US3397874A - Soaking pit and method of operating the same - Google Patents

Soaking pit and method of operating the same Download PDF

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Publication number
US3397874A
US3397874A US590265A US59026566A US3397874A US 3397874 A US3397874 A US 3397874A US 590265 A US590265 A US 590265A US 59026566 A US59026566 A US 59026566A US 3397874 A US3397874 A US 3397874A
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United States
Prior art keywords
furnace
cover
air
pressure
pit
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Expired - Lifetime
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US590265A
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English (en)
Inventor
Augustine Alfred
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Loftus Engineering Corp
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Loftus Engineering Corp
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Publication date
Application filed by Loftus Engineering Corp filed Critical Loftus Engineering Corp
Priority to US590265A priority Critical patent/US3397874A/en
Priority to FR120831A priority patent/FR1548440A/fr
Priority to ES345653A priority patent/ES345653A1/es
Priority to GB45734/67A priority patent/GB1205801A/en
Priority to ES346255A priority patent/ES346255A1/es
Priority to SE14524/67A priority patent/SE333159B/xx
Priority to NO67170262A priority patent/NO119417B/no
Application granted granted Critical
Publication of US3397874A publication Critical patent/US3397874A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/70—Furnaces for ingots, i.e. soaking pits

Definitions

  • a soaking pit having a cover is provided that is movable horizontally from a position over the pit to a position clear of the pit without the necessity of also raising and lowering the cover as is the case where conventional sand seals are employed.
  • An air duct system extending around the gap projects a high velocity curtain of air across the gap in such manner as to form a pressure barrier against the escape through the gap of furnace gases but the air flows outwardly around the outer periphery of the gap, and not into the furnace.
  • the invention not only eliminates the usual sand seals and the need for raising or lowering the cover, but provides a new method of operating a soaking pit since higher pressures can be maintained under the cover than with sand seals, making it possible to maintain a positive pressure inside the pit from the cover to the level of the pit bottom.
  • This invention relates to industrial furnaces of the type known as soaking pits, in which metal ingots are heated to rolling temperature, and to the method of operating such furnaces.
  • Soaking pits have a bottom, and enclosing walls, and they are provided with a cover which is movable from a position over the furnace to a position clear of the top to enable ingots to be placed in the furnace or removed therefrom.
  • the cover is suspended from a carriage by which it is traversed into and out of position over the furnace, and the suspension is of a type which enables the cover to be lowered after it is brought into position over the furnace and lifted clear of the furnace when it is to be moved from over the furnace.
  • the top of the furnace is provided about its periphery with a trough to retain sand and the cover has sealing plates depending from its periphery that penetrate the sand in the trough to form a seal between the cover and the top of the furnace when the cover is in closed position.
  • the raising of the cover before moving the carriage is made necessary so that the sealing plates will first be lifted clear of the sand seal and furnace walls. Whether the furnace is completely opened or only partially opened, this lifting of the cover is necessary.
  • the burner arrangements for these furnaces vary with the shape of the pit. These furnaces are usually rectangular and in recent practice have one-way firing with a fuel burner or burners firing horizontally through one end wall above the ingot charge. Burned gas outlet ports are located below the burner in the same end wall. In some cases they have two-way firing where there are burners and burned gas outlet ports below the burners in both end walls. In any case, because the ingots are charged into and removed vertically from the top, the outlet for burned gases is not through the cover.
  • the zero level in a pit fifteen feet in depth is about 7.5 feet below the cover when the pressure at the level of the top is of the order of .09 inch of water.
  • the zero pressure level is fifteen feet below the cover and the entire furnace would be at positive pressure.
  • the same conditions may be figured of course for other depths. It will therefore be seen that by increasing the pressure at the top of the furnace, a point may be reached where the entire interior of the furnace is at atmospheric pressure or above.
