JPH11302746A - Hearth roll for continuous annealing furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a roll which simultaneously solves the problems of a slip, meandering, drawing of a steel plate and the build-up of the roll by and has an excellent wear resistance by providing the coefft. of friction of a steel sheet and the roll with directivity and specifying the ratio of the coefft. of friction in the axial direction and circumferential direction of the outer peripheral part of the roll to a specific range. SOLUTION: The ratio of the coefft. of friction in the axial direction and circumferential direction of the outer peripheral part of the roll is set at >=1.5. A grooved part 12 having a plurality of grooves is formed axially in the central portion in the axial direction of the outer periphery of the hearth roll 11. The roll surface exclusive the projecting part surface of the grooved part 12 and the grooved part 12 is formed from a smooth surface having a surface roughness Ra=0.1 to 3 μm and the area rate of the projecting part surface of the grooved part 12 is preferably set at 20 to 80%. The forming range in the axial direction of the grooved part 12 is set at >=80% of a straight part length La. As a result, the steel sheet flaws may be prevented and the quality improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hearth roll for a continuous annealing furnace which is disposed in a continuous annealing furnace and is used for annealing and transporting a steel sheet.

[0002]

2. Description of the Related Art In a hearth roll which is disposed in a continuous annealing furnace and transports a steel sheet in a high-temperature atmosphere, four phenomena of slip, meandering, drawing (heat buckle) and roll-up of the steel sheet may occur. Are known. When a slip of the steel sheet occurs, the steel sheet is slipped and the grade of the steel sheet is degraded. In addition, when the steel sheet meanders, the sheet passing speed is reduced and productivity is also reduced. Further, when the steel sheet is drawn, the quality of the steel sheet becomes poor and the grade of the steel sheet is degraded. When a roll buildup occurs, it is transferred to a steel plate, causing buildup flaws, degrading the grade of the steel plate, and requiring maintenance of the roll to remove the buildup, thereby lowering productivity. Therefore, many improvement measures have been proposed for the purpose of stable operation by high-speed threading.

In order to prevent the slip of the steel sheet, it is effective to roughen the roll surface to increase the coefficient of friction with the steel sheet, and various methods of surface roughness and surface roughening have been proposed.

[0004] The meandering of the steel sheet is caused by a lack of frictional force between the steel sheet and the roll, and in order to prevent the meandering, it is effective to roughen the roll surface in the same manner as a slip prevention measure. is there. Further, in order to suppress the generated meandering, a straight portion is formed at the center portion in the axial direction of the roll, and tapered portions are formed on both sides thereof, and the steel sheet is restored to the center by the centering force of the tapered portion.

The greater the inclination of the tapered portion, the greater the centering force, and the meandering is immediately reduced. On the other hand, since the steel sheet is subjected to the centering force from both sides, a drawing phenomenon in which the central portion of the steel sheet buckles occurs. In order to suppress the meandering and reduce the occurrence of the stop, there is an appropriate taper range. Meandering and drawing of a steel sheet are contradictory phenomena, and various proposals have been made to satisfy both, such as a roll surface, a roll structure, an auxiliary roll, a thermal crown control device, and a roll surface shape.

[0006] Build-up is a phenomenon in which scales and the like of a steel sheet adhere to and accumulate on the roll surface. To prevent this, it is effective to coat the roll surface with a cermet or ceramic spray material. Has been proposed. The surface roughness and the build-up resistance are opposite to each other, and the smoother the roll, the harder the build-up occurs. On the other hand, it is necessary to increase the surface roughness from the viewpoint of preventing slip and meandering. Therefore, there is an appropriate range in which no slip occurs and build-up hardly occurs.

[0007]

As described above, various proposals have been made on the roll surface, crown design, roll structure, auxiliary roll, thermal crown control device, roll surface shape, build-up spraying resistance, and the like. ing.

[0008] First, regarding the roll surface,
Japanese Patent No. 47766 proposes an invention relating to a "hearth roll for continuous heat treatment". The present invention relates to a method in which the surface of a hearth roll is roughened by shot blasting or the like to have an Ra value of 4.5 to 20 μm, and a ceramic or a wear-resistant material is coated by spraying or plating to raise the Ra value of the surface of the hearth roll to 4. It is formed in the range of 0.5 to 20 μm. ”
The gist is that the slip, meandering, and pickup of the steel sheet can be prevented from occurring. In addition, Japanese Patent Application Laid-Open No. Hei 5-179363 proposes an invention relating to "hearth roll for continuous annealing furnace". The gist of the present invention is that "a central portion of a crown flat portion of a hearth roll having a convex crown has a concavo-convex portion having a predetermined Ra value." A steel sheet on the surface is obtained. However, the technology for the roll surface disclosed in these publications is known, and is effective in preventing a slip or the like of a steel sheet, but is not sufficient.

