Recipe for a Green Gearbox

Everyone knows that helical gearing is more efficient than standard spur gearing; most company literature, in fact, will claim that their helical gearing is up to 98% efficient (per stage of reduction). Helical gearing is machined with angled teeth, then hardened and ground, which is a complex but necessary process to achieve the high-efficiency gear mesh. The gear teeth are cut at an angle, so that during use, the gears gradually mesh. This allows two or three teeth of each gear to always be in contact, alleviating the load experienced by each individual tooth and creating a smooth transition of forces from one tooth to the next. This results is less vibration, less operating noise, and a longer gear life.

Quieter gears mean good news for employee hearing, which will please not only HR but OSHA inspectors as well. Most helical gearing is designed to be nearly maintenance-free, often requiring only regularly scheduled lubrication. Some units – such as Stober gear reducers – are packaged in sealed, oil-filled housings, and thus don’t even require oil changes.

But what makes a gearbox “green?” It’s not enough to simply benefit the user; let’s take a look at how these units can help increase overall efficiencies, thus requiring fewer resources to produce and operate.



Housings
Many gear reducers are designed for ease of assembly or for highly-automated assembly. This slightly lowers the overall cost, but it can greatly compromise the integrity of the housing of the gear reducer and adversely affect the quality. Compromised designs have additional plates and gaskets that are then bolted together to form the housing. The result is a housing assembly that flexes, causing gear misalignment, noise, vibration and limited life. Rigid, one-piece housings make gear reducer assembly more difficult and a bit more expensive, but the resultant increases in housing stiffness and rigidity keeps shafts and gears precisely aligned, even at high loads.



Lubrication
Inefficient gearing generates high heat losses that in turn elevate pressures inside the gear reducers that require venting to the outside environment. Venting lets air out, but it also lets air in. Incoming air contains contaminants and moisture, both of which work together to break down the oil inside the gear reducers. High-efficiency helical gearing such as Stober and Sumitomo do not generate as much heat, allowing gear units to be completely sealed and preventing moisture and contaminants from entering the oil chamber. Under normal operation, this oil should not break down for the life of the helical unit. Mineral oil is perfectly acceptable for most applications, although synthetic oils should be used for very demanding applications, especially applications requiring continuous use or operation in high-ambient temperature environments.



Seals
Seal surfaces run at high speed against metal surfaces, thus making them the wear items that typically determine the life of a gear reducer. The highest-quality designs, materials and handling and assembly practices are required to ensure that oil seals perform to the level required for long-life gear reducers.



Bearings
Bearings, whether roller, taper or cylindrical, are the other major wear items within gear reducers with high-speed metal-to-metal rolling contact under various load conditions. Proper selection and sizing, correct handling and assembly are all critical in ensuring long life in gear reducers. Many manufacturers find this to be the ideal location to lower the initial cost of a gearbox through the use of substandard components (although that may not be the company’s initial intent). However, for a properly-designed gearbox, cost control must be found in other areas such as operating efficiency, waste reduction, and continuous improvement; the build quality and component quality of the gearbox must never be compromised. This requires long-term thinking on the part of plant management, who must balance the higher acquisition cost of a high-efficiency gearbox with the calculated return over its service life.

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