Velocity Of Powder Particles Research Articles

Optimizing of particle accelerated rotor parameters using the discrete element method.

The acceleration capability of a centrifugal jet rotor plays a crucial role in achieving a high injection velocity of powder particles in the centrifugal impact moulding process. In this regard, the focus of this article is on optimization of the runner shape. To this end, the lengths of the first and second acceleration sections (L1 and L2), and the angles between the first and second acceleration sections and between the second and third sections (α1 and α2) are considered as the rotor parameters. Simulations were conducted using multiple discrete elements to explore the influence of multiple input parameters on the response value, and a regression model was established between the parameters and the particle injection rate. The experimental results show that the selected parameters significantly affect the rate of particle injection, and the interactions between the parameters L1 and L2, and between L2 and α2 have the largest effects. The results reveal that applying the optimized parameters improves the particle injection speed by 7.85% when compared to the pre-optimization model. This improvement in the rotor acceleration provides the basis for improving the efficiency of centrifugal impact moulding of metal powders.

Вплив діаметру частинок порошку нікелю на їх швидкість і температуру при холодному газодинамічному напилюванні

To deposit coatings in cold gas-dynamic spraying (CS), a high-speed gas flow is used to accelerate and heat particles. Therefore, first of all, it is necessary to consider the general laws of the gas flow and the movement of particles in the flow, as well as its interaction with the substrate. Due to the CS process depends primarily on the particle velocity, it is important to understand the effect of the process parameters (pressure and temperature at the nozzle inlet), the characteristics of the powder particles (material density, shape, and size), and the geometry of the nozzle. The gas velocity limits the particle velocity that can be achieved with the CS process. Utilization of high gas pressure, long nozzles, and small particles lead to the fact that the particles move at a velocity close to the velocity of the gas, which can be increased by using gases with low molecular weight, as well as heating it. As a result of the analysis of theoretical and experimental methods for studying the cold spraying process, it was found that for coating formation velocity of powder particles needs to obtain a certain value (critical velocity), which depends on particle temperature at the impact, and density of the particle material. Numerical simulation of gas dynamics of a two-phase flow in CS nozzle and at the outlet from it for the range of air temperatures from 573 K to 873 K and constant pressure of 1,0 MPa has been carried out. The influence of the diameter of nickel powder particles on their temperature and velocity at impact was investigated. Numerical simulations were performed for a range of particle diameters from 5 to 30 μm. In the future, the results obtained can be used to find the optimal size of the powder particles under certain spraying conditions, to calculate the critical particle velocity, and also to develop the window of deposition. This will make it possible to select the optimal parameters of the gas flow at the nozzle inlet (pressure and temperature), which are guaranteed to ensure the adhesion of particles to the substrate and the formation of coatings. Also, the results obtained can be used to predict the properties of coatings, as well as to achieve maximum deposition efficiency of the CS process.

Particle velocity measurement in powder gas jets of coaxial powder nozzles for laser material deposition

Laser material deposition (LMD) is a process in which a laser beam creates a melt pool on the surface of a substrate while a powder nozzle delivers a powdered additive into the melt pool, where the powder material then melts. A dense, metallurgically bonded layer forms once the melt solidifies. The velocity of powder particles in LMD is one of the key factors that influence the amount of particles’ energy absorption (along their individual trajectories) through the laser beam on the way between the powder nozzle and the substrate. The amount of energy that is absorbed by the powder particles above the melt pool determines the temperature on the substrate surface and, hence, influences the formation of the melt pool and the deposition of the powder material. Data about the particle velocity are, therefore, essential for modeling the LMD process—not only for physical simulation where a particle’s energy input can be integrated along its trajectory, but also in an experimental environment of process parameter studies, where understanding the interdependencies between the process parameters is crucial. In this study, a setup using a high-speed camera and an illumination laser is used to measure the velocity of powder particles in the powder gas jet of a coaxial powder nozzle. Several parameters that are known to influence the particle velocity are varied: Feed gas rate, shielding gas rate, nozzle geometry (width of annular gap), and powder mass flow rate. In this study, four different powder types are used. The influence of these process parameters on the particle velocity is measured. Four different methods for tracking individual particles and calculating the velocity distribution within the powder gas jet are used and compared: Manual frame-by-frame particle tracking and manual evaluation from multiple exposures in single frames, as well as particle tracking velocimetry and particle image velocimetry (PIV), which incorporate region-of-interest boxes into the algorithm. Sufficient accordance as to the measurement results is found in comparing the four methods. Further, using the highly automatable PIV method, the influence of main process parameters on particle velocity is measured. Out of the examined parameters, the feed gas rate is found to have the most immediate impact with a linear correlation to particle velocity. A correlation between different powder particle size distributions and measured particle velocities is shown as well.

