JPS63317205A - Rolling roll and its manufacturing method - Google Patents

Abstract

PURPOSE:To prolong the roll service life and to improve the productivity by forming regular rugged patterns on the surface of a rolling roll and performing chrome plating on the surface. CONSTITUTION:The surface of a rolling roll is covered with a chrome plating layer and rugged patterns are decided so that its flatness F' shown by the equation is within the range of 0.20 to 0.90. In the equation, A' is an area where the max. peak-to-valley height Rmax of unevenness is <7.0mum and B' is an area where the max. height Rmax is >=7.0mum.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention is a rolling roll, particularly used for rolling a cold rolled steel plate, and is used to transfer a regular uneven pattern to the surface of the roll to improve the quality of the cold rolled steel plate. The present invention relates to a rolling roll that provides improved image clarity and workability, and a method for manufacturing the same.

(Prior Art) Cold-rolled steel sheets include so-called prite steel sheets with smooth surfaces and dull steel sheets whose surfaces are moderately roughened by dull finishing. Cold-rolled steel sheets, which are widely used in automobile exterior panels and home appliances, require excellent workability for forming by press working, etc., so dull steel sheets with good lubricant retention properties are usually used. Ru.

In recent years, beautiful appearance of steel sheets has been required for the above-mentioned applications. This beauty is defined by the vivid appearance of R-Hiragi products after being painted, and is commonly referred to as sharpness. It is also known that the image clarity after painting is greatly influenced by the surface condition of the underlying steel plate.

In order to improve image clarity, it is desirable to make the surface of the steel plate as smooth as possible, a so-called bright surface.

However, as mentioned above, for applications that require press molding, a dull finish is essential to ensure workability.

That is, it is generally extremely difficult to satisfy both image clarity and processability with a single surface condition.

The inventors of the present invention previously developed a cold-rolled steel sheet having both excellent image clarity and workability, and filed an application as Japanese Patent Application No. 61-287109. In that invention (hereinafter referred to as the "prior invention"), a pattern in which four small parts are regularly arranged is formed on the surface of a steel plate, and a new concept of flatness ratio is defined from the area of the concave part and the area of the smooth part, and the flat ratio is By keeping the ratio within a certain range, we succeeded in simultaneously providing excellent image clarity and processability.

(Problems to be Solved by the Invention) Continuing with the development of a steel plate that has both high image clarity and workability as described above, the present inventors have developed a method for manufacturing such a steel machine as efficiently and inexpensively as possible. I worked on it. As a result, it has been found that it is practical to apply a desired pattern to the surface of a rolling roll by transferring a pattern previously provided on the surface of the roll during the final step of rolling, for example, temper rolling. It has also been found that a processing method using a high energy density laser beam or electron beam is suitable for surface processing of the rolls used in such rolling.

Such a processing method is introduced, for example, in Japanese Patent Publication No. 62-1)922.

FIG. 1 shows an example of a roll surface pattern formed by laser beam processing. (A) is approximately 5
An enlarged plan view of the roll surface magnified 0 times, (B) is (
It is a sectional view of A). (B) As shown in the figure, the portion of the roll surface that is hit by the beam is defined by melting of the metal, forming a recess 1, around which is a convex portion 2 where the molten metal bulges and solidifies. Although FIG. 1 shows an example in which the convex portion is ring-shaped around the concave portion, the planar shape of the convex portion may take various shapes such as a circle, an ellipse, and a half-moon shape. In any case, this convex portion is transferred to the surface of the steel sheet during rolling, forming an inverted concave portion on the steel sheet.

In order to provide a steel plate with excellent workability and sharpness at the same time, the pattern (size and arrangement of recesses) on the surface of the steel plate must be appropriately controlled. The pattern must be accurate, and even if the pattern on the roll surface is accurate at the beginning, if the convex portions are worn out with each repeated rolling, the surface pattern of the product steel sheet will become disordered. To prevent this, it is necessary to increase the frequency of roll replacement and repair, which poses problems such as the cost of processing the rolls, the number of man-hours for replacement, and the interruption of rolling operations during replacement, which greatly affects the manufacturing cost of steel sheets.

An object of the present invention is to provide a roll having an uneven pattern on its surface, the pattern of which does not easily disappear due to wear.
In particular, it is an object of the present invention to provide a rolling glume that can be used in the production of steel plates that must have both excellent processing and sharpness, and that can contribute to reducing production costs.

