TENSION LEVELER

Abstract

A tension leveler includes a work roll coming into contact with a metal sheet and a pair of backup rolls coming into contact with the work roll. A hardening layer harder than the inside of the backup rolls is formed on the surfaces of the backup rolls. The Shore hardness inside the backup rolls is lower than the Shore hardness in the surfaces of the backup rolls by HS23 to HS36.

Description

INCORPORATION BY REFERENCE

Priority is claimed to Japanese Patent Application No. 2012-219541, filed Oct. 1, 2012, the entire content of each of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a tension leveler, and particularly, to a tension leveler having a function of crushing scales adhering to the surface of a metal sheet, which is being passed, while correcting the shape of the metal sheet.

2. Description of the Related Art

A tension leveler including a plurality of work rolls that are alternately arranged with respect to a sheet passing line and come into contact with a metal sheet, and a backup roll that is arranged opposite to the sheet passing line with respect the work rolls and comes into contact with the work rolls, are disclosed in the related art.

SUMMARY

According to an embodiment of the present invention, there is provided a tension leveler including a work roll coming into contact with a metal sheet; and a backup roll coming into contact with the work roll. A hardening layer harder than the inside of the backup roll is formed on the surface of the backup roll. The Shore hardness inside the backup roll is lower than the Shore hardness in the surface of the backup roll by HS23 to HS36.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing the outline of a tension leveler.

FIG. 2 is a side view showing mainly work rolls and backup rolls in FIG. 1.

FIG. 3 is a view showing the comparison between a work roll in the related art and a work roll using an embodiment of the invention.

FIG. 4 is a view showing the comparison between a work roll in the related art and a work roll using the embodiment of the invention.

DETAILED DESCRIPTION

In the hot-rolling process when a metal sheet (for example, steel sheet) is manufactured, an oxide film referred to as scales is generated on the surface of the metal sheet. In order to ship the metal sheet as a product, it is necessary to remove scales from the surface of the metal sheet. Thus, the operation of crushing the scales adhering to the surface of the metal sheet, which is being passed, while correcting the shape of the metal sheet, supplying hydrochloric acid to the metal sheet in a pickling line installed on the downstream side of a tension leveler, and melting the crushed scales is performed in the tension leveler. In this case, since the scales are crushed before the metal sheet is passed through the pickling line, the scales are easily melted and removed by the hydrochloric acid. As a result, the scales may be removed in a short time and an improvement in production efficiency is achieved.

Incidentally, when crushing of the scales is performed by a tension leveler, powdered scales may accompany the surface of the work roll and be caught between the work roll and the backup rolls. Additionally, foreign matter other than the scales (for example, broken pieces in welding, rusted pieces adhering to a facility, and impurities exposed to the surface of the metal sheet) may also be caught between the work roll and the backup rolls. Since the scales and the foreign matter are very hard, when powdered scales or foreign matter is caught between the rolls, roughness or wear occurs on the surface of the work roll, and this roughness or wear develops, and thereby, defects may be caused on the surface of the metal sheet that comes into contact with the work roll. In order to avoid this, in the tension leveler, the work roll is usually replaced in a short period of time (for example, from one week to one month). However, since the work roll is very expensive, the replacement frequency of the work roll has a great influence on the manufacturing cost of the metal sheet.

Thus, it is desirable to achieve long lifespan of a work roll in a tension leveler.

In the tension leveler related to the embodiment of the invention, the Shore hardness inside the backup roll is lower than the Shore hardness in the surface of the backup roll by HS23 to HS36. Therefore, even when powdered scales or foreign matter is caught between the work roll and the backup roll, the impact is absorbed by the backup roll. Accordingly, since the influence that the powdered scales or foreign matter has on the work roll becomes very small, long lifespan of the work roll may be achieved. In addition, in the case of being lower than the above range, there is a tendency that it is difficult to obtain the effect of impact absorption by the backup roll. In the case of being higher than the above range, the deformation of the backup roll becomes excessive, and there is a tendency that it is difficult to hold down the work roll with the backup roll.

