Page 10 - Industrial Technology EXTRA 20th July 2020

PAPER INDUSTRY..

Bearings double service life

in papermaking machinery

Many sections of papermaking machinery are subject to high temperatures which

present specific challenges to bearings. NSK has addressed these issues with its new
range of products with TL technology, and reports that these are being increasingly
adopted in the papermaking industry as more machinery manufacturers and paper
mills seek to maximise operating life

he unique attributes of NSK’s TL
(tough and long life) specification is
proven to provide greater resistance
Tto hoop stress, subsequently
reducing inner ring fractures and delivering
service life more than twice that of
conventional bearings with standard heat
treatment. TL series spherical roller bearings
are specifically designed for sections of
papermaking machinery where elevated
temperatures prevail, including dryer rolls,
calender rolls, canvas rolls and PV rolls.
The bearings were developed as a solution to a of lubricant, reducing bearing life, while unwanted
specific problem: inner ring fractures. This problem creep can have a negative impact on dimensional
is common on dryer cylinders (including Yankee stability.
dryer rolls) and calender rolls, where steam is Although adopting a slow start-up procedure
passed through the hollow axis of the roll to heat it. can prevent such problems – by introducing
Here, the journal expands faster than the bearing, temperature gradually – it can take several hours
making the fit tighter. As the hoop stress (force and paper mills cannot afford the lost production
exerted circumferentially) of the inner ring and revenue. Instead, the solution lies in astute
increases, cracks can begin to appear. bearing selection.
High temperatures in papermaking machinery To counter the effects of temperature, NSK
also present further challenges to bearings. For analysed the mechanism of inner ring fracture and
instance, the presence of heat lowers the viscosity established a strength evaluation method that

July 2020 • INDUSTRIAL TECHNOLOGY EXTRA! • p10