It has been seen that Wheel life of Electric Locomotives is found to be quite low. Reduced wheel life results in excess consumption of wheel discs, loss of outage, loss of men power, loss of electric power, etc. Proper action of sheds for increasing wheel life reduced these problems. The problems of electric loco wheels have been studied by several officers and teams but the solution is still eluding us. Proper effort can improve the life of electric locos, which in turn can increase outage of locos as well as earning per loco.

The Railway Board, have allotted the review of project of "Benchmarks for Wheel life improvement of electric loco" to West Central Railway vide their L. No: 98/E&R/2800/2/New Project dated 29.05.2001. In turn, OSD/WCR has allotted this project to the team of CPO, AEEE and AEME of this Railway, vide his letter No: WCR/HQ/0106/Project/GA/06 /Pt. II dated 14.06.2001.

The team has collected all the papers available on the subject from Senior Executive Director, Electrical Directorate & Executive Direct Motive Power, RDSO Lucknow and various Electric loco sheds.

The following papers were collected:-

The Electric Loco Shed, NKJ, Central Railway and Bhilai, S. E. Railway were visited by the team. The types of Locos available and their wheel arrangements were studied and wheel profile of worn out wheel "just before wheel turning" were noted in the proforma as the sample given in Annexure –I (samples).

The report listed out all the possible reasons of wheel wear. However, it does not give detailed reasons of wheel wear and its relation with wheel wear patterns found on profile just before wheel turning but it depended mostly on theory. The main point noted and mentioned by the report are given below,

1. Maintenance strategy
2. Biased wheel management
3. Improvement of track structure & geometry
4. Optimum wheel re-profiling strategy
5. Improvement in materials and manufacturing processes.
6. Change in operating practices and
7. Wheel skidding avoidance.
8. Technological advancement.
9. Up gradation of skill of maintenance & operating staff.

The original report tells mostly about the defects and reason, which are applicable to all wheels uniformly. They have not found out reasons for variations in wheel wear rate. Such faster wheel wear is referred here as rapid wheel wear. The uniform wheel wear can not be avoided but rapid wear can be minimised. It may be seen that most of the wheels are not due for wheel turning, but they have to be machined to maintain the permissible wheel diameter range and to avoid very heavy work of changing wheels.

The original report recommended reprofiling of electric loco wheels after having 75% life of the wheel life is spent. It hopes to increase the wheel life by 20 to 40 %.

The original report has listed many reasons of wheel wear but the common sense will tell that the all the point noted by the original report will result in the uniform wheel wear of all the wheels of a locomotive.

1. The rate of wear of all the twelve wheels of locomotives were not the same even though, they are provided wheel discs of one make and one type only.
2. The rate of wear of all the twelve wheels of locomotives was not the same even though, they are provided with brake block of the same make, hardness and material.
3. The rate of wear of all the twelve wheels of locomotives were not the same even though, all the 12 wheels run equal distance.
4. The rate of wear of all the twelve wheels of locomotives were not the same even though, all the wheels run on the track having the same hardness.
5. The rate of wear of all the twelve wheels of locomotives were not the same even though, all the wheels run on the same atmospheric condition.

But non-uniform wheel wear forces to search for other reasons.

6. ACTION TAKEN BY THIS TEAM:-

The team has visited electric loco sheds and collected wheel profile just before wheel turning on the four type of loco motives on three Zonal Railway. The sample of wheel profile recorded just before wheel turning are given in Annexure –I.

The wheel wear was analysed and found to follow some patterns. These patterns are named from A, B, C, D, E, S & NS, these patterns are shown in Annexure –II.

The wear pattern of electric loco wheels just before wheel turning were categorised confirming to the wear patterns as mentioned in Annexure – II, type of locowise. It is seen that following pattern of wheel wear occurred.

Percentage of various types of wear patterns of loco wheels are illustrated in graphical representation below.

1. The rapid wheel wear does not depend upon the hardness of disc since the wheel disc of one lot was used on one loco and the wheel wear was not uniform on all the wheels.

2. The rapid wheel wear does not depend upon the track since all the wheel travel on same track in the same working condition.

3. The rapid wheel wear does not depend upon the brake block hardness since the brake block of the same lot had been used on the loco at a time but still the wear on all wheels of the loco was not uniform.

4. The rapid wheel wear does not depend upon the bogie frame. Since after the wheel turning the rate of wear for the wheels had been changing i.e. if any one wheel found to become due early, after the turning of wheels and the adjustment of brakes, that particular wheel was not the first to become due for wheel turning again.

9. FINDINGS:-

It is found that some wheel wear at higher rate than other wheels even though all the conditions of materials, atmosphere and earned kilometres is the same for all the wheels. It indicates that some local reason is making the wheel to wear at higher rate. On further investigation different wear pattern were found. The wear patterns and their remedies are given below :-

The line diagram in the side indicates the loco and its wheels. The red wheels are wearing rapidly.

It is found that brake blocks of wheels on one axle is riding on the wheel flange, the problem normally happens on axle no. 1, 3, 4 & 6 since they have brake beams.

2. Wear Pattern ‘B’:- In this case, brake block rides on a wheel only one wheel of the loco. This normally happens due to improper alignment of brake hanger as given in Annexure No: VI.

9.3 Wear Pattern ‘C’:- In this pattern, all the six wheels on one side of loco are wearing out at high speed as compared to the remaining six wheels on the other side. This type of biased wear is found to be happening on the locomotives working on a particular track repeatedly.

