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WO1999051786A1 - A direct-heated furnace and a method of reheating steel semis - Google Patents

A direct-heated furnace and a method of reheating steel semis Download PDF

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Publication number
WO1999051786A1
WO1999051786A1 PCT/SE1999/000557 SE9900557W WO9951786A1 WO 1999051786 A1 WO1999051786 A1 WO 1999051786A1 SE 9900557 W SE9900557 W SE 9900557W WO 9951786 A1 WO9951786 A1 WO 9951786A1
Authority
WO
WIPO (PCT)
Prior art keywords
zone
final
semis
protective gas
furnace
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.)
Ceased
Application number
PCT/SE1999/000557
Other languages
French (fr)
Inventor
Roland Niemi
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.)
Niemi Goran
Original Assignee
Niemi Goran
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 Niemi Goran filed Critical Niemi Goran
Priority to AU38572/99A priority Critical patent/AU3857299A/en
Publication of WO1999051786A1 publication Critical patent/WO1999051786A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • 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
    • C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/02—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity of multiple-track type; of multiple-chamber type; Combinations of furnaces
    • F27B9/028—Multi-chamber type furnaces
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D1/00—Casings; Linings; Walls; Roofs
    • F27D1/18—Door frames; Doors, lids or removable covers
    • F27D1/1858—Doors
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/04—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity adapted for treating the charge in vacuum or special atmosphere
    • F27B9/045—Furnaces with controlled atmosphere
    • F27B9/047—Furnaces with controlled atmosphere the atmosphere consisting of protective gases
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/06—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity heated without contact between combustion gases and charge; electrically heated
    • F27B9/068—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity heated without contact between combustion gases and charge; electrically heated heated by radiant tubes, the tube being heated by a hot medium, e.g. hot gases
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/14—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity characterised by the path of the charge during treatment; characterised by the means by which the charge is moved during treatment
    • F27B9/20—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity characterised by the path of the charge during treatment; characterised by the means by which the charge is moved during treatment the charge moving in a substantially straight path
    • F27B9/201—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity characterised by the path of the charge during treatment; characterised by the means by which the charge is moved during treatment the charge moving in a substantially straight path walking beam furnace
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D1/00—Casings; Linings; Walls; Roofs
    • F27D1/18—Door frames; Doors, lids or removable covers
    • F27D1/1858—Doors
    • F27D2001/1875—Hanging doors and walls

Definitions

  • This invention relates to a direct-heated furnace and to a method of reheating steel semis in a direct-heated furnace before hot rolling the semis.
  • Figure 1 is a side section through a walking beam furnace, and the section is taken along line 1-1 in figure 2.
  • Figure 2 is a horizontal section taken along the line 2-2 in figure 1.
  • Figure 3 corresponds to figure l,but it shows some details modified.
  • the walking beam furnace shown in the figures is divided into three zones, namely the two direct heating zones 12,13 and the final zone (the temperature equalising zone) 14. Baffles 15,16 separate these zones.
  • a swingable door 17 is suspended in hinges.
  • a plurality of semis (seventeen semis in the form of slabs are shown) are in the furnace and they are moved from the in-feed end at the left in the figures to the output end at the right in the figures by means of non- illustrated walking beams in a conventional way. Only the first slab 20 and the last slab 21 have been denoted.
  • the walking beams elevate the slabs about a decimetre when moving the slabs.
  • the door is controlled by a hydraulic jack or a corresponding device on the outside ofthe furnace housing.
  • An air-lock should be arranged at the output end to keep oxygen out ofthe final zone 14.
  • the conventional oxy-fuel burners that eject the hot combustion gases into the direct heating zone are not illustrated.
  • Electric radiation heaters 22 are shown in the final zone 14.
  • Conduits in the form of tubes 23,24 extend through the direct heating zones 12,13 along the sidewalls and they end in the final zone 14.
  • the tubes 23, 24 extend through a sealing threshold 25 against which the swingable door 17 seals.
  • the walking beams lift the slabs over the threshold.
  • a protective gas is supplied to the final zone 14 through the tubes 23,24 and since the tubes extend through the direct heating zones 12,13, the gas will be preheated when it reaches the final zone 14.
  • the protective gas can suitably consist of nitrogen or mainly of nitrogen. It can be advantageous to add a small amount of hydrogen or another combustible gas to the protective gas so that any oxygen in the final zone will be burnt and give a slightly reducing atmosphere in the final zone.
  • FIG 3 shows the same furnace as do the figures 1 and 2, but instead ofthe electric radiation heaters, there are radiating tubes 30 that extend from the outside ofthe furnace through the entire final zone 14 and end in the direct heating zone 13.
  • a non-illustrated burner is mounted to each tube 30 at the outside ofthe furnace and the combustion gases are conveyed through the tubes into the direct heating zone 13. In this way, the combustion gases heat the tubes 30 so that the tubes form radiation heaters.
  • the slabs have a thickness of more than 20 cm and a width of about 1 m.
  • the temperature at the surface should not increase in the final zone, but a temperature equalisation should take place.
  • the main purpose ofthe radiation heaters 22,30 is therefore to maintain the surface temperature during the temperature equalisation.
  • the extremely low oxygen content in the final zone will reduce the formation of scale considerably and the profit from the reduced scale formation will surprisingly be much greater than the additional cost for a production according to the invention. This is particularly true for some alloyed steels, for example high speed steel. It has been proven that the scale formation can be reduced by 50% when the invention is applied as described.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Tunnel Furnaces (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)