Numerical study of thermal fluid dynamics in laser welding of Al alloy with powder feeding

A numerical modeling approach is proposed for the process of powder feeding-based laser welding occurring in joining similar and dissimilar materials. For this reason, a three-dimensional computational model is developed to describe the complex physical phenomena of powder transport, laser heating, and thermal fluid dynamics in the molten pool. The VOF method in conjunction with the continuum theory is employed to study the effects of powder particles on molten pool dynamics. It is found that the addition of powder with an average temperature of 1850 K results in a lot of local low- and high-temperature zones, and small vortexes in the shallow areas of the molten pool with a depth of no more than 0.3 mm. The increasing laser power causes the smaller average depth oscillation amplitude, which visually reflects the higher keyhole stability under partial penetration welding. Note that two vortexes in the opposite direction behind the keyhole exist in full penetration welding, which are mainly driven by surface tension. The increasing average impact velocity of powder particles above 2 m/s leads to the more significant fluctuation of free surface profile, which again results in the smaller keyhole entrance size and more frequent keyhole collapses. Also, the corresponding experimental tests are carried out as verification. The findings from the study provide fundamental insights into the mechanism of melt flow and guidance in process optimization during powder feeding-based laser welding.

Brzine čestica praha u plazmi na niskom pritisku

Low pressure of inert gas in the vacuum chamber significantly affects the transfer of plasma particle velocity onto powder particles, residence time of powder particles in plasma and the kinetic energy of molten particles before the collision with the substrate. In addition to low pressure of inert gas in the vacuum chamber, the size and mass density of powder particles, together with plasma arc power, have the biggest impact on the average velocity of powder particles. To measure the velocity of powder particles in the vacuum chamber at low pressure, a laser speedometer is applied.The average velocity of molten powder particles V=s/t is calculated when the length of the path of powder particles that pass between two focus distances of the laser beam is divided by the time of particle passage between the two focuses. Measurements are done for vacuum chamber pressure, the values of which are usually from 6.7 to 80 kPa. The paper describes the relationship between the average velocity of Al2O3 and W powder particles and the vacuum chamber pressure, granulate distribution, mass density and plasma arc power. It was found that, for powder of lower mass density, the average velocity of particles can increase for 200 m/s with a decrease in chamber pressure.The effect of pressure on W particles of larger mass density is lower but still important, because a decrease in pressure increases the average velocity of particles up to 50%. Reducing plasma arc power reduces the maximum velocity of both types of powder particles. .

In-Flight Temperature and Velocity of Powder Particles of Plasma-Sprayed TiO2

This paper relates to the in-flight temperature and velocity of TiO2 particles, an integral part of the systematic research on atmospheric plasma spraying of the material. Initial powder feedstock (32-45 μm, 100% rutile phase) was introduced into the plasma jet. Six parameters were selected to represent the versatility of the plasma system and their respective influences were determined according to basic one-at-a-time and advanced Taguchi design of experiments combined with the analysis of variance analytical tool. It was found that the measured temperatures varied from 2121 to 2830 K (33% variation), while the velocities of the particles were altered from 127 to 243 m/s (91% variation). Gun net power was detected as the most influential factor with respect to the velocity of the TiO2 particles (an increase of 8.4 m/s per 1-kW increase in net power). Spray distance was determined to have a major impact on the in-flight temperature (a decrease of 10 mm in spray distance corresponds to a drop of 36 K). A significant decrease in both characteristics was detected for an increasing amount of powder entering the plasma jet: A drop of 7.1 K and 1.4 m/s was recorded per every +1 g/min of TiO2 powder.

Role of in-flight temperature and velocity of powder particles on plasma sprayed hydroxyapatite coating characteristics

This paper presents a systematic research on the process of thermal spraying of HA encompassing all stages of layer deposition: powder production and characterization (optimized production led to spherical 39.90 ± 10.61 μm powder with 0.0% content of tri-calcium phosphate [TCP] or tetra-calcium phosphate [TTCP] phases), plasma jet properties influence on the in-flight powder properties (major influence of spray distance factor), the influence of the in-flight temperature and velocity of hydroxyapatite powder particles (ranges of 2294 K–2708 K and 152 m·s −1–291 m·s −1) on the final characteristics of the deposited coatings. Six combinations of the system parameters leading the low-medium-high in-flight properties were selected and the respective coatings were investigated, with some data in contradiction to previously published results. It was found that the temperature of the particles plays a critical role for the development of detrimental CaO (content increase of up to 14.6%) and metastable TTCP (up to 49.5%) phases in the coatings. Particle in-flight velocity was found to influence the open porosity of the coatings (8.8%–27.9%) and has an impact on the micro-hardness and moduli of the coatings (relative differences of up to 2.8×). Joint incidence of both in-flight properties was found to significantly influence the microstructure of the coatings and its respective surface roughness levels (Ra = 7.4–19.4 μm). The morphology of impinging splats was found to be influenced by both the in-flight velocity (dominant factor) and temperature (secondary factor) of the HA particles.