Next, the crown design is described in
In Japanese Patent Publication No. 116522, an invention relating to "roll in a furnace of a continuous annealing furnace" is proposed. The gist of the present invention is that "the crown in the furnace is provided with a crown, and the surface of the roll is roughened to a predetermined Ra value to define the position of the crown inflection point." This prevents the occurrence of squeezing and squeezing, thereby enabling stable threading. In addition, Japanese Patent Publication No. Hei 7-116523 proposes an invention relating to "roll inside furnace of continuous annealing furnace".
The gist of the present invention is that "a crown in a furnace roll is provided and the roll surface is roughened to a predetermined Ra value to regulate the crown amount." Is prevented, and stable threading can be performed. However, the techniques for crown design disclosed in these publications cannot cope with a wide range of plate widths.

[0010] Regarding the roll structure, see JP-A-3-827.
In Japanese Patent Application Publication No. 18, an invention relating to a "thermal crown suppressing hearth roll" is proposed. The gist of the present invention is that the hearth roll is composed of a metal isothermal restraining member having the same linear expansion coefficient as the outer sleeve via a metal outer sleeve and a heat-insulating heat-resistant member. The crown can always be held.
Japanese Patent Application Laid-Open No. 63-149325 proposes an invention relating to a "hearth roll for a continuous heat treatment furnace". The gist of the present invention is that "a plurality of through-grooves are provided at regular intervals in a circumferential direction of a hollow cylindrical hearth roll and along a generatrix thereof." The ring can be prevented. Further, Japanese Patent Publication No. 4-45566 proposes an invention relating to a "method of continuously annealing steel sheets without heat buckles and meandering". The gist of the present invention is that "in a continuous annealing furnace of a steel sheet after cold rolling, the sheet is guided by a suction force generated in a suction hole facing a surface of the sheet in a continuous annealing furnace." The heat buckle and meandering, which have a high tendency to occur frequently, can be properly avoided, and stable operation of continuous annealing can be performed. However, the technology for the roll structure disclosed in these publications has a complicated roll structure and is expensive.

The auxiliary roll is disclosed in JP-A-61-26.
Japanese Patent No. 4138 proposes an invention relating to "a continuous annealing method for steel strip". The present invention relates to a steel sheet passing through a hearth roll in a vertical continuous annealing furnace for annealing when the steel strip is continuously reciprocated in the axial direction of the hearth roll by an attached control roll. The purpose is to prevent the heat buckle of the steel strip and control the meandering amount to a certain value or less. In addition, Japanese Patent Application Laid-Open No. 5-186837 has proposed an invention relating to a "method for preventing heat buckle of a strip in a continuous annealing furnace". The gist of the present invention is that "a support roll for pressing a strip against a hearth roll is provided at a predetermined position before a contact start position of the strip with the hearth roll to apply heat buckle generation limit tension." That is, it is possible to prevent the heat buckle of the strip in the continuous annealing furnace. However, the techniques for the auxiliary rolls disclosed in these publications are expensive because of the provision of the auxiliary rolls, and the control thereof is required.

The thermal crown control device is disclosed in
Japanese Patent Application Publication No. 202717 discloses an invention relating to "a crown control device for a hearth roll in a continuous heat treatment furnace". The gist of the present invention is that "a heating device and a cooling device are provided in the hollow inside of a hearth roll in a heat treatment furnace for a steel strip, and heating and cooling are performed according to the deformation of the crown of the roll." That is, it is possible to prevent the fluctuation and prevent the meandering and flaw of the steel strip. However, the technology for the thermal crown control device disclosed in the publication is expensive because a heating device and a cooling device are provided inside the hearth roll, and a complicated control system for heating and cooling is required.

The roll surface shape is described in
In Japanese Patent No. 256925, an invention relating to a "heat buckle preventing hearth roll" is proposed. SUMMARY OF THE INVENTION The present invention has a feature that "a plurality of spiral-shaped convex portions extending in a direction opposite to the roll rotation direction are formed on a roll surface", and a heat buckle prevention that does not increase the occurrence of meandering of a steel strip. Can be obtained. However, the technology for the roll surface shape disclosed in the publication is expensive in roll surface shape processing, the directionality of the friction coefficient is small, and no effect is obtained.

