FEATURE GEARS & GEARBOXES Know your gears


While you may be responsible for gear selection, you may not be an expert in gear technology. Marek Lukaszczyk, European and Middle East marketing manager of WEG, helps simplify the decision-making process by explaining each gear type


D


esigned to transmit the right amount of movement and force to ensure the smooth running of a machine, gears are one of the most


important components in a drive train. Engineers, however, require a complete understanding of the basic principles and suitable applications of each gear type before they can specify them. Today, the development of gears and geared motors is at an extremely


advanced stage. Improvements to materials, designs and efficiencies have largely been exhausted, meaning it is more likely that new developments will be seen on the electronic side. Engineers therefore need to understand how these machine components will integrate into their application and the overall digital factory package. There are five gear types that engineers need to be aware of – these are helical, parallel shaft, bevel, worm and planetary.


Helical gears: These are a common type of gear wheel, with a distinction made between the different types of gearing. The simplest is straight cut gears. As a rule, this type of gearing uses involute helix gearing. If larger torques are to be transmitted, helical cut gears are used for the gear unit design. These run more smoothly on each other, enabling quieter running gears. However, these generate axial forces which, in turn, must be absorbed by


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the bearings of the gear unit. In this case, this requires bearings that can absorb both radial and axial forces. Applications for these gearboxes include presses, conveyors, rotary tables, pumps, packaging machines and bakery equipment.


Parallel shaft gears: Parallel shaft gearboxes also utilise helical gearing but, in contrast to conventional helical gear units, the input and output shafts are offset parallel to each other. Due to this design, the axial dimensions of the parallel shaft


gear unit are compact, helping to save space. Additionally, these are usually multi-stage helical gear units with parallel shafts, comprising an output shaft which is usually a hollow shaft, allowing the gear to be mounted on an existing shaft. Typical applications include screw conveyors, extruders and travel drives.


Bevel gears: Characterised by the axes not being parallel to each other, bevel gears are used to transmit power to two axles spinning at different speeds – such as lift applications. In principle, any axis angle can be achieved with bevel gear wheels. In most cases, however, the input and output axes are at an angle of 90˚ to each other. Bevel gears are often combined with helical gearing in industrial


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gearmotors, with wide areas of application including agitators, winches, lifts, heavy-duty conveyors for bulky goods, shredders and baggage handling systems.


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Xtra compactness Xtra rigidity Xtra external loads


The Xtra powerful XP+ Planetary gearbox


WITTENSTEIN alpha – Intelligent drive systems www.wittenstein.co.uk


Worm gears: The worm gear units consist of the worm and the worm wheel, meaning a high transmission can be achieved in a small space. A worm can be imagined 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


performance


worm wheel, the efficiency of the gear unit is lower compared to helical gears. These high thermal losses necessitate good lubrication and sometimes additional cooling for high power outputs to counteract this problem. Suitable applications for these include elevators, lifts, packaging machines and light conveyors.


Planetary gears: Gear wheels with fixed axes of rotation are called central or sun gears, while the non-stationary gear wheels are called planetary gears. Planetary gears are available in many versions with various transmission ratios, depending on the shaft where the output takes place. A distinction is made between gear units with fixed ring gear, fixed sun gear, fixed rack or direct drive. The gear arrangement typically provides a high torque density and


precision, with wide-ranging fields of application, including wind turbines, track drives, crushers, shredders and robotics.


THE SPECIFICATION PROCESS When selecting which gear type, engineers should also know what loads the gear unit will be exposed to as well as the environmental factors – such as space requirements including drive output, drive control and other ambient conditions that must be considered, especially when retrofitting. This is because installing a gear unit should not require design changes to the existing machine or system.


WEG 18 FEBRUARY 2021 | DESIGN SOLUTIONS www.weg.net / DESIGNSOLUTIONS


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