Wear of Metals

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This presentation is about wear of metals and its different types with the prevention methods

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Wear of Metals

  1. 1. 1
  2. 2. Wear of Metals 2
  3. 3. What is Metallic Wear? The deterioration of metal surfaces is known as the Metallic Wear. Wear is the result of erosion, abrasion, impact, metal-to-metal contact, oxidation, oxidation and corrosion or a corrosion, combination of these. 3
  4. 4. Introduction to Wear Plastic deformation at the interface often leads to wear, i.e., deformation induced wear. Wear can also be caused by chemical p y processes. There are many different kinds of wear mechanisms We have to analyze these wear mechanisms using mechanics, thermodynamics, etc. Tribology is a multi-disciplinary subject 4
  5. 5. Types of Wear: There are generally 12 Types of Metallic Wear: 1 Mild Adhesion 1. 2. Severe Adhesion 3. Abrasion 4. Erosion 4 E i 5. Polishing g 5
  6. 6. Types of Wear: 6 Contact Fatigue 6. 7. Corrosion 8. F tti Fretting Corrosion C i 9. Brinelling 10.Electro-Corrosion 11 Electrical Discharge 11. 12.Cavitation Damage 6
  7. 7. Mild Adhesion: Mild Adhesion: Generally, removal of surface film material due to adhesion and subsequent loosening during relative motion. Mild Adhesion transfer and loosening of surface films only only. 7
  8. 8. Example: 8
  9. 9. Other names Susceptible Machine Parts Normal/Common All Mild Adhesion - How to detect it : Unaided Eye U id d E Microscopically Mi i ll Smooth micro plateaus among Low rates of wear original grinding marks No damage Slight coloration due to films Deeper original grinding Slight coloration due to films marks still visible 9
  10. 10. Mild Adhesions Solutions: Prevention Mechanical None LUBRICANT None 10
  11. 11. Severe Adhesion: Severe Adhesion: Cold welding of metal surfaces due to intimate metal to metal contact. Mechanism: when two surfaces are brought together under loadload, asperities of the two surfaces adhere to each other. The conditions at the interface of these junctions are j similar to those of a cold weld. A strong bond is formed but without much interdiffusion of atoms and recrystallization as would occur i a h t weld. t lli ti ld in hot ld 11
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  13. 13. Detection: Severe Adhesion - How to detect it : Unaided Eye Microscopically Rough, torn, Rough torn melted or plastically Rough, irregular surface deformed metal, bands or streaks Metal from other surface adhering High temperature oxidation to other surface by spot tests or microprobe analysis High friction, high rates of wear Possible seizure 13
  14. 14. Conditions Promoting Wear: Conditions: 1. High loads, speeds and/or temperatures 2. Use of stainless steels or aluminum 3. Insufficient lubricant 4. Lack of anti-scuff additives 5. No break in 6. Abrasive wear interrupting film allowing adhesion 14
  15. 15. Severe Adhesion Solutions: 1 Reduce load, speed and temperature 1. 2. Improve oil cooling 3 Use compatible metals 3. 4. Apply surface coatings such as phosphating 5 Modify surface, such as ion implantation 5. surface LUBRICANT: Use more viscous oil to separate surfaces Use "extreme pressure" (anti-scuff) additives such as a sulfur-phosphorous or borate compounds sulfur phosphorous 15
  16. 16. Abrasion: Abrasion is the wearing of surfaces by rubbing, grinding, or other types of friction. It usually occurs due to metal-to metal contact. It y is a scraping, grinding wear that rubs away metal surfaces and can be caused by the scouring action of sand, gravel, slag, earth, and other gritty material. 16
  17. 17. Example: 17
  18. 18. Detection: Abrasion - How to detect it : Unaided Eye Microscopically Scratches or parallel furrows in the d ec o o o o , s direction of motion, similar to o Ce Clean furrows, bu s, c ps u ows, burrs, chips "sanding" High rates of wear Embedded abrasive particles In sliding bearings with soft overlay embedded particles b dd d i l 18
  19. 19. Conditions Promoting Wear: Conditions: 1. Hard particles contaminating oil 2. Insufficient metal hardness 3. Hard metal with rough surface against soft metal 19
  20. 20. Prevention: MECHANICAL Remove abrasive by improved air and oil filtering, clean oil handling practices, improved seals, flushing and frequent oil changes il h Minimize shot peening, beading, or sand blasting of surfaces because abrasives cannot be completely removed Increase hardness of metal surfaces LUBRICANT Use oil free of abrasive particles Use U more viscous oil i il 20
  21. 21. Erosion: Definition: Cutting of materials by hard particles in a high velocity fluid impinging on a surface Occurrence: This type of wear results from sharp particles impinging on a surface such as the cutting of materials by hard particles in a high velocity fluid impinging on a surface. This action is very much like that of sandblasting. 21
