Exclusive Guide to Synthetic Lubricants (July 2003)

Synthetics are the logical lubricant choice in a number of applications, including when: Man-made synthetics reduce wear by providing a more robust lubricant film in the load zone or nonconforming surface of bearings, gears, compressors, rotary shaft seals, vacuum and diaphragm pumps, valves, and hydraulic systems.

By Joseph L. Foszcz, Senior Editor, Plant Engineering Magazine July 14, 2003
Key Concepts
  • These lubricants reduce wear and provide long life.

  • Synthetics can be formulated to satisfy application requirements.

  • The chart lists product offerings from 79 companies.

    Sections:
    Selection
    Types

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    Synthetics are the logical lubricant choice in a number of applications, including when:

    • Equipment failure or excessive downtime

    • is attributed to ineffective lubricationproducts or practices

    • Application demands are beyond the capabilities of mineral-based petroleum products

    • High or low temperatures (-75 to +500 F) are encountered.

      • Man-made synthetics reduce wear by providing a more robust lubricant film in the load zone or nonconforming surface of bearings, gears, compressors, rotary shaft seals, vacuum and diaphragm pumps, valves, and hydraulic systems. Reduced maintenance, parts replacement, and energy costs often result. Synthetic lubricants also provide long life because of their enhanced thermal and oxidative stability, which reduce the formation of sludge, corrosion, and deposits.

        The major drawback to synthetic lubricants is initial cost, which is typically about three times higher than mineral oil-based products. However, the initial price premium is usually recovered over the life of the product, which is about three times longer than conventional lubricants.

        Because of the initial expense, using synthetics in systems experiencing leakage or contamination is not a practical choice.

        The charts presented on the following pages serve as a guide to selecting and applying synthetic gear, bearing, hydraulic, and compressor oils, and three high/extreme pressure greases. The chart, which is updated every 3 yr, is based on information supplied by the 79 companies who responded to a written request from PLANT ENGINEERING magazine.

        Products presented in the listings are categorized by viscosity. However, there are several other important variables that should be considered when selecting and applying synthetic lubricants. These factors include pour and flash points, demulsibility, lubricity, rust and corrosion protection, thermal and oxidation stability, antiwear properties, compatibility with seals and paints, and compliance with testing and standards requirements.

        Products presented in each category are not necessarily interchangeable or compatible. These two features depend on a variety of inter-related factors, and each application requires an individual analysis.

        Selection

        A properly selected synthetic product provides the same basic lubrication functions as mineral oils. However, synthetic lubricants can be formulated with a combination of properties to satisfy specific application requirements that petroleum products cannot usually meet.

        Performance characteristics of synthetic lubricants are derived from the physical and chemical properties of the base fluid and effects of additives introduced into the final product. Physical and chemical qualities include viscosity-temperature behavior, low-temperature fluidity, volatility, compatibility with paints and elastomers, ability to dissolve chemical additives, and hydrolytic stability. Additives are introduced to influence, to a greater or lesser degree, oxidation stability, load-bearing ability, and corrosion protection.

        The table (right) shows the relative performance characteristics of seven types of synthetic lubricants and a paraffinic mineral oil.

        Types

        There are several major classes of synthetic lubricants.

      • Synthesized hydrocarbons , such as polyalphaolefins and dialkylated

      • benzenes, are the most common types. These products provide performance characteristics closest to mineral oils and are compatible with them. They are used as engine and turbine oils, hydraulic fluids, gear and bearing circulating oils, and compressor lubricants.

      • Organic esters , such as dibasic acid and polyol esters, easily accept additives, which enhance their applicability for finished product formulations, such as crankcase oils and compressor lubricants.

      • Phosphate esters are well suited for fire resistance applications. They also provide excellent wear resistance and corrosion, and are considered readily biodegradable.

      • Polyglycols are used for lubricating gears, bearings, and compressors handling hydro-carbon gases. They provide excellent wear protection at high temperatures as well as good corrosion protection.

      • Silicones are chemically inert, nontoxic, fire resistant, and water repellent. They have low pour points and volatility, good low-temperature fluidity, and good oxidation and thermal stability at very high temperatures.

        • It is important to remember that synthetics are as different from each other as they are from petroleum lubricants. Their performance and applicability to any situation depends on the quality of the synthetic base stock and additive package.

          Consulting the manufacturer early in the selection process is the best approach to ensuring the right product is chosen for the application.

          — Joseph L. Foszcz, Senior Editor, 630-288-8776, jfoszcz@reedbusiness.com

          Performance characteristics of several lubricants

          Properties Mineral oil (paraffinic) Polyalphaolefin Dialkylated benzene Polyol ester Dibasic acid ester Polyglycol Phosphate ester Silicone fluid
          E = Excellent; VG = Very good; G = Good; F = Fair; P = Poor
          Viscosity-temperature F G F G G VG P E
          Low temperature P G G G G G F G
          High-temperature oxidation stability F VG G G E G F G
          Compatibility with mineral oil E E E G F P P P
          Low volatility F E G E E G G G
          Compatibility with paints and elastomers E E E P P G P VG

          Acknowledgements
          Plant Engineering magazine extends its appreciation to The Timken Corp. for providing the cover photo.

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