JP2000239734A - Hearth roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hearth roll, with which in the case of carrying a metal strip in a continuous heat treatment furnace, the roll temp. is uniformized in a roll axial direction and the heat inertia is small and the thermal crown is restrained in a simple constitution, and meandering and ununiform flatness of the metal strip can be prevented. SOLUTION: In a hollow roll possible to raise the temp. of the barrel part 3 in the hearth roll with direct conduction of electric current, electric resistance of the barrel part in the hearth roll at least in contact with the metal strip 5 is made larger than that of the other barrel part in the hearth roll. As for the hollow roll possible to raise the temp. of the barrel part in the hearth roll with the direct conduction of electric current, the electric resistance of the barrel part at least in the hearth roll in no contact with the metal strip is made larger than that of the other barrel part in the hearth roll. On the surface of the barrel part at least in the hearth roll coming to contact with the metal strip, desirably an electric insulating layer 4 should be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hearth roll provided in a continuous heat treatment furnace for transporting a metal strip, and more particularly, to suppressing a thermal crown generated due to contact with the metal strip and stably transporting the metal strip. Regarding hearth roll to be possible.

[0002]

2. Description of the Related Art A large number of hearth rolls (hereinafter referred to as "hearth rolls") are installed in a continuous heat treatment furnace installed in a continuous annealing facility or a continuous plating facility.
(Also referred to simply as "roll"). For example,
In the continuous annealing equipment, a large number of hearth rolls are used for the heating zone, the soaking zone, and the cooling zone, respectively, and the metal strip is conveyed by these hearth rolls and subjected to a predetermined heat treatment in each furnace.

[0003] In such a continuous heat treatment furnace, meandering and buckling of the metal strip may occur, resulting in poor quality and shape, and in the worst case, the metal strip may be broken.

The occurrence of such meandering and buckling of the metal strip is affected by the cross-sectional profile (crown) of the hearth roll.

That is, when a hearth roll having a so-called convex crown in which the center of the roll swells as compared with both ends of the roll is used, a centering force toward the center of the roll is generated in the metal strip. If left and right are unbalanced,
Meandering of the metal strip is likely to occur. If the convex crown becomes large and the centering force becomes too large, the metal strip buckles in the width direction, and flatness called a heat buckle occurs. Further, even in the case of a roll having a so-called concave crown in which both ends of the roll are swelled as compared with the center portion of the roll, the metal strip buckles in the width direction, and the above-described poor flatness occurs. Therefore, the initial crown amount of the roll is determined so as to obtain an appropriate crown that does not cause meandering and flatness failure.

[0006] However, in a continuous heat treatment furnace, the thermal effect of the hearth roll is generally not uniform in the width direction, so that uneven thermal expansion (thermal crown) occurs in the width direction.

That is, in the cooling zone, the temperature of the metal strip is higher than that of the hearth roll, and heat is transferred from the metal strip to the roll at the contact portion between the roll and the metal strip. Will be higher. Therefore, a convex thermal crown is generated, and a heat buckle becomes a problem. The heat buckle generated in the cooling zone is called a cooling buckle.

On the other hand, in a heating zone or a solitary zone, the temperature of the hearth roll is higher than that of a metal strip, and a concave thermal crown is generated, which causes a problem of heat buckle.

Since the thermal effect on the hearth roll changes depending on the sheet width, sheet thickness, line speed, heat treatment temperature, etc. of the metal strip, it is not possible to completely prevent the meandering or heat buckle from occurring only with the initial crown. .

Therefore, various methods for reducing the thermal crown have been proposed. For example, there is a method in which an electric heater is arranged around the roll to heat the roll end in order to prevent a cooling buckle, but the heating efficiency is poor and a large-capacity electric heater is required, and the effect of reducing the thermal crown is insufficient. There are drawbacks.

Japanese Patent Application Laid-Open No. 3-271331 discloses a hearth roll in which a heating device such as an electric heater or an induction heater is provided inside the roll as a measure against cooling buckles in a cooling zone.

