Government of India
Ministry of Railway
“TECHNICAL PAMPHLET ON CLASS K (6 1/2" X 9”)
CTRB FITTED ON 25t AXLE LOAD LWLH BOGIE OF FREIGHT STOCK”
For Official Use Only
IRCAMTECH/GWL/MP2/2020-21/1.0
May-2020
D.D Nagar, Maharajpur, Gwalior-474005(India)
QUALITY POLICY
“To develop safe, modern and cost
effective Railway Technology
complying with Statutory and
Regulatory requirements, through
excellence in Research, Designs
and Standards and Continual
improvements in Quality
Management System to cater to
growing demand of passenger and
freight traffic on the railways”.
CONTENTS
Description Page No
Cover page i Quality Policy II
Contents III 1.0 Introduction 1-9
1.1 General Description 1
1.2 Background 1
1.3 Technical features 2-5
1.4 Pictorial View of AP-2 Class ‘K’ bearing and its advantages
1.5 Constructional & Dimensional Comparison between Class ‘E’ & Class ‘K’
5
6-9
2.0 Class ‘K’ Approved manufactures 10-13
a. Timken : AAR Approval Number- 27 10
b. BRENCO: Approval Number- 28 11
c. SKF: Approval Number- 30 12-13
3.0 Important Technical Parameters of Class ‘K’ CTRB 14-15
3.1 Operation parameters for which class ‘K’ is designed
15
ANNEXURE I 16-19
ANNEXURE II 20-21
ANNEXURE III 22-24 References 25
Disclaimer 25
Reference Letter (Railway Board) IV-V
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 1
1.0. Introduction:
1.1 General Description
Cartridge Tapered Roller Bearings Class “E” (6”x11”) to RDSO STR No. AB/RB-39-2002
(Rev. 3 with Amendment No.3) are being used on freight stock of IR. These wagons are
designed for 20.3/22.9t axle load and are in service on IR for about three decades. Even
though “E” Class CTRB is designed up to 25t axle load, it may not be suitable for 25t
operation in Indian conditions.
Studies reveal that L10 life of “E” Class bearing operating at 25t axle load will reduce by
52%. The major difference in maintenance and operation practices of American Railroad is
extensive use of way side Hot Box Detector and Acoustic Bearing Detector which provide
advance warning on the health condition of Axle bearing and Bogie suspension. Whereas on
IR, condition of Axle bearings and Bogie suspension is assessed by manual visual rolling in
examination which is not so accurate and reliable as Hot Box Detectors and Acoustic Bearing
Detectors.
In AAR, whenever wheels are re-profiled/changed the bearing must be removed from service
which is not so in IR where the bearings are inspected and reconditioned during every POH.
A policy decision has therefore been taken to adopt “K” Class CTRB on new design of 25t
axle load wagons to achieve high reliability between two successive POH.
1.2 Background
When the axle bends whilst rotating in heavy haul operations due to high wagon and dynamic
loads, small movements between the tight fitted cones and axle journal cause fretting wear on
the cone bores and journal outer diameter. This results in what is known as cone bore growth,
which damages the bearing seat and renders cones unfit for further service. It also causes loss
of internal clearance which leads to further damage of bearing components and eventually
causes a hot box set out. The greater the bending arm moment the higher will be the chance
of occurrence of such kind of abnormalities due to very high bearing loads. This axle
deflection is shown in Figure 1.0.
Due to axle flexure as discussed in the above paragraph, fretting wear also occurs between
the back face of the cone and the seal wear ring, as well as the seal wear ring and journal.
Fig: 1.0 Axle Deflection under load
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 2
The AAR has specified a limit of 0.127 mm depth in the cone back face for the cone to be
acceptable for further service. Cones with fretting wear greater than this can be salvaged by
machining the cone back face to a maximum of 0.254 rmn depth. Figure 1.1 illustrates
typical cone back face fretting wear. The AAR has specified a limit of 0.0508 mm depth for
seal wear ring grooves in axle journals. If the groove is deeper than this the axle must be
repaired by returning the journal diameter to its original size using expensive plating
methods. Figure 1.2 shows the area damaged by seal wear ring grooving.
