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In This Issue:

• Today's Tip: Selecting the Right Piping

• Book Bits: Monitoring In-service Hydraulic Oils

• Lube-Trivia: When to Condemn Grease

• Q & A: EP Oils and Worm Gears

Today's Tip

Selecting the Right Piping

• When retrofitting gear boxes for service and filtering, consider using stainless steel piping instead of black iron piping. After a rather short period of time, the inside of the black piping begins crusting and flaking off into the gearboxes giving false testing results. This is more predominant in high humidity and frequent wash-down areas. (Submitted by Jeffery May, Machine Lubrication Tech., Harmony Corp.\Tate & Lyle. Thanks Jeffery!)

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Book Bits

Monitoring In-service Hydraulic Oils

From "The Lubrication Engineers Manual"

Evaluating the most important properties of a premium hydraulic oil can be confusing. Fortunately, even if one chooses not to do extensive testing, hydraulic oil is easily rated for quality. Because certain organizations that sell hydraulic systems or hydraulically operated equipment have a vested interest in seeing that their customers use high-quality oils, they have developed their own specifications for hydraulic fluids, and they issue approvals for products developed to their specifications by the oil companies.

Purchasing products only from their approval lists provides reasonable assurance of quality. In the alternative, the end user may write a specification for hydraulic oil and ask the supplier to meet it, in which case the specification can be circulated among several oil companies to encourage competition.

After the oil has been purchased and placed in service, oil quality must be checked periodically. Representative tests might include:

• ISO contamination level

• additive level

• water

• wear metals

• ferrography

• viscosity

• neutralization number

Buying quality oil, then putting it into the system and ignoring it is foolish. Checking at regular intervals is a must.

More information about the book "The Lubrication Engineers Manual"

Lube-Trivia

When to Condemn Grease

Test your knowledge and prepare for ICML lubrication and oil analysis certification with Lube-Trivia.

QUESTION: Is oil separation or "bleeding" in a grease reason to condemn it as unfit for service?

For the answer, visit: http://www.lube-tips.com/trivia/20031029.asp

Q & A

EP Oils and Worm Gears

"We have a large worm gear drive used in a coal pulverizer bowl mill gearbox. The bowl mill manufacturer recommends using a sulfur-phosphorous EP gear oil however our lubricant supplier has sharply recommended against it. Also, there is a question with respect to which viscosity we should use: ISO VG 320 or VG 460."

There are a variety of different views about the proper way to lubricate worm gears. You can find a couple articles on the subject on our Web site as well as an article by Arnold Shugarman on active sulfur EP additives.

In general, I consider recommendations to stay clear of sulfur- phosphorous EP additives in worm gears to be an over generalization.

The AGMA 9005-D94 statement on S-P additives is cautionary, stating that, with respect to double-enveloping worm gears, that S-P be used only when specifically recommended by the gear manufacturer (as in your case). Regarding viscosity, I suggest you refer to Tables 7 and 8 in this AGMA guideline which calls out specific viscosities for worm drives - based on such factors as pitchline velocity and temperature.

Back to the S-P EP question, I believe the high friction/heat commonly generated by worm gear drives requires EP or equivalent protection (FZG Stage >12). Indeed, the sulfur of some additives systems (such as a GL-5 gear oil used in automotive differentials) may be too aggressive towards bronze.

Bronze is commonly used in the large bull gear of the worm drive. However, unlike cutting fluids and GL-5 gear oils, the sulfur in most industrial EP gear oils should not be "active" and aggressive toward copper at temperatures below 100 degrees C.

For worm gears running at higher temperatures, test for copper tarnish at the highest expected temperature (three days) using the ASTM D130 copper strip procedure.

There are S-P EP gear oils formulated specifically for worm gears with a lower treat rate (lower additive concentration). These S-P additives are pacified and don't contain active sulfur. The two varieties are either absolute inactive sulfurized EP or a medium- active sulfur carrier. When used in combination with yellow metal deactivators (special corrosion/oxidation inhibitors) there should be minimal risk of corrosive attack of the bull gear even at moderately high temperatures.

Also, many users prefer polyglycols instead of mineral base oils. Polyglycols give comparable wear control without the use of EP additives - reducing the risk of bronze corrosion.

Jim Fitch, Noria Corporation

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