JPS5933176B2 - How to set the heating zone temperature of a continuous annealing furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating zone furnace temperature setting method for a continuous annealing furnace, and particularly to a heating zone furnace temperature setting method for a continuous annealing furnace having a heating zone that sequentially heats various types of strips in a plurality of heating zones. Concerning improvements to the setting method.

Generally, a continuous annealing furnace, e.g., as shown in FIG.
Payoff reel 10, welding machine 12, steel strip cleaning device 14,
Friddle roll 16, entrance louver 18, friddle roll 20, tension device 22, vertical heating zone 2
4. A steel strip 8 consisting of a soaking zone 26, a cass jet type quenching zone 28, an overaging zone 30, a cooling zone 32, a priddle roll 34, an exit looper 36, a priddle roll 38, a shear 40, and a tension reel 42. In the continuous annealing equipment, a heating zone 24 for raising the temperature of the steel strip 8 to a temperature necessary to obtain desired material properties (hereinafter referred to as target temperature) has a control zone, for example, a second As shown in the figure, it is divided into six heating zones 24-1 to 24-6.

The heating zones 24-1 to 24-6 are thus divided in consideration of the fact that the furnace temperature distribution is difficult to be uniform for each part of the furnace, especially in the vertical direction.

The furnace temperature setting in the heating zones 24-1 to 24-6 can be set independently by the instrumentation loop for each zone, but in reality, it is shown by the solid line A in Fig. 3. According to the target plate source Ts on the heating zone outlet side, ■, the set furnace temperature for the 2nd zone is 1g1□, and the set furnace temperature Tgs for the 3rd and 4th zones.
Flat heat is often used in which the set furnace temperature Tg56 of <t5t6 zones is all given as a common value.

The outer edge curve in this case is shown by a solid line B.

However, if the set furnace temperature for each heating zone is all flat heat, as shown by the solid line C in Fig. 3, the required fuel flow rate for the 1.2 zone is F1□3゜4 zone. F34 t 5 , there is a large difference in the required fuel flow rate F56 of the 6 zones (for example, in the radiant tube heating zone, T s = 700°C, T
When g12=Tga+=Tg+5a=850℃, F
:F :F56=41:34:25)
This creates a large difference in the required fuel flow rate for each zone.

Therefore, especially in multi-purpose continuous annealing furnaces that need to handle a wide variety of copper strips and have a wide range of furnace temperature settings, it is difficult to achieve a predetermined strip temperature by simply setting the flat heat furnace temperature common to each zone when setting the high-temperature furnace edge. In order to improve the heating zone capacity, the burner capacity of the two zones must be made extremely large, which not only increases equipment costs but also reduces controllability and thermal efficiency when setting the bottom of the furnace at low temperatures. There is a problem in that there may be cases where an unfavorable and excessive turndown has to be performed.

That is, for example, in a radiant tube type heating zone, the fourth
As shown in the figure, relative to the burner's maximum gas flow rate, the exhaust gas humidity is relatively low and there is a good efficiency range of 20 to 90%, that is, a good turndown ratio (use flow rate/maximum flow rate) range. However, if the burner capacity is designed to match the furnace temperature setting with high humidity, the thermal efficiency will be extremely poor when the furnace edge is set at a low temperature, and good combustion conditions will not be ensured, making it difficult to set the furnace temperature at a low temperature. .

Therefore, there was a limit to the ability of the heating zone to be improved by increasing the burner capacity.

On the other hand, as something similar to the present invention, by utilizing the correlation between the heat crown of the roll in the furnace, the plate temperature, and the plate thickness, the furnace temperature can be set for each zone according to the plate thickness. It has also been attempted to change the so-called step heat furnace temperature settings to suppress the meandering of the copper strip and improve threading performance.
Unlike the present invention, the purpose was not to improve the performance of the heating zone.

