US3672428A - Power partition control for consumable electrode furnaces - Google Patents

Power partition control for consumable electrode furnaces Download PDF

Info

Publication number
US3672428A
US3672428A US694657A US3672428DA US3672428A US 3672428 A US3672428 A US 3672428A US 694657 A US694657 A US 694657A US 3672428D A US3672428D A US 3672428DA US 3672428 A US3672428 A US 3672428A
Authority
US
United States
Prior art keywords
electrode
oxide
mold
arc
molten pool
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US694657A
Other languages
English (en)
Inventor
Joseph W Tommaney
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Allegheny Ludlum Steel Corp
Original Assignee
Allegheny Ludlum Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Allegheny Ludlum Steel Corp filed Critical Allegheny Ludlum Steel Corp
Application granted granted Critical
Publication of US3672428A publication Critical patent/US3672428A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/16—Remelting metals
    • C22B9/20—Arc remelting

Definitions

  • ABSTRACT References Cited System for controlling the power division between the elec- UNITED STATES PATENTS trode molten pool in a consumable electrode furnace by the addition of metalllc compounds to the melt for the pur- 2,230,296 2/1941 Hopkins 1 64/52 pose of tabilizing the arc and shifting the power partition and 2,370,467 2/1945 Hopkins ..164/52 h t distribution between the electrode and molten p00], 2,825 1 at a] whereby the heat in the pool is reduced and that generated at 3,271 1 9/1966 Shelton et 1 64/52 the electrode to melt the same is increased.
  • the electrode is connected to one terminal of a direct current voltage source, while means are provided for electrically connecting the other terminal of the source to the mold and, hence, to the molten metal.
  • a small supply of chips or the like is placed in the mold so that when the arc is struck, such chips are meltedto form an initial molten metal supply in the crucible mold.
  • the arc is maintained between the electrode to be melted and the molten pool of metal beneath it such that the end of the electrode is melted due to the heat of the arc.
  • the electrode As the electrode is melted, it is deposited in the mold and forms the aforesaid molten pool, the bottom portion of which continuously solidifies as the'electrode melts to form an ingot which increases in length, starting from the bottom upwardly.
  • impurities float to and on top of the molten pool; and assuming that the pool does not solidify during the formation of the ingot, the major portion of the impurities will be excluded from the main body of the ingot.
  • the negative terminal of the direct current power supply is connected to the electrode.
  • This arrangement commonly referred to as straight polarity, leads to the development of a power partition whereby only a portion of the total power developed results in heat which consumes the electrode. The remaining power provides heat to the ingot or liquid pool in the ingot.
  • the power partition thus developed that is, the amount of heat distributed to the anode or cathode, depends upon the alloy or metal being melted. In most steels, that portion of the power represented by the total of the anode and cathode drops results in a power distribution of approximately 40 to 60 percent at the cathode (i.e., the electrode to be melted) with the balance of 60 to 40 percent at the anode.
  • One of the extreme cases is tungsten where the power distribution is such that approximately 90 percent of the power is developed at the anode compared to percent at the cathode.
  • the present invention seeks to provide a method for increasing the voltage drop at the electrode in a consumable electrode furnace while decreasing the voltage drop and excessive superheating at the pool beneath the electrode.
  • an object of the invention is to provide a method for increasing power concentration at the electrode of a consumable electrode furnace while decreasing the power concentration at the molten pool beneath it. This is achieved by the addition of a metallic compound to the pool and by reversing the normal polarity of a direct current potential applied between the electrode and the mold such that the mold is negative with respect to the electrode. This is in contrast to conventional arc furnaces wherein the electrode is negative with respect to the mold.
  • Another object of the invention is to provide a method of the type described wherein the metallic compound added to the molten pool is a metal oxide selected from the group consisting of barium oxide, calcium oxide, nickel oxide, thorium oxide, titanium dioxide, lanthanum oxide, strontium oxide, cerium oxide and cesium oxide.
  • Still another object of the invention is to provide a method for hot topping ingots in a consutrode furnace wherein the electrode is negative with respect to the molten pool beneath it, and wherein a metallic oxide is added to the molten pool immediately before hot topping begins. This signals the start of hot topping, reduces the arc voltage and stabilizes the arc to achieve ideal hot topping conditions.
  • a consumable electrode furnace of the type described above wherein an electrode is inserted into a mold and a potential established between the electrode and the mold whereby the heat developedat the electrode will cause it to melt and drop into a molten pool at the bottom of the mold.
  • a direct current potential is applied between the electrode and the mold such that the electrode is positive with respect to the mold.
  • a metal oxide preferably barium oxide but also including calcium oxide, nickel oxide, strontium oxide, titanium dioxide, lanthanum oxide, thorium oxide, cerium oxide and cesium oxide.
  • the normal power division between the electrode and the molten pool beneath it is about 50-50
  • the addition of the metal oxide and reversal of polarity results in percent or more of the heat being generated at the electrode.
  • This not only permits appreciably faster melting rates without the disadvantage of deep molten pools, but also permits the melting operation to be carried out at low pressure levels without incurring crucible damage.
