Papers by Keyword: Slurry

Abstract: High-pressure die-casting (HPDC) can be a productive process for high-quality cast aluminium alloy components. However, it is also a process prone to generate defects, such as gas porosities and incomplete fillings, resulting in rejections. One way to reduce the reject rate is to employ Semi-Solid Metal processing with HPDC. The most important advantages of Semi-Solid alloys are reduced shrinkage defects, fewer gas porosities, and fewer chances of filling-related problems. To take full advantage of a semi-solid metal slurry, the casting process must be controlled meticulously to reach homogeneous casting quality and high process repeatability. A study has been conducted on cast parts composed of two-dimensional symmetrical cavities. From the mechanical tests, unexpected differences emerged in both tensile strength and fracture elongation, which were confirmed by differences in the microstructure. The paper investigates the reasons for the asymmetry in the proprieties to avoid similar problems in future studies and maximize the effectiveness and repeatability of the high-pressure die-casting process.

Abstract: Slurry pumps in the mineral processing industry are parts that erode very quickly. Erosion is predominantly caused by abrasion from fine particles of the ores. Because of this, the erosion process takes place on impeller blades and cover plates that directly contact the slurry. This paper evaluates the wear of laser-coated pump parts in the mineral processing industry. Building upon previous research conducted by the authors, we aimed to determine the best laser coating powder system to extend the useful life of specific laser-coated pump parts. Four blades of a slurry pump impeller were each treated with a different laser powder coating, then assessed for wear after 19 days of operation. During this real-life trial, each powder system performed differently. The laser coatings were worn away in two general directions. The first direction was along with the blade pattern, and the second wear direction was from the center of the impeller to the direct blade surface. Partial surface cladding led the material to wear away faster than complete surface cladding due to perpendicular force. Based on these results, in order to use material hardness and wear resistance to higher efficiency, we need to cover all surfaces with different thicknesses depending on the wear rate of the part. This study also showed that Powder System 2 was the most suitable coating material for this type of slurry pump.

Abstract: Vat photopolymerization is one of additive manufacturing and also known as photo-curable three-dimensional printing technology. It uses light energy with the proper wavelength to expose on the liquid photo-curable resin inducing the photopolymerization process and resulting in solidification layer-by-layer. The building method is classified into two ways: free-surface and constrained-surface. The advantage and disadvantage of both methods are described and analysed according to the different material property and requirement. The basic composition for photo-curable resin consists of photo-initiator and monomer. Adding powder into photo-curable resin makes the photo-curable slurry. Literatures report that high density powder such as zirconia oxide or Inconel 718 is suitable for free-surface building method because of poor suspension. However, the volume percentage in the slurry is less than 50% causing the higher shrinkage ratio and inaccuracy after sintering process. The coupling agent may increase the suspension of powder in slurry but experimental result shows that it still cannot improve the success rate in the constrained-surface building method. Therefore, this study proposes a combination method to overcome the difficulty of making high density ceramic or metal part. In addition, the sintering process is a key factor to obtain the high dense part with no crack occurrence and desirable microstructure. The optimized sintering parameters for zirconia oxide and Inconel 718 are also introduced.

Abstract: In the present work a detailed microstructural investigation of Cobalt based microwave cladding on S-355 stainless steel was carried out. The experimentations were carried out in a home based domestic microwave oven. This article clears the circumstances of clad formation during microwave hybrid heating. The solidification texture and grain structure of the developed clad scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy, and measurement of Vicker’s microhardness. Cobalt based clads developed with an approximate thickness of 1 mm without interfacial cracking. The microstructure of clad clearly illustrated excellent metallurgical bond with S-355 substrate and found dominantly fine cellular grains. Iron and cobalt were recognized inside the cells while chromium was ascertained segregated around the cell boundaries. The average microhardness of the cobalt based clad was observed in the range of 402±60 HV.

Abstract: The rheology of A96% alumina slips and the physical and mechanical properties of slip cast samples were studied. The slips had a constant solids loading of 40 wt% alumina and a polyvinyl alcohol (PVA) content of 0-3 wt%, as a binder. The rheological behavior and viscosity of the slips were examined to determine the flowability of the slips necessary for the casting process. The slips were prepared by ball milling and the bend bar samples were cast in plaster molds. The green densities and the flexural strength of the bars were measured, and the fracture surfaces were examined by scanning electron microscopy. It was found that the slip viscosity increased with an increase of PVA content. The green flexural strength also increased to a maximum value of 0.52 MPa with increasing PVA up to 2 wt%. The further addition of PVA decreased the flexural strength. The green density did not significantly change with the PVA content, however the samples produced using 3 wt% PVA showed the lowest percentage of theoretical density of 41%. The fracture surface of the 3 wt% PVA sample showed numerous large pores compared with the other samples. Therefore, in this study it was concluded that there is in optimal amount of PVA to produce the highest green density and flexural strength of cast samples. Excess PVA reduced the flowability of the slip and resulted in excess porosity, which decreased the green density and deteriorated the flexural strength.

