Wear Mechanism SHIVAJI CHOUDHURY

Wear

Wear is the undesirable removal of solids from a sliding or rolling component.

Wear analysis

In analyzing a wear problem in a machine, it is necessary to determine the kind of wear that occurred. Analysis requires microscopic examination of the worn area and a close look at the used lubricant. Wear is generally proportional to the applied load and the amount of sliding.

Types of wear :1.Adhesive Wear 2.Abrasive Wear3.Erosion Wear 4.Polishing Wear5.Contact fatigue 6.Corrosive wear

7.Electro-Corrosive wear 8.Fretting wear 9.Electrical discharge wear 10.Cavitation damage 11.False brinelling

1.Adhesive Wear Adhesive Wear the removal of material due to adhesion between surfaces. Mild adhesion is the removal of surface films, such as oxides, at a low rate. Severe adhesion the removal of metal due to tearing, breaking, and melting of metallic junctions. This leads to scuffing or galling of the surfaces and even seizure.

1.1.Adhesive Wear -PreventionMECHANICAL Reduce load, speed and temperature Improve oil coolingUse compatible metals Apply surface coatings such as phosphating

LUBRICANT Use more viscous oil to separate surfaces Use "extreme pressure" (anti-scuff) additives such as a sulfur-phosphorous or borate compounds

2.Abrasive Wear Abrasive Wear the cutting of furrows on a surface by hard particles, (for example, sand particles between contact surfaces, or hard asperities on an opposing surface).Cause: Hard particles contaminating oil Hard metal with rough surface against soft. metal

2.1.Abrasive Wear-PreventionMECHANICALRemove abrasive by improved air and oil filtering, clean oil handling practices, improved seals, flushing and frequent oil changesMinimize shot peening, beading, or sand blasting of surfaces because abrasives cannot be completely removedIncrease hardness of metal surfaces LUBRICANT Use oil free of abrasive particles Use more viscous oil

3.Erosion Wear

Erosive Wear the cutting of furrows on a surface by hard particles contained in a fluid traveling at high velocity.

3.1.Erosion Wear -PreventionMECHANICAL Remove abrasive by improved air and oil filtering, clean oil handling practices, improved seals, flushing and frequent oil changesReduce impact angle to less than 15 degreesIncrease hardness of metal surfaces LUBRICANT Use oil free of abrasive Particles Use more viscous oil

4.Polishing Wear Polishing Wear the continuous removal of surface films, laid down via a chemical reaction from an additive in oil or by very fine hard particles in the lubricant, and so on.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.

4.1.Polishing Wear -PreventionMECHANICAL noneLUBRICANTChoose less chemically active additive Remove corrosive contaminant Remove abrasive

5.Contact fatigue

Contact Fatigue the cracking, pitting, and spalling of a surface in sequence due to cyclic stresses in a contact. Contact fatigue is most common in rolling element bearings, gear teeth, and cams.

5.1.Contact fatigue- PreventionMECHANICAL Reduce contact pressures and frequency of cyclic stress.Use high quality vacuum melted steels. Use less abusive surface finish LUBRICANTUse clean, dry oil. Use more viscous oil Use oil with higher-pressure viscosity coefficient

6.Corrosive wear Corrosive Wear the removal of corrosion products from a surface by motion, such as the rubbing off of rust.cause :water contamination most common cause

6.1.Corrosive wear-Prevention MECHANICAL Use more corrosion resistant metal (not stainless) Reduce operating temperatureEliminate corrosive material LUBRICANT Remove corrosive material such as too chemically active additive and contaminates Use improved corrosion inhibitor Use fresh oil

7.Electro-Corrosive wear

Electro-Corrosive Wear the removal of metal by dissolution in a corrosive liquid with the aid of electric currents. One source of currents is streaming potential from high velocity fluids. The oil serves as the electrolyte.

7.1.Electro-Corrosive wear-preventionMECHANICAL Decrease liquid velocity and velocity gradients Use corrosion-resistant metalsEliminate stray currents

LUBRICANTDecrease or increase electrical conductivity of lubricants or hydraulic fluids

8.Fretting wear

Fretting Wear localized wear of lubricated surfaces due to reciprocating sliding of extremely low amplitude because of vibration.

8.1.Fretting wear -PreventionMECHANICALReduce or stop vibration by tighter fit or higher load . Improve lubrication between surfaces by rougher (then honed) surface finish LUBRICANT Use oil of lower viscosityRelubricate frequently Use oxidation inhibitors in oil

9.Electrical discharge wear

Electrical Discharge Wear the removal of molten metal from surfaces due to electrical sparks between them. High static voltages are sometimes generated by large rotating machinery and these are relieved by sparking to regions of lower potential.

9.1.Electrical discharge wear-PreventionMECHANICALImprove electrical insulation of bearings Degauss magnetic rotating partsInstall brushes on shaft Improve machine grounding

LUBRICANT Use of oil of higher electrical conductivity

10.Cavitation damage

Cavitation Damage the removal of material due to cracking and pitting caused by high energy implosions of vacuous cavities in a cavitating liquid. Liquids cavitate when suddenly subjected to low pressures. Removal of metal by vapor cavity implosion in a cavitating liquid.

10.1.Cavitation damage-PreventionMECHANICAL Use hard, tough metals, such as tool steel Reduce vibration, flow velocities and pressuresAvoid restriction and obstructions to liquid flow LUBRICANT Avoid low vapor pressure, aerated, wet oils Use noncorrosive oils

11.False Brinelling False Brinelling localized wear in lubricated rolling element bearings due to slight rocking motion of rollers against raceways.

11.1.False Brinelling- PreventionMECHANICAL Reduce or eliminate impact Rotate bearings occasionally LUBRICANT Change viscosity

Microscopic Observation(Wear debris analysis) (a) Rubbing wear, (b) cutting wear, (c) fatigue wear, (d) scuffing wear, (e) corrosive wear, (f) abrasive wear.

Bearing damage classifications: ISO 15243

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