Reliability of transportation belt rollers used in surface coal digging

Transport of ground and coal at the surface coal dig in Kostolac, Serbia, is done using transportation belts (3 - 5 kilometres in length) using the systems of BTR (Bagger-Transporter-Remover) and BTM (Bagger-Transporter-Mill). The transporter belt during circular movement is suspended on carry-rollers (during transport of weight) and on support-rollers (without weight). Two or three carry-rollers, or three support-rollers make a garland. Garlands (5 carry and 3 supporting) are built into a section and they enable the movement of belt over them. The number of sections depends on the transportation system length. Reliability of these systems is governed by the reliability of the carry and support rollers. In order to determine the reliability of the BTR and BTM systems, reliability analysis of both carry and support rollers was performed using the method of Fault Tree Analysis (FTA) and Reliability Block Diagrams (RBD). In this paper the assessment of roller reliability is described using the FTA method with failure elements. The reliability function was determined on the basis of the RBD in the case where all of the constructive elements of the rollers are in operation - the complex relationship, and when some of the elements are in failure mode - the quasi-complex relationship.