JP-A-63-128124 discloses a roll for cooling or heating a strip having a plurality of cooling medium or heating medium injection nozzles inside a hollow roll.

[0013]

However, Japanese Patent Laid-Open Publication No. Hei 3-2
In the method disclosed in Japanese Patent No. 71331, when an electric heater is used, the heat transfer efficiency between the heater and the roll deteriorates particularly as the temperature becomes higher, so that uneven heating is likely to occur and an appropriate crown amount is maintained. Difficult to do.
In addition, since the heating of the roll is performed by the heat transfer from the electric heater, there is a problem that the responsiveness when the heating temperature is changed is low, and it takes time to adjust the temperature of the roll.

When an induction heating type heater is used, the thermal responsiveness is higher than that of an electric heater, but there are disadvantages that the equipment is expensive and that the internal structure of the roll is complicated and maintainability is poor. is there. Furthermore, when carbon steel is used as the roll material, for example, the Curie point (about 7
If the heating is performed to a high temperature range exceeding 60 ° C.), there is a problem that the heating efficiency is remarkably reduced because the roll body is demagnetized.

In the method disclosed in JP-A-63-128124, for example, a structure is used in which the roll body is heated using a heat medium, so that the heat medium is heated to the target heating temperature of the roll body. It is necessary to heat, and it has to be a device with large thermal inertia. Therefore, there is a disadvantage that it takes time to change the heating temperature. In addition, it is necessary to suppress the temperature of the heating medium to be equal to or lower than the evaporation point of the heating medium. For example, when a general oil is used as the heating medium, the heating temperature is limited to 250 ° or less, and there is a problem that high-temperature heating cannot be performed. . In addition, there is a disadvantage that the roll structure is complicated and maintenance and inspection time is increased, and there is a problem that equipment is expensive.

An object of the present invention is to provide a hearth roll which can suppress a thermal crown, has a small thermal inertia, and has a simple structure. More specifically, it is an object of the present invention to provide a hearth roll capable of preventing meandering and flatness of a metal strip.

[0017]

The present inventors have realized that it is important to keep the hearth roll temperature uniform in the width direction at all times in order to prevent thermal crown fluctuation, and have conducted various experiments and studies. Lamination, (a) heating the roll by direct energization, and (b) changing the electrical resistance of the roll body and other roll bodies that come into contact with the metal strip to form the roll, make the roll temperature uniform in the width direction. Was found to be effective for

The present invention has been made based on the above findings, and the gist thereof is as follows. (1) A hearth roll provided in a continuous heat treatment furnace for transporting a metal strip, wherein the hearth roll is a hollow roll capable of raising the temperature of the hearth roll body by direct energization, and the hearth roll body has a width. A hearth roll characterized in that the electrical resistance varies in different directions and the generation of a thermal crown can be suppressed.

(2) The electric resistance of at least a portion of the hearth roll body contacting the metal strip is made larger than the electric resistance of other hearth roll body parts. Hearth roll.

(3) The electrical resistance of at least a portion of the hearth roll body that is not in contact with the metal strip is greater than the electrical resistance of other hearth roll body parts. Hearth roll.

(4) The hearth according to any one of the above (1) to (3), wherein an electrical insulating layer is provided on at least a surface of the hearth roll body contacting the metal strip. roll.

Here, the electric resistance means an electric resistance when a current flows through the inside of the roll member. The electric resistance is not a fixed value such as the specific resistance value of the material itself, but varies depending on the roll structure and the shape of the member.

[0023]

FIG. 1 is a longitudinal sectional view showing an example of a roll according to the present invention. As shown in the figure, the roll body is composed of a roll shaft 1, a flange 2, a roll body 3 having a width Wb, and an electrically insulating layer 4 provided on the surface of the roll body, and the roll body is hollow. I have.