The Shore hardness in the surface of the backup roll may be HS70 to HS75, and the Shore hardness inside the backup roll may be HS39 to HS47. If the Shore hardness in the surface of the backup roll is lower than HS70 or the Shore hardness inside the backup roll is lower than HS39, the surface of the backup roll is soft and easily deformed. Therefore, the backup roll tends to wear partially. Therefore, an impact-absorbing effect in the backup roll is not sufficiently exhibited, and the work roll also tends to wear. If the Shore hardness in the surface of the backup roll is higher than HS75, the hardness of the surface of the backup roll is close to the hardness of the surface of the work roll. Therefore, when powdered scales or foreign matter is caught between the work roll and the backup roll, the impact cannot be absorbed by the backup roll, and the work roll and the backup roll tend to wear therebetween. If the Shore hardness inside the backup roll is higher than HS47, the cushioning property inside the backup roll degrades, and consequently, the surface of the backup roll tends to wear.

The backup roll may be made of hypoeutectoid steel whose carbon content is equal to or lower than 0.8%.

The Shore hardness in the surface of the backup roll may be lower than the Shore hardness in the surface of the work roll by HS8 to HS22. In the case of being lower than the above range, the hardnesses of the surfaces of both the rolls are nearly equal to each other. Therefore, when powdered scales or foreign matter is caught between the work roll and the backup roll, the impact cannot be absorbed by the backup roll, and the work roll and the backup roll tend to wear therebetween. In the case of being higher than the above range, the deformation of the backup roll becomes excessive, and there is a tendency that it is difficult to hold down the work roll with the backup roll.

The Shore hardness in the surface of the work roll may be HS83 to HS92. If the Shore hardness in the surface of the work roll is lower than H83, the surface of the work roll tends to wear greatly due to scales or foreign matter or the impact-resistant load of the work roll against scales or foreign matter tend to become low. If the Shore hardness in the surface of the work roll is higher than HS92, the toughness of the surface of the work roll becomes insufficient and the surface of the work roll become weak due to the impact received from scales or foreign matter. Thus, a phenomenon in which a portion of the surface of the work roll is missing and drops out tends to increase.

The Shore hardness in this specification is a value measured according to JIS Z 2246 “Shore Hardness Test Method”.

Although an embodiment of the invention will be described with reference to the drawings, the following present embodiment is merely illustrative for describing the invention and is not meant to limit the invention to the following contents.

A tension leveler 10, as shown in FIG. 1, includes a main body 12 and roller units 14A to 14F. The main body 12 has a passage 16 that extends in a horizontal direction from one side surface 12a toward the other side surface 12b, and a water-cooling mechanism (not shown) for cooling the roller units 14A to 14F.

A metal sheet M is passed through the passage 16 along a sheet passing line L. An opening 16a of the passage 16 on a side surface 12a side functions as an inlet when the metal sheet M is carried into the main body 12 (passage 16). A pair of guide rolls 18 for guiding the metal sheet M is arranged on the upstream side of the opening 16a. An opening 16b of the passage 16 on a side surface 12b side functions as an outlet when the metal sheet (for example, steel sheet) M is carried out of the main body 12 (passage 16). A pair of guide rolls 20 for guiding the metal sheet M is arranged on the downstream side of the opening 16b.

The roller units 14A to 14F are arranged within the passage 16. The roller unit 14A is located on the most upstream side within the passage 16, and is attached to a ceiling side of the passage 16. The roller unit 14A has a roller supporting portion 22A, a work roll 24A, and a pair of backup rolls 26A. The roller supporting portion 22A rotatably supports the work roll 24A and the pair of backup rolls 26A.

The work roll 24A is located below the pair of backup rolls 26A between the pair of backup rolls 26A. The work roll 24A comes into contact with the metal sheet M on a lower end side thereof. The pair of backup rolls 26A comes into contact with the work roll 24A on lower sides thereof and supports the work roll 24A.

