Freudenberg-NOK Sealing Technologies Develops Leak-tight Radial Shaft Seal for Roller Bearings in Steel Plants

PLYMOUTH, Mich. – Freudenberg-NOK Sealing Technologies’ (Freudenberg-NOK) unique solution to the roller bearing challenges found in steel plants – the Merkel Radiamatic RPM 41 radial shaft seal – will be on display at the AISTech Steel Premier Technology Event in Cleveland, Ohio May 4-7.

Radial shaft seals for roller bearings in steel plants, for example those used for work rolls, are replaced after 8,000 operating hours, at the longest. Until then, they are expected to function smoothly and reliably under harsh conditions and at high temperatures. They are also expected to protect the bearing internally against excessive water penetration, offer a self-retaining fit in the housing and facilitate easy assembly and repairs.

However, because these requirements cannot be achieved cost-effectively with existing seal designs and production processes, it was imperative to move in new directions. With intensive development work, Freudenberg-NOK developed the Merkel Radiamatic RPM 41 radial shaft seal, which has already been used successfully in European and North American steel plants.

In radial shaft seals, springs are traditionally used as pre-tensioning elements at the seal lip because the existing elastomer materials fatigues too quickly to produce a sufficiently high pretension force over long periods. The company’s Merkel RPM 41 radial shaft seal is unique in relying upon a springless seal lip design made from a special elastomer material with a very low compression set. The design was developed to facilitate high material elasticity without affecting properties such as high wear resistance and joining strength. The newly developed elastomer material walks this tightrope successfully.

The second new feature of the Merkel Radiamatic RPM 41 radial shaft seal is its elimination of metal cages as the typical retaining element in the installation space. These metal cages are difficult to install and remove, creating the risk of damaging the housing. Although pure elastomer or rubber/fabric designs are not suited to the self-retaining function of the seal, Freudenberg-NOK conducted a series of tests and Finite Element Method (FEM) analyses to come up with an innovative alternative: a steel element that is precisely placed inside the static rubber part of the seal during the vulcanization process. The technology eliminates exterior metal parts which can corrode and facilitates easy assembly/disassembly by hand which protects the installation space.

Another challenge Freudenberg-NOK had to overcome was ensuring rapid availability of unique seal sizes, since the company must be able to supply ideal shaft seal rings on demand – within 24 hours if necessary – and no more expensively than existing solutions. Here, the extensive experience that Freudenberg-NOK has with joining large size seals for the wind power industry became important. For precision joints, special devices were developed to bind high-quality intersections together so that they are perfectly aligned with one another. The intersections of the interior metal core, in particular, have to be aligned precisely so that the required pressure in the radial direction is maintained for the ring’s self-retaining capacity. The requirement for this is the constant position of the steel core inside the seal’s adhering piece during vulcanization, which Freudenberg-NOK achieved through a multi-step process.

Freudenberg-NOK’s Merkel Radiamatic RPM 41 radial shaft seal and other products will be on display at the AISTech show at Booth #2945. For further information, please see the company’s microsite:

About Freudenberg-NOK Sealing Technologies

Freudenberg-NOK Sealing Technologies is the Americas joint venture between Freudenberg and Co. in Germany and NOK Corp. in Japan. Freudenberg-NOK is a leading producer of advanced sealing technologies for a variety of markets including: aerospace; agriculture; appliance; automotive; construction; diesel engine; energy; food and beverage; heavy industry; and pharmaceutical. Founded in 1989 under the legal name Freudenberg-NOK General Partnership, Freudenberg-NOK is headquartered in Plymouth, Mich. and operates more than 20 facilities across the Americas. For additional information, please visit

Cheryl Eberwein, Director, Media Relations

Office: +1 734 354 5373

Cell: +1 248 767 1068


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