KR20180073386A - Skin pass rolling mill and pass rolling method using the same - Google Patents

Abstract

According to one embodiment of the present invention, provided is a temper rolling method allowing a plated steel sheet to be charged into a temper roller and subjected to temper rolling, wherein a straight line passing through the center axis of a work roll rolling the plated steel sheet and perpendicular to the direction in which the plated steel sheet is charged is closer to the direction in which the plated steel sheet is charged than the other straight line passing through the center axis of a back-up roll applying predetermined pressure to the work roll and perpendicular to the direction in which the plated steel sheet is charged.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a rough rolling mill,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roughing mill and a rough rolling method using the same, and more particularly, to a roughing mill for roughly rolling a coated steel sheet used as an automotive outer sheath or the like and a rough rolling method using the same.

Plated steel sheet plated with zinc, aluminum and so on is excellent in corrosion resistance, weldability and paintability, and is widely used as a steel plate for automotive shell plating. Since it is used as an automotive shell plate, it has excellent surface appearance as well as excellent moldability Is required.

However, unlike an alloyed hot-dip galvanized steel sheet in which microscopic irregularities are formed on the surface during the alloying process, the coated steel sheet, for example, the hot-dip galvanized steel sheet, is composed of pure zinc (eta phase, eta phase) There is a disadvantage that a galling phenomenon in which a plating layer is dropped off due to occurrence of adhesion with a press mold at the time of press molding is easy because the surface is smooth and the coating itself is soft and has a low melting point.

Galling is caused by scratches on the material surface when a new material enters the mold due to cold pressure contact with the surface of the mold after part of the coating layer is peeled, And a part of the mold material is peeled off together with peeling of the formed plating layer.

Gearing that occurs during the press forming of the hot-dip galvanized steel sheet has a great influence on the surface quality of the press-molded article using the plated steel sheet as a raw material and the life of the mold, which is a factor for raising the pressing ratio.

Therefore, in order to prevent the rolling of the steel plate for automotive outer shell plating from occurring during press forming, fine irregularities are formed on the surface thereof. Such fine irregularities reduce the contact points with the mold during press forming, and function as oil pockets for holding press oil, lubricating oil, rust preventive oil and the like, thereby reducing the sliding frictional resistance and preventing damage to the mold Goring can be prevented.

For example, Patent Document 1 discloses that a fine protrusion having a double circular shape with a maximum diameter of 500 mu m on the roll surface and a minimum diameter of 50 mu m is formed on the roll surface so that the ratio of the fine protrusions to the surface area of the roll is 10 to 35% And then transferred to a coated steel plate to form fine irregularities capable of holding lubricating oil of about 4 to 8 mu m. Patent Document 2 proposes a method of rolling by a temper rolling roll having regular fine protrusions formed by laser machining A method of improving the bone-rolling property and the ductility of the galvanized steel sheet is proposed in which the body fit of the fine irregularities per unit area is 0.0001 to 0.01 mm 2. Patent Document 3 proposes a method in which a phosphate solution of manganese-nickel is coated on a galvannealed galvanized steel sheet by electroplating to reduce friction between the plating layer and the mold during press forming, thereby preventing adhesion have.

However, in Patent Documents 1 and 2, even if the fine irregularities of the galvanized steel sheet are regularly formed and the volume sum of fine irregularities per unit area is adjusted to a predetermined value or more, the oil content and the friction characteristics are exhibited depending on the shape of the fine irregularities There is a problem that a very different rolling behavior is exhibited during press forming.

Further, in the case of Patent Document 3, since an expensive lubrication treatment is further performed in order to improve friction and press forming of the coated steel sheet, it is not economical and deteriorates other weldability and adhesiveness.

Japanese Laid-Open Patent Publication No. 1995-009016 Japanese Patent Application Laid-Open No. 1995-136701 Korean Patent Publication No. 2007-0087723

An aspect of the present invention is to provide a temper rolling mill capable of preventing occurrence of burrs on the surface at the time of forming fine irregularities of a plated steel sheet, And to provide a rough rolling method using the same.

According to an embodiment of the present invention, a straight line perpendicular to a direction in which the coated steel strip is loaded in a rough rolling mill and which is temper rolling is passed through a central axis of a work roll for rolling the coated steel strip, Wherein the steel plate is closer to a direction in which the plated steel sheet is loaded than a straight line passing through the central axis of the backup roll for applying a predetermined pressure and perpendicular to a direction in which the plated steel sheet is loaded.

