As we have seen elsewhere, there are various types of gears like spur gears, bevel gears, rack and pinion, helical gears, etc. By their very definition gears mesh with each other. It is therefore very important to keep the teeth and the meshing area free of anything that interferes with their working. The gear case is a cover or casing (typically cast in some metal) that encloses the gear mechanism.
Considerations for Gear Cases
Gears are an important and integral part of mechanical systems. Gears are needed whenever there is a need to vary the torque, speed and direction of mechanical forces. Transmission system of a car is a prime example where gears are used to transmit the power generated by the engine to the driving wheels. Since gears typically work by meshing, they generate a lot of heat. The gear case should be able to dissipate this heat. In addition, gear cases have to bear the weight of the gears. Gear cases should also give protection to the gears from natural elements like heat, rain, snow, dust, etc. They also need to dampen vibrations, especially for gears that are used in high speed applications. The sole purpose of gear cases is to protect the gear mechanism within. They should therefore be sturdy, ye lightweight. This requirement – of the gear case being lightweight – is very crucial in the manufacturing of airplanes.
Gear Case Material
The materials used for the manufacture of gear cases depend upon the strength requirements and nature of use wear, noise etc. While gear cases may be manufactured from metallic or non-metallic materials, the most popular choice for casting gear cases is cast iron and cast aluminum. Both provide excellent durability.
To some extent, the gear case material is also dependent on the type of gears used. Cast aluminium has a distinct advantage over other gear cast materials wherever dissipation of heat is required – for example in worm gears. Cast iron is almost 3 times as heavier as cast aluminium. Therefore, where weight is a constraint, like automobiles, aluminium gear cases are the preferred choice. However, cast iron (ductile, sand cast, etc,) is cheaper as compared to aluminium alloys and sturdier. In addition, iron alloys maintain their size and shape across a wide range of temperatures since they have a coefficient that is less than half of aluminium.
And of course, a one piece gear case is preferred to split gear case in order to prevent lubricant leaks.