WHEELS DEFECTS

 WHEELS DEFECTS 

Wheel is an important part of rolling stock which contributes for safe running of the trains. The wheel provided in the rolling stock of railways has dual role of bearing the weight as well as guiding the vehicle. Hence the defects in the wheel can lead to derailment and accidents. The wheel defects are mainly observed on the profile which gets worn out in service and compared with the standard profile of the tyres.

Wheel defects and their condemning limits 

Less radius at Root of Flange: When radius given at the root of flange is reduced to 13 mm is called less radius at root of flange. This defect can develop into other defects such as deep flange and hollow tyre. 246 

Sharp Flange: When the radius given at the tip of flange is worn out to 5mm, it is called sharp flange. This defect develops either due to running on the same curves for a along period or due to the defects on the rolling stock such as bent axle guard, weak springs, defective axle guides and excessive longitudinal clearance. The wheel is always pushed towards the rail and the flange starts wearing. The root of flange is first affected and then the inclination given on the flange disappears. Slowly the roundness given on the flange is reduced. Sharp flange can take wrong routes at a facing point provided the point itself is slightly defective such as a split, a worn out or damaged switch rail etc. 

Deep Flange: When the depth of the flange is increased to 35 mm for BG stock, it is called Deep flange. This happens due to the wear of the wheel tread at the root of the flange. A deep flange can cause damage to the permanent way by mounting over fish plate, fish bolts, check bolts etc. and also causes derailments especially at check blocks and check rails. 

Hollow Tyre: Due to wear on the wheel tread caused especially by wrong material composition in brake blocks, the inclination given on the wheel tread wears out and forms curve. Without this inclination on the tyre wheel will have more lateral play on a straight line causing rough riding. It will also find very difficult to negotiate curve. 

Thin tyre: When the thickness of the tyre is reduced to 25 mm for BG is called thin tyre. This happens due to wear and tear in ordinary condition. Wheel with thin tyre will not be 247 able to withstand the weight of the load. This also will cause low buffer heights. 

Thin Flange: When the thickness of flange is reduced to 16mm is called Thin Flange Thickness must be measured at a point 13 mm from the Tip.It leads to breakage of flange under the side thrust of the wheel on a curve. 

Skidded Wheel: This happens due to defective brakes or improper releasing of brakes. When a rolling stock is kept running with brakes binding the wheels do not revolve. Instead they slide over the rail surface. This cause heavy friction and wear on a particular spot on wheel tread. These worn out spots or patches will cause heavy noise on run and disturb the passengers. A skidded wheel not only damages the permanent way but also bearings. 

Limits for flat tyres: The limits for permissible maximum flat surfaces on tread for BG ICF coaches is 50 mm (reference Rly. Bd.'s Letter no. 83/M (N)/960/1/Vol I dated 15/18.3.99). 

7.1 Application of Tyre defect gauge: 

Wheel defects mentioned above, if suspected to have reached condemning limit during visual examination has to be ensured by applying tyre defect gauge (IRCA part IV, Plate No. 38 for BG coaches and Plate No.39 for MG coaches). The procedure for application of the gauge is depicted in the following pages. 

SHARP FLANGE: 

7.2 RDSO Instructions on Wheel defects as per CMI – K 003 

In addition to normal checks exercised on wheel condition during primary/secondary maintenance of coaches, a detailed inspection of wheels should be done during schedules or out of course attention. The wheels sets shall be inspected for the following conditions and action taken as indicated for each condition as per CMI – K 003.

 7.2.1 Shattered Rim: 

A wheel with a fracture on the tread or flange must be withdrawn from service. Shattered Rim is a rejectable defect. (This does not include wheels with localized pitting or flaking without presence of any rejectable condition). 

7.2.2 Spread Rim:

If the rim widens out for a short distance on the front face, an internal defect may be present. Spreading of the rim is usually accompanied by a flattening of the tread, which may or may not 256 have cracks or shelling on the tread. Such wheels must be withdrawn from service. (This condition should not be confused with a uniform curling over of the outer edge of the rim around the entire wheel, which is called rim flow. Rim flow is not a rejectable defect). 

7.2.3 Shelled Tread: 

Shelling can be identified by pieces of metal breaking out of the tread surface in several places more or less continuously around the rim. Shelling takes place when small pieces of metal break out between the fine thermal checks. These are generally associated with small skid marks or “chain sliding” Such wheels should be withdrawn from service and sent to workshops for re - profiling. 

7.2.4 Thermal Cracks: 

Thermal cracks appear on a wheel tread due to intense heating of the wheel arising out of severe brake binding. Such cracks occur on the tread and generally progress across the tread in a transverse & radial direction. Whenever such a crack becomes visible on the outer face of the rim or tread crack has reached the outer edge (non-gauge face) of the rim, the wheel should be withdrawn from service. If a crack becomes visible on the outer flange face, the wheel should be withdrawn from service. Such wheels should be sent to workshop for examination and subsequent rejection. 

Wheels involved in brake binding during service, should be examined carefully during the maintenance to rule out the possibility of rejectable thermal cracks. Such wheels may be identified by presence of flats (even within acceptable limits) and severe discoloration or blue/ black heating marks on the tread. 

Heat checks: Fine superficial cracks visible on the tread on or adjacent to the braking surface are called heat checks, which are usually denser than the thermal cracks. Heat checks are caused on the tread due to heating and cooling cycles undergone by the wheel during normal braking. Such wheels need not be withdrawn but should be carefully distinguished from the rejectable thermal cracks. 

7.2.6 Disc crack: A crack on the disc due to material failure is called disc crack. The wheel should be withdrawn from service. 

7.2.7 Loose axle: While assembling wheel with axle proper interference should be maintained between wheel and axle. Due to improper selection of interference the wheel may shift outwards or it may come out completely. Loose axle is a rejectable defect. 

Note: All wheel sets withdrawn from service for any of the conditions mentioned above must be sent to the associated workshops for detailed investigations and further disposal. 

The date and station code of the maintenance depot where the wheels are changed should be stencilled on the end panels. An entry should also be made in the maintenance card of the coach. 

No repairs, except wheel profiling of wheel sets is permitted to be done in the maintenance depot.  

7.3 Worn Wheel Profile: 

80 % of the track in Indian Railways is having rails which are already worn in service. Standard wheel profile running on these tracks tend to wear to a specific profile within short time itself, and further wear from this profile is very slow. Hence if the wheels are turned initially to this worn wheel profile, it will increase the wheel life by avoiding frequent re-profiling. 

The worn wheel profile is made standard for all the wheels in Indian railways as the standard wheel profile is found uneconomical with lesser kilometers being run by the wheels within condemnation. 

 Step Sizes of Worn Wheel Profile: The step sizes of worn wheel profile are given further to reduce the removal of material during tyre turning and increase the life of the wheel.