Arc Root Research Articles

Arc characteristics and metal transfer modes in arcing-wire gas tungsten arc welding

Arcing-wire gas tungsten arc welding is an innovative process developed as a variant of gas tungsten arc welding to reinforce the deposition rate by utilizing bypass arc energy. After establishing an experimental platform, the experiments were conducted to study the arc characteristics, interaction of the main and bypass arcs, and metal transfer behavior. Magnetic arc blow, location of the bypass arc root, and shielding gas flow were found to cause arc deflection and an invisible obstacle between the arcs in arcing-wire gas tungsten arc welding. The bypass arc voltage should be controlled carefully to maintain the stability of the welding process. Globular transfer, short-circuiting transfer, and continuous bridging transfer could be obtained, which were determined by wire feed speed (the melting current) and the distance from the wire tip to the workpiece as well as the welding direction.

U–Pb zircon dating, geochemical and Sr–Nd–Hf isotopic compositions of Motuo quartz–monzonite: Implication for the genesis and diversity of the high Ba–Sr granitoids in orogenic belt

Early Paleogene granitoids in Southern Lhasa subterrane have been widely investigated and many petrogenesis and geodynamic models have been proposed in the past few years. However, contemporaneous granitoids in the Motuo tectono-magmatic belt, southeast Lhasa terrane, are still limitedly studied. Here we present the petrology, zircon U–Pb geochronology, whole-rock geochemistry, and Sr–Nd–Hf isotope data of the Damu and 52K quartz–monzonite in the Motuo area. LA-ICP-MS U–Pb zircon dating shows that they have magma crystallization ages of 49 and 69Ma, respectively. The Damu quartz–monzonite (SiO2=63.76–68.33wt.%) is high-K calc-alkaline (K2O=2.54–4.02wt.% with K2O/Na2O=0.59–1.09) and metaluminous to weakly peraluminous (A/CNK=0.99–1.07). The 52K quartz–monzonite (SiO2=61.12–66.12wt.%) shows slightly higher K2O contents (3.80–5.28wt.% with K2O/Na2O=1.03–1.45) and metaluminous series (A/CNK=0.96–1.00). The analyzed samples are characterized by high Ba (850–2573ppm), Sr (534–986ppm) contents, and fractionated REE patterns ((La/Yb)N=22–72 and (Sm/Yb)N=4.55–8.24). These geochemical features are comparable with those of high Ba–Sr granite. They display weakly evolved Sr–Nd–Hf compositions (whole-rock (87Sr/86Sr)0=0.7068 to 0.7086, εNd(t)=−4.20 to −3.41, and zircon εHf(t)=−5.2 to −0.9). Geochemical and Sr–Nd–Hf isotopic data reflect that the Damu and 52K quartz–monzonite represent residual magma from AFC processes of lithospheric mantle-derived mafic melts. The over-thickened lower crust in the eastern Lhasa terrane had been delaminated during ca. 83–70Ma, which led to the replacement of ancient lithospheric mantle by the juvenile lithospheric mantle. The juvenile mantle wedge in the study area was suspected to be metasomatized by melts that were derived from the foundering arc root, rather than the subducted sediments. Thus, the early Paleogene high Ba–Sr magmas from the SE Lhasa terrane may provide evidence for recycling of continental lithosphere by density destruction.

The effect of external longitudinal magnetic field on laser-MIG hybrid welding

Applying the external longitudinal magnetic field to laser-metal inert gas (MIG) hybrid welding, its influence on the arc/plasma shape, motion characterization, and coupling of these two sources are researched using a high-speed camera. It is revealed that the essential effect of the external longitudinal magnetic field on laser-MIG hybrid welding arc/plasma is to make the arc and the coupling process more stable. Through analyzing the position of arc and laser-induced plasma and the mechanical model of charged particles, the energy coupling mechanics of arc and plasma under this welding condition has been proposed. The results showed that an application of a magnetic field can change the arc shape from pyramidal and static to spiral and rotational with high-speed stage and make the arc root diameter increase. It has also been found that the external longitudinal magnetic field can obviously enhance the stability of the process during laser-arc hybrid welding under the best magnetic induction intensity, which promoted efficient coupling and formed a good weld.

Direct probing of anode arc root dynamics and voltage instability in a dc non-transferred arc plasma jet

The transient dynamics of the anode arc root in a dc non-transferred arc plasma torch is captured through fast photography and directly correlated with the associated voltage instability for the first time. The coexistence of multiple arc roots, the transition to a single arc root, root formation and extinction are investigated for the steady, takeover and re-strike modes of the arc. Contrary to the usual concept, the emerging plasma jet of a dc non-transferred arc plasma torch is found to carry current. An unusually long self-propelled arc plasma jet, a consequence of the phenomenon, is demonstrated.

