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IT'S MORE THAN JUST OIL. IT'S LIQUID ENGINEERING.

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DEALING WITH COMPATIBILITY CONCERNS WHEN CHANGING TO A NEW GREASE

ENGINEERING SOLUTIONS / Post date:
7 August 2017

From time to time, you may be required to change grease products. Perhaps you are a new Castrol® customer and you are changing from a grease product provided by your previous supplier or you may be a long-time user of Castrol products, but are considering upgrading to a premium Castrol product.


With either scenario, a key issue that must be taken into consideration is the compatibility between the current and new greases. It is very common for two greases with different thickener types to be incompatible with each other. The thickener is a substance in grease that serves as a type of sponge, which holds the oil in the grease. Most grease contains around 90% oil (and additives) and around 10% thickener.


There are different types of thickeners and it is this difference that forms the biggest risk for compatibility. Most thickeners are formed by a chemical reaction… a process known as Saponification, in which a type of soap is formed in the oil.


It is the duty of the soap/thickener to hold the oil in suspension and then let it go when needed to lubricate the bearing and then take it back up again and continue to hold it in suspension. The grease performs this process of letting the oil go and taking it back up again repeatedly, as long as the grease is in place in the bearing.


If two different greases are introduced together, a problem can occur if the two thickeners are not compatible with each other. If this occurs, the thickeners will lose their ability to hold the grease in suspension. The grease will soften and release the oil causing it to run out of the bearing, which often creates a mess below and around the bearing and starves it of lubrication. If allowed to continue unabated, this can result in bearing failure.


How can a fleet manager or maintenance technician prevent this from happening? There are a number of things that can be done:

 

  1. CHECK ON COMPATIBILITY BEFORE CHANGING PRODUCTS.
    There are certain types of thickeners that are known to have poor to no compatibility with other thickeners and there are some thickeners that tend to have comparatively good compatibility. Your lube supplier should be able to provide guidance.

    A word of caution here… it is not always possible to determine ahead of time if two thickeners will be totally compatible. Based on experience, experts can tell you if they “should be,” but sometimes, when you mix two greases that are assumed to be compatible in a bearing, they turn out not to be. There really is no definitive way to tell for certain… other than mixing the two together to see what happens. If the operation is critical, this can be performed ahead of time in a lab. Most often, however, the testing occurs onsite in an actual bearing application.

  2. DISASSEMBLE THE BEARINGS AND CLEAN ALL REMNANTS OF THE OLD GREASE, THEN RE-GREASE THE BEARING USING THE NEW GREASE AND REASSEMBLE.
    This is typically only done in the case of automotive wheel bearings, when the bearings are being periodically repacked with fresh grease. The standard practice for this is to remove the bearings, clean them and repack them with fresh grease… this is a common everyday occurrence.

    But other than this application, this practice is extremely rare. The cost in time and resources to disassemble all the bearings in a plant, fleet of trucks, or mobile equipment, is just too extreme to make this practical.

  3. APPLY THE NEW GREASE, MONITOR FOR SIGNS OF INCOMPATIBILITY, AND REAPPLY FRESH GREASE AS NEEDED.
    This is the most common process of managing a change in grease products. If the two greases are not compatible, this will be evident, as described above, with a softening of the grease and the separation of the oil and thickener. The oil will run out of the bearing and will cause a mess under and around the bearing.

    In this case, the proper response is to reapply more of the new grease into the bearing, purging as much of the old grease as possible, and then allow the bearing to work. There may be additional softening and separation of the grease, which should be responded to in the same way until eventually none of the old grease remains in the bearing. At this point, the incompatibility ends and you should be able to return to your normal lubrication schedule.

    Please note that you may have to modify your schedule based on the performance of the new grease. This is not optimal, as it may result in a waste of grease and leave an unsightly mess on the equipment that can be difficult to clean. Despite this challenge, this is the most common way to manage grease incompatibility in the field.


Bottom line, changing grease products is a manageable event, but it does deserve deliberation and a commitment to provide the resources needed to manage the process and avoid component failures.


As always, please contact your Castrol sales or field engineering representative for assistance.