ΕΛΛΗΝΙΚΗ ΔΗΜΟΚΡΑΤΙΑ Ανώτατο Εκπαιδευτικό Ίδρυμα Πειραιά Τεχνολογικού Τομέα. Ξενόγλωσση Τεχνική Ορολογία. Ενότητα: An Introduction to Tribology

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1 ΕΛΛΗΝΙΚΗ ΔΗΜΟΚΡΑΤΙΑ Ανώτατο Εκπαιδευτικό Ίδρυμα Πειραιά Τεχνολογικού Τομέα Ξενόγλωσση Τεχνική Ορολογία Ενότητα: An Introduction to Tribology Παναγιώτης Τσατσαρός Τμήμα Μηχανολόγων Μηχανικών ΤΕ

2 Άδειες Χρήσης Το παρόν εκπαιδευτικό υλικό υπόκειται σε άδειες χρήσης Creative Commons. Για εκπαιδευτικό υλικό, όπως εικόνες, που υπόκειται σε άλλου τύπου άδειας χρήσης, η άδεια χρήσης αναφέρεται ρητώς. Χρηματοδότηση Το παρόν εκπαιδευτικό υλικό έχει αναπτυχθεί στα πλαίσια του εκπαιδευτικού έργου του διδάσκοντα. Το έργο «Ανοικτά Ακαδημαϊκά Μαθήματα στο Ανώτατο Εκπαιδευτικό Ίδρυμα Πειραιά Τεχνολογικού Τομέα» έχει χρηματοδοτήσει μόνο την αναδιαμόρφωση του εκπαιδευτικού υλικού. Το έργο υλοποιείται στο πλαίσιο του Επιχειρησιακού Προγράμματος «Εκπαίδευση και Δια Βίου Μάθηση» και συγχρηματοδοτείται από την Ευρωπαϊκή Ένωση (Ευρωπαϊκό Κοινωνικό Ταμείο) και από εθνικούς πόρους.

3 1. Σκοποί ενότητας Περιεχόμενα ενότητας An Introduction to Tribology Non-lubricated surfaces: Solid lubricants: Thin-film or boundary lubrication: Thick - Film lubrication: Practice and Exercise Exercise A: Open questions Exercise B: Question forming Exercise C: Matching terms and definitions... 6

4 1. Σκοποί ενότητας The aims of this unit are to: Provide authentic text and vocabulary specific to the needs of students of Mechanical Engineering Encourage students to combine their knowledge of English with their technical knowledge Enable students to find out facts about a topic Guide students into seeking specific information Help students match terms and definitions 2. Περιεχόμενα ενότητας Contents of the unit: Non-lubricated surfaces Solid lubricants Thin-film boundary lubrication Thick-film lubrication

5 3. An Introduction to Tribology 3.1 Non-lubricated surfaces: The simple "laws of friction" relating to two surfaces sliding together are usually stated in the form that frictional resistance is proportional to the normal force between the surfaces and is independent of the area of contact. This is approximately true in some cases, but obviously not so when the surfaces are very rough or very smooth. When two smooth metallic surfaces slide over each other, they rub on the high spots generating heat and causing welding to occur locally (stick) followed by rupture of the welds (slip). In the extreme case, "seizing" will occur. Rubbing produces wear, and to prevent wear a lubricant is used to keep the two load bearing surfaces apart. 3.2 Solid lubricants: Substances such as graphite and molybdenum disulphide are used as lubricants in powder form or in suspension in a liquid. Certain plastics such as PTFE and PTCFE have a low coefficient of friction and can be used in "dry" bearings. 3.3 Thin-film or boundary lubrication: An extremely small amount of lubricant is found to reduce friction. The lubricant spreads out in a microscopically thin film and does not entirely prevent welding of high spots and "stick - slip" rubbing motion. This type of lubrication occurs in slides under conditions where a thicker film of oil would leak away. Greases with extreme pressure additives are useful in such cases. 3.4 Thick - Film lubrication: Hydrodynamic lubrication A plain journal at rest in its bearing will sink through oil film until contact is made with the bearing, except for a boundary layer of lubricant. When the shaft rotates, it "pumps" the lubricant round forming a "wedge" of oil between the shaft and its bearing. The pressure in the wedge of oil supports the load on the shaft. 4. Practice and Exercise 4.1 Exercise A: Open questions Answer the following questions 1. What do the laws of friction maintain? 2. When is there an exception to the above statement? 3. What is the general purpose of a lubricant? 4. What is thin-film lubrication used for? 5. How does thick-film lubrication work?

6 4.2 Exercise B: Question forming Make questions to which the following are answers 1. To the normal force between the surfaces. 2. They generate heat and cause welding to occur. 3. Rupture of the welds. 4. By using a lubricant. 5. To keep the two load bearing surfaces apart. 6. In powder form or in suspension in a liquid. 7. An extremely small amount. 8. Under conditions where a thicker film of oil would leak away. 4.3 Exercise C: Matching terms and definitions Find the terms in the text which correspond to the following definitions 1. numerically related 2. not smooth or level, uneven 3. to move along in contact with some surface 4. to apply pressure and friction to 5. to join by applying heat 6. to happen, to take place 7. fracture, breaking 8. fastening together 9. to carry, to support 10. hanging 11. part of a machine in which another-part revolves, slides etc. 12. limit, border 13. object that fits into a narrow space