US3352665A - Degassing of melts - Google Patents

Degassing of melts Download PDF

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Publication number
US3352665A
US3352665A US429396A US42939665A US3352665A US 3352665 A US3352665 A US 3352665A US 429396 A US429396 A US 429396A US 42939665 A US42939665 A US 42939665A US 3352665 A US3352665 A US 3352665A
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United States
Prior art keywords
stirrer
melt
stirring
power
during
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Expired - Lifetime
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US429396A
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English (en)
Inventor
Stenkvist Sven-Einar
Hanas Bertil
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ABB Norden Holding AB
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ASEA AB
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Publication date
Application filed by ASEA AB filed Critical ASEA AB
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum

Definitions

  • the present invention relates to a method of degassing melts of metal or metal alloys, suc-h as steel, in which a container such as a ladle or a furnace containing a melt is enclosed in a vacuum tight tank or is provided with a vacuum tight cover which vacuum tight space is evacuated to a pressure below 50 torr, preferably below 20 torr.
  • the tank (space) is normally evacuated to a pressure of about 0.1 torr and during the first part of the vacuum treatment gas bubbles rise quickly to the surface of the melt and are then evacuated from the tank. It has been proved, however, that by this method, because of the hydrostatic pressure in the melt, the parts of the melt lying near the bottm of the ladle are not reached, and therefore are not subjected to the treatment. In order to remedy this, different ways have been tried to effect surface exchange in the melt, amongst others by applying an electro-magnetic stirrer, generally placed vertically at the side of the ladle.
  • the surface of the melt can be heated, for example by arcs or by a cover enclosed over a ladle with a heating means and because of the stirring thus quickly produces an even temperature in the whole melt in spite of the great depth. If it is desired to have the amount of degassing as complete as possible in order to have a high quality in the end product, it is necessary to take steps which further increase the degassing effect even during the final part of the treatment.
  • the present invention relates to a process which increases the degassing effect and which considerably shortens the degassing time.
  • a container (ladle, furnace or the like) is enclosed in a vacuum tight tank which is evacuated to a pressure suitably of about 0.1 torr, and the melt is stirred by means of an electro-magnetic, low frequency multiphase stirrer.
  • the invention is characterised in that during the first part of the vacuum treatment the energy supplied to the stirrer remains low, after which during the intermediate part the stirring energy is increased, and during the last part the stirring energy is further increased.
  • the gas inclusions which previously could not be lce reached during the stirring can now be brought to or in the vicinity of the melt surface, so that these can also be removed from the melt, for example the steel melt.
  • the power is kept low during a third of the treatment, for example less than half the rated power, after which the power is increased to full rated output for a third of the whole process, and the power is further increased during the final third of the treatment.
  • the first part of the treatment gas bubbles spontaneously escape from the melt, including the lower parts of the melt, whereby the rising gas bubbles themselves effect fast stirring, and the power fed to the stirrer can be kept low.
  • the power is increased to about normal power whereby a considerable movement of the melt is effected by the stirring, so that good degassing is produced.
  • FIG. 1 shows stirring under vacuum according to the invention.
  • FIG. 2 shows the relationship between the ratios of the necessary generator power to frequency and the corresponding stirring power to frequency respectively.
  • FIG. 1 a ladle 11 with a stainless steel wall is shown (a ferro-magnetic wall would lower the stirring power), containing a steel melt 12.
  • a vacuum tank 16 is connected Vacuum tightly at 13 and provided with at least one evacuating conduit 14 going to an evacuating pump, not shown.
  • the ladle on base 15 is placed inside the tank and the vacuum is raised.
  • the stirrer is enclosed in a casing of nonmagnetic stainless steel connected with the atmosphere (at 19) and with the chamber inside the tank 16 by a valve 28 opening and closing ata certain pressure.
  • a cooling fan 20 is used, intended to blow cool air along and/or through the stirrer 1-7.
  • the vair ducts 19 to the stirrer 17 and cooling fan 20 (21) can be provided with covers 22, 23, in order to maintain a certain vacuum and/ or to keep a closed cool air circulation during the degassing process itself.
  • the stirrer 17 consists usually of a rod v24 and a core 25 and is provided with longitudinal cool air ducts.
  • the electrical energy is produced from a generator (not shown) over cables 26, drawn through the vacuum tight inlets 27.
  • a strong current of rising gas bubbles is produced in the vacuum for the reason given above, which simplifiesv the stirring so that for a certain time, for example for 5 minutes, a lower power can be fed to the stirrer by using a lower voltage.
  • the frequency is kept at aboutl cycle per second during the whole treatment process.
  • the evacuation of gas inclusions in the melt proceeds easily during this first phase ⁇ of the vacuum treatment.
  • the voltage over the stirrer power output
  • the stirring power from the stirrer is increased, whereby a lively evacuation of gas can be maintained.
  • the power output in the stirrer is increased to more than 25% above the rated power, ⁇ suitably about 70% above the rated power during a further 5 minutes, so that the degassing can be maintained, and the quality of the degassed melt can be further improved.
  • this final phase higher cooling can be required, which can easily lbe ⁇ effected by increasing the number of turns of the fan 20 orby coupling in a further fan or the like.
  • the evacuation is stopped, the vacuum is eliminated, the tank 16 is opened and the melt is brought to a tapping place (not shown).
  • the frequency as mentioned will be kept between 0.2 and 1'0 cycles per second, suitably 0.3-1.5 cycles per second.
  • the rated power for the generator of the stirrer is 250-2000 kva., suitably 750-900 kva. and the melt content should lie between 15 and 200 tons/ ladle,
  • stirrer As mentioned the power increases on the stirrer (stirrers) are made intermittently in three steps, but it is also possible, of course, to make this more or less continually. It is even feasible to apply the method according to the invention to another container containing a melt, for example to are furnaces, so that vacuum can suitably be effected between the furnace and a cover closing vacuum ⁇ tightly against it. It is, of course, possible to produce an increase of the stirring by also altering the stirring frequency, which necessitates more complicated current producing devices.
  • the diagram according to FIG. 2 shows by curve S the relation between the necessary generator power S and frequency, and by curve P the corresponding relation between the stirring power measured in kiloponds (kilograms force) and the frequency.
  • Method for degassing melts of metal or metal alloys which comprises placing the melt in a container, placing the container in a vacuum tight tank, evacuating said tank to a pressure of less than 20 torr, stirring said melt by means of an electromagnetic stirrer fed with a multiphase ⁇ current of a frequency less than 10 cycles per second, and during a first interval of the stirring feeding a relatively ⁇ low power to the stirrer, during an intermediate interval of the stirring feeding a larger power to the stirrer than during said first interval, during a last interval of the stirring feeding a further increased power to the stirrer.
  • a method as claimed in claim 1 feeding to the stirrer during said first interval a power not larger than half the rated power of the stirrer, feeding to the stirrer during said' intermediate interval a power of about the rated power of the stirrer, feeding to the stirrer during the last interval a power at least 25% more than the rated power of the stirrer.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Furnace Details (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)
US429396A 1964-02-05 1965-02-01 Degassing of melts Expired - Lifetime US3352665A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SE1378/64A SE311051B (enExample) 1964-02-05 1964-02-05