[0014] Regarding build-up spraying resistance,
Japanese Patent Application Laid-Open No. 2-27133 proposes an invention relating to a “roll for a continuous heat treatment furnace”. The gist of the present invention is to spray a coating layer containing chromium oxide as a main component and having excellent heat resistance and high-temperature wear resistance on the surface of a roll in a furnace of a continuous heat treatment furnace for steel strip. That is, it is possible to prevent the occurrence of surface roughness and flaws on the roll surface. In Japanese Patent Publication No. 63-26183,
An invention relating to a "roll for heat treatment furnace" has been proposed. The present invention relates to a method for manufacturing a substrate of a hearth roll, wherein Y ₂ O ₃
And a ZrO ₂ ceramic coating layer. "
Accordingly, a hearth roll excellent in high-temperature wear resistance and build-up prevention can be obtained.
However, the techniques for build-up thermal spraying disclosed in these publications have a large effect of preventing build-up, but the thermal spraying itself is a known technique.

Various proposals for selectively solving some of the four phenomena of slip, meandering, drawing (heat buckle) and roll-up of a steel sheet in a hearth roll for conveying the steel sheet in a high-temperature atmosphere as described above. However, it has not been possible to solve all these phenomena simultaneously.

The present invention has been made in view of the above problems, and solves the four phenomena of slip, meandering, drawing (heat buckle) and roll-up of a steel sheet at the same time, and provides continuous annealing excellent in wear resistance. An object of the present invention is to provide a hearth roll for a furnace.

[0017]

In order to achieve the above object,
The present invention is arranged in a continuous annealing furnace, in a continuous annealing furnace hearth roll for annealing and transporting a steel sheet, the friction coefficient between the steel sheet and the roll has directionality, the axial direction in the roll outer peripheral portion The ratio of the coefficient of friction between the roller and the circumferential direction is set to 1.5 or more.

In the hearth roll for a continuous annealing furnace,
It is preferable that a grooved portion having a plurality of grooves along the axial direction is formed at the axial center portion of the outer peripheral portion of the roll.

The surface of the convex portion of the grooved portion and the roll surface of the portion other than the grooved portion are formed by a smooth surface having a surface roughness Ra of 0.1 to 3 μm, and the area of the surface of the convex portion of the grooved portion is adjusted. Preferably, the rate is set to 20-80%.

Further, the roll has a straight portion in the axial center portion of the outer peripheral portion of the roll and has a tapered portion on both sides thereof, and the formation range of the grooved portion in the axial direction is 80% or more of the length of the straight portion. Preferably, it is set.

The groove pitch of the grooved portion is 0.3 to 3 m
m, and the groove depth is preferably set to 20 μm or more.

In addition, the outer peripheral portion of the roll has a thickness of 20 to 20.
It is preferable that the coating layer is formed by thermal spraying using a ceramic, a cermet or a heat resistant alloy of 0 μm as a material, or thermal spraying using a cermet or a heat resistant alloy as a material.

In order to simultaneously solve the four phenomena of slip, meandering, drawing, and roll buildup of a steel sheet, the present inventor requires a high friction coefficient in the circumferential direction of the roll and low friction in the axial direction of the roll. It has been found that it is in principle the best to use a coefficient and make the contact surface with the steel plate smooth. That is, in order to prevent the slip and meandering of the steel sheet, it is preferable to have a high friction coefficient in the circumferential direction of the roll, and to reduce the drawing of the steel sheet, it is preferable to have a low friction coefficient in the axial direction of the roll. In order to suppress the build-up of the roll and improve the wear resistance, it is preferable to reduce the surface roughness (smoothness). If such a hearth roll is invented, it is considered that even if a small drawing occurs on the steel sheet, the steel sheet is restored to a flat state by the next roll. This point is referred to as “Materials and Process”, vol. 10 (1997), P320
-323.

In order to experimentally evaluate the roll surface shape of the hearth roll that satisfies the above principle, a high-temperature friction tester for a steel plate and a roll as shown in FIG. 3 was manufactured. Investigated the relationship. In FIG. 3, the high-temperature friction tester 1 has an electric furnace 3 provided in an atmosphere chamber 2, and guides a steel sheet 5 discharged from a discharge reel 4 to a test roll 6 provided in the electric furnace 3, It is configured to take up on the take-up reel 7 again. The test roll has a diameter of 40 mm and a roll length of 60 mm. The thickness of the steel plate is 50 μm and its width is 50 mm.
The atmosphere chamber 2 contains a high-temperature, non-oxidizing atmosphere (800 ° C.,
(Pure nitrogen atmosphere).

