Machinery Lubrication

ML_Sept_Oct_2017_DigitalEditon

Machinery Lubrication magazine published by Noria Corporation

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www.machinerylubrication.com | September - October 2017 | 43 As mentioned previously, if the oil is designed to flow through piping, such as a lube oil circulating system, the oil can become greatly restricted and starve the machine. Other oil-lifting devices can also lose their effective- ness under such conditions. Ring oilers start to drag, causing unwanted friction, while oil slingers hold onto the viscous oil, resulting in an insufficient distribution of lubricant to higher lubrication zones. Grease Applications Grease has similar risks in cold envi- ronments since the oil within the grease still abides by the temperature-viscosity relationship. The potential for lubricant starvation from a lack of grease application is a common issue. With any application method designed to push grease through an orifice or grease line, such as a centralized grease system, single-point lubricator or even manual greasing, grease movement may be significantly restricted in cold temperatures. Consequently, the grease may not be prop- erly applied in the component's friction zones. Certain greases intended for cold temperatures are formulated to handle these conditions. Test methods such as ASTM D4793 and D1478 have been developed to determine how grease restricts motion in a bearing under cold temperatures. Gearbox Systems Most types of gearboxes are at risk of star vation, including splash-lubricated, wet sump circulating systems or forced lube oil circulating systems. When the oil is too viscous during startup, it cannot reach the gear meshing zones due to a lack of injector pressure or channeling of the oil in splash-lubricated systems. As a result, the unlubricated high-pressure contact pivot points on the gear teeth can become damaged. In addition, any gear system that must overcome the churning effects applied by the viscous oil will experience limited power transmission as well. Engines Nowadays, it is common for machines in cold environments to be equipped with heating elements to allow the machine to start. However, as temperatures continue to drop, simply using block heaters does not eliminate the risk to engine components which have not yet mitigated localized oil that remains below the pour point. For instance, even though the machine may be freely turning over at startup, if the oil sump is still in a gelled state, the lubricant cannot perform its role properly. This can lead to engine seizure. Air pockets can form in the gelled oil, called air binding, and starve the pump of oil. To prevent this, pan heaters and higher quality lubricants are often used to help keep the viscosity down. When condi- tions are uncertain, you can observe the oil flow from the tip of the dipstick for assurance of the oil's viscous state. Journal Bearings The oil wedge formed during rotation of a journal in the bearing housing is a careful balance of speed, viscosity and load. In any circumstance when the viscosity is undesir- ably high, such as when temperatures are very low, the oil can begin to whip around the journal, causing the shaft to wobble. Excessive wear can then occur from the reduced working clearances. Hydraulics For hydraulic systems, the biggest risks in cold temperatures are cavitation and filter element failures in hydraulic pumps, as mentioned previously. Another problem that can arise involves hydraulic seals. While ML SAE GEAR OIL 75W 80W 85W 90 140 SAE ENGINE OIL 5W 10W 20 30 40 50 ISO Grade 15 22 32 46 68 100 150 220 320 460 680 °F °C Diesel 248 120 4 4 6 7 9 12 13 18 23 230 110 4 6 7 9 12 15 19 24 30 212 100 1 5 5 7 9 11 15 19 25 32 41 194 90 3 5 7 9 11 15 20 26 34 44 58 176 80 5 7 9 11 15 20 27 36 48 63 85 158 70 6 9 11 15 20 28 39 52 71 95 130 140 60 8 12 15 21 29 40 57 80 110 151 211 122 50 11 15 22 30 43 62 99 128 181 254 365 104 40 1 15 22 32 46 68 100 150 220 320 460 680 86 30 2 21 32 51 76 116 175 271 409 613 907 1,380 68 20 3 33 51 87 135 214 334 536 838 1,290 1,980 3,130 50 10 4 52 87 162 264 438 711 1,190 1,920 3,070 4,870 8,020 32 0 5 85 180 340 585 1,020 1,720 2,990 5,060 8,400 13,900 23,900 14 -10 9 185 375 820 1,500 2,770 4,880 8,890 15,700 27,200 47,000 85,000 -4 -20 15 400 800 2,350 4,650 91,20 16,800 32,300 60,000 Oil kinematic viscosity combined with temperature in centistokes (cSt) Ref. Donaldson Filtration Solutions

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