  22. 22. Mechanism: 22
  23. 23. Erosion - How to detect it: Unaided Eye Microscopically 1 Smooth, broad grooves in direction Short V-shaped furrows by of fluid flow scanning electron microscopy Matte texture, clean metal , Embedded hard particles p Similar to sandblasting 23
  24. 24. Example: 24
  25. 25. Erosion – Solutions: Prevention: MECHANICAL: Remove abrasive b i R b i by improved air and oil filt i d i d il filtering, clean oil l il handling practices, improved seals, flushing and frequent oil changes g Increase hardness of metal surfaces Reduce impact angle to less than 15 degrees LUBRICANT: Use oil free of abrasive particles Use U more viscous oil i il 25
  26. 26. Contact Fatigue: Definition: Metal removed by cracking and pitting, due to cyclic elastic stress during rolling and sliding sliding. Occurrence: This type of wear is produced when repeated sliding or rolling occurs over a track. The most common example is the action of a ball or roller bearing race. As the rolling element passes over a given spot on the raceway it is stressed as the raceway, load is applied and released. 26
  27. 27. Contact Fatigue - How to detect it: Detection: Unaided Eye Microscopically Combination of cracks and pits Cracks, pits and spalls with sharp edges p g Subsurface cracks by y metallographic cross-section. Numerous metal inclusions 27
  28. 28. Example: 28
  29. 29. Prevention: MECHANICAL: Reduce contact pressures and frequency of cyclic stress Use high quality vacuum melted steels Use less abusive surface finish LUBRICANT: Use clean, dry oil clean Use more viscous oil Use oil with higher pressure viscosity coefficient higher-pressure 29
  30. 30. Corrosion Wear: Corrosion wear is the gradual deterioration of unprotected metal surfaces, caused by the effects of the atmosphere, acids, gases, alkalies, etc. This type of wear creates pits and perforations and may eventually dissolve metal parts. 30
  31. 31. Mechanism: 31
  32. 32. Corrosion - How to detect it: Detection: Unaided Eye Microscopically Co oded e a su ace us , Corroded metal surface rust, Scale, films, pits containing l fil i i i Fe²O³H²O (hydrated iron oxide) is a corrosion products common iron corrosion product Dissolution of one phase in a 2- phase alloy 32
  33. 33. Example: 33
  34. 34. Corrosion – Solutions: Prevention MECHANICAL 1. 1 Use more corrosion resistant metal (not stainless) 2. Reduce operating temperature 3. Eliminate corrosive material LUBRICANT 1. Remove corrosive material such as too chemically active additive and contaminates 2. Use improved corrosion inhibitor 3. 3 Use fresh il U f h oil 34
  35. 35. Fretting: Definition: Wear between two solid surfaces experiencing oscillatory relative motion of l ill t l ti ti f low amplitude. lit d Occurrence: Fretting wear occurs where there is oscillatory motion with a small displacement ( ~1 micron) of 1 the contacting surfaces under load. Small wear particles are formed through the mechanism of adhesive wear 35
  36. 36. Mechanism: 36
  37. 37. Fretting - How to detect it Unaided Eye Microscopically Corroded stained surfaces Thick films of oxide and where damage on one metal. Red and black for surface is mirror image of steel mating surface Loose colored debris around real contact areas l t t Rouge (Fe?O?) colored films, debris, grease or oil 37 for steel
  38. 38. Example: 38
  39. 39. Fretting - Solutions Prevention MECHANICAL 1 Reduce or stop vibration by tighter fit or higher load 1. 2. Improve lubrication between surfaces by rougher (then honed) surface finish LUBRICANT 1 Use oil of lower viscosity 1. 2. Relubricate frequently 3 Use oxidation inhibitors in oil 3. 39
  40. 40. False Brinneling: Definition: Localized wear spots made by rolling elements on raceways due to limited rolling/repeated impact impact. Occurrence: Localized wear spots formed by rolling elements on raceways due to limited rolling/repeated impact. False Brinelling is typically characterized by indentations on the inner or outer raceway of a rolling element bearing. The indentation corresponded to the position of the rolling elements. l t 40
  41. 41. Example: 41
  42. 42. False Brinelling - Solutions Detection: Unaided Eye Microscopically Indentations on raceway Indentations on raceway Prevention MECHANICAL Reduce or eliminate impact Rotate bearings occasionally g y LUBRICANT Change viscosity Consider additives 42
  43. 43. Cavitation: Definition: Removal of metal by vapor cavity implosion in a cavitating liquid liquid. Occurrence: Cavitation happens, for example, in high-pressure pumps adjacent to the intake ports and on the blades of a ship's propellers When a sudden propellers. local reduction in fluid pressure occurs, a vapor cavity is formed When the vapor cavity later formed. collapses near a solid surface it produces a 43 mechanical shock.
