RAIL LUBRICATION ON THE RICHARDS BAY COAL LINE
  J. J. de Koker   Pr  Tech  Eng
Spoornet

Background

It is estimated that the rail industry uses more than a hundred tons of grease annually to curb wear on rail and wheel-flanges on South African railway track. 

Railways are mainly used for freight transport and transport of passengers in large cities. Because the friction between the tread of the steel wheel and rail is low, much less energy is needed to move the same tonnage as road transport. If a 36 000 kg rail freight wagon of a standard United States type were set rolling on a level railway track at 100 km/h, it would travel more than 8 kilometres before coming to a stop. A motor truck of similar weight set free on a level freeway at the same speed would roll only about 1 600 metres before stopping. Wheel loads of more than 15 tons can be accommodated.

A train is steered around a curve by the wheel flange bearing tightly against the side of the rail crown. Lateral forces of between 20 and 50 kN at speeds of 80 – 120 km/h are usually measured in this position, depending on the radius of the curve. This steel-to-steel contact causes severe wear on wheel flanges as well as the side of the rail crown. Lubricants reduce wear of rail in this area by as much as 7 800% and on wheel flanges by 2 200%, under controlled conditions.

Rail and wheel flange lubrication has been the practice in Southern Africa for many years. On other railway systems, locomotive mounted wheel lubrication systems, purpose built lubrication wagons and road-rail vehicles are used to combat wear. Until 2002, trackside lubrication was the only system used by Spoornet. Earlier, manual lubrication was common on sharp curves like the ‘Kei cuttings’ where the curves are so tight and the gradient so steep that the track passes over itself in a spiral.

Figure 1.    Worn wheel to worn rail contact in a curve: where the wear takes place.

On Spoornet track, the lubricant is applied by means of trackside lubricating machines installed on the field side of the rail. Passing trains activate the pumping mechanisms on these machines, applying lubricant by applicator plates positioned on the gauge side of the rail. Wheel flanges pick up the grease and deposit it on the wear faces of the curves ahead.
 

The Effect of Lubrication on Rail Life, Wheel Wear and Energy Consumption. 

Train resistance around curves is reduced dramatically by lubrication of the rail/wheel flange interface. Locally 48% less energy was measured to haul wagons around a lubricated curve, compared to measurements from the same dry, un-lubricated curve. The wear-rate of wheel flanges and curve rail increases as the radius of the curve decreases and speed or axle load increases.

The efficiency of the lubricant film between the rail and wheel greatly affects the improvement in rail and wheel life.  Locomotive wheel life of 35 000 km and less, and rail life of less than 25 million gross tonne have been recorded on un-lubricated Spoornet track. The economic implications of these high wear rates are astronomical, as the cost of new rail is more than R300 per metre, excluding replacement. Spoornet has achieved seven to tenfold increase in rail life under adverse track conditions with rail and flange lubrication.  This implies that rail in curves should only be replaced due to metal fatigue and not because of wear. Modern high tensile rail under high axle loading conditions has an expected life of more than 1 500 million gross tonnes (MGT) with lubrication on the Richards Bay Coal Line. 

 Fig 2.   A well-lubricated rail wear face in a Spoornet curve, with grease removed to show film thickness

Under un-lubricated conditions the coefficient of friction between wheel flange and rail can approach 0,5 whilst adequate lubrication reduces it to about 0,1.  Values of 0,2 to 0,4 are commonly measured on Spoornet track.

Spoornet reported a six-fold increase in locomotive wheel life under relatively low levels of lubrication on the Richards Bay Coal Line. Good lubrication along the entire route is essential to achieve high reduction in wear rates.  Lubrication also prevents derailments by curbing the tendency of wheels to climb up and out on dry curves.

Additional resistance is generated by wagons with misaligned axles. An average misalignment of 1 mrad on wagons is common. Reduction in rolling resistance due to rail and wheel flange lubrication of up to 50% around curves and up to 30% on straight or tangent track was measured against un-lubricated track in the USA, leading to energy savings of between 20% and 30% under service conditions.

It was found that a good correlation exists between energy saving and rail lubrication. In a test to measure the effect of rail lubrication on energy consumption on Spoornet, a curve of 200-metre radius was left un-lubricated until severe wear occurred on the high leg rail. Standard wagons were pushed around the curve and the energy needed to achieve this calculated.  The curve was lubricated and the test repeated with the same wagons.  For the un-lubricated curve the wagons required 54 Newton/ton to traverse the curve but when lubricated, only 28 Newton/ton was needed, requiring 48% less energy. A saving of 28% in power usage was reported under service conditions on the Richards Bay Coal Line, mostly because of rail lubrication.

Rail lubrication results in increased tonnage ratings where curves control train composition.  In practice, 10% to 20% more wagons can be added to a train if the line is consistently and well lubricated.
 

Grease Used for Rail and Wheel Flange Lubrication.