According to an embodiment of the present invention, there is provided a plating apparatus including: a housing having an inlet through which a coated steel strip is loaded and an outlet through which the coated steel strip is taken out; A work roll rotatably supported on the housing and rolling the plated steel sheet; And a back-up roll having a central axis arranged to be shifted from the center axis of the work roll by a predetermined angle with reference to a vertical direction of the direction in which the coated steel strip is loaded, to provide.

According to one embodiment of the present invention, it is possible to prevent the occurrence of burrs on the surface at the time of forming fine irregularities of the plated steel sheet, thereby providing a temper rolling mill and a manufacturing method using the same.

The various and advantageous advantages and effects of the present invention are not limited to the above description, and can be more easily understood in the course of describing a specific embodiment of the present invention.

1 is a cross-sectional view schematically showing a temper rolling machine according to an embodiment of the present invention.
2A is an enlarged view of a portion A in Fig.
2B is an enlarged view of a portion C of FIG. 2A.
2C is a SEM photograph of the microstructure.
Figure 3A is a drawing of a comparative example.
FIG. 3B is an enlarged view of a portion E in FIG. 3A.
3C is a SEM photograph of the microstructure of the comparative example.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the following embodiments. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art. In addition, the shape and size of elements in the figures may be exaggerated for clarity.

As a result of examining in detail the surface fine irregularities of the coated steel sheet in which galling occurred at the time of press molding of the coated steel sheet for automotive outer shell plating, the inventors of the present invention found that, as shown in FIG. 3C, burr 113, and the inside of the fine concavities and convexities is not smooth and inclined in the direction of burr formation, and the scratch 114 is formed on the bottom surface.

These burrs were separated from the surface of the plated steel sheet even by a small impact during the processing of the plated steel sheet, and it was found that there was a close relationship in which the burrs were generated at the time of press working.

The inventors of the present invention have found that, in order to confirm the conditions under which burrs are formed at the fine irregularities of the coated steel sheet at the time of temper rolling, temper rolling is performed while changing the temper rolling conditions. As a result, And the formation of burrs.

According to this, when the roll force of the temper rolling is applied in the direction perpendicular to the steel plate, the resultant force actually acting on the surface of the steel plate due to the force in the direction in which the plate goes As shown in Fig. Therefore, it is confirmed that the fine protrusions of the work roll are not transferred perpendicularly to the surface of the plated steel sheet, but fine protrusions scratch the surface of the plated steel sheet to form fine irregularities, thereby causing burr and scratch on the surface of the plated steel sheet there was. 3B and 3C, the bottom surface of the fine unevenness has a tilted cross section in the direction in which the resultant force acts, and the plated layer in the fine unevenness causes burrs in the fine uneven surface.

On the other hand, if roll down force is applied to the plated steel sheet in an inclined manner, the resultant force actually applied by the force in the direction in which the plated steel sheet advances is applied perpendicularly to the plated steel sheet, It can be transferred vertically. Therefore, it was confirmed that the micro concavity and convexity transferred onto the surface of the plated steel sheet had a flat bottom surface and no burr formed at the micro concavo-convex boundary portion.

Accordingly, in the present invention, in order to prevent galling that occurs during press forming of the coated steel sheet and to improve the press formability, burrs are not formed in fine unevenness formed after temper rolling of the coated steel sheet, Which can increase the area of the oil pocket, V2, and a rough rolling method using the same.

Hereinafter, the present invention will be described in detail.

According to an aspect of the present invention, there is provided a rough rolling method comprising the steps of charging a plated steel sheet in a rough rolling mill, subjecting the plated steel sheet to rough rolling, passing through a central axis of a work roll for rolling the plated steel sheet, Is closer to a direction in which the plated steel sheet is loaded than a straight line passing through the central axis of the backup roll for applying a predetermined pressure to the work roll and perpendicular to the direction in which the plated steel strip is loaded.

In manufacturing the coated steel sheet according to the present invention, it is preferable that the coated steel sheet is plated to form a coated steel sheet, and the plating method is not particularly limited. For example, hot dip galvanizing, electroplating, or the like can be used.

The hot-dip galvanized steel sheet may be, for example, a hot-dip galvanized steel sheet, a hot-dip galvanized steel sheet and an aluminum alloy-coated steel sheet, and may be a galvannealed steel sheet obtained by alloying the hot-dip galvanized steel sheet.

In the case of using the above electroplating, the coated steel sheet may be, for example, an electro-galvanized steel sheet or an electro-cohesive gold-plated steel sheet.

