Metal transfer during vacuum consumable arc remelting

Zanner, F.J.

doi:10.1007/bf02652456

Cited by 32 publications

(14 citation statements)

References 17 publications

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“…Direct knowledge of the electric arc behaviour in the VAR process is based on visualization studies performed first at Sandia National Laboratories 7,8) during the remelting of steel or Ni-based superalloy electrodes. Similar experiments have been carried out more recently by Chapelle et al on zirconium electrodes.…”

Section: Introductionmentioning

confidence: 99%

Arc Behaviour and Cathode Melting Process during VAR: an Experimental and Numerical Study

et al. 2013

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The present study aims to understand the melting of the consumable electrode in the VAR process and gain some insight into the influence of an ensemble arc motion on the melting behaviour. In a previous study, a 2D axisymmetric model of the heat transfer in the cathode had been developed. Using the operating parameters as model inputs, it enabled prediction of the melt rate and the evolution of the melting area. Model results were successfully compared to melt rate measurements in an industrial VAR furnace. In recent years, it has been claimed that the electric arc may not be considered as steady and axisymmetric. Our experimental investigation of the luminosity recorded during an actual VAR heat confirms that a transient 3D behaviour may take place. Therefore, a 3D version of the previous model was set up to predict the heat transfer and melting of the electrode, using the unknown ensemble arc motion as an input. The arc is assimilated to a transient distribution of energy flux density. Results evidence that the influence of the arc motion on the shape of the electrode tip can be very important. In industrial practice, the cathode tip usually remains relatively flat during melting. The shapes of the computed electrode tips enable us to propose some arc parameters which remain compatible with both the periodic behaviour of the light emitted and the flatness of the electrode.

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Section: Introductionmentioning

confidence: 99%

Arc Behaviour and Cathode Melting Process during VAR: an Experimental and Numerical Study

et al. 2013

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“…The R(t) plots support the ion starvation argument for anode spot formation as evidenced by the low resistance at arc reignition in the absence of anode spike formation (drop short C of Figure 6) and decreased resistance after anode spike formation (short A of Figure 6). It is important to point out that significant metal transfer still has not occurred at arc reignition, but occurs -0.01 s latter by the magnetic pinch and kink mechanisms described above (13).…”

Section: Metal Transfermentioning

confidence: 99%

“…The formation and evolution of these protuberances is caused by gravitational forces and the spacing between the protuberances reflects the most unstable wavelength under the action of gravity, surface tension, and viscosity (13). Figure 5 illustrates the general growth sequence of small protuberances into spikes as taken from the experimental work of Emmons et al (14).…”

Section: Metal Transfermentioning

confidence: 99%

Vacuum ARC Remelting of Alloy 718

Zanner¹,

Williams²,

Harrison³

et al. 1989

Superalloys 718 Metallurgy and Applications (1989)

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Vacuum arc remelting (VAR) is the principal secondary melting process used to produce ingots for almost all wrought Alloy 718 applications.We will attempt, with this paper, to summarize our previous work along with other unpublished work as it applies to VAR of Alloy 718.. Successful application for a particular alloy/ingot diameter combination is believed to be dependent on achieving quasisteady thermal/ solutal conditions at the solidification interfaces. Local thermal environment is strongly influenced by fluid flows which in turn are driven by global temperature gradients (convection) and magnetohydrodynamic (MHD) forces created by the arc's current distribution.Quasisteady conditions are enhanced when the metal vapor arc is stabilized in the diffuse mode where it provides optimal melting efficiency, macrouniform heating, and axisymmetical fluid flows in the molten pool atop the ingot. Furnace conditions of low ambient gas pressures (< 0.01 torr) and short electrode gaps (~10 mm) stabilize the diffuse mode. A transition from convective to magnetically dominant fluid flow occurs in the pool atop the ingot between 6.6 and 7.6 kA for production size ingots. Constricted arcs are stabilized at elevated ambient gas pressures and electrode gaps. Under these arc conditions fluid flows become unsymmetrical with respect to the ingot axis, "shelf" forms on portions of the ingot periphery, and melting efficiency is decreased.Metal transfer occurs when molten columns hanging from the cathode tip are separated from the cathode by magnetic forces and subsequently drop into the molten pool in the form of 3-10 g blobs. Actual transfer events make up less than three percent of the total melt time.For gaps <15mm metal transfer events extinguish the arc for ms time intervals and the drop short frequency is inversely proportional to the gap. Models, useful for electrode gap control, have been constructed to quantify the relationship between drop short frequency and the independent variables arc current, CO pressure, and electrode gap.

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“…Drip-shorts are momentary arc interruptions that occur when a molten-metal protuberance hanging down from the electrode tip contacts the pool surface, thereby causing a short circuit. 17 Buehl's control technique involved lowering the electrode until a drip-short having a duration of 0.1-0.3 seconds was detected, whereupon the electrode was raised a preset distance to maintain a relatively small average electrode gap. In a continuation of this patent, Buehl proposed that better gap control could be achieved by simply stopping or slowing down the electrode ram speed when drip-shorts were detected, rather than reversing the electrode motion.…”

Section: Electrode-gap Controlmentioning

confidence: 99%

Controlling remelting processes for superalloys and aerospace Ti alloys

Melgaard

Williamson²,

Beaman³

1998

JOM

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Overview Melting TechnologiesRemelting is performed to facilitate the production of clean, fully dense, homogeneous castings of superalloys and aerospace titanium alloys and is crucial to the defectfree production of these important materials. Modern electroslag remelting and vacuum arc remelting control systems are closedloop, single input-single output systems that oversimplify the physical properties of the processes; the ever-increasing demand for cleaner, more highly engineered, chemically tuned alloys has pushed these control methodologies to their limit. A new generation of these controllers is being developed by the Specialty Metals Process Consortium and Sandia National Laboratories to answer the challenges of remelting control for the next generation of alloys; these control systems will use multiple sensor inputs and apply material-specific system and process models.

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Metal transfer during vacuum consumable arc remelting

Cited by 32 publications

References 17 publications

Arc Behaviour and Cathode Melting Process during VAR: an Experimental and Numerical Study

Arc Behaviour and Cathode Melting Process during VAR: an Experimental and Numerical Study

Vacuum ARC Remelting of Alloy 718

Controlling remelting processes for superalloys and aerospace Ti alloys

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