Patent Application
20170129004
The present disclosure relates to a surface treatment method of a casting roll used in a twin roll thin plate casting process and a casting roll manufactured by the same.
In general, a casting process is a process in which molten metal is solidified to manufacture a slab having a uniform thickness. Recently, a thin plate casting technique, in which molten metal is directly solidified as a thin plate having a thickness close to that of a final product by using two casting rolls, has been developed and used.
As illustrated in
An edge dam 25 is provided on both ends of the pair of casting rolls 10, to prevent the molten steel M from flowing out toward both ends of the casting roll 10.
In general, in the casting roll 10, a cooling passage in which a coolant circulates is formed therein to cool the molten steel M, and the cooling passage is formed of a material such as copper or the like, having excellent heat transfer characteristics.
In addition, a coating layer formed using a material such as nickel or the like to improve wear resistance properties is formed on a surface of the casting roll 10. In the coating layer, non-oriented roughness is formed using a method such as shot blasting, to smoothly discharge bubbles or the like occurring a casting process, and to improve solidification characteristics by preventing crack defects or the like.
With reference to
In the casting roll 10, surface roughness may be good due to rolling in a process in which the thin plate S is manufactured, and physical properties may be good as recrystallization occurs.
For example, the casting roll 10 includes a casting roll main body 12, and a surface treated part having a concave-convex pattern 14 in which roughness is 10 μm to 20 μm is formed on a surface of the casting roll main body 12. By the surface treated part of the casting roll 10, a concave-convex pattern 14′ having surface roughness corresponding thereto, for example, having roughness of 10 μm to 20 μm, is formed on the casting Y. Roughness of the concave-convex pattern 14′ formed on the casting Y is lowered to a level of about 1 μm, as the concave-convex pattern 14′ is reduction rolled while passing through the rolling roll 30.
However, in the casting Y according to the related art, a convex portion of the concave-convex pattern 14′ may be connected to a concave portion adjacent thereto at an angle (a) of 30 degrees or more. Thus, in a process in which the casting Y passes through the rolling roll 30 to be rolled to form the thin plate S, a foreign substance such as oxide scale or the like may be present between convex portions of the concave-convex pattern 14′, and thus, the thin plate S may be manufactured in a state in which a foreign substance is contained therein.
With reference to
In the casting roll 10 according to the related art, a foreign substance may be easily inserted into a surface treated part according to a variation, a size, a shape or the like of the concave-convex pattern 14 determining surface roughness of the surface treated part. Thus, development of a technique for improving a surface shape so as not to allow a foreign substance to be inserted into a surface treated part of the casting roll 10 is required.
An aspect of the present disclosure may provide a surface treatment method capable of preventing a surface defect by improving a surface shape of a casting roll determining surface roughness, and a casting roll manufactured by the method.
According to an aspect of the present disclosure, a surface treatment method may include: a concave-convex pattern forming operation of forming a concave-convex pattern on a surface of a casting roll; and an electrolytic polishing operation of electrolytically polishing so that a plurality of convex portions and concave portions of a concave-convex pattern formed in the concave-convex pattern forming operation are treated to be rounded.
In the concave-convex pattern forming operation, a surface of the casting roll may be surface-treated using a shot blasting process.
In the shot blasting process of the concave-convex pattern forming operation, when the casting roll is surface-treated, a shot ball having a diameter of at least 2.8 mm may be projected.
According to another aspect of the present disclosure, a casting roll may include: a casting roll main body; and a surface treated part formed on a surface of the casting roll main body and formed so that a plurality of convex portions and concave portions of a concave-convex pattern are treated to be rounded by the surface treatment method described above.
Convex portions of the concave-convex pattern may be smoothly connected to concave portions of the concave-convex pattern adjacent thereto at an angle of less than 30 degrees.
The casting roll may further include a coating layer formed on the surface of the casting roll main body.
According to an exemplary embodiment in the present disclosure, a shape of a convex portion determining surface roughness of a surface treated part may be improved to prevent a phenomenon of insertion of a foreign substance. Thus, a hook defect H occurring on a surface of a cold-rolled product or the like may be reduced, thereby improving product quality.
Hereinafter, an exemplary embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. An exemplary embodiment of the present disclosure may be modified to have various other forms, and the scope of the present disclosure is not limited to an exemplary embodiment described hereinafter. A shape, a size or the like of the elements in drawings may be exaggerated for clarity of description, and elements represented by the same reference numerals in the drawings are the same.
With reference to
In an exemplary embodiment, in the concave-convex pattern forming operation, a concave-convex pattern 114 may be formed on a surface of a casting roll 110.
In detail, in the concave-convex pattern forming operation, a surface of a casting roll main body 112 configuring the casting roll 110 may be surface-treated using a shot blasting process, thereby forming the concave-convex pattern 114 through the shot blasting process.
The shot blasting process is used to treat a surface by projecting a shot ball B to a surface of the casting roll main body 112 of the casting roll 110. Here, the shot ball B described above may be a shot ball used in a shot blasting process according to the related art. Preferably, a shot ball B having a diameter of at least 2.8 mm is projected at high pressure to form a concave portion of the concave-convex pattern 114 in a concave form corresponding to a ball shape. In this case, a central part of the concave portion of the concave-convex pattern 114, pressed by the shot ball B, may be formed to be concave, and a pretreatment convex portion 114a, a part connected to another concave portion of the concave-convex pattern 114 adjacent thereto, may protrude sharply to be connected thereto.
For example, a convex portion of the concave-convex pattern 114 may be connected to a concave portion of the concave-convex pattern 114 adjacent thereto at an angle R of 30 degrees or more.