  • a further phenomenon of these furnaces is the pulsating character of the flame. Recording devices that register pit furnace pressure fluctuate rapidly, tracing a continuous sinuous path a half inch or more in width. This reflects a condition where the automatic furnace pressure control damper must continuously hunt to maintain even pressure conditions in the furnace.
  • the present invention has for its principal object to provide a seal for soaking pit covers and a method of operation which will enable higher pressures to be maintained in the pit without the escape of flames from under the cover or the inflow of air into the furnace, and which will substantial-1y reduce the amplitude of furnace pres sure pulsations, providing improved stability of the furnace pressure control.
  • a further object is to eliminate sand seals and sealing plates, and in so doing eliminate the need for raising and lowering the cover, thereby also substantially reducing the cost of the carriage and cover arrangement and reducing the time cycle for opening or closing the furnace.
  • a further object is to provide a seal which may be applied to existing pits as well as to new construction and will reduce the cost of seal maintenance. Moreover it may be adjusted to meet the irregularities in the covers or wall conditions of diflerent furnaces due to camber or sag in the covers or erosion of refractory at the top of the furnace.
  • the cover is maintained at all times at a substantially fixed level above the top surface of the furnace wall, this surface being commonly referred to as the curb or coping.
  • the usual sand trough around the curb and seal plates on the cover are omitted.
  • the air curtain is generated by a duct system around the periphery of the furnace or cover, preferably the cover, to which air under pressure is supplied.
  • This duct system is comprised principally of longitudinally-slit pipe sections with means for adjusting the width of the air discharge slit in each section, and each section is desirably independently rotatable about its axis to adjust the angle of discharge of air therefrom. This is made possible by having the ends of each pipe section received in connectors or plenums through which air under pressure is introduced into the duct system at intervals therearound.
  • FIG. 1 is a side elevation of a soaking pit, cover and cover carriage wherein the soaking pit is shown in longitudinal section and the cover is shown in side elevation, portions of the pit and cover being broken away to better illustrate the invention;
  • FIG. 2 is a top plan view of the cover and air supply system detached from the carriage;
  • FIG. 3 is an end view of FIG. 1 with only a portion of the carriage being illustrated, the top only of the furnace walls being shown in section;
  • FIG. 4 is a schematic view showing one arrangement of the air duct system removed from the cover
  • FIG. 5 is an enlarged detail of the connection between one of the air supply ducts and the duct system around the cover, the view being partly in section and partly in elevation;
  • FIG. 6 is an enlarged section through one of the slit pipes of the duct system with the outline of the top of the furnace wall and the adjacent part of the cover, the section being in the plane of line VI-VI of FIG. 2;
  • FIG. 7 is a detail view showing an end view of one of the slit pipes.
  • FIGS. 1 and 3 of the drawings there is illustrated more or less schematically a soaking pit furnace of rectangular shape having a bottom 2, end walls 3, and side walls 4 which are formed prinicpally of refractory, and which enclose the furnace pit 5.
  • a layer of loose refractory material 6 over the bottom of the furnace on which the ingots or similar objects to be heated are set.
  • the end walls and side walls terminate in a substantially flat level surface, herein sometimes referred to as the coping or curb.
  • the cover designated generally as 7 is suspended by links 8 from an overhead carriage 9 that has wheels 10 for movement along a track 11 at each side of the furnace.
  • the cover designated generally as 7 is suspended by links 8 from an overhead carriage 9 that has wheels 10 for movement along a track 11 at each side of the furnace.
  • the cover 7 itself comprises a rectangular steel framework that includes longitudinally-extending side beams 12 and cross beams 13 at each end.
  • the steel framework which may take various forms, supports a continuous refractory cover-forming body only fragmentarily indicated at 15 in FIGS. 2 and 6.
