Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/902206
www . machinerylubrication.com | November - December 2017 | 39 to work. Filters in the return line help scrub contaminants that were recently ingressed by the process. Off-line filters continually circulate oil in the reservoir through filters to further polish the oil. When all of these filters are utilized in unison, not only will the circulating oil be very clean, but vast amounts of machine wear can be reduced. Paper machine circulating systems normally hold hundreds if not thousands of gallons of oil. With this volume, the oil has adequate residence time in the reservoir, allowing parti - cles and water to fall out of suspension, air to separate, and the oil to cool. ere is also a larger volume of additives to enhance the oil's lubricating properties. All of these factors can combine to significantly extend the life of the oil and equipment. Bearings Along with serving multiple functions inside the circulating system, paper machine lubricants must lubricate numerous component types. Bearings are perhaps the most common, particularly roll bearings tied to the centralized lubrication system. ese rolls help transport, size and dry the paper. As the rolls turn, the bearings must be simultaneously lubricated and cooled. e flowing oil transfers heat away from the bearing and provides the required lubri - cating film for smooth, consistent operation. If the bearing housing allows contaminants into the system, the moving oil can carry these contaminants out of the housing to the filters or reservoir to be settled out of the system. Gears In some paper machines, the centralized lubrication system also lubricates gearing that drives certain sections of the machine. Gears present a different challenge than bearings in that the load tends to be much higher. is leads to greater stress on the lubricant film and generally requires the use of additives to protect the machine surfaces. e gears are commonly simple spur gears that mesh together. ey can handle more chemically active lubricants without the risk of corrosion or chemical degra - dation to the gear surface. ese gears often have a more defined pitch line, which makes the building of a lubricating film easier. Press and Calender Sections During the paper manufacturing process, wet pulp is placed onto a web or screen and then transported through the machine where it is dried and fashioned into the desired thick- ness. e press and calender sections are where the finished product's thickness is usually formed. In these sections, the paper machine lubricant may also be used as a hydraulic medium. e oil provides the force required to push the rolls together, determining the paper's thickness. e hydraulic pumps and valves in these areas of the machine are highly contaminant sensitive, so the oil must be kept relatively clean throughout its operating life to ensure the life of the components. Leakage With hundreds of pipe connections, lube points and machine interfaces, paper machines frequently are plagued by lubricant leaks. is leakage also leads to two other problems: capturing the leaked lubricant and continuously topping up the oil reservoir. Capturing the lubricant normally is achieved with pans or rails, which collect and funnel the used oil to a collection container. Some facilities have attempted to reclaim and recondition this leaked oil in order to reintro - duce it into the machine. Provided the base oil and additives are still healthy, this can be a viable option, but it does have inherent risks. If the oil cannot be fully filtered to remove the gross contamination, it will become yet another source of contaminant ingression for the lubrication system. Also, the practice of capturing and then reconditioning the lubri- cant may not be cost-effective. e amount of effort required to clean the oil to an acceptable level would far outweigh the cost of buying new oil and adding it to the reservoir. Continually topping up the lubricant can help to extend the time between oil changes. e new lubricant brings with it new additives and dilutes any damaged base oil, thus improving the lubricating properties of the oil overall. Some paper machines never undergo a full drain-and-fill of the oil reser- voir because of this practice of adding new oil as the used oil leaks out. ML