EP1241274B1 - Heat shielding apparatus for vertical continuous annealing furnace - Google Patents

Heat shielding apparatus for vertical continuous annealing furnace Download PDF

Info

Publication number
EP1241274B1
EP1241274B1 EP20010302309 EP01302309A EP1241274B1 EP 1241274 B1 EP1241274 B1 EP 1241274B1 EP 20010302309 EP20010302309 EP 20010302309 EP 01302309 A EP01302309 A EP 01302309A EP 1241274 B1 EP1241274 B1 EP 1241274B1
Authority
EP
European Patent Office
Prior art keywords
double
tube
roll
furnace
heat shielding
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
EP20010302309
Other languages
German (de)
French (fr)
Other versions
EP1241274A1 (en
Inventor
Naoto Tokyo Head Off. Kawasaki Steel Corp. Ueno
S. Tokyo Head Off. Kawasaki Steel Corp. Iida
Takaaki Chiba Works Kawasaki Steel Corp Kobashi
Motoki Chiba Works Kawasaki Steel Corp. Imamura
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
Original Assignee
JFE 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 JFE Steel Corp filed Critical JFE Steel Corp
Priority to DE2001615379 priority Critical patent/DE60115379T2/en
Priority to EP20010302309 priority patent/EP1241274B1/en
Publication of EP1241274A1 publication Critical patent/EP1241274A1/en
Application granted granted Critical
Publication of EP1241274B1 publication Critical patent/EP1241274B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D9/00Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54Furnaces for treating strips or wire
    • C21D9/56Continuous furnaces for strip or wire
    • C21D9/562Details
    • C21D9/563Rolls; Drums; Roll arrangements
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D9/00Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54Furnaces for treating strips or wire
    • C21D9/56Continuous furnaces for strip or wire
    • C21D9/562Details

