JP2906901B2 - Metal strip heating method in continuous metal strip processing line with direct-fired heating furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heating a metal strip in a continuous metal strip processing line having a direct-fired heating furnace.

[0002]

2. Description of the Related Art In a direct-fired heating furnace provided in a continuous processing line for a metal strip such as a continuous annealing furnace, a load is set for each zone or a target temperature of a pass entrance side or a pass exit side of each pass is set. As such, the presets and / or feedback were heated. In the case of a one-pass furnace, at least the last zone is a reduction heating zone, and in the case of a two-pass furnace, at least the last zone of the second pass is reduction heating. Further, in a furnace having two or more passes, there is a technique in which a reduction heating zone is provided in front of the roll chamber, that is, the last zone of each pass in order to prevent pick-up due to oxidation of the metal band in the roll chamber between passes.

[0003]

In the above-described method, if the setting of the heating load, the temperature of the metal zone entering the direct fire reduction heating zone, and the type of the direct fire reduction heating burner and the heating temperature match, the oxidation will be reduced. Thus, the occurrence of pickup in the roll chamber could be prevented. However, since the entire furnace equipment, including this direct-fired heating furnace, is designed to support the maximum heat treatment amount of the metal strip, if the heat treatment amount of the metal strip is relatively small, install it at each pass entry side. The heated burner is in an unburned state, and the metal strip passing through the area is heated by the combustion exhaust gas of the heating burner installed at each pass outlet side.

At this time, the oxidation of the surface of the metal strip by the exhaust gas was remarkable at a plate temperature of 550 ° C. or more, and the surface of the metal strip was oxidized even when heated by a reduction heating burner installed in the last zone of the direct-fired heating furnace. The hydrogen concentration in the atmosphere gas is increased in an indirect heating furnace or a soaking furnace using a radiant tube or an electric heater connected to the direct-fired heating furnace and discharged from the direct-fired heating furnace in a state. The surface had to be reduced.

On the other hand, with the recent diversification of products (multiple types, multiple sizes) and smaller lots, there are cases where there are a plurality of types of metal strips in the continuous heat treatment equipment. Is limited by the metal band having the smallest heat treatment amount, and thus there is a problem that oxidation of the surface of the metal band occurs frequently.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. In a direct-fired heating furnace having a plurality of passes, a non-oxidized metal strip surface is provided at a roll chamber and a direct-fired heating furnace outlet. Thus, pickup on a roll installed in a roll chamber and a furnace after the direct-fired heating furnace is prevented.

[0007]

Means for Solving the Problems] Therefore the present invention includes a plurality
It has a plurality of direct fire heating burners in each zone of each pass, and at least the final zone of the last pass is a direct fire reduction heating zone, and the direct fire generated according to the change in the heat treatment amount of the metal strip. while corresponding to the change in the total amount of combustion formula furnace, the final pass by increasing the combustion amount in the order and determines the combustion amount total in each pass, within the combustion amount totals for each path, adjacent zones mutually Of the rear zone fuel
Perform inclined heating to make the amount of firing more than the previous zone, at least
After the combustion zone where the plate temperature is high,
The basic feature is that the combustion flow rate is adjusted so that it is not formed .

[0008]

In the above construction, by changing the total combustion amount of the direct-fired heating furnace in accordance with the change in the heat treatment amount of the metal strip, a heating amount suitable for the size is given to the metal strip. determining a combustion quantity total in turn increased to each pass the combustion amount from the final pass while corresponding to the change of the combustion amount, and within a range of combustion rate sum of each path, adjacent zones mutually
Out of the front zone, the amount of combustion
Heat is applied to at least the combustion zone where the plate temperature is in the high temperature range.
Lower the combustion flow rate so that no unburned zone is formed.
By the integer, while keeping the heat treatment balance in the entire process, when continuously heated toward the inlet of the metal strip from the exit of the direct flame heating furnace, unburned in significant high temperature range is oxidation of the metal strip surface burner is not present to perform the heating as the state and the metal strip will be initiated heated from low have temperature. For this reason, even if a state occurs in which the metal band passes through the region of the unburned heating burner before the start of heating, the oxidation of the metal band surface is very slight.

[0009]

FIG. 1 shows the construction of a direct-fired heating furnace 2 provided in a continuous annealing furnace for a metal strip 1, and the method of the present invention carried out in a direct-fired heating furnace 2 having two passes. A method of heating the metal strip 1 according to one embodiment will be described.