Class E (6” X 11”) was introduced as a replacement for the widely used friction journal
bearings. This self-contained, pre-lubricated bearing package quickly became the design of
choice for the industry. Over time, rail operations evolved. The industry was challenged to
improve efficiency and productivity and to lower costs. To achieve this, freight-car weights
increased, and trains were operated at higher running speeds. Heavier loads caused more
wear and tear on equipment, including fretting wear. These factors raised concerns about
bearing reliability. To meet these growing challenges of increased loads, speeds and longer
wheel life, Class K (61/2” x 9”) is finally accepted as remedy for freight car in Indian
Railway.
Class K (61/2” x 9”) design provides for reduced journal axle flexure and less fretting wear.
Its compact design incorporates fewer components and hence less maintenance problem. The
Class K (61/2” x 9”) bearing also offers improved safety and reliability and runs at lower
operating temperatures and lower torque.
1.3 Technical Features
RDSO‟s STR No. AB/RB-41-2016 for Class „K‟ (61/
2” X 9”) Cartridge Tapered Roller Bearings
for freight stocks fitted with Light Weight Low Height (LWLH) bogies (Narrow Jaw) for 25t axle
load application.
Dominating Features which make Class K (61/2” x 9”) CTRB better than Class E
(6” X11”):
1) Fretting Index Value: It is the measurement of failure occurring due to fretting
wear. Lesser the value of Fretting Index, lower will be its chances of failure due to
fretting wear.
Fretting Index Class K 0.30
Fretting Index Class E 1.0
Fig: 1.1 Cone back face fretting
wear
Fig: 1.2 Groove caused by seal wear ring
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 3
The development of the class-K bearing had taught the rail industry the
importance of looking at the “fretting index” of an application. This calculated
measurement provides a strong indication of thepotential for a bearing to
experience cone back-face wear. It is based on formulas for bending and shear
and uses application inputs that include bearing load, journal diameter, and the
length (width) of the inboard section of the bearing. The complete formula is
shown in Figure 1.3.
Based on this formula, the fretting index for the class-K & class E can be
determined. This was achieved in the Brenco class-K bearing by shortening the
backing ring, the wear ring/seal area, and the center spacer area of the bearing.
2) L10 Life: It is defined as the number of hours in service that 90% of bearings will
survive.
L10 Life Class K 16 Lac Km
L10 Life Class E 10 Lac Km
3) Use of special type Low-Torque Seals1: Seals have following add on features-
a. It provides best protection against water and other contaminants entering the
bearing cavity..
b. It works with significantly lower torque, which results in lower fuel operating
costs.
Seals1: Brief description about seal is available at ANNEXURE I
Fig: 1.3 Groove caused by seal wear
ring
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 4
4) It is coupled with less flexure due to increased axle guard diameter, the Timken
design provides shortest distance between the cone face and the dust guard. This
design reduces the amount of movement and the resultant wear.
5) Fitted backing ring design reduces the potential for water ingress and resulting
fretting corrosion in the axle fillet area.
6) Use of Polyamide cage2: This refined cage is made of reinforced polymer and has
demonstrated excellent performance. The main user benefits are reduced friction,
roller slip, wear and operating temperature and improved safety. Even under
emergency running conditions, the unit operates without blocking.
7) Compact design: This principle offers decreased journal-length (Figure: 1.9)
opportunities and consequently lower axle bending, which allows higher loads.
The decreased distance between the rows of rollers improves internal load sharing.
The shorter axle journal design provides a longer and stiffer guard. This reduces
the stress at crucial axle fillet area.
8) By removing seal wear ring (in Timken Design), axle grooving and resulting
scrapping of seal wear ring or expensive repairs are eliminated. (See the expanded
view of Class K CTRB)
9) Use of Polymer spacer: Fretting corrosion between the backing ring and the cone
side face is caused by journal bending during operation. This corrosion not only
causes foreign particles to enter the bearing but also increases axial bearing
clearance, resulting in reduced performance and reliability. The development
target was to avoid fretting corrosion by changing the steel-to-steel contact
between the backing ring and the cone side face to steel-to-polymer contact. A
spacer of reinforced polymer material is clamped onto the bearing components.