When the concave-convex pattern 114 is formed in the concave-convex pattern forming operation, the electrolytic polishing operation may be performed.
In the electrolytic polishing operation, a plurality of convex portions and concave portions of a concave-convex pattern 114 formed in the concave-convex pattern 114 forming operation are treated to be rounded.
In detail, in the electrolytic polishing operation, in which the casting roll 110 is immersed in an electrolytic polishing solution to be polished while being electrochemically dissolved, smoothing of fine concave and convex portions of 0.01 μm to 0.1 μm and removal of relatively large concave and convex portions of tens of μm may be performed simultaneously, and polishing may be performed simultaneously.
An electrolyte used in the electrolytic polishing operation is mostly an acid solution. In addition, acetic anhydride, alkali, and phosphoric acid are used, and perchloric acid and chromic acid having strong oxidizing power are added thereto.
In the electrolytic polishing operation, the pretreatment convex portion 114a, a protruding part, is relatively quickly dissolved, thereby allowing the convex portion of the concave-convex pattern 114 after surface treatment of the casting roll 110 to be smoothly formed.
When the electrolytic polishing operation is performed for a total of 4 hours while a current is provided with a voltage of 7 V to 8 V, polishing of the pretreatment convex portion 114a, a sharply protruding part of the concave-convex pattern 114, is quickly performed. Thus, a convex portion of the concave-convex pattern 114 may be connected to a concave portion of the concave-convex pattern 114 adjacent thereto at an angle of less than 30 degrees to allow an entirety of the concave-convex pattern 114 to be smoothly formed.
In this case, electrolytic polishing conditions in the electrolytic polishing operation will be described in Table 1.
The casting roll 110 manufactured in the surface treatment method described above may include a surface treated part formed by being treated to be rounded overall while the plurality of convex portions and concave portions of a concave-convex pattern 114 on a surface of the casting roll main body 112 are electrolytically polished.
As described above, in an exemplary embodiment, while the casting roll 110 passes through the electrolytic polishing operation to be surface-treated, a convex portion and a concave portion of the concave-convex pattern 114 are smoothly connected to each other, and thus, a surface of the casting Y passing through the casting roll 110 to be manufactured, may have a convex portion and a concave portion of a concave-convex pattern 114′, which is smooth, corresponding to a surface treated part of the casting roll 110. Thus, a foreign substance such as oxide scale or the like is prevented from being inserted into convex portions adjacent thereto.
Even when a portion of a foreign substance is attached to a surface of the casting Y, the portion of a foreign substance may be easily eliminated by rolling oil L or the like in a process of being pressed by a rolling roll 130. Thus, a foreign substance is prevented from being inserted in a process of being rolled as the thin plate S. The rolling oil L allows frictional resistance between the casting Y and the rolling roll 130 to be reduced, thereby reducing insertion of a foreign substance.
Preferably, a convex portion of the concave-convex pattern 114 formed on the casting roll 110 may be connected at a smooth angle of less than 30 degrees when the convex portion thereof is connected to a concave portion adjacent thereto. In addition, a convex portion of the concave-convex pattern 114′ formed on the casting Y cast by the casting roll 110 described above may be connected at a smooth angle of less than 30 degrees when the convex portion thereof is connected to a concave portion adjacent thereto.
In an exemplary embodiment, a coating layer formed using a material such as nickel or the like may be formed on the casting roll 110 to improve wear resistance of a surface of the casting roll main body 112. In addition, a surface treated part may be directly formed on the casting roll main body 112, or may be formed on the coating layer.
In the casting roll 110 configured as described above, a convex portion of the concave-convex pattern 114 on a surface treated part is formed to be rounded. In addition, an angle in which a convex portion of the concave-convex pattern 114′ of the casting Y manufactured using the casting roll 110 according to an example is connected to a concave portion adjacent thereto was measured, and a defect of the thin plate S manufactured in the form of a finished product by rolling the casting Y thereafter was measured.
With reference to Table. 2, an angle between a convex portion and a concave portion of the concave-convex pattern 114 formed on a surface of the casting Y cast by the casting roll 110 was measured.
When the casting roll 110 according to the related art was used, the number, in which an angle between a convex portion and a concave portion of a concave-convex pattern formed on the casting Y is 25 degrees or more, was 30 per area of 100 mm2, and the number, in which an angle between a convex portion and a concave portion thereof formed on the casting Y, is 30 degrees or more, was 10 per area of 100 mm2.
A hook defect H may occur in the thin plate S in the form of a final product in which the casting Y is rolled. In this case, a hook defect index representing the number of hook defects H formed in an area of 1 m2 was measured as 10.
When the casting roll 110 according to an exemplary embodiment was used, the number in which an angle between a convex portion and a concave portion of a concave-convex pattern formed on the casting Y is 25 degrees or more was 20 per area of 100 mm2, and the number in which an angle between a convex portion and a concave portion thereof formed on the casting Y is 30 degrees or more was 0.
In an exemplary embodiment, a hook defect H does not occur in the thin plate S in the form of a final product in which the casting Y is rolled.
As described above, a convex portion and a concave portion of the concave-convex pattern 114 having an angle of 30 degrees or more on a surface of the casting Y may form a hook defect H in a rolling process. In an exemplary embodiment, a convex portion of the concave-convex pattern 114 is formed on a surface of the casting roll 110 to be rounded by electrolytic polishing to allow roughness to be an angle of less than 30 degrees, thereby preventing a hook defect H from being generated in a rolling process.
While exemplary embodiments have been shown and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present disclosure as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2015-0157703 | Nov 2015 | KR | national |
