EP4303516A1 - Vorrichtung zum verbessern der voroxidation in einem glühofen - Google Patents

Vorrichtung zum verbessern der voroxidation in einem glühofen Download PDF

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Publication number
EP4303516A1
EP4303516A1 EP22183162.1A EP22183162A EP4303516A1 EP 4303516 A1 EP4303516 A1 EP 4303516A1 EP 22183162 A EP22183162 A EP 22183162A EP 4303516 A1 EP4303516 A1 EP 4303516A1
Authority
EP
European Patent Office
Prior art keywords
temperature
strip
section
roll
time
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.)
Pending
Application number
EP22183162.1A
Other languages
English (en)
French (fr)
Inventor
Michel Dubois
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.)
John Cockerill SA
Original Assignee
John Cockerill SA
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 John Cockerill SA filed Critical John Cockerill SA
Priority to EP22183162.1A priority Critical patent/EP4303516A1/de
Priority to PCT/EP2023/067151 priority patent/WO2024008480A1/en
Publication of EP4303516A1 publication Critical patent/EP4303516A1/de
Pending legal-status Critical Current

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Classifications

    • 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
    • F27B9/30—Details, accessories, or equipment peculiar to furnaces of these types
    • 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
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • 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
    • C21D9/561—Continuous furnaces for strip or wire with a controlled atmosphere or vacuum
    • 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
    • C21D9/62—Continuous furnaces for strip or wire with direct resistance heating
    • 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 tunnel furnace
    • F27B9/24—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 tunnel furnace being carried by a conveyor
    • F27B9/2407—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 tunnel furnace being carried by a conveyor the conveyor being constituted by rollers (roller hearth furnace)
    • 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
    • F27B9/28—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity for treating continuous lengths of work
    • 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
    • F27D19/00—Arrangements of controlling devices
    • F27D2019/0028—Regulation
    • F27D2019/0059—Regulation involving the control of the conveyor movement, e.g. speed or sequences
    • 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
    • F27D19/00—Arrangements of controlling devices
    • F27D2019/0028—Regulation
    • F27D2019/0059—Regulation involving the control of the conveyor movement, e.g. speed or sequences
    • F27D2019/0062—Regulation involving the control of the conveyor movement, e.g. speed or sequences control of the workpiece stay in different zones

