JPH0830221B2 - Continuous heat treatment method for metal strip - Google Patents

Description

TECHNICAL FIELD The present invention relates to a continuous heat treatment method for metal strips,
More specifically, the present invention relates to a method for controlling the metal strip to a target plate temperature when the furnace temperature is changed by changing the plate thickness of the metal strip or the plate passing speed.

<Prior Art> A continuous heat treatment furnace for metal strips will be described by taking the horizontal continuous heat treatment furnace shown in FIG. 7 as an example.
Is composed of a pre-tropical zone 3, a heating zone 4 and a soaking zone 5. The metal strip 1 is conveyed by a conveying roll 6 and heated and soaked in a predetermined heat pattern by a heating device (not shown).

Here, the heat pattern refers to a heating rate, a heating temperature, a soaking temperature, a soaking time of the metal strip 1 and the like, and is intended to give a predetermined property to the metal strip. If the plate thickness of the metal strip and the plate running speed in the furnace are constant, the metal strip is heated to a predetermined temperature by controlling the furnace temperature or the fuel flow rate of the pre-heat zone, the heating zone, and the metal zone to a predetermined value accordingly. The pattern can be controlled.

<Problems to be Solved by the Invention> However, in the case where the metal strips having different plate thicknesses are connected and the plate thickness of the metal strip suddenly changes (the place where the metal strips having different plate thicknesses are connected is called a step point) ,
Alternatively, when the passing speed is suddenly changed, a predetermined heat pattern cannot be applied. The reason is that the heat input to the metal strip is mainly radiant heating from the furnace wall and the burner room, and it is difficult to change the so-called furnace temperature represented by the furnace wall temperature and the like in a short time. Further, when the plate passing speed is suddenly changed, the in-furnace time (that is, the heating time) of the metal strip is suddenly changed, so that the temperature of the metal strip is suddenly changed. A metal strip that has been subjected to a heat pattern far away from the predetermined heat pattern cannot be made into a product because it cannot have predetermined properties.

As a measure to connect metal strips with different plate thicknesses for continuous heat treatment, a dummy strip, which is conventionally called a strip material, is connected in the middle to avoid abnormal temperature of the metal strip at the stepped point. However, the reduction of production volume and waste of energy by passing the strip material were great.

An object of the present invention is to provide a continuous heat treatment method that solves such a problem and can always maintain a predetermined heat pattern.

<Means for Solving the Problems> The present invention uses a hollow plate temperature control roll provided in a continuous heat treatment furnace for metal strips, and when changing the furnace temperature by changing the plate thickness of the metal strips, Until the end of the change, when cooling or heating the metal strip to control the target plate temperature, the plate temperature control roll was made thicker in shell thickness in proportion to the response time peculiar to the continuous heat treatment furnace. This is a continuous heat treatment method for metal strips, characterized in that a metal strip is used.

<Operation> The operation of the present invention will be described by taking the case of changing the plate thickness of the metal strip as an example.

First, FIG. 3 shows the transitions of the metal strip temperature and the furnace temperature near the step point when the plate temperature control roll of the present invention is not used. At the heating zone outlet (soaking inlet), the time when the thickness of the metal strip changes from D ₁ to D ₂ (D ₁ <D _{2 in} this case) is t ₁ . At this time, for the sake of simplicity, the passing speed is constant.

In this case, until the time t _1, the thickness is so constant D _1, the furnace temperature Tg ₁ and the metal strip temperature Ts ₁ corresponds to the thickness D ₁ is constant until time t _1.

At time t ₁ , the plate thickness instantly changes from D ₁ to D _2, and the plate temperature of the metal strip sharply decreases. The reason is that the metal strip having the thickness D ₂ is heated to Ts ₂ (= Ts ₁ ) if the furnace temperature is Tg ₂ , but at the time t ₁ when the step point passes, the furnace temperature is Tg ₁
Therefore, it is ΔTs lower than the target plate temperature.

Then, the furnace temperature gradually changed, and when it became the furnace temperature Tg ₂ corresponding to the plate thickness D ₂ at time t ₂ after the time lag τ,
The target temperature of the metal strip is Ts ₂ (Ts ₁ = Ts _{2 in} this case)
become.

Therefore, in the conventional technique, the ΔTs temperature difference is not applied only to the trailing plate, but to the leading plate as well, and the vicinity of the stepped point of the leading plate is made higher than the target temperature Ts ₁ by ΔTs / 2, and The plate temperature near the step point of the plate is ΔTs / 2 from the target transient Ts ₂ (= Ts ₁ ).
It has been conventionally practiced to reduce the amount of deviation from the target plate temperature by just lowering it. In this case, for example, time t ₁
More about τ / 2 hours before, the method of changing the furnace temperature from Tg ₁ to Tg ₂ is used. However, even if this method is adopted,
When the change in plate thickness is large, it deviates from the target temperature.