Cage2: Brief description about cage is available at ANNEXURE II
Journal size of class K (61/
2” X 9”)
Journal size of class E (6” X11”)
Fig: 1.9 Comparison between Journal-length
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 5
10) Premium Rail Grease3: premium rail grease is specifically formulated for use in
railroad car wheel journals. It lasts longer and provides better protection against
water etching compared to conventional freight journal greases. Fortified with a
high-performance corrosion inhibitor for increased bearing protection, it can
withstand the toughest conditions including humid environments. It provides
excellent mechanical shear stability, water resistance and oxidation stability for
reliable performance. This lubricant meets AAR specification M-942-98.
1.4 Pictorial view of AP-2 Class ‘K’ bearing and its advantages
Grease3
: Brief description about grease is available at ANNEXURE III
Fig: 1.20 Pictorial View of Class ‘K’ Bearing & its adevantages
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 6
1.5 Constructional and Dimensional comparison between Class E (6” x 11”) & Class K (61/2” X 9”) CTRB
o Exploded View of Class ‘E’ and Class ‘K’ bearing
Fig: 1.21 Class E ( 6” X 11” )
Fig: 1.22 Class E ( 6 1
/2” X 9” )
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 7
Class ‘E’ Bearing comes under TIMKEN APTM
bearing with AAR
approval nos. 1 & 1A
Class ‘K’ Bearing comes under TIMKEN APTM
bearing with
AAR approval nos. 27
Fig: 1.23 Bearing Nomenclatures
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 8
o Designation Structure of bearing (FAG)
Class ‘E’ Class ‘K’
Features Bearing
Class
Class ‘K’ Class ‘E’
Journal-
size
Less Compare to Class „E‟ More Compare to Class „K‟
Bore-size More Compare to Class „E‟ Less Compare to Class „K‟
Roller
density
High Compare to Class „E‟ Low Compare to Class „E‟
Seal wear
ring
Not available/Integrated part
of inner ring(cone)
Available
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 9
NAME OF THE FIRM
AAR
Approval No.
(as on April -2011)
Diameters are averages AMOUNT OF GREASE
gram(oz.) ROLLERASSEMBLY OUTER RING/CUP BACKING
RING
MAX. BORE mm
(inch)
OUT OF ROUND
mm (inch)
MINIMUM O.D. mm
(inch)
MAXIMUM C. BORE
mm (inch)
MINIIMUM C. BORE
mm (inch)
OUT OF ROUND
mm (inch)
MAXIMUM C. BORE
mm (inch)
EACH ROLLER
ASSEMBLY
AROUND SPECER
TOTAL
QUANTITY ± 30gm
TIMKEN 1A 144.488 (5.6885)
0.076 (0.003)
220.345 (8.675)
209.677 (8.255)
209.423 (8.245)
0.127 (0.005)
178.511 (7.028)
115 (4)
170 (6)
400 (14)
BRENCO/ NBC
5A 144.488 (5.6885)
0.076 (0.003)
220.345 (8.675)
209.677 (8.255)
209.423 (8.245)
0.127 (0.005)
178.511 (7.028)
115 (4)
170 (6)
400 (14)
FAG 32 144.488 (5.6885)
0.076 (0.003)
220.345 (8.675)
209.677 (8.255)
209.423 (8.245)
0.127 (0.005)
178.511 (7.028)
115 (4)
170 (6)
400 (14)
SKF 23 144.488 (5.6885)
0.076 (0.003)
220.345 (8.675)
209.677 (8.255)
209.423 (8.245)
0.127 (0.005)
178.562 (7.030)
115 (4)
170 (6)
400 (14)
ALL DIAMETERS ARE THE AVERAGE OF 3 MEASURRMENTS, 60
0 APART
Make/ Bearing
Class ‘K’
(6 ½”X 9”)
Diameters are averages AMOUNT OF GREASE
gram
(oz.)
