Industrial Gear Lubrication
by David Doyle, CLS, OMA I, OMA II
General Manager, Tribology

Over the years industrial gear application requirements have demanded more power in a smaller footprint with decreased oil volume. This has led to gear lubricants performing the same workload under harsher operating conditions with a longer service life. Newer gearbox designs have smaller oil reservoirs, while operating with higher workloads, thus putting greater demands on lubricants. Gear applications with smaller sump volumes and higher power output with smaller gear box size (power density) are expected to be more durable while more performance is demanded of the lubricant. Tighter tolerance with higher speeds and lighter weight materials help achieve a smaller foot print and energy efficiency with increased loads. Lower operating costs, and improved efficiency is the main driver in today’s engineering designs.

Gear lubricants used in modern engineering designs are exposed to hotter operating temperatures and must perform in conditions and applications that vary significantly. A properly performing gear lubricant also needs to be able to remove contaminants. Abrasive particulate contaminants in some work environments such as manufacturing plants, mining, cement and aggregate enter gear boxes through poor seals, breathers, or vent filters. Contaminants are also internally generated due to wear and lubricant degradation products over time. The lubricant is also expected to remove heat that the machinery generates due to friction while protecting itself from viscosity breakdown due to the heat. A good gear lubricant also requires resistance to foaming and can shed water readily.

Lower viscosity lubricants with optimized additive packages improve energy efficiency performance. A balance of viscosity for the right application is critical; higher viscosity creates more heat, lower viscosity reduces the thickness of the lubricating film for wear protection, EP and lubricity additives help with this. Gears experiencing heavy loads and high temperatures require a lubricant with a high enough viscosity to prevent micropitting. Micropitting starts with fatigue cracks on the surface (or just below the surface) of the gear teeth. Micropitting eventually leads to material loss on gear teeth. There can be situations when additives used to enhance extreme-pressure properties can be prone to thermal stability issues, resulting in the formation of sludge. Newer gear oil formulation technology is required to balance thermal stability to prevent sludge formation on gear sets and extreme-pressure protection for heavy-duty durability. Proper additive compounding of the lubricant provides micropitting resistance with improved EP additives, oxidation resistance, corrosion inhibitors, control of sludge formation, and viscosity performance at greater operating temperature ranges.

Quality of the gear oil is important and should be formulated for the application needs. In some situations synthetics may be the best choice due to accessibility and limited downtime. The lubricant is required to be compatible with gearbox components, metallurgy, seals, and paints. Gear lubricant formulations can vary depending on application and design:

  • R&O Inhibiting Gear Oils: Rust and oxidation (R&O) inhibiting gear lubricants
  • EP Gear Oil: Extreme-pressure (EP) gear oils are recommended for gear drives subjected to conditions of high load, medium-to-high slide and high-power transmit
  • Compounded Gear Oils: Compounded gear oils lubricated gear drives where the high sliding of gear teeth requires a friction-reducing agent to minimize heat and improve efficiency (enclosed worm gear drives
  • Synthetics: Synthetic gear oils are primarily used in applications where mineral-based industrial gear oils are unable to perform. Synthetic gear lubricants can contain R&O inhibitive additives and/or EP additives

ALS Tribology provides standard and in-depth gear oil testing, from routine monitoring and trending analysis to wear particle analysis and product formulation compatibility.