Definitions

  • This invention relates to a heat shielding apparatus for a vertical continuous annealing furnace in which heat treatment is performed on a metal strip while the strip is continuously transported.
  • an annealing process for recrystallizing steel strip after being subjected to cold rolling and for imparting good workability to the steel strip has been primarily carried out by continuous annealing instead of batch annealing.
  • a continuous annealing furnace for carrying out the continuous annealing there are known horizontal continuous annealing furnaces, in which annealing is performed on a strip traveling along a horizontal pass, and vertical continuous annealing furnaces, in which a plurality of rolls are arranged in upper and lower portions of the furnace and annealing is performed on a strip traveling along a vertical pass.
  • the vertical furnace is more advantageous for a mass-production process that is realized by increasing the passing (threading) speed of the strip.
  • indirect heating using a radiant tube is prevalent as a heating source for the vertical continuous annealing furnace, and steel strip is mainly heated with radiant heat from the heating source.
  • each roll 12 arranged in the furnace is designed to have a convex roll crown with both shoulders tapered toward the ends.
  • This design is intended to make the steel strip pass the furnace so that the strip always travels in match with the roll center, by utilizing a centering force (arrow F) acting on the strip, which has ridden over a tapered portion, in a direction from the roll edge toward the roll center based on a self-centering motion of the strip wound on the tapered portion of the roll with angle.
  • a heating source e.g., a radiant tube
  • a thermal crown a crown imparted by the radiant heat from the heating source
  • Japanese Unexamined Patent Application Publication No. 57-79123 discloses a shielding apparatus employing a heat-resistant tube through which air, nitrogen gas or the like, flows for cooling.
  • Japanese Unexamined Patent Application Publication No. 52-71318 discloses a technique for spraying cooling gas to the roll to control the thermal crown in a positive way.
  • Japanese Unexamined Patent Application Publication No. 53-119208 discloses a technique for water-cooling a roll edge portion, or changing a thermal conductivity between the roll central portion and the roll edge portion.
  • Japanese Unexamined Patent Application Publication No. 53-130210 and Japanese Examined Patent Publication No. 57-23733 disclose techniques for arranging, separately from the rolls, a cooling apparatus that forms a cooling flow path.
  • An object of this invention is to provide an inexpensive and more efficient apparatus on the basis of the radiant heat shielding apparatus employing a cooling tube, which is disclosed in the above-cited Japanese Unexamined Patent Application Publication No. 57-79123, for example.
  • a heat shielding apparatus according to the preamble of claim 1 is disclosed in the above-mentioned Japanese Unexamined Patent Application Publication No. 53-130210.
  • a heat shielding apparatus suitable for a vertical continuous annealing furnace including upper and lower portions and a plurality of rolls arranged in the upper and lower portions, wherein heat treatment is performed on a metal strip continuously transported in the vertical direction by the rolls while changing the direction of travel from upward to downward, or from downward to upward, as the metal strip turns around each of the rolls, and wherein the heat shielding apparatus can be positioned just below a roll in the upper portion of the furnace and/or just above a roll in the lower portion of the furnace, the heat shielding apparatus comprising:
  • this invention provides a radiant heat shielding apparatus for a vertical continuous annealing furnace, in which a plurality of rolls are arranged in upper and lower portions of the furnace and heat treatment is performed on a metal strip continuously transported by the rolls.
  • the strip is transported in the vertical direction by the rolls while changing the travel direction from upward to downward, or from downward to upward, as the metal strip turns around each of the rolls.
  • the radiant heat shielding apparatus is disposed below the roll positioned in the upper portion of the furnace, and/or above the roll positioned in the lower portion of the furnace, for intercepting heat radiated from a heating source provided within the furnace.
  • the radiant heat shielding apparatus is positioned just below the roll in the upper position of the furnace, and/or just above the roll in the lower portion of the furnace.
  • the radiant heat shielding apparatus comprises a double-walled tube including an inner tube having an outside atmosphere suction port projected horizontally or downward to be exposed to an outside atmosphere, and an outer tube having an exhaust port projected upward to be exposed to the outside atmosphere.
  • some embodiments of the radiant heat shielding apparatus comprise a plurality of double-walled tubes as described above.
  • the double-walled tubes are horizontally arranged just below the roll positioned in the upper portion of the furnace and/or just above the roll positioned in the lower portion of the furnace.
  • the radiant heat shielding apparatus comprises one or more double-walled tubes as described above, and the double-walled tubes are used as support tubes and a shield plate is attached to the support tubes.
  • a radiant heat shielding apparatus of this invention is disposed below (preferably just below) a roll positioned in an upper portion of a vertical continuous annealing furnace, and/or positioned above (preferably just above) a roll positioned in a lower portion of the furnace, for intercepting heat radiated from a heating source that is provided within the furnace, and the heat shielding apparatus is almost parallel to the roll.
  • the radiant heat shielding apparatus has a structure of a double-walled tube 20 comprising an inner tube 22 having an outside atmosphere suction port 23 projected downward to be exposed to an outside atmosphere, and an outer tube 24 having an exhaust port 25 projected upward to be exposed to the outside atmosphere.
  • an inexpensive and more efficient radiant heat shielding apparatus can be realized by effectively utilizing natural convection of the outside atmosphere (e.g., air).
  • Heat-resistant alloy steel is an exemplary suitable material for forming the double-walled tube 20.
  • stainless steel having a Cr content of not less than about 18 wt% and a Ni content of not less than about 8 wt%, or special steel having high heat resistance are preferred materials.
  • Japanese Unexamined Patent Application Publication No. 57-79123 discloses that air for cooling is forced to flow into the cooling tube by a suction blower, or by a pressure blower.
  • a suction blower or by a pressure blower.
  • the blower sucks exhaust gas at high temperatures, and therefore the blower must itself be made heat-resistant, or else a device for cooling suction gas must be provided upstream of the blower. In any case, the equipment cost is necessarily increased.
  • a pressure blower is used to force the cooling air to flow into the cooling tube, there is risk that a metal (or steel) strip is oxidized due to leakage of the air from the cooling tube into the furnace.
  • the inventors fabricated radiant heat shielding apparatuses having three types of structures shown in Fig. 2, and conducted tests on those actual apparatuses.
  • the left side of Fig. 2 represents a conventional example using a shield plate 16 in the form of a simple flat plate.
  • a strip 10 typically, a steel strip
  • a roll 12 arranged in a furnace
  • a heating source 14 typically, a radiant tube
  • the center of Fig. 2 represents a comparative example using a cooling tube 18 in the form of a simple straight double-walled tube.