ROLLERASSEMBLY OUTER RING/CUP
BACKING
RING
MAX. BORE
mm
(inch)
OUT OF
ROUND
mm
(inch)
MINIMUM
O.D.mm
(inch)
MAXIMUM
C. BOREmm
(inch)
MINIIMUM
C. BOREmm
(inch)
OUT OF
ROUND
mm (inch)
MAXIMUM
C. BOREmm
(inch)
EACH
ROLLER
ASSEMBLY
AROUND
SPACER
TOTAL
QUANTITY
BRENCO
(AAR-28& 31) 157.175
(6.1880)
0.076
(0.003)
249.555
(9.825)
238.252
(9.380)
237.998
(9.370)
0.127
(0.005)
191.211
(7.528)
170
(6)
15
(1/2)
355
(12½)
TIMKEN
( AAR-27)
157.175
(6.1880)
0.076
(0.003)
249.555
(9.825)
238.252
(9.380)
237.998
(9.370)
0.127
(0.005)
191.211
(7.528)
57
(2)
170
(6)
284
(12)
Class E (6” x 11”) CTRB
Class K (61/2” x 9”) CTRB
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 10
2.0. Class ‘K’ Approved Manufacturers (AAR Approved)
a. Timken : AAR Approval Number- 27
Class & Size Roller
Assembly
Outer
Ring
Spacer HDL
Seals
Fitted
Backing
Ring
End Cap Locking
Plates
Cap
Screw
K(61/2 X 9) NP877824** NP335917 NP115833 K153401 K153494 K154496 K84324 K84351
Dimensions are average Amount of grease in Once
Classes and Size Roller Assembly Outer Ring Fitted
Backing
Ring
Each
Roller
Assembly
Around
Spacer
Total
Quantity
Max.
Bore
Out of
roundness
Min.
OD
Max.
C
Bore
Min
C Bore
Out of
roundness
Max. C
Bore
K(61/2 X 9) 6.1880 0.003 9.8250 9.380 9.370 0.005 7.258 2 6 10
Conversion
Factor
1 Ounce
=28.3495
1 Inch
= 25.4 mm
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 11
b. BRENCO: Approval Number- 28
Dimensions are average Amount of grease in Once
Classes and Size Roller Assembly
(Cone)
Outer Ring
(Cup)
Fitted
Backing
Ring
Each
Roller
Assembly
Around
Spacer
Total
Quantity
+/- 1
Max.
Bore
Out of
roundness
Min.
OD
Max.
C
Bore
Min
C Bore
Out of
roundness
Max. C
Bore
K(61/2 X 9) 6.1880 0.003 9.8250 9.380 9.370 0.005 7.258 5
1/2 1 12
Conversion
Factor
1 Ounce
=28.3495
1 Inch
= 25.4 mm
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 12
c. SKF: Approval Number- 30
Conversion
Factor
1 Ounce
=28.3495
1 Inch
= 25.4 mm
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 13
SKF
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 14
3.0. Important Technical Parameters of Class ‘K’ CTRB
The roller bearings is suitable for
axle journal to RDSO‟s drawing
number WD-15020-S-02 Alt. nil or
latest (journal of this axle is
identical to AAR Class „K‟ axle
journal of M-101 of MSRP Section
G).
Axle end Cap screws (ø 1 1/8” - 7
UNC-2A, 2 1/2” threads length to
Spec. no. IS: 1367-Part 3 Class
P8.8)
Side frame Key (item No. 2) & Key
bolt, Nut, Spg. Washer and ᶲ 4
Split pin (item no 4) to RDSO
Drawing No. WD-13012-S-04 Alt. 4
or latest
Narrow Jaw Adapter to RDSO
Drawing No. WD- 15020-S-03 Alt.
2 or latest
Tightening torque of end cap
screws mentioned above in inch
sizes is 570 N-m
Fig: 1.24 Exploded view of Class ‘K’ Bearing
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 15
3.1. Operational parameters for which bearing class ‘K’ is
designed
Operational Parameters Value
Track Gauge (mm) 1676
Maximum /Normal Axle Load 25
Weight of one wheel-set(Kg)
(840 mm Dia. Wheel-Set)
1200(Appr.)
Maximum/ Normal speed of
wagon (Kmph)
130/100
Average run of wagon(Km/day) 500(Appr.)
Weight of wagon(tonnes)
Empty Condition
Loaded Condition(max.)
