Surface Roughness of Tooth Coloured Restorative Materials

This study compared the surface roughness of selected tooth coloured restorative materials that were polished according to manufacturers’ instructions and Sof-Lex. It also assessed the surface roughness of polished materials after thermocycling. Filtek Z350XT, Beautifil-Bulk Restorative and Cention N, were used in this study. A stainless steel mould (10mm diameter x 2mm height) was used to fabricate 75 cylindrical specimens: 15 Filtek Z350XT (FZ), 30 Beautifil-Bulk Restorative (BB) and 30 Cention N (CN). All 15 FZ specimens were polished with Sof-Lex. Fifteen BB and CN specimens were polished according to manufacturers’ instructions. The remaining fifteen BB and CN specimens were polished using Sof-Lex. All the specimens were subjected to thermocycling (1000 cycles). Surface roughness was assessed quantitatively with profilometry after specimen preparation (Mylar stage), polishing and thermocycling. Data were analysed using SPSS version 25.0 at α=0.05. When polished according to manufacturers’ instructions, BB had the lowest mean surface roughness (Ra) values (0.13±0.01μm) followed sequentially by CN (0.14±0.03μm) and FZ (0.15±0.02μm). The differences were not statistically significant. When polished with Sof-Lex, BB exhibited the smoothest surface (0.116±0.03μm) followed sequentially by and FZ (0.150±0.02μm) and CN (0.157±0.02μm). Thermocycling caused an increase in the Ra. The differences were statistically significant. All materials tested had Ra values below the threshold value of 0.2 µm at Mylar stage and after polishing with their recommended polishing system and Sof-Lex. Thermocycling produced rougher surfaces that did not exceed the threshold Ra value. Polishability was material dependent.

Effect of Silica Particle Size on the Physical and Mechanical Properties of Lightweight Ceramic Composites

Ceramics hold all traditional, scientific and engineering raw materials or fabricated products used in different applications especially that performed at high temperatures through high-tempers. The remarkable progress made recently in the advancement of technology has related a prerequisite for a seriously huge number of parts with controlled porosity. In ceramic manufacturing, acquiring a porous item of such parameters and at the same time demonstrating appropriate mechanical strength isn`t a simple issue. The powder-mixing system was utilized to fabricate kaolin-silica fired composites. The main purpose of the paper was to prepare ceramic bodies rich in pores with the goal that it will have a lightweight structure. Different wt.% of silica having distinctive two-particle sizes are blended with kaolin, and afterwards, they shaped by semi-dry pressing in a hardened steel mould under 3-ton loads and sintered at four various temperatures, 900, 1000, 1100 and 1200 �C. Evaluating of composite`s physical properties showed that a good level of porosity was obtained, and it was extended; especially in mixtures contain a coarse particle size. These results are enhanced by acceptable evident comes from good apparent solid density and good strength.

Steel mould surface improvement by robot fluid jet polishing and robot pad polishing for polymer optic production

In order to improve the quality of injection-moulded polymer optic parts, it is necessary to improve the quality of the respective steel moulds. For this reason, it is not only necessary to improve the surface roughness of the mould, but also its geometrical shape. The material removal obtained from robot pad polishing is too low. This makes a shape correction after the milling step a very prolonged process. The aim of this work is to use a polishing chain to improve the surface quality of steel samples in terms of shape deviation and surface roughness. This correction polishing chain uses the robot fluid jet polishing for the geometrical shape correction and afterwards the robot pad polishing for the improvement of the surface roughness. Due to the high material removal rates of the fluid jet polishing, it is possible to correct the geometrical shape of steel moulds very fast up to a certain deviation. The pad polishing process improves the surface roughness of the steel samples. A correction of the shape deviation of more than 80% with a RMS of approximately 8 nm was obtained.

Characterization of clays from the Foumban region (west Cameroon) and evaluation for refractory brick manufacture

ABSTRACTThree clayey materials named MY3, KK and KG originating from the Foumban region (west Cameroon) were analysed to determine their granulometry, plasticity, major-element chemistry and mineralogy. Dilatometric and ceramic behaviour were also investigated. Clays were shaped by uniaxial pressing in a steel mould. Shaped samples were heated at 1300, 1400 and 1500°C. The end products were characterized in terms of their density, porosity and compressive strength. Raw materials differ in terms of their mineralogical composition, grain-size distribution, Al2O3 content and the nature and abundance of impurities inducing specific thermal behaviour during dilatometric analysis and sintering tests. The final material properties may be related to the main features of the raw materials used.

