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

118 Pages·2011·9.68 MB·English

Design and Modelling of a Piston
Accumulator for Rock Drill and its
Fatigue Strength
Nadeem Ul Haq
Division of Fluid and Mechatronic Systems
Degree Project
Department of Management and Engineering
LIU-IEI-TEK-A–10/00929—SE
Abstract
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 Divi-
sion 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 pro-
posed to replace the large oil volume by one or two piston accumulators.
This thesis work involves modelling, simulation, design and fatigue strength calcula-
tions 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 efficiency could be achieved. The performance of the rock
drill 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.
Acknowledgment
I am greatly thankful to my supervisors Maria Petterson and Prof. Karl Erik Ry-
dberg, for giving me the opportunity to do this work under their supervision, for
giving me profound understanding about formulation of problem, for being ready
all the time to discuss problems. Their politeness, patience and way of guidance
is really appreciable. They boosted my confidence and showed me how research is
performed with a good planning.
I am also thankful to Anders Johansson and Kenneth Weddfelt, for giving me sup-
port, and providing me help whenever I got stuck in HOPSAN or ANSYS related
problems during this work, for showing patience while answering my questions, for
taking their time out whenever I needed it.
Finally, I wish to express my sincere thanks to my family for their encouragement
and endless support.
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Contents
1 Rock Drilling 8
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.2 A Typical Percussive Rock Drilling System . . . . . . . . . . . . . . . 9
1.2.1 Down The Hole Rock Drilling . . . . . . . . . . . . . . . . . . 9
1.2.2 COPROD Rock Drilling . . . . . . . . . . . . . . . . . . . . . 9
1.2.3 Top Hammer Percussive Rock Drilling . . . . . . . . . . . . . 10
1.2.4 Percussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.2.5 Feed Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.2.6 Dampener System . . . . . . . . . . . . . . . . . . . . . . . . 13
1.2.7 Drill String . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.2.8 Drill Bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.2.9 Flushing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.2.10 Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2 Problem Description 15
2.1 Valveless Rock drills . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1.1 Working Mechanism . . . . . . . . . . . . . . . . . . . . . . . 15
2.2 Problem Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.3 Proposed Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3.1 Two Gas Volumes . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3.2 Research Approach . . . . . . . . . . . . . . . . . . . . . . . . 19
3 Hydraulic Accumulator 20
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2 Types of Accumulator . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2.1 Weight Loaded or Gravity Type Accumulator . . . . . . . . . 20
3.2.2 Spring Loaded Accumulator . . . . . . . . . . . . . . . . . . . 21
3.2.3 Gas Loaded Accumulator . . . . . . . . . . . . . . . . . . . . 22
3.2.4 Piston Type Accumulator . . . . . . . . . . . . . . . . . . . . 23
3.2.5 Diaphragm Type Accumulator . . . . . . . . . . . . . . . . . . 25
3.2.6 Bladder Type Accumulator . . . . . . . . . . . . . . . . . . . 25
3.2.7 Bellow Type Accumulator . . . . . . . . . . . . . . . . . . . . 26
3.2.8 Applications of Accumulator . . . . . . . . . . . . . . . . . . . 27
4 Modeling of Piston Accumulator 28
4.1 Mathematical Model of Gas . . . . . . . . . . . . . . . . . . . . . . . 28
4.2 About HOPSAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.2.1 Simulation Methodology in HOPSAN . . . . . . . . . . . . . . 30
4.2.2 Optimization Module in HOPSAN . . . . . . . . . . . . . . . 30
4.3 Simulation Model of Piston Accumulator . . . . . . . . . . . . . . . . 31
4.3.1 Orifice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
