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Title: Vacuum Arc Remelting Pool Power Control.

Abstract

Abstract not provided.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1148153
Report Number(s):
SAND2007-2656C
523205
DOE Contract Number:
AC04-94AL85000
Resource Type:
Conference
Resource Relation:
Conference: Proposed for presentation at the 2007 Int'l Symp. on Liquid Metal Processing and Casting held September 2-5, 2007 in Nancy, France.
Country of Publication:
United States
Language:
English

Citation Formats

Williamson, Rodney L, Melgaard, David Kennett, Beaman, Joseph J., Aikin, Robert M., and Erdmann, Robert G. Vacuum Arc Remelting Pool Power Control.. United States: N. p., 2007. Web.
Williamson, Rodney L, Melgaard, David Kennett, Beaman, Joseph J., Aikin, Robert M., & Erdmann, Robert G. Vacuum Arc Remelting Pool Power Control.. United States.
Williamson, Rodney L, Melgaard, David Kennett, Beaman, Joseph J., Aikin, Robert M., and Erdmann, Robert G. Sun . "Vacuum Arc Remelting Pool Power Control.". United States. doi:. https://www.osti.gov/servlets/purl/1148153.
@article{osti_1148153,
title = {Vacuum Arc Remelting Pool Power Control.},
author = {Williamson, Rodney L and Melgaard, David Kennett and Beaman, Joseph J. and Aikin, Robert M. and Erdmann, Robert G.},
abstractNote = {Abstract not provided.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2007},
month = {Sun Apr 01 00:00:00 EDT 2007}
}

Conference:
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  • Accurate control of the electrode gap in a vacuum arc remelting (VAR) furnace has been a goal of melters for many years. The size of the electrode gap has a direct influence on ingot solidification structure. At the high melting currents (30 to 40 kA) typically used for VAR of segregation insensitive Ti and Zr alloys, process voltage is used as an indicator of electrode gap, whereas drip-short frequency (or period) is usually used at the lower currents (5 to 8 kA) employed during VAR of superalloys. Modem controllers adjust electrode position or drive velocity to maintain a voltage ormore » drip-short frequency (or period) set-point. Because these responses are non-linear functions of electrode gap and melting current, these controllers have a limited range for which the feedback gains are valid. Models are available that relate process voltage and drip-short frequency to electrode gap. These relationships may be used to linearize the controller feedback signal. An estimate of electrode gap may then be obtained by forming a weighted sum of the independent gap estimates obtained from the voltage and drip-short signals. By using multiple independent measures to estimate the gap, a controller that is less susceptible to process disturbances can be developed. Such a controller was designed, built and tested. The tests were carried out at Allvac Corporation during VAR of 12Cr steel at intermediate current levels.« less
  • There are several process variables which are crucial to the control of vacuum arc remelting of segregation sensitive alloys. These are: electrode gap, melt rate, cooling rate, furnace annulus, furnace atmosphere and electrode quality (i.e. cleanliness and integrity). Of these variables, active, closed loop control is usually applied only to electrode gap. Other variables are controlled by controlling furnace operational parameters to preset schedules (e.g. melting current is ramped or held constant to control melt rate in an open loop fashion), through proper maintenance and calibration of equipment (e.g. to ensure proper cooling water and gas flow rates, or tomore » accomplish an acceptable vacuum leak rate), through proper practice of procedures, and by maintaining electrode quality control. Electrode gap control is accomplished by controlling an electrode gap indicator such as drip-short frequency (or period) to a specified set-point. This type of control, though often adequate, ignores information available from other electrode gap indicators and is susceptible to upsets. A multiple input electrode gap controller is described which uses optimal estimation techniques to address this problem.« less
  • No abstract prepared.
  • Observations have been made using high speed color photography of the vacuum arc and electrode surfaces during vacuum consumable arc remelting of a maraging steel alloy. Events on the film are coordinated with electrical signals from the vacuum arc. Based upon electrical observations, it was concluded in a previous investigation that metal transfer occurs when liquid metal spikes hanging from the cathode form a low resistance bridge (drop short) by touching the anode and then subsequently rupture. This recently proposed mechanism was visually verified with the exception that actual column rupture occurs after arc re-ignition and not at the instantmore » of re-ignition. Observations have also shown that cathode spot accumulation (attack) plays an important role in impeding metal transfer and that transfer occurs primarily by a bulk type process. Thus, inclusions and any solid particles are transferred with the bulk.« less