Liquid gold

Understanding the benefits of oil analysis can lead to optimum oil use and longer equipment life.

By Steve Waggoner

For several decades, used oil analysis has been a by-word in the realm of lubricated components in aggregate and other stationary equipment. Management and maintenance personnel in the quarrying and construction materials industries will recognize the various operational and other problems that are common to aggregate equipment, and they probably know how important oil monitoring is for the well being of their equipment. What they may not know is how to design, monitor, and benefit from a used oil analysis program appropriate for their specific operational conditions. Optimum monitoring of equipment health will require planning the appropriate array of oil tests, sampling intervals, and interpretation of analysis data.

Maintenance challenges

There are several operational problems, types of contaminants, and other external issues that may be seen during the lifetime of aggregate equipment. These include mechanical problems, oil problems, contaminants, and maintenance issues. Following are some specific types of these issues.

Mechanical problems:

• Misapplication of component (wrong load, wrong speed);

• Worn parts (bearings, bushings, gear teeth);

• Sudden failure (broken gear teeth, etc.); and

• Overheating.

Oil problems:

• Oil oxidation;

• Wrong oil;

• Under-filled; and

• Over-filled.

Contaminants

• Moisture;

• Dirt (leaking seals or missing breather vents, high-dust atmospheres); and

• Excessive wear metals.

Maintenance issues

• Missed service interval;

• Wrong or improperly installed parts at rebuild;

• Installation of wrong oil; and

• Temperature control of the lubricated component and of ambient conditions.

While these lists are not all-inclusive, they represent a reasonable sampling of the issues that may be encountered in the world of aggregate equipment.

Oil analysis options

Various oil analysis procedures can be used to monitor the overall health of a lubricated component. Those commonly used in fixed equipment monitoring may include the following:

• Spectrographic (absorption, ICP, or emission) analysis for wear metals and dirt;

• Ferrography for analysis of large-particle metal composition;

• Particle counts for ISO (International Organization for Standardization) Cleanliness Code;

• Infrared (IR) analysis for the presence of moisture contamination; and

• Analysis (usually by IR) for oxidation.

Spectrographic analysis can be performed by one of several different methods, including atomic absorption, ICP (inductively coupled plasma), or emission. The method chosen is by preference of the testing lab, but all three methods provide the same type of information: the concentration of wear metals, additive metals, or silicon (dirt) present in the oil. These methods generally detect normal-sized wear particle, usually at and below the 10µ (micron) to 12µ range. Metals detected by these methods are reported in parts-per-million (PPM), with larger particles being reported by the ferrography method. In addition, most testing laboratories can provide sampling histories for individual components and some can even provide automatic commenting based on previous sample trending.

Particle count testing is often performed to determine the ISO Cleanliness Code for the oil. The particle count test determines the number of particles of various sizes detected in one milliliter of sample. While the test looks for particles 150µ and larger, the code is determined by the count numbers at the 4µ, 6µ, and 14µ sizes. That is, the instrument counts how many particles larger than 4µ, how many larger than 6µ, and how many larger than 14µ are present. The results are then entered into a range table that determines the code (see Figure 1).

ISO has established code guidelines for several types of components, but original equipment manufacturers may have varying requirements. Shown in Figure 2 are some of the ISO guidelines.