Variable Powder Flow Rate Control in Laser Metal Deposition Processes

This paper proposes a novel technique, called Variable Powder Flow Rate Control (VPFRC), for the regulation of powder flow rate in laser metal deposition processes. The idea of VPFRC is to adjust the powder flow rate to maintain a uniform powder deposition per unit length even when disturbances occur (e.g., the motion system accelerates and decelerates). Dynamic models of the powder delivery system motor and the powder transport system (i.e., five–meter pipe, powder dispenser, and cladding head) are first constructed. A general tracking controller is then designed to track variable powder flow rate references. Since the powder flow rate at the nozzle exit cannot be directly measured, it is estimated using the powder transport system model. The input to this model is the DC motor rotation speed, which is estimated on–line using a Kalman filter. Experiments are conducted to examine the performance of the proposed control methodology. The experimental results demonstrate that VPFRC is successful in maintaining a uniform track morphology, even when the motion control system accelerates and decelerates.Mechanical Engineerin

The effect of cheese powder in the functional properties of croissant pastry : a thesis presented in partial fulfilment of the requirements of the degree of Master of Technology in Food Technology at Massey University

The increasing use of cheese powder as an ingredient used by food manufactures can be related to the changing consumer needs, identifying new consumer preferences, marketing and obtaining an acceptable capital return. Cheese powder have been used in bakery products to improve their functional properties and impart flavour. Therefore, the development of cheese flavoured croissants was chosen to increase the utilization of cheese powder in the formulation croissant pastry. For this reason, the New Zealand Dairy Board (NZDB) predicted a brighter future for this type of dairy ingredient because of its dual acceptability of providing important functional characteristics and its cost advantage over other dairy products. The addition of cheese powder to croissant pastry resulted in affecting the dough's physical properties and baking characteristics; i.e, increasing the dough elongational viscosity, decreasing the farinograph absorption values, decreasing the specific volume of baked croissants, and croissant firmness results indicating significant differences as a function of time for storage. Cheese croissants containing ten percent level of Cheddar-20 cheese powder was found to be the only one to have statistically significant differences in most of the attributes compared to CP1 and CP2 cheese powder when used in the formulation. Ten percent level of cheddar-20 cheese powder received the highest score and preferred by 77.8% of the panellists. Therefore, the ten percent of cheddar-20 cheese powder level was chosen for further development including the determination of the new cheese powder mixing method with its time-temperature relationship and evaluation of the market trial. The new cheese powder mixing method (3% cheese powder mixed with dry ingredients, and 7% used to produce cheese paste) during which the paste was applied over the laminated dough and the cheese powder combined with the dry ingredients improved the cheese croissant quality characteristics when compared to the other mixing method (total 10% cheese powder mixed with other dry ingredients). The baking time-temperature relationship of the new cheese powder mixing method was twenty seven minutes at 275°F which gave the best quality characteristics for high volume, a golden brown crust colour and flaky texture. This method received the highest scores and the most acceptable cheese croissant by the panellists. The market evaluation results indicated that 87% of potential consumers preferred the cheese croissants. The total sales potential indicated to be approximately 2.000 tonnes/annum of finished product with a population of ten percent of the market share. The estimated net present value over five year product life was $3,206,000

Shock wave initiation of the Ti5Si3 reaction in elemental powders

Elemental powder mixes were subjected to plane wave shock processing which reduced the initial porosity to essentially zero. Two powder mixes in a 5:3 Ti:Si atomic ratio were used: -325 mesh Ti and Si (<45 mu m), and -100 mesh Ti and Si (<150 mu m) with shock pressures up to 7.3 GPa and shock energies up to 671 J/g. Shock pressures were calculated using hugoniot parameters for porous elemental powder mixtures and shock energies were taken to be the work done by the shock (P Delta V/2). Shock energy thresholds for complete reaction of the elemental powders were found which depend upon powder particle size and the initial porosity of the powder. The threshold energy for the larger powder mix was found to be similar to 8O% larger than that for the smaller powder. A decrease in initial porosity from 0.49 to 0.40 caused an increase in threshold shock energy of about 75% for both powders. At shock energies slightly below the threshold energy, evidence for the reaction of solid Ti and liquid Si was observed in small isolated regions. These regions contained spherical micronodules with the composition of TiSi2 in Si. The results are compared to those of previous studies reported in the literature, and mechanisms for reaction initiation and the observed threshold values are proposed

Growth of Sr1-xCaxRuO3 thin films by metalorganic aerosol deposition

We report the growth of thin films of Sr1-xCaxRuO3 on SrTiO3 and MgO substrates by metalorganic aerosol deposition. The structure and microstructure is characterized by X-ray diffraction and room-temperature scanning tunnelling microscopy (STM), respectively. STM indicates in-plane epitaxy and a small surface roughness for films on SrTiO3. The high-quality of the films is supported by large residual resistivity ratios up to 29.Comment: 4 Pages, 2 Figures, submitted to Proceedings of ICM 2009 (Karlsruhe