  • the cover when it is in closed position, is over the open pit with the sides and ends of the covers projecting part way over the coping or rim of the furnace, and spaced above it an average distance under ideal conditions of about 1 /2 inches. In practice this distance may vary since the length of the pit is usually in excess of 20 feet, and of somewhat lesser width. Under these conditions the metal framework will be subject to expansion and contraction, and it is customary in the art to put a bow or camber in the beams 12 and to a less extent in the cross beams 13 so that when the cover is cold it bows upward to a slight extent, and as it elongates under increased temperature it may therefore straighten without sagging. By reason of this and by reason of erosion or spalling that may occur along the rim of the furnace this distance of 1 /2 inches does not remain ideally constant and may vary from point to point along the length and width of the furnace.
  • a duct system supported on the under side of the structural members 12 and 13 and recessed so that the duct is shielded by the cover from exposure to heat radiated from the interior of the furnace through the gap between the cover and furnace rim.
  • This system is comprised principally of pipe sections 16 having a longitudinal slit 17 therealong. This is best shown in FIG. 6.
  • At intervals along the length of each pipe section there are diametrically-extending bolts 18 with nuts at one end thereof.
  • Wedges may be used in the slits 17 to gauge the degree of closing or opening.
  • One end of each pipe section is closed as indicated at 19 in FIG. 4, while the other end is received in a gland portion 20 of a connector 21 which also constitutes a plenum chamber.
  • a connector 21 which also constitutes a plenum chamber.
  • there are two of these split pipe sections at each end of the cover extending horizontally from the connector 21 at the middle of the cover.
  • At each side of the cover there are two of these connectors 21, each with two pipe sections 16, one of which extends in a direction opposite the other.
  • the connectors 21 may each have a series of small openings 21a in closely-spaced relation arranged in a row along the bottom of the connector.
  • each connector 21 has a down pipe 22 secured thereto, each down pipe forming the terminal portion of a feeder line 23 leading from a plenum chamber 24 that is positioned on the cover.
  • a butterfly valve or other flow control valve 25 in each of these feeder pipes, these valves being here shown as being at the tops of the respective down pipes 22.
  • each connector 21 supplies air to two split duct sections 16 and there is a separate feeder pipe leading from the plenum chamber 24 to each connector.
  • this angle is approximately 30 off vertical so that the resulting curtain of air is not vertical, but projects inwardly under the cover.
  • the air encounters the curb, it appears that a substantial part at least is deflected upwardly and inwardly, its kinetic energy being transformed to pressure, thereby forming a barrier or dam in the gap between the inner and outer peripheries of the gap between the two confronting surfaces. The air then escapes to the outer periphery of the gap.
  • This pattern of air flow is evidenced by a visible demarcation between refractory on the furnace rim being at a visibly glowing temperature along a line inwardly in the gap from the line where the air actually impinges on the rim at some point between the air curtain and the inner periphery of the gap.
  • a piece of paper held in the stream of outflowing air at the edge of the curb is not charred by the air, although it may, after a period of several minutes, become charred primarily from the radiation of heat from the interior of the furnace. Likewise ones hand may be brought close to this position without serious discomfort.
  • the arrangement above described was applied to a pit having an overall depth of about 14 ft. on the bottom of which was placed a layer of granular magnesite about 15 in. in depth.
  • the pit was of rectangular shape having an interior length of 27 ft. and a width of 9 ft.
  • the cover from the center line of the pipe 16 at one end to the center line of the pipe 16 at the other end was approximately 29 ft. 2 in. and the width of the cover from thecenter line of pipe 16 at one side to the center line of the corresponding pipe at the other side was 11 ft. 2 in.
  • the perimeter of the cover overhangs the perimeter of the rim, but not to the full outer periphery of the furnace walls which were of such thickness that they extended outwardly beyond the center lines of the pipes or ducts 16 at both the sides and ends, in the relationship shown in FIG. 6.
  • the overall length of the combined pipes 16 and the connectors representing the perimeter of the cover at the center line of the pipes 16 was about 80 ft. 8
  • the pipes constituting the duct system around the periphery of the cover were 3 in. inside diameter, and the maximum opening of the slot was /8 in.