As shown in FIG. 1, a metal strip 1 from outside the furnace or from a pre-tropical zone via a tie 3a is first heated by a heating burner disposed in a direct-fired heating furnace 2a (zones # 1 to # 4) in the first pass. 8
The heating burner 8 is disposed in the direct-fired heating furnace 2b (# 5 to # 8 zones) of the second pass, once passing through the tie 3b.
Is further heated through the tie 3c, and is conveyed to a heating zone or a solitary zone where the radiant tube, an electric heater or the like is used to heat and maintain a uniform temperature, and is annealed.

In order to perform a predetermined heat treatment on the metal strip 1, its heat pattern is determined by a metal strip condition setting device 12 from a standard, a steel type, etc., and as shown in FIG. A target temperature Taim of the metal strip 1 at the outlet of the furnace 2b is determined by the target temperature setter 11 for metal strip, and the value is set in the temperature controller 6 for metal strip.

In the metal zone temperature controller 6, a current value Tact obtained by measuring the temperature of the metal zone 1 with a sheet thermometer 5 installed at the outlet of the direct-fired heating furnace 2b is input, and the measured value Tact
Is compared with the temperature target value Taim, and the total combustion flow rate (operating amount) Qaim of the direct-fired heating furnace is calculated. From the amount of operation and the heat band and the metal band condition of the metal band size #
Fuel flow target value Qιai for each of zones 1 to # 8
m (ι = 1 to 8) is obtained from the combustion load pattern as shown in FIG. 3 by the combustion control calculators 7a to 7h, and is actually measured (omitted in FIG. 1). (Ι = 1 to 8) and its target value Qιaim to control the blower rotation speed or the valve opening, etc.
The fuel flow rate in each zone (ι = 1 to 8) is adjusted. On the other hand, based on the theoretical air amount of the fuel used and the target air ratio, the target value of the combustion air flow rate Gιai for each zone (ι = 1 to 8)
m is calculated and actually measured for each zone (not shown in FIG. 1). The measured value Gιact of the combustion air flow rate is compared with this target value Gιaim, and the blower rotation speed or valve opening is set for each zone. And the like to adjust the combustion air flow rate.

Here, the combustion load pattern in this embodiment will be described with reference to FIG. The exit # 4 zone of the first pass and the exit # 8 zone of the second pass burn at the minimum fuel flow rate or more regardless of the total fuel flow rate Qaim (operating quantity) of the direct-fired heating furnace. According to the increase of the operation amount Qim, 2
From the # 8 zone at the exit of the pass to the # 1 zone at the entrance of the first pass , the combustion of the rear zone among the adjacent zones
It has a combustion load pattern of inclined heating in which the amount is equal to or greater than the previous zone .

Next, a second embodiment of the method of the present invention will be described with reference to FIG. 4, FIG. 5, and FIG. The difference from the configuration of FIG. 1 of the embodiment is that in the above-described embodiment, the combustion control of the entire direct-fired heating furnace is performed by one metal zone temperature controller 6 installed only at the outlet of the direct-fired heating furnace 2b. On the other hand, in the configuration of the present embodiment shown in FIG. 4, the direct-fired heating furnaces 2a and 2b are provided at the exits of the respective paths with the metal zone temperature controllers 6a and 6b, respectively. Are respectively controlled by combustion.

As shown in the equipment configuration of FIG. 4 and the control flows of FIGS. 5 and 6, the target temperature Taim1 of the metal strip 1 at the outlet of the direct-fired heating furnace 2a in the first pass is # 1 to # 8. The total Qact of measured values obtained by measuring the fuel flow rate for each of the zones (omitted in FIG. 4) is obtained by the total fuel flow rate calculator 10, and the metal zone target temperature Taiim1 at the outlet of the first pass is calculated from the total fuel flow rate Qact. The target temperature setting unit 11a determines the target temperature from the metal band target temperature setting pattern shown in FIG. 7 and sets the value in the metal band temperature controller 6a. Hereinafter, the method from the fuel flow target calculation for each of the zones # 1 to # 4 based on FIG. 8 to the fuel flow rate adjustment and the combustion air flow rate adjustment is the same as in the first embodiment described above.

The method from the determination of the target temperature of the metal zone at the outlet of the direct-fired heating furnace 2b in the second pass to the adjustment of the fuel flow rate and the combustion air flow rate for each zone is also the same as that of the first embodiment. Is performed in the same manner as described above.

