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Q & A

"What are the possible sources of silicon in oil?"

Silicon is measured by oil analysis labs to determine dirt ingression. While more often than not, high silicon readings indicate dirt, there are several other possible sources. The four most common are:

1. Defoamant additive – many oils contain defoamants based on polymeric methyl silicone. Since silicone contains the element silicon, the presence of this kind of additive will show a positive silicon reading in spectrometric analysis. The typical levels of Si seen under these conditions are around 1-10 ppm.

2. Silicone based sealant – many sealants used for industrial and mobile applications are silicone based. The level of silicon observed will of course be directly related to the amount of sealant leaching into the lube system.

3. Casting sand – some components are made by casting in sand (silicon oxide). Although new components are cleaned thoroughly prior to installation, it is not uncommon to see 50-100 ppm of silicon from new equipment. This level should drop as the component breaks-in and regular oil changes take place.

4. Coolant contamination – many engine coolants contain inhibitors which contain silicon. In an engine application, high Si readings in conjunction with other elements such as Na, K and B may indicate a coolant leak.

Without other evidence differentiating between additives, silicone and casting material as the source of silicon is difficult. However, dirt ingression can be determined by tracking both silicon and aluminum. For most common dirt, which contains the minerals silica and alumina, tracking Si and Al, which should show up in lock step trend in the ratio 3.4:1, can be used to confirm dirt ingression.

Today's Tip

• For equipment working in dusty environments, one of the main sources of dirt and contaminant ingression is through inadequate or faulty air breathers. In this case, consider using an upturned high-efficiency oil filter as an air filter. Oil filters are typically more effective at removing particles from the air than they are from removing them from oil.

For systems that do not need to breathe excessively (splash lubricated gearboxes), the use of an expansion chamber breather, which effectively seals the gearbox from the outside, is the best option.

• Ask and learn on the Machinery Lubrication Message Boards! Click Here

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Book Bits

From the book "Filtration Technology":

Contaminant Levels Vary by Location

The amount of contaminant in a system varies by location as well as time. Besides external factors, the contaminant level at any location depends heavily on the type and number of components used.

In some systems, the fluid flows past a given point only once. The fluid may be consumed in the process, or packaged at the end for later use. If not consumed or packaged, spent fluid may be discarded, or it could be reconditioned off-line to become essentially new fluid. These are single-pass systems. Examples are fuel systems, pneumatic fluid power systems, and beverages bottled for consumption.

In such a system, it is convenient to think in terms of a linear process in which contaminant levels vary by location. A certain amount of contaminant may be present at the start of the process, typically entering the system with the original fluid. A certain amount of contaminant will be added due to wear in system components. Filters or separators may be placed near the end of the process to remove some contaminants.

For more information about the book "Filtration Technology " go to:

http://www.noria.com/secure/product_detail.asp?catalogid=49

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