Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/629709
60 | January - February 2016 | www.machinerylubrication.com ASK the EXPERTS "We previously tried a 10-micron filter but had problems with higher oil differential across the filter and were very close to bypassing. What would be your recommendation for an appropriate filter micron size?" Pulverizer gearboxes are very robust pieces of equipment, but they still benefit from additional filtration and having cleaner oil. From a design standpoint, if you would like to move to finer filtration without increasing the pressure differential across the filter to the point of bypass, a few changes should be made in order to achieve additional surface area and a lower flow rate. There are multiple ways to get more surface area. The most popular would be to add additional filter housings to the system parallel to the current housing. Another would be to simply procure a larger filter housing (if it fits the application). The last and often forgotten solution is to change the filter media type itself. Materials such as synthetic fiberglass have a much smaller "We have 18 large pulverizer gearboxes that hold nearly 175 gallons of oil. The gearbox manufacturer recommends a 40-micron filter, but we use a 20-micron filter. "How can you find the root cause of increasing water contamination in a coal mill gearbox?" Water can find its way into a machine by a variety of ways. The first place to start is by testing the new or stored lubricant that will be going into the gearbox. Studies have shown that new oils are not clean and sometimes not dry. By testing new oils or oils that have been stored for an extended amount of time, you can obtain an accu- rate baseline not only for water content but also for a particle count to determine overall cleanliness. Oil storage should be addressed as well. Testing lubricants upon delivery can provide information on their initial proper- ties and contamination levels, but then you must store them in a manner that is condu- cive to maintaining or improving their condition. This includes decontaminating the oil with the use of a filter cart or some other means of circulation through a filter. You also need to ensure that the storage area is clean and dry. Water ingression often occurs when oil drums and totes are stored uncapped and outdoors. Water from rain, sleet, melting snow or simply high humidity can find its way into the oil and begin increasing the water content of the storage device. In some cases, enough water can migrate into the oil that it can begin to displace the volume of oil and push it out of the top of the drum. Drums and totes "breathe" throughout the day and night, and when they are stored outside, this process is more dramatic. Any rain water or moisture will be drawn into the oil during the inhaling process. Once in the oil, the water coalesces and sinks to the bottom of the drum. It then begins displacing the oil as mentioned above. Oil has the tendency to be hygroscopic, which means it absorbs moisture from the ambient environment. Simply leaving oil drums unsealed or open to the atmosphere can increase the water content due to the natural affinity of oils for moisture. Don't forget to consider the machine as well. Look for any areas of possible ingres- sion. There are several areas where water can enter a machine. If it is operating in a humid environment, a desiccant breather should be installed to dry the air entering the gearbox during the inhalation process. In addition, check seals and replace any that are worn or leaking. Also, inspect for steam leaks that may be blowing on the gearbox. If the gearbox has a lube- cooling system that uses water, it should be checked for leaks in the piping or the heat exchanger. While there are many ways water could be entering the gearbox, only by doing a thorough inspection of the machine, its surroundings and the new oil can you begin to determine the reason behind the high water content.