20(Appr.)
100
Type of brake system Air Brake(Graduated release )
Type of wheel braking Trade Braking (One brake block
„K‟ type per wheel)
Maximum braking force per
wagon in loaded condition(Kg)
18955
Wheel Trade Diameter (mm) New
Condemning
840
780
Atmospheric Temparature
Range(°C)
Maximum
Minimum
50
-10
Loaded to Empty ratio of wagon
operation
80:20
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 16
ANNEXURE I
Low Torque Bearing Seals
I. Timken HDL(Hydrodynamic Labyrinth) Seal (AAR-27 Class K bearing)
HDL™
Seals
This close-clearance designed seal never touches the mating surface. Its benefits include
lower torque, lower temperatures and better fuel efficiency with fewer set outs, higher
service speeds and lower operating costs than other lip-type seals.
Applications
Railroad journal roller bearing application
Design Attributes
Low torque
Low temperatures
Better fuel efficiency
Details
Timken‟s Hydrodynamic Labyrinth (HDL) seal is one of the key components in the
industry-leading packaged rail bearing design. This seal marries the best lip-type and
labyrinth (close-clearance) sealing technology.
Compared to conventional lip-type seals, the HDL design:
Reduces seal torque and operating temperatures
Extends grease life and fatigue life
Improves lube film
Enhances overall bearing life and performance
Bearings with HDL seals run cooler and keep more grease in the bearing, which keeps
dirt, debris and water out.
Fig: 1.4 HDL Seal
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 17
II. SKF LL (Labyrinth Lip) Seal
New integrated low torque seal
The new compact design principle makes additional spacers or seal wear rings
unnecessary. The sealing function is integrated into the bearing unit between the outer
ring and the inner ring. This feature helps save space and, as a result, minimises axle
bending in many applications. The design is based on a low-friction rubber seal
principle; the main features are a combination of labyrinth, lip and flinger elements.
Improved protection against contamination extends service life.
Fig: 1.5 LL Seals design for
compact TBU
Fig: 1.6 Inch size compact TBU
for Class K for Freight car
Fig: 1.4 Comparison among seals designed by TIMKEN
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 18
Friction torque is reduced by 75% compared with a garter seal arrangement. As a
consequence, the operating temperature is reduced by 20°C, which contributes to longer
grease life and energy savings. Results from the SKF seal test, which evaluates water
and dust contamination, confirmed that the design was effective in excluding
contamination. Long-term endurance tests have been conducted under very severe
operating conditions. The new integrated seal has also passed all AAR approval tests.
For new freight cars with increased cargo, the inch size compact TBU class K is used.
This SKF design is fitted with LL seals (Figure: 1.5) and a polymer clip ring and is
approved by AAR.
III. BRENCO® Tru-Guard® Seal
Over the years, in addition to increasing bearing life and reliability, Brenco product
engineers have developed new sealing technologies that lower bearing operating
torques and temperatures. These seals have been benefiting customers in the form of
reduced set-outs and fuel savings.
In fact, The Ausbrid bearing came standard with a BRENCO® ST-212™ seal, our first
low-torque seal without a garter spring. More recently, a new sealing technology has
been developed that reduces seal torque to essentially zero while improving moisture
exclusion. The new seal (Figure: 1.7), dubbed the BRENCO® Tru-Guard®, has been
successfully running in the Russian market in metric bearings since 2010. This seal
utilizes the successful labyrinth “insert” and “rotor” from the BRENCO® Efficiency
Plus™ seal, and replaces the “dust guard” with a “slinger” / shield that forms a
labyrinth with the seal case.
Fig: 1.7 BRENCO® Tru-Guard®
Seal
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 19
The result, shown in Figure 1.8, is a seal that retains grease and excludes contaminants
without moulded rubber lips and the friction they generate. Friction is only produced by
the shearing of a small quantity of grease located between the walls of the labyrinth.
The first field testing of a Tru-Guard seal took place on the JSC Railway Research
Institute (VNIIZhT) test loop in Shcherbinka, Russia. The bearings were run under load
at various speeds. During periodic stops for bearing inspection, the bearings were found
to be cool enough to make full prolonged hand contact. In addition to running in the
Russian market, a class-K version of the Tru-Guard has been conditionally approved
by the AAR and is running in North American service.
