Wear of rock cutting tools: laboratory experiments on the abrasivity of rock

153 Pages·49.432 MB·English

by  Deketh, H J R

WEAR OF ROCK CUTTING TOOLS
LABORATORY EXPERIMENTS ON THE ABRAS!VJTY OF ROCK
Taylor & Francis

Taylor & Francis Group
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WEAR OF
ROCK CUITING
TOOLS
Inboratory experiments
on the abrasivity ofrock
H.J.R. DEKETH
Technical University Delft, Section Engineering Geology, Delft
0
CRC Press
c;Il!
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Contents
Preface VIII
1 Introduction 1
2 Rock cutting theories 4
3 Possible wear mechanisms at the wear-flat of rock cutting tools 7
3.1 Introduction 7
3.2 Wear type classifications 8
3.2.1 The motion category classification 8
3.2.2 The wear mechanism classification 8
3.3 Wear mechanisms relevant to rock cutting tools 10
3.3.1 Abrasive wear 11
3.3.2 Adhesive wear 14
3.3.3 Sliding wear 16
3.3.4 Total wear due to sliding motion contact 16
4 Wear mode hypothesis 18
4.1 Introduction 18
4.2 Cutting forces 18
4.2.1 Influences of rock material properties on cutting forces 19
4.2.2 Influences of rock mass properties on cutting forces 19
4.2.3 The influence of some operating condition factors on cutting
forces 19
4.3 Rock relief strength 20
4.3.1 The influence of rock material strengrn properties on relief
strength 20
4.3.2 The influence of the geometry of the relief on relief strength 21
4.3.3 Hardness of the mineral grains 21
4.4 Wear mode prevalence 22
5 Rock cutting tests to study wear 26
5.1 Introduction 26
5.2 The scraping test 28
v
VI Contents
6 Rock properties with respect to wear 34
6.1 Introduction 34
6.1.1 Rock property based rock cutting wear index values 34
6.1.2 Some considerations on the non-intrinsic rock property
parameters 35
7 Experiments 40
7.1 Introduction 40
7.2 Scraping test experiments 40
8 Chisels used in the experiments 44
8.1 Introduction 44
8.2 Chisel material 44
8.3 Chisel shape 45
8.4 Thermocouple 46
9 Properties of rock types used in the experiments 48
9.1 Rock material properties 48
9.1.1 Interpretation of the measured and derived rock properties 49
9.2 Rock sample preparation 55
I0 Test results on artificial rock (mortar) 56
10.1 Repeatability and the effect of groove spacing 56
10.1.1 Effect of spacing of the grooves, sawn into the rock disc 56
10.1.2 Repeatability of the experiments, with respect to the
amount of wear 56
10.2 Scraping test experiments on mortar at constant cutting velocity 57
10.2.1 Experiments on mortar composition 1 58
10.2.2 Results ofexperiments on three mortars of different
strength 61
10.2.3 Results of experiments on four mortars of different grain
size 13
10.2.4 Results ofexperiments on three mortars of different
volume percentage of abrasive grains 78
10.2.5 Results of experiments on two mortars of different shape
of the quartz grains 82
10.2.6 Results of experiments on mortars ofdifferent mineral
content 84
10.3 Specific wear equations based upon scraping test experiments on
mortar 87
10.4 Scraping test experiments on mortar with varying cutting velocity 89
10.4.1 Experiments on mortar composition 8 91
10.4.2 Experiments on different mortars 91
10.5 Comments on the experiments on artificial rock (mortar) 99
11 Test results on natural rock types
100
11.1 Introduction
100
Contents vn
11.2 Experimental results 100
11.2.1 Experiments on sandstones 100
11.2.2 Experiments on limestones 105
11.2.3 Co"elation of test results obtained in experiments on
artificial or natural rock 105
11.3 Comments on the experiments on natural rock I09
12 Relation of the scraping tests with rock cutting projects in practice 110
12.1 Description of the T-850 rock cutting trencher 114
12.2 Calculation of the feed of a single bit of the T-850 rock cutting
trencher 114
12.3 The specific wear in the schnarrtanne granite and the oberdorfer
sandstone, predicted on the basis of results from the scraping test
experiments 115
12.4 Comparison of the field results with the experimental results 117
13 Conclusions 121
14 Closing remarks and recommendations 124
Nomenclature 125
List of abbreviations and symbols 126
References 127
Appendix 1: Comparison of porosity values determined by different methods 132
Appendix II: Petrographic descripitions 133
Appendix Ill: Momentary cutting forces in tests on Elb-sandstone D 143
Preface
The need to get a better understanding of the basic processes of wear in rock cutting
