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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As shown in Fig. 5 for pipe conveyor applications, it is very important to consider the influence of the conveyor routing on belt tracking. The overlap area in the perimeter of the pipe conveyor belt forms the belt section with the highest mass, as well as the highest concentration of tension member. When being moved through curves the belt therefore tries to assume a condition of lowest tension by turning the overlap towards the inner side of the curve.

Fig. 5: Tracking of a pipe conveyor belt in curves.

When loaded, the material stabilises the pipe belt by keeping the overlap in the “12-o’clock-position”. The balance point is below the centre of the pipe and the belt is in a balanced position. When the overlap is in the 12-o’clock-position, however, the unloaded belt is unstable due to the weight distribution, with most of the belt weight positioned on top of the pipe (Fig. 6). This condition creates the tendency for the belt to rotate.

Fig. 6: Centre of gravity of the loaded (left) and unloaded (right) belt.

The initially installed pipe conveyor belt St1000 (1000 N/mm), 1600 mm width, covers 9 mm + 6 mm had a layer of transverse fabric reinforcement (breaker) above and below the steel cables, which were separated by a rubber layer from the steel cords [1]. Such design is very beneficial in keeping the overlap in the 12-o’clock-position and provides good belt guidance in curves. Nevertheless, because of the large number of sharp horizontal and vertical curves and based on the experience with the initially installed pipe conveyor belt of a third party manufacturer, Contitech designed a new pipe conveyor belt. The new belt utilised a combination of fabric and steel transverse reinforcements: Rollgurt 1000 S-K2, 8T:6S, 1600 mm width, Contiextra with a nominal breaking strength of kN = 1000 N/mm.

Special attention was given to the design of edge areas of the new pipe conveyor belt and to the correct selection of the rubber compound. The new design allows a safe operation at a minimum curve radius Rmin of 365 m (1200 ft) and a more stable tubular shape, so the possibility that the belt can collapse in the future is greatly reduced. The selected rubber compound Contiextra works at the temperature of T = -40°C (-40°F) even with strong deformations resulting from the conveyor profile and the pipe forming.

The final tests, including analysing and establishing the forming forces, confirmation of the tubular shape and form of overlap, and defining the behaviour of the pipe belt sample in a curve at the temperature range of +38°C (+100°F) to -40°C (-40°F), were conducted at Contitech test facilities in Northeim, Germany.

The considerations, as stated above, show that the most important parameter is a sufficient contact length and contact force between the belt and the idlers, in order to guide the belt through a curved conveyor. This can only be achieved by a belt design with optimised transversal stiffness and flexibility. Hence, it is evident that a pipe conveyor belt is designed and specified in order to gain an optimised solution for the specific application cases with respect to tracking capabilities, as well as power demand.

Consequently, the design of a pipe conveyor and of a pipe conveyor belt is significantly different from the common design of a standard belt conveyor and of a belt that is used for troughed conveyor applications. That is why OEMs and belt manufacturers should work side by side to optimise the pipe conveyor in detail.

Pipe Conveyor Belt Replacement Procedure

When a new conveyor belt has to be installed as a retrofit, upgrade or replacement of an existing transport method, the impact of the conveyor system downtime and the resultant lost production should be minimised. After analysing the terrain and routing and in consultation with the customer, Contitech decided to pre-splice and pull in the new belt from behind of the BC-8 head station. Similar to the KPC-project [3], the new pipe belt was connected to the existing old belt via a temporary (dummy) splice. As the new belt was pulled into the system, the old belt was pulled out. This temporary splice, however, needs to be a 100%  functional splice for the occasions when the system needs to be restarted at normal operating parameters, before the belt replacement is completed.

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