The seizing of metal — plastic slide bearings in presence of hard abrasive particles Текст научной статьи по специальности «Физика»

106

Проблематика транспортных систем

Если V - абсолютная оценка погрешности измерения вероятности Рк , то можно предположить, что A < V- n , V = 2-b и b - велико.

Заключение

Использование градиентных методов и стохастических вычислительных устройств позволяет сократить время выполнения каждой итерации за счет избавления от «трудоемких» операций перемножения многоразрядных чисел. Увеличение скорости обработки контейнера и установки факта скрытой передачи сообщения позволит обрабатывать информацию, передаваемую по каналу связи в режиме реального времени, без накопления очереди.

Библиографический список

1. Provos N. Defending Against on Statistical Steganalysis // Proceeding of the 10 USENIX Security Symposium, 2001.

2. Provos N., Honeyman P. Detecting Steganographic Content on the Internet // Proceeding of the 10 USENIX Security Symposium, 2001.

3. Грибунин В. Г., Оков И. Н., Туринцев И. В. Цифровая стеганография. - М.: СОЛОН-Пресс, 2002.

4. Westfeld A., Pfitzmann A. Attacks on Steganographic Systems. Breaking the Steganographic Utilities EzStego, Jsteg, Steganos, and S-Tools - and Some Leassons Learned // Proceeding of the Workshop on Information Hiding, 1999.

5. Fridrich J., Goljian M. Practical steganalisis of digital image - state of the art, Security and Watermarking of Multimedia Contents, vol. SPIE-4675. - 2002.

6. Гурвич А. К. Неразрушающий контроль рельсов при их эксплуатации и ремонте. - М.: Трактат, 1983.

7. Поляков Б. Т. Введение в оптимизацию - М.: Наука, 1983.

8. Левин Б. Р. Теоретические основы статистической радиотехники. Кн.2 - М.: Сов. радио, 1968.

9. Урясьев С. П. Адаптивные алгоритмы стохастической оптимизации и теории игр. - М.: Наука, 1990.

УДК 531.8

A. Polak, K. Voinov

THE SEIZING OF METAL - PLASTIC SLIDE BEARINGS IN PRESENCE OF HARD ABRASIVE PARTICLES

The paper presents the results of seizing process tests of the tribologic pair: steel-polymer. Limits of seizing process of the pairs working in technical dry friction and in the presence of hard abrasive particles of quartz have been compared. Process of destruction of the sliding film and mechanism of hard abrasive particles action in seizing conditions has been presented.

2006/3

Proceedings of Petersburg Transport University

Проблематика транспортных систем

107

А. Полак, К. Н. Войнов

СХВАТЫВАНИЕ В ПРИСУТСТВИИ АБРАЗИВНЫХ ЧАСТИЦ ПОДШИПНИКОВ СКОЛЬЖЕНИЯ ТИПА МЕТАЛЛ-ПОЛИМЕР

Статья содержит результаты тестирования процесса заедания трибологической пары сталь-полимер. Проведено сравнение переделов процессов схватывания пар, работающих при сухом трении и в присутствии твердых абразивных частиц кварца. Показаны процессы механизма разрушения тонкого поверхностного слоя подшипника скольжения и действие твердых абразивных частиц кварца в условиях схватывания.

трибологическая пара, абразивные частицы, подшипник скольжения.

1 Introduction

Automotive vehicles and other machines often work in an atmosphere of heightened dustiness. Even during normal exploitation the air is never free from dust. The highest dustiness is present, among others, on various building sites, in mines (shaft and strip ones), in quarries and gravel pits. Terrain vehicles, tractors and farm machines, as well as military vehicles also work in considerably heightened dustiness conditions. High dustiness, most often occurring in exploitation practice, is also typical of industrial areas and large city agglomerations [3], [14].

The abrasive interaction mechanism in metal - metal pair has been known quite well. In case of plastic - metal interacting pair we can expect a different mechanism. It results from a considerable difference in hardness between plastic and metal and between plastic and the interacting particle and also from the fact that in the self-lubricating - steel slide bearing there occurs a phenomenon of material transfer [1], [2], [3], [4], [5], [6], [7],

During their operation the real sliding pairs are exposed to dustiness. In such conditions on the surfaces of the elements of a sliding pair there takes place abrasive wear. The effect of abrasive medium on the process of a metal sliding pair wear is generally known and ways of reducing the wear or protecting the pair against the effects of abrasive particles are also known [3], [8], [9], [10].