Abstract

Steel slabs (20, 21) are heated in a reheating furnace before the hot rolling. A final zone (14) is separated from a direct heating zone (12, 13) and protective gas is conveyed to the final zone in conduits (23, 24) that lead through the direct heating zone so that the protective gas is heated before being released into the final zone. In the final zone, there are radiation heaters (22, 30) for the final heating and temperature equalisation of the slabs. In this way, the formation of scale is reduced and the profit of the scale reduction is much greater than the additional cost. This is true in particular for certain alloyed steel such as high speed cutting steel.

Description

1 A direct-heated furnace and a method of reheating steel semis
This invention relates to a direct-heated furnace and to a method of reheating steel semis in a direct-heated furnace before hot rolling the semis.
The two most common types of reheating furnaces are walking beam furnaces and pusher-type furnaces. Scale (oxide) is formed during the heating and it must be removed. There will also be a decarburisation ofthe surface. Particularly in the case of alloyed steels, for example high speed cutting steel, these effects will cause high costs because of loss of material. It is an object ofthe invention to reduce the formation of scale and the decarburisation and it is fulfilled in principle by the separation of a final zone from the direct heating zone and the conveying of a protective gas through conduits that lead through the direct heating zone and end in the final zone so that a preheated protective gas is released into the final zone. The invention has been given the characteristics that are defined in the claims.
The invention will be described with reference to the drawings that show schematically and fragmentary a walking beam furnace as an example ofthe invention.
Figure 1 is a side section through a walking beam furnace, and the section is taken along line 1-1 in figure 2.
Figure 2 is a horizontal section taken along the line 2-2 in figure 1.
Figure 3 corresponds to figure l,but it shows some details modified.
The walking beam furnace shown in the figures is divided into three zones, namely the two direct heating zones 12,13 and the final zone (the temperature equalising zone) 14. Baffles 15,16 separate these zones. A swingable door 17 is suspended in hinges. A plurality of semis (seventeen semis in the form of slabs are shown) are in the furnace and they are moved from the in-feed end at the left in the figures to the output end at the right in the figures by means of non- illustrated walking beams in a conventional way. Only the first slab 20 and the last slab 21 have been denoted. The walking beams elevate the slabs about a decimetre when moving the slabs. The door is controlled by a hydraulic jack or a corresponding device on the outside ofthe furnace housing. The arrangements for the input and for the output ofthe slabs are not shown. 2 An air-lock should be arranged at the output end to keep oxygen out ofthe final zone 14. The conventional oxy-fuel burners that eject the hot combustion gases into the direct heating zone are not illustrated. Electric radiation heaters 22 are shown in the final zone 14.
Conduits in the form of tubes 23,24 extend through the direct heating zones 12,13 along the sidewalls and they end in the final zone 14.The tubes 23, 24 extend through a sealing threshold 25 against which the swingable door 17 seals. The walking beams lift the slabs over the threshold. A protective gas is supplied to the final zone 14 through the tubes 23,24 and since the tubes extend through the direct heating zones 12,13, the gas will be preheated when it reaches the final zone 14. The protective gas can suitably consist of nitrogen or mainly of nitrogen. It can be advantageous to add a small amount of hydrogen or another combustible gas to the protective gas so that any oxygen in the final zone will be burnt and give a slightly reducing atmosphere in the final zone.
Figure 3 shows the same furnace as do the figures 1 and 2, but instead ofthe electric radiation heaters, there are radiating tubes 30 that extend from the outside ofthe furnace through the entire final zone 14 and end in the direct heating zone 13. A non-illustrated burner is mounted to each tube 30 at the outside ofthe furnace and the combustion gases are conveyed through the tubes into the direct heating zone 13. In this way, the combustion gases heat the tubes 30 so that the tubes form radiation heaters.
Usually, the slabs have a thickness of more than 20 cm and a width of about 1 m. The temperature at the surface should not increase in the final zone, but a temperature equalisation should take place. The main purpose ofthe radiation heaters 22,30 is therefore to maintain the surface temperature during the temperature equalisation. The extremely low oxygen content in the final zone will reduce the formation of scale considerably and the profit from the reduced scale formation will surprisingly be much greater than the additional cost for a production according to the invention. This is particularly true for some alloyed steels, for example high speed steel. It has been proven that the scale formation can be reduced by 50% when the invention is applied as described.

