Plasma Gas Flow Rate Research Articles

Chipboards with Plasma Protective Decorative Coatings

A plasma technology has been developed for the production of chipboard with vitreous protective decorative coatings. To prevent high temperatures of the plasma jet from being applied to the front surface of the chipboard, an intermediate layer was applied, which included a mixture of sodium liquid glass with colored glass powders based on profiled and sheet cullet. The technology of a two-stage deposition of an intermediate layer before plasma spraying of the main vitreous coating has been developed. The technology provides for the preliminary front surface preparation and the liquid glass application on a wood chipboard, the intermediate layer application and subsequent drying at 95 °C. The adhesion strength of the intermediate layer with the matrix was 1.6–1.8 MPa. The optimal technological parameters of plasma-chemical modification of a protective decorative coating based on fine powders of sheet and profiled glasses have been established: the power of an electric arc plasma installation operation is 8 kW, the flow rate of argon plasma gas - 2.0 m3/hour. It is shown that the water resistance of protective decorative coatings based on profiled and sheet glass is III hydrolytic class. Vitreous coatings had high reliability and durability, in particular, acid resistance, alkali resistance and microhardness. Due to the electric arc plasma installations use for plasma-chemical modification of protective decorative coatings based on profiled and sheet glass cullet, the technology is resource and energy efficient, and is also recommended for introduction both in furniture industry and in the construction industry.

Effect of N2 and O2 on OH radical production in an atmospheric helium microwave plasma jet

UV-pulsed laser cavity ringdown spectroscopy of the hydroxyl radical OH(A–X) (0–0) band in the wavelength range of 306–310 nm was employed to determine absolute number densities of OH in the atmospheric helium plasma jets generated by a 2.45 GHz microwave plasma source. The effect of the addition of molecular gases N2 and O2 to He plasma jets on OH generation was studied. Optical emission spectroscopy was simultaneously employed to monitor reactive plasma species. Stark broadening of the hydrogen Balmer emission line (Hβ) was used to estimate the electron density ne in the jets. For both He/N2 and He/O2 jets, ne was estimated to be on the order of 1015 cm−3. The effects of plasma power and gas flow rate were also studied. With increase in N2 and O2 flow rates, ne tended to decrease. Gas temperature in the He/O2 plasma jets was elevated compared to the temperatures in the pure He and He/N2 plasma jets. The highest OH densities in the He/N2 and He/O2 plasma jets were determined to be 1.0 × 1016 molecules/cm3 at x = 4 mm (from the jet orifice) and 1.8 × 1016 molecules/cm3 at x = 3 mm, respectively. Electron impact dissociation of water and water ion dissociative recombination were the dominant reaction pathways, respectively, for OH formation within the jet column and in the downstream and far downstream regions. The presence of strong emissions of the bands in both He/N2 and He/O2 plasma jets, as against the absence of the emissions in the Ar plasma jets, suggests that the Penning ionization process is a key reaction channel leading to the formation of in these He plasma jets.

Non-linear modeling of mechanical properties of plasma arc welded Inconel 617 plates

Abstract In the present research paper, an attempt is made to perform non-linear modeling of the plasma arc welding (PAW) of Inconel 617 plates with the help of experiments conducted using a central composite design of experiments (CCD). It is to be noted that the PAW is a high depth to width ratio welding process that can be used to join high strength materials like Inconel 617. Furthermore, mechanical properties such as ultimate tensile strength (UTS), percentage of elongation, flexural strength and hardness of the welded joints are highly dependent on the conditions under which the welding is performed. In the present paper, the weld current, weld speed and plasma gas flow rate of PAW are considered as input process parameters to study the effect of these variables on the above mentioned mechanical properties. Industrial pure argon (99.99 %) is used as both plasma and shielding gas during the welding of the 2 mm thick Inconel 617 plates. Surface plots and analysis of variance (ANOVA) are used to test the statistical adequacy of the models. Moreover, the prediction accuracy of the models is tested with the help of experimental test cases and found to be in good agreement.

Online Monitoring and Model-Free Adaptive Control of Weld Penetration in VPPAW Based on Extreme Learning Machine

Monitoring and controlling of weld joint penetration are essential issues in variable polarity plasma arc welding (VPPAW). In this paper, we develop a flexible visual sensor system to measure the backside keyhole characteristic parameters such as keyhole length, width, and area. Further, data analysis from dynamic welding experiments reveals a nonlinear correlation of the keyhole features and the backside beam width. To provide accurate feedback information, an extreme learning machine method is applied to predict the weld width with sufficient accuracy and less computing time. Then a novel model-free adaptive control (MFAC) is designed to control the weld penetration evaluated by the weld width. Closed-loop experimental results confirm that the MFAC system can simultaneously adjust the welding current and plasma gas flow rate to control the VPPAW process for obtaining a full-penetrated weld under various initial welding conditions and disturbances.

