JP3465742B2 - Hearth roll for vertical heat treatment furnace and vertical heat treatment furnace using the hearth roll - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical heat treatment furnace which heats a metal strip such as a cold rolled steel strip through a plate.

[0002]

2. Description of the Related Art In a vertical heat treatment furnace, a plurality of hearth rolls are disposed as upper and lower parts of the furnace as conveying rolls, and metal strips are passed through the hearth rolls while being sequentially suspended. The necessary heat treatment is performed. But,
Since the metal strip to be passed is not a flat one at all, and there are bends and local elongations, it is easy for transport troubles such as meandering to occur during passing.

Particularly, in recent years, a large vertical heat treatment furnace (class in which the distance between the upper roll and the lower roll exceeds 15 to 20 m)
It is no exaggeration to say that the prevention of transport problems is a major issue in such equipment. In order to prevent the trouble of transporting the metal strip, a roll shape such as a crown provided on the hearth roll has been conventionally devised. However, if a large crown is added in order to prevent meandering in the transport trouble, then there is a risk that the metal strip will be squeezed. Such a phenomenon is remarkable especially when the temperature in the furnace is high, which leads to troubles on the strips and is one of the main causes of the decrease in product yield.

In order to effectively prevent meandering and throttling, which are problems in transporting a metal strip passing through the inside of a vertical heat treatment furnace, various measures have been conventionally made. For example, as an example of devising the internal structure of the hearth roll to control the roll crown by utilizing the thermal expansion inside the roll, Japanese Patent Laid-Open No.
-100919 and Japanese Patent Laid-Open No. 57-137431 can be cited.

Further, Japanese Patent Laid-Open Nos. 7-331335 and 3-47
Japanese Patent No. 926 discloses a technique of controlling the temperature of a hearth roll by applying heat from the outside of the hearth roll to control the crown of the hearth roll. On the other hand, as a conventional example in which the shape of the hearth roll itself is devised, Japanese Patent Laid-Open No. 8-199247,
7-138656, JP-A-58-120739, JP-A-52-1
No. 36812 can be cited. These publications relate to a one-step taper hearth roll in which the central portion of the hearth roll has a flat shape or a crown shape, and tapers are provided on both sides thereof.

Here, in the Japanese Patent Laid-Open No. 59-116331, the applicant of the present invention may use a two-stage taper roll as the hearth roll in addition to the one-stage taper roll and the crown roll. It has already been disclosed that this can be done (see FIG. 3 of the same publication).

[0007]

However, in recent years,
As a steel plate for integral molding of an automobile body, a steel plate wider than ever has been required. Therefore, in one vertical heat treatment furnace, it is required to pass a metal plate having a wider plate width range than ever before, particularly a steel plate.

In the case of steel sheets for automobiles, conventionally, the sheet width is 800-
The operation was performed in the plate width range of 1500 mm, but in recent years, plate widths of about 800 to 1800 mm on the same line, and in some cases, plate widths wider than that have been required. When the plate width range is wide as described above, it is not possible to sufficiently cope with the transport trouble by simply devising the roll shape itself as in the conventional case.

With regard to the one-stage taper roll, the optimum roll shape has already been known, and it has been considered as an effective means for preventing the meandering and drawing in the conventional operation of the plate width range. It cannot be directly applied to a wide plate width range where the plate width ratio is 2 or more. In the case of the one-step taper roll, the present inventor can effectively prevent the occurrence of the restriction on the metal strip having a wide strip width by reducing the taper, but on the other hand, the meandering is likely to occur in the metal strip having a narrow strip width. Also, if the taper is increased, the meandering can be effectively prevented with a narrow metal strip, but there is a problem that a narrow metal strip, especially when the strip is thin, tends to cause throttling. Found. Therefore, it is not possible to follow a wide plate width range and cope with it by using the one-step taper roll.