Claims

Claims
1. A direct-heated furnace for reheating semis (20,21), for example steel slabs, before hot rolling, characterised in that a final zone (14) is separated from a direct heating zone (12,13) and conduits (23,24) for protective gas lead through the direct heating zone and end in the final zone so that the protective gas is pre-heated before it is released into the final zone.
2. A furnace according to claim 1, characterised by a heating device (22,30) in the final zone for final heating ofthe semis.
3. A furnace according to claim 2, characterised in that the heating device comprises radiation heaters (22,30).
4. A furnace according to any one ofthe preceding claims in which the furnace is a walking beam furnace, characterised in that the gas conduits (23,24) lead along the sides ofthe direct heating zone.
5. A method of reheating steel semis (20,21) in a direct heated furnace before hot rolling the semis, characterised in that a final zone (14) is separated from a direct heating zone (12,13) and a protective gas is supplied to the final zone, the protective gas being pre-heated by being conveyed in conduits (23,24) that lead through the direct heating zone to the final zone.
6. A method according to claim 5, characterised by a final heating ofthe semis (20,21) in the final zone.
7. A method according to claim 6, characterised in that the semis (20,21) are heated by radiation in the final zone (14).
8. A method according to any one ofthe claims 5-7, characterised in that nitrogen is used as a protective gas. 4
9. A method according to any one ofthe claims 5-8, characterised in that a small amount of a combustible gas is added to the protective gas.
10. A method according to claim 9, characterised in that hydrogen is used as the combustible gas added to the protective gas.
PCT/SE1999/000557 1998-04-07 1999-04-06 A direct-heated furnace and a method of reheating steel semis Ceased WO1999051786A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU38572/99A AU3857299A (en) 1998-04-07 1999-04-06 A direct-heated furnace and a method of reheating steel semis

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9801260A SE510931C2 (en) 1998-04-07 1998-04-07 Direct-fired oven and ways to reheat steel materials
SE9801260-2 1998-04-07

Publications (1)

Publication Number Publication Date
WO1999051786A1 true WO1999051786A1 (en) 1999-10-14

Family

ID=20410921

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1999/000557 Ceased WO1999051786A1 (en) 1998-04-07 1999-04-06 A direct-heated furnace and a method of reheating steel semis

Country Status (3)

Country Link
AU (1) AU3857299A (en)
SE (1) SE510931C2 (en)
WO (1) WO1999051786A1 (en)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1808152A (en) * 1925-08-06 1931-06-02 Thaddeus F Baily Continuous annealing apparatus
US3554505A (en) * 1967-12-20 1971-01-12 Heurtey Sa Walking beam furnaces
US4469314A (en) * 1981-05-21 1984-09-04 Ishikawajima-Harima Jukogyo Kabushiki Kaisha Metal heating furnace
EP0168788A2 (en) * 1984-07-17 1986-01-22 Chugai Ro Co., Ltd. Continuous type atmosphere heat treating furnace
EP0175430A2 (en) * 1984-09-17 1986-03-26 Kabushiki Kaisha Itoh Seitetsusho Apparatus for soaking steel pieces

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1808152A (en) * 1925-08-06 1931-06-02 Thaddeus F Baily Continuous annealing apparatus
US3554505A (en) * 1967-12-20 1971-01-12 Heurtey Sa Walking beam furnaces
US4469314A (en) * 1981-05-21 1984-09-04 Ishikawajima-Harima Jukogyo Kabushiki Kaisha Metal heating furnace
EP0168788A2 (en) * 1984-07-17 1986-01-22 Chugai Ro Co., Ltd. Continuous type atmosphere heat treating furnace
EP0175430A2 (en) * 1984-09-17 1986-03-26 Kabushiki Kaisha Itoh Seitetsusho Apparatus for soaking steel pieces

Also Published As

Publication number Publication date
SE9801260L (en) 1999-07-12
SE9801260D0 (en) 1998-04-07
AU3857299A (en) 1999-10-25
SE510931C2 (en) 1999-07-12

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