Droplet transfer behaviour in twin-body plasma arc welding

A novel process, named twin-body plasma arc welding (PAW), is proposed in this study. In this novel process, the wire is used as introduced electrode to adjusting the energy distribution between base metal and droplet, and a strong plasma flow force is applied to the droplets. To understand the characteristics of droplet transfer behaviour in this process, this paper analyses the changes in the forces acting on the droplet and carry on experiments to study the effect of the current separation ratio and plasma gas flow rate on droplet transfer behaviour. The results show that as the current separation ratio increases, the total energy acting on the droplet and the promoting force of droplet transition are enhanced, and the droplet transfer behaviour and wire melting speed are changed significantly. As the plasma gas flow rate increases, the plasma flow force is enhanced, and the droplet transfer behaviour is changed, but the droplet transfer position is almost unchanged. Through reasonable parameter matching, the spray transfer could be realized under low current, and the droplet transfer mode could be freely changed from globular to spray when the total current remains unchanged.

Arc discharge and pressure characteristics in pulsed plasma gas of PAW

This paper investigated the arc characteristics in pulsed plasma gas of plasma arc welding using a synchronous image- and electrical signal-acquisition system. The arc sizes (including the arc length L, the arc width on the water-cooling copper plate surface Wa, and the arc width under the nozzle Wc) and arc voltage changed regularly with the plasma gas periodically on/off. And the changing trends of arc sizes were affected by the plasma gas flow rate and the plasma gas switching frequency. The changing scale of arc voltage was proportional to the plasma gas flow rate and was inversely proportional to the plasma gas switching frequency. The average plasma arc welding (PAW) and plasma arc welding with pulsed plasma gas (PPG-PAW) arc voltages were equal when the plasma gas flow rate was the same. The arc pressure also presented cyclical changes during the plasma gas on/off, and the changing scale and the axial mean value were inversely proportional to the plasma gas switching frequency. The periodically oscillating arc and arc pressure would be beneficial to the refinement of grain structure during the welding process.

Influence of Critical Plasma Spray Parameter on Microstructural and Tribological Characteristics of Nanostructured Tungsten Carbide-Cobalt Coatings

Nanostructured tungsten carbide-cobalt coatings were deposited by air plasma spraying (APS) technique, using nitrogen as primary plasma gas. The characteristics of nanostructured coatings are typically affected by the percentage of unmelted/partially-melted regions present in the coatings. Hence, the coatings were obtained as a function of critical plasma spray parameter (CPSP), which is defined as the ratio of arc power to the primary plasma gas flow rate. It was observed that tungsten (W) rather than tungsten carbide (WC) was the dominant phase in nanostructured coatings due to decarburization. CPSP was found to have a significant effect on wear performance of APS nano-structured coatings. Wear resistance was highest for coatings deposited at lowest CPSP. Flaking was more prevalent in nanostructured coatings deposited at the highest CPSP.

Plasma Modification and Synthesis of Membrane Materials-A Mechanistic Review.

Although commercial membranes are well established materials for water desalination and wastewater treatment, modification on commercial membranes is still necessary to deliver high-performance with enhanced flux and/or selectivity and fouling resistance. A modification method with plasma techniques has been extensively applied for high-performance membrane production. The paper presents a mechanistic review on the impact of plasma gas and polymerization, at either low pressure or atmospheric pressure on the material properties and performance of the modified membranes. At first, plasma conditions at low-pressure such as plasma power, gas or monomer flow rate, reactor pressure, and treatment duration which affect the chemical structure, surface hydrophilicity, morphology, as well as performance of the membranes have been discussed. The underlying mechanisms of plasma gas and polymerization have been highlighted. Thereafter, the recent research in plasma techniques toward membrane modification at atmospheric environment has been critically evaluated. The research focuses of future plasma-related membrane modification, and fabrication studies have been predicted to closely relate with the implementation of the atmospheric-pressure processes at the large-scale.