This pattern can result only when the under-frame of the locomotives is not flat or otherwise the liners provided in the side bearers are not proper. The wheel wearing faster indicates more load on it and the wheel having less wear has less load on it.

Solution:– This problem can be solved by providing suitable side bearer liners below the side bearers near to wheels having less wear.

The twist of the under frame of locomotives should also be checked and brought to the prescribed limits if not within the limit.

9.5 Wear Pattern ‘E’:- In this pattern, all the twelve wheels are wearing out on the quite a rapid speed. This will happen for the following reasons.

1. Wider brake block - It is found that many time brake block are wider than the approved drawing or having fins at the joint due to poor quality / warn out brake block die. This extra material rubs against the wheel flange whenever the brakes are applied. Thus result in faster wear out of wheel flange of all the wheels.
2. Use of step size brake block – Use of step size brake blocks are in vogue. These brake blocks are much thicker and heavier than standard brake blocks. In the brake rigging, the brake block is kept in proper alignment by the small spring. As the result, standard brake block remains almost parallel to the circumference of the wheel. But when step size brake blocks are used, the coil spring is unable to maintain it in proper alignment. As a result the step size brake block is tilted and the top head of the brake block is always rubbing on the wheel. If vertical alignment of the brake block is also not correct this brake block rubbing is against wheel flange. In this way, all the twelve wheels are wearing at the faster rate on a loco whose wheel diameter is on lower side due to old wheels.

Solution:– This problem can be solved by using standard size brake block only. The use of step size brake block can be avoided by the use of modified slack adjuster upper. The drawing No. CR/NKJ/SK/R48 of modified slack adjuster upper for WDM2 prepared by diesel loco shed NKJ are enclosed herewith as Annexure IV. This will also bring down the maintenance of two inventories of brake blocks as well as handling of heavier brake blocks.

9.6 Wear Pattern "S" (Skidding):- In this case, the wheel get flat spots. This happens due to wheel getting locked by the application of loco brakes during movement. But the loco continue to move due to its own inertia or being pushed by the trailing load. The wheel gets locked due to brake cylinder pressure being higher than required to achieve 100% braking effort.

Solution:– This problem can be solved by reducing the braking efforts to 100% by suitably reducing the brake cylinder pressure. This may be done by reducing the brake cylinder pressure, to about 3.0 Kg/cm2 from the present pressure of 3.5 kg/cm2 so that the wheels do not lock at all.

The proportionate brake system:– This system ensure that the loco brake come into action a few seconds after application of brake on the rake by use of ‘A9’. The rake being long take some time for affecting application of brake. If the system is not functioning properly, the loco brake get into action earlier, resulting in locking and skidding of locomotive wheels. This problem can be avoided by reducing the brake cylinder pressure also, so that the loco brake work under "limiting friction conditions". Theory also tells that the limiting friction is the maximum. This problem of skidding can be avoided if the brake cylinder pressure is reduced from 3.5 to about 3 Kg/cm² (Trial of 3 Kg/cm² was done by diesel loco shed. Correct pressure for electric locomotives is to be found out by trials.)

9.7. Wear Pattern ‘NS’: - The wheel pattern observed on some locomotives one not confirming to any one of the patterns mentioned above. It is possible due to improper alignment or fitment of brake rigging components in electric loco shed or at manufacturing production unit.

The original report tells mostly about the defects and reason, which are applicable to all wheels uniformly. They have not found out reasons for variations in wheel wear rate. Such faster wheel wear is referred here as rapid wheel wear. The uniform wheel wear can not be avoided but rapid wear can be minimised. It may be seen that most of the wheels are not due for wheel turning, but they have to be machined to maintain the permissible wheel diameter range and to avoid very heavy work of changing wheels. Periodical measurement of wheel profile of one such loco as a sample, is given in Annexure – V. Such wheel indicate that the wheels can have a life of about 2 years between two wheel turnings, if rapid wheel wear of some wheels of the loco could be avoided. A loco wheel has initial wheel diameter of 1092 mm and condemning limit is 1016 mm. A normal wheel turning cuts about 15 mm of material in diameter. A wheel has a fresh profile and then four to five wheel turnings. Thus the total life of a loco wheel may extend upto 6 to 8 years.

To achieve this, following actions must be taken by electric loco sheds

1. Brake blocks should be aligned properly so that it rubs on the tread of wheel when brakes are applied. Riding of brake block on flange must be avoided.
2. Brake beams should be of proper length and checked for straightness every week or the lowest schedule.
3. The loco having biased wear should be direction changed every month.
4. The locos having wheel wear on the diagnostically opposite and should be added side bearer liners on the less wearing wheel side.
5. Brake block of standard size and proper shape i.e. without any fin and with proper weight should only be used. Use of step size brake block must be stopped.
6. The Brake cylinder pressure should be brought down so that loco wheels do not get locked and skid.

1. Loco No.:- 27168 2. Type of Loco:- WAG-7

3. Year of built :- 4. Wheel arrangement:- Co-Co (16/65)

(A). Date of wheel turning:-24.05.01 Time from last wheel turning:- Months

(B). Date of wheel turning:- 06.02.01 Time from last wheel turning:- Months

ANNEXURE-II

ANNEXURE IV

Loco No: 23843 Type of loco : WAG-5 Shed: ELS/NKJ

Effect of misalignment of Brake Beam