The process is different when one part of the pair is made of plastic the mechanical properties of which are usually poorer than those of metals [1], [2], [4], [10], [11], [12].

Such a pair can work in conditions close to seizing, even with no hard abrasive particles, and then it is the plastic part that is damaged. In the literature on the application of plastic materials as sliding elements there is no information on the behavior of a sliding pair in which one part is made of a plastic material and

ISSN 1815-588 X. Известия ПГУПС

2006/3

108 Проблематика транспортных систем

the whole node is used in abrasive medium, in extreme conditions close to seizing [5]; [13], [14], [15].

The aim of the research the results of which are presented below was to learn the influence of dustiness on the mechanism of material transfer and wear in slide bearings.

2 Test conditions

The friction pair was a model of a slide bearing: steel journal mates with plastic bearing bush (fig. 1). The pair was placed in friction test bench head [6].

Fig. 1. Bearing bush and journal

The materials used in tests were graphite modified polymers PA and PE (10% by weight) and carbon material (W-G).

The friction conditions for a single test were: at the same velocity (range: 0-4 m/s) the load (range: 0 to 4 MPa) was gradually increased. The load was increased after friction forces and temperature were stabilized. The test was continued till symptoms of seizing appeared, i.e. a rapid growth of friction force intensity. After ten minutes the test was stopped.

The abrasive in the form of quartz dust particles 2-35 mm in diameter (fig. 2) was continuously provided from a container in the bearing bush [6].

Fig. 2. Scanning electron SEI micrographs of the hard particles using to tests.

Magnified 500 x

2006/3

Proceedings of Petersburg Transport University

Проблематика транспортных систем

109

3 Results of tests

The curves characterizing the seizing points for the tested materials are given in Fig. 3. For comparison, Figs 4, 5 and 6 show the results of tests of seizing process for the same materials for cases with and without hard abrasive particles.

p, MPa

♦ PA

■ PE

▲ W-G

— W-G

■ - - PA

PE

v, m/s

Fig. 3. Seizing points PA, PE and carbon material W-G

Fig. 4. Seizing point of graphite modified polyamide in the presence of abrasive particles and

without

♦ W-G

■ W-G+QUARC

----WG

----W-G+QUARC

Fig. 5. Seizing point of carbon material W-G in the presence of abrasive particles and without

ISSN 1815-588 X. Известия ПГУПС

2006/3

110

Проблематика транспортных систем

v, m/s

Fig. 6. Seizing point of polyethylene PE in the presence of abrasive particles and without

An analysis of diagrams in Figs 3-6 shows that the presence of hard abrasive particles within the sliding pair, in which one element was made of plastic, affects the curves characterizing the seizing points in different ways. For polyamide (fig. 4) the hard abrasive particles in the bearing considerably lower the seizing point. Both the allowable pressure p and velocity v at which value seizing occurs as compared to the case of absence of hard abrasive particles are lower. The hard abrasive particles in the pair in which the bearing bush was made of carbon material (fig. 5) also lower the seizing point but the decrease is rather inconsiderable, and what is most important they do not much lower the allowable velocity of the journal. Unlike the other materials, carbon material is hard and brittle, porous and lead modified. So the penetration of hard abrasive particles into the transfer film is more complex.

In case of polyethylene (fig. 6), which is relatively soft, the curves characterizing the seizing point are almost identical in both cases - with or without hard abrasive particles. This proves that this material is almost insensitive to hard abrasive particles in the bearing. The abrasive particles penetrate into the bush material, so the mechanical component of friction is lowered. Moreover, in case of material flow larger abrasive particles or their clusters restrict the dislocation of the material plasticized layer (fig. 7).

When work in seizing conditions lasts longer than ten minutes, on the journal interacting with polyethylene there is formed a high transfer film (sometimes higher than 25|mm) (fig. 8). The structure of the film proves that it was formed due to the heat affecting the bush material. What is significant is the fact that the film does not combine with the bush surface. It can be explained by faster heat abstraction from the friction surface to rough the steel journal. This is so because of better thermal conduction of steel as compared with polymers and because of journal rotary motion (the friction zone covers subsequent parts of the journal surface, they are warmed by friction and then cooled when they leave the friction zone). The bush, on the other hand, interacts with the journal the same surface all the time. And thus the transfer film on the journal is cooled when it leaves the friction zone.