Modeling of Plasma Arc Welding of Inconel 617 Super Alloy Plates using RSM

In the present work, an attempt is given to study the outcomes of input process parameters, namely weld current, weld speed and plasma gas flow rate on the bead geometry, that is bead width (BW) and bead height (BH) of Plasma Arc Welded Inconel 617 plates. In the present study, Bead on Plate (BoP) welding was done on 2 mm thick plates with the help of experiments designed using central composite design of experiments (CCD). The non-linear regression equations developed during this study were validated through experimental test cases. Further, it was depicted that the developed regression models were found to forecast the bead geometry with a reasonably good accuracy.

Effect of Melt-In and Key-Hole Modes on the Structure and Mechanical Properties of AISI 430 Steel Welded Using Plasma Transfer Arc Welding

In this study, AISI 430 stainless steel couple 10 mm thick were welded in the butt position by melt-in and key-hole plasma transfer arc welding (PTAW) processes without using any filler wire addition and pretreatment. Welded joints were manufactured choosing a constant nozzle diameter (2.4 mm), welding speed (0.01 m/min), shielding gas flow rate (25 L/min), two different plasma gas flow rates (0.8 and 1.2 L/min), three different welding currents in melt-in PTAW process (80, 85 and 90 A), and three current intensities of the key-hole PTAW process (120, 125, and 130 A). In order to determine the microstructural changes that occurred, the interface regions of the welded samples were examined by scanning electron microscopy (SEM), optic microscopy (OM), X-ray diffraction (XRD) after PTAW. Microhardness and V-notch impact tests were applied to determine the mechanical properties of the welded samples. In addition, fracture surface were examined by SEM after impact tests.

An investigation on plasma-MIG hybrid welding of 5083 aluminum alloy

Plasma-MIG (metal inert-gas) hybrid welding is an advanced welding technology of aluminum alloys, which integrates the advantages of deep penetration in plasma arc welding and excellent filling ability in MIG welding. In this paper, the 5083 aluminum alloy plates with 6-mm thickness were welded using paraxial plasma-MIG hybrid welding. The influence of processing parameters such as the welding speed, plasma current, MIG current, and plasma gas flow rate on the weld forming was investigated, and the microstructure and mechanical behavior of welded joint under the typical parameters were studied. Both the penetration depth and weld width decreased with the increase of welding speed, increased with the increase of MIG current. While plasma arc current and plasma gas flow rate mainly affected penetration depth. The welding joint underwent the different thermal cycles in the different regions, which resulted in the different microstructure. Compared with the lower part of welding joint, the secondary phases in the upper part were bulkier and the dendrite arm spacing was wider, and the width in the partially melted zone (PMZ) was smaller. The tensile strength and the elongation of the welding joint were 274 MPa and 12.42%, which is approximately 85.63 and 95% of that of base metal, respectively.

Plasma-assisted chemical vapor synthesis of indium tin oxide (ITO) nanopowder and hydrogen-sensing property of ITO thin film

Transparent conducting indium tin oxide (ITO) nanoparticles were synthesized by plasma-assisted chemical vapor synthesis route using indium nitrate and tin nitrate as the precursors. The injected precursors were vaporized in the plasma flame followed by vapor-phase reaction and subsequent quenching of the vaporized precursors produced nanosized ITO. The amount of tin nitrate was varied to obtain 5, 10 and 15 atomic percent Sn designated as ITO1, ITO2 and ITO3, respectively. The grain size of the produced ITO powder increased with increasing plasma torch power. On the other hand, it decreased with increasing plasma gas flow rate. The electrical and optical properties of ITO films prepared by spin-coating a dispersion of synthesized nanoparticles on a glass substrate vary as a function of tin content. Hall effect measurements showed that the minimum resistivity of 6.65 × 10−4 Ωcm was obtained for ITO2 film. ITO1 and ITO2 film exhibited an average transmission of 85% indicating their suitability in optoelectronic applications. The ITO gas sensor was exposed to different concentrations of H2 gas and temperatures to evaluate its gas sensitivity. The optimum operating temperature and gas concentration of H2 showing the highest sensitivity was determined to be 350 °C and 400 ppm, respectively. The linear relation between sensitivity and concentration up to 400 ppm of H2 can benefit the actuator to detect the concentration of H2 and thus making it suitable for high-performance hydrogen gas sensing applications.

