Before adding antifoam agents to get a handle on a foaming problem in a circulating system, one of the first things to check is the oil level. Both too much, and too little oil can lead to a foaming problem. Too much and there may be a piece of the machinery touching the surface of the oil that shouldn't, churning and slinging the oil (high-speed pinion in gearbox). Too little oil, and a vortex can form inside the reservoir at the inlet for the circulating pump, sucking in air.

If you cannot tell the level due to the foam, you may be able to stick a clear piece of tubing straight down to the bottom of the reservoir. Cover the end of the tubing to create a seal, and pull it out to observe the actual oil level. Don't put anything into an oil reservoir unless you are certain of its internal configuration and components. (Van Richard, Sr. Reliability Engineer, Georgia Gulf Corporation)

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In many companies, it's common practice to review and re-tender MRO contracts on a three- to seven-year cycle. Lubricants are no exception, particularly in today's economy where lubricant prices, like those for every other crude oil-based commodity product, are rising to unprecedented levels.

While this practice is not inherently bad, there are certain pitfalls which can occur when switching lubricant suppliers. Beyond the business aspects of a change in supplier - such as price, distribution network, service and support - perhaps the single-biggest problem companies face when working with a new supplier is the issue of lubricant incompatibility. Read entire article.

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"I am wondering about our lubricator's practice of pumping oil into oven roll bearings periodically to refresh the grease? Is this a good practice?"

I've never heard of this practice, but it is a good question. The short answer is that this is not a good practice. As you know, grease is a product of dispersion of a thickening agent in a liquid lubricant. Over time while in service, grease separates or dries out. The oil eventually goes away and the thickener is left behind. I assume your technicians are trying to replace the oil that has separated and under certain conditions, this might be possible. However, you should replenish the grease rather than the oil. As I see it, there are two problems with this practice.

The first problem is that it is not that easy to mix grease. You cannot simply pour oil onto the thickening agent to get grease. Most greases are formed by dissolving the thickener reagents in oil where they react to create the thickener plus by-products in solution under controlled conditions (temperature and pressure). Next, the by-products are removed and other additives and oil are added to give the desired consistency. Then the mixture is homogenized to provide consistent properties throughout the batch. As you can see, by just adding some "light" oil you are probably just washing out some old grease.

The other problem could come from successfully mixing the oil with the grease. If the new oil did mix with the old grease, you could significantly alter the properties of the grease or even introduce incompatible components that could lead to a number of problems. You could alter the consistency of the grease, the viscosity of the base oil, dilute additive concentration, or create a number of chemical reactions between incompatible components which lead to additive neutralization, changes in lubricant chemistry, and certainly impaired performance properties. I could go on, but you get the idea.

What you should do is make sure you are using the right grease for the application, use appropriate methods to determine the right amount of grease for replenishment, and select the best relubrication frequency. These values will rely on the type of bearing, speed, bearing geometry, and heavily on the operating conditions (temperature, moisture, particle contamination, seal type, etc.). The only other consideration is manual application vs. continuous (automatic) application. Once you've made these determinations correctly, there should be no need to refresh the grease.

Jarrod Potteiger, Noria Corporation

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