EP0216561B1 - Preheating method of steel strips - Google Patents

Preheating method of steel strips Download PDF

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Publication number
EP0216561B1
EP0216561B1 EP86306940A EP86306940A EP0216561B1 EP 0216561 B1 EP0216561 B1 EP 0216561B1 EP 86306940 A EP86306940 A EP 86306940A EP 86306940 A EP86306940 A EP 86306940A EP 0216561 B1 EP0216561 B1 EP 0216561B1
Authority
EP
European Patent Office
Prior art keywords
steel strip
preheating
temperature
heated
heating
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
EP86306940A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0216561A2 (en
EP0216561A3 (en
Inventor
Sachihiro c/o Kawasaki Steel Corp. Iida
Norihisa c/o Kawasaki Steel Corp. Shiraishi
Kazumasa c/o Mitsubishi Jukogyo Mihara
Kaneaki C/O Mitsubishi Jukogyo Hyodo
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.)
JFE Steel Corp
Mitsubishi Heavy Industries Ltd
Original Assignee
Mitsubishi Heavy Industries Ltd
Kawasaki 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 Mitsubishi Heavy Industries Ltd, Kawasaki Steel Corp filed Critical Mitsubishi Heavy Industries Ltd
Priority to AT86306940T priority Critical patent/ATE92969T1/de
Publication of EP0216561A2 publication Critical patent/EP0216561A2/en
Publication of EP0216561A3 publication Critical patent/EP0216561A3/en
Application granted granted Critical
Publication of EP0216561B1 publication Critical patent/EP0216561B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • 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
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • 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
    • C21D1/34—Methods of heating

