Diamond impregnated segments and their wear behaviour used in reinforced concrete core drilling
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2023
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Doctoral Thesis
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Abstract
The presented work describes an experimental analysis of the wear behaviour of two metallic materials and, subsequently, the material removal behaviour of monocrystalline synthetic diamonds as used in diamond impregnated segments. A specially developed experimental set-up is used to simulate a realistic application environment and to investigate the different wear characteristics under laboratory conditions. In order to be able to investigate the bond wear, a standardized B611-13 test rig is modified so it is possible to simulate the two dominant wear patterns, such as abrasive and adhesive wear. For this purpose, a sintered silicon carbide wheel is introduced as a counter body in addition to the steel wheel. The silicon carbide wheel makes it possible to imitate drilling in pure concrete, whereas the steel wheel represents rebar core drilling. The two tested diamond segment alloys, the copper-rich Segment A and the iron-rich Segment B, are standard alloys as used in the construction industry. As a first step, parameter investigations are carried out. Here, the wear behaviour is compared at a set upper and lower parameter limit. The upper limit of 200 N and 4 m/s describes the force and speed acting on the segment during core drilling, whereas the lower limit of 59 N and 2 m/s is intended to simulate moderate application parameters in the experiment. While the iron-rich segment B wears similarly to what is observed in core drilling experiments, the wear of the copperbased segment decreases with increasing force and test speed. It is subsequently shown that a hardened layer forms on the copper-based segment, which protects it from further wear. It is possible to detect this layer not only by metallographic methods but also as a result of an increase in hardness measured by nanoindentation methods. In addition to the parameter studies, special attention is paid to the influence of different pH values on segment wear. Wear tests are carried out on the modified B611-13 test rig with two different pH values. For this purpose, a dilute sulphuric acid or sodium hydroxide solution is used to adjust the water-slurry mixture to pH2 and pH13, showing a significantly reduced wear when changing to pH13 solutions instead of pH7. The wear is again reduced in experiments performed at pH2. At pH13, this can be explained by the formation of oxide/hydroxide layers in the interface between the wheel and the segment. Whereas the formation of low friction sulphide films at pH2 explain the low wear, it is shown that by modifying the B611-13 test the same binder material wear values can be measured as observed under real core drilling conditions and that this test is a valuable tool for the development of new binder systems. In addition to the investigation of the binder system, the cutting behaviour of individual diamond grains is investigated. Here, the focus is on conditions close to the application. For this reason, a 5-axis milling machine is modified to examine single grain scratch tests. Diamond particles with a defined orientation are subsequently brazed onto a steel pin and connected to a force measurement platform. The crystallographic orientation is taken into account and the diamonds are applied in (111) or (100) orientation. In order to compare the measured process forces with the wear tests or with real application conditions, a cutting speed of 4 m/s is set. Since the focus is mainly on concrete core drilling, both concrete and steel are selected as the base material. An important factor for determining the material removal behaviour is the process temperature. For this purpose, the measuring tip of a 2-colour pyrometer is positioned directly in front of the cutting edge and the average temperature for both steel and concrete is displayed. To reduce the effort for future investigations regarding cutting behaviour of single grain diamonds in different orientations or geometries, a Smoothed Particle Hydrodynamics (SPH) simulation approach is presented in this work. The SPH model describes process forces and temperatures of diamonds of different orientations, which remove the steel material at increasing penetration depths. The simulated values show very good agreement with the experimentally determined data for both the predicted process forces and temperatures. This work thus shows that it is possible to carry out both an application-oriented and laboratory based development of metallic binder systems and to analyse the influence of different diamond orientations on the removal behaviour by means of SPH simulation. These two approaches subsequently lead to a resource-saving and cost-effective alternative compared to costly prototype tests in the field of diamond segment development.
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Examiner : Wegener, Konrad
Examiner : Antretter, Thomas
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ETH Zurich
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03641 - Wegener, Konrad (emeritus) / Wegener, Konrad (emeritus)