Next, the case of the method of the present invention is shown in FIG. When the plate thickness of the metal strip increases from D ₁ to D _{2 at the} stepped point, the plate temperature control roll is heated by contacting it with the strip D _1, and the average shell temperature of the plate temperature control roll is set. T _R1
The metal strip is set to a temperature at which a sufficient amount of heat can be applied to prevent the temperature drop of ΔTs. Specifically, T _R1 is set to a temperature substantially equal to the strip temperature Ts ₁ . Therefore, the metal strip can maintain the target plate temperature substantially without abruptly lowering the plate temperature due to heat input by contact conduction from the plate temperature control roll.

Although FIGS. 3 and 4 describe the case where the plate thickness increases, conversely, the same phenomenon occurs when the plate thickness decreases.
Also, when changing the strip passing speed, the metal strip can be controlled to the target strip temperature in the same manner.

<Example> Next, a method for determining the shell thickness of the plate temperature control roll will be described. The shell thickness of the plate temperature control roll and the plate temperature control roll have an effect for smoothing the plate temperature deviation ΔTs. As shown in Fig. 6, the relationship with the is substantially proportional. Therefore, the shell thickness of the plate temperature control roll can be set according to the response time (which is unique to the furnace) when the furnace temperature of the continuous heat treatment furnace is changed. Make sure you choose. For example, in the case of a direct fired furnace, the responsiveness of the furnace is good, and the effective working time of the plate temperature control roll is within 5 min, so it is possible to select 50 mm as the shell thickness.

An embodiment of the plate temperature control roll used in the continuous heat treatment method for metal strips of the present invention will be described with reference to FIGS.

FIG. 1 is a cross-sectional view of one embodiment of the plate temperature control roll 7, in which the inside 8 is hollow, and the metal strip 1 wound around this is made equal to the roll shell temperature. The thickness of the shell 9 is increased to increase the heat capacity and enhance the heat buffering property.

FIG. 2 shows an arrangement example of the plate temperature control rolls 7, and the plate temperature control rolls 7 are arranged between the transport rolls 6 so as to be vertically movable by the roll moving device 10. FIG. 2A shows the temperature control when the metal strip 1 is wound around the roll moving device, and the plate temperature control roll 7 is rotated at the same peripheral speed as the plate passing speed of the metal strip 1. FIG. 2 (b) shows the metal strip 1 at the time of threading (threading).

 Next, specific examples will be described.

FIG. 5 shows the plate thickness change rate and the plate temperature deviation ΔTs (see FIG. 3) when the method of the present invention is applied and when the conventional method is used.
The results of the investigation of the relationship are shown.

 However, the survey was conducted under the following conditions.

Furnace temperature ≈ 900 ° C, target metal strip plate temperature at heating zone outlet ≈ 750 ° C, plate thickness: D ₁ = 0.8 mm, plate speed = 60 mpm, plate temperature control roll: diameter = 800φ, shell thickness = 50 mm Shell material ... SUS, metal strip winding angle = 180 ° Plate temperature control roll number = 4

From FIG. 5, it can be seen that the plate temperature deviation ΔTs becomes about 1/5 of that of the conventional method by the method of the present invention.

<Effects of the Invention> As described above, the method of the present invention can control the metal strip to the target plate temperature when the furnace temperature is changed by changing the plate thickness of the metal strip or the plate passing speed. And the waste of energy can be prevented, and a great effect can be obtained especially in high-mix low-volume production.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an embodiment of a plate temperature control roll used in the method of the present invention, FIG. 2 is a layout view of the plate temperature control roll used in the method of the present invention, and FIG. Is a graph showing the transition of the plate temperature and the furnace temperature of the metal strip near the step point when the plate temperature control roll of the present invention is not used, and FIG. 4 is the plate temperature of the metal strip near the step point according to the present invention. , Furnace temperature,
A plate temperature control roll shell average temperature change graph, FIG. 5 is a graph showing the relationship between the plate thickness change rate and temperature deviation (ΔTs) in the present invention and the prior art, and FIG. 6 is the shell thickness and plate temperature. FIG. 7 is a graph showing the relationship of the effective action time of the control roll, and FIG. 7 is an explanatory diagram of the horizontal continuous heat treatment furnace. 1 ... Metal strip, 2 ... Continuous heat treatment furnace, 6 ... Conveying roll, 7 ... Plate temperature control roll, 9 ... Shell.

Claims (1)

[Claims] 1. When using a hollow plate temperature control roll provided in a continuous heat treatment furnace for metal strips to change the furnace temperature by changing the plate thickness of the metal strip, until the change of the furnace temperature is completed. When cooling or heating the metal strip to control the target plate temperature, the plate temperature control roll is characterized by using a shell thickness increased in proportion to the response time peculiar to the continuous heat treatment furnace. Continuous heat treatment method for metal strip.