The coefficient of friction between the steel plate and the roll is substantially zero when there is no speed difference, and when there is a speed difference, a frictional force due to slip occurs. Therefore, the friction coefficient was measured while rotating the test roll, maintaining the steel plate speed constant, and changing the roll peripheral speed. This data shows that the relative sliding speed is 0.1m
/ S. The coefficient of friction measured thereby is the coefficient of friction in the circumferential direction. Since it is difficult to accurately measure the friction coefficient in the axial direction, the friction coefficient when the direction of the pattern is changed by 90 degrees in a directional surface pattern is defined as the friction coefficient in the axial direction. The coefficient of friction obtained with an axial groove test roll having grooves along the axial direction is the circumferential coefficient of friction. On the other hand, the friction coefficient obtained with a test roll having a circumferential groove having a groove along the circumferential direction is an axial friction coefficient.

FIG. 4 is an explanatory view showing the results of a laboratory test of a conventional smooth (polishing) roll to roughening (shot blast) roll having no directivity in the coefficient of friction. As the test piece, a base material made of heat-resistant cast steel, which was formed by spraying CoNiCrAlY with a heat-resistant alloy and having a film thickness of 100 μm after processing was used. A test was conducted for a smooth roll to a roughened roll, and the smooth roll was polished after thermal spraying to obtain a surface roughness Ra = 0.
The surface roughening roll was subjected to shot blasting after thermal spraying to have a surface roughness Ra of 4 to 8 μm.

As shown, the coefficient of friction increased with increasing surface roughness. From the actual operation results of the actual machine, even if the operation conditions (steel plate material, steel plate tension, heating temperature, etc.) change, the surface roughness Ra ≧ 5 μm of the hearth roll becomes a region in which no slip or meandering occurs. It has been confirmed that when the surface roughness Ra ≦ 1 μm, a region where no aperture occurs does not occur. For this reason, in the actual machine roll, in consideration of build-up resistance, a method in which the entire length of the roll is set to a surface roughness Ra = 3 to 5 μm is generally adopted as an area where slipping and meandering are unlikely to occur and squeezing hardly occurs. I have.

From the results of the laboratory tests, the roll surface roughness Ra =
Coefficient of friction μ = 0.6 at 5 μm, roll surface roughness Ra
= 1 μm, the friction coefficient μ is 0.4, and the circumferential friction coefficient is 0.6 or more and the axial friction coefficient is 0.4 or less. That is, the friction coefficient ratio in the circumferential direction / axial direction ≧
1.5 is satisfied. Therefore, it is understood that the roll having the directionality in the friction coefficient can simultaneously prevent the slip, the meandering, and the drawing.

FIG. 5 is an explanatory view showing the results of a laboratory test of working rolls having various surface shapes. From this, it was confirmed that the axial grooved roll having a smooth convex surface had a high coefficient of friction in the circumferential direction and a low coefficient of friction in the axial direction. The test piece was made of CoNiCrAl on a base material made of heat-resistant cast steel.
A film obtained by spraying Y with a heat-resistant alloy to have a film thickness of 100 μm after processing was used. The grooved roll has an axial direction of 45 degrees,
And using a groove formed along the circumferential direction, the roll base material is machined and then thermally sprayed to obtain a surface roughness Ra = 1 μm
And The grooves were formed as V-grooves having a groove pitch of 1 mm and a depth of 50 μm. The axial grooves and the 45-degree grooves were formed by knurling, and the circumferential grooves were formed by cutting. As the roughening roll, a roll base material having a surface roughness Ra of 4 μm by spray blasting after thermal spraying was used. As the smooth roll, a roll base material was sprayed and then polished to have a surface roughness Ra of 1 μm.

The test was performed in a high-temperature non-oxidizing atmosphere (800 ° C., 100% nitrogen atmosphere). As a result, the friction coefficient of each roll was as follows: axial groove> shot blast to oblique 45 degree groove> circumferential groove. Therefore, in the case of a roll with an axial groove and a smooth convex surface, a high coefficient of friction in the circumferential direction and a low coefficient of friction in the axial direction are excellent in preventing slip, meandering, and drawing, and the surface roughness is high. It was confirmed that being small (smooth) was excellent in suppressing buildup and improving wear resistance.

FIG. 6 is an explanatory diagram showing the results of a lab test of the axially grooved roll. As the test piece, the same axial grooved roll and circumferential grooved roll as in FIG. 5 were used. By polishing and shot blasting, the surface roughness of the convex portion surface is Ra =
It was adjusted to 0.1 to 8 μm. As a result, when the circumferential friction coefficient is ≧ 0.6 and the axial friction coefficient is ≦ 0.4, that is, the ratio of the circumferential / axial friction coefficient is ≧ 1.5,
It was confirmed that the surface roughness Ra of the convex surface was in the range of 0.1 to 3 μm. The test was performed by changing the groove shape.
No change was observed in the friction coefficient in both the V-groove and the square groove.

