EXPERIMENTAL STUDIES CONCERNING DAMAGE OF TWO LUBRICANT GREASES IN SEVERE WORKING CONDITIONS

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1 45 EXPERIMENTAL STUDIES CONCERNING DAMAGE OF TWO LUBRICANT GREASES IN SEVERE WORKING CONDITIONS Nicolae DIACONU Department of Mechanical Engineering, University Dunarea de Jos of Galati, Romania ABSTRACT In this paper certain results regarding behavior of two greases used in lubrication of rolling and rolling-sliding tribosystems are presented. For this aim, a specialised stand has been used. The experimental tests were done for different loading, sliding levels and temperatures in the range of C. The damage degree of lubrication greases was investigated by IR spectrometry. A correlation between testing conditions and changes in IR spectra has been established. The obtained data can be used both in establishing the damage level of lubrication capacity and in monitoring the lubrication system in order to optimization the lubrication process of studied trybosystems. The structural changes in the superficial layer after friction process, carried out by X-ray diffractometry. A relationship between structural changes and lubricating capacity of greases has been established. KEYWORDS: Tribomodel, greases, infrared spectrometry. 1. INTRODUCTION Studying lubrication in severe working conditions has been taken into account starting from actual problems met at the main reducing gear of the material distribution machine working on blast furnaces in metallurgical plants. The air pressure at the furnace throat is about 2.1 bars but temperature may reach 800 o C. It is well known that lubricant viscosity decreases as the temperature is increasing. Lubricant catalogues do not contain recommendations for special applications as high temperature. Fig. 1. The model of tribosystem. This is the cause of the future investigation, this paper presenting the design solution and the results obtained in laboratory, on a specialised testing machine. The tribomodel will keep the same materials for the triboelements (fig. 1) and environment but there will be tested several lubricant in order to compare the results and to give a better solution for the actual tribosystem. 2. THE TESTING MACHINE The testing machine was designed for using a rolling or rolling+sliding tribomodel (figures 2 and 3). This type of tribosystem is characterised by three groups of parameters: external, internal and interacting ones and wear behaviour will be similar if the testing conditions applied to the model, are close to the actual ones. The superficial layers of the materials in contact are characterised by microgeometry, hardness, structure, chemical composition, purity and stress state. During the running-in process and in functioning there are taking place changes within the superficial layers and inevitably, complex wear processes having overlapping components. For the analysed case, thermal wear is predominant because of the environment temperature and also to high loads and sliding component of motion. The high flash temperatures on the asperities ' peaks induce thermo-plastic deformations, softening and even local melting, the result being undesirable changes of tribological behaviour of lubricant and tribolayers. The author was monitoring the greases ' spectrum before and after the work, this evolution revealing changes in

circulating grease; 15- gears transmission. Fig. 3. The working zone 8-up-roller; 10-limiting spring; 12-heating system; 13-ball bearings. lubricant and tribolayers.

2 46 THE ANNALS OF UNIVERSITY DUNĂREA DE JOS OF GALAŢI Fig. 2. The testing machine 1-engine; 2-rigid coupling; 3-reducing gear; 4-rigid coupling; 5-torque transducer; 6-shafts; 7-thermal insulated system; 9-rigid coupling; 11-belt transmission; 14-engine for circulating grease; 15- gears transmission. Fig. 3. The working zone 8-up-roller; 10-limiting spring; 12-heating system; 13-ball bearings. lubricant and tribolayers. For these analysis it was used the spectrophotometer SPECORD IR 75 with double fascicle. The testing block is formed by a wear testing tribometer for rolling and rolling+sliding motion, including a simple mechanism with engine, belt and gear transmissions, the transducer for friction torque measuring (Hottinger Society- Germany), and a device for fixing the tested rollers. The rollers are mounted on two shafts with ball bearings. The advantages of this solution are the simplicity of the design and the safety during exploitation. 3. EXPERIMENTAL RESULTS There were tested two types of grease: a multifunctional grease UM185Li2EP and the grade UMLiCaPb2 (M). There were plotted spectrograms for the initial state of the grease and after testing at elevated temperature. Spectrograms obtained for the initial (nontested) grease (figures 4 and 5)allow selecting two main absorption bands situated around values cm -1 and cm -1 for the grade UMLiCaPb2 (M) and around values cm -1 and cm -1 for the grade UM185Li2EP. Therefore, in the greases structure there were identified components of alkaline types, methylene group (CH 2 ) and methyl group (CH 3 ) but also complex components of type: CH 3 -(CH) n -COOH, CH 3 (CH2) n - COOMe + or even link of type C=O. The greases were tested in the following conditions: normal load on the roller G= kn, n 1 =750 rotations per minute for the drive roller, working temperature in the testing box ~100 C, testing time ~240 minutes. The pairs of roller were chosen to have pure rolling regime and rolling-sliding regime (40%). The spectrograms obtained for already tested greases (figures 6, 7, 8, 9) clearly pointed out changes of their structures as compared to the initial ones. Fig. 4. The initial spectrum for the grease UM170LiCaPb2 (M).