On the other hand, the coated steel sheet that can be used as the base steel sheet is not particularly limited, and any coated steel sheet that can be manufactured from a coated steel sheet may be used, but it may preferably be a cold rolled steel sheet. The process of plating the coated steel sheet and the rolling process of the coated steel sheet may be performed in a batch process, but may be performed in a separate process.

The coated steel sheet produced in the above manner can be charged into a temper rolling mill to perform temper rolling. In the present invention, by controlling the action direction of the roll down force applied by the work roll of the temper rolling mill to the coated steel sheet, surface quality and press formability This improved coated steel sheet can be produced.

This will be described with reference to Figs. 1 to 2C. 1 is an enlarged view of part A of FIG. 1, FIG. 2B is an enlarged view of part C of FIG. 2A, and FIG. 2C is an enlarged view of part A of FIG. SEM photograph showing fine unevenness.

1, the temper rolling machine 1 includes a housing 60 having an inlet IN for loading a plated steel plate 10 and an outlet OUT for taking out the plated steel plate 10, A work roll 20 and 30 for rolling the plated steel sheet 10 and backup rolls 40 and 50 arranged to apply a predetermined pressure to the work rolls 20 and 30, . At this time, the coated steel strip 10 can be loaded into the temper rolling mill 1 at a speed of 120 to 150 mpm.

The work rolls 20 and 30 may include a first work roll 20 and a second work roll 30 disposed on the upper and lower surfaces of the coated steel sheet 10, And the fine irregularities 12 to which the fine protrusions 21 are transferred can be formed on the plated layer 11 of the plated steel sheet 10 to be rolled. The axes CW1 and CW2 of the first and second work rolls 20 and 30 are disposed on a straight line L4 perpendicular to the direction D1 in which the steel plate 10 is loaded .

The backup rolls 40 and 50 apply first and second backup rolls 40 and 50 to the first and second work rolls 20 and 30, . ≪ / RTI > The axes CW1 and CW2 of the first and second work rolls 20 and 30 and the axes CB1 and CB2 of the first and second backup rolls 40 and 50 are rotatably mounted on the housing 60 Can be supported.

The axes CB1 and CB2 of the first and second backup rolls 40 and 50 are positioned in a direction perpendicular to the direction D1 in which the coated steel strip 10 is loaded, Can be shifted so as to have predetermined angles? 1 and? 2 with the axes CW1 and CW2 of the work rolls 20 and 30, respectively. At this time,? 1 and? 2 may be angles in the range of 1 to 5 degrees, and may be the same angle to each other. A straight line L4 passing through the axes CW1 and CW2 of the first and second work rolls 20 and 30 passes through the axes CB1 and CB2 of the first and second backup rolls 40 and 50 The first and second work rolls 20 and 30 are disposed at positions B1 and B2 where the first and second work rolls 20 and 30 are in contact with the steel plate 10, May be disposed closer to the inlet IN than the outlet OUT.

The axes CW1 and CW2 of the first and second work rolls 20 and 30 and the axes CB1 and CB2 of the first and second backup rolls 40 and 50 are positioned on the plated steel plate 10, The first and second back-up rolls 40 and 50 are disposed on the first and second work rolls 20 and 30 as the first and second backup rolls 40 and 50 are staggered with respect to the vertical direction D2 of the loaded direction D1. The roll force F1 is applied to the plate steel plate 10 in an inclined direction so that the roll force F1 is combined with the force F2 in the direction in which the plate steel plate advances and the resultant force F3 perpendicular to the plate steel plate 10 is applied. . Therefore, the fine protrusions 21 of the first and second work rolls 20 and 30 can be transferred perpendicularly to the surface of the plating layer 11. [ Therefore, as shown in FIG. 2B, the shape of the fine irregularities 12 transferred to the surface of the plating layer 11 may be flat on the bottom surface, and burrs may not be formed on the fine irregularities. FIG. 2B is an SEM photograph of the fine irregularities 12, and it can be confirmed that the bottom surface is flat and burrs are not formed in the fine irregularities.

On the other hand, when the axis of the work roll and the axis of the backup roll are arranged perpendicular to the running direction of the coated steel sheet, the same effect as that of the present embodiment can not be expected. This will be described with reference to the drawings of comparative examples in Figs. 3A to 3C. 3A is a comparative example, FIG. 3B is an enlarged view of part E of FIG. 3A, and FIG. 3C is a SEM photograph of a micro irregularity of a comparative example.