FIG. 7 is an explanatory diagram showing the results of a laboratory test of the axially grooved roll, and is a summary of FIGS. 4 and 6 in terms of the friction coefficient ratio. In FIG. 7, the friction coefficient ratio in the circumferential direction / axial direction ≧ 1.5 and the surface roughness Ra = 0.1 to 3 μm fall within the scope of the present invention.

FIG. 8 is an explanatory view showing the results of a lab test of an axially grooved roll, in which the groove depth is changed. The test piece was made of CoNiCrA on a base material made of heat-resistant cast steel.
1Y was subjected to thermal spraying with a heat-resistant alloy to have a thickness of 100 μm after processing. The grooved roll having grooves formed in the axial direction and the circumferential direction was used. The roll base material was machined and then sprayed to have a surface roughness Ra of 1 μm. The groove processing was a V groove having a groove pitch of 1 mm and a depth of 10 μm to 1 m.

As a result, the friction coefficient ratio (axial friction coefficient /
The groove depth satisfying the circumferential friction coefficient) ≧ 1.5 is 20
It was confirmed that it was not less than μm. If the groove depth is 20 μm or more, the friction coefficient ratio becomes ≧ 1.5. However, making the groove deep increases the processing cost. Therefore, even if the adhesion of the scale or the like to the groove during use is considered, a groove depth of 1 mm is sufficient.

FIG. 9 is an explanatory view showing the results of a laboratory test of the axial grooved roll, in which the area ratio of the surface of the convex portion is changed. The test piece has a base material made of heat-resistant cast steel,
oNiCrAlY is sprayed with a heat-resistant alloy, and the film thickness after processing is 1
One having a thickness of 00 μm was used. The grooved roll having grooves formed in the axial direction and the circumferential direction was used. The roll base material was machined and then sprayed to have a surface roughness Ra of 1 μm. Groove processing is groove pitch 0.3-3mm, depth 20μm
V groove of 〜2 mm, area ratio of smooth surface of convex portion surface of 10 to 90
%. As a result, it was confirmed that the area ratio of the convex portion surface satisfying the friction coefficient ratio (axial friction coefficient / circumferential friction coefficient) ≧ 1.5 was 20 to 80%.

FIG. 10 is an explanatory diagram showing the results of a lab test of an axially grooved roll, in which the groove pitch is changed. The test piece was made of CoNi on a base material made of heat-resistant cast steel.
CrAlY is sprayed with a heat-resistant alloy, and the thickness after processing is 100μ.
m was used. The grooved roll having grooves formed in the axial direction and the circumferential direction was used. The roll base material was machined and then sprayed to have a surface roughness Ra of 1 μm. The groove processing was performed with a V-groove having a depth of 20 μm to 2 mm, an area ratio of the smooth surface of the convex portion of 20 to 80%, and a groove pitch of 0.2 to 5 mm. As a result, the groove pitch that satisfies the friction coefficient ratio (axial friction coefficient / circumferential friction coefficient) ≧ 1.5 is 0.3 to 3
mm.

FIG. 11 is an explanatory view showing the results of a lab test of an axial grooved roll, in which the range of the grooved portion is changed. From this, it was confirmed that the range of the groove processing is preferably 80% or more of the length of the straight portion of the roll.
The test piece was made of CoNiCr on a base material made of heat-resistant cast steel.
AlY was sprayed with a heat-resistant alloy to have a thickness of 100 μm after processing. A tapered roll having a straight portion in the center portion in the axial direction of the roll and tapered portions on both sides of the roll has a straight portion of 40 mm and each tapered portion of 10 m.
m. The grooved roll having grooves formed in the axial direction and the circumferential direction was used. The roll base material was machined and then sprayed to have a surface roughness Ra of 1 μm.
The groove processing was a V-groove having a groove pitch of 1 mm and a groove depth of 50 μm, an area ratio of the convex surface of 50%, a groove processing range of 20 to 60 mm, and a ratio of groove processing portion / straight portion = 50 to 150%.

As a result, the groove processing range is ≧ 32 mm, the ratio of the groove processing part / straight part is ≧ 80%, the friction coefficient ratio in the circumferential direction / axial direction is ≧ 1.5, and the groove processing range is the length of the straight part. It was confirmed that 80% or more of the total length of the roll was preferable. In the case of a tapered roll, the length of the straight portion is designed to be 70 to 80% of the minimum plate width. In the hearth roll shape, besides tapering, there is also a crown roll having a constant convex curvature such as a SIN curve. Also in this case, the range of the groove processing may be determined by replacing with the corresponding tapered roll.