3 47 Fig. 5. The initial spectrum for the grease UM185Li2EP. Fig. 6. Spectrum after pure rolling for the grease UM185Li2EP. Fig. 7. Spectrum after pure rolling for the grease UM170 LiCaPb2 (M).

4 48 THE ANNALS OF UNIVERSITY DUNĂREA DE JOS OF GALAŢI Fig. 8. Spectrum after rolling + sliding 40% for the grease UM185Li2EP. Fig. 9. Spectrum after rolling +sliding 40% for the grease UM170LiCaPb2 (M). For the majority of spectrograms, one may notice an increase of absorption intensities, displacements left - right of the absorption bands, ramification and supplementary occurrence of some sharpen peaks, demonstrating the unbinding and rebinding of some chemical links reflecting the changes that will affect the lubricating properties, especially in a negative way. 4. CONCLUSIONS The main cause of grease lubricant degradation is the thermal oxidation as pointed out by changes in infraredspectra. The infrared spectrometry may be successfully used for characterising the lubricant capacity of the greases functioning in severe and normal conditions. The infrared spectrum of grease is determined by the nature, number and position of the atoms, so any change in atom position, link and number will change the initial spectrum, obtained for the non-used (genuine) grease. The concentration of the compounds characterising the methylene group (CH 2 ) and the methyl group (CH 3 ) have recorded important variations, pointed out by the help of the author s methodology. This study could give some solution for monitoring and increasing the lubrication capacity of industrial greases.

5 49 REFERENCES 1. Crudu I., 1985, On the concept of tribosystem and a tribomodelling criterion, 4-eme Congres Europeen de Tribologie, Ecully France. 2. Crudu, I., 2000, Bazele proiectării în organe de maşini, Editura Alma, Galaţi. 3. Diaconu N., 1998, Instalaţie experimentală pentru studiul comportării lubrifianţilor la temperaturi ridicate în atmosferă controlată, A 9-a Conferinţă privind elastohidrodinamica lubrificaţiei şi tracţiunea, VAREHD 9, Suceava, Romania. 4. Diaconu N., 1998, Stand for studying the lubricants behaviour of high temperature and controlled environment, 50 Years of Universitary Life in Galati, Annals of University "Dunărea de Jos", Fascicle VIII, Tribology, Galati. 5. Diaconu N., Crudu I., Gheorghieş C., 2000, Studiul degradării capacităţii de ungere a unor unsori utilizate în diverse medii de lucru, Sesiunea de comunicări ştiinţifice Realizări şi perspective în Metalurgie şi Stiinţa materialelor, Universitatea Dunărea de Jos din Galaţi, Editura Stiinţifică F.M.R. 6. Diaconu N., Gheorghieş C., Crudu I., 2000, Degradarea capacităţii de ungere a unor unsori utilizate în medii agresive de lucru, A 10-a Conferinţă de lubrificaţie şi tracţiune EHD VAREHD 10, Suceava, Romania, ACTA TRIBOLOGICA. 7. Diaconu N., Gheorghieş C., Crudu I., 2001, Aprecierea capacităţii de ungere a unor unsori utilizând spectrometria de infraroşu, Conferinţa Stiinţifică Internaţională TMCR 2001, vol. 2, Chişinău, Moldova. 8. Rush, E.R., 1997, A Review of the More Common Standard Grease Tests in Use Today, Lubricating Engineering no Pugh B., 1973, Friction and wear, London, Newnes-Butterworth. 10. Bhushan B., Gupta B.K., 1997, Handbook of Tribology Materials, Coatings and Surface Treatments, Krieger Publishing Company Malabor, Florida, SUA. 11. Szymanski A. Hermann F., Infrared band handbook, Plenum Press, New York, Avram M. et al., 1966, Spectroscopia în infraroşu-aplicaţii în chimia organică, Editura Tehnică., Bucureşti. 13. Grigoraţ P., 1993, Lubrifianţi plastici-fabricare şi utilizare, S.C.Tipocart Braşovia S.A., Braşov.

The 3 rd International Conference on

The 3 rd International Conference on DIAGNOSIS AND PREDICTION IN MECHANICAL ENGINEERING SYSTEMS DIPRE 12 LUBRICATING REGIME AN IMPORTANT CRITERION FOR EVALUATING AND PREDICTING THE EFFICIENT FUNCTIONING OF THE SLIDING AND SLIDING/ROLLING