3A, when the roll down force F4 acts vertically, the resultant force F6 actually acting by the force F5 in the direction in which the plated steel sheet advances is smaller than the predetermined force F2 in the direction D2 in which the plated steel sheet advances 3 by an angle? 3. Therefore, the fine protrusions 121 of the work roll 120 are not vertically transferred to the plating layer 111, but the surface of the plating layer 111 is scratched and transferred to form the burrs 113 on the surface of the plating layer 111 Scratch 114 is generated. 3B and 3C, the transferred fine unevenness 112 has an inclined cross section in the direction in which the resultant force F6 acts, and burrs 113 are formed at the fine unevenness boundaries, Scratch < RTI ID = 0.0 > 114 < / RTI >

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

 ( Example )

A cold rolled steel sheet having a composition of 0.002% C-0.003% Si-0.08% Mn-0.028% Al-0.0114% P-0.0052% S as a base steel sheet was prepared and then the coated amount of the coating on one surface of the cold rolled steel sheet was adjusted to 60 g / Hot dip galvanizing was performed to obtain a hot-dip galvanized steel sheet. Thereafter, the hot dip galvanized steel sheet was subjected to EDT or EDT and then subjected to a superfinishing treatment and a topochrome (TCT) to obtain an average roughness Ra of 2.7, 2.0 and 1.4 μm, (Hereinafter referred to as an 'inlet') when the axis of the back-up roll of the work roll is vertical (hereinafter referred to as the "entrance") when the position of contact with the work roll and the hot dip galvanized steel sheet is closer to the entrance than the axis of the backup roll (Hereinafter, referred to as an "exit") when the position of contact with the work roll and the hot-dip galvanized steel sheet is closer to the exit than the axis of the back-up roll, Fine unevenness was transferred to the surface of the hot-dip galvanized steel sheet.

According to the above, whether or not burrs were generated at the fine unevenness boundary portions of the surface of the plating layer and whether or not the occurrence of the galls occurred was measured according to the positions where the work rolls contacted with the hot-dip galvanized steel sheets, and the results are shown in Table 1 below. The shape parameters such as average roughness (Ra) and V2 of fine irregularities on the surface of the plating surface were measured using a surface roughness meter (Veeco, NT8000). Whether or not burrs were formed on the fine irregularities were measured with a scanning electron microscope (SEM) Were observed and evaluated. Here, V2 (Lubricant Filled Profile Valley Area) is a shape factor indicating a profile area where oil such as lubricating oil of fine irregularities can remain.

Whether or not the gauling occurred was evaluated based on whether the coating layer fell off during the repeated friction test. The repetitive friction coefficient was measured by using a high-speed rotating friction tester with a surface of a 200 x 200 mm zinc plated steel sheet subjected to a load of 18 x 28 mm Was repeated 40 times at a speed of 200 mm per second at 5 MPa.

River
Bell Work roll position and angle Work roll roughness and operating conditions Plating surface properties Press formability division location Angle of incidence
(?) Ra
(탆) Roll force
(ton) Elongation
(%) V2
(n m2) Presence or absence of burr Repeat Coefficient Number of Golings One Perpendicular 0 2.7 200 1.5 255 Occur 0.268 15 Comparative Example 1 2 exit One 2.7 200 1.5 250 Occur 0.264 15 Comparative Example 2 3 exit 2 2.7 200 1.5 255 Occur 0.255 9 Comparative Example 3 4 exit 3 2.7 200 1.5 274 Occur 0.279 7 Comparative Example 4 5 exit 4 2.7 200 1.5 265 Occur 0.277 7 Comparative Example 5 6 Entrance One 2.7 200 1.5 355 Not occurring 0.195 Not occurring Inventory 1 7 Entrance 2 2.7 200 1.5 354 Not occurring 0.195 Not occurring Inventory 2 8 Entrance 3 2.7 200 1.5 389 Not occurring 0.192 Not occurring Inventory 3 9 Entrance 4 2.7 200 1.5 375 Not occurring 0.192 Not occurring Honorable 4 10 Entrance 5 2.7 200 1.5 320 Not occurring 0.195 Not occurring Inventory 5 11 Entrance 6 2.7 200 1.5 292 Not occurring 0.225 35 Comparative Example 6 12 Perpendicular 0 2 200 1.5 275 Occur 0.245 9 Comparative Example 7 13 exit One 2 200 1.5 322 Occur 0.254 15 Comparative Example 8 14 Entrance One 2 200 1.5 378 Not occurring 0.178 Not occurring Inventory 6 15 Perpendicular 0 1.4 200 1.5 295 Occur 0.215 35 Comparative Example 9 16 exit One 1.4 200 1.5 356 Occur 0.238 20 Comparative Example 10 17 Entrance One 1.4 200 1.5 408 Not occurring 0.142 Not occurring Honorable 7

