Engrenagens retas: o que são e onde são utilizadas?

Spur gears: what are they and where are they used?

what are cylindrical gears

Spur gears are a type of cylindrical gear, with parallel and coplanar axes and straight teeth oriented parallel to the axes. They are probably the simplest and most common type of equipment : easy to produce and suitable for a wide range of applications.

The teeth of a spur gear have an involute profile and engage one tooth at a time. The involute shape means that spur gears produce only radial forces (no axial forces), but the tooth meshing method causes high stress on the gear teeth and high noise production. For this reason, spur gears are generally used for lower speed applications, although they can be used at almost any speed.

An involute gear tooth has a profile that is the evolution of a circle, meaning that when two gears mesh, they come into contact at a single point where the involutes meet. This point moves along the surfaces of the teeth as the gears rotate and the line of force (known as the line of action) is tangent to the two basic circles. Therefore, gears adhere to the fundamental law of gears, which states that the ratio of gear angular velocities must remain constant throughout the mesh .

Spur gears can be made from metals, such as steel or brass, or plastic, such as nylon or polycarbonate. Plastic gears produce less noise but degrade strength and load capacity. Unlike other types of gears, spur gears do not suffer large losses due to slipping, so they generally have high transmission efficiency .

Multiple spur gears can be used in series (referred to as a gear train) to obtain high transmission ratios.

There are two main types of spur gears: external and internal. External gears have teeth cut into the outer surface of the cylinder. Two external gears engage and rotate in opposite directions. Internal gears, on the other hand, have teeth cut into the inner surface of the cylinder. An outer gear sits inside the inner gear and the gears rotate in the same direction. Because the shafts are positioned closer together, internal gear sets are more compact than external gear sets. Internal gears are mainly used for planetary gears.

Spur gears can be supplied with a hub or can be simple without a hub, in general they are generally considered the best for applications that require speed reduction and torque multiplication such as ball mills and crushing equipment.

Examples of high-speed applications using spur gears, despite their high noise levels, include household appliances such as washing machines and blenders. And although noise limits the use of spur gears in passenger cars, they are often used in aircraft engines, trains, and even bicycles.

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