JP7036617B2 - Scale removal method - Google Patents

Description

The present invention relates to a scale removing method.

For example, as described in Japanese Patent Application Laid-Open No. 2016-20608, when a rolled steel material is manufactured, by removing the scale on the surface of the steel piece (billet) before rolling, for example, self-injection flaw detection, ultrasonic flaw detection, etc. Since the defect detection accuracy in the inspection process of the above is improved and the defect can be removed more reliably, the quality of the finally obtained rolled steel material can be improved. As a method for removing scale on the surface of a steel piece, shot blasting in which particles are projected onto the steel piece is known as described in the above-mentioned publication.

Such billets include columnar ones and prismatic ones. In the case of a prismatic billet, the entire scale is removed by projecting a projection material onto each of the four planes.

The prismatic billet has curved corners rather than sharp corners. There are finer irregularities on the corners, and scales often exist in the recesses. Therefore, it may not be possible to remove a part of the scale existing in the corner portion only by projecting the projection material on the flat surface portion. In recent years, higher quality rolled steel materials have been required, and it is desired to remove scale slightly remaining at the corners of billets.

Japanese Unexamined Patent Publication No. 2016-20608

In view of the above inconvenience, it is an object of the present invention to provide a scale removing method capable of reliably removing the scale of the corner portion of the prismatic steel piece.

The scale removing method according to one aspect of the present invention, which has been made to solve the above problems, is a method of removing scale on the surface layer of a prismatic steel piece, and the steel piece is conveyed in the longitudinal direction while the steel piece is conveyed. A step of projecting a projection material onto one corner is provided, and the intersection angle of the projection central axis of the projection material with respect to one of the two planes adjacent to the corner of the steel piece and the projection onto the other plane. It is characterized in that the difference from the intersection angle of the projection central axis of the material is 30 ° or less.

In the scale removing method, since the projection material is projected onto the corners of the steel piece, the scale of the corners can be efficiently removed. Further, the projection material is projected from the inclined direction on the flat surface portion, but the scale is removed twice by the projection on the corner portions on both sides of the flat surface portion, so that a sufficient scale removal effect can be obtained. Further, by setting the difference in the angle of intersection with respect to the two planes adjacent to the corner portion to be equal to or less than the above upper limit, the difference is relatively high with respect to the entire curved surface of the corner portion, that is, with respect to the portion having an angle close to the adjacent plane. The scale removal effect can be obtained.

In the scale removing method, it is preferable to project the projection material using a centrifugal projector. As described above, by using the centrifugal projector, the scale can be reliably removed at a relatively low cost.

In the scale removing method, the rotating surface of the impeller of the centrifugal projector may be inclined with respect to the longitudinal direction of the steel piece. In this way, by inclining the rotating surface of the impeller of the centrifugal projector, the projection range of the projection material can be expanded in the width direction of the steel piece, so a relatively small centrifugal projector is used. Therefore, the projection material can be projected onto the entire two planes adjacent to the corner portion.

In the scale removing method, it is preferable that the projection density of the projection material on the virtual intersection of the two planes forming the corners is 35 kg / m ² or more. As described above, by setting the projection density of the projection material with respect to the corner portion to the upper limit or higher, the scale of the corner portion of the steel piece, which is relatively prone to unevenness, can be removed more reliably.

Here, the "projection center axis" means a virtual center axis in the projection direction in which the projection density of the projection material is maximized. "Projection density" means the mass of projectile material projected per unit area unit time. Further, the "intersection angle" means the minimum angle between a plane and a straight line.

As described above, the scale removing method according to the embodiment of the present invention can surely remove the scale at the corners of the prismatic steel pieces.

It is a schematic front view which shows the structure of the scale removal apparatus used in the scale removal method of one Embodiment of this invention. It is a schematic plan view of the scale removing device of FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[First Embodiment]
1 and 2 show a scale removing device used in the scale removing method according to the embodiment of the present invention.

The scale removing device of FIG. 1 has a plurality of transport rollers 1 that transport a prismatic steel piece (billet) B in the longitudinal direction, and four transport rollers 1 that project a granular projection material onto the steel piece B conveyed by the transport roller 1. It is provided with a projection device 2. This scale removing device can be used to remove the scale on the surface layer of the steel piece B by the scale removing method according to the embodiment of the present invention.