The roller unit 14B is located on the downstream side of the roller unit 14A within the passage 16, and is attached to a floor side of the passage 16. The roller unit 14B has a roller supporting portion 22B, a work roll 24B, and a pair of backup rolls 26B. The roller supporting portion 22B rotatably supports the work roll 24B and the pair of backup rolls 26B.

The work roll 24B is located above the pair of backup rolls 26B between the pair of backup rolls 26B. The work roll 24B comes into contact with the metal sheet M on an upper end side thereof. The pair of backup rolls 26B comes into contact with a lower side of the work roll 24B on upper sides thereof and supports the work roll 24B.

As shown in FIG. 2, the work roll 24B is located slightly further toward the downstream side than the work roll 24A. An upper end of the work roll 24B is located slightly above a lower end of the work roll 24A. Therefore, the metal sheet M passed between the work roll 24A and the work roll 24B is deformed in a wavelike fashion by the work rolls 24A and 24B. Due to this deformation, the shape of the metal sheet M is corrected and scales adhering to the surface of the metal sheet M are crushed.

Returning to FIG. 1, the roller unit 14C is located on the downstream side of the roller unit 14B within the passage 16, and is attached to the ceiling side of the passage 16. The roller unit 14C has a roller supporting portion 22C, a work roll 24C, and a pair of backup rolls 26C. The roller supporting portion 22C rotatably supports the work roll 24C and the pair of backup rolls 26C.

The work roll 24C is located below the pair of backup rolls 26C between the pair of backup rolls 26C. The work roll 24C comes into contact with the metal sheet M on a lower end side thereof. The pair of backup rolls 26C comes into contact with an upper side of the work roll 24C on lower sides thereof, and supports the work roll 24C.

The roller unit 14D is located on the downstream side of the roller unit 14C within the passage 16, and is attached to the floor side of the passage 16. The roller unit 14D has a roller supporting portion 22D, a work roll 24D, and a pair of backup rolls 26D. The roller supporting portion 22D rotatably supports the work roll 24D and the pair of backup rolls 26D.

The work roll 24D is located above the pair of backup rolls 26D between the pair of backup rolls 26D. The work roll 24D comes into contact with the metal sheet M on an upper end side thereof. The pair of backup rolls 26D comes into contact with a lower side of the work roll 24D on upper sides thereof and supports the work roll 24D.

The positional relationship between the work roll 24C and the work roll 24D is the same as the positional relationship between the work roll 24A and the work roll 24B that are shown in FIG. 2. That is, the work roll 24D is located slightly further toward the downstream side than the work roll 24C. An upper end of the work roll 24D is located slightly above a lower end of the work roll 24C. Therefore, the metal sheet M passed between the work roll 24C and the work roll 24D is deformed in a wavelike fashion by the work rolls 24C and 24D. Due to this deformation, the shape of the metal sheet M is further corrected and scales adhering to the surface of the metal sheet M are further crushed.

The roller unit 14E is located on the downstream side of the roller unit 14D within the passage 16, and is attached to the ceiling side of the passage 16. The roller unit 14E has a roller supporting portion 22E, a work roll 24E, and a pair of backup rolls 26E. The roller supporting portion 22E rotatably supports the work roll 24E and the pair of backup rolls 26E.

The work roll 24E is located below the pair of backup rolls 26E between the pair of backup rolls 26E. The work roll 24E comes into contact with the metal sheet M on a lower end side thereof. The pair of backup rolls 26E comes into contact with an upper side of the work roll 24E on lower sides thereof, and supports the work roll 24E.

The roller unit 14F is attached to the floor side of the passage 16 so as to face the roller unit 14E within the passage 16. The roller unit 14F has a roller supporting portion 22F and a pair of work rolls 24F. The roller supporting portion 22F rotatably supports the pair of work rolls 24F.

The pair of work rolls 24F comes into contact with the metal sheet M on upper end sides thereof. The pair of work rolls is located so as to face the pair of backup rolls 26E of the roller unit 14E. When viewed from an up-and-down direction, the work roll 24E of the roller unit 14E is located between the pair of work rolls 24F. Therefore, the metal sheet M passed between the work roll 24E and the pair of work rolls 24F comes into contact with the rolls 24E and 24F in order of the upper end side of the work roll 24F on the upstream side, the lower end side of the work roll 24E, and the upper end side of the work roll 24F on the downstream side.