The most popular greases used to lubricate rails and wheel flanges are calcium-based graphited grease and lithium-based grease with molybdenum disulphide.  Under normal working conditions a reasonable consumption of the locally produced calcium-based graphited grease is ± 1 kg of grease for every 5 000 axles, that is 0,2 gram/axle. Application of the correct amount of lubricant has hardly any negative effects.  Over‑lubrication, however causes loss of adhesion when the lubricant gets on the running surface of the rail, resulting in wheel-slip and train delays.  Braking is not reported to be adversely affected by over‑lubrication since the heat generated when brakes are applied burns off the lubricant.

Spoornet objectively considered the environmental impact of the normal splatter and wastage of grease around trackside lubricators. When trains pass the trackside lubricator at speed, a thin film of grease builds up on the ballast adjacent to the lubricator due to splatter, becoming thicker as time goes by. After extensive evaluation of many alternatives the placement of catch mats to arrest grease splatter was found to be the most effective and economic solution to the problem. 

Fig 3. An experimental grease catch mat at an M&S trackside lubricator on the Richards Bay Coal Line

 A Brief History of Trackside Lubrication on the Richards Bay Coal Line.

Due to an oversight by construction engineers not familiar with track maintenance practice, the Vryheid-Richards Bay section of the line was commissioned in 1976 without any provision for rail and flange lubrication. The severe wear caused speedy discovery of the oversight. The service life of those un-lubricated 48 kg HCOB rails ranged from 21 MGT to about 35 MGT, depending on the radius of the particular curve.

The introduction of P&M type trackside lubricators with 8-kg grease capacity to the line coincided with the replacement of most of the rails. Due to the remoteness of large sections of the line, the standard of maintenance was mostly well below the acceptable norm. Nonetheless, at the time of replacement due to upgrading of the line, lubricated rails had reached about 70% of their wear life after carrying approximately 135 MGT, representing an improvement of around 700%.

The trackside lubrication system was labour intensive, the grease capacity of the machines and the supervision and training of maintenance staff inadequate. No proper figures were available of the actual cost of the lubrication effort, but it was recognised that the results were unacceptable. It was agreed to evaluate large capacity “state of the art” mechanical lubricators on the line. As an interim measure, electronic, gas-operated machines, mounted on inspection trolleys, were used to lubricate sections of the line. This system failed because of leakage in the gas lines and the mechanical unreliability of the trolleys.

Just after the large machines had been ordered, a policy decision was made to upgrade the whole line to twenty-six tonne axle load capacity with appropriate heavier track structure and high stability self steering bogies on the coal wagons. In theory, the self-steering bogies would obviate the need for rail and flange lubrication and alternative sites for the evaluation of the lubricators had to be found. Warnings that lubrication would still be needed on the line were not heeded and the upgrading continued minus rail lubrication.

No sooner were the new upgraded rolling stock commissioned, when it was found that the locomotives still required lubrication, since they were not equipped with self steering bogies. With no lubrication on the line, the wheels had to be re-profiled after only 35 000 km. Locomotives were often not available for revenue earning service due to the frequent and expensive re-profiling of the wheels.

A decision was taken to lubricate the line again with trackside lubricators, since evaluation with on-board lubricators on the locomotives did not produce the desired results. As the large capacity trackside machines proved to be prone to mechanical failure, small capacity machines were again installed on the line.

Meanwhile, hydraulically operated trackside lubricators were developed in the USA. These machines boasted large grease reservoirs and proved to be fairly reliable. Two new trackside systems were evaluated: the hydraulically operated M&S machines and an electrically operated system. The latter was found to be impractical due to the sophistication of the system.

About three hundred M&S hydraulically activated machines with 120 kg grease capacity were installed on the line, increasing locomotive wheel life to around 220 000 km, an increase of more than 600%. The installation of this system solved the problem of excessive wear on locomotive wheels. A formula was also developed to optimise the number and positioning of the lubricators along the track.

Problems Encountered with the Trackside Lubrication System.

The M&S machines were also labour intensive and sometimes installed in hard to reach positions. Soon, the same problems were encountered with the maintenance staff as in the past. To counter this, a monitoring system was implemented and the efficiency of the lubrication measured at regular intervals. Grease consumption and availability were monitored. The positioning of the machines was optimized and the supply of spares streamlined. Staff members were re-trained regarding maintenance of the machines and new supervisory structures implemented. Consumption figures were kept and the whole system regularly inspected, monitored, and effectively managed.

Table 1.  Cost of Trackside Lubrication on the Richards Bay Coal Line, April 1998 to March 2003

Since the management of trackside lubrication was found to be out of proportion with the other track functions, it was decided to maintain the lubricators under contract. The lubricator maintenance contract was implemented successfully but the monitoring and management there off still had to be done by highly trained technical staff. This factor led to the decision to introduce an alternative used successfully overseas, namely Hi-Rail Lubrication.
 

