Design Of Torch Research Articles

Design and Study of a Large-Scale Microwave Plasma Torch with Four Ports

The microwave plasma torch (MPT) has gained popularity in industrial applications due to its high energy density, ionization levels, and high temperature. However, the non-uniform and unstable plasma generated by microwave plasma sources has limited the production of large-scale MPTs. This paper proposes a novel MPT device utilizing a four-port microwave source (2.45 GHz, 4 kW) to address these issues. The improved plasma uniformity and stability are achieved through the new structure, and the microwave efficiency is enhanced by introducing the focusing dielectric in the coupled cavity. Using a 3D electromagnetic field model, microwave plasma model and fluid model, the paper optimizes the geometry and inlet mode of the MPT device. Experimental results show that the novel MPT device can generate a plasma torch with a maximum height of 545 mm, a working range of 10–95 L/min, and a microwave efficiency up to 86%. The proposed device not only competently meets industrial requirements, but also provides design ideas and methods for future MPT devices.

Study of the Gas-Dynamic Features of the Design of the Gas-Air Path of the Plasmatron

The aim of the study is to consider a method for improving the energy efficiency of the technological process of plasma recovering of turbine blades of CHP through the development and implementation of a three-way vortex mixer into the design of the plasma torch. By changing the operating parameters of the mixer, it is possible to adaptively control not only the recovery modes, but also the physical and mechanical properties of the coating. It has been established that structural changes in the technological elements of the plasmatron significantly change its structural characteristics, which leads to a change in the gas-dynamic processes occurring in it. The changes consist in the appearance of additional hydraulic and gas resistance to the flow of the carrier gas with the powder composition. Modernization of the plasmatron and optimization of technological regimes require a gas-dynamic calculation of each element of the gas-air path at the design stage. Studies of the principles of pressure distribution, flow rate, changes in the flow rate of the transporting gas and powder composition made it possible to design the optimal design of the plasmatron while retaining its technical characteristics, regulated by the GOST 4.140-85 standard «System of product quality indicators. Electric welding equipment. Nomenclature of indicators»

A novel method for predicting the occurrence of the large-scale shunting in the reverse-polarity plasma torch

The reverse-polarity plasma torch (RPT) is a promising high enthalpy plasma source for material processing, e.g. plasma atomization for spherical powders and plasma synthesis for the nanostructured carbon. The quality and yield of the final product highly depend on the working stability of the RPT, which may be undermined by the large-scale shunting. Large-scale shunting is an abnormal discharge phenomenon existed in the RPT, which leads to the sudden drop of the arc voltage and shrink of the generated plasma jet. Inter-electrodes between the cathode and anode are designed to limit arc fluctuations and thus large-scale shuntings. However, the construction and maintenance of the RPT with inter-electrodes are highly complex. To alleviate the large-scale shunting and retain the advantage of simple structure of the conventional RPT, a novel method for predicting the occurrence of the large-scale shunting is proposed for optimizing the RPT’s internal structure and operation condition. The method is based on the thermal non-equilibrium modelling of the RPT to calculate the thickness of the cold boundary layer (CBL) and breakdown voltage. Then, the occurrence of the large-scale shunting is predicted by comparing the breakdown voltage with the voltage drop between the electrode inner surface and arc column. Three different shapes of the front electrode (cathode) corresponding to different thicknesses of the cold boundary layer (CBL) were manufactured based on the proposed numerical method. Experimental and numerical studies on the effect of the electrode geometry, arc current and gas flow rate on the working stability of the RPT and thickness of the CBL were conducted. Results showed the quantitative correlations between operating parameters and the instability of the RPT and verified that the proposed numerical method is useful for optimizing the design and operation of the plasma torch with minimizing large-scale shunting instabilities.