  • the right side of Fig. 2 represents the first embodiment of this invention including a cooling tube 20 in the form of the double-walled tube shown in Fig. 1.
  • Fig. 3 is a graph showing test results obtained by measuring a surface temperature of an outer tube of each double-walled tube and a flat plate (on the side facing the roll 12 arranged in the furnace), which is represented by the vertical axis, relative to a flow rate of cooling gas (air) measured at the exhaust port of the outer tube of each double-walled tube, which is represented by the horizontal axis.
  • Measurement conditions were set such that the furnace temperature was 900°C, the temperature of the outside atmosphere (cooling gas) was 300°C, the outer tube diameter of the double-walled tube was 100 mm, the inner tube diameter of the double-walled tube was 40 mm, and the level difference H between the outside atmosphere suction port 23 and the exhaust port 25 of the double-walled tube was 200 mm.
  • the surface temperature of the flat plate reached 860 °C.
  • the flow rate of the cooling gas reached to 5.0 ⁇ 10 -3 (Nm 3 /s) and the surface temperature of the outer tube was reduced down to about 500°C.
  • Fig. 4 is a graph showing the relationship between the flow rate of cooling gas (air) measured at the exhaust port of the outer tube of the double-walled tube according to this invention and a temperature difference ⁇ T developed on a temperature measuring roll in the width direction of a strip.
  • the roll temperature measured had thermocouples embedded therein in the width direction of the roll and was positioned just above the radiant heat shielding apparatus which is almost parallell to the roll. Measurement conditions were set such that the length of a roll barrel was 2000 mm, the average width of steel strips passed through the furnace was 1260 mm, and the average furnace temperature was 900°C.
  • the graph of Fig. 4 shows that the minimum temperature difference ⁇ T, at which the roll crown is rendered concave and the steel strip undergoes snaking, is about 150°C, and that the flow rate of the cooling gas required for preventing snaking of the steel strip is not less than 3.0 ⁇ 10 -3 (Nm 3 /s).
  • the outside atmosphere suction port is described as being projected downward.
  • the outside atmosphere suction port is not limited to such an arrangement.
  • the outside atmosphere suction port may alternatively be projected at a different orientation, e.g., horizontally.
  • the chimney effect developed on a flow in the double-walled tube from suction of the outside atmosphere to exhaust thereof is utilized to satisfy the above-mentioned required flow rate of the cooling gas.
  • the flow rate Q of the cooling gas is proportional to the outer diameter D of the outer tube and is also proportional to the square root of the level difference H between the outside atmosphere suction port and the exhaust port of the double-walled tube.
  • Fig. 5 is a graph plotting actually measured data representing the relationship between the parameter D 2 ⁇ (H) indicated by the horizontal axis, and the flow rate Q (Nm 3 /s) of the cooling gas, indicated by the vertical axis.
  • the graph of Fig. 5 shows that D 2 ⁇ (H) ⁇ 2.2 x 10 -3 is needed to satisfy the required flow rate Q of the cooling gas that is not less than about 3.0 ⁇ 10 -3 (Nm 3 /s).
  • the furnace temperature ranges from about 500°C to about 900°C during actual operation, and when the furnace is within this temperature range, the flow rate of the cooling gas not less than the above-mentioned value is sufficient to achieve the desired cooling.
  • D 2 ⁇ (H) ⁇ 2.2 ⁇ 10 -3 is satisfied, a sufficient cooling effect can be provided during actual operation.
  • Fig. 6 is a graph showing the relationship between the flow rate Q (Nm 3 /s) of the cooling gas and the level difference H (mm) between the outside atmosphere suction port and the exhaust port of the double-walled tube.
  • the graph of Fig. 6 shows that if the level difference is less than about 150 mm, the cooling gas becomes difficult to flow because the level difference H is substantially at the same level as that corresponding to the diameter of the double-walled tube. Therefore, the level difference H between the outside atmosphere suction port and the exhaust port of the double-walled tube is preferably set to be not less than about 150 mm.
  • the outer diameter of the outer tube of the double-walled tube is small, the outer tube is more easily susceptible to creep due to the radiant heat. From the actual operation of the invention experienced so far, it has been confirmed that the outer diameter of the outer tube is preferably not less than about 60 mm.
  • outer diameter ratio between the outer tube and the inner tube of the double-walled tube is preferably in the range of from about 2.0 to about 4.0.
  • the outer tube is preferably made of stainless steel having a Cr content of not less than about 18 wt% and a Ni content of not less than about 8 wt%, which is represented by, for example, SUS304, SUS316 and SUS316L according to the JIS (Japanese Industrial Standards).
  • the outside atmosphere suction port of the double-walled tube is preferably spaced about 100 mm or more from the furnace wall.
  • a plurality of double-walled tubes 20 are arranged side-by-side horizontally just below the roll positioned in the upper portion of the furnace, and/or positioned just above the roll positioned in the lower portion of the furnace.
  • Figs. 7 and 8 also show the arrangement of rolls 12, heating sources 14 and strips 10.
  • the double-walled tube shown in Fig. 1 was fabricated using SUS316 stainless steel.
  • the double-walled tube had an outer diameter D of the outer tube of 114.3 mm, an inner diameter of the outer tube of 97.1 mm, an outer diameter of the inner tube of 48.0 mm, and an inner diameter of the inner tube of 41.2 mm.
  • the level difference H between the outside atmosphere suction port and the exhaust port of the double-walled tube was 200 mm.
  • a plurality of radiant heat shielding apparatuses each comprising the double-walled tube thus fabricated were installed in upper and lower stages of a heating zone of a vertical continuous annealing furnace, as shown in Fig. 13.
  • the radiant heat shielding apparatus was installed in the upper stage of the heating zone at a level spaced 400 mm from each roll just below it. Also, the radiant heat shielding apparatus was installed in the lower stage of the heating zone at a level spaced 400 mm from each roll just above it. The shielding effect of the actually installed radiant heat shielding apparatus was measured by operating the furnace for about two years under ordinary conditions.
  • Fig. 9 incidence of snaking
  • Fig. 10 replacement frequency of the radiant heat shielding apparatus.
  • the incidence of snaking is reduced down to about 1/3 as compared with both the conventional and comparative radiant heat shielding apparatuses using respectively a flat plate and a simple cooling tube.
  • the useful life of the radiant heat shielding apparatus is greatly prolonged in this invention as compared with both the conventional and comparative apparatuses, because the cooling action is enhanced in this invention by effectively utilizing the chimney effect developed on a flow in the cooling tube from suction of the outside atmosphere to exhaust thereof.
  • the radiant heat shielding apparatus of this invention including double-walled tubes 20 is disposed in the upper stage at a position between adjacent passes, i.e., at a position not just below each roll 12, as well.
  • the shielding effect can be increased by so arranging the radiant heat shielding apparatus.
  • this invention can provide a radiant heat shielding apparatus, which is inexpensive, effective in preventing snaking of a strip, and has the prolonged useful life, because of effective utilization of the chimney effect that is developed for flow in a double-walled cooling tube from suction of an outside atmosphere to exhaust thereof.