Surface decontamination of eggshells by using non-thermal atmospheric plasma

In this study, the possibility of using an effective short time non-thermal plasma (NTP) treatment to inactivate Salmonella enterica serovar Enteritidis on eggshell surface was investigated. The eggshells were artificially contaminated with S. Enteritidis at an initial concentration of 107cfu/egg and then treated with an atmospheric pressure plasma jet by using air as process gas under different experimental settings with various frequencies (20–25kHz) and reference voltages (100–80%), exposure times (60–120s), distances from plasma jet (15 or 40mm) and gas flow rates (2000–3000L/h). The best result was obtained at maximum plasma power of 655W (25kHz–100% V), where S. Enteritidis concentration on egg surface was reduced below the detection limit (102cfu/egg) after 120s of treatment. The temperature remained below 35°C after all plasma treatments in order to minimize the risk of egg quality alterations. Specific measurements demonstrated that there were no negative effects on egg quality after NTP treatment. The effect of plasma process on the egg cuticle was demonstrated by using scanning electron microscopy.

Preliminary measurements on microwave plasma flame for gasification

In this paper, the effects of plasma power and plasma gas flow rate on the geometrical dimensions, the shape of plasma flame and temperature distribution in gasification reactor have been investigated. The effects of plasma power and plasma gas flow rate on the geometrical dimensions, shape of plasma flame and temperature distribution in gasification reactor are presented. The plasma pictures at a variety of plasma power ranging from 300 to 4200 W with the range of plasma gas which is air from 50 to 100 L/min are presented. As expected, an increase in power causes the generation of intensive plasma with enhancement of the plasma flame volume. On the other hand, air flow rate is inversely proportional to the volume of the plasma flame. It is observed that both power and air flow rate has a significant effect on plasma flame shape. The spreading shape of plasma flame is observed at low powers. However, the shape of flame is pointed toward its end with an increase in plasma power. Meanwhile, reducing air flow rate causes a change in shape at lower power levels. The interactive influence of air flow rate and plasma power is confirmation of different plasma flow regimes. The temperature measurements confirm the effects of air flow rate and power on plasma flame regime from 1800 to 6000 W power. Increasing power level causes increment in the reactor temperature. The average temperature in the reactor is increased from 480 °C at 1800 W power to 1018 °C at 6000 W power. The flow rate has a reverse effect on magnitude of the temperature. The average temperature in the reactor is reduced from 480 to 348 °C at 1800 W power and 1018 to 918 °C at 6000 W power when the flow rate is increased from 50 to 100 L/min. However, the temperature distribution is more uniform in higher flow rates. It is also related with the shape of plasma. While the magnitude of temperature and its gradient is high in pointed end plasma, the effects are reversed in spreading shape plasma.

Dry Etching Characteristics of MOVPE-Grown CdTe Epilayers in CH4, H2, Ar ECR Plasmas

Dry etching characteristics of single crystal (100) CdTe epitaxial layers grown on GaAs substrates were studied using CH4, H2, and Ar as process gases in an electron cyclotron resonance plasma. A smooth and anisotropic etching was obtained with CH4, H2, and Ar. No hydrocarbon polymer was found on the etched surface, which was confirmed by x-ray photoelectron spectroscopy measurement. Etching of the CdTe surface was also possible with H2 and Ar; however, no etching was observed in the absence of H2. Dependence of the etch rate on plasma gas composition and flow rates was studied. Mechanisms of etching with and without CH4 supply were also studied. Etched CdTe layers also showed no deterioration of electrical properties, which was confirmed by photoluminescence measurement at 4.2 K and Hall measurement at 300 K.

Visual sensing of the weld pool geometry from the topside view in keyhole plasma arc welding

Weld pool and keyhole behaviors are the key factors to determine the process stability and weld joint quality in keyhole plasma arc welding. In this study visual sensing of the topside weld pool based on a low-cost CCD camera was realized. A visual sensing system with special dimmer glass and bandpass filtering was developed for solving the problems like strong arc disturbances and large radiation intensity gradient. Boundaries of the complete topside weld pool were acquired through image processing of the captured raw images. Weld pool dimensions were then calculated and calibrated. The relationships between the dimensions and welding current, welding speed and plasma gas flow rate were investigated. Three stages, including blind keyhole, unsteady keyhole and steady keyhole, were defined to describe the weld pool behaviors along with the keyhole’s evolution. The variation trends of weld pool shapes were discussed to study the possible mechanism of the complex physical processes. For keyhole plasma arc welding, this provides the industry a prospective low-cost way to predict the penetrations by sensing weld pool and keyhole from topside.

