油样分析基础知识

1.  How particles affect the oil - Particles, especially catalytic metal particles like copper, iron and lead increase the rate at which oxidation occurs. Particles also strip the oil of its polar additives, including anti-wear additives, extreme pressure additives, rust inhibitors and dispersants. Also, numerous very small particles in stable suspension can cause the oil's viscosity to increase.

How particles affect the machine - Abrasive particles are responsible for much of the wear leading to premature failure of mechanical components. Under sliding conditions, clearance-sized particles enter the oil film between surfaces and cut away material much like a lathe cuts metal. Under rolling contact conditions, particles transfer concentrated load between two surfaces in relative motion, resulting in surface fatigue, pitting, and spalling. Particle-contaminated oil traveling at high velocity can also cause erosive wear.

2.  Rate-of-change alarms are typically set to measure properties that are being progressively introduced into the oil, such as wear debris. The add rate (change) can be calculated per unit of time, hours, cycles, etc. For example, a 100 ppm increase in iron over a period of 100 operating hours could be stated as one ppm per hour of operation. When the parameter is plotted against time, the rate-of-change (add rate) equals the current slope of the curve.

Unlike level limits, rate-of-change limits ignore the absolute value of the data parameter, emphasizing instead the speed at which the level is changing. Rate-of-change limits are effectively applied to particle counting (unfiltered systems), elemental wear metals, ferrous density, acid number (AN) and RPVOT. It can also be effectively applied to monitor abnormal degradation of additives with elemental and FTIR spectroscopy.

3.  The amount of water that a given fluid will absorb depends upon its base stock, viscosity, additive package, and temperature. The amount of water that can dissolve in a fluid is termed its saturation level. The saturation level for a hydraulic fluid is 200-300 ppm while for a lubricating oil it is around 500-600 ppm. Oil is cloudy when it is above its saturation level. The saturation level for a synthetic fluid is generally much higher than for a mineral base fluid.