The diameter of the work rolls 24A to 24D may be set to, for example, about 80 mm. The diameter of the work rolls 24E and 24F may be set to, for example, about 120 mm. The diameter of the backup rolls 26A to 26E may be set to, for example, 120 mm.

A hardening layer with a thickness of, for example, about 5 mm to 7 mm is formed on the surfaces of the work rolls 24A to 24F and the backup rolls 26A to 26E by, for example, high-frequency hardening. The hardness in the surfaces of the work rolls 24A to 24F and the backup rolls 26A to 26E is secured by this hardening layer.

The Shore hardness in the surfaces of the work rolls 24A to 24F may be set to, for example, about HS83 to HS92. If the Shore hardness in the surfaces of the work rolls 24A to 24F is lower than HS83, the surfaces of the work rolls 24A to 24F tend to wear greatly due to scales or foreign matter or the impact-resistant load of the work rolls 24A to 24F against scales or foreign matter tend to become low. If the Shore hardness in the surfaces of the work rolls 24A to 24F is higher than HS92, the toughness of the surfaces of the work rolls 24A to 24F becomes insufficient and the surface of the work rolls becomes weak due to the impact received from scales or foreign matter. Thus, a phenomenon in which portions of surfaces of the work rolls 24A to 24F are missing and drop out tends to increase. The Shore hardness inside the work rolls 24A to 24F may be set to about HS36 to HS40.

The Shore hardness in the surfaces of the backup rolls 26A to 26E is preferably lower than the Shore hardness in the surfaces of the work rolls 24A to 24F by about HS8 to HS22, and may be set to, for example, about HS70 to HS75. If the difference between the Shore hardness in the surfaces of the work rolls 24A to 24F and the Shore hardness in the surfaces of the backup rolls 26A to 26E is lower than the above range, the hardnesses of both the surfaces become nearly equal to each other. Therefore when powdered scales or foreign matter is caught between the work rolls 24A to 24F and the backup rolls 26A to 26E, the impact cannot be absorbed by the backup rolls 26A to 26E, and the work rolls and the backup rolls tend to wear therebetween. If the difference between the Shore hardness in the surfaces of the work rolls 24A to 24F and the Shore hardness in the surfaces of the backup rolls 26A to 26E is higher than the above range, the deformation of the backup rolls 26A to 26E becomes excessive, and there is a tendency that it is difficult to hold down the work rolls 24A to 24F with the backup rolls 26A to 26E. If the Shore hardness in the surfaces of the backup rolls 26A to 26E is lower than HS70, the surfaces of the backup rolls 26A to 26E are soft and easily deformed. Therefore, the backup rolls 26A to 26E tend to wear partially. Therefore, an impact-absorbing effect in the backup rolls 26A to 26E is not sufficiently exhibited, and the work rolls 24A to 24F also tend to wear. If the Shore hardness in the surfaces of the backup rolls 26A to 26E is higher than HS75, the hardness of the surfaces of the backup rolls 26A to 26E is close to the hardness of the surfaces of the work rolls 24A to 24F. Therefore, when powdered scales or foreign matter is caught between the work rolls 24A to 24F and the backup rolls 26A to 26E, the impact cannot be absorbed by the backup rolls 26A to 26E, and the work rolls and the backup rolls tend to wear therebetween.