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4.3.2 Volume with Mechanical Ends . . . . . . . . . . . . . . . . . . 32
4.3.3 Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.3.4 Mechanical Connection . . . . . . . . . . . . . . . . . . . . . . 33
4.3.5 Speed Selector . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.3.6 Frictional Force . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3.7 T-Orifice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.3.8 Miscellaneous Components . . . . . . . . . . . . . . . . . . . . 36
4.3.9 Piston Accumulator Simulation Model . . . . . . . . . . . . . 37
4.4 Breaking Chamber in Simulation Model. . . . . . . . . . . . . . . . . 39
4.5 Effect of Breaking Chamber . . . . . . . . . . . . . . . . . . . . . . . 40
4.6 Description of Piston Accumulator/Simulation Model . . . . . . . . . 42
4.6.1 Advantages of the invention . . . . . . . . . . . . . . . . . . . 42
4.6.2 Optimization of Piston Accumulator over Rock Drill . . . . . 44
5 Performance of Rock Drill Without Piston Accumulator 47
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.2 Calculation of large oil volume . . . . . . . . . . . . . . . . . . . . . . 48
5.3 A Large Oil Volume . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5.4 Simulation Results with Large Oil Volume . . . . . . . . . . . . . . . 51
5.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
6 Performance of Rock Drill With One Piston Accumulators 54
6.1 Rock Drill Simulation Model With One Piston Accumulator . . . . . 54
6.2 Sizing of Piston Accumulator . . . . . . . . . . . . . . . . . . . . . . 54
6.3 Performance of Rock Drill with One Piston Accumulator . . . . . . . 56
6.3.1 Performance of Piston Accumulator . . . . . . . . . . . . . . . 57
6.4 Optimization with One Accumulator . . . . . . . . . . . . . . . . . . 58
6.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
7 Performance of Rock Drill With Two Piston Accumulators 61
7.1 Theoretical Background . . . . . . . . . . . . . . . . . . . . . . . . . 61
7.2 Model of Rock Drill with Piston Accumulators . . . . . . . . . . . . 63
7.2.1 Sizing of Piston Accumulators . . . . . . . . . . . . . . . . . . 63
7.2.2 Performance of Low Pressure Accumulator . . . . . . . . . . . 64
7.2.3 Performance of High Pressure Accumulator . . . . . . . . . . . 65
7.2.4 Performance of Rock Drill . . . . . . . . . . . . . . . . . . . . 66
7.3 Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
7.3.1 Performance of Low Pressure Accumulator . . . . . . . . . . . 69
7.3.2 Performance of High Pressure Accumulator . . . . . . . . . . . 71
7.4 Performance of Rock Drill . . . . . . . . . . . . . . . . . . . . . . . . 72
8 Fatigue Analysis 77
8.1 An Introduction to Fatigue . . . . . . . . . . . . . . . . . . . . . . . . 77
8.1.1 Fatigue Life at Different Stress Levels . . . . . . . . . . . . . . 77
8.2 Stress Based fatigue Design . . . . . . . . . . . . . . . . . . . . . . . 77
8.2.1 General Procedure for Predicting the Fatigue Life . . . . . . . 79
8.2.2 Rain Flow Count Method . . . . . . . . . . . . . . . . . . . . 79
8.3 Stress Analysis Using Ansys . . . . . . . . . . . . . . . . . . . . . . . 81
8.3.1 Problem Description . . . . . . . . . . . . . . . . . . . . . . . 81
8.3.2 Dynamic Analysis in Ansys . . . . . . . . . . . . . . . . . . . 81
8.3.3 The Full Method . . . . . . . . . . . . . . . . . . . . . . . . . 82
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8.3.4 Critical Cases in Piston Accumulators . . . . . . . . . . . . . 82
8.4 Solution Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
8.5 First Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
8.6 Second Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
8.6.1 Static Analysis with Pressure Loading . . . . . . . . . . . . . 96
8.6.2 Transient Analysis with Speed . . . . . . . . . . . . . . . . . . 96
8.6.3 Fatigue calculations for Critical Point . . . . . . . . . . . . . . 96
8.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
9 Summary and Results 102
9.1 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Appendix: A FORTRAN code for the Calculation of Friction