Figure shown bellow depicts a chart of data collected over a 1.5 day period during a
seal life test. With above ambient cup temperatures of about 15°F [8°C] and unloaded
bearing torques averaging 10 to 11 lb.×in., the test result were similar to those of
bearings without seals. As a performance benefit, the Tru-Guard seal has been made
standard on both the Ausbrid Plus and MEGA-TONNE bearings.
Fig: 1.8 BRENCO True –Guard Seal Performance
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 20
ANNEXURE II
Cage for Bearing
Historically cages used for railway axle boxes have been -
Machined brass cages in a two-piece design with rivets or one-piece cages for
cylindrical roller bearings; and pressed steel cages for taper roller bearings and units
such as tapered bearing units, TBU. Today both bearing types are offered with a
polymer cage.
In general engineering applications, a polymer material is chosen for two important
reasons. The first is its specific properties such as low weight and wear, high toughness
and elasticity with an additional damping effect. The second is the moulding process,
which allows the production of complex shapes that cannot be produced efficiently by
traditional machining methods
Polymer Cage
Significantly improved performance can be achieved through the use of polymer cages
for roller bearings in railway journal bearing applications.
Today, all new German rolling stock, ICE high-speed trains, locomotives, passenger
coaches and multiple units as well as freight cars have polymer cages as standard. Also,
other main European railway companies use the same bearing design with excellent
results. Detailed information about this can be found in Evolution 4/1998.
Four main customer benefits can be identified:
The polymer material is resilient, unlike soft, malleable steel that can cause pitting,
spalling and fretting within the bearing.
The channelled roller pocket design reduces roller slip and improves the distribution
of grease throughout the bearing.
Polymer has a lower friction coefficient than steel, and these results in lower bearing
operating temperatures and frictional moment values, lower wear and less fatigue of
components and lubricant.
The polymer is a self-lubricating material that enables the bearing add on feature of
lubrication. This helps prevent bearing seizure, burn-offs and derailments.
Increased safety and performance is also an important consideration. One question
sometimes asked by railway companies is “How much time do we have to detect a hot
running bearing?” This is strongly influenced by the cage type and design. To evaluate
this, a lubrication shut-off test can measure the time between the loss of lubrication and
bearing failure. A steel cage can operate for a short period without lubrication, after
which the bearing temperature increases considerably to reach the hot running condition
that causes the bearing to seize.
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 21
The polymer cage can operate under the same conditions for much longer without any
lubrication. After this period, the temperature increases, the cage bars melt and coat the
rolling elements. This serves as an additional emergency lubricant. Even under such
severe conditions (essentially without a cage), the bearing runs for several hours as a
full complement bearing without seizing. In those cases where infrared methods are
used to detect hot boxes, bearings with a polymer cage allow much more time for
railway operators to react.
The graph illustrates the lubrication starvation comparison test between a steel-cage
bearing and polymer-cage bearing, conducted at the SKF Railway Test Center. Both
bearings were placed on a test rig where the lubrication was removed after the initial
run-in period. The steel-cage bearing temperature rose dramatically; bearing seizure and
failure occurred at 70 km (44 miles). The polymer-cage bearing temperature rose to a
sustained level and continued operating effectively for 500 km (311 miles), at which
point the test was concluded.
The SKF polymer cage is standard for all kinds of railway journal bearing applications
such as high-speed trains, locomotives, coaches, freight cars and mass-transit vehicles
made from a special polymer material, the new Universal Polymer Cage (UPC) design
universally replaces the conventional steel cages within a tapered bearing unit.
The railway operators or wheel-set maintenance companies no longer need to acquire
new bearings to take advantage of this polymer cage technology, and the benefits of the
SKF Universal Polymer Cage are not just limited to safety. This cage also helps to
extend the service life, performance and reliability of the bearing. Positive field-test
results in North American rail services led to the conditional approval from the AAR
for SKF to retrofit and upgrade existing bearing units, manufactured by all major
bearing suppliers to the North American market, with the SKF UPC.