When importance is attached to the build-up resistance of the outer peripheral portion of the roll, two-layer thermal spraying is used in which the surface layer is a ceramic spray. The intermediate layer laminated thereunder is applied by thermal spraying of a cermet or a heat-resistant alloy in order to alleviate thermal stress and secure adhesion to a base material. When importance is placed on wear resistance, single layer thermal spraying is used, and cermet or heat resistant alloy is used.

The sprayed film thickness is set to 20 to 200 μm.
The reason why the minimum film thickness is set to 20 μm is that it is the lower limit value of the application by the thermal spraying method. On the other hand, the maximum film thickness is set to 200 μm because the ceramic layer is sprayed by two layers and the intermediate layer is 50 to 100 μm, so that the ceramic layer can have a minimum thickness of 50 μm after surface polishing.
Metal or cermet is used for the intermediate layer. Cermet or heat-resistant alloy spraying (single layer spraying) has a film thickness of 100
μm is sufficient.

[0041]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic view showing an appearance of a hearth roll for a continuous annealing furnace according to an embodiment of the present invention. Hearth roll 1 of the present embodiment
Reference numeral 1 denotes a roll disposed in a continuous annealing furnace for annealing and transporting a steel sheet. As shown in the drawing, a straight portion 11a is formed at an axially central portion of the outer peripheral portion of the roll, and crowns are formed on both sides thereof. Constituent tapered portions 11b and 11c are formed. The base material of the hearth roll 1 is SCH-22,
It is formed of a heat-resistant cast steel such as SCH-13.

The hearth roll for a continuous annealing furnace of the present embodiment has directionality in the friction coefficient between the steel sheet and the roll.
The ratio of the friction coefficient between the axial direction and the circumferential direction at the outer periphery of the roll is set to 1.5 or more. The reason for setting the friction coefficient ratio in the circumferential direction / axial direction to ≧ 1.5 is that, as shown in FIG. 4, when the surface roughness Ra of the roll is Ra ≧ 5 μm, a region where slip and meandering do not occur is formed. Surface roughness Ra
It has been confirmed that when ≦ 1 μm, an area where no drawing occurs is observed. When the roll surface roughness Ra = 5 μm, the friction coefficient μ = 0.6, and when the roll surface roughness Ra = 1 μm, the friction coefficient μ = 0.4. This is because the circumferential friction coefficient is 0.6 or more and the axial friction coefficient is 0.4 or less.
That is, when the circumferential / axial friction coefficient ratio ≧ 1.5 is satisfied, slip, meandering, and squeezing can be simultaneously prevented by a roll having a directional friction coefficient.

More specifically, in order to satisfy the condition of the friction coefficient ratio in the circumferential direction / axial direction ≧ 1.5, the center portion in the axial direction of the outer peripheral portion of the roll, that is, the straight portion 11a, A grooved portion 12 having a plurality of grooves is formed along the groove. The groove shape of the grooved portion 12 is as shown in FIG.
It may be a V-shaped groove 13 as shown in (a) or a square groove 14 as shown in (b).

That is, whether the groove shape is the V-shaped groove 13 or the square groove 14, the surface c of the convex portion of the grooved portion 12 and the roll surface of the portion other than the grooved portion have a surface roughness Ra = 0.1 to 3 μm.
m, and the area ratio of the convex surface c of the grooved portion 12 may be set to 20 to 80%. The reason why the surface roughness of the roll surface of the portion other than the convex surface c of the grooved portion 12 and the grooved portion was Ra = 0.1 to 3 μm, as shown in FIG. The coefficient of friction is ≧ 0.
6, the coefficient of friction in the axial direction is ≦ 0.4, ie, in the circumferential direction /
The ratio of the friction coefficient in the axial direction is ≧ 1.5 because the surface roughness is in the range of Ra = 0.1 to 3 μm. The reason why the area ratio of the convex surface c of the grooved portion 12 is set to 20 to 80% is that, as shown in FIG. 9, the friction coefficient ratio (axial friction coefficient / circumferential friction coefficient) ≧ 1. This is because the area ratio of the surface of the convex portion satisfying 0.5 is 20 to 80%. Accordingly, when the width of the smooth surface of the convex surface is c and the pitch of the groove in the axial direction is p, the area ratio f of the smooth surface of the convex surface is f = c / p × 100.
(F = 20-80%).

