the lowest operating temperatures.

An evaluation of the relationship between the low temperature torque, the apparent viscosity and the low temperature cone penetration of lubricating greases

Anuj Mistry and Ron Bradbury (DERA Fuels and Lubricants Centre)

In the low temperature testing of lubricating greases, at ­54ºC, a linear relationship was shown to exist between the results for low temperature torque (IP 186), apparent viscosity (ASTM D1092) and low temperature cone penetration (NFT 60-171). Five different greases were used to provide an extended range of base oils and thickeners in the experiment. The results for the low temperature torque and the apparent viscosity were found to be within the stated precision of the test methods. The Low Temperature Cone Penetration Test had an overall mean repeatability ± 11 per cent. The investigation has highlighted the relative significance of each of the test methods and their uses in reviewing or producing grease specifications. It has also revealed the importance of setting meaningful specification limits for starting torque values for the IP 186 test.

David Margaroni