  • yields are increased by reducing hot top losses; and the quality of the resulting ingot is increased.
  • the metal oxide is added to the melt by encasin g it within a metal tube which is welded to the side of the electrode such that it melts and deposits the oxide in the molten pool progressively during the entirety of the melting operation.
  • the oxide may be added in the form of a powder or granules during the initial stages of the melting operation or continuously during the melting operation, preferably the latter.
  • a metal oxide to the melt can also be used under straight polarity conditions to signal the start of a hot topping operation.
  • the oxide is preferably encased in a rod welded to the top of the electrode. When the arc reaches the area of the rod, the oxide is freed and drops into the molten pool, thereby stabilizing the arc and reducing arc voltage to achieve ideal hot topping conditions. This permits the current to be reduced to much lower levels than could be tolerated on conventional vacuum melts and results in the ideal condition of little or no melting of the electrode during hot topping.
  • the furnace comprises a conductive mold or crucible 12 which may, for example, be fabricated of copper. Covering the upper open end of the mold 12 is a gas-tight housing 14 having a connection 16 to means, not shown, for evacuating chamber 18 formed by the mold 12 and housing 14 covering it. Alternatively, the chamber 18 could be filled with inert gas; however in either case, the metal to be melted is protected from oxidation.
  • a water jacket 20 Surrounding the mold 12 is a water jacket 20 having inlet and outlet ports 22 and 24, respectively, connected thereto. The water jacket 20 is secured to the mold l2 and housing 14 by means of circumferentially spaced bolts 25 and suitable gaskets, substantially as shown.
  • the mold 12 contains the ingot 26 which solidifies from a molten pool 28 adjacent the lower end of an electrode 30 of the metal to be melted.
  • the electrode 30 is welded as at 32 to a stub shaft 34.
  • the stub shaft 34 is secured by means of an electrode clamp 36 to the lower end of a vertically reciprocable ram 38.
  • Any type of suitable electrode clamp 36 may be utilized in accordance with the invention; however one illustrative type is shown in U.S. Pat. No. 3,046,319.
  • While the ram 38 may be reciprocated by any one of a number of different mechanical drives, the system herein illustrated comprises a pair of hourglass rolls 40 and 42, the roll 42 being connected to a drive motor 44 through a mechanical linkage, schematically illustrated by the broken line 46.
  • the motor 44 is controlled by means of an arc voltage control circuit 48 which may, for example, comprise the usual arc voltage control system wherein the ram 38 is raised or lowered as a function of the total voltage existing across the arc between the bottom of electrode 30 and the molten pool 28.
  • a ram clamp 50 Surrounding the ram 38 is a ram clamp 50 connected through a first flexible cable or lead 52 to a source of direct current power 54. The other terminal of the power source 54 is connected through a cable or lead 56 to the-mold 12. Upon application of a direct current potential between the clamp 50 and the mold 12, an are or are plasma 58 is formed between the bottom of the electrode 30 and the molten pool 28.
  • the melt it is usual, in starting the melt, to place a small supply of chips or the like at the bottom of the mold 12 such that when the arc is struck, the chips are melted to form an initial molten metal supply in the crucible mold.
  • the arc is initially struck, it is maintained between the electrode to be melted and the molten pool beneath it, the electrode being melted due to the heat of the arc.
  • the electrode is moved downwardly by motor 44 to maintain the desired arc gap.
  • the position of the electrode 30 with respect to the pool 28 may be controlled in various ways; however, by way of illustration, the voltage existing between the clamp 50 and mold 12 (i.e., the arc voltage) may be applied to the arc voltage control circuit 48 via leads 60 and 62.
  • arc voltage normally means the total voltage drop across the furnace system. This would be the voltage read on a meter connected between leads 60 and 62. This total are voltage, however, is divided into parts according to the following equation:
  • V total are voltage existing between leads 60 and 62
  • V voltage drop at the anode (i.e., at the upper surface of the molten pool 28 on straight polarity)
  • V,. resistive voltage drops in the system.
  • V includes those voltage drops through leads 52 and 56, the clamp 50, ram 38, clamp 36, the electrode 30 itself and mold 12. In certain cases,
  • these voltage drops may be relatively high due to arcing and heating which occurs at the clamp 50 or electrode clamp 36, for example.
  • a 12- inch diameter, high-speed tool steel was vacuum melted on straight polarity (i.e., the electrode negative) under conventional conditions at a total are voltage, V,, of 25 volts and arc current of 4,000 amperes with a melt race of 5 pounds per minute.
  • the resistive voltage drops, V,, and the voltage drop in the arc plasma, V,, were determined by driving the electrode slowly into the pool.
  • the voltage decreased from the previous 25-volt level.
  • the voltage reached a value of 23.5 volts, it dropped immediately to a short-circuit value of 1 volt. From this, values of 1 volt for V, and 1.5 volts for V, can be assigned.
  • P,, P,,, P, and P represent the power generated due to resistive voltage drops, in the arc plasma, at the cathode and at the anode, respectively.
  • the heat generated in the pool 28 is reduced and that developed at the tip of the electrode 30 is increased for a given power input by reversing the normal polarity of the electrode with respect to the ingot and by adding to the melt a metallic oxide which is preferably barium oxide but which also can be calcium oxide, nickel oxide, strontium oxide, thorium oxide, titanium dioxide, lanthanum oxide, cerium oxide and cesium oxide.