Forming range Lg of grooved portion 12 in the axial direction
Is preferably set to 80% or more of the straight portion length Ls. The reason why the formation range Lg of the grooved portion is set to 80% or more of the length Ls of the straight portion is that, as shown in FIG. This is because the coefficient ratio becomes ≧ 1.5.
Therefore, in FIG. 1, when L: roll body length, Ls: straight portion length, and Lt: taper portion length, the axial groove processing range Lg is represented by 0.8 × Ls ≦ Lg ≦ L.

The groove pitch p of the grooved portion 12 is 0.3 to
Preferably, it is set to 3 mm and the groove depth d is set to 20 μm or more. The reason why the groove pitch p of the grooved portion 3 was set to 0.3 to 3 mm is that the friction coefficient ratio (axial friction coefficient / circumferential friction coefficient) as shown in FIG.
This is because the range of the groove pitch satisfying ≧ 1.5 is 0.3 to 3 mm. The reason for setting the groove depth d to 20 μm or more is that
As shown in FIG. 8, the groove depth satisfying the friction coefficient ratio (axial friction coefficient / circumferential friction coefficient) ≧ 1.5 is 20 μm.
That's all.

As described above, the grooved portion 3 is formed on the straight portion 11a.
The outer peripheral portion of the hearth roll 11 on which is formed is coated by thermal spraying using a ceramic, a cermet or a heat resistant alloy having a thickness of 20 to 200 μm, or thermal spraying using a cermet or a heat resistant alloy as a material. As described above, the thermal spraying of the outer peripheral portion of the roll is a two-layer thermal spraying in which the surface layer is a ceramic spray when importance is attached to build-up resistance. The intermediate layer laminated thereunder is applied by thermal spraying of a cermet or a heat-resistant alloy in order to alleviate thermal stress and secure adhesion to a base material. When importance is placed on wear resistance, single layer thermal spraying is used, and cermet or heat resistant alloy is used.

The reason for setting the sprayed film thickness to 20 to 200 μm is that 20 μm is the lower limit value for the application by the thermal spraying method, and since the intermediate layer is 50 to 100 μm, the ceramic layer must be at least 50 μm after surface polishing. This is because the possible film thickness is 200 μm. Metal or cermet is used for the intermediate layer. For cermet or heat-resistant alloy spraying (single-layer spraying), a film thickness of 100 μm is sufficient.

Thus, according to this embodiment, by setting the friction coefficient ratio (axial friction coefficient / circumferential friction coefficient) to 1.5 or more, slip, meandering, drawing, and roll-up of the steel sheet can be achieved. The above four phenomena can be simultaneously solved, the steel plate flaw caused by the hearth roll 11 can be prevented, the steel plate quality can be improved, and the productivity can be improved by high-speed stable passing. In addition, since the surface of the convex portion of the grooved portion is a smooth surface and the coating layer is formed by thermal spraying using ceramics, cermet or heat-resistant alloy, or thermal spraying using cermet or heat-resistant alloy, wear resistance is improved. It has excellent properties and can greatly extend the life of the roll.

[0050]

Next, a preferred embodiment of a hearth roll for a continuous annealing furnace according to the present invention will be described. The hearth roll for the continuous annealing furnace of the steel plate of the actual machine is obtained by conventional thermal spraying of a roughened ceramic and has a surface roughness Ra of 3 to 4 μm. The roll has a diameter of 800 mm, a body length of 2,300 mm, a straight portion of 500 mm, and a tapered portion of 700 mm.

An axial groove is formed by using such an actual roll. Groove processing, groove pitch 0.5mm, groove depth 50
μm and a groove processing range of 1,600 mm. The method for producing a hearth roll for a continuous annealing furnace according to the present invention comprises the steps of: knurling a roll base material to form an axial groove; performing shot blasting as a base treatment to a surface roughness Ra of 4 μm;
After spraying CoNiCrAlY 100 μm, Z
100 μm of nO ₂ -8% Y ₂ O ₃ was sprayed. afterwards,
Roll surface is cylindrically polished with a grindstone and surface roughness Ra = 1.0
μm, and the film thickness after polishing was 150 μm.

When the hearth roll for a continuous annealing furnace of the present invention thus manufactured was used for one year on an actual machine, the occurrence of slip and build-up flaw of the steel sheet was zero. Conventionally, slip and build-up flaws occurred 3 to 4 times / year. The occurrence of meandering of the steel sheet was also zero. Conventionally, meandering occurred once or twice / month. Furthermore, the occurrence of drawing of the steel sheet was zero. Conventionally, the aperture is 1-2 times /
The moon had occurred. In addition, the roll surface was kept smooth. Conventionally, replacement was performed in two to three years due to a reduction in surface roughness. Thus, according to the present embodiment,
It was confirmed that the problems of slip, meandering, drawing, and roll build-up of the steel sheet can be simultaneously solved, and that the roll life can be greatly extended.