The present invention has been made to solve the above-mentioned conventional drawbacks, and is a heating zone of a continuous annealing furnace that can improve the capability of the heating zone and perform efficient heat treatment over a wide range of furnace temperature settings. The purpose is to provide a furnace temperature setting method.

The present invention provides a heating zone furnace temperature setting method for a continuous annealing furnace having a heating zone that sequentially heats various types of strips in a plurality of heating zones, in which the plate temperature required to obtain desired material properties on the exit side of the heating zone is If the humidity is higher than the upper limit of the flat heat capacity obtained within a good turndown ratio range of the burner, the set furnace temperature of the heating zone is gradually increased to create a step heat, and the target plate temperature is set to the flat heat. If the flow rate is less than the upper limit of capacity, the above objective is achieved by setting the furnace temperature of the heating zone to be the same to achieve flat heat.

The present invention will be explained in detail below.

Currently, a thickness of 0 is being conveyed at a line speed of 150 m/min.
．． 65mrn.

A copper strip with a plate width of 1000 mm is heated to Ts-900 on the heating belt exit side.
Let's compare and examine the experimental results of step heat and flat heat when heating to ℃.

Setting furnace temperature Tg12tT gs+
s T gsa are the same, Tg12 and Tgs
If we use a step heat setting in which the set furnace temperature is sequentially increased by △Tg = 30℃ between Tg3+ and Tg5a, and △Tg = 30℃ between Tg3+ and Tg5a, as shown by the dashed line E in Fig. 5, in this case Set furnace temperature Tg of 1st and 2nd zone, 2 is 8
85℃, set furnace temperature Tg34 of 3rd and 4th zone is 915
The set furnace temperature Tg56 for the fifth and sixth zones is 945°C.

The outer edge curve at this time is as shown by the dashed-dotted line F in Figure 5, and the required fuel flow rate in each heating zone at this time is as shown by the dashed-dotted line G, where F12 is 1224Nr.
n'/hour, F34 is 11079N"7 o'clock, F56 is 63
At 8Nrrt1, F56 becomes 638Nm'/hour.

Therefore, the total required fuel flow rate in this case is 29
41Nrri'/hour.

On the other hand, as in the past, Tg1□, T g34
In the case of flat heat setting where all t T g56 are equal, the set furnace temperature is 928.5 as shown by solid line A.
℃, the outer edge curve at this time is as shown by solid line B, and the required heat flow rate is F12 as shown by solid line C.
= 1393 Nm"7 o'clock, F34 = 117 ON
At m37 hours, F56 = 507 Nm3/hour.

The total required fuel flow rate in the case of this flat heat setting is 307 ONm/hour, which is 129 Nm'/hour, about 7% lower than that in the case of the step heat setting.

Therefore, it can be seen that the step heat setting allows fuel savings.

Further, in FIG. 5, the maximum burner capacity in each zone is indicated by a broken line H, and furthermore, the favorable turndown ratio range described in FIG. 4 is indicated by hatching.

From this, it can be seen that the fuel required for flat heat (solid line C) in zone 2 is outside the hatching range, and the fuel required for step heat (dotted chain line G) is within the hatching range.

Furthermore, this clearly shows the above-mentioned fact that the total amount of fuel required for flat heat is about 7 times larger than that for step heat.

Also, the maximum burner capacity in zones 1 and 2 is 145ON.
For 771″/h (broken line H), step heat has a larger margin and can improve performance.

According to the step heat setting, the required fuel flow rate F56 in the downstream heating zones 5 and 61 is larger than the required fuel flow rate F56 in the case of the flat heat setting.
Since the burner capacity of the , 6 zones is originally a small value, there is no problem from a design point of view.

In addition, since the burner capacity is averaged over zones 1 to 6, it is only necessary to change the orifice diameters of gas and air in the same burner, and the burner design is easy.

Note that the temperature difference ΔTg of the step heat is desirably about 50°C at maximum because if the temperature difference is too large, it may have an adverse effect on the furnace. It is desirable that the temperature is around ℃.

