Bevel gears are solid blocks that are used primarily to change the directions of power transmissions. They are also used to change directions of rotational power at right angles without changing the speed to torque. The movement involves rolling of two bevels and this is how these gears got their name. They are conical in shape and they operate continuously without the need of lubricants and without the energy getting dissipated. Generally, their functional responsibility is to vary the direction of the drive within the power transmission systems by ninety degrees. The teeth are ground with precision and they can be straight, spiral or hypoid. Bevel gears gained plenty of importance with a boom in the automobile industry, in the early part of the last century.
Ø500mm max. ; Teeth L=80mm; Nr. of teeth 10-200; Max Module=up to 8mm which covers a vast range in size of bevels
Materials used to make Bevel Gears
It is important to note that bevel gears are either straight-toothed or helical-toothed. The latter get further classified into spiral and hypoid bevel gears. Gears with helical teeth are used for greater and smoother torque transmission. The basic requirements for materials that are used in the manufacturing of bevel gears are that they should be mechanically strong in bending and shear; they have to be resistant to chemical degradation and also resistant to wear and they should provide ease during the process of manufacturing.
Load size is an important factor for selection of materials
The materials that are used in the manufacture of bevel gears will vary depending on the size of the load. For high loads, ferrous metals are used. For example, grey cast iron can be used due to its low cost characteristics and high resistance to wear. Forged or rolled carbon and alloy steel can also be used under high speed and high stress conditions. Non-ferrous metals such as aluminum and its alloys along with non-metals like plastics are used generally in case of lighter loads.
The Manufacturing Process of Bevel Gears
The manufacturing process is divided into
- Pre-forming the blank with or without the teeth.
- Annealing of the blank when required. This is required in the case of cast or forged steels. Preparation of the gear blank is done to the needed dimensions by means of machining when teeth are produced or the pre-formed teeth are finished with the help of machining.
- Surface or full hardening of the machined teeth of the gear, when required.
- Finishing the teeth by means of grinding or shaving.
- Inspecting the finished bevel gear.
Types of Bevel Gears
Straight Bevel Gears – They are the most common type of bevel gear in which teeth are finished straight with slight curvature which is also known as crowning. This allows for a little misalignment during assembling with gearbox. The load carrying capacity with straight gears is high. Teeth are generally made from alloy steel.
Spiral Bevel Gears – They are used to transmit power between the shafts which are a right-angle orientation to each other. These custom parts are manufactured with precision teeth that have a unique curve and are oblique in their shape. The teeth of spiral bevel gears have one concave side and a convex side that feature a curve and they have a spiral angle. This angle is located from the trace of the tooth and the pitch cone, resembling a helix angle. There is less chance of the gears sliding within the gear teeth as these gears are not offset. This results in operation at low temperatures with efficient functionality. As there is a large amount of tooth surface, it allows for greater interlocking during the process of rotation. The customized spiral bevel gear are ideal for high speed and high torque transmissions and power generation. Their capabilities are M2 to M15 and they are made by initially cutting and then preparing the curved teeth so that the engagement of mating gear will be slow and with a higher tooth to tooth contact in comparison with straight bevel gearing. Spiral bevel gear have lower tooth loading when compared to straight bevel gears and they can turn eight times faster, permitting higher load capacity.
Zerol Bevel Gears – These gears are similar to the straight bevel gears. The main difference is in the shape of their teeth as they are curved in the case of straight gears while they are conical in the case of zerol bevel gears. A major variation is the spiral angle of the teeth of zerol bevel gears as they are machined. These teeth are manufactured in such a way that they maintain a gradual curve on both the convex and the concave sides. The manufacturing is done with high precision equipment for the purpose of surface finishing and tight tolerances.
Hypoid bevel gears – These gears are similar to the spiral bevel gears. The difference lies in the central lines of both shafts as they do not intersect each other. Hypoid bevel gears are used in the differentials of automobiles.
Applications of Bevel Gears
- Automobile Industry
- Manufacture of Electric and Diesel Locomotives
- Cooling Towers
- Firearms Manufacturing
- Marine Industry
- Heavy Duty Machinery Manufacturing
- Power Plants
- Printing Presses