January 2022

36 n GEARS AND GEARBOXES January 2022 www.drivesncontrols.com Know your gears: choose the right technology G ears are among the most important components in a wide variety of drivetrains, transmitting the right amount of movement and force to ensure the smooth running of machinery. Today, the development of gears and geared motors is extremely advanced. Improvements to materials, designs and efficiencies are approaching their limits, meaning that new developments are more likely to be seen on the electronic side. But engineers still need to understand how these vital components will integrate into their applications. There are five main types of gear that engineers need to be aware of: helical, parallel shaft, bevel, worm and planetary. Helical gears are the most common type of gear wheel. You need to distinguish between different types of gearing. The simplest are straight-cut gears. These typically use involute helix gearing. If higher torque levels need to be transmitted, helical-cut gears can be used. They run more smoothly on each other, resulting in quieter running. A disadvantage of helical-cut gears is that they generate axial forces, which must be absorbed by their bearings. The bearings must be able to absorb both radial and axial forces. Helical gearmotors are used in applications such as presses, conveyors, rotary tables, pumps, packaging machines and bakery equipment. Parallel shaft gears also use helical gearing, but unlike conventional helical gears, the input and output shafts are offset parallel to each other. This results in compact axial dimensions, helping to save space. Additionally, these are usually multi-stage gearboxes with parallel shafts, typically with a hollow output shaft, allowing the gear to be mounted on an existing shaft. Typical applications for parallel shaft gearboxes include screw conveyors, extruders and travel drives. Bevel gears are characterised by axes that are not parallel to each other and are used to transmit power to two axles spinning at different speeds – such as in lifts. In principle, bevel gear wheels can achieve any axis angle. In most cases, however, the input and output axes are at an angle of 90 degrees to each other. Bevel gears are often combined with helical gearing in industrial gearmotors for applications such as agitators, winches, lifts, heavy-duty conveyors for bulky goods, shredders and baggage-handling systems. Worm gears consist of a worm and worm wheel, and can achieve high transmission values in a small space. A worm can be envisaged as a screw, with the number of teeth in the gear wheel corresponding to the number of gears in the worm. However, due to the friction that occurs on the flanks of the worm and wormwheel, their efficiency is lower than helical gears. To counteract this and to tackle the high thermal losses, good lubrication is needed – sometimes with additional cooling for high power outputs. Worm gears are used in applications such as lifts, packaging machines and light conveyors. Planetary gears consist of gear wheels with fixed axes of rotation (called central or sun gears) used in combination with non- stationary gear wheels (planetary gears). They are available in many versions with differing transmission ratios, depending on the shaft where the output takes place. A distinction is made between fixed ring gears, fixed sun gears, fixed racks or direct drives. Planetary gears typically provide high torque densities and precision for applications such as wind turbines, track drives, crushers, shredders and robots. When choosing gearboxes, engineers should be aware of what loads and environmental factors the gears will be exposed to. You also need to consider requirements such as drive outputs, controls and ambient conditions, especially when retrofitting. Installing a gearbox should not require design changes to an existing machine. While there is a lot of published information about gears, it is not always clear or correct. WEG has produced a free gearbox guidebook, called What mechanical engineers and plant operators need to know about gears , (downloadable from https://weg-wg20.com ) to ensure that engineers choose the most appropriate type of gear for their application, and to quash a few misconceptions. n Engineers and plant operators who specify industrial gearboxes are not always experts in gear technology – and the published data on gears is not always clear or correct. To help simplify the decision-making process, Marek Lukaszczyk, WEG’s European and Middle East marketing manager, explains the main types of gear. Geared motors are available with a choice of gear technologies to suit different applications