  • the metallic oxide is packed into a tube, identified by the reference numeral 64 in the drawing, formed from the same metal as the electrode 30 itself. After the metallic oxide is packed into the tube 64, its ends are sealed and the tube swaged to consolidate the oxide and form what might be described as an inverse welding rod. Only a single rod my be utilized as shown in the drawing, or two or more rods may be used, depending upon requirements. As the electrode 30 melts, the rod 64 will also melt, thereby freeing the metal oxide which drops into the molten pool 28.
  • the effect of the oxide addition on power partition and arc stability is not proportional to its concentration. Heats made at a 0.007 percent oxide addition by weight of the ingot behave similarly to those melted at a 0.15 level. A heat made with 0.0016% BaO showed no effect on the arc. Generally speaking, the oxide addition should be at least 0.005 percent by weight, or enough to achievethe aforesaid power partition.
  • the pool 28 is now negative with respect to the electrode 30; and as the electrode drops into the pool it will, of course, be reduced, thereby releasing the metal which, it is theorized, changes the emission characteristics of the cathode such that electrons can more easily leave the cathode. Hence, the voltage and power developed in the pool 28 decreases while that developed at the tip of the electrode 30 increases.
  • an electrode 4% inches in diameter of Type A151 321 stainless steel was welded to the bottom of the ram 34 and the power source connected to the ram and the mold such that the mold was negative with respect to the electrode.
  • the metal oxide added was barium oxide; and this was packed into stainless steel tubes of about 0.25 inch outer diameter. The ends of the tubes were sealed and the tubes swaged to 0.125 inch outer diameter, thereby consolidating the barium oxide to produce a barium oxide content of 0.35 gram per inch. Two such rods were welded on the electrode 180 apart. The average melt rate was 3.5 pounds per minute and the vacuum level within the chamber containing the electrode was 1 micron.
  • the power distribution is, therefore, as follows:
  • cathode voltage decreases markedly with the additions.
  • Similar results are obtained with calcium oxide, nickel oxide, titanium dioxide, lanthanum oxide, cerium oxide and cesium oxide, with varying degrees of success.
  • calcium oxide does not produce results as good as those produced by thori- 0 um and strontium oxides; and nickel oxide and titanium dioxide are poorer than calcium oxide.
  • those oxides can be used which are good electron emitters (i.e., those compounds which make it easy for electrons to leave the cathode). It is also feasible to use combinations of the oxides enumerated above.
  • the oxide rods or other suitable addition method could be mounted on the side of the electrode at a point at which it was desired to start the hot top cycle. That is, the rods would be much shorter than rod 64 shown in the drawing and would preferably be welded to the top of the electrode 30. When the arc reaches this area, the nominal arc voltage of 25 volts would be reduced to the 10 to volt level, thus signaling the start of the hot top. The presence of the oxide also stabilizes the arc to such an extent that much lower current levels can be achieved with control. This coupled with the advantage of no electrode burn-off results in ideal hot top conditions.
  • barium oxide to the molten pool is also useful as a desulfurizer, ad in one heat of carbon steel, the sulfur was reduced from 0.021 to 0.011.
  • An additional benefit of using barium oxide is in the area of crucible protection. It was determined previously that vacuum consutrode melting on reverse polarity was effective in eliminating freckles in the resulting ingot, but resulted in damage to the crucible wall. It was subsequently shown that the use of argon gas above the bath in a quantity sufficient to pinch the are away from the crucible wall was sufficient to prevent this crucible damage and at the same time preserve the freckle-free condition. Chemical analyses of a number of heats in which the barium oxide addition was made indicate that the residual barium oxide level is less than 0.01 percent and does not materially affect the characteristics of the resulting ingot.
  • the steps comprising placing an end of an electrode formed from essentially non-oxide bearing metal within a mold, passing a direct electrical current between the electrode and the mold with the electrode positive with respect to the mold to establish a direct current are between the bottom of the electrode and the metal below it whereby the electrode is progressively melted from said end and is deposited in the bottom of said mold, the molten metal pool deposited in the mold progressively solidifying to build up an ingot, and during the melting cycle progressively adding to the molten pool from a point adjacent the electrode a metal oxide which governs the characteristics of the arc existing between the end of the electrode and said molten pool but which does not build up a substantial slag formation on the top of the molten pool, the addition of said oxide and the positive polarity of said electrode acting to concentrate the major portion of the heat of the are at the bottom of the electrode while reducing the heat generated at said molten pool.
  • metal oxide is selected from the group consisting of barium oxide, calcium oxide, nickel oxide, strontium oxide, thorium oxide, titanium dioxide, lanthanum oxide, cerium oxide and cesium oxide.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Plasma & Fusion (AREA)
  • Materials Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Furnace Details (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Nonmetallic Welding Materials (AREA)
  • Discharge Heating (AREA)
US694657A 1967-12-29 1967-12-29 Power partition control for consumable electrode furnaces Expired - Lifetime US3672428A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US69465767A 1967-12-29 1967-12-29