in Piston Cylinder Device II
Appendix: B *.ODAT and *.HCOM Files for Optimization
in HOPSAN III
Appendix: C ANSYS Command Line for Fatigue Analysis V
Appendix: D Wohler Curve IX
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List of Figures
1.1.1Atlas Copco Rocket Boomer WL4 C30 . . . . . . . . . . . . . . . . . 8
1.2.1Percussive Rock Drilling Methods . . . . . . . . . . . . . . . . . . . . 10
1.2.2Top Hammer Drill Basic Principle . . . . . . . . . . . . . . . . . . . . 11
1.2.3Top Hammer Drill . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.2.4The Percussive Rock Drilling Principle . . . . . . . . . . . . . . . . . 12
1.2.5Feed Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.2.6Drill String . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.2.7Bit and Buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1.1Valveless Rock Drill . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1.2Valveless Rock Drill, Theoretical Blow Cycle . . . . . . . . . . . . . . 16
2.2.1Energy Loss during Piston Motion . . . . . . . . . . . . . . . . . . . . 18
3.2.1Weight Loaded Accumulator . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.2Spring Loaded Accumulator . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.3Non-Separator Type Accumulator . . . . . . . . . . . . . . . . . . . . 23
3.2.4Piston Type Accumulator . . . . . . . . . . . . . . . . . . . . . . . . 24
3.2.5Diaphragm Accumulator . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.2.6Bladder Accumulator . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.2.7Metal Bellow Accumulator . . . . . . . . . . . . . . . . . . . . . . . . 27
4.1.1Accumulator volume and pressure during simulation . . . . . . . . . . 29
4.2.1Optimization Procedure . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.3.1Orifice with Diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.3.2Volume with Mechanical Ends . . . . . . . . . . . . . . . . . . . . . . 32
4.3.3Mass Component (Steel) . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.3.4Mechanical Connection Between Nodes . . . . . . . . . . . . . . . . . 33
4.3.5speed Selector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.3.6Friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3.7Frictional Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3.8T-Orifice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.3.9Initial Simulation Model of Piston Accumulator . . . . . . . . . . . . 37
4.3.10Accumulator Simulation Model Test . . . . . . . . . . . . . . . . . . . 37
4.3.11Piston Accumulator Performance . . . . . . . . . . . . . . . . . . . . 38
4.3.12Piston Accumulator Performance . . . . . . . . . . . . . . . . . . . . 38
4.3.13Piston Accumulator Performance (mass effect) . . . . . . . . . . . . . 39
4.4.1Modified Simulation Model of the Piston Accumulator . . . . . . . . 40
4.5.1Test Model for Piston Accumulator with Breaking Chamber . . . . . 40
4.5.2Piston Accumulator Performance with Breaking Chamber . . . . . . 41
4.6.1A Sketch of the Piston Accumulator . . . . . . . . . . . . . . . . . . . 43
4.6.2wvs0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.6.3wpo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
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4.6.4wve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.1.1Rock Drill Machine Simulation Model . . . . . . . . . . . . . . . . . . 48
5.2.1Valveless Rock Drill Mechanism . . . . . . . . . . . . . . . . . . . . . 49
5.4.1Rock Drill Performance with large Volume in Piston Chamber . . . . 51
5.4.2Rock Drill Performance with large Volume (pressure in piston cham-
ber) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5.4.3Rock Drill Performance with large Volume in Piston Chamber(1.5 lit) 52
6.2.1Rock Drill Simulation Model with One Accumulator . . . . . . . . . . 56
6.3.1Rock Drill Performance with One Accumulator . . . . . . . . . . . . 57
6.3.2Rock Drill Performance with One Accumulator(pressure in piston
chamber) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
6.3.3Performance of One Accumulator with Rock Drill . . . . . . . . . . . 58
6.4.1Rock Drill Performance with One Accumulator (Optimization) . . . . 59