Temperature vs Distance for Steel Cage & Polymer Cage Roller Slip vs Speed for Steel Cage & Polymer Cage
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 22
ANNEXURE III
Lubricants used for rail bearings (Grease):
Selecting grease can be a delicate process. SKF has developed several tools in order to
facilitate the selection of the most suitable lubricant. The wide range of tools available
includes those from easy-to-use application driven tables to advanced software allowing
for grease selection based upon detailed working conditions. The basic bearing grease
selection chart provides you with quick suggestions on the most commonly used
greases in typical applications.
**For more about grease specification see AAR M-942-2012/2020 or RDSO STR No.
AB/RB-41-2016
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 23
Grease
Lubricating grease is a mixture of a lubricating base fluid, a thickening agent, and
additives. The thickening agent is a material that, in combination with the base fluid,
produces the solid to semi fluid structure. The primary type of thickeners typically used
in grease is metallic soaps. These soaps include, among others, lithium, aluminium,
clay, polyurea, sodium, and calcium. The base oil that performs the actual lubrication
can be mineral oil, synthetic oil, or biobased oil. The thickener gives grease its
characteristic consistency and is sometimes thought of as a “sponge” that holds the oil
in place. The majority of greases on the market are composed of mineral oil blended
with a soap thickener although the use of synthetic greases and bio based greases are
growing. Additives enhance performance and protect the grease and lubricated surfaces.
Grease is classified by penetration number and by the type of soap thickener. The
consistency, or rigidity, of a grease is a measure of its resistance to deformation by an
applied force and is, in most cases, the most important characteristic of a grease. A
grease that is too stiff may not feed into areas requiring lubrication, while a grease that
is too fluid may leak out. Grease consistency depends on the type and amount of
thickener used and the viscosity of its base oil. In the United States, penetration
classifications have been established by National Lubricating Grease Institute (NLGI)
and range from 000 to 6. A penetration number indicates how easily a grease can be fed
to lubricated surfaces or its pumpability, and also how well it remains in place. The
number 000 is a semi fluid and the number 6 is a solid. Grease penetration numbers of
0, 1, and 2 are the most common for hydraulic gate drives and gate pivot points.
Dropping point is an indicator of the heat resistance of grease. At or above the
dropping point, grease will act as a fluid. As grease temperature rises, penetration
increases until the grease liquefies and the desired consistency is lost. Dropping point is
the temperature at which a grease becomes fluid enough to drip and indicates the upper
temperature limit at which a grease retains its structure. It is not the maximum
temperature at which grease may be used. Some greases have the ability to regain their
original structure after cooling down from the dropping point. Operating condition of
the grease be at least 56°C or 100°F below the dropping point.
Oxidation stability is the ability of a grease to resist a chemical union with oxygen.
The reaction of grease with oxygen produces insoluble gum, sludge, and lacquer-like
deposits that cause sluggish operation, increased wear, and reduction of clearances.
Prolonged high-temperature exposure accelerates oxidation in greases.
Pumpability is the ability of a grease to be pumped or pushed through a system at very
low temperatures. More practically, pumpability is the ease with which pressurized
grease can flow through lines, nozzles, and fittings of grease dispensing systems. An
example of this is grease lines for miter gate pintle bearings and radial gate trunnion
bearings. In northern climates, it is important that grease reach the bearing surfaces of
the pintles. Feedability is its ability to be drawn (sucked) into a pump. Fibrous greases
tend to have good feedability but poor pumpability. Buttery-textured greases tend to
have good pumpability but poor feedability.
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 24
Water resistance is the ability of grease to withstand the effects of water with no
change in its ability to lubricate. Soap/water lather may suspend the oil in the grease,
forming an emulsion that can wash away or, to a lesser extent, reduce lubricity by
diluting and changing grease consistency and texture.
Consistency of Grease depends on the type and amount of thickener used and the
viscosity of its base oil. Grease‟s consistency is its resistance to deformation by an
applied force. The measure of consistency is called penetration. Penetration depends on
whether the consistency has been altered by handling or working. ASTM D 217 and D
1403 methods measure penetration of un-worked and worked greases.
