Call number: LD2668 .T4 1951 W3 / Master of Science

Abstract Grinding mills are generally very inefficient, difficult to control and costly, in terms of both power and steel consumption. Improved understanding of temperature behaviour in milling circuits can be used in the model-based control of milling circuits. The loss of energy to the environment from the grinding mill is significant hence the need for adequate modeling. The main objectives of this work are to quantify the various rates of energy loss from the grinding mill so that a reliable model for temperature behaviour in a mill could be developed. Firstly models of temperature behaviour in a grinding mill are developed followed by the development of a model for the overall heat transfer coefficient for the grinding mill as a function of the load volume, mill speed and the design of the liners and mill shell using the energy balances in order to model energy loss from the mill. The energy loss via convection through the mill shell is accounted for by quantifying the overall heat transfer coefficient of the shell. Batch tests with balls only were conducted. The practical aspect of the work involved the measurement of the temperatures of the mill load, air above the load, the liners, mill shell and the environmental temperature. Other measurements were: mill power and sound energy from the mill. Energy balances are performed around the entire mill. A model that can predict the overall heat transfer coefficient over a broad range of operating conditions was obtained. It was found that the overall heat transfer coefficient for the grinding mill is a function of the individual heat transfer coefficients inside the mill and outside the mill shell as well as the design of the liners and shell. It was also found that inside heat transfer coefficients are affected by the load volume and mill speed. The external heat transfer coefficient is affected by the speed of the mill. The values for the overall heat transfer coefficient obtained in this work ranged from 14.4 – 21W/m2K. iv List of Publications The author has published the following papers based on the contents of this dissertation as follows: Published conference abstract Kapakyulu, E., and Moys, M.H., 2005. Modelling of energy loss to the environment from the grinding mill, Proceedings of the Mineral Processing 2005’ Conference, SAIMM, Cape Town, South Africa, 4-5 Aug. pp 65-66 - SP03 Research Papers: Accepted for publication and currently in press in Minerals Engineering: Kapakyulu, E., and Moys, M.H., 2006. Modelling of energy loss to the environment from a grinding mill, Part I: Motivation, Literature Survey and Pilot Plant Measurements, (Currently in press in Minerals Engineering) Kapakyulu, E., and Moys, M.H., 2006. Modelling of energy loss to the environment from a grinding mill, Part II: Modeling the overall heat transfer coefficient, (Currently in press in Minerals Engineering)

Este trabalho tem por objetivo desenvolver o processo de retificação a alta velocidade de superligas utilizando rebolos de CBN vitrificados. Para tanto, foram estudadas diversas condições de dressagem, ou seja, as influências dos parâmetros de dressagem no desempenho do rebolo CBN de liga vitrificada. A partir da escolha desses parâmetros, foi também determinado o desgaste do rebolo em diversas condições de velocidade de avanço, e a qualidade superficial das peças retificadas. Foi utilizado um sistema de mapeamento topográfico do rebolo, baseado na emissão acústica emanada da interação entre rebolo-peça, para o monitoramento do processo. Como resultado foi determinada a influência da velocidade de dressagem e da relação de velocidades na rugosidade da peça retificada. Ficou determinado também, o desgaste do rebolo de CBN em função do volume de material retificado para os diferentes materiais das superligas testadas. Através do sistema de mapeamento topográfico, determinou-se os padrões gráficos do comportamento do rebolo de CBN vitrificado. Sendo assim, verificou-se que o sucesso da aplicação de rebolos CBN vitrificados na retificação de superligas depende da qualidade superficial do rebolo após a dressagem e da escolha certa dos parâmetros de retificação, os quais dependem da constituição das ligas testadas. / The aim of this work is to develop a high speed grinding process for super alloys using vitrified CBN wheels. For that, dressing conditions were studied in order to determine its influence on the CBN wheel performance. From the chosen parameters, the wheel wear and the ground surface quality were measured for different infeed speeds. A topographical mapping system based on acoustic emission was used to monitor the grinding process. As a result, the best dressing speed and speed ratio which generated the smallest surface roughness values could be found. The CBN wheel wear was measured and its ratio to the ground volume was evaluated. Through the mapping system, some visual patterns were obtained defining the grinding wheel behavior when dressing and grinding. Thus, the success vitrified CBN wheel application for super alloys depends basically on the wheel topography after dressing and the grinding parameters, which are dose related to the work material composition.

Grinding operations can be analyzed through monitoring and analysis of the spindle power during the process. Due to the complexity of the process, the analysis on grinding processing signal still heavily relies on personal experience of the engineer instead of having a standard structured method. Therefore, subjectivity and inconsistency is introduced into the analysis procedure. In this thesis, a general method is established to characterize signal, utilize the characterization result to predict the real time condition of grinding wheels and the impact on the process performance measures, and provide suggestions in modification of process parameters to improve the grinding operation. This method is initiated from signal acquisition and conducted based on characterizing the signal and organizing expert knowledge. When the standard procedure to analyze the grinding process through power signal is established, the correlation between input and output can be understood, which can later be utilized for diagnostic applications. During the diagnosis, the real-time grinding wheel status is estimated and the output of the process is predicted. Then, suggestions on modifying the input parameters to address given output issue are generated. Therefore, a signal analysis and knowledge based monitoring and diagnosing system is developed to help enhance the current grinding process planning. This system is realized with a software tool developed with specifically designed algorithms under Matlab environment, upgrading from manual signal processing to an automated characterization procedure and providing process evaluation and improvement suggestions, which will improve the objectivity, consistency and accuracy in the analysis of grinding processes.

