Papers by Keyword: Grinding

Abstract: The article investigates the influence of the water content during grinding the raw material mixture on the formation of monoclinic phases M1 and M3 of alite using the Rietveld method. Four identical raw material mixtures were chosen, differing only in the water content for the grinding process. The milling process in a water environment in a PULVERISETTE 6 planetary mill was chosen for the preparation of the raw material mixture. Based on previous research in this area, a firing temperature of 1450 °C with soaking for 60 minutes was chosen. The results showed that the monoclinic M3 phase is predominantly formed. In contrast, the monoclinic M1 phase forms at lower firing temperatures than the M3 phase and with fewer crystallization nuclei due to less fine grinding. The results show that the amount of water used to grind the feedstock does not make any difference in the final amount of monoclinic M1 and M3 phases.

Abstract: Insufficient offer of high-temperature fly ash meeting the requirements of standard EN 4501 is becoming an increasingly significant problem for concrete technology. This trend is generally caused by relentless effort to green electricity generation and reduce the carbon footprint, leading to the decommissioning of coal-fired power plants and the greening of existing. The most often ways are combustion processes of fluidized-bed and selective non-catalytic nitrogen oxide reduction (SNCR) processes. Thanks to these processes, the demand for this raw material has significantly exceeded its supply in recent years. It is, therefore, more than current to look for ways to use the large amount of ash produced from coal combustion, which is not high-temperature fly ash, but can be classified as a bed combustion fly ash or cinder. The paper aims to show the possible processing and subsequent use of these waste materials for the production of cement composites. The possibilities of grinding these coarse-grained fly ashes and the subsequent impact of their use on the cement composite in comparison with conventional fly ash according to the standard EN 450 from the same sources were verified. The impact of their use on the properties of composites in the fresh and hardened state was analysed, and these impacts were related to, for example, their chemistry, grain morphology, loss on ignition, or fineness.

Abstract: This article aims to explain the reasons leading to the damage of a drill during its final grinding. Metallographic analysis using light and scanning electron microscopy was used to determine whether the damage was related to the structure of the material, which is given by its chemical composition, forming, and especially its heat treatment, or the grinding methodology. The drill was made of HS 2-9-1-8 tool steel. Fractographic analysis showed a cleavage fracture. In terms of the heat treatment used, the measured hardness of the analysed samples was appropriate for the requirements and possibilities of the tool steel. The metallographic analysis showed that the microstructure contained areas with clusters of primary carbides. These clumps significantly reduce the toughness of the material. In addition, there was a structural notch in the form of a white layer with a higher carbon content on the outer circumference of the samples. This layer also significantly contributed to the reduction of toughness. The hardened layer below the structural notch also contributed to the reduction in toughness. All of these microstructural defects were caused by poor grinding, which led to damage to the tool.

Abstract: The present paper shows a new fixed abrasive bond-grit formulation aimed for best-in-class, low-cost and high-quality finished SiC wafer surfaces. Grinding wheels manufactured with this technology can accomplish ultra-smooth SiC (Ra = 0.55 nm and TTV < 1 μm) surfaces due to their unique bonding structure and their tailored grit size. Additionally, SiC wafers ground with these wheels exhibit reduced sub-surface crystal damage, mirror-like polished surface and improved wafer geometry while both the grinding forces and the wheel wear are kept low.

Abstract: The article describes studies of the quality of the surface layer of the deposited metal of a cylindrical part when combining the processes of surfacing and milling, as well as subsequent grinding of the deposited metal in hot and cold states. Photos of the surface of the deposited and processed parts are presented, showing the effect of the processing method on the metal structure and data on the distribution of residual stresses in the surface layer of the metal.

Abstract: The paper proposes an approach to assessing the grinding wheel wear, which includes the wear of grains and pulling them out of the bond, based on fatigue failure under cyclic loads caused by cutting forces, with a period of the order of microseconds. This approach is implemented on the basis of stress life calculation in the ANSYS Fatigue module using loading data obtained from the numerical simulation of grain-workpiece interaction. The simulation results allows to obtain the grain wear area, the level of bond fatigue fracture and the possibility of self-sharpening of the grinding wheel for a given grain size and operation conditions.

Abstract: The article presents the results of a single grain scratching simulation of a ceramic workpiece using the smoothed particle Galerkin method. The studies were carried out for 0.1-0.8 μm depths of cut, matching the ductile-brittle transition of ceramics grinding with minimum subsurface damage. The crack depth and scratching force were obtained for scratching speed of 40-140 m/s.

Abstract: Ti-based intermetallic compounds are characterized by low machinability, therefore, to obtain accurate dimensions and shape of the surface grinding and Wire EDM are used. The unique properties of NiTi intermetallic alloys are largely influenced by structural phase transformations and variations in microhardness caused by processing accompanied by thermal phenomena. Having an understanding of the physics of the process, it is possible to counteract negative effects, which helps to preserve thermomechanical properties of the final NiTi products. Accumulation of knowledge about the quality of processing with various abrasive tools is part of the larger research presented in this article. Samples of titanium nickelide with a temperature A_f=+25 ⁰С were abraded with ordinary and high porosity SiC wheels. The article studied phase transformations using X-ray diffraction analysis and microhardness. The experimental data were processed using mathematical statistics. X-ray diffraction patterns and microhardness analysis showed that a significant effect on the structural transformation and corresponding increase in microhardness is exerted by grinding with green SiC wheels with normal porosity caused by an increased thermal effect on the surface. Simultaneously, the impact of Wire EDM process on microhardness in preparing workpieces for grinding was evaluated. It was established that grinding of Ti-based intermetallic compounds with memory effect should be performed by SiC wheels with an open structure of high porosity.

Abstract: The Moroccan cement industry is looking for new processes to effectively minimize the high energy costs associated to cement manufacturing. This work presents the effect of three types of limestone with different chemical compositions and different CaCO₃ contents on the physical and mechanical properties of resulting composite cements by the addition of fly ash in the proportions by weight of: 5 % and 10 %. The samples are studied in order to evaluate the interaction between different types of limestone and fly ash. Ternary cements based on fly ash-limestone-clinker induce a significant prolongation of the setting time compared to binary cements based on limestone-clinker. The substitution of clinker by limestone induces an improvement in mechanical strength compared to ternary cements in the first days; at 28 days, cements prepared with fly ashes reach significant strength due to their pozzolanic reaction.

Abstract: 7075 aluminum alloy is widely used due to its great performance, especially in aerospace area. In this paper, ultrasonic-assisted grinding technology is used to process 7075 aluminum alloy. The data is obtained through experiments, and the surface roughness and morphology of ultrasonic assisted grinding and conventional grinding under different spindle speeds, feed rates, and amplitudes are analyzed. Research has found that the increase in spindle speed and amplitude will improve the quality of the machined surface and reduce the surface roughness by 82.1% and 36%. However, with the increase of feed rate, the surface quality decreased significantly, and the surface roughness increased by 55.6%. The surface micro-morphology of the machined workpiece is observed, and the effects of different processing parameters on the surface micro-morphology are obtained.