eSource 102 Case Study in Understanding Metallurgy of the Key Components

eSource 102 Case Study in Understanding Metallurgy of the Key Components

Posted 06 November 2017
Elemental analysis is a fundamental tool in used oil analysis. Used appropriately, trends in different wear metals can indicate a problem, allowing corrective action to be taken before catastrophic failures occur.
In order to make the most of elemental spectroscopic data, it is a good practice to spend some time gathering information about the metallurgy of a component, and compiling a reference in advance of the lab reporting a problem. In particular, identifying not just major elements such as iron from steel, but also minor elements such as chromium and nickel, and trace elements such as vanadium and manganese, can help differentiate between different alloys of steel or other components. It may also be appropriate to record the relative ratios of different elements in the various alloys present, so that these ratios can also be used as a characteristic fingerprint. 

The following is a real case study of wear analysis in a cone crusher:  

Trend analysis of oil samples that were taken routinely on the cone crusher showed a steady increase in the amount of iron wear over successive samples, indicating an active wear problem. Each sample report was carefully reviewed by the original equipment manufacturer (OEM), who agreed with the lab’s assessment that iron levels were excessively high. Because the OEM was involved in the evaluation of the sample data, each wear metal present was carefully considered, as were the metals that did not show up in the analysis.

Increasing iron in the cone crusher could have been caused by any number of wear problems. However, there was no chromium in the oil analysis, indicating wear from bearing races was not an issue because it was known that the bearings were made from high alloy steel containing a fairly high degree of chromium. Additionally, normal levels of copper, lead and aluminum indicated that bearing cages were not wearing excessively, also a clue that the wear problem was located somewhere other than the bearings.

The fact that iron was the only wear metal that was high and getting worse, ultimately narrowed the potential problem to a floating plate (similar to a universal joint) or a gear set itself, not bearing wear. Familiarization with the cone crusher and commonly encountered failure modes led the OEM to believe that the floating plate would be the most likely cause of the high iron level.
 
Based on the OEM’s review of the oil analysis data, the customer was advised to pull the cone head and inspect the unit. The customer was told where to look and what to look for, allowing the initial inspection to be completed in less than five minutes.

Upon inspection of the unit, it was discovered that the floating plate did indeed have extensive wear and was close to catastrophic failure. In other cases where this problem had not been diagnosed soon enough, the floating plate wore so thin that it broke apart, distributing large particles into the bearings, causing additional and more widespread damage. Based on the oil analysis data and visual inspection, immediate replacement of the floating plate was recommended. 
Replacing a single $700 part (the floating plate) in one hour of downtime enabled this unit to be quickly put back into service. By contrast, not catching the worn part in time could have cost from $2,000 to $12,000 in additional damage, and an estimated minimum two-day downtime.

In this instance, understanding metallurgy of the key components and the typical failure modes of this system, along with using oil analysis as a predictive maintenance tool, allowed the construction company to prevent a larger problem. Knowing what to look for and having the right parts on hand kept a relatively minor problem from becoming major.
 

Written By:

David Doyle, CLS, OMA I, OMA II
General Manager, ALS Tribology

 

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