Another object of the invention is to provide a new method for manufacturing the above-mentioned rolls.

(Means for Solving the Problems) The first invention of the present application is "a rolling roll having a regular uneven pattern on its surface and covered with a chrome plating film" The gist is:

As clarified in the prior invention, in order to give a steel plate excellent workability and sharpness, the surface flatness ratio (F)
It is necessary to set the value to 0.55 to 0.95.

(Here, F is defined by the following formula.

F-A/ (A+B) A: Maximum height Rs+ax of unevenness on the steel plate surface is 3.0 μm
Area that is less than.

B: Area where Rmax is 3.0 ttvg or more) And the flat ratio (F゛) of the rolling roll required to give the above flat ratio to the steel plate surface is 0.20 to
It is 0.90. This F' is defined as follows.

F" = A' / (A' + B') Ao: Area of the portion where the maximum height Rmax of the unevenness on the roll surface is less than 7.0 μ■.

B' i Same < Area of the part where Rmax is 7.0 μm or more.

Figures 2 (A) and (B) are local enlarged views of the chrome-plated roll surface of the present invention, and are schematic diagrams of Figures 1 and 1 (IIJ) shown above. In (B), A+, Ax, . . . and Bls th, . If it represents A'-A, +A, +... (xiangΣAi)B'-BI
+8, +... (-=IΣBi).

One desirable embodiment of the present invention is that the surface is covered with a chromium plating film, and the flat ratio is 0.2.
It is a rolling roll having a surface shape with a regular uneven pattern of 0 to 0.90.

Here, the reason why there is a difference between the flat ratio of the steel plate and the flat ratio of the roll is that it is usually impossible for the unevenness of the roll surface to be completely transferred to the steel plate surface as it is. In other words, when rolling with rolls as shown in Fig. 2, the extent to which the protrusions (2) of the rolls bite into the steel sheet depends on the rolling reduction ratio, and the extent to which the protrusions (2) of the rolls bite into the steel sheet depends on the rolling reduction ratio, and the extent to which the protrusions (2) of the rolls bite into the steel sheet depends on the rolling reduction ratio. This part is almost a flat part in a steel plate. Due to these circumstances, the total area of the recessed portions of the steel sheet is smaller than the total area of the uneven portions of the roll. In other words, the flat ratio of the steel plate is greater than that of the roll. Therefore, in order to give the steel plate the flat ratio of 0.55 to 0.95, it is necessary to keep the roll flat ratio in the range of 0.20 to 0.90.

The chrome plating that covers the roll surface can be normal hard chrome plating that is used to impart wear resistance to steel materials.
The appropriate thickness of the plating film is about 5 to 20 μm.

The surface hardness of the polished roll is Hv750.
That's about it. However, the hardness of the protrusions formed by the solidification of the metal melted by the high energy density beam is lower than the hardness of the original roll surface, and in one example measured by the present inventor,
It is about 50 Shiloh. Therefore, the convex portions of the rolls wear quickly, and the rolls must be replaced early in order to maintain a predetermined flatness ratio on the surface of the steel plate.In contrast, the roll of the present invention, which has a chrome plating film, Abrasion resistance is also improved, and the time until replacement (roll life) is significantly extended.

Special consideration is required in manufacturing the rolling roll of the present invention. In other words, if the plating film peels off as shown in Figure 3 during use of the roll, the uneven pattern on the roll surface will be disturbed, and as a result, the flatness ratio of the surface of the steel sheet rolled with this roll will fall within a predetermined range. A plating film applied to a surface with minute irregularities, such as the roll of the present invention, is particularly susceptible to peeling at the convex portions.

As shown in FIGS. 1(A) and 1(B), there is extremely fine polishing a:3 on the roll surface before pattern formation.

This flaw has an anchor effect on the plating film and increases its adhesion. However, after the pattern forming process, in the parts 1 and 2 that have been melted and resolidified by a laser beam or the like, these polishing scratches disappear and the above-mentioned anchor effect is lost. Therefore, as shown in FIG. 3, peeling of the plating film is likely to occur at and around the most important convex portions.

In order to deal with such problems, the present inventors have also developed a new method for manufacturing rolls. Here, the gist of the second invention of the present application is the following roll manufacturing method.