6.4.2Rock Drill Performance with One Accumulator (pr. piston chamber) 59
6.4.3Performance of Accumulator with Rock Drill (Optimization) . . . . . 60
6.4.4Rock Drill Performance with One Accumulator (drain line flow) . . . 60
7.1.1Two Piston Accumulator Mechanism with Rock Drill . . . . . . . . . 61
7.1.2Characteristic Curve of Valveless Rock Drill Mechanism . . . . . . . . 62
7.2.1Rock Drill Simulation Model With Two Accumulators . . . . . . . . . 63
7.2.2Performance of Low Pressure Accumulator (plot 1) . . . . . . . . . . 65
7.2.3Performance of Low Pressure Accumulator (plot 2) . . . . . . . . . . 65
7.2.4Performance of High Pressure Accumulator (plot 1) . . . . . . . . . . 65
7.2.5Performance of High Pressure Accumulator (plot 2) . . . . . . . . . . 66
7.2.6Performance of Rock Drill with Two Piston Accumulators . . . . . . 66
7.2.7Performance of Rock Drill with Two Piston Accumulators (impact
force) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
7.2.8Performance of Rock Drill and Two Accumulators . . . . . . . . . . . 67
7.2.9Performance of Rock Drill with Two Accumulators (pressure piston
chamber) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
7.2.10Performance of Rock Drill with Two Accumulators (flow rates) . . . . 68
7.3.1Performance of Low Pressure Accumulator (plot 1: Optimization) . . 69
7.3.2Performance of Low Pressure Accumulator (plot 2: Optimization) . . 70
7.3.3Performance of Low Pressure Accumulator (plot 1: breaking chamber) 70
7.3.4Performance of Low Pressure Accumulator (plot 2: breaking chamber) 70
7.3.5Performance of High Pressure Accumulator (plot 1: Optimization) . . 71
7.3.6Performance of High Pressure Accumulator (plot 2: Optimization) . . 71
7.3.7Performance of High Pressure Accumulator (plot 1: breaking chamber) 72
7.3.8Performance of High Pressure Accumulator (plot 2: breaking chamber) 72
7.4.1Performance of Rock Drill with Two Accumulators (Optimization) . . 73
7.4.2Performance of Rock Drill with Two Accumulators (impact force) . . 73
7.4.3Performance of Rock Drill and Two Accumulators (Optimization) . . 74
7.4.4Performance of Rock Drill with Two Accumulators (pressure piston
chamber) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
7.4.5Performance of Rock Drill with Two Accumulators (flow rates) . . . . 74
7.4.6Schematic Drawing of High Pressure Accumulator . . . . . . . . . . . 76
7.4.7Schematic Drawing of Low Pressure Accumulator . . . . . . . . . . . 76
5
8.1.1Fatigue life as a function of applied stress represented by a so called
W¨ohler curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
8.2.1Stress at Time Varying Load . . . . . . . . . . . . . . . . . . . . . . . 80
8.4.1Sketch of Piston . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
8.4.2Ansys Model for Low Pressure Accumulator . . . . . . . . . . . . . . 85
8.5.1Initial Loading and Boundary Conditions . . . . . . . . . . . . . . . . 86
8.5.2Stress Distribution Due to Static Pressure . . . . . . . . . . . . . . . 86
8.5.3Piston with Speed of 2 m/s . . . . . . . . . . . . . . . . . . . . . . . 87
8.5.4Critical Point with Maximum Principal Stress . . . . . . . . . . . . . 88
8.5.5Stress variation at Node 262 . . . . . . . . . . . . . . . . . . . . . . . 89
8.5.6Stress Variation at Node 262 w.r.t New Coordinate System . . . . . . 89
8.5.7Stress Cycles for Node 262 . . . . . . . . . . . . . . . . . . . . . . . . 90
8.5.8Critical Point (node 1) with maximum Principal Stress . . . . . . . . 92
8.5.9Stress Variation at Node 1 in the Piston . . . . . . . . . . . . . . . . 93
8.5.10Stress Variation at Node 1 w.r.t New Coordinate System . . . . . . . 94
8.5.11Stress Ranges Obtained Using Rain Flow Count Method . . . . . . . 94
8.6.1Ansys Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
8.6.2Stress Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
8.6.3Variation of Stresses at Critical Node 2 . . . . . . . . . . . . . . . . 98
8.6.4Variation of Stresses at Critical Node 2 w.r.t New Coordinate System 99
8.6.5Stress Ranges Obtained by Rain Flow Count Method . . . . . . . . . 99
6
Nomenclature
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