has resulted into the study "Wear of Rock Cutting Tools". Two inter-related books
were produced in close cooperation of the authors. The books highlight different
aspects of the study and may be read standing alone as well as a couple. Both studies
are mainly directed towards the effects of different rock types (and geological setting)
on the processes of tool wear during rock cutting.
"Laboratory Experiments on the Abrasivity of Rock" by Jan Reinout Deketh
provides a better understanding of basic wear processes in laboratory rock cutting
wear experiments, by which the site investigation for rock cutting projects like
dredging, trenching and tunnelling may be tuned.
"Site Investigation for Rock Dredging" by Peter Verhoef provides a general view
over the wide range of aspects which are involved in engineering geological site
investigation for rock dredging.
At the time I started this work a lot of preliminary investigations were already
carried out by and under the supervision of Peter Verhoef. Moreover also during my
work into this subject I was supported by him and other people from the Section
Engineering Geology at the Faculty of Mining and Petroleum Engineering of Delft
University of Technology. I thank Peter Verhoef for all this and for giving me the
opportunity to write this book.
My dearest friend, Marina Giezen, supported me during the years and helped me
completing this thesis. She contributed to this work directly by performing a study
into the wear of bits of rock cutting trenchers. Her study of wear and production of
rock cutting trenchers in different types of rock was essential by demonstrating the
relevance of the laboratory experiments to a specific example of rock cutting in
practice. Her work was made possible by Vermeer Manufacturing Company (Pella,
Iowa, USA).
This research has been sponsored by the Dutch Technology Foundation (STW
Stichting Technische Wetenschappen).
Jan Reinout Deketh, December 1994
VIII
CHAPTER 1
Introduction
In many civil engineering and mining projects the earth surface has to be remodelled,
prepared or removed for the benefits and needs of a specific project. Such projects
involve, for example, open pit or underground mines, tunnels, dredging works,
trenches etc. Nowadays manpower is aided or replaced by blasting techniques and
excavation machines like dredgers, trenchers, roadheaders, tunnel boring machines
etc., which all have their specific advantages and applications. A common problem
of most excavation machinery, based on mechanical action, is the unknown
interaction of cutting tools with varying types of rock and geological settings. The
development of more powerful machines and improved technology enables the cutting
of increasingly stronger rock. Unexpected high rates of wear of the cutting tools and
low production rates resulting in high financial losses and law-suits between
contractors, clients and consultants may be the consequence. The financial losses can
be so substantial that the existence of major dredging firms could be endangered. In
the work by P.N.W.Verhoef (1995) some cases are discussed of dredging projects
which had major problems with wear of the cutting chisels which had not been
anticipated.
A large number of investigations has been carried out to determine which factors
are of influence to tool wear due to rock cutting. It seems, that wear problems are
system dependent problems. Therefore studies about wear are only comparable when
the wear system and conditions are more or less equal. Many studies look at a part
of a wear problem and therefore only describe the factors which affect that part.
Most factors that influence wear due to rock cutting can be placed into the following
groups.
1.rock material properties (texture, strength, composition, hardness etc.)
2.rock mass properties (structure, inhomogeneities etc.)
3.type of machinery (type of tools, machine cutting principle etc.)
4.choice of machine settings (thrust, r.p.m. of the rotary cutting device etc.)
5.environment (submerged or dry, weather conditions, operator skills etc.)
For example quartz grains are abrasive to cutting tools made of steel but are hardly
abrasive to cutting tools made of tungsten carbide. This is the case at room
temperature. If temperatures at the wear-flat of a cutting tool become as high as ±
800 °C, the hardness of tungsten carbide decreases and quartz (and possibly even
softer minerals) becomes as abrasive to the tungsten carbide as to steel. High
1