JPS5941427A - Roll-cooling means for metal strip - Google Patents

Abstract

PURPOSE:To suppress the formation of buckling or area contraction, and defective configuration, by providing rear and front tension stretchers at the upper stream and downstream sides of a cooling roll zone, respectively, and making said cooling roll zone small in diameter at the upper stream side. CONSTITUTION:Rear and front tension stretchers 12, 13 are provided at the upper stream and downstream sides of a cooling roll zone 11, respectively, and the upper stream side of said cooling roll zone 11 is made small in diameter. Hence, a strip X being affected by tension with the rear and front tension stretchers 12, 13 is cooled from 500-900 deg.C to 150-450 deg.C during its passage through the cooling roll zone 11. Since the cooling roll zone 11 at the upper stream side comprises a small-diameter roll zone 11a, compression stress to the strip X is reduced to suppress defective configuration, buckling etc.

Description

[Detailed description of the invention] The present invention relates to a roll cooling device for metal strip.

A roll cooling method is one of the methods for cooling a metal strip in a continuous annealing furnace or the like.

This cooling method cools the strip by bringing it into direct contact with a cooling roll.The cooling rate is relatively fast, the overaging process is short, and there is no need for post-processing (pickling, etc.) after rapid cooling. It has the following advantages.

[Cooling power in this cooling method] The roll has a cooling water circulation mechanism inside it, and the cooling water is circulated to cool the roll surface that comes into contact with the strip. It consists of

Conventional problems in such roll cooling include the tendency for the shape to collapse due to thermal stress generated during the cooling process, and buckling that occurs between the cooling rolls.

In extreme cases, this buckling causes vertical wrinkles in the line direction called "shrinkage", which can lead to strip breakage within the line, resulting in serious problems.

In order to solve the problem of the shape of the strip and the product quality, various ideas have been made in the past, such as Japanese Patent Application No. 56-206075 and Utility Model Application No. 56-150123 filed by the applicant of the present invention.

Although these methods are effective in themselves and have been practically used, for example, the former requires the addition of a large-scale hydraulic device to make the crown of the water-cooled roll variable; In the latter case, it is necessary to strictly control the surface roughness of the water-cooled roll surface, and it cannot be denied that maintenance is complicated.

The present invention has been made based on the principle of generation of thermal stress that occurs in contact cooling with a cooling roll, and is based on the results obtained from both theory and experiment. This relieves thermal stress, thereby suppressing buckling and constriction, as well as shape defects.

Figure 1 (a) is a schematic diagram of a roll cooling device using five HC cooling rolls, and Figure 1 (b) is a diagram showing seven trips (X) extended in a plane.

The strip (X) is cooled while sequentially contacting each cooling roll (#1 to #5). (A) (CXE) (G)
(I) is the entrance side of the cooling roll (1), i.e. the strip (X
) indicates the point of contact with the cooling roll (1). Further, (BXDXFXHXJ) indicates the exit side of the cooling roll (1), that is, the point where the strip (X) is out of contact with the cooling roll (1).

(1) The cooling rate is high in the contact areas (AB, CD, EF, GH, IJ), and the non-contact areas (BC, DE, FG).

At HI), the steel strip (X) becomes smaller and cools stepwise. The point at which this cooling rate changes from large to small and from small to large is the point of contact with the cooling roll (2) mentioned above (
A) to (J), which are referred to herein as cooling rate inflection points. Furthermore, the cooling rate changes from small to dog (
That is, the inlet side AICII:IGIII) of the cooling roll is called the α inflection point, and the point where the cooling rate changes from large to small (i.e., the exit sides B, D, F, H, J of the cooling roll) is called the β inflection point. shall be.

Figure 1) is the result of analyzing thermal stress (two-dimensional plane stress) assuming that the cooling curve in Figure 1 (c) is the same in the width direction. Law (Finite)
This is the result of numerical calculation using element method).

Note that the calculation conditions for FIG. 1 above are shown below.

Cooling roll diameter: 1400 nm Number of cooling rolls = 5 Contact length Al = ts): 1000 tm
Constant total contact length: 5Xtt=50.00m Non-contact length Lx”L4): 775 wa Constant line unit tension: IKg/-♂ Strip width = 1000W+ S) Lip thickness: 1.01rm Line speed: 19 B mpm '(3,3m
pa) Cooling start temperature: 600℃ Cooling stop temperature: 400℃ (Note) The cooling rate of the contact area between the cooling roll and the strip is constant at 125℃ 1 sec, and the non-contact area also undergoes convection with the surrounding gas and radiation with the surroundings! l:j7 cooled to υ13℃
It was set constant at /sec.

Although the above conditions are very model-like, they are similar to the actual two conditions.
For example, the cooling capacity of each cooling roll can vary within a short range depending on the amount of water flowing through each cooling roll, the water inlet temperature, etc., so please consider carefully. It can be regarded as a condition for According to the numerical calculation results shown in Figure 1 (B), when focusing on the stress in the width direction of the plate, there is a large compression in the center of the plate width at the α inflection point of the cooling rate, and at the β inflection point. A large tensile strain occurs at the center in the width direction of the plate.

This is extremely characteristic υ, and regarding the stress in the width direction, no particularly large compressive stress or tensile stress is observed in other parts.

On the other hand, in the field of roll cooling in continuous annealing furnaces, it is known from experience that the center of the roll is difficult to cool compared to conventional methods, and that the most amount of drawing occurs in the center of the sheet width. Considering the above experimental results, the direct cause of the cooling bugs and poor shape of the strip is the α inflection point of the cooling rate (cooling roll entrance side A, C+) shown in Fig. 1 (C-).
1! It is expected that the compressive stress has a peak point at each point: + G + I).

