JPH068462B2 - Heat treatment method for strip - Google Patents

Description

The present invention relates to a heat treatment method for strips in continuous annealing equipment.

<Prior Art> Various methods have been proposed as a method for cooling a strip by a cooling roll in a continuous annealing facility.
Japanese Unexamined Patent Publication (Kokai) No. 58-96824 discloses a method of cooling a strip with a cooling roll satisfying a certain relationship with the roll diameter. The present invention relates to a strip cooling roll, the roll diameter of which is determined based on the temperature drop amount of the strip cooled by one roll. That is, when the cooling amount per roll is 20 ° C. or less, the cooling efficiency is poor and the number of cooling rolls increases, so that it is difficult to apply it to an actual machine. Further, when the amount of cooling with one roll is 150 ° C. or higher, uneven cooling is likely to occur in the strip, and it is difficult to obtain a good strip.

Based on these recognitions, in JP-A-58-96824, a heat transfer model is created, and the strip heat radiation amount Q _s is expressed by the following equations (1) and (2).
And the heat transfer amount Q _r between strip rolls
Substituting into (3), the relationship between the roll outer diameter D, the heat passage amount K, the plate thickness t, and the line speed L _s is defined as in equation (4).

Q _s = WltγC _p ΔT _s (1) Q _r = A _s K ΔT _mt / 3600 (2) 20 <ΔT _s <150 (° C) (3) <Problems to be Solved by the Invention> The inventors of the present invention repeated a few hundred experiments on a method of heating or cooling a strip with a roll as in the case of the prior applicants, and found that Japanese Patent Application No. 58-96824. It turns out that the conditions disclosed in the issue are still insufficient. For example, some strips have a temperature unevenness after cooling, or some strips are deformed and buckled significantly during cooling, resulting in wrinkle-like distortion, so-called cooling buckle.

As a result of detailed analysis of experimental data of heating and cooling by hundreds of rolls for these causes, the present inventors have found that the contact state between the roll and the strip has a great influence on the temperature unevenness after the strip cooling (or heating). It has been found that the heat strain of the roll itself is greatly controlled by the self-weight of the roll itself, the weight of the heat medium being circulated, the deflection due to the strip tension, and the thermal strain of the roll caused by contact with the hot strip.

An object of the present invention is to provide a heat treatment method for a strip that can prevent uneven heating and cooling of the strip and deformation of the strip due to the uneven heating and cooling of the roll shell.

<Means for Solving Problems> The structure of the present invention for achieving such an object is a method of heating or cooling by contacting a strip with a heating or cooling roll in which a heating medium is circulated, and the following formula is used. A heat treatment method for a strip in a continuous annealing facility, characterized in that a roll having a roll outer diameter D and a roll shell thickness δ _R that satisfies the relationship of is used.

<Operation> The restriction on the thermal strain of the roll shell will be described with reference to FIG. As shown in FIG. 1 (a), the strip 3
In the case of cooling, the roll shell temperature T _{δ ( δ )} of the portion 1a in contact with the strip 3 is determined by the refrigerant 2 as shown in the following formula (5).
Above the temperature T _{R of} the strip 3 and below the temperature T _{s of the} strip 3.

T _s > T _{δ ( δ )} > T _R (5) On the other hand, the roll shell temperature T _δ ′ of the portion 1b where the strip 3 is not in contact is the temperature T of the refrigerant 3 because the outer surface of the roll is almost adiabatic. _It is almost equal to _R.

_{T δ '≒ T R ...... (} 6) As a result, the roll shell expands the portion 1b of the strip 3 are in contact, inquiries occurs between the portion 1b in which the strip is not in contact, FIG. 1 (b) Roll 1 as shown in
Wavy irregularities occur on the outer surface of the. For this reason, a portion of the strip 3 that comes into contact with the roll 1 and a portion that does not come into contact with the roll 1 are produced, and uneven cooling occurs. In simple terms, the following formula is established when the arithmetic mean temperature of the roll shell temperature generated by the cooling heat flow is taken as the representative temperature.

Where q is the heat flux between strip heating media (kcal / m ² h), λ _R is the thermal conductivity of the roll shell (kcal / mh ° C), and ΔD is the roll where the strip cooling part and the strip are not in contact. The difference in diameter (m).

According to the results of experiments conducted by the present inventors, if the following formula (9) is not satisfied in the range up to the strip width of 1.8 m,
It has been confirmed that the strips are significantly lifted from the rolls and the strips are deformed due to uneven cooling, which is not cooled and adversely affects the final product quality.

ΔD <3 × 10 ⁻³ (m) ……… (9) Then, substituting equations (9) and (10) into equation (8) gives the following.

Solve this for D.

<Examples> Using rolls of φ750 and φ1500 mm, changing the shell thickness,
Fig. 2 shows the results of an experiment conducted on a 0.5t to 1.0t strip at a line speed of 200 to 400mpm and a roll contact angle of 20 to 120 °.
The strip begins contact with the roll at 700-650 ° C, and 650
Separated from the roll at ~ 250 ° C. Under conditions outside the scope of the present invention in which the roll is thermally deformed (thermal crown), the strip cannot be made smooth, and an edge portion remains on the strip and a cooling buckle is produced.

<Effects of the Invention> As described specifically above with reference to the examples, the heat treatment method of the present invention heats or cools the strip by using a roll in consideration of restrictions on thermal strain. In a close state, it is possible to prevent deformation of the strip due to uneven temperature of heating and cooling of the strip or thermal crown of the roll.

[Brief description of drawings]

FIG. 1 (a) is an explanatory diagram showing the temperature distribution of the roll shell, FIG. 1 (b) is an explanatory diagram showing the thermal deformation of the outer surface of the roll, and FIG. 2 is the result of the experiment conducted by the inventors. It is a graph shown. In the drawing, 1 is a roll, 2 is a heating medium, and 3 is a strip.

Claims (1)

[Claims] 1. In a method of heating or cooling by contacting a strip with a heating or cooling roll in which a heating medium is circulated, a roll having a roll outer diameter D and a roll shell thickness δ _R that satisfies the following relationship is used: A method for heat treating a strip in continuous annealing equipment, comprising: Where D is the outer diameter of the roll (m), K is the heat transfer coefficient between strip heating media (kcal / m ² h ℃), T _si is the strip temperature (℃) immediately before contact with the roll, and T _so is the heat between the roll and the roll. strip temperature immediately after leaving the roll after replacing (℃), T _R is the heat medium temperature (℃), λ _R is the thermal conductivity of the roll shell (kcal / mh ℃), α i between the heat medium and the roll inner surface Is the heat transfer coefficient (kcal / m ² h ° C.), β is the linear expansion coefficient (1 / ° C.) of the roll shell, and δ _R is the roll shell thickness (m).