Modeling and analysis of the plasma primary atomization for controllable preparation of high-quality spherical metal powders

Plasma primary atomization (PPA) is a unique and critical process in the plasma atomization (PA), which is a highly recognized materials processing technology for producing high-quality spherical powder, but there lacks of in-depth understanding and models on how the metal wire is converted into high-quality spherical metal powders. Therefore, experimental observations and theoretical analysis on the PPA process were carried out to reveal the behavior of molten metal for controllable preparation of the metal powders. Firstly, the typical stages in the PPA were firstly revealed by experimental observations. Secondly, heat and mass transfer models on PPA were established to reveal how the molten metal is generated and transferred on the wire surface. Thirdly, the behavior of the molten metal in PPA was phenomenologically modeled and quantitatively analyzed based on the experimental observations and the proposed models. As such behavior determines the average size and yield of the produced powders, two key influencing parameters were identified to quantitatively reflect the melting and transfer behavior of the molten metal respectively. Then, calculation equations for them were established based on the proposed models of PPA and then verified. With the proposed models of PPA and the established calculation equations of the key influencing parameters, the quality of the produced powders may be quantitatively controlled by optimal design of the plasma torch and selection of the processing parameters of PA.

Characterisation of a Cold Atmospheric Pressure Plasma Torch for Medical Applications: Demonstration of Device Safety

The safety and effectiveness of plasma devices are of crucial importance for medical applications. This study presents the novel design of an atmospheric plasma torch (SteriPlas) and its characterisation. The SteriPlas was characterised to ascertain whether it is safe for application on human skin. The emission spectrum discharged from the SteriPlas was shown to be the same as the emission from the MicroPlaSter Beta. The UV emitted from the SteriPlas was measured, and the effective irradiance was calculated. The effective irradiance enabled the determination of the maximum UV exposure limits, which were shown to be over two hours: significantly longer than the current two-minute treatment time. The use of an extraction system with a higher flow rate appears to reduce slightly the effective irradiance at the treatment area. The NOx and ozone emissions were recorded for both SteriPlas configurations. The NOx levels were shown to be orders of magnitude lower than their safety limits. The ozone emissions were shown to be safe 25 mm from the SteriPlas cage. A discussion of how safety standards differ from one regulatory body to another is given.

The design and analysis of a novel low power atmospheric plasma jet torch for optical fabrication

Over the past few years, atmospheric Inductively Coupled Plasma (ICP) has aroused extensive attention in optical fabrication field since its chemical etching-based processing mode does not mechanically damage work-pieces. However, commercial Fassel-type torch are commonly employed in processing, and the high temperature plasma jet generated by commercial Fassel-type torch will cause thermal damage to optical elements. In this paper, an ICP jet torch is developed for optical fabrication, capable of maintaining plasma jet under a low power of 156 W. By reducing the minimum maintenance power of plasma jet, the processing temperature is down-regulated to 112 °C. To explain the low maintenance power principle in this research, the effect of radial confinement and axial pushing-off on the plasma are analyzed by simulation and experiment processes. Moreover, the effect of these two phenomena on the maintenance power is analyzed experimentally. Subsequently, the experiments are performed to verify the processing temperature, removal efficiency and removal stability of the torch. As revealed from the experimental results, the proposed torch exhibits the stability of footprint up to 97.5%.

On the Efficiency of Nitrogen-Containing Gaseous Waste Plasma Afterburning

The paper is devoted to the study of the plasma neutralization technology for toxic waste in the gaseous phase. It is noted that for effective implementation of plasma processes in waste processing technologies, it is necessary to search the optimal solutions taking into account the criteria of quality, productivity, cost and safety. In order to determine the feasibility of using plasma incineration technology, attention is paid to the definition of the appropriate nomenclature for gaseous toxic waste. The technology of plasma neutralization for thermal waste processing products - superoxicants (dioxins) and nitrogen-containing gas emissions (ammonia and nitrogen oxides) is studied. A modernized design of the plasma torch for the gaseous waste utilization is proposed. The known methods of thermal destruction for ammonia and nitrogen oxides are considered. Temperature approximations of their decomposition duration and efficiency in the range of plasma heating temperatures are found. The gas-dynamic parameters of the air-plasma flow in the process of nitrogen-containing gases thermal heating by plasma jet are determined using machine modelling methods. The effectiveness of the considered plasma neutralization technology is proved. The results of these studies should allow us to further formulate commonly used in engineering practice principles and methods for designing high-performance plasma heating technology.

Development of a compact plasma torch design for welding and surfacing

The article discusses the development of the design of the plasma torch used for welding and surfacing, the relevance of the plasma type of welding, the stages of work necessary to develop this design, modeling the flow of protective and working gas.