Landscapes

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

Description

    BACKGROUND OF THE INVENTION 1. Field of Invention
  • This invention relates to a heat shielding apparatus for a vertical continuous annealing furnace in which heat treatment is performed on a metal strip while the strip is continuously transported.
  • 2. Description of Related Art
  • Recently, an annealing process for recrystallizing steel strip after being subjected to cold rolling and for imparting good workability to the steel strip has been primarily carried out by continuous annealing instead of batch annealing. As a continuous annealing furnace for carrying out the continuous annealing, there are known horizontal continuous annealing furnaces, in which annealing is performed on a strip traveling along a horizontal pass, and vertical continuous annealing furnaces, in which a plurality of rolls are arranged in upper and lower portions of the furnace and annealing is performed on a strip traveling along a vertical pass. Of these continuous annealing furnaces, the vertical furnace is more advantageous for a mass-production process that is realized by increasing the passing (threading) speed of the strip.
  • Also, at present, indirect heating using a radiant tube is prevalent as a heating source for the vertical continuous annealing furnace, and steel strip is mainly heated with radiant heat from the heating source.
  • In a vertical continuous annealing furnace wherein a plurality of rolls are arranged in upper and lower portions of the furnace and annealing is performed on a steel strip being transported in the vertical direction by the rolls, while changing a travel direction from upward to downward or vice versa as the strip turns around each roll, it is important to prevent the steel strip from snaking or mistracking and to ensure stable passage of the strip. Generally, as shown in Fig. 11, each roll 12 arranged in the furnace is designed to have a convex roll crown with both shoulders tapered toward the ends. This design is intended to make the steel strip pass the furnace so that the strip always travels in match with the roll center, by utilizing a centering force (arrow F) acting on the strip, which has ridden over a tapered portion, in a direction from the roll edge toward the roll center based on a self-centering motion of the strip wound on the tapered portion of the roll with angle.
  • As shown in Fig. 12, however, radiant heat from a heating source (e.g., a radiant tube) 14 provided in the furnace heats not only a steel strip 10, but also the roll 12 arranged in the furnace. Therefore, an actual crown of the roll arranged in the furnace is given by the sum of a crown initially imparted to the roll (called an initial crown) and a crown imparted by the radiant heat from the heating source (called a thermal crown). As a result, when the temperature of the steel strip is lower than the roll temperature and when the thermal crown is larger than the initial crown, the temperature of a roll central portion is relatively reduced and the roll crown is rendered concave as indicated by solid lines in Fig. 12. If the steel strip 10 travels over the roll 12 having such a concave crown, a force produced in the width direction of the steel strip acts from the roll center toward the roll edge. Accordingly, once the steel strip undergoes snaking or mistracking, the strip is forced to ride over the roll edge beyond it at a stroke, which causes the problem during the strip passage that the strip comes into contact with the furnace wall.
  • To cope with this problem, some devices are proposed to prevent the roll temperature from being higher than the strip temperature, so, a shield plate has previously been provided to intercept the heat radiated from the heating source 14 toward the roll 12, as disclosed in Japanese Unexamined Utility Model Application Publication No. 63-119661. Also, Japanese Unexamined Patent Application Publication No. 57-79123 discloses a shielding apparatus employing a heat-resistant tube through which air, nitrogen gas or the like, flows for cooling.
  • Further, in view of the finding that a shield plate alone is not sufficient to suppress the thermal crown, Japanese Unexamined Patent Application Publication No. 52-71318 discloses a technique for spraying cooling gas to the roll to control the thermal crown in a positive way. Moreover, for the same purpose, Japanese Unexamined Patent Application Publication No. 53-119208 discloses a technique for water-cooling a roll edge portion, or changing a thermal conductivity between the roll central portion and the roll edge portion. In addition, Japanese Unexamined Patent Application Publication No. 53-130210 and Japanese Examined Patent Publication No. 57-23733 disclose techniques for arranging, separately from the rolls, a cooling apparatus that forms a cooling flow path.
  • Among the above-mentioned examples of the related art, techniques for suppressing the thermal crown imparted to the roll in a positive way are effective in preventing snaking of the strip, but have the problem of requiring a very large amount of equipment investment. Another problem is that, because of an increase in size of the apparatus itself, heat capacity of the apparatus is necessarily increased, which deteriorates the fuel unit consumption in the heating zone.
  • SUMMARY OF THE INVENTION
  • This invention has been made with the view of overcoming the above-described problems of the related art. An object of this invention is to provide an inexpensive and more efficient apparatus on the basis of the radiant heat shielding apparatus employing a cooling tube, which is disclosed in the above-cited Japanese Unexamined Patent Application Publication No. 57-79123, for example.
  • A heat shielding apparatus according to the preamble of claim 1 is disclosed in the above-mentioned Japanese Unexamined Patent Application Publication No. 53-130210.
  • According to the present invention, there is provided a heat shielding apparatus suitable for a vertical continuous annealing furnace including upper and lower portions and a plurality of rolls arranged in the upper and lower portions, wherein heat treatment is performed on a metal strip continuously transported in the vertical direction by the rolls while changing the direction of travel from upward to downward, or from downward to upward, as the metal strip turns around each of the rolls, and wherein the heat shielding apparatus can be positioned just below a roll in the upper portion of the furnace and/or just above a roll in the lower portion of the furnace, the heat shielding apparatus comprising:
  • at least one double-walled tube, each double-walled tube including:
  • an inner tube including an outside atmosphere suction port projected horizontally or downward so as to be exposed to the outside atmosphere, and an outer tube having an exhaust port exposed to the outside atmosphere; characterised in that the exhaust port of each double-walled tube is projected upward; and in that the outer tube of each double-walled tube has an outer diameter of not less than about 60 mm, a level difference H between the outside atmosphere suction port and the exhaust port of each double-walled tube of not less than about 150 mm, and the outer diameter D (unit: m) of the outer tube of each double-walled tube and the level difference H (unit: m) satisfy the relationship: D2x√(H)≥2.2 x 10-3.
  • Thus, to achieve the above object, this invention provides a radiant heat shielding apparatus for a vertical continuous annealing furnace, in which a plurality of rolls are arranged in upper and lower portions of the furnace and heat treatment is performed on a metal strip continuously transported by the rolls. The strip is transported in the vertical direction by the rolls while changing the travel direction from upward to downward, or from downward to upward, as the metal strip turns around each of the rolls. The radiant heat shielding apparatus is disposed below the roll positioned in the upper portion of the furnace, and/or above the roll positioned in the lower portion of the furnace, for intercepting heat radiated from a heating source provided within the furnace. Preferably, the radiant heat shielding apparatus is positioned just below the roll in the upper position of the furnace, and/or just above the roll in the lower portion of the furnace. The radiant heat shielding apparatus comprises a double-walled tube including an inner tube having an outside atmosphere suction port projected horizontally or downward to be exposed to an outside atmosphere, and an outer tube having an exhaust port projected upward to be exposed to the outside atmosphere.
  • Further, according to this invention, some embodiments of the radiant heat shielding apparatus comprise a plurality of double-walled tubes as described above. The double-walled tubes are horizontally arranged just below the roll positioned in the upper portion of the furnace and/or just above the roll positioned in the lower portion of the furnace.
  • Alternatively, in some embodiments, the radiant heat shielding apparatus comprises one or more double-walled tubes as described above, and the double-walled tubes are used as support tubes and a shield plate is attached to the support tubes.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • Fig. 1 is a vertical sectional view showing the construction of a double-walled tube for use in a first embodiment of a radiant heat shielding apparatus according to this invention;
  • Fig. 2 includes side views and front views showing, for comparison, arrangements of a conventional example using a flat plate, a comparative example using a simple cooling tube, and the first embodiment using a cooling tube in the form of the double-walled tube according to this invention;
  • Fig. 3 is a graph showing, for comparison, the relationships between the flow rate of cooling gas (Q) and the surface temperature of an outer tube of each double-walled tube and a flat plate for explaining the principles of this invention;
  • Fig. 4 is a graph showing the relationship among the flow rate of cooling gas, the temperature difference (ΔT) on a roll in the width direction of a strip, and the occurrence of snaking of the strip;
  • Fig. 5 is a graph showing the relationship between the flow rate of cooling gas and the product of the square of an outer diameter (D) of the outer tube and the square root of level difference (H);
  • Fig. 6 is a graph showing the relationship between the flow rate of cooling gas (Q) and the level difference (H);
  • Fig. 7 is a side view showing the construction of a second embodiment of the radiant heat shielding apparatus according to this invention;
  • Fig. 8 is a side view showing the construction of a third embodiment of the radiant heat shielding apparatus according to this invention;
  • Fig. 9 is a graph showing, for comparison, the incidence of snaking in the conventional example using a flat plate, the comparative example using a simple cooling tube, and this invention;
  • Fig. 10 is a graph showing, for comparison, the replacement frequency of the radiant heat shielding apparatus in the conventional example, the comparative example, and this invention;
  • Fig. 11 is a front view showing a roll that is arranged in a furnace and has a convex roll crown;
  • Fig. 12 is a front view showing a state where a strip is transported by a roll that is arranged in a furnace and has a concave crown due to a thermal crown imparted to the roll; and
  • Fig. 13 is a schematic view of an annealing furnace including an embodiment of the radiant heat shielding apparatus of this invention.
  • DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
  • Embodiments of this invention will be described below in detail with reference to the drawings.
  • A radiant heat shielding apparatus of this invention is disposed below (preferably just below) a roll positioned in an upper portion of a vertical continuous annealing furnace, and/or positioned above (preferably just above) a roll positioned in a lower portion of the furnace, for intercepting heat radiated from a heating source that is provided within the furnace, and the heat shielding apparatus is almost parallel to the roll.
  • In a first embodiment of this invention, as shown in Fig. 1, the radiant heat shielding apparatus has a structure of a double-walled tube 20 comprising an inner tube 22 having an outside atmosphere suction port 23 projected downward to be exposed to an outside atmosphere, and an outer tube 24 having an exhaust port 25 projected upward to be exposed to the outside atmosphere. With such a structure, an inexpensive and more efficient radiant heat shielding apparatus can be realized by effectively utilizing natural convection of the outside atmosphere (e.g., air).
  • Further, as a result of repeated experiments on the relationship among the flow rate of cooling gas (air) flowing through the double-walled tube 20, a radiant heat shielding effect, and high-temperature creep resistance of the double-walled tube, the inventors discovered a condition range suitable for intercepting the radiant heat in which an outer diameter D of the outer tube 24 of the double-walled tube 20 is not less than about 60 mm, a level difference (distance) H between the outside atmosphere suction port 23 and the exhaust port 25 is not less than about 150 mm, and the outer diameter D (unit: m) of the outer tube 24 of the double-walled tube and the level difference H (unit: m) satisfy the following formula (1): D2 ×(H)≥ 2.2x10-3
  • Heat-resistant alloy steel is an exemplary suitable material for forming the double-walled tube 20. For example, stainless steel having a Cr content of not less than about 18 wt% and a Ni content of not less than about 8 wt%, or special steel having high heat resistance, are preferred materials.
  • The inventors discovered that the radiant heat shielding apparatus employing a conventional cooling tube, disclosed in Japanese Unexamined Patent Application Publication No. 57-79123, has a limitation in its cooling capability utilizing natural convection of an outside atmosphere (air). Japanese Unexamined Patent Application Publication No. 57-79123 discloses that air for cooling is forced to flow into the cooling tube by a suction blower, or by a pressure blower. However, when a blower is provided on the suction side, the blower sucks exhaust gas at high temperatures, and therefore the blower must itself be made heat-resistant, or else a device for cooling suction gas must be provided upstream of the blower. In any case, the equipment cost is necessarily increased. On the other hand, when a pressure blower is used to force the cooling air to flow into the cooling tube, there is risk that a metal (or steel) strip is oxidized due to leakage of the air from the cooling tube into the furnace.
  • Based on the above findings, the inventors fabricated radiant heat shielding apparatuses having three types of structures shown in Fig. 2, and conducted tests on those actual apparatuses.
  • The left side of Fig. 2 represents a conventional example using a shield plate 16 in the form of a simple flat plate. A strip 10 (typically, a steel strip); a roll 12 arranged in a furnace; and a heating source 14 (typically, a radiant tube) are shown. The center of Fig. 2 represents a comparative example using a cooling tube 18 in the form of a simple straight double-walled tube. The right side of Fig. 2 represents the first embodiment of this invention including a cooling tube 20 in the form of the double-walled tube shown in Fig. 1.
  • Fig. 3 is a graph showing test results obtained by measuring a surface temperature of an outer tube of each double-walled tube and a flat plate (on the side facing the roll 12 arranged in the furnace), which is represented by the vertical axis, relative to a flow rate of cooling gas (air) measured at the exhaust port of the outer tube of each double-walled tube, which is represented by the horizontal axis. Measurement conditions were set such that the furnace temperature was 900°C, the temperature of the outside atmosphere (cooling gas) was 300°C, the outer tube diameter of the double-walled tube was 100 mm, the inner tube diameter of the double-walled tube was 40 mm, and the level difference H between the outside atmosphere suction port 23 and the exhaust port 25 of the double-walled tube was 200 mm.
  • In the comparative example using the cooling tube (simple straight double-walled tube) in which no improvements were made on the outside atmosphere suction port and the exhaust port, as indicated by marks A in Fig. 3, the flow rate of the cooling gas due to natural convection was small and the outer tube surface temperature of the double-walled tube reached 800°C.
  • In the conventional example (using the flat plate), as indicated by marks □, the surface temperature of the flat plate reached 860 °C.
  • By contrast, in the first embodiment of this invention in which the double-walled tube was improved to have the outside atmosphere suction port and the exhaust port projected respectively downward and upward to be exposed to the outside atmosphere, as indicated by marks O in Fig. 3, the flow rate of the cooling gas reached to 5.0 × 10-3 (Nm3/s) and the surface temperature of the outer tube was reduced down to about 500°C.