  • the inside diameter of the feeder and down pipes was 4 in.
  • the openings 21a in the connectors were about A; in. spaced about one diameter apart.
  • the pipes 16 at the corners practically abut so that there is no break in the air curtain.
  • the blower was driven by a 7 /2 horsepower motor operating at a speed of 3600 rpm. and was rated to produce 2300 c.f.m. at oz. pressure in the plenum 24, and in this example was so operated.
  • the valves 25 between the feeders and the down legs 22 were adjusted to provide a pressure in each of 3.5 oz. and an internal static pressure was maintained in the pipes 16 of 2.3 oz.
  • the furnace was operated with a charge of ingots in the usual manner.
  • the curb had been spalled in some places and the cover, upon heating, developed uneven spacing between the cover and the curb, but in general the distance of the gap separating the cover and furnace curb was about 1 /2 in. In no case was the space more than 3 in.
  • the shape and dimensions of the furnace above described is typical of most soaking pit furnaces. Generally they are rectangular and generally they range between 10 and 15 ft. in depth so that the conditions of operation in the above example would be applicable to most soaking pits. For soaking pits of greater depth than 15 ft., one skilled in the art may be. required to make some changes. A deep pit, for example, may have greater dimensions in which greater fan capacity would be required to maintain the desired velocity of the air curtain, but on the basis of the information herein given, one skilled in the art would have no difficultay in adapting such a furnace for the practice of the invention.
  • the invention simplifies the construction of the carriage and cover because of the elimination of expensive hoisting mechanism for raising and lowering the cover which in itself weights several tons, since the cover can be traversed without any vertical movement being necessary. Time lost in repeated raising and lowering of the cover is eliminated. Closer integration between the carriage and cover becomes possible to a point where they may be combined into a unitary structure in new furnace construction.
  • a soaking pit comprising a pit furnace having a bottom and surrounding walls forming an enclosure in which objects are placed to be heated
  • a cover structure coextensive with the area of the enclosure and projecting over the rim of the furnace walls when it is in closed position for confining combustion gases therebeneath
  • said cover-supporting means being arranged to hold the cover in closed spaced relation to the rim when the cover is in furnace-closing position whereby there is a continuous open gap under the cover above the rim of the furnace, and
  • connectors for delivering air to said pipes, feeder pipes leading to the connectors
  • a soaking pit having an open top furnace with a bottom and vertical walls enclosing a pit, and a cover that is supported for movement from a position over the furnace to a position clear of the open top of the furnace with the cover at a level spaced from the top of the furnace, there being spaced confronting surfaces on the cover and top of the furnace walls when the cover is over the furnace, with a gap around the furnace ranging between about 1 /2 inches and 3 inches between the confronting surfaces
  • a duct system arranged to project a curtain of air across the gap between the top of the furnace structure and the cover inwardly at an angle to a direction normal to the confronting surfaces entirely into the gap about the perimeter of the walls and cover when the cover is positioned over the furnace
  • said means comprising a series of separate pipe sections, each section having a longitudinal slit extending therealong,
  • a furnace having a bottom and vertical refractory walls enclosing a pit with the tops of the vertical walls providing a rim surface around the entire periphery of the furnace, the furnace having a refractory cover for the pit supported for movement into and out of operative position over the pit, the cover having a peripheral surface which extends over the rim surface of the side Walls in spaced confronting relation thereto when the cover is in operative position providing a peripheral gap between said surface, the invention comprising:
  • a duct means extending around the furnace arranged to discharge an effectively continuous curtain of air therefrom across the gap from one confronting surface toward the other at a velocity suflicient to impinge against the opposite confronting surface and at an inwardly-directed angle such that it impinges said confronting surface between the inner and outer boundaries of the gap, whereby the kinetic energy of the air is converted to pressure to block the escape of furnace gases while the air escapes outwardly from the gap,

