A look at the three most critical activities in the production of high-quality gears and gear boxes

By Chinnappan Selvaraj

Think gears, and you probably think cars. But gears are so much more than that. Used across a plethora of industries – from automotive to aerospace and even sugar and steel manufacturing – gears are one of the oldest, and most important mechanical components used in manufacturing. The manufacturing of gears themselves, then, is a complex and intricate process, with precision required each step of the way. Let us dive into the three key stages that make up the gear manufacturing process.

Raw Materials Manufacturing

It all begins at the design stage. Based on the safety factor required for a particular application, the correct raw materials are identified. For instance, gears and pinions are usually made out of case-hardened alloy steels. It is ideal if this alloy steel is produced using the Vacuum Degassing method.

During the steel smelting process, unwanted gases often get dissolved into the liquid, which could produce any number of imperfections and defects. A common method used to remove these undesired gases is Vacuum Degassing. The process is done after the molten steel has left the furnace and before being poured into ingots or introduced into a continuous caster.

During the steel-making process (while the molten steel is still in the ladle, and before it is poured), it is degassed in order to:
a) reduce/eliminate dissolved gases, especially hydrogen and nitrogen;
b) reduce dissolved carbon (to improve ductility); and
c) promote preferential oxidation of dissolved carbon (over chromium) when refining stainless steel grades.

This method enables the production of alloy steels with minimal oxygen, hydrogen and nitrogen contamination. Doing so helps avoid embrittlement of the steel. Next, the chemical and mechanical properties of the alloy steel are verified via Ultrosonic Testing. This is carried out to ensure crack-free material.

Heat treatment

Heat Treatment is a critical stage of the gear manufacturing process.

Depending on the application, designers choose Gas Carburising and Hardening, Nitriding, Induction Hardening process. During these processes, it is important to check the carbon potential on the alloy steels. Based on the gear modules, case depth must be maintained.

To ensure correct case depth, a test piece should be loaded along with the components. After carburising, this case depth should be verified. Finally, during the heat treatment process, the case depth, hardness and microstructure has to be checked. This is necessary to ensure the production of a good-quality gear.

Gear Profile Grinding

This is the third critical process in the performance of a gear box. Profile grinding helps to get a better contact pattern between the pinion and mating gear, which will ensure smooth rotation and less noise during operations.

During profile grinding, the required gear profile accuracy can be ensured by dressing of grinding wheels properly. The Face Runout of the gears (the inaccuracy in radial location of the gear teeth with reference to the pitch circle, according to ScienceDirect.com) must also be controlled before starting the profile grinding.

Profile graphs must be made check the level of accuracy. Generally, the standard used is AGMA10. The chart below demonstrates some of the other country-wide accuracy standards used in the industry.

The above three major activities are critical to the production of high-quality gears and gear boxes. Paying attention to these processes will contribute to reducing gear box noise, vibration and temperature. This in turn, will have a huge impact on improving gear box life, and ensure good performance.

The author, C Selvaraj, has four decades of experience in the field of gears and gearbox manufacturing, as well as servicing of gearboxes