The portion of the roll body 3 having a width Ws in contact with the metal strip 5 is made thinner by Te-T, so that this thin portion has a width We that does not contact the metal strip 5 of the roll body 3. The electric resistance is larger than that. A sliding brush 6 for energizing and heating the roll body 3 is attached to both roll shafts 1.
Are electrically connected to a power supply 8 via a short-circuit member 7.

When the roll is directly energized, the short-circuit member 7, the roll shaft 1, the flange 2, and the roll body 3
As a result, an electric closed loop is formed, and the thin portion is heated by Joule heat. Therefore, the roll of the present invention can make the temperature in the roll width direction uniform by using the roll in a heating zone or the like in which the temperature of the roll body that comes into contact with the metal strip decreases due to the contact with the metal strip.

In the above example, the thickness of the roll body contacting the metal strip is reduced in order to make the electric resistance of the roll body contacting the metal strip greater than the electrical resistance of the other roll body. However, the thickness of the roll body may be made uniform, and the roll body in contact with the metal strip may be made of a member having a large specific electric resistance. For example, the roll body that does not come into contact with the metal strip is made of copper, a copper alloy, or a composite member of these materials and carbon steel or stainless steel, and the roll body that comes into contact with the metal strip is made of carbon steel or stainless steel that has a large specific electrical resistance. Or titanium steel.

Increasing the electrical resistance of the roll body at least in contact with the metal strip means increasing the electrical resistance of the roll body corresponding to the width of the metal strip at a minimum. In consideration of the meandering of the metal strip at the time of passing, it is preferable to increase the electric resistance at a width slightly larger than the width of the metal strip.

FIG. 2 is a longitudinal sectional view showing an example of another roll of the present invention. As shown in the figure, the roll body is composed of a roll shaft 1, a flange 2, a roll body 3 having a width Wb, and an electrically insulating layer 4 provided on the surface of the roll body, and the roll body is hollow. .

Since the roll body 3 is configured so that the portion of the width We not in contact with the metal strip 5 becomes thinner by T-Te, the thin portion has a width Ws in contact with the metal strip of the roll body 3. The electric resistance is larger than the part. In addition, both roll shafts 1 have a roll body 3
Is mounted, and the sliding brush 6 is electrically connected to a power source 8 via a short-circuit member 7. When the roll is directly energized, an electrical closed loop is formed by the short-circuit member 7, the roll shaft 1, the flange 2, and the roll body 3, and the thin portion is heated by Joule heat. Therefore, the roll of the present invention
The temperature in the roll width direction can be made uniform by using it in a cooling zone or the like where the roll body contacting the metal strip is heated.

In the above example, at least the electrical resistance of the roll body not in contact with the metal strip is made larger than the electrical resistance of the roll body in contact with the metal strip. ing. However, the thickness of the roll body may be uniform, and the roll body not in contact with the metal strip may be made of a member having a large specific electric resistance. For example, the roll body contacted by the metal strip is made of copper or a copper alloy or a composite member of these materials and carbon steel or stainless steel, and the roll body not contacted by the metal strip is made of carbon steel, stainless steel, titanium steel, or the like. do it.

To increase the electric resistance of the roll body at least not in contact with the metal band means to increase the electric resistance of the roll body outside the roll body at least corresponding to the width of the metal band. I do. In consideration of the meandering of the metal strip at the time of passing, it is preferable to increase the electric resistance of the roll body outside the roll body corresponding to the width slightly smaller than the width of the metal strip.

In FIGS. 1 and 2, the flange 2 is configured to be smaller than the electric resistance of the roll body 3 in order to prevent excessive heat generation due to energization. Therefore, it is preferable to increase the thickness of the flange or use a member having a small specific electric resistance such as copper or a copper alloy.

As shown in FIGS. 1 and 2, the temperature of the roll shaft needs to be suppressed to about 250 ° C. or less in consideration of the durability of the slide brush, since the sliding brush for energization is attached to the roll shaft. . For this reason, the roll shaft may have a multi-layer structure of a member having a low specific electric resistance such as copper or a copper alloy and a strength member such as carbon steel or stainless steel, and may further include a cooling mechanism such as water cooling.