Porous sintered ceramic foam made of 99.8% Alumina (AL2O3) was investigated for grinding applications in metallic bearings. The properties of this alumina foam were investigated and correlated to the grinding performance in an I.D. grinding application. The mechanical properties, such as density and Young's Modulus, were correlated to grinding performance. The physical properties, investigated with Scanning Electron Microscope (SEM) analysis and a CT Scan, were used to study sintering behavior and porosity size and distribution. This work found an optimal friability and sintering temperature for the alumina foam grinding wheels. This will enable the alumina foam to become a viable grinding product and compete with the conventional vitrified products. This would be significant since the alumina foam has mainly one ingredient and is manufactured with a simpler process. It can also support a higher porosity than conventional grinding wheels, which has proven to provide better grinding performance and coolant access, keeping the work piece cooler and avoiding thermal damage.

In this study, two sizes of diamond grinding wheels which are the diameter of 3 mm with thickness of 0.2 mm and the diameter of 1 mm with thickness of 0.1 mm are fabricated by a creative composite electroforming method. The pure nickel metal is set as anode. The micro cylindrical bar of tungsten carbide acted as spindle of the micro diamond grinding wheel, which is inserted into the hole of ABS mold and the conducting layer pre-coated on the local surface of ABS mold are set as cathode. The nickel sulfate bath mixing a constant amount of diamond particle is selected as electrolyte bath. At the current density of 2.5 ASD, the nickel-diamond composite layer with a constant thickness is electrodeposited on the ABS mold. When the ABS mold is dissolved by using acetone liquid, then the nickel-diamond composite layer could be used as the micro diamond grinding wheel is obtained. Moreover, in the study, the effects of electroforming method, composition of the electrolyte and current density on the surface quality of nickel-diamond composite layer are investigated. From the experiment results, it can be know that at the current destiny of 2.5 ASD, the covered area of diamond particle in this composite layer is 54.19% using the external hanging pump. And the flatness on the surface of this composite layer electroformed in the nickel sulfamate bath is better than that in nickel sulfate bath.

This study makes a simple model of ball grinder to simulate the dynamics of grinding process. This theoretical analysis of the dynamic characteristics can be used to explain the phenomenon of the Kato¡¦s experiment and it hopes to a useful tool for the design of the ball grinder. The high removal rate is obtained with magnetic fluid grinding when high sliding velocity occurs between the ball and a high rotating drive shaft. When the balls circulation rate breaks away from the shaft speed can be used to predict the onset of skidding. Since the maximum driving friction force is proportional to contact normal force and frictional coefficient, the skidding occurs at the smaller normal force and frictional coefficient. The high viscosity of fluid, the larger fluid drag force is, when overcome the driving force then the skidding occurs. The magnetic gradient is steeper when the width of magnet of the bed is thinner, the effects of supporting stiffness of the floating pad is higher. When the magnetic buoyant force of the ball is larger, the contact normal force is larger, then the removal rate is higher.

Precision measurement technologies have been developed for a long time. Measuring the displacement of meso-scale objects became an important issue in the recent years. In this study, a displacement measurement system for meso-scale objects is developed by combining the measurement technique of using position sensing detectors (PSD) and the grinding skill of fabricating micro scale reflection surfaces on optical fiber tips. This measurement system can be used for detecting the postweld shift (PWS) of a laser-welded butterfly-type laser diode module package. The PWS affects the coupling efficiency of a laser-welded butterfly-type laser diode module package quite a lot. Although there are many papers studied the measurement of PWS, most of the measurements are less than 6 degrees of freedom (DOF). The system developed in this paper can measure the 6 DOF displacement of the PWS. An attachment for carrying 3 micro reflection probes is designed firstly which will be settled on the fiber ferrule of a laser diode module. After all the coordinate transformation matrices of the laser beam light source, micro reflection surfaces, and the position sensing detectors are derived as well as the PSD readings are taken, displacements of the ferrule of a laser diode module can be solved from the displacement equations by using numerical method. The system developed in this paper is implemented on a Newport butterfly-type laser diode module package station (Model LW4200) for demonstration. The testing results show that the resolution of this system is 1£gm and the accuracy is 2£gm. Beside the application of measuring the 6 degrees of freedom PWS of a laser diode module package, the system developed in this paper can also be applied for measurement the displacement of other meso-scale objects.

Diss.--Technische Hochschule, Hannover. / Bibliography: p. 9-13.

Diss.--Technische Hochschule, Hannover. / Bibliography: p. 9-13. Also issued online.