The scale removing method using this scale removing device is used, for example, in the production of rod-shaped or linear rolled steel materials.

The production of rolled steel includes a process of casting molten steel to obtain bloom, a process of slab-rolling bloom to obtain steel piece B, a process of removing scale of steel piece B by the scale removing method, and a scale. It can be carried out by a method including a step of rolling the removed steel piece B to obtain a rolled steel material having a desired cross-sectional shape. The method for manufacturing the rolled steel material includes a step of confirming whether or not scale remains on the surface of the steel piece after removing the scale of the steel piece B by the scale removing method, and a step of removing the scale confirmed to remain. You may also prepare further.

The scale removing method includes a step of projecting a projection material onto a corner portion of the steel piece B by the projection device 2 while transporting the steel piece B in the longitudinal direction by the transport roller 1.

The plurality of transport rollers 1 are arranged in a V shape in a front view (viewing in the transport direction of the steel piece B), and transport the steel pieces B while aligning them by gravity.

The transport speed of the steel piece B by the transport roller 1 may be, for example, 10 m / min or more and 80 m / min, although it depends on the capacity of the projection device 2, the capacity of the front and rear manufacturing equipment, and the like. If the transport speed of the steel piece B is too low, the manufacturing efficiency of the rolled steel material may be insufficient. On the contrary, if the transport speed of the steel piece B is too high, the scale may be insufficiently removed.

The projection device 2 is arranged so as to project the projection material onto the corner portion of the steel piece B. In order to project the projection material onto the four corners of the steel piece B, four projection devices may be arranged at the same position in the transport direction of the steel piece B so as to surround the steel piece B. In order to prevent the projecting material that did not hit the steel from damaging the other projecting device 2, even if the four projecting devices 2 are arranged at different positions in the transport direction of the steel piece B as shown in FIG. good.

The projection device 2 is preferably arranged so that the projection central axis X of the projection material is parallel to the straight line orthogonal to the central axis of the steel piece, and the projection central axis X of the projection material is orthogonal to the central axis of the steel piece. Is particularly preferred. That is, it is preferable that the projection device 2 is arranged so that the projection density with respect to the corner portion of the steel piece B is maximized.

Further, in the projection device 2, the difference between the intersection angle α of the projection center axis X of the projection material with respect to one of the two planes adjacent to the corner and the intersection angle β of the projection center axis X of the projection material with respect to the other plane is It is preferably arranged so as to be small.

The upper limit of the difference (absolute value) in the intersection angle of the projection central axis X with respect to the above two planes is 30 °, preferably 20 °, and more preferably 10 °. If the difference in the angle of intersection of the projection center axis X with respect to the two planes exceeds the upper limit, the scale of the plane with the smaller angle of intersection may not be sufficiently removed.

As the projection device 2, a centrifugal projector that projects a projection material by the rotational force of an impeller is preferably used. Since the centrifugal projector can easily increase the projection speed of the projection material and has high energy efficiency, it is possible to realize the projection device 2 having a low running cost and a large scale removal ability at a relatively low cost.

When a centrifugal projector is used as the projection device 2, the rotating surface of the impeller of the centrifugal projector may be tilted with respect to the longitudinal direction of the steel piece B so as to rotate about the projection center axis X. In the centrifugal projector, the projection density of the projection material is sufficiently large at a width substantially equal to the width of the impeller, and the projection density of the projection material is compared in the direction perpendicular to the projection center axis X and along the direction of the rotation surface of the impeller. It is distributed in a wide mountain shape. Therefore, by inclining the rotating surface of the impeller of the centrifugal projector, the projection range of the projection material can be expanded in the width direction of the steel piece B. Therefore, by inclining the rotating surface of the impeller, the projection material can be projected onto the entire two planes adjacent to the corners by using a relatively small centrifugal projector.

