A new generation of yoke and stud type track rollers
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A new generation of
yoke and stud type track rollers
Dipl.-Ing. Helmut Bode
INA reprint from ÒDer KonstrukteurÓ
Special issue ASB, April 1997
Verlag fŸr Technik und Wirtschaft
A new generation of yoke and stud type track rollers
Optimized design gives decisive increase in cost-efficiency
Dipl.-Ing. Helmut Bode
A comprehensive assessment of 2 High basic load rating 3 A new generation of yoke
the cause of failures in yoke and = long operating life? and stud type track rollers
stud type track rollers in relation to
the specific application has shown In order to meet the high requirements on The aim in the new designs of yoke and
this machine component, the rolling stud type track rollers was therefore the
that only a very small proportion of
element sets were designed primarily for provision of large grease reservoirs,
failures are caused by rolling optimum load ratings and thus for the improvement of the tilted running
contact fatigue. The factors which maximum fatigue life (Figure 1). This is behavior and the Hertzian contact on
are far more significant for often to the detriment of the lubricant the outer ring and the simplification of
premature failure are wear of the resources and the optimum guidance fitting and relubrication arrangements.
outer ring, inadequate lubrication characteristics of the rolling elements. These requirements have been fulfilled
and tilted running. New designs An assessment of the causes of failure in with the new series PWTR and PWKR.
have been developed which yoke and stud type track rollers in relation Figure 3 shows the significantly larger
optimize the running characte- to the specific application over many lubricant volume compared with the
ristics of yoke and stud type track years (Figure 2) gives some surprising conventional design (Figure 1). Further-
rollers and give significantly longer results. It now becomes clear that only more, the central rib ensures optimum
operating life values. 10% of failures can be attributed to rolling guidance of the rolling elements, signifi-
contact fatigue. Failure is influenced cantly improving tilted running behavior.
1 Introduction much more frequently by wear of the Contact seals on both sides retain the
outer ring, lubrication problems and tilted grease in the bearing and give protection
Due to their wide range of potential against harmful external influences.
running. A long operating life for yoke and
applications, yoke and stud type track
stud type track rollers is not necessarily In the design of the grease reservoir, it
rollers have built a broad appeal in the
achieved by maximizing the basic load must be ensured that the grease is not
machine components market. The basic
ratings but by optimum lubrication, good subjected to continuous overrolling
design of these products is essentially
tilted running behavior and low wear of (churning) by the rolling element set. This
that of a conventional rolling bearing,
the outer ring. These issues have leads to a premature breakdown in the
except that they have a thick-walled outer
previously received too little consideration grease structure and a reduced grease
ring. Stud type track rollers have a shaft
in design work. operating life. In series PWTR and PWKR,
stud at one end.
the grease between the rolling elements
In the majority of applications, the outer sets can continuously dispense oil to the
ring is subjected to circumferential load, rolling element set.
i.e. the outer ring rotates while the inner
These design improvements result in
ring or stud remains stationary. The thick-
significantly longer operating life, as
walled outer ring prevents excessive
shown by running tests and practical
deformation of the track roller and
experience.
ensures that the rolling element set is
uniformly loaded.
2
109 175
Figure 1 Yoke type track roller NUTR Figure 2 Yoke and stud type track rollers, causes of failure in relation to specific application
Running tests were carried out on a In practice, however, relubrication is applications, the bearing arrangements
statistically sufficient number of test inadequate or non-existent in most cases. can be considered maintenance-free.
pieces of the sizes NUTR 2052 and The new series PWTR gave a significantly Even under extreme operating conditions,
PWTR 2052.2RS under the following longer operating life, although its rating life where initial greasing of the bearings is not
conditions: was actually shorter. The mean running sufficient for the whole operating life, the
Bearing load F = 5 100 N time of all test pieces is 184% of the rating relubrication intervals are increased several
life. None of the test pieces achieved the times over compared to their original
Speed n = 1 900 1/min.
end of the grease operating life [1]. values.
Grease: Lithium soap grease
with mineral oil base 5 Improved tilted running
4 Increased operating life
The bearings were not relubricated during
The bearing factor KL [2] is an important
behavior
the test.
parameter for determining the basic Due to the improved lubrication and the
Figure 4 gives a comparison of the lubrication interval of rolling bearings. This central rib guidance, these new yoke and
nominal (calculated) life and the actual life factor takes into consideration the design, stud type track rollers have significantly
values. Series NUTR, which is designed e.g. the track roller, and the grease better tilted running behavior. The sub-
for optimized basic rating life, had a mean reservoir. For the new series, this value stantial improvement in the guidance
running time which was about 14% of the was set at 0,6 which is almost twice that characteristics of the rolling elements
rating life. All the test piece failures re- of conventional designs. Based on the leads to reduced axial friction, resulting in
corded were attributed to lubricant failure. results of the comprehensive tests, this lower bearing temperatures and reduced
Theoretically, the operating life would value can be increased to 1,0 [3]. In prac- strain on the lubricant.
