Equipment World Digital Magazine
Issue link: http://read.dmtmag.com/i/389791
EquipmentWorld.com | October 2014 55 I n July, we showed the impor- tance of keeping our weapon (grease gun) in good condi- tion and using the proper gun. Now we'll look at keep- ing the ammo (lubricant) clean and free of contaminants. Machine owners are seeking ways to make their businesses more prof- itable. But you may be failing to recognize one of the most signifi- cant impacts on your equipment: contaminants in lubricating oils and hydraulic fluids. The importance of cleanliness In general industry, it's widely recog- nized contaminants contribute either directly or indirectly to 60 to 70 percent of all failures of oil-wetted components. In earthmoving equip- ment, this number is even higher – perhaps as high as 85 to 90 percent. While inside a manufacturing plant equipment can be isolated from the elements, the same is obviously not true with construction equipment. Contamination is anything in the oil that doesn't belong there, includ- ing dirt, water, air, wear debris, unburnt fuel in engines and leaked coolant. While all of these contami- nants cause real damage to equip- ment, we'll focus on particles and moisture. In a construction environment, particles and moisture are every- where, and both can have a devas- tating effect. For example, failure to control particles in an engine can result in as much as a threefold to fourfold reduction in engine life. In hydraulic systems, water can readily cause valve and hydraulic pump fail- ures. While most operators appreci- ate that dirt and water are "bad" for equipment, they often don't under- stand the level and type of particle and moisture contamination that cause all the problems. Dirt is obvious. But it's not just the visible dirt that causes the problems. If we can see or feel dirt, it's likely that the particles are in excess of 100 micron (4/1000 of an inch). The real troublemakers, however, are silt particles in the 1- to 5-micron size range. You can typically see a 40-mi- cron dot on a white piece of paper, but a 3-micron dirt particle is far too small to see without a microscope. In a study conducted by Cum- mins Engine, sub-10 micron-sized particles produced wear rates that were three to four times greater than those produced by 20-micron and larger particles. Dirt has a similar impact on hy- draulic systems. In many hydraulic pumps, clearances are also below 5 microns, while hydraulic valve clearances range anywhere from 1 micron to 10 microns, depend- ing on valve type and operating pressures. In hydraulic systems, the impact of particle contamination is particularly insidious. It's not just dirt particles that get in from the outside that cause all the problems. And studies have shown not only does dirt cause machine wear, but the particles generated through abrasive wear have a snowball ef- fect inside the machine. Avoiding water Water is perhaps the second-most pervasive contaminant found in construction equipment. Water in oil can exist in three distinct forms: free, emulsified and dissolved. Free water refers to water that has separated from oil and settled to the bottom of the sump or tank. Emulsified water mixed with the fluid being supplied to moving parts, however, is the biggest problem. Water is not a good lubricant, but this issue goes beyond its poor lubricating properties. Water mixed with oil in an emulsion has poor film strength and is unable to support a dynamic load the way clean, dry oil can. Also, as water flows through lubrication boundar- ies, sudden pressure changes can result in microscopic implosion events, which are especially hazard- ous to pumps. So how much is too much water? The answer is surprisingly little. As little as 500 ppm (about 6 fluid ounces of water in a 100-gallon tank) is sufficient to reduce pump life by a factor of two. The impact of water is even more pronounced in equipment used intermittently. At 250 ppm, any water present in a hydraulic system will be in the dissolved state and relatively in- nocuous at operating temperatures. However, when the machine is shut down and the oil cools down to ambient temperatures overnight, most water will come out of solu- tion and become free or emulsified, resulting in corrosion and other water-related failure modes. maintenance | by Preston Ingalls and Mark Barnes Contamination control Keeping the ammo clean in the war on friction