Publications (1)

Publication Number Publication Date
US3672428A true US3672428A (en) 1972-06-27

Family

ID=24789761

Family Applications (1)

Application Number Title Priority Date Filing Date
US694657A Expired - Lifetime US3672428A (en) 1967-12-29 1967-12-29 Power partition control for consumable electrode furnaces

Country Status (7)

Country Link
US (1) US3672428A (de)
AT (1) AT300223B (de)
BE (1) BE726122A (de)
DE (1) DE1811151A1 (de)
FR (1) FR1598672A (de)
GB (1) GB1240550A (de)
SE (1) SE356315B (de)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3905804A (en) * 1973-06-07 1975-09-16 Lukens Steel Co Method of decarburization of slag in the electroslag remelting process
US4131752A (en) * 1977-03-01 1978-12-26 Wooding Corporation Current conducting atmosphere control sleeve for electroslag furnace
US4729421A (en) * 1983-10-28 1988-03-08 Werner Schatz Method and device for the production of metal blocks, castings or profile material with enclosed hard metal grains
US5296667A (en) * 1990-08-31 1994-03-22 Flame-Spray Industries, Inc. High velocity electric-arc spray apparatus and method of forming materials
US5411611A (en) * 1993-08-05 1995-05-02 Cabot Corporation Consumable electrode method for forming micro-alloyed products
US5708677A (en) * 1995-04-21 1998-01-13 Sandia Corporation Arc voltage distribution skewness as an indicator of electrode gap during vacuum arc remelting
WO2015057888A1 (en) * 2013-10-15 2015-04-23 Retech Systems Llc System and method of forming a solid casting

