Gears or cogwheels are devices made of toothed wheels that transfer mechanical power between two elements. They are commonly used in machines employed in numerous industrial processes, such as production lines and drive systems, but also in sectors as diverse as mining, aeronautics, pharmaceuticals or textiles. The purpose for which they are manufactured determine the design of the gears (bevel gears, spur gears, helical gears, etc.) as well as their materials.
The use of gears is widespread because they offer many advantages:
- They occupy little space
- They can transfer large amounts of power
- They have a high performance
- They require very basic maintenance
- They eliminate any chance of slippage
In this article, we will focus on what a bevel gear is and how it works, so as to understand its uses and learn how to select the most appropriate for our project.
Free Ebook: Gear calculation: Boosting efficiency in your transmissions
Bevel gear characteristics
Bevel gears are those that use two conical toothed wheels to transfer power between axes that are cut within the same space; however, hypoid gears can transfer power between two axes that cross each other.
Teeth of a bevel gear can be either straight or spiraled, which is also known as a conical helix. Different types of gears can be classified based on their tooth width, but also on the tooth face width or the center’s circular pitch.
The following graph shows the gear nomenclature and its parts:
Types of bevel gears
There are several types of bevel gears based on the shape of their teeth. We will study them below:
Helical bevel gear
By combining a right-handed and left-handed helix, this type of gear is used to transfer motions between axes that intersect on the same plane. Therefore, they reduce the speed of a shaft at a 90 degree angle.
They are usually employed in rear axle transmissions of motor vehicles, and they are known for their low noise generation.
The main difference when compared to straight gears is that the edges of the teeth are not parallel to the axis of rotation, but they are angled instead.
Hypoid gear
It is less common and can be considered as a helical bevel gear, but the main difference lies in that these devices are composed of a speed-reducing pinion that has few teeth and a gear that has a high number of teeth.
They are used in situations in which the shafts are perpendicular but are not within the same plane.
In addition to being used in industrial machinery, they are commonly used in the automotive industry, where it is used in rear-wheel drive vehicles to connect the driveshaft with the wheels. They use a kind of oil that is characterized by its high pressure.
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Straight bevel gear
Its straight teeth are placed on bevel surfaces thanks to their milled outer surface.
They are useful to verify the transmission of the motion that is generated between axes that intersect within one same plane, almost always at a 90-degree angle.
Even though they are only used to achieve a speed reduction in shafts placed at straight angles, they can also operate a 45, 60 and 70 degrees. Unlike helical bevel gears, they have little mating surface.
Spiral bevel gear
These bevel gears have the particularity of operating at very steep and varying planes.
Their meshing sets them apart, since the pinion’s teeth are wider than those of the main gear.
This makes it easier for them to transfer very high torques without wear, since the pinion’s teeth mesh with the various teeth of the main gear.
What are bevel gears used for?
Each type of bevel gear is usually employed in specific operations:
Straight bevel gears
Even though they are somewhat in disuse when compared to other types of gears, partly due to the noise that they generate during their operation, straight bevel gears still have many uses in watches, dentist drills, hand drills and vending machines.
They are also still used in certain sectors, such as in the handling of materials, etc. they are commonly seen in food packaging and canning, lawn and garden equipment, machines such as drills and mills, compression systems for the gas and oil market and flow control valves.
Spiral bevel gears
These gears have modified teeth. Bevel gears are used in situations in which it is important to invert the direction of rotation of the shafts.
In spiral bevel gears, the teeth are curved in order to provide for a smoother meshing and greater tooth vs. tooth contact when compared to a straight bevel gear.
This reduces the vibrations and noise that usually take place when gears such as straight bevel gears and others move at high speeds.
Related reading: Guide for preventing annoying noises and vibrations in your speed reducers
Spiral bevel gears provide a high level of control over the way in which teeth mesh, and their design allows for certain mounting deflections without excessively increasing the load on either end of the teeth.
They can be used at high speeds, and are usually employed in motorcycle and bicycle gears.
Hypoid gears
Hypoid gears are used, in many cases, when speeds exceed 1,000 revolutions per minute.
In spite of this, they are useful for low-speed applications that require an extremely smooth motion or a silent operation.
In multistage gearboxes, hypoid gears are often used at the output stage, which requires lower speeds and higher torques.
The most common application of hypoid gearboxes is in the automotive industry, where they are used in rear axles – especially in big trucks.
Their angles – a right-hand spiral on the main gear and a left-hand spiral on the pinion – allow for a motion “below the center.” This allows for the driveshaft to be placed at the bottom, which leads to a lower center of gravity for the vehicle and does not affect the passenger compartment so much.
Real applications of bevel gears
Bevel gears are used in a wide variety of applications, which range from the mining sector (wheeled excavators, stacker and scoop actuators, dredges, mill actuators, conveyor belts, etc.) to the aerospace sector (high-speed straight and spiral bevel gears, special steels and processes, air pre-heater, etc.).
They are also common in conical mills and sand mixers, forklifts, cooling towers, ship actuators and propellers, high-speed offset printing, pharmaceutical packaging machines, polyethylene sheet production and automotive and rail transmissions.
In robotics, angled bevel gears are used for small spaces, while in ferrous metallurgy they are used in rolling mill vertical supports.
In regard to food processing, bevel gears play a major role in the packaging and processing of food and in can manufacturing equipment.
Now that you know all the uses and characteristics of bevel gears, you might want to go one step further and start applying them to your own projects.
Need more information when choosing the type(s) of bevel gear(s) for your projects? Contact us and our team of experts will advise you to select the best gears for your plans.
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