Abstract: Deoiled asphalt (DOA) and slurry are by-products of petroleum refining process. In this paper, blending asphalt (DST) based on DOA, slurry and vacuum gas oil and SBS modified DST (SMDST) were prepared. The aging resistance of SMDST was investigated by thermal aging (TA) and ultraviolet (UV) aging. Meanwhile, the chemical structure and microstructure of SMDST before and after aging were characterized by Fourier transform infrared spectroscopy (FTIR) and fluorescence microscopy. The results showed that the softening point, ductility at 5 °C and low temperature flexibility of SMDST increased gradually with the increase of SBS content. When SBS content was 12 wt%, the softening point, ductility at 5 °C and low temperature flexibility of SMDST were 105 °C, 55 cm and -25 °C, respectively. After TA and UV, the low temperature flexible reductions of SMDST with 12 wt% SBS were 3 °C and 2 °C, respectively, which demonstrated that aged SMDST still had good crack resistance in low temperature. FTIR analysis indicated that the carbonyl (C=O) and the sulfoxide (S=O) characteristic peaks of SMDST were enhanced after aging to a certain extent. However, the fluorescence microscope observation showed the network structure of SMDSB was not damaged significantly, which implies that SMDST has a favourable anti-aging performance.

Abstract: An internal cooling agent is used in rapid slurry forming (RSF) process to produce a high solid fraction slurry for a short period of time. In the process used in this research, the swarf which is known to be a low enthalpy material was added to the melt as the internal cooling agent. During the process, the swarf started to melt and a semi-solid slurry with a relatively high solid fraction was formed. This slurry was formed by exchanging the enthalpies between the low and high enthalpy materials. A commercial Al-Si-Cu alloy, i.e. AS9U3 Aluminum alloy, was used in this investigation. The microscopic examination showed that the Al-Si eutectic colonies start to melt during the melting process of swarf material resulting in the formation of globular Alpha-Al grains due to the multiplication of secondary dendrites arms. The fracture of dendrites arms and the subsequent spheroidization were suggested to be the origin of non-dendritic globular grains in the final microstructure. The amount of primary globular Alpha-phase was measured by the image analysis software. The results showed that during high pressure die-casting of AS9U3 Aluminum alloy using 4 mm thick samples, around 35 percent solid has been formed at the temperature of 580 oC.

Abstract: Porous ceramic body is broadly utilized in the engineering discipline in this globalization era especially in the industrial applications. This is due to the advantages of one of the ceramic foams characteristics that can exhibit highly open pore and have a good interconnectivity. At the present study, the formation of Silica-Nickel oxide (SiO₂-NiO) foams was developed by using the replication method with various solid loadings of 20wt. %, 25wt. %, 30wt. %, 35wt. % by adding a fixed amount of 5wt. % composition of Nickel Oxide (NiO) and sintered at a temperature of 1250°C. The Polyethylene Glycol (PEG) and Carboxymethyl Cellulose (CMC) as the binders to bind the particles and as thickening agent for the slurries formation. The cylindrical shape polyurethane acts as a template of the SiO₂-NiO foams. The properties of physical and mechanical of the SiO₂-NiO foams are being characterized through the morphology analysis via the Scanning Electron Microscope (SEM). Bulk density and apparent porosity tests are determined by adapting the Archimedes Principles. The compressive test has been carried out to identify the compressive strength of SiO₂-NiO foams. The results obtained during the morphology analysis show the size of the pores appeared differently between the ranges of 268.81µm to 516.17µm. The result of the density and porosity of the porous SiO₂-NiO foams recorded results between the ranges of 0.452g/cm³ to 0.775g/cm³ and 68.5% to 81.2%. This indicates that the variable of solid loading reveals the effect on the properties of the SiO₂-NiO foams. Thus, the increasing of the solid loading will decrease the average size of the pores. However, with the decreasing of the average size of the pores will increase the density and the compressive strength of SiO₂-NiO foams.

Abstract: From making steel process result dust and slurry that can be used as a secondary raw material in the composition stack of ferrous materials for the sintering process. Together with other raw materials rich in Fe, SiO2, CaO, this waste can be significant on quality ferrous agglomerate due to the useful elements contained.The paper presents the results of chemical and mineralogical analysis of steelworks dust and experimental research with a view to introduce dust in the sintering process to increase the quality of agglomerate.

Abstract: In order to avoid the environmental pollution and the harm to body of traditional polishing slurries, an environment-friendly chemical mechanical polishing technology is proposed for SiC wafer in this study. With this method, SiC material is removed by utilizing the strong oxidability of nanotitanium dioxide particles in chemical mechanical slurry in the existence of ultraviolet. While, the oxidbillity will recede in absence of ultraviolet when the polishing process finishes. On the basis of investigating in the reaction mechanism between SiC and nanotitanium dioxide, the slurries are prepared for the environment-friendly chemical mechanical polishing technology. The results show that the ultraviolet-assisted CMP slurry has strong oxidation for SiC material. This method is high-efficient for polishing SiC wafer. The surface roughness is reduced to about Ra 0.1μm from Ra 0.818μm after polishing for one hour.