Design and characteristics of a triple-cathode cascade plasma torch for spheroidization of metallic powders

Arc plasma torch is an effective tool for spheroidization of metallic powders. However, as most conventional plasma torches were not specifically designed for plasma spheroidization, they may exhibit the disadvantages of the radial injection of powders, large fluctuations in the arc voltage, large gas flow rate, and disequilibrium between multiple plasma jets during the spheroidization process. Therefore, this paper presents a triple-cathode cascade plasma torch (TCCPT) for plasma spheroidization. Its structural design, including three cathodes, a common anode, and three sets of inter-electrodes, are detailed to ensure that powders can be inserted into the plasma jet by axial injection, the arc voltage fluctuations are easily maintained at a low level, and the plasma torches can work at a relatively small gas flow rate. Experimental results showed that the proposed TCCPT exhibits the following characteristics: (1) a relatively small arc voltage fluctuation within 5.3%; (2) a relatively high arc voltage of 75 V and low gas flow rate range of 10–30 SLM; (3) easy to be maintained at the equilibrium state with the equilibrium index of the three plasma jets within 3.5 V. Furthermore, plasma spheroidization experiments of SUS304 stainless steel powers were carried out using the proposed TCCPT. Results verified that the proposed TCCPT is applicable and effective for the spheroidization of metallic powders with wide size distribution.

Experimental Study on the Design and Characteristics of a Laminar Plasma Torch With Medium Working Power and its Applications for Surface Hardening

Due to its favorable temperature and velocity distributions, a lamina plasma jet, generated by a laminar plasma torch (LPT), is superior to a turbulent plasma jet on some applications. However, most of the reported LPTs usually work at a relatively low output power with a relatively low arc voltage and thermal efficiency, limiting its capability in the applications such as the surface hardening, synthesis of nanoparticles, remanufacturing of large components, and so on. Therefore, this article aims at designing an LPT with medium level output power and a relatively low arc current but a high thermal efficiency. The characteristics and applications of the proposed LPT have been obtained by experiments. The experimental results show the following characteristics: 1) the mean arc voltage of the proposed LPT is higher than 190 V with a maximum working power larger than 25 kW; 2) its mean thermal efficiency and jet length arrive at 50% and 450 mm, respectively; 3) the experimental data of the proposed LPT were used to fit its theoretical characteristics by using the least squares method. According to these fitted curves, the theoretical characteristics of the proposed LPT at a specified working conditions can be predicted; and 4) in addition, the surface of 45# steel was hardened by using the laminar plasma jet to obtain a hardening surface. The maximum hardness of the treated substrate arrives at about 600 HV, which is three times of the untreated substrate.

High-performance electric arc source of ultraviolet radiation to ozone generate

Studies of electric arc сombustion in the swirling flow of a cylindrical discharge chamber of a plasma torch at oxygen consumption of 10-160 g/s are carried out. It is established that the electric field strength is constant along the channel at the initial section of the arc, and the length of this section is determined. On the basis of the similarity theory in a wide range of changes in the parameters of the plasma torch, methods for determining the electric field strength of the arc and the length of the initial section are obtained. The length of the plasma torch is calculated, which mainly includes the length of the initial section, where the voltage is constant, and the current-voltage characteristics. The design of the plasma torch was created. Theoretical studies of near-electrode processes at the cathode and anode were carried out, on the basis of which electrode materials were selected and cathode and anode structures were created that provide high thermal efficiency and service life of the plasma torch. The developed plasma torch can be used as a highly efficient arc source of ultraviolet radiation for generating ozone, for heating oxygen, as well as in metallurgy, chemical industry, for example, the production of titanium dioxide and ozonation.

Design and characteristics of a new type laminar plasma torch for materials processing

Laminar plasma jet (LPJ) generated by laminar plasma torch (LPT) has a favorable temperature and velocity distribution. Thus, it is superior to the turbulent plasma jet in material processing. However, most of the reported LPTs usually operate at a relatively low output power with a relatively low arc voltage and thermal efficiency, which limits its capabilities. In this context, this paper attempts to design a new type of high-power LPT with a relatively low arc current and a high thermal efficiency. In the first section, the design principle of the main components is studied and discussed in detail, and a new high-power LPT is proposed. Then, the experimental characteristics of the proposed high-power LPT are examined. Experimental results reveal the following characteristics of the proposed LPT. (1) The max jet length of the proposed LPT reaches at 540 mm. (2) Its mean arc voltage is higher than 290 V when the LPT works with arc currents lower than 200 A, leading to an output power greater than 50 kW. (3) The mean thermal efficiency is higher than 50%. Lastly, the proposed LPT has been applied to spheroidize the aluminum oxide powers. The experiment results for the production of spherical powders show that the proposed LPT has a good characteristic for material processing.

