Gear Lubricants
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Background & Properties
July 2017
Types of Gears
Gears are the most common way to transmit power from one revolving shaft to another. Different combinations of
gears are responsible for increasing speed, decreasing speed and changing the direction of the shaft. Gears are usually
found in meshed pairs; the smaller gear is called the pinion and is responsible for speed reduction, and the larger gear
is called the ring gear and is used to increase speed.
Due to varying needs and applications, there are several different types of gears. A basic knowledge of the most
common types of gears, their components and method of operation is helpful in understanding which lubricants will
enhance gear performance. Below are some of the types of gears encountered in today's equipment. Each gear is
typically named for its general shape or by the arrangement of its teeth.
Spur Gears
A spur gear is a toothed wheel whose teeth run parallel to the gear shaft or axle. Spur gears are simple to
manufacture, limited in their load-carrying ability and known for their noisy operation. A variation of the spur gear can
be found in planetary gear sets.
Helical Gears
Helical gears transmit motion between non-intersecting parallel and nonparallel shafts. Similar in design to the spur
gear, the teeth of the helical gear are angled or twisted to allow several teeth to be in mesh at the same time. Because
the gear teeth engagement area is larger, helical gears can carry greater loads and tend to be much quieter and
smoother in operation than spur gears.
Herringbone Gears
A double helical gear is commonly called a herringbone gear based on the opposing angles of the gear teeth.
Herringbone gears can carry heavy loads at high speeds.
Bevel Gears
Bevel gears employ two intersecting shafts with meshing teeth cut straight across the face of a cone-shaped gear
blank. Bevel gears are commonly used when a 90-degree change in direction of shaft power is required. A special
grouping of bevel gears in automotive applications are known as differential gear sets. These gears are used to divide
power between two variable speed shafts.
Spiral Bevel Gears
The teeth of an ordinary bevel gear can be twisted to form a spiral bevel gear. The "spiral" look results from cutting
angled teeth into a cone-shaped gear. The angled teeth allow for a quiet, smooth transfer of power and a strong gear
system. Spiral bevel gears are typically found in off-highway equipment.
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