Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1103301
16 | March - April 2019 | www . machinerylubrication.com is very slow, the temperature is high, or the load is extreme. Since mixed and boundary lubrication provide only partial separation between moving parts, extreme-pressure (EP) and anti-wear (AW) additives may be required for optimum component performance in these conditions. Slip friction under dry contact is essentially the coefficient of sliding friction. Dry slip, boundary slip and mixed-mode slip lubrication regimes are preferable to the alternatives where much higher stick-friction forces lead to severe sliding, galling and adhesion, which can cause extreme heating and plastic deformation of metal surfaces. ese slip-friction events can be revealed by an ultrasonic DNA12 value that is greater than 25 percent of the sonic DNA500 value. Alternatively, plastic deformation events typically do not slip, so the DNA12 value is less than 25 percent of the DNA500 value. Ultrasonic stress waves originate when asperities and grain boundaries slide across one another during slip motion. is occurs under boundary and mixed-mode lubrication regimes where the solid surfaces are so close together that appreciable contact between the opposing asperities is possible. According to W.E. Campbell, "Friction and wear in boundary lubrication are deter- mined primarily by interaction between the solids. Bulk flow properties of the liquid play little part in friction and wear behavior." Compression and Shear at Load-bearing Interfaces Compression is the normal function under- taken by most rotating machinery components. Whether dynamic or static, compression loading transfers forces from the roller to the race or from the shaft to the journal. is is how most work gets done in rotating machinery tribosystems. e forceful compres- sion is transferred from one solid element to another through the lubricant film by a hydro- static, hydrodynamic or elastohydrodynamic SONIC STRESS WAVES Sonic DNA500 reveals forceful events including compression, impact and severe sliding in time domain: • Rolling • Compression • Impacting • Severe Sliding ULTRASONIC STRESS WAVES Ultrasonic DNA12 compared with sonic DNA500 distinguishes hard-surface slip intervals in time domain: • Slipping • Polishing • Rubbing True contact area Nominal contact area N Sonic stress waves detect forceful events, while ultrasonic stress waves identify slip events. A modified Stribeck diagram showing the lubrication regimes plus dry contact for rolling, sliding, slipping and impacting OIL ANALYSIS