Reliability-based maintenance scheduling of hydraulic system of rotary drilling machines Mohammad Javad Rahimdel a,⇑ , Mohammad Ataei b , Reza Khalokakaei b , Seyed Hadi Hoseinie c a Faculty of Mining Engineering, Sahand University of Technology, Tabriz 51335-1996, Iran b Faculty of Mining Engineering, Geophysics and Petroleum, Shahrood University of Technology, Shahrood 36155-316, Iran c Division of Operation and Maintenance Engineering, Lulea University of Technology, Lulea S-971 87, Sweden article info Article history: Received 16 December 2012 Received in revised form 13 January 2013 Accepted 9 February 2013 Available online 31 August 2013 Keywords: Reliability Drilling Hydraulic Maintenance abstract Hydraulic system has a critical and important role in drilling machines. Any failure in this system leads to problems in power system and machine operation. Since the failure cannot be prevented entirely, it is important to minimize its probability. Reliability is one of the most efficient and important method to study safe operation probability of hydraulic systems. In this research, the reliability of hydraulic system of four rotary drilling machines in Sarcheshmeh Copper Mine in Iran has been analyzed. The data analysis shows that the time between failures (TBF) of Machines A and C obey the Weibull (2P) and Weibull (3P) distribution, respectively. Also, the TBF of Machines B and D obey the lognormal distribution. With regard to reliability plots of hydraulic systems, preventive reliability-based maintenance time intervals for 80% reliability levels for machines in this system are 10 h. Ó 2013 Published by Elsevier B.V. on behalf of China University of Mining & Technology. 1. Introduction Nowadays, rotary blasthole drilling machines were used in sur- face mines and in large size quarries for drilling the soft and med- ium-hard formations. Generally, these machines consist of five main subsystems, as shown in Fig. 1. Only a hydraulic system is capable for generating the linear mo- tion with very high pressure required for such operations, such as mast raising/lowering and leveling the machine by hydraulic jacks. Also, in many drilling machines, hydraulic system supplies high- pressure hydraulic oil to many hydraulic motors to generate rotary motion. So, in this machine, hydraulic system has a critical role and considering its failure rate and the reliability is essential. Major items of hydraulic system are hydraulic reservoirs, filters, pumps, tubing, valves, motors, cylinders, etc. The functions of components in hydraulic system of drilling machines include the following items [1,2]. (1). Tower raising cylinder The mast is raised and lowered by means of two hydraulic cyl- inders. Mast cylinders are often hydraulically extended and mechanically locked so the longer fixed length gives necessary rigidity to the mast. (2). Jack cylinder A rotary blasthole machines equipped with four leveling jacks. Therefore, the blasthole drilling machines must be equipped with four hydraulic jacks, unless a very compelling reason exists. This is particularly important in the case of a rotary blasthole drilling machines, because it has a very heavy mast, pipe changer and hea- vy drill head. All these assemblies take the center of gravity of the rotary blasthole drilling machines to a higher level. (3). Rod changer In blasthole drilling machines, after the addition of a drill rod to drill string and its removal and drilling a blasthole to the desired depth, the extra drill rod is to be added. For this reason, almost blasthole machines have an arrangement for storing additional drill rods in the mast, using hydraulic ranch, and mechanically joining them to the drill string. This mechanism is called a rod changer. (4). Proper motor On one side of the drill crawler, a sprocket is mounted. The sprocket is also called a drive tumbler. A sprocket has many teeth. These teeth interlock with the track pads. When the sprocket is ro- tated, the track pads are forced to move. The rotary motion to the sprockets is imparted by means of a high torque hydraulic motor that is known as proper motor. 2095-2686/$ - see front matter Ó 2013 Published by Elsevier B.V. on behalf of China University of Mining & Technology. http://dx.doi.org/10.1016/j.ijmst.2013.08.023 ⇑ Corresponding author. Tel.: +98 4113444311. E-mail address: mj.rahimdel@yahoo.com (M.J. Rahimdel). International Journal of Mining Science and Technology 23 (2013) 771–775 Contents lists available at ScienceDirect International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst