JPH10245631A - Steel sheet annealing furnace in continuous hot dipping line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an annealing furnace which has the strengths of both a horizontal and vertical furnace respectively and free from the weaknesses of the both furnaces. In the two types of annealing furnaces used in continuous hot dipping line, the horizontal type allows uniform heat treatment for a long time, which is a requisite for a steel sheet whose mechanical properties are important fat has drawbacks of heavy energy consumption and maintenance workload. The vertical type furnace, on the other hand, is free from such weaknesses but does not allow a long heat treatment time. SOLUTION: This annealing furnace has a heating treatment zone 10 for executing the surface cleaning and the recrystallizing treatment, etc., of the steel sheet and a horizontal type furnace structure for executing horizontal shifting with hearth rolls (RH) in a cooling treatment zone 30 for lowering the steel sheet temp. to cool from the annealing temp. to a hot-dipping bath temp. A soaking treatment zone 40 positioned between the above both zones has the vertical type furnace structure for shifting while meandering so as to ascend/ descend by winding the steel sheet S around bottom rolls RB and top rolls RT.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous hot-dip metal plating line which performs a heat treatment for imparting required mechanical properties to a steel sheet, as well as cleaning and activating the surface of a steel sheet to be plated to be supplied to a plating bath. Related to the annealing furnace to be performed.

[0002]

2. Description of the Related Art In an aluminum plating or galvanizing operation using a continuous hot-dip metal plating line, a steel sheet (a cold-rolled steel sheet) fed to a plating bath is subjected to an annealing furnace before being introduced into the plating bath. Heat treatment is performed.
Contaminants such as rolling fats and oils and scales adhere to the surface of the steel sheet, which causes deterioration of plating quality, and the steel sheet is work-hardened by cold rolling, and as such is required for product plated steel sheets. Mechanical properties cannot be satisfied. The heat treatment of the steel sheet by the annealing furnace is performed for the purpose of modifying the surface of the steel sheet and improving the mechanical properties to prevent such problems.

In FIG. 4, (1) is an annealing furnace, (3) is a molten metal plating bath, and a steel sheet S is an annealing furnace at a constant transfer speed (line speed) set according to plating operation conditions and the like. (1) After passing through the inside and subjected to a predetermined heat treatment, through a snout (2) (maintained in a reducing atmosphere such as AX gas for protecting the surface of the annealed steel sheet). And introduced into the plating bath (3). As the well-known annealing furnace, there are a horizontal annealing furnace and a vertical annealing furnace. In the horizontal annealing furnace, as shown in FIG. 2, a steel sheet S is placed on a hearth roll (R _H ) arranged in the furnace and is transferred in a horizontal direction, while a heat treatment zone (10), a soaking zone ( 20) and a furnace structure for performing a predetermined heat treatment by sequentially passing through each zone of the cooling zone (30). On the other hand, the vertical annealing furnace
As shown in FIG. 3, the steel sheet S is stretched over a bottom roll (R _B ) disposed on the hearth and a top roll (R _T ) provided above, and the meandering traveling is performed in the vertical direction. (10) Each of the soaking zone (20) and the cooling zone (30) is sequentially passed.

[0004]

The horizontal annealing furnace in which a steel sheet is placed on a hearth roll and transported horizontally is not as complicated as the furnace structure of a vertical annealing furnace, and has a burden on equipment costs and operation management. This also has the advantage of requiring relatively little.
However, the furnace length (steel transfer distance from inlet to outlet)
Is relatively short. For this reason, steel sheets that can be treated in the horizontal annealing furnace are limited to general grades that require relatively short annealing time, and grades that require improvement in mechanical properties by long-time annealing (for example, I for deep drawing and ultra deep drawing
The treatment of F steel etc.) must rely on a vertical annealing furnace. In order to enable long-time annealing in a horizontal annealing furnace,
Furnace lengths must be significantly increased, and installation of such furnaces is practically impossible.