By the way, if a current is directly applied to the roll while the metal strip and the roll are in contact with each other, a spark may be generated at the contact surface between the roll body and the metal strip, which may cause a surface defect. In particular, sparks are likely to occur in metal strips having shape defects such as ear waves and middle elongation. This spark can be prevented by providing an electrically insulating layer on the surface of the roll body that contacts the metal strip. The electrically insulating layer is preferably a ceramic sprayed layer that can withstand a high temperature range.

Next, in the present invention, the width Wb of the roll body is described.
Among them, the reason why the electric resistance needs to be changed between the portion having the width Ws in contact with the metal strip and the other portion will be described in more detail below by taking a roll installed in a heating zone as an example.

FIG. 3 is a longitudinal sectional view of a normal hollow roll, in which the whole roll is made of the same material and the thickness of the roll body is uniform. 1 and 2 are denoted by the same reference numerals.

FIG. 4 shows the surface temperature of the roll body pre-heated to 800 ° C. by directly energizing the roll having the structure shown in FIG. 3 and, after preheating, bringing the metal strip at 700 ° C. into contact with the roll surface. 6 is a graph showing the surface temperature of the roll body after passing through the sheet.

As shown in FIG. 4, before the sheet is passed, the roll body is almost uniformly heated to 800 ° C., but after the sheet is passed, the roll body is in contact with the metal strip due to heat removal by the metal strip. A temperature drop occurs. The roll body having the lowered temperature has a small electric resistance. Since the roll body has a part in contact with the metal strip and the other part in an electrically series circuit, the roll body other than the roll body that comes into contact with the metal strip having a relatively large electric resistance. The heat generation in the loudspeaker gradually increases. Therefore, the temperature of the roll end becomes high and the temperature of the body contacting the metal strip becomes lower than that, and the temperature of the roll body becomes uneven in the width direction.

When a current is directly applied to the roll using a solid roll, the roll shaft and the roll body have different electrical resistances due to the difference in cross-sectional area. Resistance decreases. As described above, since the roll shaft and the roll body are connected in series, the calorific value of the roll shaft having a large electric resistance increases, which causes damage such as breakage of the sliding brush and seizure.
Conversely, the heat generated by the roll body is also reduced, so that there is no function of heating the roll body.

On the other hand, in the roll of the present invention, the amount of temperature rise in the roll body contacting the metal strip having relatively high electric resistance is large. Therefore, the temperature of the roll body can be kept constant in the width direction by adjusting the amount of temperature rise according to the amount of temperature decrease due to contact with the metal strip. That is, in the time period in which the metal strip is in contact with the metal strip, a current necessary to supply a Joule heat amount equal to the heat removal amount from the roll body may be applied. Also,
It only keeps the roll surface temperature when it is not in contact with the metal strip, in other words, the surroundings (atmosphere)
It is sufficient to carry out energization only to maintain the heat balance with the above.

When a roll having a relatively large electric resistance of the roll body not in contact with the metal strip of the present invention is used in a cooling zone or the like, the temperature of the roll body can be made uniform in the width direction for the following reasons. That is, in the cooling zone, since the temperature of the metal strip is higher than the roll temperature, the roll body contacting the metal strip is heated, but the roll body is usually water-cooled from the inside of the roll and has a predetermined surface temperature. Is held. On the other hand, the roll body that does not come into contact with the metal strip is removed by internal cooling, but has a relatively large electric resistance. Therefore, the roll body is adjusted by adjusting the temperature rise by energization according to the temperature drop by internal cooling. Can be kept constant in the width direction.

As described above, by using the roll of the present invention, the nonuniformity of the roll temperature in the width direction is suppressed.
The generation of the thermal crown is suppressed, and the metal strip can be stably transported without meandering or shape defects.