Further, even if the method of controlling the crown of the hearth roll by temperature control is applied, it is not possible to follow such a wide plate width range as it is, and thus such a wide plate width range can be applied. In order to follow and respond to the above, a major equipment modification is required. Also, in the vertical heat treatment furnace, if it is a steady state where the steel is passed at a substantially constant speed, it can be passed to some extent with the conventional hearth roll, but the operating conditions such as a multi-dimensional and multi-steel type compatible furnace When the operating conditions are changed or the operating conditions are changed in response to an abnormal operation, the plate passing speed is often changed considerably. During such speed changes (during fluctuations equivalent to 40 to 50% of the steady speed), meandering and throttling often occur, and with conventional hearth rolls, stable threading is performed even after considering these speed changes. Achievement is extremely difficult to achieve, and even with a double taper roll this has not been easy.

For example, in the case of a continuous annealing furnace for steel strips,
The strip running speed in a steady state is usually about 200 to 400 m / min. INDUSTRIAL APPLICABILITY The present invention makes it possible to cope with conveyance of a wide plate width range only by inexpensive equipment cost and simple optimization of hearth roll without requiring major equipment modification. In particular, it is particularly suitable for a vertical heat treatment furnace having a wide plate width range in which the maximum and minimum plate width ratios are 2 or more.

[0012]

By optimizing the shape and arrangement of the two-stage taper roll, the present inventor has achieved a meandering and drawing in correspondence with a wider plate width range and speed change than ever before. I found that I could prevent it. That is, a flat portion is provided in the central portion, and two tapered portions are symmetrically provided on both sides of the flat portion, and the second tapered portion is further inclined to the flat portion. Is greater than the inclination of the flat part and the length Lc (mm) of the flat part
The above problem was solved by the hearth roll for a vertical heat treatment furnace in which the length L1 (mm) of the taper portion has a relationship defined by the following equations (1) and (2).

A convex curvature portion is provided at the boundary between the flat portion and the first taper portion, and a concave curvature portion is provided at the boundary between the first taper portion and the second taper portion. It has been found that it is preferable to provide the above. The inclination R1 of the first taper portion is 0.2 to 10
It is in the range of × 10 ^-3 , and the inclination R2 of the second taper portion is 0.05.
It has been found that it is preferably in the range of up to 4 × 10 ^-3 . However, R1 = C1 / L1, R2 = C2 / L
It is 2. Where C1 is the first tapered portion of length L1
It is the roll radius difference between both ends, and C2 is the second of the length L2.
It is the roll radius difference at both ends of the taper portion.

Further, in the vertical heat treatment furnace which uses the above-mentioned vertical heat treatment furnace hearth roll as a transfer roll, the inlet side hearth roll of the vertical heat treatment furnace has the following equations (3) and (4).
The hearth roll from the middle to the exit side satisfies the formula (5) below.
In the hearth roll groups of the upper roll and the lower roll, which satisfy the formulas and the formula (6) and are arranged side by side in the furnace, the length Lc and (Lc + 2 × L1) are from the entrance side of the furnace. The above problem was solved by the vertical heat treatment furnace, which is characterized in that it gradually increases toward the delivery side.

Further, in the vertical heat treatment furnace using the above-mentioned vertical heat treatment furnace hearth roll as a transport roll, the hearth roll on the inlet side of the vertical heat treatment furnace is represented by the following formula (3),
The equations (4), (7) and (8) are satisfied, and the hearth rolls from the middle to the outlet side are the following equations (5), (6) and (9).
In the hearth roll groups of the upper roll and the lower roll, which satisfy the formulas (10) and are arranged side by side in the furnace, the length Lc and (Lc + 2 × L1) are from the entrance side of the furnace. The vertical heat treatment furnace is characterized in that the taper slopes R1 and R2 are gradually increased toward the outlet side and gradually decreased from the inlet side toward the outlet side of the furnace. The problem was solved.

Here, 0.5 Wmin ≤ Lc ≤ Wmin (1) Wmin ≤ Lc +2 x L1 ≤ Wmax -400 (2) 0.5 Wmin ≤ Lc ≤ 0.7 Wmin (3) Wmin ≤ Lc + 2 x L1 ≤ (Wmin + Wmax -400) / 2 (4) 0.7 Wmin ≤ Lc ≤ Wmin (5) (Wmin + Wmax -400) / 2 ≤ Lc +2 x L1 ≤ Wmax -400 (6) 3.0 x 10 ^-3 ≤ R1 ≤ 10 × 10 ^-3 (7) 1.2 × 10 ^-3 ≤R2 ≤4.0 × 10 ^-3 (8) 0.2 × 10 ^-3 ≤R1 ≤3.0 × 10 ^-3 (9) 0.05 × 10 ^-3 ≤R2 ≤ 1.2 × 10 ⁻³ (10) where Wmin: minimum width (mm) of metal band to be heat-treated Wmax: maximum width (mm) of metal band to be heat-treated.

Incidentally, here, the inlet side, the middle side, and the outlet side of the furnace may be arbitrarily divided. However, as a matter of course, the hearth rolls on the most entrance side and the most exit side (when the upper roll and the lower roll are treated as different roll series, the uppermost hearth rolls on the uppermost side and the lowermost side are one pair) , Respectively,
Belongs to the outgoing area. Also, to increase gradually,
In some cases, the adjacent rolls (when the upper roll and the lower roll are treated as different roll series, the adjacent rolls in each series) have the same values such as Lc, but at least from the entry side to the exit side. At any one point, these values indicate that the roll next to the adjacent roll is larger. The same applies when the size is reduced stepwise. As a typical form of these, it is considered that the roll in the furnace is divided into several blocks and the value is changed between the blocks.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION First, a two-stage taper roll applied as a hearth roll of the present invention will be described with reference to FIG. The hearth roll 1 of the present invention has a flat portion having a length Lc (mm) at the center thereof, a first taper portion having a length L1 (mm) on both sides of the flat portion, and a length L2 on both sides.
There is a second taper part (mm), which has a symmetrical double-step taper structure.

The flat portion may be substantially flat, for example, a smooth curved surface having a radius of curvature of 100 m or more may be formed. Here, the inclination of the first taper portion (C1 / L
1) is R1, and the inclination (C2 / L2) of the second taper part is R
2 and R1> R2. Further, the boundary between the flat portion and the first taper portion and the boundary between the first taper portion and the second taper portion have a rounded shape with no corners to prevent snaking and constriction. It is preferable that the convex curvature portion 11 and the concave curvature portion 12 are respectively provided. However, since it is desirable to make the joint as smooth as possible, it is preferable that each curvature is 20 m or more.

Next, FIG. 2 shows an outline of a typical vertical heat treatment furnace to which the present invention is applied. In the example of FIG. 2, the vertical heat treatment furnace 2 comprises a heating furnace 3 for heating and a soaking furnace 4 for soaking, and these furnaces are continuous. A preheating furnace may be provided in front of the heating furnace 3. However, since the plate temperature is generally much lower than that in the heating furnace, it is often not possible to identify it with the heating furnace in the roll design concept. Need not be included in the heat treatment furnace. The metal strip 7 enters the furnace from the inlet of the vertical heat treatment furnace 2, that is, the heating furnace 3.
The upper hearth roll 1a and the lower hearth roll 1b provided above and below the furnace are suspended and threaded. The metal strip 7 passed through the furnace is heated by the heating element 5 as required. Here, although only a part of the heating elements 5 is shown for the sake of easy viewing of the drawing, in reality, a large number of heating elements 5 are arranged at required locations of the heating furnace 3 and the soaking furnace 4 in the furnace. Has been done. A radiant tube or the like is used as an actual heating element.

Here, in order to block the heat from the heating element so that the hearth roll is not deformed by the influence of heat,
As shown in the figure, it is preferable to dispose the shield plate 6 between the hearth roll and the heating body. In the soaking furnace 4, the temperature of the metal strip has already become almost equal to the temperature inside the furnace and the temperature of the heating body, and the need for this shielding plate is small, but in the heating furnace 3, the metal strip is heated and rises. Since it is warm, the temperatures greatly differ, and the influence of heat on the hearth roll becomes relatively large. Therefore, it is extremely necessary to dispose the shielding plate.

In FIG. 3, the horizontal axis represents the width of the metal strip passing through the furnace, and the vertical axis represents the plate thickness. Compared with the conventional single-stage taper roll, the two-stage taper roll applied in the present invention. 6 is a graph explaining how the meandering / drawing property is improved and the operation can be stabilized by the application of. Here, the taper angle of the roll, the radius of curvature of the taper boundary portion, and the like used those satisfying the preferable conditions described in the present invention. The occurrence of each striping trouble in △ and ◇ was judged by the occurrence of trouble when the striping speed was reduced by 50% from the steady speed (300 m / min). The same applies to FIGS. 4 and 5 described later.

