Belt Replacement at a Long Distance Pipe Conveyor at the Skyline Mine

Conveyor Maintenance

Belt Replacement at a Long Distance Pipe Conveyor at the Skyline Mine

Belt Design, Installation and Power Measurements
When the Arch Western Coal Skyline Mine decided to replace the old belt of its long distance BC-8 pipe conveyor, a new belt had to be designed to be suitable to the existing routing. In addition, a special installation procedure had to be developed to minimise downtime during the belt installation and commissioning.
(ed. WoMaMarcel - 18/10/2014)
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The Contitech experience shows that the total break-in period can take up to several months when the belt is running. When the break-in period is over, the measured power consumption level remains constant for several months during the same season of the year.

Usually the system is operated at 80% of the maximum belt speed. Other speeds, as shown in Fig. 18, are commissioning presets. The power demand of the system follows the belt speed almost linearly; therefore the resistance to motion in the system is not influenced by the belt speed.

When the new belt was operated for the first time, without material, during the initial commissioning of the system, approx. 90% of nameplate motor power was used when running at 90% at full speed.

After the break-in period was over, the power consumption dropped by approximately 30% during the same warm season. This behaviour is a result of the transversal rigidity of the pipe belt and its high forming forces at the beginning of the break-in period. The power consumption reduces as the belt adapts to the conveyor system.

Furthermore, from Fig. 18 it is evident that the temperature has a very strong influence (over 20%) on power consumption. This can be explained by the increase of the transversal rigidity of the pipe conveyor belt (rubber becomes stiff when cold) and the escalation of the general friction in the conveyor system (e.g. idlers) at low temperatures.

Fig. 19 shows the power consumption during commissioning, after commissioning and after the break-in period when loaded in summer. All these measurements were made at temperatures of approx. +15°C (59°F), to avoid the temperature influence on the results.

Fig. 19: Power consumption versus belt speed during and after commissioning and after break-in period in summer.

During commissioning, with material, the system’s power demand in the loaded condition was approx. 75% of the installed motor power. After nearly two weeks of operation, this value had reduced by approx. 11%.

After the break-in period, the power consumption dropped by another 18%. Consequently, the difference in the power consumption between the commissioning time and the time after break-in is approx. 30%. As mentioned previously, the high transversal rigidity of the pipe belt reduces over time. This is a result of the belt running and adapting to the conveyor system over several months of initial operation.

In the winter, the belt continues to operate with sufficient safety factors, showing the highest belt tension at the tail pulley in the return strand.

Since the day of commissioning, the system has operated with outstanding stability, regardless of the circuitous routing. The belt overlap in all sections is steady and keeps the desired 12- and 6-o’clock-position in the carry and return strand, respectively. Even with the sections partially loaded the behaviour of the belt is stable, showing that under the given challenging circumstances (downhill application, age of the system, condition of idlers, curved routing) the belt for this pipe conveyor application is obviously the determining element for the safe operation of the system.

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