I tried to cover as much information as possible from various sources about manufacturing , properties and various wheel defects in wheels of trains in railway indutsry

1. WHEELS
INTRODUCTION
Wheels are most critical part of rolling stock. Utmost care
is taken right from the manufacture to its last use on the
trains. Wheels are most stressed components of railway
vehicles. They carry axle load of up to 25 tonnes and more.
They guide the train on the tracks through curves and
switches and are subjected to constant wear process.
Different functional parts of the wheel (as shown in Fig 1
below) such as flange (4), rim (3), centre (2) or hub (1)
fulfill different task and have therefore different material
properties. Railway wheel is high safety part and special
attention is given during production process of wheel to
the reliability, availability, and safety of the product.
Railway wheels are usually made of unalloyed or low
alloyed steels with a high degree of purity. Tight tolerances
for the single alloying elements are desired in order to
assure a low variation of material properties from heat to
heat.
European standard EN 13262 defines four different steel grades which mainly consist of up
to 0.6wt% of carbon, up to 0.8 wt% of manganese and up to 0.4wt% silicon. National and
international standards such as UIC 812-3V, GOST 10791, AAR M107-84, EN 13262 define
the wheel steel grades and partly their manufacturing.
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2. MANUFACTURING PROCESS
 STEEL MAKING PROCESS
Steel for the production of railway wheels is
melted in the electric furnace at 3200deg F with
the charge of 250 tonnes and tapping in two
ladles. High quality characteristic of steel is
provided by the subsequent processing at the
out of furnace complex of steel treatment. The
ladles with metal are delivered in turn to the
unit furnace-ladle, where the metal finishing
and refining takes place. Steel blowing in the
ladle by argon along with the refining process
provide for the sculpture content in the finished metal equal to 0.010% phosphorus –
0.015% and less, and uniform distribution of another elements. Degassing process is
affected by means of removing the hydrogen, nitrogen, oxygen dissolved in metal at the
vacuum degassing set simultaneously with argon blowing. Hydrogen content in steel is
within the limits up to 2 ppm.
 WHEEL MANUFACTURING
From electric furnace molten metal is transferred to ladle which pours metal in graphite
moulds to make ingots. Each ingot is approximately 20 feet long. Ingots are then cut into
small pieces called billets. Each weight around about 1000 pounds.
Billets are then transferred to rotary furnace where they are heated to 2400 deg F. From
other end of furnace machine transfer these billets to scaling unit where their outer
most layers are removed. After that these billets are subjected to pressure of
9000tonnes in a press which forge these billets to rough shape of a wheel. The train
wheel increases 20% in diameter when it rolled on rolling mill. Then it goes to final
shaping press where centre hole is punched in it. After heat treatment, machine sprays
cold water to harden the steel. Wheels are machined to correct shape of rim, axle hole
and imbalance checking. Various Non destructive tests like magnetic particle and
ultrasonic tests are carried out to check any abnormalities in the wheel. The chemical
composition of steel is checked by spectrometer. Automated brinell is used for
measuring hardness.
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3. The Technology of the Production of Railway Wheels
Open-hearth furnace Ladle Ladle-furnace Vacuum degassing set
Notching and breaking Billets inspection Billets heating in Hydroscaling of Open forging on the
of ingot into initial billets and repairing the rotary furnace cinder press 20MN
Closed forging on the Punching on the press Wheel rolling on the Wheel calibration on the
press 50MN 100MN rolling mill press 35/8 MN and
piercing of central hole
Intermediate cooling Cooling of the wheel Machining Wheels heating
and anti-flocking in open air
isometric holding
Rim quenching Tempering in pit Adjustable cooling CNC machining,
in the furnaces imbalance checking
Automated non- Wheels inspection and Testing of mechanical Storage
destructive measuring, hardness and other properties
control (ultrasonic test, determination on the samples
magnetic particle
inspection etc.)