Here, the metal band target temperature setting pattern in this embodiment will be described with reference to FIG. This metal zone target temperature setting pattern is a sum Qc of the total value of the maximum fuel flow rates in zones # 5 to # 8 in the second pass and the minimum fuel flow rate in zone # 4 of the exit in the first pass, and the total fuel flow rate Qact. Under the condition that Qc> Qact, that is, until the entire zone in the second pass reaches the maximum fuel flow rate, the metal zone target temperature Taim1 is set to 400 ° C. or less, and conversely, Qc ≦ Qac
Under the condition t, that is, after all the zones in the second pass reach the maximum fuel flow rate, the metal zone target temperature Taim1 is 250
The target temperature Taim1 is changed in the range of not less than 550 ° C. and not more than 550 ° C. according to the progress of the total fuel flow rate Qact. As the temperature setting pattern, a plurality of patterns are prepared in consideration of a heat pattern and a metal band size.

Using the above method, a steel strip (carbon 0.
Table 1 shows the results of a heating experiment conducted on a low-carbon aluminum killed steel (04%).

[0019]

[Table 1]

In this experiment, a direct-fired heating furnace having two passes is used. The first pass is composed of # 1 to # 4 zones, the # 1 to # 3 zones are non-reduction type heating burners, and #
In the fourth zone, a reduction heating burner is used, and in the second pass, zones # 5 to # 8 are used. In zones # 5 to # 7, a non-reduction heating burner is used. In the zone # 8, a reduction burner is used. The air ratio is adjusted in the range of 0.86 to 0.96.

In the conventional method in which the steel strip is heated such that the steel strip passes through the unburned zone in a high temperature range of 500 ° C. or higher, the color of the steel strip surface is blue or blue at the outlet of the direct-fired heating furnace. In contrast to the dark blue color and oxidation observed, in this example, it was observed that the heating of the steel strip was completed in the non-oxidized state even at the outlet of the direct-fired heating furnace.

[0022]

According to the method of the present invention described in detail above, a non-oxidized metal strip surface can be obtained at the outlet of the direct heating furnace in the direct heating furnace having a plurality of passes. It is also possible to prevent occurrence of pickup on a roll arranged on a tie connecting the path and the path.

[Brief description of the drawings]

FIG. 1 is a side view of a two-pass direct-fired heating furnace in which the method of the present invention is performed.

FIG. 2 is a flowchart showing a control flow of the method of the present invention performed with the above configuration.

FIG. 3 is a graph showing a combustion load pattern of a heating burner performed in the present embodiment.

FIG. 4 is a side view of a two-pass direct-fired heating furnace in which a second embodiment of the method of the present invention is performed.

FIG. 5 is a flowchart showing a control flow of the method of the present invention performed in the above configuration.

FIG. 6 is a flowchart showing a control flow of the method of the present invention performed in the same configuration.

FIG. 7 is a graph showing a metal band target temperature setting pattern at the exit of the first pass in the present embodiment.

FIG. 8 is a graph showing a combustion load pattern of a heating burner in the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal strip 2a, 2b Direct-fired heating furnace 3a, 3b, 3c Connecting 4 Roll 5, 5a, 5b Sheet thermometer 6, 6a, 6b Metal-zone temperature controller 7a-7h Combustion control calculator 8 Direct-fired heating Burner 9 Flow control valve 10 Total fuel flow calculator 11, 11a, 11b Metal band target temperature setting device 12 Metal band condition setting device

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyoo Omori 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Naoto Kitagawa 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Japan Inside Kokan Co., Ltd. (72) Inventor Hidemine Kobayashi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Kokan Co., Ltd. (56) References JP-A-54-83608 (JP, A) (58) Fields investigated Int.Cl. ⁶ , DB name) C21D 1 / 52,9 / 52 C21D 9 / 56,11 / 00

Claims (1)

(57) [Claims] The present invention has a plurality of passes, a plurality of direct heat heating burners in each zone of each pass, and a direct heat reduction heating zone at least in a final zone of a final pass, and a change in heat treatment amount of a metal strip. While corresponding to the change in the total combustion amount of the direct-fired heating furnace generated according to the above, the combustion amount is sequentially increased from the final pass to determine the total combustion amount in each pass,
Within the total combustion volume of each pass ,
Of which, inclined heating to make the combustion amount in the rear zone higher than that in the front zone
And at least after the combustion zone where the plate temperature is in the high temperature range.
The combustion flow rate so that no unburned zone is formed
A method for heating a metal strip in a continuous metal strip processing line having a direct-fired heating furnace.