In brief
A worm gearbox is a right-angle gearbox in which a worm shaft drives a worm wheel, achieving high ratios in a single stage.
Contents
What is Worm gearbox?
In a worm gearbox, the input and output shafts are usually at right angles to each other without intersecting. The worm resembles a threaded spindle and meshes with the worm wheel. High reduction ratios are possible with just one stage. The tooth flanks slide on one another, so worm gearboxes run very quietly and absorb shocks, but they have a lower efficiency than helical or bevel gearboxes.
A common pairing is a hardened steel worm with a bronze worm wheel, optimised for sliding properties. At high ratios, the gearbox can be statically self-locking; however, this does not count as a reliable brake or protection against back-driving, because vibration can cancel the self-locking effect. Key parameters are ratio, centre distance, output torque, efficiency, mounting position and shaft design, often with a hollow shaft.
Worm gearboxes are widely used in conveyor systems, lifting tables, agitators, packaging machines and dosing equipment. Typical damage is wear of the bronze wheel, leaks at shaft seals and overheating due to incorrect or aged oil. Wear of the wheel often shows up as bronze particles in the oil and increasing play at the output.
In practice: maintenance and procurement
When sourcing a replacement, the ratio, centre distance, mounting position and shaft design are important, as the oil quantity depends on the mounting position. The lubricating oil must be suitable for the bronze pairing; oil changes should only be carried out with the oil type approved by the manufacturer.
Synonyms and abbreviations: worm gear · worm gear reducer · worm drive · right-angle gearbox · wormwheel gearbox
Frequently asked questions
Is a worm gearbox self-locking?
That depends on the ratio, the lead angle of the worm, friction and the operating state. At high ratios, a worm gearbox can be self-locking at standstill. During operation or under vibration, however, this self-locking can be cancelled. Where back-driving would be dangerous, for example in lifting equipment, an additional brake must therefore be provided.
Why does a worm gearbox have lower efficiency?
The tooth flanks of the worm and worm wheel slide on one another to a large extent instead of mainly rolling. This generates frictional heat. The higher the ratio, the lower the efficiency as a rule. For long operating times, a bevel-helical gearbox may therefore be more energy-efficient, even if it costs more to buy.
What information is needed to replace a worm gearbox?
Needed are type designation, size or centre distance, ratio, mounting position, input and output design such as hollow shaft, solid shaft or flange, and also motor power and motor mounting. For installation compatibility, the fixing dimensions and housing shape are important. The nameplate contains most of this information.
What oil does a worm gearbox need?
Worm gearboxes with a bronze wheel need oils suitable for this material pairing. Synthetic polyglycol oils are often used, but they are not miscible with all other oils. The lubricant specification of the gearbox manufacturer is decisive. Changing to a different oil base usually requires thorough flushing.