  44. 44. Cavitation - How to detect it Detection: Unaided Eye Microscopically Clean frosted or rough Clean, metallic bright rough appearing metal pp g metal, p , pits Removal of softer phase from 2-phase metal 2 phase Deep, rough pits or grooves (graphite phase in cast iron is susceptible) 44
  45. 45. Cavitation - Solutions Prevention: MECHANICAL Use hard, tough metals, such as tool steel Reduce vibration, flow velocities and pressures Avoid restriction and obstructions to liquid flow LUBRICANT Avoid low vapor pressure, aerated, wet oils Use noncorrosive oils 45
  46. 46. Polishing: Definition: Continuous removal of surface films byy very fine abrasives. Polishing wear is characterized by very shiny, very smooth, mirror like metal surfaces. Fine abrasives wear away the surface films as they form and reform 46
  47. 47. Mechanism: 47
  48. 48. Polishing - How to detect it Detection: Unaided Eye Microscopically Featureless surface except High wear but a bright scratches at high mirror finish magnification by electron microscopy Wavy profile 48
  49. 49. Example: 49
  50. 50. Polishing - Solutions Prevention MECHANICAL None LUBRICANT Choose less chemically active additive Remove corrosive contaminant Remove abrasive 50
  51. 51. Electro-Corrosion Definition: Dissolution of a metal in an electrically conducive li id b l d i liquid by low amperage currents. t 51
  52. 52. Mechanism: 52
  53. 53. Electro corrosion Electro-corrosion - How to detect it Detection: Unaided Eye Microscopically Featureless surface except F l f High wear but a bright mirror scratches at high magnification finish by electron microscopy Corrosion pits, films, dissolution Local corroded areas of metals Black spots such as made by a small drop of acid p Corroded, worn metering edges 53
  54. 54. Example: 54
  55. 55. Electro corrosion Electro-corrosion – Solutions: Prevention MECHANICAL Decrease liquid velocity and velocity gradients Use corrosion-resistant metals Eliminate stray currents y Use nongalvanic couples LUBRICANT Decrease or increase electrical conductivity of lubricants or hydraulic fluids Highly compounded oils can act as electrolytes and be electrolytes, conductive. Phosphate ester hydraulic fluids are 55 conducive
  56. 56. Electrical Discharge Electrical Discharge: Removal of metal by high amperage electrical discharge or spark between two surfaces g p 56
  57. 57. Electrical Discharge - How to detect it Unaided Eye Microscopically Metal surface appears Pits, near edge of damage, etched. In thrust bearings, showing once molten state, sparks make tracks like an such as smooth bottoms, electrical engraver rounded particles, gas holes Rounded particles welded to surface near pits 57
  58. 58. Example: 58
  59. 59. Electrical Discharge - Solutions Prevention MECHANICAL Improve electrical insulation of bearings Degauss magnetic rotating parts Install brushes on shaft Improve machine grounding LUBRICANT Use of oil of higher electrical 59
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