Publications (1)

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US3352665A true US3352665A (en) 1967-11-14

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US429396A Expired - Lifetime US3352665A (en) 1964-02-05 1965-02-01 Degassing of melts

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US (1) US3352665A (enExample)
DE (1) DE1458803B1 (enExample)
FR (1) FR1423440A (enExample)
GB (1) GB1090152A (enExample)
SE (1) SE311051B (enExample)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3452973A (en) * 1965-12-29 1969-07-01 Nippon Kokan Kk Vacuum degasifying apparatus with electromagnetic stirring means
US4427443A (en) 1979-11-28 1984-01-24 Etude Et Developpement En Metallurgie Process and apparatus for automating a vacuum degasification cycle for metal alloys
US20110140318A1 (en) * 2009-12-10 2011-06-16 Reeves Eric W Molten metal containment structure having flow through ventilation

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2071942A (en) * 1933-08-30 1937-02-23 Heraeus Vacuumschmelze Ag Method of manufacturing iron alloys
US3230073A (en) * 1962-07-20 1966-01-18 Asea Ab Process for vacuum degassing with electromagnetic stirring
US3239204A (en) * 1963-02-05 1966-03-08 Pennsalt Chemicals Corp Vacuum degassing apparatus
US3240588A (en) * 1961-01-09 1966-03-15 Finkl & Sons Co Method and apparatus for treating molten metal

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2071942A (en) * 1933-08-30 1937-02-23 Heraeus Vacuumschmelze Ag Method of manufacturing iron alloys
US3240588A (en) * 1961-01-09 1966-03-15 Finkl & Sons Co Method and apparatus for treating molten metal
US3230073A (en) * 1962-07-20 1966-01-18 Asea Ab Process for vacuum degassing with electromagnetic stirring
US3239204A (en) * 1963-02-05 1966-03-08 Pennsalt Chemicals Corp Vacuum degassing apparatus

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3452973A (en) * 1965-12-29 1969-07-01 Nippon Kokan Kk Vacuum degasifying apparatus with electromagnetic stirring means
US4427443A (en) 1979-11-28 1984-01-24 Etude Et Developpement En Metallurgie Process and apparatus for automating a vacuum degasification cycle for metal alloys
US20110140318A1 (en) * 2009-12-10 2011-06-16 Reeves Eric W Molten metal containment structure having flow through ventilation
CN102812319A (zh) * 2009-12-10 2012-12-05 诺维尔里斯公司 具有流通通风的熔融金属容纳结构
US8883070B2 (en) * 2009-12-10 2014-11-11 Novelis Inc. Molten metal containment structure having flow through ventilation

Also Published As

Publication number Publication date
GB1090152A (en) 1967-11-08
SE311051B (enExample) 1969-05-27
FR1423440A (fr) 1966-01-03
DE1458803B1 (de) 1970-12-10

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