Optimization of Powder Layer Density in Selective Laser Sintering

An important parameter for the overall quality of SLS parts is the density of powder layers before sintering. Previous studies have shownthatthe control of powder particle shape and size distribution can increase the density of non-packed powder beds. However, these studies concerned beds several orders of magnitude larger than the SLS layers. The purpose ofthis study. is to determine if,and to what extent, the density of thin powder layers can be ineteased. Experiments show that the density of thin layers increases from 53% to 63% when adding 30% fine powder to the coarse powder,/with a coarse-to-fine ratio of 1:10. Compared with the bulk experiments, this density improvement method is less efficient, because the particles do not arrange as efficiently, and the wall effects can become predominant.Mechanical Engineerin

Influence of excipients on spray-dried powders for inhalation

Two areas attracting considerable attention when developing effective pulmonary drug delivery systems include the improvement of aerosolisation efficiency of the inhaled formulation and the controlled release of drug from the formulation following deposition within the lung. In this study, four saccharides were employed as excipients in the preparation of spray-dried powder formulations for the pulmonary drug delivery. Beta-cyclodextrin-, starch-, and sodium carboxymethylcellulose (NaCMC)-based spray-dried powders showed a significant (one-way ANOVA, Duncan's test, p < 0.05) increase in lower stage drug deposition in the Next Generation Impactor (NGI) when compared to lactose-based spray-dried powders. Furthermore, NaCMC-based spray-dried powder formulations exhibited a sustained drug release profile in dissolution testing; approximately 80% of salbutamol sulphate was released after an hour, whereas drug from the lactose-based spray-dried powder formulation was released within 5 min. Our results clearly demonstrate that the inclusion of NaCMC in spray-dried powder formulations increases the aerosolisation efficiency of the powder and also offers the potential for sustained drug release, which may be of benefit in the treatment of local and systemic conditions

Investigation of the effect of consolidation on cement flow behaviour

International audienceOne of the main problems affecting the flow of cement bulk powder is the formation of cohesive arching at the outlet of the hopper, causing blockage of the silo opening and bridge formation. A simple concept is established which outlines these complications. In this context, the interactions of particles lead to a high degree of consolidation of the cement powder and an increase of adhesion force due to the small size and the large surface area of the cement particles. The results from the consolidation test and the flow properties (cohesion) show that the cement powder flow is mainly controlled by internal forces (Van der Waals and adhesion forces) and external forces. These forces have a direct influence on the powder structure, leading to a variable packing behaviour. Since the problem is attributable mainly to interparticle forces, before storage of the cement powder in the silo, the powder should be fluidised with air at a high velocity to disintegrate the cohesive structure and to overcome this undesirable property of cement flow

An Investigation of Gas-Powder Flow in Laser-Based Direct Metal Deposition

Laser-Based Direct Metal Deposition (LBDMD) is a blown-powder laser deposition process which can produce fully-dense and metallurgicaly sound parts by a layered manufacturing method. Since a deposition head equipped with discontinuous radially symmetric nozzles has the potential to be tilted without influence of the gravity on the powder stream shape, it can be used for multi-axis deposition. The shape of the gas-powder stream with respect to the shape of laser beam and the size of the molten pool, have a large influence on the size and shape of the buildup. They determine the geometrical accuracy and the surface quality of the buildup. This paper examines gas-powder flow from radially symmetric nozzles using computational fluid dynamics method. For verification purpose the powder flow was investigated by a visualization method and powder concentration distribution was analyzed using image processing technique. The obtained results are in good agreement with numerical model.Mechanical Engineerin

Effects of Nanosilica Powder from Rice Hull Ash on Seed Germination of Tomato (Lycopersicon esculentum)

open5noNanosilica powders were synthesized from rice hull ash (RHA) and their effects on seed germination of tomato plants were investigated. Synthesized nanosilica powder was subjected to various characterization studies for identification of the size, structure, morphology and elemental composition. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) results showed that the nanoparticles were in agglomerated form with an average diameter of 46.5 nm and 40 nm, respectively. X-ray diffractometry (XRD) indicated that nanosilica powder is amorphous in nature. The nanosilica powder was also characterized as having a purity of 98.33% using EDXRF spectroscopy and having a surface area 172.19 m2 g-1 using the Brunauer-Emmett-Teller (BET) method. The study showed that nanosilica powder significantly improved germination parameters such as germination percentage, germination index, vigor index, mean germination time and average shoot length of tomato but not fresh weight and dry weight. The best results were found at 5gL-1 nanosilica powder. The increase over untreated control seeds was 22% for germination percentage, 47% for germination index, 92% for vigor index and 55% for average shoot length with the addition of 5 gL-1 nanosilica powder. Nanosilica powder-mediated improvement of seed germination in tomato suggests a potential application of nanosilica powder in seed germination of the plant. The study can serve as theoretical basis for further agricultural applications of nanosilica powder.openMaria Morissa Lu, Diana Marie De Silva, Engelbert Peralta, Alvin . Fajardo, Milagros PeraltaMaria Morissa, Lu; DE SILVA, DIANA MARIE; Engelbert, Peralta; Fajardo, Alvin.; Milagros, Peralt