  • Fig. 4 is a graph showing the relationship between the flow rate of cooling gas (air) measured at the exhaust port of the outer tube of the double-walled tube according to this invention and a temperature difference ΔT developed on a temperature measuring roll in the width direction of a strip. The roll temperature measured had thermocouples embedded therein in the width direction of the roll and was positioned just above the radiant heat shielding apparatus which is almost paralell to the roll. Measurement conditions were set such that the length of a roll barrel was 2000 mm, the average width of steel strips passed through the furnace was 1260 mm, and the average furnace temperature was 900°C. Herein, the temperature difference ΔT was defined by ΔT = Te (roll surface temperature at a point spaced 100 mm from the roll edge) - Tc (roll surface temperature at the roll center). The graph of Fig. 4 shows that the minimum temperature difference ΔT, at which the roll crown is rendered concave and the steel strip undergoes snaking, is about 150°C, and that the flow rate of the cooling gas required for preventing snaking of the steel strip is not less than 3.0 × 10-3 (Nm3/s).
  • In the above-described first embodiment of this invention, the outside atmosphere suction port is described as being projected downward. However, the outside atmosphere suction port is not limited to such an arrangement. The outside atmosphere suction port may alternatively be projected at a different orientation, e.g., horizontally.
  • In the radiant heat shielding apparatus according to this invention, which comprises a double-walled tube having an outside atmosphere suction port projected horizontally or downward to be exposed to the outside atmosphere, and an exhaust port projected upward to be exposed to the outside atmosphere, the chimney effect developed on a flow in the double-walled tube from suction of the outside atmosphere to exhaust thereof is utilized to satisfy the above-mentioned required flow rate of the cooling gas.
  • From the law of conservation of mass for a fluid, the flow rate Q (m3/s) of the cooling gas is given by the following equation: Q = Vg × π × (D/2)2 where Vg is the flow speed (m/s) of the cooling gas at the exhaust port and D is the outer diameter (m) of the outer tube.
  • Also, from the law of conservation of energy for a fluid, the flow speed (m/s) of the cooling gas at the exhaust port is given by the following equation: Vg = (2gH) where g is the acceleration of gravity (= 9.8 m/s2) and H is the level difference (m) between the outside atmosphere suction port and the exhaust port of the double-walled tube.
  • Combining formulae (2) and (3) results in the formula: Q = (2gH) × π × (D/2)2
  • According to formula (4), the flow rate Q of the cooling gas is proportional to the outer diameter D of the outer tube and is also proportional to the square root of the level difference H between the outside atmosphere suction port and the exhaust port of the double-walled tube.
  • Fig. 5 is a graph plotting actually measured data representing the relationship between the parameter D2 × (H) indicated by the horizontal axis, and the flow rate Q (Nm3/s) of the cooling gas, indicated by the vertical axis. The graph of Fig. 5 shows that D2 × (H) ≥ 2.2 x 10-3 is needed to satisfy the required flow rate Q of the cooling gas that is not less than about 3.0 × 10-3 (Nm3/s). Stated otherwise, it is known that the furnace temperature ranges from about 500°C to about 900°C during actual operation, and when the furnace is within this temperature range, the flow rate of the cooling gas not less than the above-mentioned value is sufficient to achieve the desired cooling. Thus, if D2 × (H) ≥ 2.2 × 10-3 is satisfied, a sufficient cooling effect can be provided during actual operation.
  • Fig. 6 is a graph showing the relationship between the flow rate Q (Nm3/s) of the cooling gas and the level difference H (mm) between the outside atmosphere suction port and the exhaust port of the double-walled tube. The graph of Fig. 6 shows that if the level difference is less than about 150 mm, the cooling gas becomes difficult to flow because the level difference H is substantially at the same level as that corresponding to the diameter of the double-walled tube. Therefore, the level difference H between the outside atmosphere suction port and the exhaust port of the double-walled tube is preferably set to be not less than about 150 mm.
  • Also, if the outer diameter of the outer tube of the double-walled tube is small, the outer tube is more easily susceptible to creep due to the radiant heat. From the actual operation of the invention experienced so far, it has been confirmed that the outer diameter of the outer tube is preferably not less than about 60 mm.
  • Further, the outer diameter ratio between the outer tube and the inner tube of the double-walled tube is preferably in the range of from about 2.0 to about 4.0.
  • The outer tube is preferably made of stainless steel having a Cr content of not less than about 18 wt% and a Ni content of not less than about 8 wt%, which is represented by, for example, SUS304, SUS316 and SUS316L according to the JIS (Japanese Industrial Standards).
  • When installing the double-walled tube, the outside atmosphere suction port of the double-walled tube is preferably spaced about 100 mm or more from the furnace wall.
  • When the roll arranged in the furnace has a diameter several times as large as that of the double-walled tube of the radiant heat shielding apparatus, it is difficult to sufficiently intercept the heat radiated from the heating source toward the roll surface by using the radiant heat shielding apparatus that comprises one unit of double-walled tube. In such case, the radiant heat can be effectively intercepted by other embodiments of this invention shown in Figs. 7 and 8. In the second embodiment of the invention shown in Fig. 7, a plurality of double-walled tubes 20 are arranged side-by-side horizontally just below the roll positioned in the upper portion of the furnace, and/or positioned just above the roll positioned in the lower portion of the furnace.
  • In the third embodiment of the invention shown in Fig. 8, one or more (two are shown) double-walled tubes 20 are used as support tubes and a shield plate 30 is attached to the support tubes as illustrated. Figs. 7 and 8 also show the arrangement of rolls 12, heating sources 14 and strips 10.
  • Example
  • Based on the above-described results obtained from the tests performed on actual apparatuses, the double-walled tube shown in Fig. 1 was fabricated using SUS316 stainless steel. The double-walled tube had an outer diameter D of the outer tube of 114.3 mm, an inner diameter of the outer tube of 97.1 mm, an outer diameter of the inner tube of 48.0 mm, and an inner diameter of the inner tube of 41.2 mm. The level difference H between the outside atmosphere suction port and the exhaust port of the double-walled tube was 200 mm. A plurality of radiant heat shielding apparatuses each comprising the double-walled tube thus fabricated were installed in upper and lower stages of a heating zone of a vertical continuous annealing furnace, as shown in Fig. 13. The radiant heat shielding apparatus was installed in the upper stage of the heating zone at a level spaced 400 mm from each roll just below it. Also, the radiant heat shielding apparatus was installed in the lower stage of the heating zone at a level spaced 400 mm from each roll just above it. The shielding effect of the actually installed radiant heat shielding apparatus was measured by operating the furnace for about two years under ordinary conditions.
  • Results of the measurement are shown in Fig. 9 (incidence of snaking) and Fig. 10 (replacement frequency of the radiant heat shielding apparatus). In this invention, as shown in Fig. 9, the incidence of snaking is reduced down to about 1/3 as compared with both the conventional and comparative radiant heat shielding apparatuses using respectively a flat plate and a simple cooling tube. Also, as shown in Fig. 10, the useful life of the radiant heat shielding apparatus is greatly prolonged in this invention as compared with both the conventional and comparative apparatuses, because the cooling action is enhanced in this invention by effectively utilizing the chimney effect developed on a flow in the cooling tube from suction of the outside atmosphere to exhaust thereof.
  • Additionally, in the arrangement of Fig. 13, the radiant heat shielding apparatus of this invention including double-walled tubes 20 is disposed in the upper stage at a position between adjacent passes, i.e., at a position not just below each roll 12, as well. The shielding effect can be increased by so arranging the radiant heat shielding apparatus.
  • As described above, this invention can provide a radiant heat shielding apparatus, which is inexpensive, effective in preventing snaking of a strip, and has the prolonged useful life, because of effective utilization of the chimney effect that is developed for flow in a double-walled cooling tube from suction of an outside atmosphere to exhaust thereof.