The influence of process parameters and heat treatment on the properties of cold sprayed silver coatings

Cold spray coating technology is a promising low temperature variant of thermal spray technology which can deposit pure, dense and thick coatings at a rapid rate. Unlike the other thermal spray coating techniques, cold spray is especially suitable for depositing coatings with high electrical and thermal conductivity as the integrity of the feedstock is maintained during the coating process. In the present study, the effect of process parameters and heat treatment on the properties of silver coatings has been investigated. An attempt has been made to correlate the powder particle velocity with the properties and microstructure of the coating. The effect of heat treatment temperature and atmosphere on the properties of the coatings, especially electrical conductivity, has been studied in detail in conjunction with a thorough analysis of the evolution of microstructure of the coatings.

The Influence of Powder Particle Velocity and Microstructure on the Properties of Cold Sprayed Copper Coatings

No literature exists on the influence of the velocity of Cu powder particles (during cold spraying) on the properties of the coatings like porosity, hardness, electrical conductivity, residual stress, and microstructure. Similarly, though the occurrence of dynamic recrystallization in the Cu powder particle during its deformation under the cold sprayed process has been well documented, its influence on the properties of the coating has not been studied. In this study, it is shown that while porosity of the coating is determined directly by the powder particle velocity, the other properties like hardness, electrical conductivity, and residual stress are determined not only by the particle velocity which depends on stagnation pressure and preheating temperature of the air (process gas) but also additionally on preheating temperature of air per se. The extent of powder particle fragmentation and dynamic recrystallization as a function of particle velocity has been quantified in terms of the grain boundary area fraction and the influence of the latter parameter on the coating properties has also been presented.

Experimental Design to Study the Effect of APS Process Parameters on Friction Behaviour of Alumina‐Titania Coatings

A factorial design was considered to study the effect of APS energetic and injection parameters on friction coefficient of alumina – titania coating. A first analysis suggested that wear resistance improvement was related to those conditions decreasing spray temperature and increasing in‐flight powder particle velocity before substrate impingement.

Analysis of the impact velocity of powder particles in the cold-gas dynamic-spray process

Abstract While built on a sound physical foundation, isentropic, one-dimensional models generally used to analyze the dynamics of dilute two-phase (feed-powder particles suspended in a carrier gas) flow during the cold-gas dynamic-spray process, require the use of numerical procedures to obtain solutions for the governing equations. Numerical solutions, unfortunately, do not enable an easy establishment of the relationships between the gas, process and feed-powder parameters on one side and the gas and the particle velocities at the nozzle exit and the particle impact velocity, on the other. Analytical solutions for the governing equations in the limits of small and large relative particle/gas velocities and a multiple non-linear regression analysis are used, in the present work, to develop analytical functions which can be used to compute the gas and the particle exit velocities and the particle impact velocity for a given set of the gas, process, and feed-powder parameters. The results obtained using the analytical functions are found to be in a very good agreement with their numerical and experimental counterparts.

WC–Co coatings deposited by the electro-thermal chemical spray method

A novel thermal spray technology — an electro-thermal chemical spray (ETCS) for producing hard coatings is presented. The experimental coating apparatus consists of a machine gun barrel, a cartridge containing the coating material in powder form, a solid propellant, and a plasma ignition system. The plasma ignition system produces plasma in pulsed mode to ignite the solid propellant. On ignition, the drag force exerted by the combustion gases accelerates the powder particles towards the substrate. Using the ETCS technique, the process of single-shot WC–Co coating deposition on stainless steel substrate was studied. The influence of process parameters (plasma energy, mass of the solid propellant and the coated powder, distance between the gun muzzle and the substrate) on the coating structure and some of its properties were investigated. It was shown that ECTS technique effectively deposited the WC–Co coating with deposition thicknesses of 100–200 μm per shot, while deposition yield of ∼70% was attained. The WC–Co coatings consisted of carbide particles distributed in amorphous matrix. The powder particle velocity was found to depend on the solid propellant mass and was weakly dependent on the plasma energy, while the particle processing temperature was strongly dependent on the plasma energy and almost independent of the solid propellant mass. Whilst increasing the solid propellant mass from 5 to 7 g, the deposition rate and yield correspondingly increased. When increasing the plasma energy, the temperature of the powder particles increased, the average carbide particle size decreased and their shape became more rounded. The deposition yield and microhardness at first increased and then achieved saturation by increasing the plasma energy.