To measure penetration, a cone of given weight is allowed to sink into a grease for five
seconds at a standard temperature of 25°C (77°F).The depth, in tenths of a millimeter,
to which the cone sinks into the grease is the penetration. A penetration of 100 would
represent a solid grease while a penetration of 450 would be semi-fluid. The NLGI has
established consistency numbers or grade numbers, ranging from 000 to 6,
corresponding to specified ranges of penetration numbers.
Composition of Grease
“Grease” is basically oil that contains a thickening agent to increase its viscosity. The
thickening agent may be a soap or it can be a solid with a high surface area. Fatty-acid
soaps of lithium, calcium, sodium, aluminum, and barium are commonly used in
concentrations of 8%–25%. Finely divided clays such as bentonite and hectorite are
used as high-surface solids, usually after coating with a quaternary ammonium
compound for improved compatibility with the oil.
The clays were used more commonly in early greases and the soap-thickened greases
are more common today. Compared to the other thickeners, PTFE has the lowest COF
and is suitable for use up to 300°C but is typically considered for use only with up to
moderate loads. PTFE is used as a “fortifier” in combination with one of the other
thickeners or is used alone, especially for greases that are for high temperature use or
applications involving long life expectations
IRCAMTECH/MP2/Class ‘K’ Bearing/Pamphlet/May 2020/1.0 Page 25
References:
1. Schedule of Technical Requirements No. AB/RB-41-2016 for Class „K‟ (6 1/2” X
9”) Cartridge Tapered Roller Bearings for freight stocks fitted with light weight low
height (LWLH) bogies (narrow jaw) for 25t axle load application- Jan-2018, RDSO,
Lucknow. 2. Installing and Maintaining Timken
AP™ and AP-2™ Bearings, Maintenance
instructions via website
3. Williams, S.R. "The Timken Company railroad bearing low-resistance seal
development program", The Winter Annual Meeting of the American Society of
Mechanical Engineers. VoL 3, 1989, pp 39-44.
4. Williams, S.R., "Seal technology to enhance railroad journal roller bearing
performance", International Wheel-set Congress, Sydney, 27 September - I October,
1992.
5. Association of American. Railroads, Roller Bearing Manual, Manual of Standards and
Recommended Practices, 1994, Section H - Part II, Washington, D.C.
6. Williams, S.R., "Evolution of journal roller bearings for heavy-haul freight car
service", International Heavy Haul Association Conference on Freight Car Bogies,.
Montreal, 9 -12 June 1996.
7. Williams, S.R., "Bearing design and maintenance to maximise operating reliability",
Sixth International Heavy Haul Railway Conference, Cape Town, 6 - 10 April 1997.
8. Fetty, M., Evolutionary and Revolutionary Changes of the Journal Roller Bearing
for Today's Heavy Haul Railroad Markets, Proceedings of 7th International Heavy
Haul Association Conference, Brisbane, June 2001, June, Brisbane Old Australia.
9. Ker, P., Fortes cue takes another step in plan to boost Pilbara railway loads, The
Sydney Morning Herald, October 24, 2011, Sidney, AUD.
10. Mark Fretty, AUSBRID PLUS® AND MEGA-TONNE™ – New Bearings for
increased reliability and capacity in iron-ore operations, IHHA 2015 Conference, 21-
24 June 2015, Perth, Australia.
DISCLAIMER
THE INFORMATION GIVEN IN THIS PAMPHLET DOES NOT SUPERSEDE
ANY EXISTING PROVISIONS LAID DOWN IN RDSO AND RLY. BOARD’S
INSTRUCTIONS. THIS DOCUMENT IS NOT STATUTORY AND
INSTRUCTIONS GIVEN IN IT ARE FOR THE PURPOSE OF GUIDANCE
ONLY. IF AT ANY POINT CONTRADICTION IS OBSERVED, RLY.
BOARD/RDSO’S GUIDELINES OR ZONAL RLY.’S INSTRUCTIONS MAY BE
FOLLOWED.
The information given in this pamphlet is only for guidance. If you have any suggestion
or comment, please write to:
Email ID- [email protected], FAX – 0751 2 470841.
Director (Mechanical), CAMTECH, Maharajpur, Gwalior (M.P.) – 474 005