Lines suggesting a technical drawing of a gearbox over a mechanical shaft

Worm gear units

They are compact, robust and have been an integral part of KEB's portfolio for a long time: worm gear units. KEB gearboxes are made in Germany and are manufactured at the motor and gear unit factory in Schneeberg. When is it best to use worm gear units and how do they work? Here we give you an insight into the technical features.

The self-locking gearbox

Worm gear units are angular gearboxes that combine space-saving installation with a high gear ratio. Consisting of a helical shaft (worm shaft) and a gear wheel (worm wheel), the gearbox is used to reduce the input or motor speed and increase the torque.

Worm gear unit shaft mounted version with asynchronus motor

At a glance: What are the advantages of a worm gear unit?

Safety: The self-locking property of the gearboxes is desirable in many applications
High performance: Gear ratios of 1:40 or higher can be realised
Space-saving: Angular gearboxes can be integrated even where installation space is limited
High-quality: Worm wheel made of bronze with special sliding friction properties
Cleverly combined: At KEB, worm gearboxes are always combined with a helical gear stage
High load capacity: Suitable for heavy machinery and industrial applications

Cutaway model of a worm gearbox from the outside. Some areas are clearly marked, like the cutting points in yellow — Cutaway model of a worm gearbox from the outside... (picture 1/2)

Cutaway model of a worm gearbox from the inside. The focal point is the side on which the motor is normally mounted. Some areas are clearly marked, e.g. the intersections in yellow. The worm wheel and the bronze worm shaft underneath are clearly visible — ...and from the inside. The worm shaft is installed below the bronze worm wheel (picture 2/2)

How does a worm gearbox work?

In a worm gearbox, the worm shaft engages with the worm wheel and drives it. The worm gear set enables ratios of 1:40 or higher. This makes it ideal whenever high speed reductions are required. One of the main features of the gearbox, which is one of the so-called angular gearboxes, is the 90 degree arrangement of the output axis to the input axis. As with the bevel gearbox, this has the advantage that the worm gearbox has particularly compact dimensions and is therefore designed for tight installation spaces.

A classic transmission of movement from one wheel to the other does not take place in a worm gearbox. Instead, there is a sliding movement between the worm shaft and worm wheel. This is where the worm gear differs from helical gearbox or gear unit, for example, where the gear wheels roll against each other. The sliding movement in the worm gear unit is quiet, but has an impact on efficiency, which is why measures are usually taken to optimise this. This includes that the worm wheel is usually made of special materials such as bronze, which have very good sliding friction properties. A speciality at KEB: To improve efficiency, worm gearboxes are always combined with a helical gear stage, which efficiently distributes the transmission ratio in the gearbox.

Is a worm gearbox always self-locking?

The question of self-locking is directly linked to the efficiency of the worm gearbox. Depending on the ratio, worm gearboxes are self-locking and thus provide an additional safety aspect that is desirable in various applications. The self-locking function of the gearbox can be derived from the efficiency of the gearbox: The higher the self-locking function, the lower the efficiency.

In certain applications, self-locking is a desirable property. The self-locking worm gearbox cannot be moved backwards by the load of the application, as the movement is braked. This is advantageous, for example, when a load is lifted to a position in a lifting application or similar and cannot fall down due to the self-locking of the gearbox.

Do worm gear units have a high degree of efficiency?

As already described, there is a sliding movement between the worm shaft and worm wheel. This results in friction, which leads to a lower efficiency compared to other gearboxes. By using appropriate materials (e.g. bronze) with good sliding friction properties, the loss in efficiency can be partially mitigated. It should be noted that the friction between the worm shaft and the wheel generates heat, which must be dissipated. However, the lower efficiency also has advantages such as lower noise levels and self-locking properties. Depending on the design, an efficiency of less than 50 percent or up to over 90 percent can be achieved. The efficiency also depends on the speed: the faster the movement, the higher the efficiency. The individual efficiencies can be viewed in the corresponding documentation and are taken into account in the geared motor configurator "KEB-DRIVE" from KEB.

What worm gear designs does KEB offer?

Shaft mounted with torque arm + hollow shaft with shrink disc

Shaft mounted with foot area and hollow shaft

Flange mounted with foot area and hollow shaft

Helical worm gear unit in a warehouse at a conveyor system. The motor has an integrated frequency inverter — A worm gear unit in a conveying application

In which cases are worm gearboxes used?

When using a worm gearbox, it must be taken into account that the angular play between the worm wheel and worm shaft changes over the service life. For applications such as CNC machines or in medical technology, where precision must always remain unchanged due to delicate movements, the use of helical gearboxes is more suitable.

With this in mind, worm gearboxes are integrated in particular in applications that do not involve particularly complex movements. In principle, the compact dimensions of the angular gearbox, which also includes the bevel gearbox in addition to the worm gearbox, are an argument in favour of using them in applications with limited installation space. As worm gearboxes are self-locking (this will be discussed in more detail on this page), they are particularly interesting for use in lifts or hoists. This is because the self-locking function provides additional safety, as a lifted load cannot fall when the motor is switched off. Basically, the gearboxes are useful in applications that have to be kept under tension and wherever backward movements are not allowed to take place on their own.