Definitions

  • This invention relates to a preheating method in the continuous heat-treatment of steel strip for progressively heating the steel strip in a plurality of stages to temperatures as near to those in the heating zone as possible.
  • a steel strip continuous heat-treating installation for example, a steel strip continuous annealing installation, usually comprises heating, soaking and cooling zones.
  • a steel strip is heated to 650°C-850°C in the heating zone.
  • radiant tube heating has been employed which, however, makes the installation of the heating zone complicated and large-sized. It is therefore important to preheat the steel strip on the entry side of the heating zone in order to make the installation compact and improve the production efficiency.
  • Japanese Laid-open Patent Applications Nos.57-41,330 and 58-73,727 disclose a method of preheating a steel strip in which sensible heat of burned waste heat from a heating zone is recovered in a heating medium by means of a heat-exchanger and the heating medium is introduced into passages formed in rolls about which the steel strip is wound.
  • the sensible heat of the burned waste heat at 300-350°C is recovered in the heating medium until the temperature becomes approximately 150°C in order to avoid a problem of dew point of oxygen, and thereafter the steel strip is preheated. In this manner, it is possible to preheat the steel strip to approximately 130-140°C to improve the recovery of waste heat.
  • the steel strip preheated to approximately 130-140°C is rapidly heated to 600-850°C by radiation heating mainly by radiant tubes.
  • a heating has a limitation of heating speed, a huge installation is needed in order to increase the production.
  • the preheating temperature is relatively low, it would be desirable to improve the thermal efficiency.
  • Japanese Laid-open Patent Application No.57-76,133 discloses a heating method using rolls heated by induction heating coils without using the burned waste gas.
  • This publication discloses an example of heating steel strips to 800°C using heated rolls at 1,000°C. Because of the great temperature difference between the steel strip and the rolls when the steel strip is wound about the rolls, there is a risk of serpentine movement of the steel strip caused by concave thermal crowns on the rolls due to temperature fall at outer peripheries of the rolls about which the steel strip is wound.
  • Japanese Laid-open Patent Application No.60,135,530 discloses a preheating method in which sensible heat of burned waste gas from a radiant-tube equipped heating furnace is recovered by using it to heat an atmospheric gas stream in a heat exchanger and the resulting heated gas stream is blown on to steel strip to preheat it.
  • the preheating temperature of the steel strip is at the most 100-200°C. It is impossible to obtain higher preheating temperature.
  • the temperature of preheated steel strips is within 100-200°C, bad configuration of the rolled steel strips is not straightened by such a low temperature preheating and is maintained even when the steel strips are in an upstream half of a heating zone.
  • unevenness of the rolled steel strip is of the order of 1%, therefore, serpentine movements of the steel strips occur while being heated, so that the feeding speed of the steel strips cannot be increased resulting in lower production efficiency.
  • the word "unevenness” is intended to mean a deviation of a steel strip from a complete flatness per a unit length.
  • a method of continuously annealing steel strip in which the strip is preheated and then heated indirectly in a heating zone by means of radiant tubes heated by burned waste gas, characterised in that the preheating is effected progressively in two stages, in the first of which the strip is heated to not more than a maximum predetermined first temperature by direct contact with a gaseous stream which has been heated in a heat exchanger by means of the burned waste gas from the heating zone, and in the second of which the preheated strip from the first preheating stage is further heated to a desired second temperature higher than said maximum first temperature by winding the steel strip over heated rolls through which is circulated a fluid heat medium which has been heated in a heating device to a desired temperature sufficient to cause the strip in the second preheating stage to be raised to said desired higher temperature before entering the heating zone, whereby serpentine movement of the steel strip is substantially reduced.
  • a progressive preheating of steel strip in two stages for the purpose of minimising serpentine movement of the steel strip in the continuous annealing of steel strip by indirect heating with radiant tubes in a heating zone, the first preheating being effected by direct heating with a gaseous atmosphere containing sensible heat recovered by heat exchange with burned waste gas from the heating zone, and the second preheating being effected by heated rolls through which a fluid heat medium which has been heated to a desired temperature in a heating device is circulated so as to preheat the steel strip to a higher temperature than that reached in the first preheating stage.
  • the temperature of the steel strip is maintained lower than a predetermined temperature, such as by controlling amounts of the gas directed onto the steel strip, in order to prevent formation of thick oxide films on the steel strip.
  • the second stage preheating is preferably effected in a non-oxidizing atmosphere.
  • a heat medium is heated in a heat medium heating device and supplied and circulated into the rolls, thereby heating the rolls to a desired temperature.
  • the temperature of the steel strip is preferably maintained lower than a predetermined temperature by controlling at least one factor among flow rate and temperature of the heat medium and winding angles of the steel strip about the rolls.
  • a steel strip 1 is preheated to 100-200°C in a first preheating zone 2 at a first preheating stage and to 250-500°C in a second preheating zone 3 at a second preheating stage.