[0043]

(Example 1) A roll having a reduced thickness of a body portion having a roll body width of 1600 mm and a roll diameter of 800 mm according to the main specifications shown in FIG. 1 and Table 1 was manufactured, and was applied to a heating zone of a continuous annealing furnace. installed. As shown in FIG. 3, the rolls of the comparative example have a constant thickness of the roll body and do not have the function of direct energization (Comparative Example 1), and the rolls have the function of direct energization (Comparative Example 2). Was used. In addition, the roll of Example 2 of the present invention was sprayed with a ceramic having a thickness of 1.0 mm as an electrical insulating layer on the roll surface.

[0044]

[Table 1]

The roll temperature is set to the ambient temperature of the heating zone (about 80
0 ° C), the sheet thickness is 0.2 mm and the sheet width is 800
180 ° carbon steel metal strip on the roll body
Wound and contacted. Strip transport speed is 100
m / min.

In Examples 1 and 2 of the present invention and Comparative Example 2, the energization was started at the start of the passing of the strip, an alternating current of about 10,000 A was applied immediately after the start of the passing of the strip, and then the current amount was gradually increased to about 15 After a lapse of minutes, it was kept constant at about 30,000 A.

30 minutes after the transfer of the metal strip is started.
After a lapse of minutes, the surface temperature distribution of the roll body and the surface temperature of the roll shaft were measured. Table 2 shows the results. The surface temperature of the roll body is shown only at both ends of the roll and at the center and both edges in the width direction at the contact portion with the metal strip.

[0048]

[Table 2]

As shown in Table 2, in Examples 1 and 2 of the present invention,
The surface temperature of the roll body was made uniform in the width direction. As a result, the thermal crown was suppressed to a small value, and stable conveyance could be performed without meandering or surface defects. In Example 1 of the present invention, sparks occurred at a flat defect portion such as an ear wave, but in Example 2 of the present invention, no spark was generated and the surface properties were extremely good. The temperature of the roll shaft with the water-cooled structure to which the sliding brush was attached was 200 ° C or less.
No trouble such as breakage of the sliding brush occurred.

On the other hand, in Comparative Example 1, the temperature of the contact portion with the metal strip dropped immediately after the start of the passing of the metal strip, and the roll became a concave crown. did.

In Comparative Example 2, the temperature of the roll surface at the portion in contact with the metal strip was reduced due to the heat removal from the contact with the metal strip. The temperature was large, and the unevenness of the surface temperature of the roll body in the width direction was not improved. In addition, heat was conducted from the roll body even though water cooling was performed on the roll shaft, and the temperature was interrupted halfway because the temperature of the brush mounting portion became 350 ° C. or higher. In addition, a spark was generated between the roll and the strip during energization, and the surface properties of the strip were poor.

(Example 2) Rolls having a roll body width of 1600 mm and a roll diameter of 800 mm and having an increased body wall thickness as shown in FIG. 2 and Table 3 were manufactured and placed in a cooling zone of a continuous annealing furnace. As the rolls of the comparative example, as shown in FIG. 3, a roll having a constant thickness of the roll body and having no direct energizing function (Comparative Example 3) and a roll having a direct energizing function (Comparative Example 4) were used. Was. In addition, the inventive example 3 and the comparative examples 3 and 4
In each case, a water cooling mechanism was provided inside the roll, and adjustment was made so that the roll temperature did not rise above the set value due to heat input from the metal strip. In addition, the rolls of Inventive Example 3 and Comparative Example 4 were sprayed with a 1.0 mm thick ceramic as an electrical insulating layer on the roll surface.

[0053]

[Table 3]

The roll temperature is set to the ambient temperature of the cooling zone (about 50
0 ° C), the sheet thickness is 0.2 mm and the sheet width is 800
180 ° carbon steel metal strip on the roll body
Wound and contacted. Strip transport speed is 100
m / min.

