Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/431954
ASK the EXPERTS There are multiple sources for the sodium found in your diesel engine oil. Based on your operational environment and equipment type, you should be able to narrow this down to a smaller list of causes. Potential sources of sodium include coolant, salt water, additives, grease thick- ener, base stocks, dirt and road salt. On the other hand, potassium has only one real major source when found in engine oil — antifreeze. Other key elements that you will want to look for are boron, chro- mium, phosphorus and silicon. All of these elements are associated with antifreeze and, if found in engine oil, can be an indi- cator that you have a coolant leak. The causes of this coolant leak will take some investigation. Trouble areas include defective seals, electrochemical erosion, cavitation erosion, corrosion of the liners, a damaged cooler core, a blown head gasket, or a crack in the cylinder head or block. The effects of antifreeze contamination are a rise in the oil's viscosity or a thickening of "The oil analysis report we received from our lab showed elevated levels of sodium and potassium in our engine oil. This oil has also become significantly thicker. What could be causing this to occur?" "After removing a failed bearing, we saw that the cage was a dark bluish color. Does this provide any indication as to why the bearing failed?" Once a bearing or any compo- nent fails, it is important to look at the evidence left behind to determine a root cause. There could be pits, spalls or in this case a bluish tint to the cage. Each failure mode is indicative of a specific problem the bearing has faced. For the cage to change colors, you more than likely are looking at a problem involving heat. Heat can be generated in a bearing by a few different processes. Overgreasing or packing too much grease into the bearing cavity can create a heat issue. Grease does not dissipate heat as well as oil does, so it tends to stay hotter longer. Also, if a bearing is completely filled with grease, it can cause churning and produce heat in the form of friction. This is similar to running through water. It is easier to run when the water is only ankle deep as opposed to waist deep. Now imagine the bearing trying to displace all the grease that has been packed around it. This is how the friction and heat are generated. Understanding the loading that the bearing is experiencing can also help you identify where excess heat could be originating. If the load is severe enough that the elements are being pushed into the race with excessive force, this can lead to boundary lubrica- tion, with heat being produced by the friction between the metal surfaces (the rolling element and the race). Various types of rolling-element bear- ings can withstand different levels and types of loading. Learning the difference between axial and thrust loading will help you determine if you are using the correct type of bearing. Some loads may be too severe for a ball bearing, but a spherical roller bearing might adequately support the same load. Just looking at the design strength and the recommended loading of the bearing will tell you if you are using the correct style. It is important to point out that a single bearing can fail due to multiple reasons, but if this failure becomes common, you should be proactive and attack the root cause. To mitigate overgreasing, calculate the volume of grease needed to properly relubricate the bearing and ensure this volume is not exceeded. To prevent heat caused by overloading, confirm that the proper style of bearing is being used and that it is sized accordingly to handle the load it is encountering. 46 November - December 2014 | www.machinerylubrication.com