  • burned waste gas is collected from a heating zone 4 including radiant tubes 5 into waste gas collecting ducts 6 and is introduced into a heat-exchanger 7 wherein sensible heat of the waste gas is given to a gas such as the air while the waste gas whose temperature has been lowered is exhausted through a chimney 9 with the aid of a waste gas suction fan 8.
  • the temperature of the waste gas is usually of the order of 400°C which is lower than those at which the fan and chimney can thermally resist.
  • the heated gas heated in the heat-exchanging (which is referred to hereinafter "hot blast") is circulated by a hot blast circulating fan 10 to be supplied into hot blast chambers 11 arranged in the first preheating zone 2, so that the hot blast is directed onto the steel strip to heat it to 100-200°C.
  • nitrogen, nitrogen mixed with hydrogen somewhat, or the like is suitable as the gas directed onto the steel strip in the first preheating zone 2.
  • a heat medium 12 in a reservoir 17 is heated in a heat medium heating device 13 and supplied and circulated into rolls 15 with the aid of a circulating pump 14.
  • the heated medium 12 flows through the rolls 15 which are heated by the medium, so that the steel strip 1 from the first preheating zone 2 is wound about the rolls so as to pass through the second preheating zone 3 to heat the steel strip 1 to 250-500°C
  • the heat medium 12 which has heated the rolls is returned through a return line 16 into the reservoir 17.
  • the heat medium may be thermo-oil, metallic sodium, or a molten salt such as a nitrate, for example sodium nitrate or potassium nitrate, or a chloride, for example calcium chloride or sodium chloride.
  • a molten nitrate salt is preferable for preventing corrosion of the rolls.
  • thermometer or thermometers 18 for the steel strip are provided on an exit side of the first preheating zone 2 to monitor whether the steel strip 1 is heated at temperatures between 100 and 200°C in the first preheating zone. If the temperature of the steel strip is higher than 250°C, thick oxide films are produced on surfaces of the steel strip to lower the quality of the surfaces.
  • the amount of the hot blast directed onto the steel strip is controlled by adjusting numbers of revolution of the hot blast circulating fan 10 or provision of dampers in the lines in order to maintain the temperature of the preheated steel strip lower than 250°C.
  • thermometer or thermometers 19 for the steel strip are provided on an exit side of the second preheating zone 3 to monitor whether the temperature of the steel strip on the exit side of the second preheating zone 3 is maintained within 250-500°C while one or more of the flow rate and temperature of the heat medium 12 flowing into the rolls 15 and winding angles of the steel strip about the rolls are controlled.
  • Figs. 2-8 illustrate results of investigation of thermal efficiency, serpentine movement of steel strips, surface conditions and installation investment concerning the invention.
  • Fig. 2 and 3 illustrate thermal efficiencies in cases of the present invention, reference example A using only radiant tubes and reference example B using hot blast and radiant tubes.
  • the thermal efficiency is greatly improved by effecting the second stage preheating with rolls mainly by the heat transmission between directly contacting metals.
  • Fig. 3 is a graph illustrating the fall in production efficiency due to serpentine movements of steel strips occurring before the heating zone when unevennesses of the steel strips are 0.5-1.0% before the heat treatment. This graph clearly shows the superiority of the present invention.
  • Fig. 4 illustrates the fall in production efficiency due to serpentine movements of steel strips similar to those in Fig. 3, in comparison with the reference example B. It is clear that the serpentine movements can be prevented by rapidly raising the temperature of the steel strips to the order of 500°C by preheating with rolls.
  • an abscissa indicates temperature difference between the heat medium and steel strips on the exit side of the second preheating zone and an ordinate indicates serpentine movement of steel strips per one heating roll.
  • the temperature difference is more than 300°C, the serpentine movements increase to an extent that the practical use is prohibitive. It is understood from this fact that the progressive heating with less temperature difference is suitable.
  • Fig. 6 illustrates the relation between thickness of oxide films and the temperature of steel strips on the exit side of the first preheating zone heating with hot blast. It is clearly evident that when the temperature of the steel strips is more than 250°C, the thickness of the oxide films increases. Even if the steel strips were reduced after preheating, the bad surface conditions of the steel strips could not be amended as shown in Fig. 7.
  • Fig. 7 illustrates observation of surfaces of steel strips which were subjected to the treatment for forming phosphate or chromium oxide films thereon after the continuous heat treatment and degreasing. An ordinate indicates the surface conditions of the strips.
  • Fig. 8 illustrates the surface condition of steel strips in case of the second preheating zone with the air or non-oxidizing atmosphere.
  • the quantity of heat and flow rate of the respective gases when the temperature of the steel strips on the exit side of the heating zone became 750°C are as follows under the same conditions as those above described.
  • Sensible heat of the heat-up gas was given through a heat-exchanger to the air to be used in the first preheating zone, so that the temperature of the heat-up gas dropped from 600°C to 350°C.
  • the amount of the air circulating through the first preheating zone was 80,000 Nm/h.
  • the quantity of heat of 2x106 Kcal/h was obtained by heat-exchanging.
  • the air temperature was 250°C on an entry side of the heat-exchanger and 330°C on an exit side thereof.
  • Table 1 shows the temperatures of steel strips on the exit side of the first preheating zone.
  • This invention allows steel strips to be preheated to higher temperatures for the purpose of preventing serpentine movements of the steel strips, thereby improving the production efficiency and compacting the installation.