As mentioned above, if step heat is used, the copper strip can be heated to the same temperature with less fuel, and if the burner capacity is the same, the copper strip can be heated to a higher temperature. The temperature needs to be determined by trial and error or empirically after predetermining Tg for step heating, and this calculation is extremely troublesome.

Therefore, instead of performing this step heat in all cases, in the present invention, if the target plate temperature on the heating belt outlet side is less than a predetermined temperature, flat heat is performed as in the conventional method. Calculation of furnace temperature is made easy.

Here, the predetermined temperature is a plate temperature that corresponds to the upper limit of heating capacity, which has been empirically determined within a range that does not significantly impair thermal efficiency such as the fuel consumption rate depending on the burner capacity of the heating zone in flat heat.

That is, for example, in the case of flat heat in FIG. 5, the required fuel flow rate in each zone falls within the hatched range, and it is the highest plate temperature on the heating zone exit side that is obtained at this time.

Note that the hatching range, that is, the good turndown ratio range varies depending on the burner characteristics, and must be determined as appropriate depending on the burner used.

Examples of the present invention will be described in detail below.

In this embodiment, as shown in FIG. 6, first, the dimensions of the copper band and the target plate temperature Ts on the exit side of the heating band are read.

This target plate temperature Ts is set to a predetermined temperature Tso (for example, 850°C
), and if the temperature is greater than the predetermined temperature Tso, the maximum step heating △ allowed for the material depending on the plate dimensions.
Load Tg.

In accordance with this maximum step heating ΔTg, a step heat furnace setting value is calculated using a step heat furnace setting capacity calculation formula.

This calculation is performed as follows.

That is, first, the following relational expression is derived from the heat balance equation.

QcXF= Ls xdxwxaQs+ (1-μ)Q
gF+QL-(1) where Qc is fuel gas calories, F
is the amount of fuel gas, Ls is the line relationship, d is the plate thickness, W is the plate width, ΔQs is the amount of heat absorbed by the copper strip depending on the target plate temperature Ts,
μ is recuperator efficiency, Qg is exhaust gas sensible heat (-KTg
: Tg is the set furnace temperature, K is a constant), QL is the loss due to furnace body dissipation, etc. The left side of equation (1) is the total calorific value, and the first term on the right side is the calorific value used for heating the copper strip, the right side is The second term corresponds to the amount of heat recovered, and the third term on the right side corresponds to the loss.

Rearranging this equation (1), it becomes as shown in the following equation.

(Qc (1-μ)KTg, IF QLLsXd-□
(2) W△Qs The relationship between the plate width W and LsXd is illustrated in FIG. 7 based on the equation (2).

The solid line ■ in Fig. 7 is the LsXd limit line corresponding to flat heat when the target plate temperature Ts = 700°C, and the solid line J
is the LsXd limit line corresponding to flat heat when the target plate temperature Ts=950°C.

On the other hand, in the case of step heat, it is assumed that equation (1) is established for each zone, and a curve as shown in FIG. 7 is obtained from the sum of the values determined for each zone.

The broken line in Figure 7 shows the target plate temperature T
The LsXd limit line and dashed line when s=700℃ and step heating ΔTg=50℃ are L when the target plate temperature Ts=950℃ and step heating 50℃ were obtained in the same way.
This is the sXd limit line.

This LsXd limit line is approximately expressed using the constant ABCDE, for example, as shown in the following equation.

LsXd=ATs+Bw+cw2-I-DXTsXw+
E-・(3) From this LsXd limit line, when heating a plate with a width of 1000 mm to 950℃ using flat heat, L
The maximum value is sXd=50, but it can be seen that LsXd=100 can be achieved by step heat.

That is, if the plate thickness d is 0.5 mm, the line speed Ls can be up to a maximum of 200 m/min in step heat, but only up to 100 m/min in flat heat.

At the same time, when heating up to 700° C., it can be seen that LsXd=158 is the maximum in flat heat, but LsXd=195 is possible in step heat.