Modelling and Measurements of Particle in‐flight Characteristics of Atmospheric Plasma Sprayed Yttria Stabilised Zirconia

ABSTRACT: Stabilised ZrO2 particle in flight characteristics in an Ar‐H2 atmospheric plasma jet have been studied using analytical and experimental techniques. A commercial code was used to simulate the plasma flow. A standard k‐ɛ turbulence model was used. Powder particle velocity, temperature history and trajectory were calculated using a stochastic discrete particle model and compared with measurements. A good correlation was found between predictions and measurements. Relationships between the sprayed particle velocity, temperature and size were investigated and a clear correlation was found. The method presented here seems to be a powerful and cost‐effective tool, which could be used to optimise spray parameters off‐line.

The Modeling of Coating Thickness, Heat Transfer, and Fluid Flow and Its Correlation with the Thermal Barrier Coating Microstructure for a Plasma Sprayed Gas Turbine Application

The plasma sprya deposition of a zirconia thermal barrier coating (TBC) on a gas turbine component was examined using analytical and experimental techniques. The coating thickness was simulated by the use of commercial off-line software. The impinging jet was modeled by means of a finite difference elliptic code using a simplified turbulence model. Powder particle velocity, temperature history, and trajectory were calculated using a stochastic discrete particle model. The heat transfer and fluid flow model were then used to calculate transient coating and substrate temperatures using the finite element method. The predicted thickness, temperature, and velocity of the particles and the coating temperatures were compared with these measurements, and good correlations were obtained. The coating microstructure was evaluated by optical and scanning microscopy techniques. Special attention was paid to the crack structures within the top coating. Finally, the correlation between the modeled parameters and the deposit microstructure was studied.

Plasma-arc spray-coating of powders of self-fluxing iron-base alloys 1. Estimation of the temperature and velocity of powder particles in the plasma flow

Mathematical simulation has been used to estimate the effect of technological factors on the variation of the temperature and velocity of particles of self-fluxing iron-base powder in a plasma flow of propane-butane combustion products. The influence of the plasma generator arc current, the flow rates of the plasma-forming gases and their relations, the powder particle size, the diameter of the plasma generator nozzle, the powder flow rate, and the spraying distance are analyzed. Optimal spraying conditions are determined for various powder fractions.

Acceleration of powder materials in an electrothermal launcher

The flow of heated dense plasma obtained in the discharge region of an electrothermal launcher can be used for acceleration of powder material particles. After being accelerated and heated in the plasma flow, particles impact substrates and produce coatings with strong adhesion and low porosity. An electrothermal launcher system which includes a discharge unit, a discharge initiation unit, and a powder injector was constructed. A theoretical model of the launcher based on one-dimensional nonstationary hydrodynamic analysis of plasma flows was developed. Relationships among the major output parameters (the plasma flow density, velocity, temperature, the particle velocity) on the parameters of the power supply system, the geometrical dimensions of the discharge gap, and the barrel are examined. The construction of accelerator elements such as the discharge initiation element which provide a possibility of repetitive operation, is described. Experimental results the plasma flow velocity, the flow pressure upon substrates, plasma temperature and powder particle velocity are presented. Coatings made from metal and nonmetal powders, including diamond powder on metal and nonmetal substrates, were obtained. >

Fluid flow behaviour and solidification studies during ultrasonic gas atomization

Fluid flow behaviour during ultrasonic gas atomization was studied. The gas velocity was determined by total pressure measurement and Schlieren photography, and the metal powder particle velocity was calculated. The gas velocity reaches about 1700 m s −1 (Mach. 1.7) in the supersonic flow region for helium gas at a backing pressure of 6.9 M Pa. An Al5wt.%Mn2.5wt.%Cr powder particle 15 μm in diameter is accelerated to a maximum velocity of about 1200 m s −1, while a particle 150 μm in diameter of the same alloy reaches a maximum velocity of about 400 m s −1. Solidification studies were carried out by collecting powder particles at different flight distances from the atomization nozzle. A comparison between a theoretical solidification model and the experimental result shows good agreement.