Determination of regression materials mircohardness, processed by low-temperature plasma dependence on process conditions

The influence of conditions of plasma surface treatment on hardening of carbon steel technological process was analyzed. Hardening was carried out in plasma electrothermal line with an electrolytic cathode. When processing, steel crystal grains are crushed and the structure is changed from ferrite-pearlite to bainite-troostite and martensite, depending on the processing conditions. In this case the surface microhardness increase in 2 - 3 times. The dependence of the carbon steel surface microhardness on the discharge current (2 - 10 A), the distance between the heat source and the surface, the plasma gas flow rate and treatment duration was found. On the basis of multifactor experiment planning methods and the method of least squares, the formula that describes this relationship was found. This allowed to conduct a targeted search of optimal conditions of processes of hardening steel and improve the efficiency and quality of research.

The Investigation of Morphology Characteristics and Compositional Distribution of Tantalum Metal Coatings with Different Power Levels of Vacuum Plasma Spraying

Tantalum (Ta), a non-toxic metal, has become one of the most important medical materials, because of its excellent biocompatibility, corrosion resistance, and mechanical properties. In this study, vacuum plasma spray (VPS), was utilized for the spraying process Ti6Al4V and Ta powder were utilized as substrate and coating material, respectively. Different levels of power were set for the coating parameters with the same conditions of plasma gas, plasma gas flow rate, powder feed gas, spraying stand-off distance and chamber pressure. The influence of Ta coating between morphology and chemical composition were investigated with different power levels. The results showed that all specimens have performed a good bonding between the substrate and coating. The coatings all display a rough surface with pores, which is beneficial to the joining of human bone tissue and the implant. With an increasing in power, the coating becomes denser to prevent the release of harmful ions. The hardness along the coating section is between 167 ± 11~ 229 ± 8 HV, and is relatively lower than the substrate (292 ± 10 HV). As a result, it can reduce the stress shielding effect between the implant and the human bone tissue.

Comparison of energy acted on workpiece among Twin-body Plasma Arc Welding, Non-transferred Plasma Arc Welding and Plasma Arc Welding

A novel welding process named Twin-body Plasma Arc Welding (TPAW) is proposed in this paper. The main arc in TPAW is established between tungsten electrode and guide electrode. In comparison with Non-transferred Plasma Arc Welding (NPAW) where one of the arc terminal is the nozzle, the workpieces are both not connected into the circuit loop, and the energy loss is less than that of NPAW. In comparison with Plasma Arc Welding (PAW) where one of the arc terminal is the workpiece, the nozzles are both not connected into the main arc circuits, and the anode effects are not worked on the workpieces. To examine the energy of these arcs by an intuitive way, a series of experimental system were designed and stagnation ablation experiments were conducted on Gr. D steel workpieces. The ablation regions which characterize the energy received by the workpiece are observed, measured and analyzed. It is found that the diameter of ablation region (i.e., the energy received by the workpieces) from TPAW is smaller than that of PAW, but is much larger than that of NPAW, as increasing the welding current and plasma gas flow rate. The welds by TPAW have smaller MZ area and smaller HAZ area but similar penetration in comparison with those by PAW, the ones by NPAW could not observe MZ or HAZ under the same parameters, indicating that the total heat input distribution of TPAW is smaller than that of PAW and much larger than that of NPAW. This tendency provides a possible method to better control the energy of plasma arc and expand the application of plasma arc.

Modeling of weld bead geometry on HSLA steel using response surface methodology

With increasing requirements of higher strength to low weight ratio materials, high-strength low-alloy (HSLA) steel has achieved higher commercial importance. Plasma arc welding has the capability to join metals without edge preparation, weldment in a single pass and minimum angular distortion. Due to these embedded capabilities, plasma arc welding is preferred over conventional joining processes for HSLA steel applications involving part thickness greater than 3 mm. The quality of plasma arc-welded joints is highly dependent on input process parameters. This paper aims to develop empirical models for the prediction of weld bead geometry including front bead height, back bead height, front bead width, and back bead width. A series of tests were conducted to investigate the effect of four input process parameters including current, voltage, welding speed, and plasma gas flow rate on weld bead geometry using a face-centered central composite design. The confirmation experiments and ANOVA results validated the models within 95 % accuracy. Current was found to be the most influential factor affecting the weld bead geometry followed by speed. Furthermore, current and speed and speed and gas flow rates were identified as most influencing interaction factors. The innovation in this research is the empirical modeling of weld bead geometry for HSLA using plasma arc welding.