[0053]

As described above, according to the present invention,
By setting the ratio of the friction coefficient between the axial direction and the circumferential direction at the outer periphery of the roll to 1.5 or more, the four phenomena of slip, meandering, drawing, and roll-up of the steel sheet can be simultaneously solved. Thus, the quality of the steel sheet can be improved by preventing the steel sheet flaws caused by the hearth roll, and the effect of improving the productivity by the high-speed stable threading is extremely large. In addition, the surface of the convex portion of the grooved portion is a smooth surface, and by coating the sprayed layer, the abrasion resistance is excellent and the roll life can be greatly extended.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an appearance of a hearth roll for a continuous annealing furnace according to an embodiment of the present invention.

FIG. 2 shows a cross-sectional shape of a grooved portion of a hearth roll for a continuous annealing furnace of the present embodiment, wherein (a) is a schematic view of a V-groove,
(B) is a schematic view of a square groove.

FIG. 3 is a schematic view showing a high-temperature friction tester used for measuring a friction coefficient between a steel plate and a roll in the present invention.

FIG. 4 is an explanatory diagram showing the results of laboratory tests of a smooth (polishing) roll to a roughening (shot blast) roll having no directivity in the coefficient of friction in the present invention.

FIG. 5 is an explanatory view showing the results of a laboratory test of processing rolls having various surface shapes in the present invention.

FIG. 6 is an explanatory view showing a lab test result of an axial grooved roll in the present invention.

FIG. 7 is an explanatory view showing the results of a laboratory test of an axially grooved roll in the present invention, and is obtained by rearranging FIGS. 4 and 6 in terms of a friction coefficient ratio.

FIG. 8 is an explanatory view showing the results of a laboratory test of an axial grooved roll in the present invention, in which the groove depth is changed.

FIG. 9 is an explanatory view showing a lab test result of the axial grooved roll in the present invention, in which the area ratio of the surface of the convex portion is changed.

FIG. 10 is an explanatory view showing a lab test result of an axial grooved roll in the present invention, in which a groove pitch is changed.

FIG. 11 is an explanatory view showing a lab test result of an axial grooved roll in the present invention, in which a range of a grooved portion is changed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High-temperature friction tester 2 Atmosphere chamber 3 Electric furnace 4 Discharge reel 5 Steel plate 6 Test roll 7 Winding reel 11 Hearth roll 11a Straight part 11b, 11c Taper part 12 Grooved part 13 V groove 14 Square groove

Claims (6)

[Claims] 1. A hearth roll for a continuous annealing furnace disposed in a continuous annealing furnace for annealing and transporting a steel sheet, wherein the friction coefficient between the steel sheet and the roll has directionality, and a shaft at an outer peripheral portion of the roll is provided. A hearth roll for a continuous annealing furnace, wherein a ratio of a friction coefficient between a direction and a circumferential direction is set to 1.5 or more. 2. A hearth for a continuous annealing furnace according to claim 1, wherein a grooved portion having a plurality of grooves along the axial direction is formed at a central portion in the axial direction of the outer peripheral portion of the roll. roll. 3. The surface of the convex portion of the grooved portion and the surface of the roll other than the grooved portion are formed of a smooth surface having a surface roughness Ra of 0.1 to 3 μm. Rate 2
2. The method according to claim 1, wherein the value is set to 0 to 80%.
Or a hearth roll for a continuous annealing furnace according to 2. 4. A roll having a straight portion at an axially central portion of an outer peripheral portion of a roll and a tapered portion on both sides thereof, wherein a forming range of the grooved portion in the axial direction is 80% or more of the length of the straight portion. 2. The setting is set.
4. A hearth roll for a continuous annealing furnace according to any one of claims 1 to 3. 5. The continuity according to claim 1, wherein the groove pitch of the grooved portion is set to 0.3 to 3 mm, and the groove depth is set to 20 μm or more. Hearth roll for annealing furnace. 6. The outer peripheral portion of the roll has a thickness of 20 to 200 μm.
The continuous annealing furnace according to any one of claims 1 to 5, wherein the coating layer is formed by spraying using a ceramic, a cermet or a heat-resistant alloy as a material, or spraying using a cermet or a heat-resistant alloy as a material. For hearth roll.