have been extended by regular relubri- tice, this gives significantly increased grease
cation of the track rollers during operation. Figure 5 shows the tilted running behavior
operating life and means that, in most of the various designs in relation to speed
Rolling element set guided by ribs
Large grease reservoir
Contact
110 079
seals on both sides
Figure 3 Yoke type track roller PWTR Figure 4 Operating life of yoke and stud
type track rollers
3
Drop in speed / % continuous speed
Load ratio: C0W/P = 20
Stud temperature: JB = 70 °C
Ambient temperature: JU = 20-26 °C
Angular misalignment: a = 0-3 mrad
Tilting angle: b < 0,05°
Set up with track roller before
measurement test
Angular misalignment a / mrad
Figure 5 Continuous speed under tilted running of PWTR/NUTR
and based on a maximum bearing 6 Simplified fitting and The design work required with stud type
temperature of +70°C. This demonstrates relubrication facility track rollers is usually very high since a
that, as the angular error increases, the relubrication facility from several sides
speed decrease in the new design PWTR Although the relubrication intervals for the must be offered. For the first time, the
is not only lower than with the design new series have been significantly new designs allow a hexagonal socket
NUTR but that the curve has a noticeable increased and this means that the for simplified fitting; relubrication can be
asymptotic character. With a tilted bearings are greased for life in most cases, carried out through this hexagonal
running angle a of more than 2 mrad a relubrication facility must sometimes be socket.
(about 0,1°), no additional decrease in provided. This applies in particular to the Figure 6 shows relubrication by a
speed is recorded [4]. series NUKR and NUTR which are conventional grease gun and the facility
designed for optimum basic load rating. for connecting the bearing to a central
lubrication system using an adapter
(special accessory). Such solutions could
not previously be applied in combination
with a hexagonal socket.
➀ ➁ ➂
Figure 6 New generation of yoke and stud type track rollers. Hexagonal socket with relubrication facility on both sides
➀ Simplified assembly due to hexagonal pocket at both ends
➁ Relubrication facility for grease lubrication via lubrication nipple at both ends
➂ Connection to central lubrication system possible at both ends via adapter (special accessory)
4
Cylindrical profile Profile R = 500 Optimized INA profile
Level running
b = 0 mrad
Cw/P = 5
Tilted running
b = 3 mrad
Cw/P = 5
Figure 7 Influence of profile on Hertzian pressure. Optimized INA outer ring profile compared
with conventional profiles
7 Optimized outer profile contact point. On the basis of exhaustive Literature:
calculations and tests, the outer ring [1] INA test report VA-64892
With the new generation of yoke and stud profile has been optimized to give a
type track rollers, it has been possible not “Gebrauchsdauer von Stütz- und
substantial reduction in Hertzian pressure Kurvenrollen”, Herzogenaurach 1995
only to achieve significant improvements whether the track roller is fitted with
in lubrication and tilted running behavior precise alignment or with an angular [2] INA publication LFR, “Track rollers”
but also to optimize the wear behavior of error. [3] INA catalog 307, “Needle roller
the outer ring. From the causes of failure bearings, Cylindrical roller bearings”,
in relation to the specific application sho- Figure 7 shows the superiority of the new
profile compared to the cylindrical profile 1997
wn in Figure 2, it is noticeable that the
and the conventional radius R = 500 mm. [4] Welter, R. und Miko, J.: “Track rollers
most frequent reason for failure
In addition to the improvements in with optimized functional and life
is wear of the outer ring.
grease operating life and tilted running characteristics”, Konstruktionspraxis,
Wear investigations have shown that behavior, it has been possible to Heft 3 and 4, März and April 1995
wear between the outer ring and the significantly reduce the Hertzian pressure [5] INA publication “A wealth of
mating track can be significantly reduced at the contact point between the outer experience with track rollers”,
by correct material selection and,as far as ring and mating track. In addition to Herzogenaurach 1995
possible, by minimal lubrication. improved rigidity, this also improves the
However, these investigations also fatigue life, especially of the mating track.
show that the load at the contact surface In conjunction with correct material
has a disproportionate influence on the selection [2], this leads to a significant
wear [5]. It is therefore important to reduction in wear.
reduce the Hertzian pressure at the
Dipl.-Ing. Helmut Bode is Industrial
Sector Manager for Production Machinery
at INA Wälzlager Schaeffler KG,
Herzogenaurach (Germany)
5
Art.Nr. 006-936-920/GSK US-US 0997 INA Bearing Company, Inc. 308 Springhill Farm Road Fort Mill, South Carolina 29715 Telephone 803-548-8500
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