Claims (3)

  1. A heat shielding apparatus suitable for a vertical continuous annealing furnace including upper and lower portions and a plurality of rolls arranged in the upper and lower portions, wherein heat treatment is performed on a metal strip (10) continuously transported in the vertical direction by the rolls while changing the direction of travel from upward to downward, or from downward to upward, as the metal strip (10) turns around each of the rolls, and wherein the heat shielding apparatus can be positioned just below a roll (12) in the upper portion of the furnace and/or just above a roll (12) in the lower portion of the furnace, the heat shielding apparatus comprising:
    at least one double-walled tube (20), each double-walled tube including:
    an inner tube (22) including an outside atmosphere suction port (23) projected horizontally or downward so as to be exposed to the outside atmosphere, and an outer tube (24) having an exhaust port (25) exposed to the outside atmosphere;
       characterised in that the exhaust port (25) of each double-walled tube (20) is projected upward; and in that the outer tube (24) of each double-walled tube (20) has an outer diameter of not less than about 60 mm, a level difference H between the outside atmosphere suction port (23) and the exhaust port (25) of each double-walled tube (20) of not less than about 150 mm, and the outer diameter D (unit: m) of the outer tube (24) of each double-walled tube (20) and the level difference H (unit: m) satisfy the relationship: D2x√(H)≥2.2 x 10-3.
  2. The heat shielding apparatus according to claim 1, wherein each double-walled tube (20) is usable as a support tube and a shield plate (30) is attached to each support tube.
  3. A vertical continuous annealing furnace, comprising:
    upper and lower portions;
    a plurality of rolls arranged in the upper and lower portions;
       wherein heat treatment is performed on a metal strip (10) continuously transported in the vertical direction by the rolls while changing a travel direction from upward to downward, or from downward to upward, as the metal strip (10) turns around each of the rolls; and
       a heat shielding apparatus as claimed in any preceding claim disposed just below a roll positioned in the upper portion of the furnace and/or just above a roll positioned in the lower portion of the furnace.
EP20010302309 2001-03-13 2001-03-13 Heat shielding apparatus for vertical continuous annealing furnace Expired - Lifetime EP1241274B1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
DE2001615379 DE60115379T2 (en) 2001-03-13 2001-03-13 THERMAL SHIELDING DEVICE FOR A VERTICAL BREATHING OVEN
EP20010302309 EP1241274B1 (en) 2001-03-13 2001-03-13 Heat shielding apparatus for vertical continuous annealing furnace