Landscapes

  • 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 Treatment Of Strip Materials And Filament Materials (AREA)
  • Coating With Molten Metal (AREA)
  • Manufacturing Of Steel Electrode Plates (AREA)
  • Coating By Spraying Or Casting (AREA)
  • Heat Treatments In General, Especially Conveying And Cooling (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
EP86306940A 1985-09-10 1986-09-09 Preheating method of steel strips Expired - Lifetime EP0216561B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT86306940T ATE92969T1 (de) 1985-09-10 1986-09-09 Verfahren zum vorwaermen von stahlband.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP60198625A JPS6260825A (ja) 1985-09-10 1985-09-10 鋼帯の連続熱処理における予熱方法
JP198625/85 1985-09-10

Publications (3)

Publication Number Publication Date
EP0216561A2 EP0216561A2 (en) 1987-04-01
EP0216561A3 EP0216561A3 (en) 1988-08-03
EP0216561B1 true EP0216561B1 (en) 1993-08-11

Family

ID=16394308

Family Applications (1)

Application Number Title Priority Date Filing Date
EP86306940A Expired - Lifetime EP0216561B1 (en) 1985-09-10 1986-09-09 Preheating method of steel strips

Country Status (8)

Country Link
EP (1) EP0216561B1 (enrdf_load_stackoverflow)
JP (1) JPS6260825A (enrdf_load_stackoverflow)
KR (1) KR910009967B1 (enrdf_load_stackoverflow)
AT (1) ATE92969T1 (enrdf_load_stackoverflow)
AU (1) AU573988B2 (enrdf_load_stackoverflow)
CA (1) CA1286575C (enrdf_load_stackoverflow)
DE (1) DE3688868T2 (enrdf_load_stackoverflow)
ES (1) ES2002294A6 (enrdf_load_stackoverflow)

Families Citing this family (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2820148B1 (fr) * 2001-01-31 2003-10-31 Stein Heurtey Perfectionnements apportes aux procedes de chauffage de bandes d'acier dans des fours verticaux
JP5043587B2 (ja) * 2007-10-12 2012-10-10 中外炉工業株式会社 金属ストリップ連続熱処理設備
AT507669B1 (de) * 2009-07-03 2010-07-15 Ebner Ind Ofenbau Verfahren zum erwärmen von leichtmetallblöcken
CN103103323A (zh) * 2013-01-21 2013-05-15 江苏沙钢集团有限公司 无保温坑式冷坯硅钢生产方法
KR101631034B1 (ko) * 2015-09-07 2016-06-16 주식회사 포스코 강판 표면 처리장치 및 이를 이용한 강판 제조방법
AT520134B1 (de) * 2017-07-13 2020-03-15 Andritz Tech & Asset Man Gmbh Verfahren zur reduktion von stickoxiden in bandbehandlungsöfen
CN109321741A (zh) * 2017-07-31 2019-02-12 湖北华鑫科技股份有限公司 精密钢带自动退火机
CN111879116A (zh) * 2020-07-30 2020-11-03 泰兴市天一冶金科技发展有限公司 一种钢坯冶炼燃气步进式加热炉分段加热机构
CN114807583A (zh) * 2022-03-21 2022-07-29 光丰(肇庆)钢业有限公司 一种钢带的生产工艺

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS60135530A (ja) * 1983-12-22 1985-07-18 Kawasaki Steel Corp 鋼帯の連続焼なまし方法

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4069008A (en) * 1976-03-19 1978-01-17 Allegheny Ludlum Industries, Inc. Method and apparatus for heating a workpiece
AU509460B2 (en) * 1976-12-23 1980-05-15 Armco Steel Corporation Treating steel strip prior to metal coating
DE3142860A1 (de) * 1981-10-29 1983-05-11 Italimpianti (Deutschland) Industrieanlagen GmbH, 4000 Düsseldorf "verfahren und vorrichtung zum vorwaermen"
AU576272B2 (en) * 1984-11-13 1988-08-18 Kyorin Pharmaceutical Co. Ltd. Quinolone carboxylic acid derivates

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS60135530A (ja) * 1983-12-22 1985-07-18 Kawasaki Steel Corp 鋼帯の連続焼なまし方法

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
CHEMICAL ABSTRACTS, vol. 103, 09 December 1985, Columbus, OH (US); p. 219, no. 199435u; JP-A-60 135530 (Kawasaki Steel Corp.; Mitsubishi Heavy Industries, Ltd) 18-07-1985 *

Also Published As

Publication number Publication date
KR870003212A (ko) 1987-04-16
DE3688868D1 (de) 1993-09-16
DE3688868T2 (de) 1993-11-25
ES2002294A6 (es) 1988-08-01
EP0216561A2 (en) 1987-04-01
JPS6260825A (ja) 1987-03-17
ATE92969T1 (de) 1993-08-15
JPS6344805B2 (enrdf_load_stackoverflow) 1988-09-07
AU6255586A (en) 1987-03-12
CA1286575C (en) 1991-07-23
KR910009967B1 (ko) 1991-12-07
EP0216561A3 (en) 1988-08-03
AU573988B2 (en) 1988-06-23

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