Observation of Thermal Cathodic Hot Spots in a Magnetically Rotating Arc Plasma Generator

At atmospheric pressure, cathodic arc root tends to shrink to a luminous hot spot, which limits arc column expanding and accelerates cathode ablative rates. To obtain a nonconstricted cathodic arc root, we built a magnetically rotating arc plasma generator that mainly consists of a cylindrical graphite anode chamber, a concentric lanthanum tungsten cathode, and a solenoid coil for producing an axial magnetic field (AMF). Evolution of self-organized multihot spots on cathode end is observed in this study. Results show that with the AMF, arc currents, or/and cathode temperature increasing, the spot’s quantity gradually increases, and at last multispots evolve into a diffuse annular one. When the arc column is constricted, the arc moves on the spots periodically. Thus, a single constricted cathodic root is formed. By controlling the axial gas flow, the constricted arc converts into a diffusive one which covers all spots simultaneously, and then multiroots or diffuse annular root are developed. The cathodic spots and roots formation mechanism are proposed, and experimental results support the prediction of nonlinear surface heating model .

Geochronology and geochemistry of a suite of mafic rocks in Chencai area, South China: Implications for petrogenesis and tectonic setting

Paleozoic crust–mantle interaction and geodynamic setting of the South China Block have remained largely elusive due to the scarcity of mafic rock suites. Here we report data from a suite of mafic rocks including norite, mafic granulite, garnet-bearing amphibolite, biotite-bearing amphibolite, and amphibolite from the Chencai region in the northeastern Cathaysia Block of South China, that mostly record amphibolite to granulite facies metamorphism. U–Pb dating of zircons from the mafic granulite and biotite-bearing amphibolite show broadly coeval magmatism, and amphibolite- to granulite-facies metamorphism during 435–438Ma. The garnet-bearing amphibolite also records metamorphism at 436Ma and the magmatic age of its protolith is constrained to be between 436Ma and 496Ma. The norite has an emplacement age of 422Ma. Geochemically, the amphibolite and granulite have high Al2O3 contents and belong to the high-alumina group. The garnet-bearing amphibolite belongs to the intermediate-alumina group, whereas the norite and biotite-bearing amphibolite belong to the low-alumina group. A cumulate origin is proposed for the norite with orthopyroxene as the main cumulus phase. Based on their similar trace element and Lu–Hf isotopic signatures, it is inferred that the protoliths of amphibolite and granulite belonging to high-alumina group were likely generated from the same source. Furthermore, their LREE enrichment relative to HREE, positive Eu anomaly, and negative Nb, Ta and Zr anomalies suggest derivation from the same enriched mantle source, perhaps in a continental arc environment. Zircons from the garnet-bearing amphibolite belonging to intermediate-alumina group have high positive ɛHf (t) values with a peak of +14 and trace element signatures similar to N-MORB, suggesting a depleted asthenospheric mantle source. The rock suite from Chencai suggests formation in an active continental margin, with the garnet-bearing amphibolite representing relics of the Paleozoic oceanic crust in northeastern South China and the high- and low-alumina mafic rocks representing layered cumulates that developed in the arc root. The amphibolite to granulite facies metamorphism recorded by these mafic and supracrustal rocks of Chencai Complex is consistent with high heat flow in an arc root.

Magma Transfer and Evolution in Channels within the Arc Crust: the Pyroxenitic Feeder Pipes of Sapat (Kohistan, Pakistan)