Root Cause Analysis of an Oil-Burning Tabletop Torch Explosion

Recent severe burn injuries and at least one death have been attributed to the sudden explosion of a particular type of tabletop fuel oil-burning torch when moved by or somehow affected by the user while lit. An investigation was performed to determine the variables involved in the design and operation of the subject torch that provided the necessary and sufficient conditions for the occurrence of the above explosions. The investigation findings strongly suggest that the explosions were caused by a faulty design of the tabletop torch that failed to separate the fire (ignition source) from a fuel that had too low of a flashpoint.

Optimization of the design of the plasma torch for using gas fluxes

The paper presents the results of plasma torch development and gas fluxes using possibility in plasma welding process. As part of the work, existing plasma torches were analyzed in order to identify opportunities for their modernization. The literature data was analyzed for identifying the optimal design of the plasma torch. During the study of literature data, it was found that the diameter of the nozzle tip has a great influence on the plasma welding process. Therefore, it was decided to model the processes occurring in the plasma torch using tips with different diameter sizes. Parameters that effects on the stability of plasma welding process were presented. Possible and potential effective plasma torch tip designs were proposed. The model of the behavior of argon in a plasma torch was constructed, which made it possible to draw conclusions about the optimum diameter of the plasma torch tip. Also, was shown the effect of the diameter of the plasma torch on the behavior of plasma gas.

Control-oriented dynamic model of an inductively coupled plasma torch by artificial intelligence methodology

Inductively coupled plasma (ICP) torches have been widely used in various materials processing. To improve the control of their processes, there has been a growing demand for simplified numerical models which can rapidly predict the dynamics of plasma jets subject to time-varying inputs or external disturbances. In this paper, control-oriented dynamic models of an ICP torch are developed as an alternative to the complex, high-level 2D time-dependent numerical model (i.e. a model based on magneto-hydrodynamic equations). Prior to model development, the detailed dynamic and nonlinear nature of the ICP torch to its time-varying operation conditions was numerically investigated using a 2D numerical model to gain insight into choosing appropriate dynamic model structures. Linear ARX (AutoRegressive with eXogenous input) and ARX-type neural network models were selected in the model identification, and their parameters or weightings were determined using the input/output data obtained from the 2D time-dependent numerical model. The dynamic behaviours of the ICP torch predicted from the developed models were in good agreement with the data from the 2D time-dependent numerical model. Using the developed models, a simple control system for the plasma temperature and axial velocity regulations was also designed and tested. The feedback control simulations demonstrated good set point tracking and disturbance rejection performances, indicating that the developed approach can be directly applied to the model-based control system design of an ICP torch as well as other thermal plasma torches.

Design and optical study of a microwave plasma torch in nitrogen used for the evaporation of aluminium wires

A microwave torch in nitrogen has been designed for the evaporation of aluminium (Al) wires potentially to be used for the synthesis of aluminium nitride (AlN). The torch, created on the tip of a metallic nozzle, is compatible with vacuum conditions and can be operated in continuous mode up to atmospheric pressure. Al wires to be evaporated are fed through the axis of the nozzle. Time‐resolved photography is applied to analyse the time evolution and stability of the interaction of the Al wire with the discharge. Optical emission spectroscopy is used (a) for the determination of the gas temperature of the active discharge, which is found to be in the range 1500–3500 K depending on the experimental conditions, and (b) for the estimation of the densities of Al and N atoms in the afterglow region, which are in the range 1011–1012 and of 1013–1014 cm−3, respectively. It is found that the part of the Al wire that is directly exposed to the nitrogen torch absorbs a considerable amount of the microwave energy, supporting its evaporation. In addition, the dissociation of molecular nitrogen has to be considered as an important process of power dissipation. Further technical development of the torch is necessary for the envisaged synthesis of AlN.

