SMS Elotherm offers innovative machine concepts for the hardening of gear rings and large rings. High-throughput processes are available for hardening the teeth and bearing races of large rings. For bearing race hardening, SMS Elotherm has developed and patented the progressive scan hardening method, which avoids the otherwise customary soft zone – a new milestone in ring hardening. With the SMS Elotherm Configurator, systems that fulfil all customer requirements can be assembled from individual modules. The modular architecture facilitates economically-tailored and suitably-dimensioned hardening systems with optimised set-up times.


Whether in salt water environments, on the open sea or in dusty mining areas, gear rings must be able to withstand extreme conditions. It is essential that dynamically-loaded components in offshore wind turbines or in large mining machinery function reliably and with virtually zero maintenance.

The wear-resistant surfaces necessary for this are produced by induction hardening.

With wind turbines, for example, three different processes are used for induction surface hardening: scan hardening with or without a soft zone, and single-shot (full area) hardening.


Scan hardening and single-shot hardening

Diameter up to 10 m

Sensor-based inductor positioning

Hardening of ring segments


Ring hardening machine

Controlled microstructure modification

The microstructure of the steel is modified in a controlled manner by a combination of defined induction heating and quenching with a fluid, resulting in hardening of the material. This physical effect is used for the teeth as well as the bearing races. The induction machines from SMS Elotherm induce precisely the energy necessary for the ring hardening process. Systems such as patented workpiece performance measurement or sensor-based inductor positioning enhance the effectiveness and precision of the hardening method and ensure consistent and repeatable high workpiece quality.

Hardening of gear rings

A versatile ring hardening machine from SMS Elotherm is the ideal solution for the induction hardening of gear rings with scan or single-shot hardening and spray quenching. With all necessary components and units mounted on a base frame, the most impressive features of the compact hardening machine are its high precision and productivity for ring hardening.

Short cycle times are achieved by using satellite tables. Loading and unloading are horizontal, while the induction hardening machine operates with a fully automatic NC controller. The regulated feed speed can be precisely adjusted to match the workpiece. Precise induction hardening of the gear teeth is ensured through a touch sensor on the inductor. A spray head mounted directly on the inductor quenches the workpiece to achieve an optimal microstructure. The flow rate can also be programmed for individual workpieces.

Ring hardening
Ring hardening horizontal

Ring hardening machine for large gears

EloRing Horizontal

The EloRing Horizontal ring hardening machine is mainly used for the induction hardening of large gears. Compared to a case hardening furnace, the induction ring hardening machine requires less capital expenditure, while offering higher process reliability as well as significantly higher energy efficiency and therefore a lower environmental impact.

The challenge in ring hardening is that due to upstream production steps, the rings no longer match their predefined dimensions. This means that a preconfigured hardening process will not lead to optimal results.

To counter this, SMS Elotherm uses a combination of NC-controlled and sensor-based inductor guidance. This technologically mature method ensures precise positioning of the inductor between two tooth modules. It also ensures perfect spacing between the inductor.

Bearing race hardening

SMS Elotherm offers two solutions for bearing race hardening: the standard machine EloRing Vertical with a workpiece orientation of 70° for scan hardening of large roller bearings, and the pivoting EloRing Tilt with workpiece orientation from 0° to 70° for scan hardening of large roller bearings and large gears.

For hardening of single-row or multi-row races of large roller bearings, the standard version of the EloRing Vertical machine is the right choice. It enables scan hardening with a soft zone. With this machine, the ring rotates and is guided past the inductor with the quenching device, resulting in a soft, unhardened zone at the end of the cycle. Rings with a diameter of about 3 m can be completely hardened in less than one hour.

Ring hardening vertical
Inductive hardening of rings

Progressive scan hardening for rings

SMS Elotherm has developed and patented the progressive scan hardening method for rings of any size. With EloRing Seamless, the soft zone otherwise resulting from the process can be avoided.

Rings hardened on this machine are suitable for all high-load applications, such as vibration loads in nuclear spin tomography machines, extreme mechanical stresses in tunnel boring heads, or weather-resistant and permanently installed rings in offshore installations.

EloRing Seamless has only two inductors instead of the usual three, making it easier to maintain and reducing the complexity of the mechanical and control subsystems. In the start sequence the inductors are moved together. After moving together in the same direction for a short while, one of the inductors starts moving in the opposite direction, which avoids leaving a soft zone at the start of hardening.

The inductors meet again after each has travelled around half of the circumference. At this point, correctly controlled quenching is essential to avoid tempering or a soft zone.