On the other hand, in the vertical annealing furnace, since the steel plate travels in the furnace for a long time, the long-time treatment required for the IF steel and the like for deep drawing and ultra deep drawing described above can be sufficiently ensured. However, compared to a horizontal annealing furnace, the furnace volume is extremely large, the amount of energy consumption such as atmospheric gas and fuel required for the furnace operation is remarkably large, and the furnace structure is complicated, and a heavy burden is required for maintenance. As described above, the horizontal annealing furnace and the vertical annealing furnace have advantages and disadvantages, and need to be properly used in accordance with the type of steel sheet, required mechanical properties, and the like, which is extremely inconvenient. The present invention provides an annealing furnace that complements the drawbacks of the horizontal annealing furnace and the vertical annealing furnace and has both advantages.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a heat treatment zone (10) for performing surface purification / activation and recrystallization treatment of a steel sheet fed to a molten metal plating bath, and holding the steel sheet at an annealing temperature for a predetermined time. In the continuous annealing furnace of the continuous hot-dip metal plating line, which comprises a soaking zone (20) for cooling and a cooling zone (30) for cooling and lowering the soaked steel sheet to a temperature suitable for the plating process, a heating zone (10). And the cooling zone (30) has a horizontal furnace structure for transferring the steel sheet horizontally along the hearth roll of the hearth, and the soaking zone (20) is arranged above the bottom roll of the hearth. It is characterized by having a vertical furnace structure in which a steel plate is suspended over a top roll and transported while meandering up and down.

In the present invention, the soaking zone (20)
In addition, by providing a vertical furnace structure for vertical and meandering transfer of a steel sheet, it is possible to perform a long-time soaking process, which is difficult with a conventional horizontal annealing furnace, and to perform a heating treatment zone (10) and a cooling treatment zone ( By adopting the horizontal furnace structure 30), a compact configuration of the entire furnace is enabled. The combined structure of the horizontal furnace and the vertical furnace makes it possible to control the grade, mechanical properties, etc. of the target steel sheet without disadvantages such as a large furnace volume and an increase in energy consumption as in the conventional vertical annealing furnace. For a long period of time required according to the temperature.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. In FIG. 1, a heating zone (10) on the upstream side of the soaking zone (20) and a cooling zone (30) on the downstream side include a steel sheet S on a hearth roll (R _H ) of the hearth.
The has a horizontal furnace structure for transferring horizontally placed, soaking zone (20), steel plates and the hearth of the bottom roll (R _B) and the installed top roll upward (R _T) It has a vertical furnace structure that performs vertical meandering transfer by bridging S.

The heat treatment zone (10) has the same structure and form as those of the heat treatment zone in the conventional horizontal annealing furnace. The illustrated heat treatment zone (10) includes a preheating furnace (1).
1), a non-oxidizing furnace (12) and a heat treatment zone (10), which are the same as those of the heat treatment zone in the horizontal annealing furnace of FIG. The preheating furnace (11) uses a combustion exhaust gas or the like as a heat source to heat the steel sheet S to an appropriate sheet temperature (for example, 100 to 100).
(140 ° C), and in the non-oxidizing furnace (12), for example, rapid heating of the steel sheet by the combustion flame of natural gas whose air-fuel ratio has been adjusted, and as a gas cleaning effect, contamination of oil and the like on the steel sheet surface and scale, Is removed. Heating zone (1
In 3), the oxide film is removed by indirect heating of the steel sheet with a radiant tube in an inert atmosphere such as nitrogen gas.
Activation of the surface takes place. The steel sheet S is heated to a predetermined annealing temperature (for example, 700 to 800 ° C.) while passing through the steel sheet S, recrystallized, and sent to the next soaking zone (20).

[0010] The steel sheet S introduced into the soaking zone (20)
Is transported while meandering up and down in the vertical direction via a bottom roll (R _B ) on the hearth and a top roll ( _RT ) arranged above. The furnace structure / form of the soaking zone (20) is the same as that of the soaking zone in the vertical annealing furnace shown in FIG. The soaking zone (20) is, for example, AX
It has a reducing atmosphere by gas or the like, and heats and holds the steel sheet S at a predetermined annealing temperature. The steel sheet S is given a sufficient soaking time (for example, 30 to 50 seconds) in the course of the vertical meandering transfer, is given predetermined mechanical properties by the soaking effect, and moves to the cooling treatment zone (30).