Our understanding of the mode of transfer and evolution of arc magmas in the lower arc crust is limited by the accessibility of arc roots, which are mainly documented by remote geophysical methods. At the same time, the fractionation processes of primitive parental melts defining a liquid line of descent from basalt to dacite are well defined by experimental petrology. However, the structural evidence for transfer of magmas evolving during their ascent remains basically uncharacterized. The Sapat Complex represents a lower crust segment of the exhumed Kohistan paleo-island arc and exposes kilometer-sized pyroxenite bodies that grew at the expense of host metagabbroic sill sequences. The largest of these pyroxenite bodies are mainly composed of wehr-lite to olivine-clinopyroxenite, whereas the smaller bodies show a sequence of cumulative rocks, from ol-clinopyroxenite through various gabbros to tonalite. Inside the bodies, vertical magmatic and reactional structures indicate magma ascent accompanied by cumulate formation. Altogether, cumulates document the evolution of an initially primitive basaltic melt (at similar to 7 kbar) that contained >= 5wt % H2O. After cotectic olivine and clinopyroxene fractionation, the appearance of hornblende at the expense of clinopyroxene marks a stepping stone in the melt evolution. From this point, the appearance of orthopyroxene and hornblende at the expense of olivine drives the magma towards an andesitic composition, from which the crystallization of An-rich plagioclase and hornblende drives the melt to evolve further. During peritectic hornblende crystallization fluid-precipitated assemblages occur showing that the melts have reached water-saturation while they were crystallizing and percolating, thus degassing H2O-rich fluids. Structural observations, mineral and bulk-rock compositions, and calculated seismic P-wave velocities identify the ultramafic pipe-shaped bodies as magmatic conduits in which melt ascended from the mantle through the lower crust to feed upper crustal magma chambers and volcanic systems.

New mathematical formulations for calculating residual resistance in a static arc model of ice-covered insulators

This paper develops two new mathematical formulations for calculation of the residual resistance in a static arc model to predict ac and dc flashover voltages of heavy ice-covered insulators. In the first formulation, appropriate for dc with a small insulator string, the residual resistance is considered as a resistance between a small circular conductor where it models the arc root and the ground electrode. It is shown that using this new formula for a static dc arc model with heavy ice-covered insulators leads to an improved model to predict flashover voltage. In the second formulation, appropriate for ac and dc with long insulator strings, the residual resistance is considered as a resistance between two small circular conductors modeling two arc roots where the arcs are on air gaps formed near the high voltage and ground electrodes. The method of image charges is used in both formulations. The capability of this improved static arc model is confirmed when it is compared to that of previous static and dynamic models. This improved arc model has a better correspondence with the experimental results than the previous static and dynamic models. It can be used as a powerful tool for the design and selection of insulators subjected to ice accretion.

Cyclical processes in the North American Cordilleran orogenic system

Research Article| June 01, 2015 Cyclical processes in the North American Cordilleran orogenic system P.G. DeCelles; P.G. DeCelles 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar S.A. Graham S.A. Graham 2Department of Geological and Environmental Sciences, Stanford University, Stanford, California, 94305, USA Search for other works by this author on: GSW Google Scholar Author and Article Information P.G. DeCelles 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA S.A. Graham 2Department of Geological and Environmental Sciences, Stanford University, Stanford, California, 94305, USA Publisher: Geological Society of America Received: 26 Nov 2014 Revision Received: 13 Mar 2015 Accepted: 16 Mar 2015 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2015 Geological Society of America Geology (2015) 43 (6): 499–502. https://doi.org/10.1130/G36482.1 Article history Received: 26 Nov 2014 Revision Received: 13 Mar 2015 Accepted: 16 Mar 2015 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation P.G. DeCelles, S.A. Graham; Cyclical processes in the North American Cordilleran orogenic system. Geology 2015;; 43 (6): 499–502. doi: https://doi.org/10.1130/G36482.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract To understand linkages among processes that combined to build the North American Cordillera, we synthesize its tectono-magmatic history from the California accretionary wedge to the retroarc foreland of Wyoming. At this latitude, the Cordilleran magmatic arc experienced high-flux events (HFEs) at ca. 160–150 Ma and ca. 105–90 Ma. Retroarc shortening provided the main source of HFE magmas, which in turn created eclogitic arc roots that later foundered into the mantle and cleared the sub-arc region of excess mass, and provided space to accommodate renewed retroarc shortening. The forearc, arc, and retroarc regions all responded variably to this cycle of tectono-magmatic processes, and Laramide flat-slab subduction may have both disrupted and been enhanced by events within this cycle. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Arc Magmatic Tempos: Gathering the Evidence

Arc Magmatic Tempos: Gathering the Evidence

Spectral characteristics of arc plasma during laser-arc double-sided welding for aluminum alloy

In laser-arc double-sided welding, the spectral characteristics of the arc plasma are calculated and analyzed by spectroscopic diagnosis. The results show that, compared with conventional tungsten inert gas (TIG) welding, the introduction of a laser changes the physical characteristics of the arc plasma regardless of whether laser plasma penetration takes place, and that the influence of the laser mainly affects the near-anode region of the arc. When the laser power is relatively low, the arc column tends to compress, and the arc spectral characteristics show no significant difference. When the arc root constricts, compared with pure TIG arc, the electron density increases by ∼2.7 times and the electron temperature decreases by ∼3000 K. When the arc column expands, the intensities of spectral lines of both the metal and Ar atoms are the strongest. But it is also observed that the electron density reduces, whereas there is no obvious decrease of electron temperature. OCIS codes: 140.3390, 350.3390, 300.6170. doi: 10.3788/COL201513.061403.

