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Hardened Solutions in linear motion

The benefits of induction hardened linear guides in heavy duty applications.

To better manage heavy loads and to better resist both wear and deformation, thus ensuring a greater number of cycles and an higher performance.These are just some of the benefits that an adequate hardening process can offer to a linear guide in industrial and heavy duty applications. Rollon Group, global provider of solutions for linear motion, has gained significant knowledge in raceways induction hardening. This particular heat treating process allows to achieve considerable results in terms of quality, durability and reliability of linear guides.



When it comes to linear motion rails, a high hardness value is critical. The less the surfaces is hardened, the sooner the rail will become susceptible to damage. If hardness doesn’t extend to a sufficient depth, the component won’t be able to withstand heavy loads over the course of its lifetime, which can result in time-consuming and costly downtime for the system. For Rollon, when choosing a linear guide for an industrial application, three main factors have to be considered:

INDUCTION HARDENED RACEWAYS: this heat treating process brings out the tough natural properties of steel, creating a thick zone around the raceway and ensuring hardness levels are achieved at critical depth and effective hardness.

MATERIAL PURITY: to achieve maximum hardness levels, rails should be made from highquality, high-carbon composition steel that is specifically made for bearing applications.

ADDITIONAL SURFACE FINISH: once a raceway undergoes induction hardening, its surface can be further machined to improve its anti-friction capabilities. Induction hardening and subsequent grinding and honing remove tool marks and high spots. The extra smoothness, along with the hardness, both work to extend the life of the system.



How is it possible to achieve an efficient hardening process?

Unfortunately, some rail manufacturing processes don’t impart sufficient hardness to the rails. When you consider the kinds of heavy loads that are applied to industrial raceways in warehouse automation, robotic cells, railway, machine tools and more, rails that have thin hardened surfaces will tend to crack under load. To avoid bearing failure, it’s important to know the location of the point of stress between the bearing and the rail. The maximum stresses, which are called Hertzian contact stresses, aren’t on the surface at all, but beneath it. For that reason, a rail’s hardened layer needs to extend deep enough below the surface—something many other processes simply cannot achieve. That’s where Rollon’s induction hardening comes in.



Rather than creating a case-hardened surface, induction hardening creates a zone around the raceway with effective depths of 1.2 mm, successfully encompassing the maximum point of stress located beneath the rail’s surface. As a result of this process, an induction hardened rail can operate under heavy loads with no damage to the raceways over the course of its lifetime. In properly sized linear bearings, typical life ratings range from thousands to hundreds of thousands of kilometers of travel.

In this form of heat treatment, the metal first undergoes induction heating, a non-contact process that uses an electric current to create heat in the surface layer of a conductive material. The surface layer is then quenched, causing it to undergo a martensitic transformation and become harder than the base metal. Compared to other conventional heat treatments, induction hardening offers several advantages, including fast heating rates, low energy consumption and cost savings. It also refines the structure and mechanical properties of the treated parts. Because the subsurface stresses on a loaded raceway can hit 500,000 psi, both rail hardness and hardness depth are critical values to measure during the induction hardening process. Measured on a “C” scale, Rollon’s bearings hardness varies from 58 to 62 HRC. A rail’s hardness depth will vary, as will the rail’s overall size, based on the requirements of your applica-tion. Small models, such as Rollon’s size 18 Compact Rail, integrate a hardness depth of 2 mm. By contrast, large rails, such as Rollon’s size 63 Compact Rail, feature a hardness depth of 1.2 mm.


BOX: Lubricating the hardened rail

A lack of effective lubrication on the surface of your linear bearing can reduce its lifespan by a factor of 10. Although lubrication is something you can’t avoid, you can choose bearings that have minimal lubrication needs by design, such as those with well-sealed rolling elements. Rollon’s Compact Rails, for example, integrate sealed rolling elements that require only a small amount of external lubrication every 2 millions cycles, depending on the application. The need to add lubrication in Compact Rail linear guides is therefore very limited.


FOCUS: Railway applications

Telescopic guides and linear rails are used in many parts of trains. When a train is running, the balls and bearings in the doors and battery boxes, for example, are subject to hours of constant vibration while remaining in the static position. For these reasons, a bearing with insufficient hardness levels can easily become damaged or crack. In an industry where passenger safety is paramount, only induction hardened rails can stand up to the ongoing vibration trains experience. By avoiding the need to shut down an entire train for repairs, these sturdy components also help railcar manufacturers avoid troublesome and costly downtime.