Book Bits

From "Filtration Technology":

Water Exclusion is Difficult

Water is a common contaminant in hydraulic and lubricating systems. Moisture can enter these systems at several points:

• Through reservoir breather caps in humid air. System fluid absorbs some of this moisture, while some is condensed on the inside surfaces of the reservoir.

• Through worn seals. Besides humid air, coolant and cutting fluid sprays can enter hydraulic systems through worn rod seals as the cylinder moves. In lubricating systems, these water base fluids can enter through rotating shaft seals on pumps, machine tool spindles and gear boxes.

• Through heat exchangers. Worn and damaged heat exchangers can allow cooling water to leak through seals and ruptured lines into the oil system, and vice versa.

• In new oil. An oil barrel stored outside in a vertical position is likely to have rainwater collect around its bung. With changes in temperature, some of this moisture will be sucked into the barrel. Eventually, this water enters the system fluid when the reservoir is filled.

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Today's Tip

• The operating temperature of a static or circulated oil bath has a direct impact on the useful lifespan and effectiveness of the lubricant. Above 130°F, for every 18°F increase in temperature the rate of chemical reactivity doubles. In practical terms, if you are achieving a two-year lifecycle on a charge of hydraulic oil in a tank operating at 136°F and if you can find a way to decrease the temperature of the oil to 118°F, then you can expect to double your hydraulic fluid life.

  An easy way to check to see if you have room for improvement is to lay your hand on the side of the tank. If it is hot enough that you cannot leave your hand on the tank for more than a couple seconds, then you are operating at roughly 145-150°F. A fan type heat exchanger can be installed for less than a thousand dollars, and with the right flow and ambient temperature, could reduce tank temperatures to the desired level.

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Q & A

"I am preparing to upgrade the lubrication program at the mill. Do you have any suggestions for where I should begin the process?"

If is often tempting to make a clean break from poor lubrication conditions by changing suppliers, bringing in a fresh perspective and having a new lubrication survey performed as the backbone of the rejuvenating process. This is quick and clean but may not deliver appreciably different results.

We should start with a look at the maintenance objectives. What are we striving to do with the maintenance program? Have we identified the critical systems in the plant? Do we know what the failure modes for those systems are? Have we decided what courses of action will best address and correct the problems identified in the failure modes? Do we have a time table for completing these actions, prioritized from most to least critical?

The lubrication strategy should complement the overall maintenance strategy. We must first determine what we want to accomplish and where we want to accomplish it before we begin to address how the lubrication processes can help or hinder our efforts.

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