``Manufacturing of rolling rolls characterized by forming a regular uneven pattern on the surface by high-energy-density beam processing, roughening the surface by electrolytically etching it in a chrome plating solution, and then applying chrome plating. Method" In the above method, the roll surface before the uneven pattern is polished to a surface roughness equivalent to that of a roll normally used for finishing prite steel sheets, that is, less than Rmax 7.0. This surface is polished with a laser beam. A regular uneven pattern as shown in FIG. 1 is created using a high energy density beam such as . In this case, the uneven pattern is selected so that the flat ratio after plating is 0.20 to 0.90.

After the uneven pattern has been applied, the surface of the roll is first roughened appropriately by electrolytic etching.

FIG. 4 is an enlarged cross-sectional view of the surface portion of the plating roll, particularly in the vertical direction. In the figure, 6 is the roll surface roughened by electrolytic etching and serves as a base for plating, and 4 is the chrome plating film. The purpose of this surface roughening is to give the roll surface to be chromium plated, especially the irregularities that have been melted and solidified as described above, extremely minute undulations by electrolytic etching, thereby providing an anchoring effect for the chrome plating film. It is. As mentioned above, the smooth parts of the roll surface still have fine scratches from the final polishing, so we can expect the plating film to have an anchoring effect, but the uneven parts that have been melted by a laser beam and then resolidified are smooth. Therefore, the plating adhesion is particularly poor.

And the plating film on this uneven part! Since it is important that there be no NUIL, it is important to carry out the above-mentioned surface roughening process especially after the formation of the uneven pattern.

Electrolytic etching can be performed in the same bath in which chromium plating is subsequently performed. However, it goes without saying that the roll side is used as the anode, contrary to the case of plating.

Examples of the bath composition and other conditions are as follows.

Electrolyte...Chromic acid 100-300g/l Sulfuric acid 1-
58/1 aqueous solution.

Temperature: 20~50℃ Current density: 20~60 A/da+"hours...
...2 to 15 minutes The degree of this electrolytic etching is PPI (Peak
It is desirable to manage on a per inch basis. This is a method for evaluating surface roughness that is widely used in the industry. (For details, see "Surface Polishing and Finishing Technology Collection" supervised by Naoji Kinoshita, Nikkei Gijutsu Tosho-P, 233) Electrolytic etching of the present invention In the process, it is desirable to increase the number of peaks measured by the PPI by 1 to 50% compared to before etching.The longer the electrolytic etching is prolonged and the PPI is increased, the better the adhesion of the plating film will be.However. , Excessive etching will make the roll surface too rough, which will even affect the surface after plating.This rough surface is shown at 7 in Figure 4. The surface loses its gloss, which in turn has a negative effect on the sharpness of the steel sheet rolled by these rolls.

The roll whose surface has been roughened (activated) by the electrolytic etching is plated with chromium in the same bath by reversing the polarity and using the roll side as the cathode. The thickness of the plating is determined by taking into consideration the usage conditions of the roll, the required lifespan, etc., but the practical range is 5 to 20 μm as mentioned above.
When the thickness is less than 5 μm, the effect of improving wear resistance is insufficient, and when it exceeds 20 μm, the plating film tends to peel off.

The roll treated and plated as described above has a localized plating film as shown in Figure 3! There is almost no IJI separation, and the lifespan is several to ten times longer than that of unplated bare rolls.

One way to further improve the adhesion of the plating film and further extend the life of the roll is to strengthen electrolytic etching. However, as mentioned above, when etching is strengthened, the surface of the plating film is affected by the unevenness of the underlying layer. Fourth
Although such a state is exaggerated in the figure, if the plating surface becomes rough in this way, the luster will be lost and the sharpness of the steel plate will also be impaired.

Therefore, as a preferred embodiment of the present invention, there is a method in which relatively strong electrolytic etching is performed to improve the adhesion of the plating film, and the roughness of the surface of the plating film is corrected by light final polishing.

Light final polishing (herein defined as "soft polishing") is sufficient to remove minute irregularities (surface roughness) on the surface as shown in 7 in Figure 4, and is sufficient to remove plating. This refers to polishing that does not involve grinding the film or applying polishing pressure. In practice, such polishing can be performed using a soft brush such as a brass wire brush or a nylon brush, or a fibrous abrasive material such as Itobuff. At this time, if a powdered oil-based liquid polishing agent such as chromium hydroxide, alumina, or iron oxide is used in combination, the efficiency of the final polishing will be increased.

By performing the above-mentioned soft polishing, the surface of the plating film becomes smooth and glossy without destroying the basic uneven pattern of the roll surface. Furthermore, since the plating film has high adhesion, the life of the roll is further extended.

(Example) A concavo-convex pattern as shown in FIG. 2 was formed on the surface of a forged steel roll with a diameter of 600 mm and a diameter of 1700 mm by laser beam processing.

The average diameter <r> of the uneven patterns was 200 μm, and the average interval (1) of the uneven patterns was 280 μm.

This roll was immersed in a chromium plating bath (225 g/N of chromic acid, 2.5 g of sulfuric acid) at a temperature of 50°C, and then plating at 30 A/N.
Electrolytic etching was performed at a current density of 4 minutes.

With this treatment, PPI increased by 10%.

Next, in the same chromium plating bath, plating was carried out for 40 minutes at a current density of 25 A/d1) with the scratch resistance reversed.
Chrome plating with a thickness of μm was applied.

Finally, while applying an oil-based liquid abrasive containing chromium hydroxide powder to the roll surface, soft polishing was performed using a brass wire brush.

As a result of the above, a roll with a flatness ratio of 0.85 and excellent gloss was obtained, and a rolling test of a cold rolled steel plate was conducted using this roll to examine the life of the roll.

The rolled steel plate is an annealed material equivalent to JIS 5PCC.

Rolling was carried out using IA using the above rolls as upper and lower work rolls.
It is quality rolled (reduction ratio 1.0%).

The flat ratio of the steel plate obtained by this was 0.90,
Both image clarity and processability were excellent.

FIG. 5 shows the results of investigating the relationship between the cumulative length of the steel plate rolled by the chromium-plated roll and the decrease in the height of the roll convex portion (h) in FIG. 4, that is, the amount of wear. For comparison, a similar investigation was conducted on a roll (bare roll) that was only subjected to laser beam processing and was not chromium plated.

If the life of the roll is considered to be when the height h) of the convex portion reaches 5 μm, the life of the chrome-plated roll of the present invention is approximately 10 times longer than that of a bare roll.

Furthermore, when the surface plating layer of the roll of the present invention was observed during the testing process, it was found that almost no local peeling was observed and the plating adhesion was extremely excellent.

(Effects of the Invention) According to the present invention, the service life of expensive rolls that have been precisely processed by laser beams, electron beams, etc. is extended, and production efficiency is improved by reducing the number of roll replacements. Many practical effects can be obtained, such as homogenization of the surface properties of product steel sheets.

[Brief explanation of the drawing]

FIG. 1 is a locally enlarged view illustrating the uneven pattern on the roll surface, in which (A) is a plan view and (B) is a sectional view taken along the line a-a of (A). FIG. 2 is a view similar to FIG. 1 showing the chrome plating roll of the present invention, and (B) A+, At..., B+,
Bg, . . . indicate the areas of the flat portion and the uneven portion, respectively. Fig. 3 is an enlarged cross-sectional view of the roll surface to explain peeling of the plating film. Fig. 4 is a schematic % formula of a local area on the surface of the chrome-plated roll. Fig. 5 shows the chromium-plated roll of the present invention and the unplated roll. FIG. 3 is a diagram showing test results of roll wear conditions. Applicant Sumitomo Metal Industries, Ltd. (1 other person) Agent Patent attorney Akira Hirose - (1 other person) 1st figure 3 concave roll junior officer #21! I a bird 4 concave

Claims (4)

[Claims] (1) A rolling roll having a regular uneven pattern on its surface and covered with a chrome plating film. (2) The rolling roll according to claim 1, wherein the uneven pattern satisfies a flat ratio F'=0.20 to 0.90 defined by the following formula. F'=A'/(A'+B') However, A': Maximum height Rmax of unevenness on the roll surface is 7
．． The area of the part that is less than 0 μm. B': Similarly, the area of the portion where Rmax is 7.0 μm or more. (3) A rolling roll whose surface is roughened by electrolytic etching in a chromium plating solution on a roll whose surface has been formed with a regular uneven pattern by high energy density beam processing, and then chromium plated. manufacturing method. (4) The method for manufacturing a rolling roll according to claim 3, wherein the surface is soft-polished after being chromium-plated.