[0011] The steel sheet S introduced into the cooling zone (30)
During the horizontal transfer while being carried on a hearth roll ( _RH ), a temperature substantially equal to the plating bath temperature (for example, 450 to
460 ℃). The furnace structure and form are the same as those of the cooling zone in the conventional horizontal annealing furnace. The cooling processing of the steel sheet is performed by, for example, spraying a jet stream of furnace atmosphere gas or the like onto the steel sheet surface.

The illustrated cooling treatment zone (30) is provided for cooling the horizontal annealing furnace shown in FIG. 2 in order to avoid material deterioration (hardening, generation of heat cracks, etc.) associated with rapid cooling and cooling of the steel sheet S. As with the treatment zone, the primary cooling zone (3
1), a cooling zone (32) and a secondary cooling zone (33). In the primary cooling zone (31), the steel sheet S is heated from an initial sheet temperature (for example, about 900 ° C.) to an intermediate temperature (for example, about 700 ° C.).
° C), forced cooling is interrupted in the cooling zone (32), and then cooled to a predetermined plate temperature (for example, about 460 ° C) in the secondary cooling zone (33). The steel sheet S derived from the cooling zone (30) passes through the snout (2) via the bridle roll (BR) at the furnace end, is introduced into the plating bath (3) as shown in FIG. After being led out onto the bath according to 4), the amount of plating is adjusted by a gas wiping device (5), and then a predetermined processing device (6)
(A forced cooling device in hot-dip aluminum plating, an alloying treatment furnace in alloyed zinc plating, etc.) to finish the product plated steel sheet.

In the annealing furnace of FIG. 1, the heat treatment zone (1
0) is constituted by a preheating furnace (11), a non-oxidizing furnace (12) and a heating zone (13), and a cooling treatment zone (30)
Is composed of a primary cooling zone (31), a cooling zone (32), and a secondary cooling zone (33), but is not necessarily limited thereto. The heat treatment zone (10) is used to clean the surface of the steel sheet before the steel sheet S is introduced into the soaking zone (20).
If a predetermined treatment such as recrystallization is achieved, a horizontal furnace configuration other than the above may be employed, and the cooling treatment zone (30) can also be used without causing a material defect of the steel sheet due to cooling and cooling. As long as it can be cooled to a predetermined plate temperature, a horizontal furnace configuration other than those described above may be adopted.

[0014]

The steel sheet annealing furnace of the present invention has a furnace structure in which a horizontal furnace structure in a heat treatment zone and a cooling treatment zone and a vertical furnace structure in a soaking zone are combined. While avoiding such an increase in furnace volume, it enables long-term soaking that is impossible with conventional horizontal annealing furnaces, and the compact structure of the entire furnace enables energy consumption of furnace atmosphere gas, fuel, etc. Efficient annealing treatment of various steel sheets in a continuous hot-dip metal plating line, such as performing long-term soaking heat required according to the grade, mechanical properties, etc. of the target steel sheet while maintaining the amount relatively low And maintenance of the furnace is also good.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of an annealing furnace according to the present invention.

FIG. 2 is a view showing a horizontal annealing furnace.

FIG. 3 is a view showing a vertical annealing furnace.

FIG. 4 is a diagram showing a continuous hot-dip metal plating line.

[Explanation of symbols]

1: annealing furnace 2: snout 3: molten metal plating bath 10: heat treatment zone 11: preheating furnace 12: non-oxidizing furnace 13: heating zone 20: soaking zone 30: cooling zone 31: primary cooling zone 32: cooling band 33: secondary cooling zone R _H: hearth rolls R _T: top roll R _B: bottom roll S: steel plate

Claims (1)

[Claims] 1. A heat treatment zone (10) for performing surface purification / activation and recrystallization treatment of a steel sheet fed to a hot-dip metal plating bath, and a soaking zone (20) for holding the steel sheet at an annealing temperature for a predetermined time. And a continuous annealing furnace of a continuous molten metal plating line comprising a cooling treatment zone (30) for cooling and lowering the soaked steel sheet to a temperature suitable for the plating treatment.
The heat treatment zone (10) and the cooling zone (30) have a horizontal furnace structure for transferring a steel sheet horizontally along the hearth roll of the hearth, and the soaking zone (20) is located at the bottom of the hearth. A steel plate annealing furnace for a continuous hot-dip metal plating line, having a vertical furnace structure for transferring a steel sheet while rolling the steel sheet between a roll and a top roll disposed above and moving it up and down.