Study of the Influence of External Environment to Arc Channel in Argon with Laminar Flow

A 3D model is used to simulate free burning arc, and the influence of external environment to arc channel are discussed. The commercial CFD code FLUENT is used to model the plasma and the solid anode part. The cross-flow (2m/s, 5m/s, and 10m/s) and external magnetic fields (2mT, 5mT, and 10 mT) are applied to deflect arc. And then the condition they work together have also be discussed. Because the mechanisms of the influence are different, they only influences are reflect on the arc root displacement. The influence of arc root displacement to potential drop has been explained.

Mechanisms and processes of arc propagation over an ice-covered surface

The general objective of this paper is to investigate the physical mechanisms and processes involved in the propagation of arc over the surface of ice. In the present research work, high-speed imaging and optical emission spectroscopy techniques were synchronized with the electrical measurements to study the various parameters of arc on an ice surface, i.e. channel radius, propagation velocities, arc column temperature and electron density. These results, together with observation of the propagation patterns and arc foot geometries, calculation of arc energy and the examination of the state of thermal equilibrium provide background information for understanding the ice-covered insulator flashover phenomenon. Arc root structure, current profile, propagation pattern and velocity were investigated under different type of applied voltage and different polarities. Water film conductivity and thickness, relative air humidity and the direction of arc propagation were also analyzed as influencing parameters of arc propagation. The effects of different possible mechanisms, e.g. collision and thermal ionization, buoyancy force and electrostatic force, on different stages of arc propagation has been discussed.

Modeling of AC flashover on ice-covered composite insulators with different shed configurations

The shed configuration has an obvious effect on flashover performance of ice-covered composite insulators. Based on the flashover arc path, a “multi-arc, multi-ice-layer” mathematical model is proposed to predict AC flashover voltages of ice-covered composite insulators with different shed configurations during the melting period. The model takes into account two different arc paths across the tip of each un-bridge icicle. Moreover, the arc across the air gap is distinguished from the arc on the ice surface, and the residual ice layer resistance is divided into icicle resistance, arc root resistance and shed surface ice resistance. In order to verify this model, four kinds of 220 kV composite insulators with different shed configurations are tested under different icing conditions. The theoretical results from the model are found to be in good agreement with the experimental results.

Thermal features of low current discharges and energy transfer to insulation surfaces

The thermal features of low current AC discharges, of between 2 and 5 mA, between water droplets are presented in this paper. The ‘Best-fit’ method of optical emission spectroscopy (OES) analysis is applied to measure the discharge temperature. The discharge temperature increased from 1200 K to 1500 K when the current level rose from 2.5 mA to 5 mA, and its temperature was less sensitive to arc length than arc current. Measurements of the distribution of temperature along a 4 mm discharge showed that the regions including the arc roots do not have a higher temperature than the discharge column, despite appearing brighter. The introduction of a silicone rubber insulation surface adjacent to the discharge increased the discharge temperature, typically by ~160 K, and its energy per half cycle by 150%. The resulting temperature distribution on the insulation surface was captured by infrared thermal imaging. Finite element analysis (FEA) software successfully simulated heat transfer between discharge and surface, and showed good agreement with experimental results: highest temperatures being seen under the centre of the arc, where damage is also first seen in practice. FEA can thus be used to model, for example, the impact of thermal conductivity on insulation surface temperature.

Dynamic Evolution of 50-Hz Rotating Gliding Arc Discharge in a Vortex Air Flow

A 50-Hz rotating (annular-mode) gliding arc plasma in a vortex air flow is generated. Its dynamic evolution has been investigated through the electrical measurements and highspeed imaging, which shows that the arc is formed after several breakdowns of the gas and then glides stably with a low-discharge current. The intensity of the light emitting from the arc root at the cathode is remarkably higher than that at other areas during the arc gliding.