In the conventional one-stage taper roll, meandering and throttling can be almost prevented within a range where the maximum / minimum strip width ratio (Wmax / Wmin) of the metal strip is at most 1 to less than 2, and the operation can be stabilized. It is possible to And Wmax
When / Wmin is 2 or more, the length of the flat portion of the hearth roll,
No matter how the taper length or the like is adjusted, it is not possible to completely prevent the occurrence of a diaphragm in a metal band having a wide plate width and a thin plate thickness. On the other hand, in the two-stage taper roll used in the present invention, Wmax /
In a wide range where Wmin is 2 or more, meandering and throttling can be effectively prevented.

The inventor of the present invention has conducted more detailed research based on the above findings and has completed the present invention. Hereinafter, the findings obtained as a result of the research conducted by the present inventor will be described. First, the optimum value of the length Lc of the flat portion of the hearth roll which is a two-stage taper roll (see FIG. 1) is determined by the minimum strip width Wmin of the metal strip to be passed, and 0.5 Wmin ≤Lc ≤Wmin (1 ) Is optimal.

When Lc becomes 0.5 Wmin or less, normally,
The width of the plate in the taper portion becomes too large, so that throttling is likely to occur. Here, this value is preferably changed according to the position where the hearth roll is arranged in the furnace of the vertical heat treatment furnace, and the plate width is narrow at the entrance side of the furnace (that is, the heating furnace entrance side). In order to prevent the meandering of the metal strip, 0.5 Wmin ≤ Lc ≤ 0.7 Wmin, and 0.7 Wmin because the temperature of the metal strip is rising from the middle of the furnace to the outlet side (that is, the soaking furnace outlet side). It has been found that it is optimal to set ≤Lc ≤Wmin.

In the latter half of the furnace, the plate shape is usually improved and the meandering is less likely to occur. Therefore, L
It was found that increasing the value of c in the range of 0.7 × Wmin or more is effective in preventing the diaphragm. As shown in Fig. 4, if Lc is too large on the inlet side of the heating furnace, the shape of the metal strip has not yet been completely repaired. Therefore, no matter how the taper on both sides of the hearth roll is adjusted, there is often a meandering. Trouble occurs, and troubles such as slowdown occur.

On the contrary, as shown in FIG. 4, from the center of the heating furnace to the soaking furnace, Lc must be made larger than the inlet side of the heating furnace to adjust the taper on both sides of the hearth roll. However, drawing troubles often occur in wide metal strips. However, the maximum value of Lc does not exceed Wmin. If Lc is designed to be larger than Wmin, the shape of the metal strip is corrected from the center of the heating furnace to the soaking furnace, but in the case of Wmin, meandering occurs from the center of the heating furnace to the soaking furnace. .

Next, as a result of repeated studies on the width L1 of the first taper portion and a test on an actual machine, Wmin≤Lc + 2 * L1≤Wmax-400 (2) and Lc + 2 * L1. However, it has been found that it is optimal to design the heating furnace so that it becomes larger in order from the inlet side to the outlet side.

Lc + 2 × L1 is required to be at least the minimum width Wmin of the metal strip in order to prevent meandering of the narrow metal strip. If Lc +2 x L1 is larger than the maximum width Wmax -400, no matter how the slopes R1 and R2 of the taper portion having two steps of the hearth roll are selected, it is easy to cause a narrow metal band to be drawn. Become. FIG. 5 shows the optimum range of Lc + 2.times.L1 and the occurrence of meandering and aperture when the range is out of this range. No matter how R1 or R2 is selected, Lc +
It was found that it is difficult to completely prevent the meandering and the stoppage if 2 × L1 is not appropriate.

