Metallurgy of Oil Wetted Components in Engines
Lubricant analysis has three dimensions:
- to monitor for the overall particle cleanliness of the oil for the purpose of contamination control,
- to compare the chemicals and physicals of the oil against the virgin oil to determine if the oil is still an adequate lubricant, and
- to analyze for metal particles to determine the condition of the machine's oil wetted (wearing) parts.
Monitoring the wear condition of a machine is one of the three important facets of oil analysis. Relative motion between lubricated parts is always accompanied by friction between the contacting surfaces. This friction causes a gradual wearing away of these surfaces, despite the fact that the parts themselves are usually coated with a thin film of oil. Metal particles rubbed off in this manner are small enough to remain suspended in a circulating lubrication system, and since these wear products are always composed of the same materials from which they originated, the relative level of each metal present in the used oil relates directly to the wear condition of the lubricated assemblies. The primary method used today for determining the wear metal concentration is atomic emission spectroscopy. This note is designed to serve as a guide for determining the sources of these wear metals in common engines available today.
Atomic Emission Spectroscopy (Spectrometric Analysis
This is a technique for detecting and quantifying metallic elements in used oil resulting from wear, contamination and additives. The oil sample is energized to make each element emit or absorb a quantifiable amount of energy, which indicates the element’s concentration in the oil. The results reflect the concentration of all dissolved metals (from additive packages) and particulates. This test is the backbone for all oil analysis laboratories today, as it provides information on machine, contamination and wear condition relatively quickly and accurately. It’s major limitation is that it’s particle detection efficiency (see Application Note on Rotrode Filter Spectroscopy).
| Standard Elements Tested for By Wear Particle Analysis | ||||
| CONTAMINANT OR ADDITIVE | WEAR METALS | COOLANT OR ADDITIVE | OIL ADDITIVE | CONTAMINANT OR WEAR METAL |
| silicon< | iron aluminum chromium copper lead tin nickel silver |
sodium boron |
zinc phosphorous calcium magnesium barium molybdenum |
vanadium |
Sources of Wear Metals and Contaminants in Engines (Caterpillar) |
|
| Wear Metal | Source |
| Iron | Most common of the wear metals. Engines: Cylinder Liners, Piston Rings, Valve train, Crankshaft, rocker arms, sping gears, lock washers, nuts, pins, connecting rods, engine block. Bearings: Rolling element Bearings: rollers, raceways and cages, journal bearing shoe backing. |
| Copper | Piston pin bushings, rocker arm bushings, oil cooler core, Connecting rod bearings, Main bearings |
| Lead | Connecting rod bearings, Main bearings, Contaminated fuel (lead from gasoline) |
| Tin | Connecting rod bearings, Main bearings overlay (tri-metal bearing systems) |
| Chrome | Piston rings, cylinder liners, |
| Aluminum | Connecting rod and main bearing inserts, pistons(certain models), |
| Silica | Defoamant additive in new oil, sand/dirt ingression from breathers |
Sources of Wear Metals and Contaminants in Engines (Wartsila, Waukesha) |
|
| Wear Metal | Source |
| Iron | Cylinder Liners, Piston Rings, Valve train, Crankshaft, Gearing |
| Copper | Bearing Wear, Copper indicates bearing layer is worn and bearing bronze is visible. |
| Lead | Connecting rod bearings, Main bearings, Contaminated fuel (lead from gasoline) |
| Tin | Connecting rod bearings, Main bearings overlay (tri-metal bearing systems) |
| Chrome | Piston rings |
| Aluminum | Grease contamination |
| Silica | Defoamant additive in new oil, sand/dirt ingression from breathers, catalytic residues |
| Nickel | Contamination from Fuel(outside US), Bearings |
Sources of Wear Metals and Contaminants in Engines (Cummins) |
|
| Wear Metal | Source |
| Iron | Cylinder Liners, Piston Rings, Valve train, Crankshaft, Gearing |
| Copper | Bearing Wear, Copper indicates bearing layer is worn and bearing bronze is visible. |
| Lead | Connecting rod bearings, Main bearings, Contaminated fuel (lead from gasoline) |
| Tin | Connecting rod bearings, Main bearings overlay (tri-metal bearing systems) |
| Chrome | Piston rings |
| Aluminum | Grease contamination, engine block wear (some models), cooler |
| Silica | Defoamant additive in new oil, sand/dirt ingression from breathers, catalytic residues |
| Nickel | Contamination from Fuel(outside US), Bearings |
The above sources are provided only as a general guideline. Always consult your engine manufacturer for more details. Engine technologies are rapidly changing, particularly with new materials because of the fuel saving and environmental concerns.