Railway Wheels are the foremost important components of trains, which over the time degenerate due to wear and fatigue. Over the time with the use of wheels there can be several types of wheel defects such as corrugation, flat, spalling and shelling and may improvise itself in creating a high impact force which will be worst for the tracks and safety of the train and thus passengers and goods. Usage of Rail traffic whether for travel of passengers or freight the most important is safety. Therefore from safety point of view, the defects of wheelsets are the main reasons of train accidents. The developed High impact forces due to defects of the wheel are detrimental to the track and train and increase the maintenance cost. The unexpected wheel failures in the train also negates the availability of trains and cause delay and leads to heavy accidents in the transport services that reduces the reliability of the entire railway system. Hence, the maintenance of the wheels is the most important task in maintaining a reliable system.

The wheel defect which are normally found are

Thermal Cracks Class 1, class,2, class,3, class-4 and class-5. No action is required normally for class 1 thermal cracks which are up to 10mm long on the tread surface but not extending onto the rim face of the wheel. Other class of thermal cracks need action and repair.

• Fractured wheels are considered as Class 5 defect in railway wheel
• Spalling or shelled tread defect in railway wheel
• Skidded wheels defect in railway wheel
• Scaled wheels defect in railway wheel
• Arrises defect in railway wheel
• Tread/Flange wear defect in railway wheel
• Damaged wheel due to manufactured defects in railway wheel.

Railway axles all over the world are one of the most highly stressed components of the various rolling stocks in use by different railways. The safety and reliability of different types of axles being used are therefore of importance. The defects can be of varied types which are normally found in the wheelsets, these are :-

(A) STEEL MAKING

• The steels required for manufacture of axles should be of good quality in order to have maximum fatigue strength under condition of dynamic loading. The steel required to have a maximum of 0.007% of nitrogen and 2ppm of hydrogen if produced by basic oxygen processes. These two elements have the tendency to develop crack/brittleness during subsequent manufacturing operations or service.
• In order to obtain the desired mechanical properties and freedom from hot shortness and cold shortness, sulphur and phosphorous contents should not exceed 0.05%. The steel so produced are in the form of ingots which is further worked down to obtain the final product. In order to ensure freedom from undesirable piping and harmful segregation, sufficient discard is necessary from the ingot.

(B) AXLE FORGING

• The ingots so produced are converted in the form of blooms in a blooming mill and the finished shape of the forged axle is obtained by forging the bloom in a press or a forging hammer. The reduction ratio from ingot to axle should not be generally less than 4:1. The forged axles are allowed to cool slowly after forging. The forged blanks are thereafter suitably heat treated (normalized or quenched and tempered) to obtain the desirable micro structure and mechanical properties.
• During the process of manufacture of steel and also during subsequent mechanical working operations for producing the final shape of axle, it is essential to ensure freedom from defects e.g. pipe, segregation, cracks, flakes, laps, seam, etc. These defects are undesirable as their presence leads to failure of axles in service.
• During the process of manufacture of steel and also during subsequent mechanical working operations for producing the final shape of axle, it is essential to ensure freedom from defects e.g. pipe, segregation, cracks, flakes, laps, seam, etc. These defects are undesirable as their presence leads to failure of axles in service.
• Sufficient control of heat treatment process is essential to obtain the desired mechanical property and avoid undesirable micro structure (e.g. overheated or burnt structures).

(C) MACHINING

• The forged and heat treated blocks are thereafter machined to drawing dimensions providing generally 60 included angle for lathe centers. Utmost care is essential in maintaining the specified surface finish especially on the journals and wheel seat areas. The fillet radii at each change of section has to be a gradual transition and of correct dimension. Sharp changes in section, tool marks, dent marks, machining marks etc. on the surface of the axle are undesirable. The fatigue properties on the axles are highly sensitive to the surface imperfections. It is only logical, therefore, that the handling of the machined axles also warrants due care to prevent surface damage.

(D) DEFECT OBSERVED ON THE AXLES AND THEIR ORIGIN

• The defects arising on the axle are therefore primarily due to short comings during manufacture and also during manufacture and also due to a variety of service conditions to which they are subjected.
• The sources of various defects are - a) steel- making and shaping operation b) machining operation c) heat-treatment operation d) assembly operation e) repair practice f) maintenance practice and g) corrosion.
• The defects encountered during steel-making and subsequent shaping operations are piping, segregation, slag inclusions, cracks, laps, seams, rokes etc. The defects in the heat treatment operation could be non-uniform micro structure, overheated or burnt structure, decarburization, surface defects etc. Machining if not carried out properly
• can lead to rough turning marks, tool marks, insufficient fillet radii etc. Unorthodox methods of assembly, use of oxy-acetylene flame/ incorrect treatment and interferences, insufficient pressing-in pressure, all have detrimental effects on the life of the axle. The axle boxes are required to be properly maintained in respect of lubrication, tightening torque and ingress of foreign matter. The areas exposed to the atmosphere are prone to corrosion and the corrosion pits formed work as stress concentration areas. The most vulnerable locations of fracture in axles have been found to be inner wheel seat, journal and transition zones or fillets.
• Causes of inner wheel seat failure have been attributed to sharp edged hubs, hubs shorter than wheel seats, fretting corrosion and machining marks giving rise to crack initiation and finally fracture.Failures in fillet area are attributable to insufficient fillet radii, tool marks etc.
• Journal breakages have been found to be caused by notches, produced by inner race edges, local heating and pressing in discrepancies.
• Dynte has the competence to set up the wheelset repair facilities anywhere in the world wherein at-least 40,000 to 50,000 wheelsets are required annually. Dynte will set up, operate, run, maintain, the wheel-setup repair facility for the customers at its own cost and wherein the customer has to guarantee offtake of numbers of wheelsets at a fixed value for 20 years. After 20 years the facilities shall get transferred to the customer.
• Dynte has long associations with the wheelset repair facilities all over the world to provide a full wheelset service package to its customers, which includes inspection, rewheeling, reprofiling, skimming of axles and brake discs, supply of new axles, overhaul of axle box bearings, painting and despatch. A experienced workforce in these facilities caters for both coded wheelset maintenance programmes and casualty repairs. Other components such as brake discs, axle bearings and axle bearing boxes are sourced from original equipment manufacturers for assembly on to wheelsets.
• Dynte India remains invested with its partners in taking care of the gearboxes fitted in the trains. A highly trained team of Dynte offers range of services from condition monitoring to full overhaul and maintenance of EMU gearboxes and DMU final drives. We offer cost effective solutions for the powered wheelsets.