Microstructure of the Bonding Zone Between AZ91 and AlSi17 Formed by Compound Casting

This paper discusses the joining of AZ91 magnesium alloy with AlSi17 aluminium alloy by compound casting. Molten AZ91 was cast at 650°C onto a solid AlSi17 insert placed in a steel mould under normal atmospheric conditions. Before casting, the mould with the insert inside was heated up to about 370°C. The bonding zone forming between the two alloys because of diffusion had a multiphase structure and a thickness of about 200 μm. The microstructure and composition of the bonding zone were analysed using optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results indicate that the bonding zone adjacent to the AlSi17 alloy was composed of an Al3Mg2intermetallic phase with not fully consumed primary Si particles, surrounded by a rim of an Mg2Si intermetallic phase and fine Mg2Si particles. The bonding zone near the AZ91 alloy was composed of a eutectic (an Mg17Al12intermetallic phase and a solid solution of Al and Si in Mg). It was also found that the compound casting process slightly affected the AZ91 alloy microstructure; a thin layer adjacent to the bonding zone of the alloy was enriched with aluminium.

EFFECTS OF RHEOCASTING AND THIXOFORMING ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A356 ALUMINIUM ALLOY

This paper presents the changes in mechanical properties and microstructure of aluminium alloy A356 that undergoes cooling slope casting. The alloy was cut into small cubes with an estimated weight of 400g before it was heated in a crucible induction casting machine. The temperature was set to 880 oC with a heating rate of 15 oC per min. Then, the metal was cooled to 620 oC until it turns to a semisolid, before pouring into a stainless steel mould through a 250 mm long and 60o cooling slope before it was cooled to room temperature. For the thixoforming experiments, the liquid fraction was between 30% and 50%, with various semisolid temperatures (583 oC-585 oC). The ram speed and die temperature were 85 mm/s and 200 oC, respectively. The microstructure and mechanical properties of rheocast feedstock in T6 condition were determined and compared with the metal without any heat treatment, rheocast and thixoformed alloy. It was found that thixoformed metal had the highest ultimate tensile and yield strength with reduced ductility. The microstructures are rosette, near globular and spherical, and were obtained in rheocast and thixoformed alloys, respectively. The α-Al grains were larger at higher semisolid temperatures.

STUDI PENGARUH ALUMINIZING TERHADAP PEMBENTUKAN DIE SOLDERING

A mould in die casting industri has a problem like a die soldering. The die soldering due to a molten aluminium stick on a mould surface and hold on although a casting produk has been rejected. Removing the die soldering need cost and time. So the mouldshoul be protected from the die soldering. In this research, an aluminizing process is used as an alternatif method to protect the mould from die soldering defect. The hot dip aluminizing process increases the corrosion resistance of steel. The aim of reseach is to answer the question “Do the hot dip aluminizing process (Al-53%Cu) protect a mould steel from the die soldering?”. Researchmethodologi. First, the steel samples as assumed as a steel mould are immersed into molten of Al-53%Cu (750 oC) for 3 minutes. Secondly a molten aluminium (700 oC) is poured onto the aluminized steel mouldsamples .it is called as a die casting simulation. The results. The hot dip aluminizing (Al-53%Cu) process at 700 oC can not protect the steel mould surface from the die soldering.

Formation of Al-alloyed Layer on Magnesium with Use of Casting Techniques

Al-enriched layer was formed on a magnesium substrate with use of casting. The magnesium melt was cast into a steel mould with an aluminium insert placed inside. Different conditions of the casting process were applied. The reaction between the molten magnesium and the aluminium piece during casting led to the formation of an Al-enriched surface layer on the magnesium substrate. The thickness of the layer was dependent on the casting conditions. In all fabricated layers the following phases were detected: a solid solution of Mg in Al, Al3Mg2, Mg17Al12 and a solid solution of Mg in Al. When the temperature of the melt and the mould was lower (variant 1 – 670°C and 310°; variant 2 – 680°C and 310°C, respectively) the unreacted thin layer of aluminium was observed in the outer zone. Applying higher temperatures of the melt (685°C) and the mould (325°C) resulted in deep penetration of aluminium into the magnesium substrate. Areas enriched in aluminium were locally observed. The Al-enriched layers composed mainly of Mg-Al intermetallic phases have hardness from 187-256 HV0.1.