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4. MAJOR WHEEL DEFECTS IN RAILWAY INDUSTRY
New designs and modern equipment have culminated in a shift in the mechanisms of
wheel damage over the last 15 years. In 1992 when the last metallurgical survey was
carried out by BR Research, about 80% of wheels were reprofiled due to thermal
damage, largely as a result of inefficient wheel slide protection (WSP) systems. The other
causes of premature wheel turning were identified as wear, including flange wear and
thermal damage caused by wheel slide and tread braking. Today it is estimated that up
to 80% of wheels are reprofiled due to rolling contact fatigue (RCF), and although an
increase in total wheel life has been achieved, improvements are still sought.
The British Standard and European specifications for railway wheels describe classes of
heat treated wheels. The choice of the class of wheel to be used for any particular type
of rolling stock and service is based on the conditions to be met.
WEAR
Wheel life depends largely on the resistance of the wheel to wear and its immunity to
tread failures caused by thermal cracking and shelling as a result of RCF.
Wear of wheels occurs on the wheel tread and flange. This can be minimized by
Correct alignment of the wheels, flange lubrication, material of wheel and rail being
similar and equipment in proper mechanical condition. Every effort should be made to
avoid the abnormal loss of tread metal caused by thermal cracking and shelling. The
most effective form of flange wear reduction is by flange lubrication, which can reduce
wear by at least six times. Where this is cost prohibitive or not practical, wear can be
improved by increasing the carbon content of the steel, and by promoting the
morphology of the pearlite microstructure by altering the quench rate. A typical wear
profile is shown in Figure given below
EXAMPLE OF FLANGE WEAR
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5. HOLLOW WHEEL OR DEEP FLANGE
While the wheel moves there is constant wear on the tread and thus the diameter of wheels at tread
start reducing. Due to which wheel flange height increases. Deep flange is dangerous because it
starts damaging fish plate, fish plate bolts, distance blocks, points and crossings etc. Moreover
inclination of 1 in 2.5 and 1 in 20 (1in 50 in Dubai Metro trains ) practically vanishes which results in
higher friction and there is every possibility of wheels to derail on curves for two wheels on same
side cannot be suitably converted with different diameters to suit longer outer and shorter inner
rails automatically.
HOLLOW WHEEL OR DEEP FLANGE
RADIUS TOO SMALL AT THE ROOT OF FLANGE
Root radius in Dubai Metro trains is R15. In service radius at the root of flange is subjected to
maximum wear on curves and by snaking effect of the wheels. When it is reduced to R13 gauge will
fit properly as shown in fig below.
Defect results in to increased friction between rail and flanges because of reduction in taper of 1 in
2.5 given on wheel flange which affects hauling capacity of the train besides wearing effect on the
rails also.
FIGURE SHOWING RADIUS TOO SMALL AT ROOT OF THE FLANGE.
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6. THIN FLANGE
Flanges are subjected too severe side thrusts during the run and as such the strength of the flanges
ought to be adequate to sustain all the severest side thrusts and maintain smooth running. When
they wear thin they become weaker and there are cases when flanges could not sustain side thrusts
and broke causing mid section accidents. Besides thin flanges cut through the partly opened facing
points due to any signal or permanent way or other defect causing two roads under same train and
serious accidents follow thereafter.
THIN WHEEL
Wheels become thinner because of continuous wear and metal removal in wheel reprofiling. Thin
wheels are considered unsafe because it can further be thinned due to hammering impact at rail
joints resulting into cracks and breakages etc.
SHARP FLANGE
Tip of the flange is not square but given the radius R10 and R18. Flange wears sharp when
continuously wheel negotiates curves and during snaking effect of the wheels. When top radius at
the corner towards tread reduces beyond tolerable limit (5mm in IR) is called sharp flange also
known as knife edged flange. It is highly dangerous as it mounts the rails at points and nose and heel
of the switch rails and crossing. It also mounts rail on the curves and easily cause accidents if
happens to negotiate outer rail.
