Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/704613
IN THE TRENCHES their effectiveness as a result of a number of issues. Perhaps one of the most widespread is the contamination of the oil. Any contam- inant that impairs the oil's surface tension can diminish the performance of the defoamant. Water is one of the most common contaminants that reduces surface tension and leads to excess foaming. Other contaminants include detergents, solvents, fuels and oxidation byproducts. By keeping out contaminants and main- taining clean oil, you can proactively manage foaming. Another reason defoamants become ineffective is because of their removal from the oil. This can occur due to filtration, which will be discussed later, or from the oil being stored for an extended period of time. Since these additives are suspended and not dissolved, they are prone to settling out of the oil. Without sufficient agitation, defoamants may not fully suspend when the oil is added to a machine, especially if the oil has been in storage for a consider- able length of time. This is why performance testing of stored lubricants is highly recom- mended. It is also one of the many issues that can arise from lubricants exceeding their shelf life in storage. Why Defoamants Are Needed In most cases, oils will allow air to sepa- rate and keep foam at a manageable level. The problem comes with how quickly this must take place once the lubricant is applied to the equipment. Not all machines have adequate reservoirs to give the lubri- cant maximum dwell time to cool, shed contaminants and allow entrained air to rise and foam to settle. In fact, many machines don't have reservoirs, so the oil is in a constant state of turbulence. This is most common in splash-lubricated equip- ment such as pumps and gearboxes. In these applications, the defoamant must keep foam at a minimum so as not to impair lubrication for the rest of the machine. Machines with circulating oil use defoamants to prevent foam in the reser- voir and to reduce air-related issues such as vapor lock in other locations within the lubricant system. These additives greatly increase how fast foam settles and disap- pears so it doesn't impair the function or health of the machine in which the lubricant is operating. Risks Associated with Foam While a certain amount of foam is acceptable, it can easily get out of control and lead to decreased lubrication. In splash-lubricated machines, excess foam can reduce the oil's splashing ability and result in lubricant star vation for some components. In circulating systems, foam may restrict the oil's ability to flow through piping and cause issues such as pump cavitation. Hydraulics may also experience spongy or erratic control if the fluid is foamy. In terms of lubricant health, foam is detrimental to the overall life of the oil. The most common form of oil degradation is oxidation. Foam has a high percentage of air, which is the chief ingredient in the oxidation process. As foam progresses and limits the equipment's lubricating tendency, the oil temperature begins to rise. With an increase in operating temperature and plenty of air intermingled in the oil, oxida- tion occurs at an increased rate. This By keeping out contaminants and maintaining clean oil, you can proactively manage foaming. How temperature and viscosity influence the foam tendency for mineral oils