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4204757C2 (de) * 1992-02-18 2001-02-15 Ald Vacuum Techn Ag Umschmelzofen

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3905804A (en) * 1973-06-07 1975-09-16 Lukens Steel Co Method of decarburization of slag in the electroslag remelting process
US4131752A (en) * 1977-03-01 1978-12-26 Wooding Corporation Current conducting atmosphere control sleeve for electroslag furnace
US4729421A (en) * 1983-10-28 1988-03-08 Werner Schatz Method and device for the production of metal blocks, castings or profile material with enclosed hard metal grains
US5296667A (en) * 1990-08-31 1994-03-22 Flame-Spray Industries, Inc. High velocity electric-arc spray apparatus and method of forming materials
US5442153A (en) * 1990-08-31 1995-08-15 Marantz; Daniel R. High velocity electric-arc spray apparatus and method of forming materials
US5411611A (en) * 1993-08-05 1995-05-02 Cabot Corporation Consumable electrode method for forming micro-alloyed products
US5846287A (en) * 1993-08-05 1998-12-08 Cabot Corporation Consumable electrode method for forming micro-alloyed products
US5708677A (en) * 1995-04-21 1998-01-13 Sandia Corporation Arc voltage distribution skewness as an indicator of electrode gap during vacuum arc remelting
WO2015057888A1 (en) * 2013-10-15 2015-04-23 Retech Systems Llc System and method of forming a solid casting
US9434000B2 (en) 2013-10-15 2016-09-06 Retech Systems, Llc System and method of forming a solid casting

Also Published As

Publication number Publication date
AT300223B (de) 1972-07-25
DE1811151A1 (de) 1969-08-07
GB1240550A (en) 1971-07-28
BE726122A (de) 1969-06-27
SE356315B (de) 1973-05-21
FR1598672A (de) 1970-07-06

Similar Documents

Publication Publication Date Title
US3775091A (en) Induction melting of metals in cold, self-lined crucibles
US4738713A (en) Method for induction melting reactive metals and alloys
US2085450A (en) Apparatus for producing metallic ingots
EP1045216B1 (de) Schmelzverfahren in einer Induktion-Kalt-Schmelz-Tiegelanlage
US3005246A (en) Method of producing high-quality ingots of reactive metals
US3672428A (en) Power partition control for consumable electrode furnaces
Bomberger et al. The melting of titanium
US3546348A (en) Non-consumable electrode vacuum arc furnaces for steel,zirconium,titanium and other metals and processes for working said metals
US3469968A (en) Electroslag melting
US3680163A (en) Non-consumable electrode vacuum arc furnaces for steel, zirconium, titanium and other metals and processes for working said metals
US2958719A (en) Production of metal
EP0073585A1 (de) Umschmelzverfahren für Legierungen
US2951890A (en) Method of operating an electric arc furnace
US4145562A (en) DC Arc furnace melt electrode
US3582528A (en) Treatment process
US4036278A (en) Process for the production of large steel ingots
US4167963A (en) Method and apparatus for feeding molten metal to an ingot during solidification
US3400206A (en) Consumable electrode stabilized against warping, formed from compacted refractory metal particles
US3615345A (en) Method for producing ultra-high purity metal
JPH0639635B2 (ja) 銅及び銅合金のエレクトロスラグ再溶融方法
US3617596A (en) Nonconsumable electrode vacuum arc furnace for steel, zirconium, titanium and other metals
US3708279A (en) Process of refining metal in a vacuum with coaxially mounted non-consumable electrodes
JPH02236232A (ja) チタン及びチタン合金の溶解、鋳造方法
Butler et al. Arc Melting in High-Vacuum Environments
US3410946A (en) Alternating current hot topping