The Shore hardness inside the backup rolls 26A to 26E is lower than the Shore hardness in the surfaces of the backup rolls 26A to 26E by about HS23 to HS36, and may be set to, for example, about HS39 to HS47. If the difference between the Shore hardness in the surfaces of the backup rolls 26A to 26E and the Shore hardness inside the backup rolls 26A to 26E is lower than the above range, there is a tendency that it is difficult to obtain the effect of impact absorption by the backup rolls 26A to 26E. If the difference between the Shore hardness in the surfaces of the backup rolls 26A to 26E and the Shore hardness inside the backup rolls 26A to 26E is higher than the above range, the deformation of the backup rolls 26A to 26E becomes excessive, and there is a tendency that it is difficult to hold down the work rolls 24A to 24E with the backup rolls 26A to 26E. If the Shore hardness inside the backup rolls 26A to 26E is lower than HS39, the surfaces of the backup rolls 26A to 26E are soft and easily deformed. Therefore, the backup rolls 26A to 26E tend to wear partially. Therefore, an impact-absorbing effect in the backup rolls 26A to 26E is not sufficiently exhibited, and the work rolls 24A to 24E also tend to wear. If the Shore hardness inside the backup rolls 26A to 26E is higher than HS47, the cushioning property inside the backup rolls 26A to 26E degrades, and consequently, the surfaces of the backup rolls 26A to 26E tend to wear.

The work rolls 24A to 24F may be made of, for example, powdered high-speed steel. The backup rolls 26A to 26E may be made of, for example, hypoeutectoid steel (for example, chromium molybdenum steel (SCN440)) whose carbon content is equal to or lower than 0.8%. The Shore hardness of chromium molybdenum steel (SCN440) before hardening is about HS39.

In the present embodiment as described above, the Shore hardness inside the backup rolls 26A to 26E is lower than the Shore hardness in the surfaces of the backup rolls 26A to 26E by HS23 to HS36. Therefore, even when powdered scales or foreign matter is caught between the work rolls 24A to 24E and the backup rolls 26A to 26E, the impact is absorbed by the backup rolls 26A to 26E. Accordingly, since the influence that the powdered scales or foreign matter has on the work rolls 24A to 24E becomes very small, long lifespan of the work rolls 24A to 24E may be achieved. As a result, it is possible to significantly reduce the manufacturing cost of the metal sheet M. In addition, as for the lifespan of the work rolls 24A to 24E, the surface state of the metal sheet M to be processed by the tension leveler 10 is observed, and it is determined whether or not there is damage or the like.

The result of comparison between a work roll in the related art and a work roll using the embodiment of the invention is shown in FIG. 3. A work roll on an upper side in FIG. 3 is the work roll in the related art. A work roll on a lower side in FIG. 3 is the work roll using the embodiment of the invention. The respective work rolls are rolls after 20 days have passed from the beginning of use. On the surface of the work roll in the related art, damage of a striped pattern referred to as chatter marks is caused. In contrast, the damage as being caused on the surface of the work roll in the related art is not seen on the surface of the work roll using the embodiment of the invention.

The result of comparison between a work roll in the related art and a work roll using the embodiment of the invention is also shown in FIG. 4. A work roll on an upper side in FIG. 4 is the work roll in the related art. A work roll on a lower side in FIG. 4 is the work roll using the embodiment of the invention. The work roll in the related art is a roll after 20 days have passed from the beginning of use. The work roll using the embodiment of the invention is one after 3 months have passed from the beginning of use. Spots whose surfaces are shaved off and discolored are present in the work roll in the related art. In contrast, the shaving or discoloring as being caused on the surface of the work roll in the related art is not seen on the surface of the work roll using the embodiment of the invention.

It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention.

Claims

1. A tension leveler comprising: a work roll coming into contact with a metal sheet; anda backup roll coming into contact with the work roll,wherein a hardening layer harder than the inside of the backup roll is formed on the surface of the backup roll, andwherein the Shore hardness inside the backup roll is lower than the Shore hardness in the surface of the backup roll by HS23 to HS36.

2. The tension leveler according to claim 1, wherein the Shore hardness in the surface of the backup roll is HS70 to HS75, and the Shore hardness inside the backup roll is HS39 to HS47.

3. The tension leveler according to claim 1, wherein the backup roll is made of hypoeutectoid steel whose carbon content is equal to or lower than 0.8%.

4. The tension leveler according to claim 1, wherein the Shore hardness in the surface of the backup roll is lower than the Shore hardness in the surface of the work roll by HS8 to HS22.

5. The tension leveler according to claim 1, wherein the Shore hardness in the surface of the work roll is HS83 to HS92.