Hi-Rail Lubrication.

Hi-Rail Lubrication means the lubrication of the line by the controlled application of a bead of grease directly to the wear face of the rail from a vehicle travelling on the track. The Hi-Rail vehicle, sometimes referred to as a Road-Rail vehicle, is usually an adapted delivery vehicle, equipped with a special storage and application system.

Experience with the Hi-Rail Lubrication System.

Five vehicles service the Richards Bay Coal Line, four running full time and one to be used when another vehicle is serviced or repaired. This works well as long as one of the vehicles does not suffer major damage. The first vehicle was commissioned in February 2003. As soon as satisfactory results were obtained, the trackside machines were removed. This decision left no back-up system in the event of an emergency affecting the availability of the Hi-Rail vehicles.

Fig 5.  The grease application nozzle positioned behind the flange of the steel wheel of the Hi-Rail vehicle

It is imperative that the Hi-Rail vehicle runs consistently according to schedule. When the vehicle does not lubricate every day, the curves become dry. When the line is not lubricated for two days in a row, the grease is consumed and severe wear sets in after the third day. Since there is no back-up track-mounted system, any deviation from the norm is immediately noticed. However, curves on the up-line carrying mostly empty coal traffic, can withstand longer periods without lubrication.

It was found that the grease application on the curves was sufficient and most curves were well lubricated throughout. Long curves previously considered ‘problem curves’ were lubricated right through. Some curves, however, were found to be poorly lubricated because train speed at these curves was consistently higher than the rest of the line due to their positioning at the beginning of momentum gradients. The super-elevation on these curves was not adjusted for the higher speed, resulting in higher flange forces and grease consumption.

The vehicle operator was requested to run the vehicle at half speed around these curves, resulting in a doubling of the grease delivery on the rail. This higher application rate had a very positive effect and the curves were adequately lubricated. The possibility of increasing the super-elevation of these curves is being investigated.

The nozzles are adjusted to position the grease bead about 10 mm from the running surface of the rail. When the grease is applied either too low or too high, the efficiency of the system is compromised. The lithium-based grease used in the system seems to be superior to the standard grease previously used by Spoornet, particularly when the vehicle has not lubricated the line for a day or two.

Since the Hi-Rail vehicle is light and the wheels of small radius, the vehicle is not easily detected by the electronic track circuiting.  To overcome this problem, a special pantograph pressing onto the rails was added to enable detection at difficult spots. It was also found that the vehicle is sometimes not detected when travelling at too high speed.
 

The Vehicle.

A 2-ton Toyota Dyna truck was fitted with hydraulically lowered and lifted flanged steel wheels, enabling it to get on and off the track at level crossings. The vehicle is operated by a driver and an assistant, lubricating and inspecting a designated section of track on a daily basis.

The Spoornet specification calls for a dual mode automatic rail lubrication vehicle of not less than 9 500 kg, adapted to travel on road as well as on rail for inspection and lubrication, fitted with an automatic, high pressure airless grease delivery system. The time required for mounting or dismounting the track at level crossings must not exceed five minutes. 

Fig  4.  The Hi-Rail vehicle on track , lubricating the Richards Bay Coal Line north of Vryheid

A service life of at least 10 years is specified with a proven track record of reliability, maintainability, cost- and user-friendliness with accuracy of lubricant application. The vehicle must lubricate and inspect daily in all weather conditions at a top speed of at least 100 km/h for road and rail, and be able to safely negotiate gradients of 1:40 and curves of 85-m radius. A minimum operating range of at least 400 km is required. 
 

The system is equipped with a compressor delivering an operating pressure of 142 bar, the lubrication system with a 50-kg grease reservoir and two 210 litre spare grease drums. Since the calcium-based graphited trackside grease apparently clogs the thin pipes in the feeding system, special lithium-based molybdenum di-sulfide grease is used. The grease is applied with a 0,5-mm aperture nozzle running in the shade of the wheel flange so as not to be damaged by obstructions on the track. The vehicle is equipped with cameras showing the driver in the cab how the grease is being applied. It has an on-board computerised control system, which also monitors grease usage.

The operator manually switches the system on at the beginning of a curve. The grease application is set, as required, on a time basis, e.g. one second on, one second off, or three seconds on, one second off. Since the pressure in the system remains constant, the grease application rate is determined by the speed of the vehicle.  The designed rate of application of grease is achieved at a speed of 60 km/h.

Fig 6.  The start of the bead of grease applied to the side of the rail by the Hi-Rail vehicle

Conclusion

From the experience gained over the first year of operation, the Hi-Rail lubrication system is considered to be an improvement over the trackside system. The overall annual cost of the Hi-Rail lubrication system is still to be calculated, but preliminary figures suggest that it will be higher than that of the trackside system. Better overall lubrication of the line is achieved and less time is spent managing and monitoring the system, making the higher cost worthwhile.