Design and Modeling of a Piston Accumulator for a Rock Drill and its Fatigue Strength

This Master Thesis has been performed at Atlas Copco Rock Drills AB, Orebro and at Linkoping University, Sweden from February 2010 through August 2010.The project deals with performance improvement of hydraulic rock drill machine manufactured by Atlas Copco Rock Drills. Atlas Copco Rock Drills AB is a world leading supplier of percussive rock drilling equipment for surface and underground applications. HOPSAN, a software developed at Linkoping University, provides an integrated simulation environment for simulation of fluid power systems. During the work, a HOPSAN model of a piston accumulator has been developed and its performance with a rock drill has been studied. Furthermore, the fatigue strength calculations of a piston accumulator has been made on the basis of stress analysis performed using the ANSYS software.One of the rock drills of valveless type, developed at Atlas Copco Rocktec Division works at higher efficiency than the conventionally used rock drills. But the problem with this type of drill is that the piston swings between two large and highly pressurized oil volume which causes strength problems in the housing of the rock drill. The aim of this work is to achieve the higher efficiency of the rock drill without having any strength problems. Therefore, some study and research is proposed to replace the large oil volume by one or two piston accumulators.This thesis work involves modelling, simulation, design and fatigue strength calculations of a piston accumulator and its implementation to the rock drill. Optimization of the piston accumulator has also been conducted while working with the rock drill so that highest possible eciency could be achieved. The performance of the rockdrill with piston accumulator has been analyzed and results are studied. In the end, a short fatigue life calculations are performed and results are discussed. Prior to fatigue life calculations, a transient dynamic stress analysis has been performed and stress amplitudes are identified which contributes to the accumulated damage to piston in accumulator.