Page 11 - Industrial Technology EXTRA 20th July 2020

subsequently led to the development of the AIP, a comprehensive application review was
proprietary TL specification. The type of steel used commenced.
in these bearings is case-carburised using a special The NSK specialists soon discovered that the
method of heat treatment that attains both high standard spherical bearings being used in the
raceway surface hardness and dimensional stability calender roll did not feature carburised inner rings,
under high temperatures. Importantly, the strength leaving them susceptible to the high heat of the
of the inner ring is increased sufficiently to better application, and cracking of the inner rings. It was
resist hoop stress, even at temperatures up to therefore recommended that the paper mill switch
200°C. to NSK spherical roller bearings with TL technology.
The resistance of inner rings that meet the TL The innovative chemical steel composition and
specification is higher than the resistance of inner greater resistance to hoop stress and cracks,
rings made from bainitic steel or bearing steel, while doubled operating life and reduced the cost of
the surface hardness of the rolling surface is greater replacement bearings and downtime. Over a five-
than the hardness of rolling surfaces made from year period since the change was made, the paper
bainitic steel or case-hardened steel. These factors mill has saved around €430,000.
underpin the ability of TL bearings to provide longer NSK spherical roller bearings with TL technology
service life when used on calenders, guide rolls and have been in operation on dryer cylinders and other
smoothing rolls, for example. papermaking machinery rolls since 1994, with no
A case in point involves a major paper mill that problems reported. Today, over 100 different TL
was experiencing problems with its calender rolls, bearing sizes/types are produced, helping a wide
where multiple cracks were developing on the inner range of customers achieve better and more cost-
rings of the roll bearings. Frustrated by up to 12 effective performance. In addition, to accommodate
failures annually, which led to excessive downtime bearings for Yankee dryer rolls, NSK can offer large
and maintenance, the mill invited NSK´s team of TL series self-aligning roller bearings with diameters
expert engineers to investigate and resolve the up to 1,360 mm.
issue. As part of NSK’s Added Value Programme www.nskeurope.com

July 2020 • INDUSTRIAL TECHNOLOGY EXTRA! • p11