Definitions

  • the present invention relates to the heating process used in annealing lines of cold rolled steel strips of high strength, especially those intended for the automotive industry.
  • the invention also concerns the industrial installation for carrying out the heating process.
  • the total heat transfer power results from the sum of convective and radiative heat transfers and that the radiative one is proportional to the difference of temperature in kelvin at the 4 th power between the hot and the cold body. It can be shown that if the temperature difference between the hot and the cold body is higher that about 500°C the temperature of the cold body has no effect and the radiative heat transfer is then only proportional to the 4 th power of hot body temperature multiplied by the shape factor and the emissivity of the hot and cold surfaces as well as by the Boltzmann constant.
  • the inventors confirm that the quality of the final product is improved when the oxidation is reasonably uniform/homogeneous. Considering the explanations above, it practically means that the strip temperature uniformity must be good enough, that means a strip temperature within +/-10°C but more preferably within +/-5°C, at the time the strip enters in the preoxidation box.
  • oxidation takes place, i.e. a layer of iron oxide is formed on the surface of the steel sheet while an internal oxidation occurs under this iron oxide: internal oxides within a depth of 100 ⁇ m, which can contain one or more of Si, Mn, Al, Ti, are thus created. If the oxidation depth is above 100 ⁇ m, the steel surface will be heavily oxidized, which will be difficult to be reduced, and coating quality will be deteriorated.
  • the inventors propose a process for the heat treatment of a moving high-strength steel strip, comprising a step of strip temperature homogenization in a homogenization chamber comprising at least one radiant heating tube under a no-oxygen atmosphere, so as to homogenize the temperature of the strip after it has passed through the direct flame heating zone of the previous step, and before a step of oxidizing the strip in an oxidation chamber with an oxidizing atmosphere having an oxygen concentration by volume greater than 1%, and further a step of strip reduction in a reduction zone.
  • the kinetics of formation of an oxide layer on the surface of a strip of high strength steel depends mainly on the surface temperature of the strip, the steel composition and of course time, as well as the composition of the oxidizing atmosphere in the chamber of oxidation.
  • the oxidation time is defined by the line speed and the section length. So good control of the temperature of the strip during its oxidation in the oxidation chamber makes it possible to obtain a surface oxide layer having a more homogeneous thickness over the entire surface of the strip.
  • this patent does not teach the length of the homogenization chamber, nor the time to be spent by the strip in that chamber, which renders the teaching of poor practical use for the skilled person.
  • the invention aims at improving longitudinal and transversal temperature homogeneity of a strip after the step of heating the same in a DFF or a RTF furnace and before the step of preoxidation, inhomogeneity being mostly attributed to local variation of strip emissivity.
  • the invention aims at providing guidelines in terms of designing the length of a homogenization section needed and residence time of the strip therein in order to attain a predetermined temperature homogeneity target at the exit of the section.
  • Another aspect of the invention relates to an industrial installation for carrying out the method for improving longitudinal and/or transversal temperature homogeneity of a low carbon alloyed steel strip dedicated to liquid metal coating, preferably with in a mixture of Zn and Al, possibly with Si, Fe, and with inevitable impurities, continuously running at a line speed in a temperature homogenization section provided with electric resistances, as described above, wherein said installation successively comprises :
  • a uniform strip transversal temperature is difficult to obtain when the surface emissivity varies and when the heating rate is high because the thermal conduction has not the time to spread and establish.
  • the inventors have found that, in order to improve the transversal temperature uniformity, not only a certain time is required but also that the section where this levelling will take place must also have a uniform temperature equal to the target strip temperature. This is to minimize the possible radiative heating difference due to the heating element that needs to be installed to compensate for the heat losses.
  • the inventors have also found in that context that the use of a radiant tubes furnace (RTF) is not a good solution due to the small radiative surface thereof compared to the whole surface of the chamber.
  • RTF radiant tubes furnace
  • gas-flame heated radiant tubes is even worse as it is known that, due to the flame development in the tube, even the temperature of the tube itself is not uniform and depends on the firing rate.
  • a non-uniform tube temperature may be very detrimental to the target as some radiative heating may be in competition with the thermal conductive process that is used to improve the temperature uniformity of the strip.
  • the inventors have found that the most efficient way to improve the longitudinal temperature uniformity when it is of limited length, as it is for example the case with coil heads and tails, is to use the heat capacity of rolls the strip wraps around. This is based on the fact that it is well-known that, when the strip has a constant temperature, the contact roll has the same temperature on the contact area and all through the shell thickness.
  • a low carbon strip undergoes a heat treatment in a heating installation 1 that consists in heating the strip 100 by radiation either in a direct fired furnace or a full radiant tube furnace 11 to a temperature between 650 and 750°C, and preferably between 650 and 700°C, followed by a dedicated temperature homogenization section 12 located before a preoxidation chamber 13 and a reduction chamber 14 ( Figure 1 ).
  • the strip temperature is measured at the end of the temperature homogenization section 11.
  • the line speed is adjusted in such a way that the target temperature, preferentially between 650 and 700°C, is reached.
  • conduction through the strip width can proceed thanks to the time spent in the chamber and the heating by radiation and/or convection is/should be minimized.
  • the design of the chamber comprises a refractory lining intended to minimize heat losses.
  • a controlled electric heating is implemented possibly on the four walls of the section but preferably on the two sides facing the strip (not shown).
  • the electric heating is exclusively made of resistances 2 (preferably facing the strip uniformly), electric radiant tubes being excluded. It is therefore intended to provide a targeted so-called "uniform" wall temperature in section 12, that means a temperature with temperature variations of the resistances defined to be lower than about 20°C.
  • the temperature of the resistances is ensured with a measuring device contacting the heating elements on different points but preferentially on each side of the section and preferably on those facing the strip individually.
  • the power of the different resistance panels will be advantageously controlled separately in order to obtain a target temperature that is preferentially between 650 and 700°C.
  • Figure 2 shows the evolution of the temperature gradient with time for a case where the initial temperature difference across the strip width (100mm) is 32°C.
  • Time in abscissa is in this case started when the strip enters the furnace but the graph only shows time when the strip enters the homogeneous section of the invention.
  • the dotted line refers to 50% of temperature gradient decrease (which also corresponds to a STDGP of 50%). It comes then that 20sec are required for 50% reduction.
  • the low carbon strip undergoes a heat treatment that consists in heating the strip 100 by radiation either in a direct fired furnace or a full radiant tube furnace 11 to a temperature between 650 and 750°C, and preferably between 650 and 700°C followed by passing the strip in a dedicated temperature homogenization section 12 containing at least one contact roll 3, and preferably more contact rolls 3, in order to provide sufficient contact (time) to allow a significant heat exchange between the roll(s) 3 and the strip 100.
  • a dedicated temperature homogenization section 12 containing at least one contact roll 3, and preferably more contact rolls 3, in order to provide sufficient contact (time) to allow a significant heat exchange between the roll(s) 3 and the strip 100.
  • Different configurations of section 12 are shown on figures 3A to 3D , mainly differing by the number and the location of contact rolls 3 and/or the strip wrapping angle of the rolls 3.
  • the at least one contact roll 3 is preferably made of a material having of thickness such that to provide sufficient heat capacity (Cp), for example a refractory steel or alternatively a high heat capacity material like carbon.
  • Each roll 3 has a shell thickness between 10 and 60mm, and preferably between 20 and 40mm precisely to provide sufficient heat capacity.
  • the strip tension is controlled in the range of 0.4 to 2kg/mm 2 , and preferably between 0.8 and 1.2kg/mm 2 to ensure a good contact without inducing excessive plastic deformation of the strip that could be detrimental for final flatness.
  • the shape of the rolls 3 is preferably cyclindrical that means without special crown but a light crown would be acceptable.
  • the rolls have a diameter between 600 and 1500mm, and preferably between 1000 and 1200mm to ensure reasonable contact length per roll without providing specific layout problems.
  • Section 12 is also provided with a number of electric heating devices 2, preferably electric resistances, that are controlled in temperature.
  • the incoming strip temperature 100 is measured at the end of the temperature heating section 11.
  • the strip temperature at the exit of the series of rolls of the homogenization section 12 is also measured (not shown).
  • Figure 4 shows the time evolution of the roll/strip temperature gradient.
  • Figure 5 shows the respective variations of strip temperature and of roll surface temperature with the time spent in the dedicated homogenization section 12, considering a roll initially at 650°C and a strip entering in the section at 600°C (1mm strip, rolls made of refractory steel and with a shell thickness of 25mm).
  • the number of rolls required and so the total wrapping contact according to the invention will depend on the size thereof, the inhomogenization reduction target, the line speed and the strip thickness.
EP22183162.1A 2022-07-05 2022-07-05 Vorrichtung zum verbessern der voroxidation in einem glühofen Pending EP4303516A1 (de)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP22183162.1A EP4303516A1 (de) 2022-07-05 2022-07-05 Vorrichtung zum verbessern der voroxidation in einem glühofen
PCT/EP2023/067151 WO2024008480A1 (en) 2022-07-05 2023-06-23 Device for improving preoxidation in an annealing furnace