2006/3

Proceedings of Petersburg Transport University

Проблематика транспортных систем

111

Fig. 7. Scanning electron SEI micrographs of the polyethylene bush sliding surface interacting longer time in seizing conditions. Magnified 99 x

Fig. 8. Scanning electron SEI micrographs of the sliding surface of journal interacting with polyethylene bush longer time in seizing conditions. Magnified 49 x

While during the tests without abrasive particles the prevailing type of wear was adhesive wear, it could be assumed that in the presence of hard abrasive particles there is also abrasive wear despite the fact that abrasive particles are driven in the friction surface and placed flat surfaces on the outside (fig. 9, 10).

ISSN 1815-588 X. Известия ПГУПС

2006/3

112 Проблематика транспортных систем

Fig. 9. Scanning electron SEI micrographs of the polyamide bush sliding surface with embedded hard particles. The flats of particles are faced parallel to friction surface.

Magnified 1000 x

Fig. 10. Scanning electron SEI micrographs of the polyamide bush sliding surface under seizing conditions. Magnified 1030 x

Conclusions

Summing up, it should be stated that value changes of: seizing point are results of continuous processes connected with forming and destroying the sliding layer on both interacting surfaces. Distribution of abrasive particles in the sliding layers depends on the kind of the material and modifier. Yet, in all conditions a big amount of abrasive particles driven into the sliding layer surface

2006/3

Proceedings of Petersburg Transport University

Проблематика транспортных систем

113

places with their flat surfaces parallel to friction surfaces, without increasing the wear of the friction pair.

Hard abrasive particles, in the polluted atmosphere, do not cause processes hindering material transfer in pair steel - polymer. In certain conditions they are even elements which strengthen the sliding layer structure formed on both interacting surfaces and thus they play the role of the agent preventing these elements from destruction. The presence of hard abrasive particles makes the seizing process in plastic-steel pair faster, however.

References

1. Amelisko M.M., Snezkov V.V., Bachareva V.E., Rubin M.B., Koreckaja L.S.

Issledovanie struktury i svojstv poverchnosti trenija epoksidnogo ugleplastika. Trenie i iznos, 1984, TV.

2. Ashceofort N.W., Mermin N.D. Solid state physics. Holt 1976.

3. Baczewski K., Hebda M. Filtracja plynow eksploatacyjnych. Radom, MCNEMT 1991/1992.

4. Pielichowski J., Puszynski A. Wybrane dzialy z technologii chemicznej organicznej. Wyd. PK. Krakow 1987.

5. Povstugar V.I., Kodolov V.I., Michajlova S.S. Stroenie i svojstva poverchnosti polimernych materialov. Moskva, Chimija 1988.

6. Polak A. Przenoszenie materialu w lozysku slizgowym tworzywo sztuczne - stal. Monografia. Wyd. PK, Krakow 1998.

7. Briscoe B.J. Isolated Contact Stress Deformations of Polymers. Mat. konf. World Tribologi Congress. London 1997.

8. Polak A., Grzybek J., Pytko S. Friction processes in disc brake -brake pad couple, International Off-Highway & Powerplant Congress, March 2002, Las Vegas, NV, USA, , SAE Paper 2002-01-1484.

9. Polak A., Grzybek J. The mechanism of changes in the surface layer of grey cast iron automotive brake disc, 59th ABM Congress, Sao Paulo, Brasil, 2004.

10. Gudmand-Hoyer L., Bach A., Nielsen G., Morgen P. Tribological properties of automotive disc brakes with solid lubricants, Wear 232, 1999.

11. Eriksson M. Friction and contact phenomena of disc brakes related to squeal, Comprehensive Summaries of Uppsala Dissertations from the Faculty Of Science and Technology 537, Acta Universitatis Upsalensis, Uppsala 2002.

12. Bettge D., Starcevic J. Topographic properties of the contact zones of wear surfaces in disc brakes, Wear, 254, 2003.

13. Stachowiak G.W., Podsiadto P. Characterization and classification of wear particles and surfaces, Wear 249, 2001.

14. Dryzek J., Polak A. Subsurface zone studied by positron lifetime measurements. Tribology Letters 7 (1999).

15. Polak A. Mechanism of transfer film formation on metal surface. Applied Mechanics and Engineering, 1999, vol. 4.

УДК 337

ISSN 1815-588 X. Известия ПГУПС

2006/3