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP20010302309 EP1241274B1 (en) 2001-03-13 2001-03-13 Heat shielding apparatus for vertical continuous annealing furnace

Publications (2)

Publication Number Publication Date
EP1241274A1 EP1241274A1 (en) 2002-09-18
EP1241274B1 true EP1241274B1 (en) 2005-11-30

Family

ID=8181785

Family Applications (1)

Application Number Title Priority Date Filing Date
EP20010302309 Expired - Lifetime EP1241274B1 (en) 2001-03-13 2001-03-13 Heat shielding apparatus for vertical continuous annealing furnace

Country Status (2)

Country Link
EP (1) EP1241274B1 (en)
DE (1) DE60115379T2 (en)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS53130210A (en) * 1977-04-20 1978-11-14 Chugai Ro Kogyo Kaisha Ltd Continuous vertical heat treating furnace having roll chamber
JPS5779123A (en) * 1980-10-31 1982-05-18 Kawasaki Steel Corp Continuous annealing method for cold rolled steel strip and its device
JPS6184332A (en) * 1984-10-03 1986-04-28 Kawasaki Steel Corp Continuous annealing furnace of meal strip
JP2914840B2 (en) * 1993-02-26 1999-07-05 新日本製鐵株式会社 Crown control method of hearth roll in continuous annealing furnace

Also Published As

Publication number Publication date
DE60115379D1 (en) 2006-01-05
DE60115379T2 (en) 2006-07-06
EP1241274A1 (en) 2002-09-18

Similar Documents

Publication Publication Date Title
RU2592653C2 (en) Method of controlling protective gas atmosphere in protective gas chamber for treatment of metal strip
Wu et al. Heat transfer and combustion characteristics of an array of radial jet reattachment flames
EP1241274B1 (en) Heat shielding apparatus for vertical continuous annealing furnace
US6444163B1 (en) Heat shielding apparatus for vertical continuous annealing furnace
CA2339706C (en) Heat shielding apparatus for vertical continuous annealing furnace
KR100580063B1 (en) Heat shielding apparatus for vertical continuous annealing furnace
JP3596371B2 (en) Radiation heat shield device for vertical continuous annealing furnace
CN202595217U (en) Band steel cooling system
US5827056A (en) Device and method for improving strip tracking in a continuous heating furnace
JP3116724B2 (en) Roll crown adjustment device in furnace of heating furnace
CN201331256Y (en) Air blocking device for high temperature furnace tube
JP2914840B2 (en) Crown control method of hearth roll in continuous annealing furnace
JP3116725B2 (en) Roll crown adjustment device in furnace of heating furnace
JP3114498B2 (en) Method of adjusting the amount of roll crown in a heating furnace
JP4069642B2 (en) Horizontal furnace for continuous strip annealing
JP2693689B2 (en) Furnace body partitioning device for vertical open flame heating furnace
JP4126463B2 (en) Furnace temperature setting method in continuous annealing furnace heating furnace
FI107940B (en) Device in continuous heat treatment furnaces to support materials to be treated
JPS5940437Y2 (en) Furnace with radiant tube
JP2010150614A (en) Heating furnace and heating method
US20010037877A1 (en) Device and method for cooling fume intakes
JPH06158181A (en) Method for direct fire heating of steel strip and furnace used therefor
JP2733885B2 (en) Continuous heat treatment of steel strip
JPH083652A (en) Method for sealing inlet of preheating furnace for directly firing furnace and device therefor
KR101189109B1 (en) Fire-roller for thick slab heating furnace

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE TR

AX Request for extension of the european patent

Free format text: AL;LT;LV;MK;RO;SI

17P Request for examination filed

Effective date: 20030212

AKX Designation fees paid

Designated state(s): BE DE FR GB

RAP1 Party data changed (applicant data changed or rights of an application transferred)

Owner name: JFE STEEL CORPORATION

17Q First examination report despatched

Effective date: 20041223

GRAP Despatch of communication of intention to grant a patent

Free format text: ORIGINAL CODE: EPIDOSNIGR1

GRAS Grant fee paid

Free format text: ORIGINAL CODE: EPIDOSNIGR3

GRAA (expected) grant

Free format text: ORIGINAL CODE: 0009210

AK Designated contracting states

Kind code of ref document: B1

Designated state(s): BE DE FR GB

REG Reference to a national code

Ref country code: GB

Ref legal event code: FG4D

REF Corresponds to:

Ref document number: 60115379

Country of ref document: DE

Date of ref document: 20060105

Kind code of ref document: P

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: GB

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20060313

ET Fr: translation filed
PLBE No opposition filed within time limit

Free format text: ORIGINAL CODE: 0009261

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: NO OPPOSITION FILED WITHIN TIME LIMIT

26N No opposition filed

Effective date: 20060831

GBPC Gb: european patent ceased through non-payment of renewal fee

Effective date: 20060313

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: FR

Payment date: 20110317

Year of fee payment: 11

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: BE

Payment date: 20110311

Year of fee payment: 11

BERE Be: lapsed

Owner name: *JFE STEEL CORP.

Effective date: 20120331

REG Reference to a national code

Ref country code: FR

Ref legal event code: ST

Effective date: 20121130

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: FR

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20120402

Ref country code: BE

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20120331

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: DE

Payment date: 20190226

Year of fee payment: 19

REG Reference to a national code

Ref country code: DE

Ref legal event code: R119

Ref document number: 60115379

Country of ref document: DE

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: DE

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 20201001