Technical PresentationExternal Gears & its Application

Presented By: Prathamesh Deshpande

IntroductionA gear or cogwheel is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part to transmit torque.Geared devices can change the speed, torque, and direction of a power source. Gears almost always produce a change in torque, creating a mechanical advantage, through their gear ratio, and thus may be considered a simple machine. The teeth on the two meshing gears all have the same shape. Two or more meshing gears, working in a sequence, are called a gear train or a transmission. A gear can mesh with a linear toothed part, called a rack, thereby producing translation instead of rotation.The gears in a transmission are analogous to the wheels in a crossed belt pulley system. An advantage of gears is that the teeth of a gear prevent slippage.

History of GearEarly examples of gears date from the 4th century BCE in China, which have been preserved at the Luoyang Museum of Henan Province, China. The earliest gears in Europe were circa CE 50 by Hero of Alexandria, but they can be traced back to the Greek mechanics of the Alexandrian school in the 3rd century BCE and were greatly developed by the Greek polymath Archimedes.

Comparison with drive mechanisms

The definite velocity ratio that teeth give gears provides an advantage over other drives in precision machines such as watches that depend upon an exact velocity ratio. In cases where driver and follower are proximal, gears also have an advantage over other drives in the reduced number of parts required; the downside is that gears are more expensive to manufacture and their lubrication requirements may impose a higher operating cost per hour.

Single stage gear reducer

Gear Nomenclature

Types of Gear

External & Internal GearAn external gear is one with the teeth formed on the outer surface of a cylinder or cone. Conversely, an internal gear is one with the teeth formed on the inner surface of a cylinder or cone. For bevel gears, an internal gear is one with the pitch angle exceeding 90 degrees. Internal gears do not cause output shaft direction reversal.

External Gear Internal Gear

External Gear PumpAn external gear pump uses two external gears that displace non-lubricating fluids. The mechanism is usually driven by one of the toothed gears, which in turn drives the other. Three factors are involved in the regulation of flow: volume of cavity between the teeth, speed of gears, and the amount of fluid that slips back to the inlet via the mechanism. There are three main types of external gears: spur, helical and herringbone. Helical and herringbone deliver more flow at higher pressure while also being quieter, but may require a greater inlet pressure than spur.

Internal Gear PumpAn internal gear pump uses internal and external gears. The gears themselves are lubricated by the fluid, which is of a lubricating nature. The internal design is seen as being reliable, easy to operate and maintain due to only two moving parts being present. Only one drive gear is required for the mechanism to function but it is possible to use two.The design can also be modified to include a crescent shaped portion that improves performance when pumping high viscosity fluids. Internal gear pumps have relatively low speed and inlet pressure requirements.

External & Internal Gear Pump

External Gear Pump Internal Gear Pump

Application

References Linkshttp://processprinciples.com/2012/07/gear-pumps/http://www.slideshare.net/Nishalkadli/introduction-to-gears-15838360?next_slideshow=1https://en.wikipedia.org/wiki/Gearhttp://mechanicalmania.blogspot.in/2011/07/types-of-gear.htmlhttp://www.engineersedge.com/gear_design.htm