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatments In General, Especially Conveying And Cooling (AREA)
  • Working Measures On Existing Buildindgs (AREA)
  • Furnace Details (AREA)
  • Heat Treatment Of Articles (AREA)
US590265A 1966-10-28 1966-10-28 Soaking pit and method of operating the same Expired - Lifetime US3397874A (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
US590265A US3397874A (en) 1966-10-28 1966-10-28 Soaking pit and method of operating the same
FR120831A FR1548440A (enrdf_load_html_response) 1966-10-28 1967-09-13
ES345653A ES345653A1 (es) 1966-10-28 1967-09-20 Metodo para hacer funcionar un horno de tratamiento termi- co.
GB45734/67A GB1205801A (en) 1966-10-28 1967-10-06 Soaking pit and method of operating the same
ES346255A ES346255A1 (es) 1966-10-28 1967-10-09 Perfeccionamientos en los hornos de tratamiento termico.
SE14524/67A SE333159B (sv) 1966-10-28 1967-10-24 Gropugn
NO67170262A NO119417B (enrdf_load_html_response) 1966-10-28 1967-10-25

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ES (2) ES345653A1 (enrdf_load_html_response)
FR (1) FR1548440A (enrdf_load_html_response)
GB (1) GB1205801A (enrdf_load_html_response)
NO (1) NO119417B (enrdf_load_html_response)
SE (1) SE333159B (enrdf_load_html_response)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3623714A (en) * 1969-12-02 1971-11-30 Rust Furnace Co Method of and apparatus for operating a furnace
US4448616A (en) * 1981-07-20 1984-05-15 Union Carbide Corporation Process for reducing backmixing
US4457706A (en) * 1982-08-02 1984-07-03 Bloom Engineering Company, Inc. Ladle station seal
CN112522500A (zh) * 2020-11-19 2021-03-19 湖南力方轧辊有限公司 一种工作辊热处理用井式炉
CN115654911A (zh) * 2022-11-04 2023-01-31 宿迁市华力新材料科技有限公司 一种腐蚀箔氮气处理炉装置

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2139741B (en) * 1983-05-04 1988-06-08 Air Prod & Chem Method of operating heat treatment furnace

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US713288A (en) * 1902-03-31 1902-11-11 John B Moran Device for protecting furnace-doors.
US1131385A (en) * 1913-05-10 1915-03-09 Andrew C Kephart Attachment for blacksmiths' blowers.
US1911394A (en) * 1931-10-07 1933-05-30 John H Ritter Door for glass tanks
US2269645A (en) * 1939-07-18 1942-01-13 Topping Brothers Forge
US2407047A (en) * 1944-10-20 1946-09-03 Blaw Knox Co Furnace closure
US2474504A (en) * 1944-10-20 1949-06-28 Blaw Knox Co Heating ingots
US2954968A (en) * 1956-10-11 1960-10-04 Pangborn Corp Fluid barrier

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US713288A (en) * 1902-03-31 1902-11-11 John B Moran Device for protecting furnace-doors.
US1131385A (en) * 1913-05-10 1915-03-09 Andrew C Kephart Attachment for blacksmiths' blowers.
US1911394A (en) * 1931-10-07 1933-05-30 John H Ritter Door for glass tanks
US2269645A (en) * 1939-07-18 1942-01-13 Topping Brothers Forge
US2407047A (en) * 1944-10-20 1946-09-03 Blaw Knox Co Furnace closure
US2474504A (en) * 1944-10-20 1949-06-28 Blaw Knox Co Heating ingots
US2954968A (en) * 1956-10-11 1960-10-04 Pangborn Corp Fluid barrier

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3623714A (en) * 1969-12-02 1971-11-30 Rust Furnace Co Method of and apparatus for operating a furnace
US4448616A (en) * 1981-07-20 1984-05-15 Union Carbide Corporation Process for reducing backmixing
US4457706A (en) * 1982-08-02 1984-07-03 Bloom Engineering Company, Inc. Ladle station seal
CN112522500A (zh) * 2020-11-19 2021-03-19 湖南力方轧辊有限公司 一种工作辊热处理用井式炉
CN112522500B (zh) * 2020-11-19 2023-09-22 湖南力方轧辊有限公司 一种工作辊热处理用井式炉
CN115654911A (zh) * 2022-11-04 2023-01-31 宿迁市华力新材料科技有限公司 一种腐蚀箔氮气处理炉装置
CN115654911B (zh) * 2022-11-04 2023-11-28 宿迁市华力新材料科技有限公司 一种腐蚀箔氮气处理炉装置

Also Published As

Publication number Publication date
ES345653A1 (es) 1968-11-16
NO119417B (enrdf_load_html_response) 1970-05-19
SE333159B (sv) 1971-03-08
GB1205801A (en) 1970-09-16
ES346255A1 (es) 1969-01-01
FR1548440A (enrdf_load_html_response) 1968-12-06

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