Investigation of the AC Plasma Torch Working Conditions for the Plasma Chemical Applications

The presented design and parameters of a three-phase AC plasma torch with the power up to 500 kW, flow rate of air 30–50 g/s (temperature up to 5000 K) could be used in different plasma chemical processes. Range of measured plasma temperature is 3500–5000 K. The paper presents investigations of the plasma torch operation modes for its application in plasma chemical technologies. Plasma chemical technologies for various purposes (processing, destruction of various wastes, including technological and hazardous waste, conversion or production of chemicals to obtain nanoscale materials, etc.) are very promising in terms of the process efficiency. Their industrial use is difficult due to the lack of inexpensive and reliable plasma torches providing the desired level of temperature, enthalpy of the working gas and other necessary conditions for the process. This problem can be solved using a considered design of a three-phase alternating current plasma torch with power of 150–500 kW with working gas flow rate of 30–50 g/s with mass average temperature up to 5000K on the basis of which an industrial plasma chemical plant can be created. The basis of the plasma torch operation is a railgun effect that is the principle of arc movement in the field of its own current field. Thanks to single supply of power to the arc, arcs forming in the discharge chamber of the plasma torch move along the electrodes under the action of electrodynamic forces resulting from the interaction of the arc current with its own magnetic field. Under the condition of the three-phase supply voltage, arc transits from the electrode to the electrode with change in the anodic and cathodic phases with frequency of 300 Hz. A special feature of this design is the ability to organize the movement of the arc attachment along the electrode, thus ensuring an even distribution of the thermal load and thus achieve long time of continuous operation of the plasma torch. The parameters of the plasma jet of the plasma torch and the single-phase three-phase plasma injector for use in a plasma-chemical unit for production of nano-dispersed materials are described in the paper.

Design and Characteristics of a Laminar Plasma Torch for Materials Processing

Thermal plasma jets have been widely used in various materials processing techniques. However, the conventional thermal plasma torches usually generate turbulent plasma jets with the disadvantages of high axial temperature gradient, a short jet length and difficulties in the process control relatively, limiting its applications to materials processing. Therefore, this paper proposes a new laminar plasma torch (LPT) working with pure nitrogen to generate laminar plasma jet (LPJ). Its design and structural characteristics, e.g. segmented anode, axial gas injection, parallel water cooling structure, etc., are detailed to ensure the stability, the favorable temperature and velocity distribution of the generated LPJ. Experiments on the characteristics of the LPT showed that the generated LPJ possessed high specific enthalpy (ranging between 10 and 90 kJ/g), long jet length (maximum length: 480 mm) and low axial temperature gradient, and its output power a current and the gas flow rate. In addition, the thermal efficiency of the LPT was experimentally determined to be ranging between 25 and 45 %. Furthermore, experiment and simulation on the application of the LPJ for surface quenching verified the even radial temperature distribution of the plasma jet and high heat flux density brought to the surface.

Pulsed laminar arc jet with synchronized suspension injection-spectroscopic studies

The uncontrolled arc plasma instabilities are one of the difficulties encountered in in suspension plasma spraying. The improvement of this process is usually attempted by means of the reduction of arc fluctuations. The following paper presents a new approach to overcome these arc instabilities. The principle is to produce a pulsed laminar plasma jet combined with phased injection of liquid droplets. This is achieved by the particular design of the plasma torch which allows coupling two modes of the plasma oscillations, restrike and Helmholtz. The plasma produced in a new mode is laminar and pulsed, characterized by a modulated enthalpy, what permits to make the synchronization with the suspension injection. The droplets are injected using a piezoelectric device, based on drop-on-demand method, triggered by the voltage signal. The results are evaluated by time-resolved imaging technique and Time- Resolved Optical Emission Spectroscopy.

Synchronization of Suspension Plasma Spray Injection with the Arc Fluctuations

Poorly controlled heat and momentum transfers between plasma and material, plasma instabilities are some of the difficulties encountered in suspension plasma spraying. The improvement of this method is usually attempted by means of the reduction of arc fluctuations. This paper presents a new approach to the injection of reactive material in an arc jet. The principle is to produce a pulsed laminar plasma jet combined with phased injection of liquid droplets. This is achieved by the particular design of the plasma torch that works at moderate power and following a resonant mode. The droplets are injected using a piezoelectric device, based on drop-on-demand method, triggered by the voltage signal sampled at the torch connections. The results are evaluated by time-resolved imaging technique that shows how the trajectories are influenced by the moment at which the droplets penetrate the plasma jet.