As shown in Table 1, when the work roll and the hot-dip galvanized steel sheet are in contact with each other vertically (Comparative Examples 1, 7 and 9) or at the outlet of the coated steel sheets (Comparative Examples 2 to 5, 8 and 10) It was confirmed that burrs were formed on the surface of the plated steel sheet, and the bottom surface of the fine unevenness was formed inclined in the direction of advance of the hot-dip galvanized steel sheet so that V2 was 300 n㎡ or less, the repetitive friction coefficient was 0.2 or more, It was confirmed that the plating layer had already fallen off and the golning occurred before the casting.

On the other hand, in the case where the contact position between the work roll and the plated steel sheet is the inlet of the plated steel sheet and the angle of incidence is 1 to 5 degrees (Examples 1 to 5, 6 and 7), in the boundary of the fine unevenness formed on the hot- And the bottom surface of the fine irregularities was flat so that the V2 was 300 n m2 or more, the repetitive friction coefficient was 0.2 or less, and it was confirmed that the plated layer did not fall off even when the repetitive friction was performed 40 times.

In the case where the angle between the work roll and the backup roll exceeds 5 deg. (Comparative example 6) although the position where the work roll and the plated steel plate are contacted is the exit of the coated steel plate, no burr occurs but V2 decreases It was confirmed that the plating layer had already fallen off and the golning occurred before the friction was performed 40 times.

Accordingly, it has been confirmed that when the angle between the axis of the work roll and the axis of the back-up roll is 1 to 5 °, burr and gulling do not occur at the position where the work roll comes into contact with the plated steel sheet .

1: Temper rolling machine
10: Plated steel sheet
20: first work roll
30: second work roll
40: first backup roll
50: second backup roll
60: Housing
θ1, θ2, θ3: angle of incidence
IN: entrance
OUT: exit

Claims (10)

A coated steel sheet is charged into a temper rolling mill and subjected to temper rolling,
A straight line passing through the center axis of the work roll for rolling the plated steel sheet and perpendicular to a direction in which the plated steel plate is loaded passes through a central axis of the backup roll for applying a predetermined pressure to the work roll, Wherein the steel plate is closer to a direction in which the plated steel sheet is loaded than a straight line perpendicular to the direction.
The method according to claim 1,
Wherein the straight line connecting the center axis of the work roll and the center axis of the backup roll is inclined at a predetermined angle with respect to a straight line perpendicular to a direction in which the coated steel strip is loaded.
3. The method of claim 2,
Wherein the predetermined angle is 1 DEG to 5 DEG.
The method according to claim 1,
Wherein the work roll includes a first work roll and a second work roll for rolling each side of the coated steel sheet,
Wherein the backup roll includes a first backup roll and a second backup roll that apply a predetermined pressure to the first work roll and the second work roll, respectively.
5. The method of claim 4,
Wherein the central axis of the first work roll and the central axis of the second work roll are located on the same straight line with respect to a direction perpendicular to a direction in which the coated steel sheet is loaded.
5. The method of claim 4,
Wherein the center axis of the first backup roll and the center axis of the second backup roll are located on the same straight line with respect to a direction perpendicular to a direction in which the coated steel sheet is loaded.
7. The method according to any one of claims 1 to 6,
Wherein the plated steel sheet is one of a hot-dip galvanized steel sheet, a hot-dip galvanized steel sheet, an aluminum alloy-plated steel sheet, an electro-galvanized steel sheet, an electro-galvanized steel sheet and a galvannealed hot-dip galvanized steel sheet.
A housing having an inlet through which the coated steel strip is loaded and an outlet through which the coated steel strip is taken out;
A work roll rotatably supported on the housing and rolling the plated steel sheet; And
And a back-up roll having a central axis arranged to be shifted from the central axis of the work roll by a predetermined angle with respect to a vertical direction of the direction in which the coated steel strip is loaded, and arranged to apply a predetermined pressure.
9. The method of claim 8,
Wherein a straight line connecting the center axis of the work roll and the center axis of the backup roll is shifted by an angle of 1 to 5 degrees with respect to a direction perpendicular to a direction in which the coated steel plate is loaded.
9. The method of claim 8,
Wherein fine irregularities are formed on a surface of the work roll contacting the plated steel plate.

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