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Knowledge Center Gear Oils: Part 1 – How Different Base Stock Chemistries Affect Industrial Gear Oil Performance Discover how different base stock oils (mineral, PAO, ester, PAG) make a big difference in gear oil performance.

  • Mineral oils and synthetic lubricants – polyalphaolefins (PAO), esters and polyalkylene glycol (PAG) – are common base stock chemistries used for industrial gear oil.
  • This quick overview explains their different chemistries to provide a basic understanding of benefits and drawbacks.

There are two categories of common base stock chemistries for industrial gear oils:

  1. Mineral Oil Stocks (Typical temperature range: -4 to +212°F/-20 to +100°C)
    Mineral oils can be defined as either paraffinic or naphthenic base stocks. The three main grades of base stock are defined by API groups: Groups I, II, and III. As a basic rule of thumb, each group is refined using different techniques, which results in typically higher purity and, therefore, better properties with the higher group numbers. Mineral oils are widely used, because they are typically the least expensive and easiest to manufacture. They usually have lower viscosity indices (VI) than most other gear oils.
  2. Synthetic Lubricant Stocks
    Synthetic oils have specific properties to increase and enhance their performance when used in severe applications. Many of the various synthetic oil types have improved low-temperature performance, better pour points and are much more stable at higher temperatures than mineral oil formulations. This increased temperature stability also translates to better viscosity indices, so they will hold a more stable viscosity over a wider temperature range.Some of the physical, chemical and thermal advantages to synthetics can also result in a more efficient gearbox. These advantages can also lead to a gearbox running cooler, which can extend the life of various components, as well as the life of the oil. Several different types of synthetic oils are available:

    • PAO (Typical operating temperature range: -40 to 140°C)
    • Biodegradable Esters (Typical operating temperature range: -25 to 100°C)
    • PAG (Typical operating temperature range: -35 to 160°C)

Read Part 2 on making the proper gear oil specification.

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