Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/778560
www.machinerylubrication.com | January - February 2017 | 21 (most likely involving anti-wear additives), but this alone would not be sufficient to disqualify the mixture for compatibility if the resulting product still functioned effectively with regard to wear resistance. The table at the top of page 20 shows the rheological values for the two worked refer - ence samples and the 50-50 worked mixture. The areas highlighted in yellow indicate values of concern. In this case, each of the values for the 50-50 mixture is significantly different than the expected numerical average of the unmixed greases. This demonstrates a change in properties due to mixing and raises concerns about this mixture's performance in the long term. It could be expected that the mixture may be subject to softening, oil separation and a tendency to channel when allowed to persist in a mixed state in the motor housing. For this reason, the mixture was not permitted at the facility, and the decision was made to keep two greases in place until the motors could be removed and thoroughly cleaned of the existing product. Strategies to Minimize Mixing Effects It can be difficult to avoid mixing greases in a plant environment, but several steps can be taken to minimize the impact and likelihood of mixing incompatible greases. Step 1: Provide Clear Guidance All personnel involved in applying grease to equipment should be trained and receive instruction on the proper product to use on each piece of equipment and the location. This includes employees and contractors who may be working in the facility. Provide labels and color codes where possible to prevent confusion. Step 2: Involve Purchasing in Grease Specification A common area for grease mixing is in new and rebuilt equipment. Even when all plant personnel are given clear guidance on using the correct products, equipment may be returned to the facility with a grease that is different than what will be added while in service. New bearings, gears, motors, etc., often come supplied with a product that is incompatible with the grease being used to relubricate. Step 3: Consolidate Lubricants Identify the minimum number of prod- ucts required to meet the design of the equipment in use and consolidate to that number. Do not stock additional products for convenience or brand loyalty. This increases the likelihood of mixing. Step 4: Test Potential Mixtures If the wrong grease has been inadver- tently added to a machine or consolidation is required that will transition the use of a product in a machine, perform simulated mixing and working of the mixtures as well as dynamic properties testing to evaluate the mixture's performance. For those mixtures that prove to be incompatible, the extra effort must be taken to thoroughly clean all traces of grease from the housing, supply lines and bearings/gears to ensure long life and reliable machinery operation. Grease compatibility charts may seem to be a convenient way to make decisions based on actual or potential grease mixing. However, the unreliability of these charts and the complex interaction of base oils, additives and grease thickeners require that a more certain approach be employed for optimal equipment performance. The efforts to avoid mixing where possible and to test mixtures for compatibility issues as well as taking the appropriate actions will be an investment in reliability that will pay dividends. ML