Regarding the inclinations R1 and R2 of the taper portion, it is preferable that R1> R2, R1 is 0.2 to 10 × 10 ^−3, and R2 is 0.05 to 4 × 10 ^−3. Became clear. Further, regarding R1 and R2, further 3.0 × 10 ⁻³ ≦ R1 ≦ 10 × 10 at the inlet side of the furnace.
^-3 , 1.2 × 10 ^-3 ≤ R2 ≤ 4.0 × 10 ^-3, and 0.2 × 10 ^-3 ≤ R1 ≤ 3.0 × 10 ^-3 at the exit side of the furnace.
, 0.05 × 10 ⁻³ ≦ R 2 ≦ 1.2 × 10 ⁻³ has been found to be more preferable. The reason for this is that, as in the case of Lc, etc., it is preferable to design in the latter half of the furnace with more emphasis on prevention of throttling.

Here, L1, Lc + 2 × L1, R1, R
It is preferable that the respective values of 2 be sequentially increased from the inlet side to the outlet side of the vertical heat treatment furnace or be made equal in some cases. Here, as a method of sequentially increasing the size, the inside of the furnace may be divided into two parts to be changed in two stages of a front stage and a rear stage, or the stages may be sequentially increased in about 3 to 5 stages. Further, the size may be continuously increased.

The hearth rolls are provided above and below in the furnace of the vertical heat treatment furnace. The upper and lower sides of the hearth roll have different tensions applied to the metal strip due to the influence of gravity, etc. It has also been clarified that it is preferable to increase the roll parameters sequentially in each roll group of the upper roll and the lower roll. Table 1 shows some actual roll shapes of the hearth roll (defined by Lc and L1).

[0033]

[Table 1]

Table 1 shows the relationship between Lc and L1 of the hearth roll applied in the furnace for each case of the minimum plate width Wmin and the maximum plate width Wmax of the metal strip that passes through the vertical heat treatment furnace. . In Table 1, for each case of Wmin and Wmax, the minimum value (min) of Lc, the median value (mid), and the maximum value (max) of Lc, the minimum value (min), median value (mid) of L1, The maximum value (max) is displayed as a matrix. Here, the numerical values shown in parentheses are values that do not actually apply.

In the present invention, values in the range of Lc min, mid and L1 min, mid are used at the inlet side of the vertical heat treatment furnace, and Lc mid at the middle to outlet side of the vertical heat treatment furnace.
, Max and the mid and max values of L1 are preferably used. In Case 7, in which Lc + 2 × L1 became too large, there was almost no restriction, but meandering occurred frequently, causing a major obstacle to the strip.

On the contrary, in case 8 where Lc + 2 × L1 becomes too small, the occurrence of meandering can be suppressed, but the material is wide and the diaphragm frequently occurs. Continuous annealing furnace (No. 1, 2, 4, 5, 6) or continuous hot dip galvanizing furnace (No. 3, 7, 8) with roll constitution shown in Tables 2 to 4 (upper roll to lower roll 20
m, a steady strip running speed of 300 m / min) was used to strip the steel strip.

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

In the present invention, in a furnace having a wide plate width corresponding range (Wmax / Wmin ≧ 2), the sheet passing speed is 40%.
It has been confirmed that even if speed fluctuations occur (50% under optimal conditions), stable passage is possible without causing problems such as meandering and throttling.

[0041]

Industrial Applicability According to the present invention, the hearth roll in the vertical heat treatment furnace can be optimized, stable operation can be performed in a wide range of metal strips without causing meandering and drawing, yield reduction, line stoppage. It was possible to eliminate troubles such as line speed reduction.

[Brief description of drawings]

FIG. 1 is an explanatory view of a hearth roll of the present invention.

FIG. 2 is a schematic view of a vertical heat treatment furnace.

FIG. 3 is a graph for explaining the conditions under which meandering and drawing occur depending on the plate width and plate thickness.

FIG. 4 is an L in which a meandering and drawing occurs in a vertical heat treatment furnace.
It is a graph which shows the conditions of c.

FIG. 5 is a graph showing a condition of (Lc + 2 × L1) in which meandering and drawing occur in a vertical heat treatment furnace.