Based on the above findings, the present inventors have conducted various experimental studies and found that the above compressive stress can be significantly reduced by reducing the diameter of the cooling roll.

The reason for this is that first of all, by reducing the roll diameter, the contact length between the cooling roll and the metal strip (i.e., BC,
DE , FG , HI ) are short, so that α
This is thought to be because the inflection point and the β inflection point are close to each other.

In other words, this phenomenon occurs because compressive stress acts at the α inflection point, and tensile stress in the opposite direction acts at the β inflection point, so when these two inflection points are brought closer together, mutual interference occurs, causing each to cancel out the other. However, it is inferred that this is a result that approaches the situation of stress-free cooling.

Second, when the roll diameter is made smaller, the distance between the cooling rolls can be made closer, resulting in ~ the non-contact length between the cooling roll and the metal strip (i.e. ~ BC, DE, FG, HI).
This is because the α inflection point and the β inflection point become close to each other.

Thirdly, when the diameter of the cooling roll is made small, the cooling rate of the strip due to contact is small, and as a result, the thermal stress generated is also small. This is because the inner surface of the cooling roll is cooled with cooling water, so if you take out only a part of the roll's shell in the circumferential direction and pay attention to it, that part will be heated by contacting the high-temperature strip, and the strip will be heated. If there is no contact with the air, the cooling water will only cool the air. As the picks and cooling rolls rotate, the heating process by the strips and the process of cooling only by the cooling water are carried out; however, the larger the diameter of the roll, the faster the rate of cooling only. Since the process takes a long time, the roll shell must be sufficiently cooled before contacting the strip. In other words, the average temperature of the shell of the cooling roll is lower as the roll diameter increases, so the cooling capacity for the strip also increases as the roll diameter increases. In general, the larger the temperature gradient that occurs in the strip, the greater the thermal stress that occurs, so when a small diameter roll is used, the temperature gradient becomes smaller and the thermal stress that occurs as a result also becomes smaller.

For the above reasons, it can be seen that if the diameter of the cooling roll is made as small as possible, the compressive stress can be reduced, and the occurrence of buckling, poor shape, or constriction can be suppressed.

However, when small diameter rolls are used, the number of required rolls increases, requiring a long roll row, which causes difficulties in manufacturing and maintaining the equipment. In the present invention, the above-mentioned problems caused by making the cooling roll small in diameter are solved by using a part of the cooling roll on the upstream side of the cooling roll band as a cooling roll with a small diameter, and further providing tension devices at the front and rear of the cooling roll band, respectively. This has achieved a reduction in shape defects, buckling, and shrinkage.

FIG. 2 shows an embodiment of a roll cooling device in which the present invention is applied to a continuous annealing furnace.

The strip (X) is heated in a heating furnace/soaking furnace (not shown).
After being heated to about 0° C., it is introduced into a roll cooling device α0. The roll cooling device α1 is composed of a cooling port “roll band α, a rear tension tensioning device (6) provided upstream thereof, and a front tension tensioning device 01 provided downstream thereof.

The upstream side of the cooling roll band αη is a small diameter cooling roll band (ll
a), followed by a medium-diameter roll band (llb) and a large-diameter roll band (lie) in this embodiment. Each roll band (11a) (11b) (11c) is composed of four rolls. Small diameter roll band (ll
The roll diameter of a) is 400mm121~800ttrml
It is desirable that the roll diameter of the large diameter roll band (llc) be approximately 1000 times or more the thickness of the strip (X).

The reason why we decided to provide the small diameter roll band (lla) on the upstream side is because the yield strength of the strip is generally lower on the high temperature side of the strip, so there is a risk of large buckling growth and the risk of poor shape or shrinkage. This is because the effect of preventing buckling and the like is greater when a small-diameter roll band is provided on the high-temperature side of the strip, that is, on the upstream side. Furthermore, if a cooling roll with a small diameter is used on the low temperature side of the strip, there is a risk of damaging the material of the strip as described above.

The tension tensioning device (2) 01 has the same structure as the conventional one, and each roll consists of three rolls. This tension tension device (12) can apply tension to the support lip (X) to prevent shape defects, buckling, and constriction.

In the roll cooling device 00 configured as above, the strip CX) passes through the cooling roll zone αp while being subjected to tension by the rear tensioning device 0o and the front tensioning device (g), and is heated to a temperature of 500 to 900°C. to 150-450°C. At this time, since the upstream cooling roll band O) is a small diameter roll band (lla), the compressive stress of the strip (X) is reduced here. As a result, poor shape, buckling, etc. are suppressed. In addition, since the small diameter roll band (lla) is only a part of the cooling roll band 01), the roll row does not become long or large, and since the strip (X) in the small diameter roll band (11a) is high temperature, the strip Good rapid cooling is possible without damaging the material.

As explained above, according to the roll cooling device of the present invention,
(Metals) IJ tubes can be rapidly cooled without causing shape defects, buckling, or constriction. Moreover, the roll row does not become long and the material quality of the metal strip does not deteriorate.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the temperature gradient and stress in the width direction during roll cooling, and FIG. 2 is a front view showing an embodiment of the roll cooling device according to the present invention. CLq: Roll cooling device, αl): Cooling roll band, α: Rear tension tensioning device, a: Front tension tensioning device. Patent applicant Nippon Kokan Co., Ltd.

Claims (1)

[Claims] A roll cooling device for a metal strip, characterized in that a rear tensioning device and a front tensioning device are provided on the upstream and downstream sides of a cooling roll band, respectively, and the upstream side of the cooling roll band is a small diameter cooling roll band.