The scale removing method can be performed by changing the arrangement of the projection device 2 which has conventionally projected the projection material perpendicularly to the plane of the steel piece B. At this time, the width of the steel piece B as seen from the projection device 2 becomes large, but the scale of the entire steel piece B is removed by inclining the rotating surface of the impeller to widen the effective width of the projection device 2 as described above. be able to. At this time, the scale removal ability is relatively small near both ends of the effective width of the projection, but it is possible to secure the projection density and demonstrate sufficient scale removal ability for the corners where scale removal is most difficult. can. On the other hand, on the flat surface portion where the scale removing ability is reduced, the projection material is projected onto the two adjacent corner portions by different projection devices 2, so that the projection material overlaps with the two projection devices 2. Is projected, so a sufficient scale removal effect can be obtained.

In the scale removing method, the lower limit of the projection density of the projection material on the virtual intersection of the two planes forming the corners of the steel piece B is preferably 35 kg / m ² and more preferably 50 kg / m ² . On the other hand, the upper limit of the projection density of the projection material on the virtual intersection of the two planes forming the corners of the steel piece B is preferably 120 kg / m ² and more preferably 100 kg / m ² . If the projection density of the projection material on the virtual intersection of the two planes forming the corners of the steel piece B is less than the above, the scale removing ability of the corners may be insufficient. On the contrary, if the projection density of the projection material on the virtual intersection of the two planes forming the corners of the steel piece B exceeds the above upper limit, the steel piece B under the scale may be damaged or not. It may be necessary to use an expensive projection device 2 as necessary.

As the lower limit of the average hardness of the projection material, the Vickers hardness (Hv) is preferably 200 kgf / mm ² and more preferably 300 kgf / mm ² . On the other hand, as the upper limit of the average hardness of the projection material, 800 kgf / mm ² is preferable, and 600 kgf / mm ² is more preferable. If the average hardness of the projection material used for shot blasting is less than the lower limit, the scale removal efficiency may decrease. On the contrary, if the average hardness of the projection material used for shot blasting exceeds the upper limit, the steel piece B under the scale may be damaged. The "Vickers hardness" is a value measured in accordance with JIS-Z2244 (2009).

Examples of the material of such a projection material include sand, iron, steel and the like.

The shape of the projection material is not particularly limited, and may be a grit-like shape having an angular grit, a shot shape having no corners, or the like, but a shot shape that does not easily damage the steel piece B under the scale is particularly preferable.

The lower limit of the average diameter of the projection material is preferably 0.8 mm, more preferably 1 mm. On the other hand, as the upper limit of the average diameter of the projection material, 3 mm is preferable, and 2 mm is more preferable. If the average diameter of the projecting material is less than the lower limit, the collision energy of the projecting material becomes small, which may reduce the scale removal efficiency. On the contrary, when the average diameter of the projecting material exceeds the upper limit, there is a possibility that the scale may be removed unevenly or the steel piece B under the scale may be damaged. The "average diameter" means a value having a mass integrated value of 50% obtained from the particle size distribution measured in accordance with JIS-Z0311 (2004).

The lower limit of the average projection time of shot blasting (the time during which the projection material is projected at the same position) is preferably 0.5 seconds, more preferably 1 second. On the other hand, as the upper limit of the average projection time of shot blasting, 10 seconds is preferable, and 3 seconds is more preferable. If the average projection time of shot blasting is less than the lower limit, a sufficient projection amount may not be secured, or the projected projection materials may collide with each other to hinder the removal of scale. If the average projection time exceeds the upper limit, productivity may be hindered by overprojection.

The lower limit of the average projection speed of shot blasting is preferably 20 m / sec, more preferably 50 m / sec. On the other hand, the upper limit of the average projection speed of shot blasting is preferably 100 m / sec, more preferably 80 m / sec. If the average shot blast rate is less than the lower limit, scale removal may be inadequate. On the contrary, if the average projection speed of shot blasting exceeds the upper limit, the steel piece B under the scale may be damaged.

As the lower limit of the kinetic energy per projection material, 1 × 10 ⁶ J is preferable, and 1 × 10 ⁵ J is more preferable. On the other hand, as the upper limit of the kinetic energy per projection material, 1 × 10 ² J is preferable, and 1 × 10 ³ J is more preferable. If the kinetic energy per projectile is less than the lower limit, scale removal may be inadequate. On the contrary, if the kinetic energy per projection material exceeds the upper limit, the steel piece B under the scale may be damaged.