[Explanation of symbols]

1 Hearth Roll (Conveyor Roll) 1a Upper Hearth Roll 1b Lower Hearth Roll 2 Vertical Heat Treatment Furnace 3 Heating Furnace 4 Soaking Furnace 5 Heating Body (Radiant Tube) 6 Shielding Plate 7 Metal Strip (Steel Strip) 11 Convex Curved Part 12 Concave concave portion Lc Length of flat portion (mm) L1 Length of first taper portion (mm) L2 Length of second taper portion (mm) R1 Taper of first taper portion from roll axis direction Angle (rad) R2 Tapered angle of the second taper part from the roll axis direction (rad)

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) C21D 9/52-9/66 C21D 1/00

Claims (5)

(57) [Claims] 1. A flat part is provided in the central part, and two tapered parts are symmetrically provided on both sides of the flat part, and the inclination of the first tapered part connected to the flat part is further continued. Is larger than the inclination of the taper part and the length Lc of the flat part
(Mm) and the length L1 (mm) of the first taper part are the following (1)
A hearth roll for a vertical heat treatment furnace having a relationship defined by the formula and the formula (2). Note 0.5 Wmin ≤ Lc ≤ Wmin (1) Wmin ≤ Lc +2 x L1 ≤ Wmax -400 (2) where Wmin: minimum width of heat-treated metal strip (mm) Wmax: maximum width of heat-treated metal strip (mm) ) 2. A convex curvature portion is provided at a boundary portion between the flat portion and the first taper portion, and a concave curvature portion is provided at a boundary portion between the first taper portion and the second taper portion. The hearth roll for a vertical heat treatment furnace according to claim 1, wherein the hearth roll is provided as described above. 3. The inclination R1 of the first taper portion is 0.2 to
It is in the range of 10 × 10 ^-3 , and the inclination R2 of the second taper portion is 0.
The hearth roll for a vertical heat treatment furnace according to claim 1 or 2, wherein the hearth roll is in the range of 05 to 4 x 10 ^-3 . However,
R1 = C1 / L1 and R2 = C2 / L2. here,
C1 is the roll radius difference between both ends of the first taper portion of length L1
And C2 is the width of the ends of the second taper of length L2.
This is the radius difference. 4. A vertical heat treatment furnace using the hearth roll for a vertical heat treatment furnace according to claim 1 as a transport roll, wherein the hearth roll on the inlet side of the vertical heat treatment furnace has the following (3): ) And (4) are satisfied, the hearth rolls from the middle to the exit side satisfy the following formulas (5) and (6), and the upper roll and the lower roll arranged side by side in the furnace are In each hearth roll group, the length Lc and (Lc + 2 × L1
) Is increased stepwise or sequentially from the inlet side to the outlet side of the furnace. Note 0.5 Wmin ≤Lc ≤0.7 Wmin (3) Wmin ≤Lc +2 x L1 ≤ (Wmin + Wmax -400) / 2 (4) 0.7 Wmin ≤Lc ≤Wmin (5) (Wmin + Wmax -400) / 2 ≤ Lc +2 x L1 ≤ Wmax -400 (6) 5. A vertical heat treatment furnace using the hearth roll for vertical heat treatment furnaces according to claim 3 as a transport roll, wherein the hearth rolls on the inlet side of the vertical heat treatment furnace are the following (3) formulas:
The equations (4), (7) and (8) are satisfied, and the hearth rolls from the middle to the outlet side are the following equations (5), (6) and (9).
In the hearth roll groups of the upper roll and the lower roll, which satisfy the formulas (10) and are arranged side by side in the furnace, the length Lc and (Lc + 2 × L1) are measured from the entrance side of the furnace. A vertical heat treatment furnace characterized in that the taper slopes R1 and R2 are gradually increased toward the outlet side and gradually decreased from the inlet side to the outlet side of the furnace in a stepwise manner. Note 0.5 Wmin ≤Lc ≤0.7 Wmin (3) Wmin ≤Lc +2 x L1 ≤ (Wmin + Wmax -400) / 2 (4) 0.7 Wmin ≤Lc ≤Wmin (5) (Wmin + Wmax -400) / 2 ≤ Lc + 2 × L1 ≦ Wmax -400 ... (6) 3.0 × 10 -3 ≦ R1 ≦ 10 × 10 -3 ... (7) 1.2 × 10 -3 ≦ R2 ≦ 4.0 × 10 -3 ... (8) 0.2 × 10 - ³ ≤ R1 ≤ 3.0 × 10 ^-3 (9) 0.05 × 10 ^-3 ≤ R2 ≤ 1.2 × 10 ^-3 (10)