Papers by Keyword: Degassing

Abstract: Ultrasonic processing is known to be an efficient means of aluminium melt degassing and structure modification with additional benefits of being economical and environment friendly. This paper reports on the kinetics of ultrasonic degassing effect of foundry alloys. Direct measurements of hydrogen concentration in the melt by Foseco Alspek-H probe are used along with the reduced-pressure test. The effects of ultrasonic processing on structure, i.e. grain size and porosity, are studied using metallography and 3D X-ray tomography. This work is performed within the Ultragassing project funded by the European Union’s 7^th Framework Program.

Abstract: Silicone rubber mold is regarded as an important method of reducing the cost and time to market in a new product development process. Commercial automatic vacuum machine is widely used to degas in the manufacturing of silicone rubber mold, but the cost of hardware is very expensive. A high efficiency degassing system is designed and implemented from regular vacuum machine. It is found that degassing process includes explosion phase, balance phase and convergence phase. The maximum saving in the degassing time is about 63.7%. The advantages of this system include reducing human error of operator, reducing noise and air pollutions derived from the vacuum pump.

Abstract: Melt quality is crucial for both continuous and shape casting of light alloys. Gas, oxides and other inclusions in the melt usually deteriorate the quality of the casting products. Conventional refining techniques, such as filtration and rotary degassing, can refine the melt by removing the inclusions although they are costly and time-consuming. A new technology for liquid metal treatment through intensive melt shearing was developed recently to improve the melt quality prior to metal casting. The new technology uses a simple rotor-stator unit to provide intensive melt shearing, which disperses effectively the harmful inclusions into fine particles to enhance nucleation during the subsequent solidification processing. Experimental results have demonstrated that the high shear unit can be used for general melt treatment, physical grain refinement, degassing and preparation of metal matrix composites and semisolid slurries. In this paper we offer an overview of the high shear device and its application in processing light alloys.

Abstract: The effects of chlorine on improving hydrogen diffusion have been studied by first principle calculations and we obtain the diffusivity of hydrogen in liquid aluminum which is in agreement with the experimental data. It can be concluded that the diffusion of hydrogen in aluminum melts can be enhanced in the presence of chlorine and mobility of aluminum is depressed by forming alumina layer which can impede the diffusion of hydrogen.

Abstract: A comprehensive introduction of current aluminum refining technology is reviewed in this work especially the effects of chlorine on refining process is discussed. The mechanism of chlorine on improving hydrogen diffusion has been studied by ab initio molecular dynamics calculations and we obtain the diffusivity of hydrogen in liquid aluminum which is in agreement with the experimental data. It can be concluded that the diffusion of hydrogen in aluminum melts can be enhanced on the presence of chlorine.

Abstract: For well over a decade, Almex USA Inc. has been supplying hard alloy casting technology to the aluminum industry. Today, customers on five continents produce 2000 and 7000 series aluminum billets using this technology in sizes ranging from 75mm through to 1080mm in diameter. In order to produce such a range of sizes in hard to cast alloys and to aerospace standards, Almex has imparted complete casthouse process understanding and know-how, along with equipment supply to its customers. This paper provides an overview of Almex’s hard alloy casthouse technology and describes some of the critical parameters which must be controlled throughout the process route in order to produce defect free alloys for forging, extrusion and flat rolled applications. Explanation is also made of the microstructural requirements of the as cast product and how these influence the final product; along with the range of quality control solutions supplied by Almex to ensure these requirements are met on a continuous and repeatable basis by Almex’s technology users.

Abstract: In the present paper, TiB2/Al composite with 5% volume fraction of TiB2 was fabricated by LSM method. The effects of purification and degassing methods on TiB2/Al composite were examined by means of X-ray diffraction (XRD) and image analysis. Hydrogen contents in the molten composites were detected and compared among flux, inert gas and vacuum purification processes. The experimental results indicate that under general cast condition a majority of the TiB2 particles distribute on grain boundary, and only a few particles disperse within grains. The flux and vacuum purifications have no virtual impact on the distribution of TiB2 and the fraction of TiB2 remains the same after purification. However, degassing with inert gas will be detrimental; the TiB2 particles will be separated and removed from the matrix. The hydrogen contents for flux, inert gas and vacuum processes are 0.15ml/100g/Al, 0.12ml/100g/Al and 0.12ml/100g/Al respectively.

Abstract: The flow field and gas-bubble size during the process of aluminum melt degassing were investigated in water model. A Φ400mm×400mm transparent water model and an impellor degassing device were used in this study. The instantaneous velocity fields of water and bubbles under the mixture of rotary injector were measured with PIV velocity field measurement technique. Then the pictures of bubbles gained from PIV were analyzed with software to get the bubble size distribution. The results showed that bubble flow field and bubble size were influenced by rotary speed of rotor and gas flow-rate. With the increase of rotary speed of rotor, the horizontal velocity components of bubbles became larger, the stagnant time of bubbles in water increaseed correspondingly and bubble size became smaller. With the increase of gas flow-rate, the longitudinal velocity components of bubbles became larger, the stagnant time of bubbles in water decreased correspondingly, and the bubble size became larger also.

Abstract: Thermal surface purification in an inert gas flow and densification processes of SiC and diamond nanocrystalline powders with specific surface in the range of 60 – 300 m2/g and average grain sizes from 5 to 15 nm in diameter were examined. Termogravimetric Analysis (TGA) linked with mass spectrometry of outgassing products show that surface impurities desorb at up to 450°C. Further heating above 450°C leads to oxidation of the powder surface. Small Angle X-Ray Scattering (SAXS) and gas porosimetry (ASAP) was applied to investigate densification of the nanocrystalline powders. Compaction under 1GPa or higher pressure was found necessary for obtaining the ceramic matrix with porosity in the nanometer range.