<Advantage>
In the scale removing method, since the projection material is projected onto the corners of the steel piece B, the scale of the corners having fine irregularities can be removed particularly efficiently. Further, the projection material is projected from the inclined direction on the flat surface portion, but the projection of the projection material on the corners on both sides of the flat surface portion causes the scale to be removed twice on the same flat surface portion. A sufficient scale removal effect can be obtained.

[Other embodiments]
The embodiments do not limit the configuration of the present invention. Accordingly, embodiments may be omitted, substituted or added to components of each embodiment based on the description and common general knowledge of the present specification, all of which should be construed as belonging to the scope of the present invention. be.

In the scale removing method, as a method of projecting the projection material, air blasting using high-pressure air, wet blasting using high-pressure water, or the like may be adopted.

In the scale removing method, in addition to the four projectors that project the projection material on the corners of the steel pieces, an additional projection device or other scale removing means such as a rotary brush or a high-pressure water injection device may be used as an auxiliary. good.

In the scale removing method, the steel pieces may be conveyed by using a horizontal transfer roller and a guide for guiding the steel pieces.

Hereinafter, the present invention will be described in detail based on Examples, but the present invention is not limitedly interpreted based on the description of this Example.

An experiment was conducted in which a shot-shaped projecting material was projected from all sides by a centrifugal projector while transporting a square steel piece (billet) having a cross section of 155 mm on a side in the longitudinal direction. The billet transfer speed was 40 m / min. As the centrifugal projector, a motor having a motor capacity of 45 kW and a maximum projection amount of 720 kg / min was used, and the rotating surface of the impeller was arranged at an angle of 15 ° with respect to the longitudinal direction of the steel piece.

(Test 1)
The projection center axis of the projection material was set to the center in the width direction of each plane of the steel piece, the intersection angle of the projection center axis with respect to the plane of the steel piece was 90 °, and the projection density was set to 35 kg / m ² . .. As a result, the scale of the flat portion was successfully removed, but the scale of the corner portion could not be sufficiently removed.

(Test 2)
Projection was performed with the same settings as in Test 1 except that the projection density was set to 50 kg / m ² . As a result, the scale on the flat surface was removed well, but the scale on the corner could not be sufficiently removed.

(Test 3)
The position of the projection center axis of the projection material is the corner of the steel piece, and the projector is installed so that the intersection angle of the projection center axis with respect to the two planes adjacent to the corner of the steel piece is both 45 ° (difference in intersection angle is 0 °). After arranging, the projection density was set to 35 kg / m ² and projection was performed. As a result, both the scale of the corner portion and the scale of the flat portion were successfully removed.

(Test 4)
Projection was performed with the same settings as in Test 3 except that the projection density was set to 50 kg / m ² . As a result, both the scale of the corner portion and the scale of the flat portion were successfully removed. In addition, no scratches on the corners were formed on the steel pieces.

As described above, it was confirmed that the scale of the corner portion and the flat portion of the steel piece can be reliably removed by projecting the projection material on the corner portion of the steel piece.

The scale removing method according to the present invention can be particularly preferably used for producing rod-shaped or linear rolled steel materials.

1 Conveyor roller 2 Projector B Steel piece X Projection center axis α, β Intersection angle

Claims (4)

It is a method of removing the scale of the surface layer of the prismatic steel piece.
It comprises a step of projecting the granular projection material on each corner of the steel piece at least once while transporting the steel piece in the longitudinal direction.
In the above step, at each corner of the steel piece, the intersection angle of the projection center axis of the projection material with respect to one of the two planes adjacent to the corner and the projection center axis of the projection material with respect to the other plane. A scale removing method, characterized in that the projection of the projection material having a difference of 30 ° or less from the intersection angle of the above-mentioned projection material is performed at least once . The scale removing method according to claim 1, wherein the projection of the projection material is performed using a centrifugal projector. The scale removing method according to claim 2, wherein the rotating surface of the impeller of the centrifugal projector is inclined with respect to the longitudinal direction of the steel piece. The scale removing method according to claim 1, claim 2 or claim 3, wherein the projection density of the projection material on the virtual intersection of the two planes forming the corner portion is 35 kg / m ² or more.

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