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP22183162.1A EP4303516A1 (de) 2022-07-05 2022-07-05 Vorrichtung zum verbessern der voroxidation in einem glühofen

Publications (1)

Publication Number Publication Date
EP4303516A1 true EP4303516A1 (de) 2024-01-10

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP22183162.1A Pending EP4303516A1 (de) 2022-07-05 2022-07-05 Vorrichtung zum verbessern der voroxidation in einem glühofen

Country Status (2)

Country Link
EP (1) EP4303516A1 (de)
WO (1) WO2024008480A1 (de)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2112238A1 (de) * 2007-02-14 2009-10-28 JFE Steel Corporation Dauerglühgerät
US20170137906A1 (en) 2014-06-06 2017-05-18 Arcelormittal High Strength Multiphase Steel, Production Method and Use
EP3286343B1 (de) 2015-04-22 2019-06-05 Cockerill Maintenance & Ingéniérie S.A. Verfahren zur reaktionskontrolle
US20200232063A1 (en) * 2019-01-23 2020-07-23 Drever International Method and furnace for thermally treating a high-resistance steel strip comprising a temperature homogenisation chamber

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2112238A1 (de) * 2007-02-14 2009-10-28 JFE Steel Corporation Dauerglühgerät
US20170137906A1 (en) 2014-06-06 2017-05-18 Arcelormittal High Strength Multiphase Steel, Production Method and Use
EP3286343B1 (de) 2015-04-22 2019-06-05 Cockerill Maintenance & Ingéniérie S.A. Verfahren zur reaktionskontrolle
US20200232063A1 (en) * 2019-01-23 2020-07-23 Drever International Method and furnace for thermally treating a high-resistance steel strip comprising a temperature homogenisation chamber
EP3686534B1 (de) 2019-01-23 2021-03-10 Drever International Verfahren und ofen für die wärmebehandlung eines hochwiderstandsfähigen stahlbandes, der eine temperatur-homogenisierungskammer umfasst

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
KANG ZONG-WEI ET AL: "Three-dimensional temperature distributions of strip in continuous annealing line", APPLIED THERMAL ENGINEERING, PERGAMON, OXFORD, GB, vol. 58, no. 1, 17 April 2013 (2013-04-17), pages 241 - 251, XP028575393, ISSN: 1359-4311, DOI: 10.1016/J.APPLTHERMALENG.2013.03.062 *
PAULUS PH ET AL: "STUDY OF THE HEAT BUCKLING AND SHAPE PROBLEMS IN CONTINUOUS HEAT TREATING LINES AND DISCUSSION OF PROPOSED SOLUTIONS", STUDY OF THE HEAT BUCKLING AND SHAPE PROBLEMS IN CONTINUOUS HEAT TREATING LINES AND DISCUSSION OF PROPOSED SOLUTIONS, METALLURGICAL SOC OF AIME, WARRENDALE, PA, 1 January 1985 (1985-01-01), pages 419 - 439, XP008093355, ISBN: 978-0-89520-491-2 *

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