Generation Process and Electric Arc Motion Characteristics of DC Vortex Gliding Arc Plasma

Generation process of vortex gliding arc plasma (VGAP) and corresponding motion characteristics of the electric arc are recorded and investigated by the macroscopic and microcosmic point of view. The generation of VGAP is divided into excitement, development, and stabilization stages, sorted according to the balance of input energy and heat dissipation. The periodic (~30 ms) development process and the shape of electric arc are influenced by gas flow field, and the arc roots on anode and cathode perform different. The thorough development and stretching of the electric arc of VGAP provide a good application prospect.

Characteristics of Secondary AC Arc Column Motion Near Power Transmission-Line Insulator String

Power system secondary ac arcs are plasma discharges in free space with dimensions in meters. The motion of secondary arcs was investigated experimentally using high-speed video on a 1-m scale with a 3-MVA source. The measurements that were evaluated imposed forces, including wind, effects of the arc root, as well as early-stage horizontal and late-stage vertical movement. Partial short circuits of the arc column were observed. The arc column elongated with the de-ionization effect being increased. The column approached a maximum length before the arc extinction. An arc chain model was applied to establish the governing velocity equation. Based on the proposed model, simulations agreed well with the physical experiments.

Composition and evolution of the Ancestral South Sandwich Arc: Implications for the flow of deep ocean water and mantle through the Drake Passage Gateway

The Ancestral South Sandwich Arc (ASSA) has a short life-span of c. 20m.y. (early Oligocene to middle–late Miocene) before slab retreat and subsequent ‘resurrection’ as the active South Sandwich Island Arc (SSIA). The ASSA is, however, significant because it straddled the eastern margin of the Drake Passage Gateway where it formed a potential barrier to deep ocean water and mantle flow from the Pacific to Atlantic. The ASSA may be divided into three parts, from north to south: the Central Scotia Sea (CSS), the Discovery segment, and the Jane segment. Published age data coupled with new geochemical data (major elements, trace elements, Hf–Nd–Sr–Pb isotopes) from the three ASSA segments place constraints on models for the evolution of the arc and hence gateway development. The CSS segment has two known periods of activity. The older, Oligocene, period produced basic–acidic, mostly calc-alkaline rocks, best explained in terms of subduction initiation volcanism of Andean-type (no slab rollback). The younger, middle–late Miocene period produced basic–acidic, high-K calc-alkaline rocks (lavas and pyroclastic rocks with abundant volcanigenic sediments) which, despite being erupted on oceanic crust, have continental arc characteristics best explained in terms of a large, hot subduction flux most typical of a syn- or post-collision arc setting. Early–middle Miocene volcanism in the Discovery and Jane arc segments is geochemically quite different, being typically tholeiitic and compositionally similar to many lavas from the active South Sandwich Island Arc front. There is indirect evidence for Western Pacific-type (slab rollback) subduction initiation in the southern part of the ASSA and for the back-arc basins (the Jane and Scan Basins) to have been active at the time of arc volcanism. Models for the death of the ASSA in the south following a series of ridge–trench collisions are not positively supported by any geochemical evidence of hot subduction, but cessation of subduction by approach of progressively more buoyant oceanic lithosphere is consistent with both geochemistry and geodynamics. In terms of deep ocean water flow the early stages of spreading at the East Scotia Ridge (starting at 17–15Ma) may have been important in breaking up the ASSA barrier while the subsequent establishment of a STEP (Subduction-Transform Edge Propagator) fault east of the South Georgia microcontinent (<11Ma) led to formation of the South Georgia Passage used by the Antarctic Circumpolar Current today. In terms of mantle flow, the subduction zone and arc root likely acted as a barrier to mantle flow in the CSS arc segment such that the ASSA itself became the Pacific–South Atlantic mantle domain boundary. This was not the case in the Discovery and Jane arc segments, however, because the northward flow of the South Atlantic mantle behind the southern part of the ASSA gave an Atlantic provenance to the whole southern ASSA.

Typical Motion and Extinction Characteristics of the Secondary Arcs Associated with Half-Wavelength Transmission Lines

Secondary arc discharge is a complicated physical phenomenon and one of the key fundamental issues associated with ultra high voltage (UHV) half-wavelength transmission lines (HWTL). With the establishment of a physical simulation platform for the HWTLs, experiments were carried out regarding the motion and extinction characteristics of secondary arcs. The cathode arc root and the anode arc root were found to show an obvious polarity effect while the arc column was moving in a spiral, due to their different motion mechanisms. The extinction behavior was also recorded and experiments were designed with different compensation conditions. Results show that the arcing time can be greatly reduced if there exists an electrical compensation network. The research provides fundamentals for understanding the physics involved, especially the motion and extinction mechanisms of the secondary arcs.