Conversely, from this curve, the maximum temperature of the flat heat can be determined according to the line speed Ls, plate thickness d, and plate width w.

On the other hand, as described above, in flat heat, there is a predetermined temperature Tso determined from experience, that is, an economical maximum temperature Tso determined within a range that does not impair thermal efficiency.

An example of this is shown by a dashed line M shown in FIG.

Therefore, when the target temperature Ts is equal to or higher than the predetermined temperature Tso, flat heat would result in poor thermal efficiency, so step heat is used.

For example, if the target temperature is 950°C, the step heat shown by the curve in Figure 7 is used, and the plate width is 100°C.
If the plate thickness is 0 mm and the plate thickness is 0.5 mm, the maximum line speed Ls at this time is 200 m/min, so the line speed Ls
200 m/min or less, and determine the set furnace temperature in each heating zone of the heating zone.

On the other hand, the target plate mixture Ts on the heating belt output side is at the predetermined temperature Ts.

If the line speed is less than that, calculate the maximum allowable line speed from the flat heat furnace condition setting capacity calculation formula corresponding to the solid line in Figure 7, reduce the line speed in the heating zone to less than that, and change the line speed from the conventional one. Similarly, the same set furnace temperature is determined for each heating zone to achieve flat heat.

For example, if the target temperature Ts is 700°C, flat heat as shown by curve
000 myn and the plate thickness is 0.5 mvt, the maximum line speed Ls at this time is 15810.5 to 316 m/min, so the line speed Ls is set to 316 m/min or less and the furnace temperature to be set is determined.

Although the above embodiments apply the present invention to a continuous annealing furnace for copper strips, the scope of application of the present invention is not limited thereto, and can similarly be applied to heating control of general metal or non-metal strips. The applicability is clear.

As explained above, according to the present invention, the capacity of the heating zone of a continuous annealing furnace can be improved with a relatively small burner capacity, and efficient heat treatment can be performed over a wide range of furnace temperature settings.

Further, by changing the step heating, the performance conditions can be changed, and the meandering of the strip can be easily prevented, which is an excellent effect.

[Brief explanation of the drawing]

Fig. 1 is a process diagram showing an example of a continuous annealing furnace, and Fig. 2 is a process diagram showing an example of a continuous annealing furnace.
FIG. 3, a cross-sectional view showing an example of the heating zone in the continuous annealing furnace, shows the position of the conventional heating zone in the furnace, the set furnace temperature,
Figure 4 is a diagram showing the relationship between the Sotobuchi curve and the required fuel flow rate.
Figure 5 is a diagram showing the relationship between the gas flow rate and exhaust gas hot water temperature in a radiant tube type heating zone, and the relationship between the furnace position in the heating zone, the set furnace temperature of the step heat setting, the outer edge curve, and the required fuel flow rate. , set furnace temperature for flat heat settings,
Diagram showing a comparison with the relationship between the Sotobuchi curve and the required fuel flow rate, No. 6
The figure is a flowchart showing a furnace temperature setting method in an embodiment of the present invention, and FIG. 7 is a diagram showing the relationship among the product LsXd of plate width W, line speed, and plate thickness in an embodiment of the present invention. 8... Steel strip, 24... Heating zone, 24-
1-24-6... Heating zone.

Claims (1)

[Claims] 1. In a heating zone furnace temperature setting method for a continuous annealing furnace having a heating zone that sequentially heats various types of sl-IJ tubes in a plurality of heating zones, the plate temperature necessary to obtain desired material properties on the exit side of the heating zone, If the temperature is higher than the upper limit of the flat heat capacity obtained within a good turndown ratio range of the burner, the set furnace temperature of the heating zone is increased sequentially to carry out step heat, and the target plate source is heated to the flat heat. A heating zone furnace temperature setting method for a continuous annealing furnace, characterized in that when the temperature is lower than the temperature corresponding to the upper limit of capacity of the heating zone, the set furnace temperature of the heating zone is set to be the same and flat heat is performed.