In Example 3 of the present invention and Comparative Example 4, the energization was started at the same time as the start of the passing of the strip, and about 10 minutes immediately after the start of the passing of the strip.
An alternating current of 000 A was applied, and thereafter the current amount was gradually increased. After about 15 minutes had elapsed, the current was kept constant at about 30,000 A.

30 minutes after the transfer of the metal strip is started.
After a lapse of minutes, the surface temperature distribution of the roll body and the surface temperature of the roll shaft were measured. Table 4 shows the results. The surface temperature of the roll body is shown only at both ends of the roll and at the center and both edges in the width direction at the contact portion with the metal strip.

[0057]

[Table 4]

As shown in Table 4, in Comparative Example 3, since the temperature of the roll body contacting the metal strip was increased, the roll surface was maintained at a predetermined temperature by internal water cooling. As a result, the roll end was cooled and the roll body was cooled. The surface temperature of the sample had large non-uniformity in the width direction. For this reason, the roll crown became convex, and the generation of a cooling buckle was recognized on the cooling band exit side.

On the other hand, in Example 3 of the present invention, since the temperature at the roll end can be increased by energizing heating, a decrease in the temperature at the roll end as occurs in the roll of Comparative Example 3 is suppressed, and the roll body is reduced. Was made uniform in the width direction. Therefore, the thermal crown was suppressed to a sufficiently small value, and the metal strip could be transported stably without meandering or cooling buckle. In addition, no spark was generated and the surface properties were good.

On the other hand, in Comparative Example 4, since the temperature of the roll body in contact with the metal strip, whose temperature rises due to the heat input from the metal strip and the electrical resistance becomes relatively high, further rises due to the electric heating, the internal cooling causes As a result of maintaining the roll surface at a predetermined temperature, the roll end was supercooled, and the temperature difference in the width direction of the roll body surface became larger than that in Comparative Example 3, and as in Comparative Example 3, a cooling buckle was generated. Canceled.

[0061]

According to the present invention, when a metal strip is transported in a continuous heat treatment furnace, generation of a thermal crown due to contact with the metal strip can be suppressed, meandering and poor flatness can be prevented, and stable transport can be achieved. Make it possible. Further, the thermal inertia is small, the structure is simple, and it can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an example of a roll of the present invention.

FIG. 2 is a longitudinal sectional view showing an example of another roll of the present invention.

FIG. 3 is a longitudinal sectional view of a normal hollow roll, in which the whole roll is made of the same material and the thickness of the roll body is uniform.

4 is a diagram showing the surface temperature of the roll body preheated to 800 ° C. by directly energizing the roll having the structure shown in FIG. 3 and a metal strip at 700 ° C. contacting the roll surface after preheating; It is a graph which shows the surface temperature of the roll body part after having made it.

[Explanation of symbols]

1: roll shaft, 2: flange, 3: roll body, 4: electrically insulating layer, 5: metal strip, 6: sliding brush,
7: short circuit member, 8: power supply.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K034 AA05 AA09 AA19 BA09 CA04 CA05 EA12 EB03 4K043 AA01 CA05 DA05 EA05 GA08 HA04

Claims (4)

[Claims] 1. A hearth roll provided in a continuous heat treatment furnace for transporting a metal strip, wherein the hearth roll is a hollow roll capable of raising the temperature of the hearth roll body by direct energization. The hearth roll is characterized in that the electric resistance differs in the width direction and the generation of a thermal crown can be suppressed. 2. The hearth roll according to claim 1, wherein the electrical resistance of at least a portion of the hearth roll body that contacts the metal strip is larger than the electrical resistance of other hearth roll body parts. 3. The hearth roll according to claim 1, wherein the electrical resistance of at least a portion of the hearth roll body that does not contact the metal strip is greater than the electrical resistance of other hearth roll body parts. 4. The hearth roll according to claim 1, further comprising an electrical insulating layer on at least a surface of the hearth roll body that comes into contact with the metal strip.