In this article, we will explore some of the most common types of gears and their applications.
Types of gears
There are many types of gears, and the most common classification method is based on the axial characteristics of the gears. It is generally divided into three types: parallel axis, intersecting axis, and staggered axis.
- Parallel axis gears include spur gears, helical gears, internal gears, rack and helical gears, etc
- Intersecting axis gears include spur bevel gears, spiral bevel gears, zero degree bevel gears, etc.
- Cross axis gears include cross axis helical gears, worm gears, hypoid gears, etc
Introduction to specific types
- Spur Gear.
- Helical Gear.
- Gear Rack.
- Bevel Gear.
- Spiral Bevel Gear.
- Screw Gear.
- Double Helical Gear
- Herringbone Gear
- Hypoid Gear
- Miter Gear.
- Worm Gear.
- Internal gear
It is necessary to accurately understand the differences among gear types to accomplish necessary force transmission in mechanical designs.
Spur Gear
Spur gears feature a simple design of straight, parallel teeth positioned around the circumference of a cylinder body with a central bore that fits over a shaft.
In mechanical applications, spur gears transmit motion and power from one shaft to another through a series of mating gears. Thereby increasing or decreasing equipment speed or increasing torque.
Spur gears are used to transfer motion and power from one shaft to another in a mechanical setup. This transference can alter machinery’s operating speed, multiply torque, and allow for the fine-tuned control of positioning systems. Their design makes them suitable for lower-speed operations or operational environments with a higher noise tolerance.
Helical Gear
Helical gears are one type of cylindrical gear with a slanted tooth trace. Compared to spur gears, they have a larger contact ratio and excel in quietness and less vibration, and are able to transmit large force. A pair of helical gears have the same helix angle but the helix hand is opposite.
The teeth of a helical gear are set at an angle (relative to the axis of the gear) and take the shape of a helix. This allows the teeth to mesh gradually, starting as point contact and developing into line contact as the engagement progresses.
One of the most noticeable benefits of helical gears over spur gears is less noise, especially at medium- to high speeds. Also, with helical gears, multiple teeth are always in mesh, which means less load on each individual tooth. This results in a smoother transition of forces from one tooth to the next, so that vibrations, shock loads, and wear are reduced.
Gear Rack
Same sized and shaped teeth cut at equal distances along a flat surface or a straight rod is called a gear rack. A gear rack is a cylindrical gear with the radius of the pitch cylinder being infinite. By meshing with a cylindrical gear pinion, it converts rotational motion into linear motion.
Gear racks can be broadly divided into straight tooth racks and helical tooth racks, but both have straight tooth lines. By machining the ends of gear racks, it is possible to connect gear racks end to end.
Bevel Gear
A bevel gear is a toothed rotating machine element used to transfer mechanical energy or shaft power between shafts that are intersecting, either perpendicular or at an angle. This results in a change in the axis of rotation of the shaft power. Aside from this function, bevel gears can also increase or decrease torque while producing the opposite effect on the angular speed.
A bevel gear can be imagined as a truncated cone. At its lateral side, teeth are milled which interlock to other gears with its own set of teeth. The driver gear is a gear that transmits shaft power, while the driven gear is a gear that transmits power
The number of teeth of the driver and driven gear are usually different to produce a mechanical advantage. The ratio between the number of teeth of the driven to the driver gear is known as the gear ratio, while the mechanical advantage is the ratio of the output torque to the input torque.
Spiral Bevel Gear
Spiral bevel gears are bevel gears with curved tooth lines. Due to the higher tooth contact ratio, they are superior to straight bevel gears in efficiency, strength, vibration, and noise. On the other hand, they are more difficult to produce.
Also, because the teeth are curved, they cause thrust forces in the axial direction. Within the spiral bevel gears, the one with zero twisting angles is called zerol bevel gear.
Screw Gear
Screw gears are a pair of same hand helical gears with the twist angle of 45° on non-parallel, non-intersecting shafts. Because the tooth contact is a point, their load carrying capacity is low and they are not suitable for large power transmission.
Since power is transmitted by the sliding of the tooth surfaces, it is necessary to pay attention to lubrication when using screw gears. There are no restrictions as far as the combinations of a number of teeth.
Double Helical Gear
Double helical gears are a variation of helical gears in which two helical faces are placed next to each other with a gap separating them. Each face has identical, but opposite, helix angles.
Employing a double-helical set of gears eliminates thrust loads and offers the possibility of even greater tooth overlap and smoother operation. As the helical gear, double helical gears’ commonly application: enclosed gear drives.
Herringbone Gear
Herringbone gears are very similar to the double-helical gear, but they do not have a gap separating the two helical faces. And herringbone gears are usually smaller than similar double helix gears and are very suitable for high impact and vibration applications.
Hypoid Gear
Hypoid gears look very much like spiral bevel gear, but unlike spiral bevel gears, they operate on shafts that do not intersect. In the hypoid arrangement, because the pinion is set on a different plane than the gear, the shafts are supported by the bearings on either end of the shaft.
Miter Gear
Miter gears are bevel gears with a speed ratio of 1. They change the direction of power transmission without changing speed. There are straight miter and spiral miter gears. When using the spiral miter gears, it becomes necessary to consider using thrust bearings since they produce thrust force in the axial direction.
Angular miter gears is besides the usual miter gears with 90° shaft angles, miter gears with any other shaft angles
Worm Gear (Different types of gears)
What is worm gear?
A screw shape cut on a shaft is the worm, the mating gear is the worm wheel, and together on non-intersecting shafts . Worms and gears are not just cylindrical. There is the hour-glass type which can increase the contact ratio, but production becomes more difficult.
Due to the sliding contact of the gear surfaces, it is necessary to reduce friction. Therefore, worm gears typically use hard materials, while worm gears typically use soft materials. Even though the efficiency is low due to the sliding contact, the rotation is smooth and quiet. When the lead angle of the worm is small, it creates a self-locking feature.
Internal gear (Different types of gears)
External gears matches to the internal gears have teeth cut on the inside of cylinders or cones . The main use of internal gears is for planetary gear drives and gear-type shaft couplings. There are limitations in the number of teeth differences between internal and external gears due to involute interference, trochoid interference, and trimming problems.
The rotational directions of the internal and external gears in the mesh are the same while they are opposite when two external gears are in the mesh.