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7. WHEEL FLAT
Jamming of brakes or seizure of wheels cause skidding of wheels continuous for some distance thus
damaging tread which wears excessively at the point of contact with rail and becomes flat to certain
length and depth. In such cases wheel starts rolling but with unpleasant noise one like we hear on
rail joints. This defect also irks passengers and add to their discomfort. This cause hot axles, journal
breakage, derailments and skidding if allowed for long. It also cause false flanges on tread which is
highly detrimental to safe running of train
Tread Damage occurs from a number of mechanisms including severe tread braking at high speeds
or high speed slip, caused for example by faulty WSP systems or WSP activity combined with low
adhesion conditions, resulting in a heat input into the wheel tread. This locally heated metal then
quenches rapidly due to the ‘colder’ bulk material of the wheel, which acts a heat sink. This phase is
typically 20-30mm wide and 1mm deep. A typical example is shown in Figure below.
This damage on the wheel tread may develop into larger cracks through rolling contact and thermal
input and must be turned out. Resistance to thermal damage can be improved by lowering the
carbon content of the steel. There are also other tread damage mechanisms such as thermal fatigue,
which is associated with tread braking, but would generally be worn away due to the action of
scraping whilst braking on the tread. Low speed slide can induce local heating below the
transformation temperature and at an increased depth. The temperature is high enough, however,
to overload the wheel due to loss of strength as the temperature increases which leads to
mechanical damage of the wheel tread in the form of a ‘flat.
WHEEL SLIP /SLIDE DAMAGE ON TREAD
ROLLING CONTACT FATIGUE
Rolling Contact Fatigue is the failure of the wheel tread due to cyclic fatigue. In Britain, there are two
notions of rolling contact fatigue;
a) Generally fatigue of the tread contact area due to high loads leading to shelling of the surface, an
example is shown in Figure1 below. This surface breakdown can be greatly accelerated if abnormal
conditions exist and may occur under relatively light static loads.
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8. b) Curving forces experience by the wheel will also cause rolling contact fatigue of the wheel tread; it
is generally seen off centre of the tread towards the field side. This type of rolling contact fatigue is
generally associated with the low of an axle in a curve and leads to chevron type indications on the
field side of the tread, as shown in Figure2 below. It can occasionally be seen towards the flange root
on some wheels and is attributed to the action of the high wheel in curves.
FIGURE 1 FIGURE 2
Fatigue failures of wheels can be surface induced, where initiation is due to gross plastic
deformation of the wheel close to the running surface. This is normally due to high loading and/or
low material strength, and leads to cracks that grow some millimeters into the wheel before
deviating back to the surface and leading to small sections falling away from the tread. This is a
progression from the initial RCF crack initiation shown in Figure 1 and 2 above. Sub surface fatigue
failures occur below the running surface and initiate on a macroscopic defect, although they can
occur in a virtually defect free material if the stresses are too high. These defects can typically grow
to 30mm below the tread before deviating back to the surface, so larger sections of the tread can
break loose. This type of failure is therefore potentially very serious as can be seen in Figure 3 below.
Figure 3
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9. The following factors are found to be detrimental to wheel fatigue life:
High wheel loads
High impurity levels
Small wheel diameters
Small rail radius
Tensile residual stresses
Other damage mechanisms related to premature wheel tread turning are local tread collapse;
indentation damage, rim face bulging, and tread roll over.
High strength and higher carbon content are required for maximum resistance to shelling. On the
other hand, thermal cracking is minimized by lowering the carbon content. These two causes of
failure, thermal cracking and shelling, call for remedies which are the opposites of each other.
For this reason, it is not possible to precisely specify the appropriate class of wheel for the severity
of service which develops under various conditions. The following five factors have an important
influence on the wheel life:
• Static stress in the wheel treads
• Maximum train speed
• Braking requirements
• Track conditions
• Design and condition of equipment
Bibliography
 Wheel Steel Handbook By Rail Safety and Standards Board
 The Journal of Rail wheel interaction
 KLW Wheelco, Ukraine
 The Book of Railway Engineering By PC Gupta , Carriage and Wagon inspector, HQ N.
Railway, New Delhi
 European Railway Review
Prepared By Nishan Singh
Rolling stock Technician
Date 30/06/2010
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