JPH0765227B2 - Method for manufacturing chrome plating roll - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a rolling roll, in particular, a chrome-plated roll having excellent wear resistance, which is used for bright rolling of a cold-rolled steel sheet.

(Prior Art) Cold-rolled steel sheets include so-called bright steel sheets having a smooth surface and dull steel sheets appropriately roughened by dull finishing. The surface condition of these products is usually adjusted depending on the type of rolling roll used in the final step of cold rolling. That is, the bright steel sheet has a surface roughness of about 0.1 to
It is rolled with a so-called bright roll finished to about 0.3 μmRa to make the surface a smooth bright surface.

Conventionally, such a bright roll is made of forged steel. In such a roll, not only the wear of the entire roll but also the edge marks on the edges of the steel plate (wear of both ends of the roll against which the edges of the material to be rolled hit) and flaws on the entire roll surface are conspicuous. In order to produce bright steel sheets, the rolls have to be changed frequently. That is, the roll life is short. In order to extend the roll life, high chromium alloy cast iron containing about 10 to 20% of chromium may be used, but the roll life is still only about 1.1 to 1.2 times at most.

Another way to extend roll life is to apply a wear resistant coating on its surface. For example, there is a case where a tungsten carbide or a certain kind of ceramics is spray-coated, but such a build-up is not only difficult to construct, but the build-up layer itself is apt to crack and peel due to a high rolling load or impact, and Abnormal wear may occur at the so-called bead mark portion where the overlays overlap, and an average roll life extension cannot be expected.

The most practical means for extending the roll life is chromium plating on the roll surface. The chrome plating technology is a technology that has been put to practical use in many fields, and it is relatively easy to form a uniform film having excellent wear resistance. However, in order to apply a chromium plating having a predetermined characteristic to a special article called a bright roll for rolling a steel sheet, it is necessary to take appropriate measures.

As a chrome plating method for rolling rolls, there have already been proposed JP-A-61-201800 and JP-A-61-202707. However, the method proposed therein, that is, the method of lowering the roughness of the roll surface to be the base before plating, in the test of the present inventors, a significant effect of extending the roll life can be obtained. I can't.

(Problems to be Solved by the Invention) In order to extend the life of a rolling roll, the present inventors have made an invention characterized by roughening the surface of a base roll and increasing the PPI when applying chromium plating. None already Japanese Patent Application Sho 62-
Filed as No. 29409.

As disclosed in the above-mentioned prior invention, prior to applying chromium plating to the roll surface, if the roll is electrolytically treated to give a suitable roughness to the roll surface as a plating base, the adhesion of the plating film is It is remarkably improved, and the roll life is greatly extended. However, if the electrolytic treatment is strengthened to roughen the underlayer in order to improve the adhesiveness, the effect appears on the surface after chromium plating.

FIG. 1 is an enlarged sectional view of a roll surface portion for explaining such a phenomenon. As shown in the figure, the unevenness of the base 1 roughened by the electrolytic treatment is reflected even on the surface of the plating film 2, and a minute roughness 3 appears. Since the roughness of the surface of the plating film is as small as a roughness of about 0.1 to 0.7 μm Ra, it does not have a bad influence on general rolling. However, in order to improve the sharpness of a steel plate which has become a serious problem in recent years, such fine roughness is not preferable for producing a high quality brid steel plate. The surface of the roll thus roughened loses its luster and becomes milky white, and the rolled steel sheet has poor image clarity.

The present invention further develops the above-mentioned prior invention and provides a new method for producing a chrome-plating roll used particularly for rolling a pride steel sheet having high image clarity.

(Means for Solving Problems) The present invention uses a bright-finished forged steel roll as an anode in a chromium electroplating bath having a bath temperature of 20 to 60 ° C. and an integrated current represented by electrode density × time of 40 to 900 A. / dm ² · min electrolytic treatment is performed, the number of ridges on the roll surface indicated by PPI is increased by 1.3 to 15 times compared to the number before ridge, and then the polarity is reversed and chromium plating is applied. The essence is a method for producing a chrome-plated roll, which is characterized by polishing the surface of the plated roll.

In the above method, the surface of the roll before the electrolytic treatment is polished to have a surface roughness equivalent to that of a roll usually used for finishing a steel plate, that is, about 0.1 to 0.3 μm Ra. The electrolytic treatment (electrolytic etching) is performed in a bath for chromium plating next. However, needless to say, the roll side is the anode, which is the opposite of the plating. By this electrolytic etching, the number of ridges on the roll surface indicated by PPI (Peak Count per Inch) is increased by 1.3 to 15 times as compared with the number of ridges before electrolysis which is usually within the range of PPI = 20 to 80. PPI is a surface roughness evaluation method widely used in the industry. (For details, refer to P.233, Nikkei Technical Book Co., Ltd., “Surface Polishing / Finishing Technology Collection” supervised by Naoji Kinoshita.) Here, increasing the PPI by 1.3 times or more is sure to improve the adhesion of the plating film. This is to further extend the roll life. As the electrolytic etching is strengthened and the PPI is increased, the adhesion of the plating film is improved. However, excessive etching makes the surface of the roll too rough and affects the surface after plating. In the method of the present invention, since the plating film surface is polished after plating, the degree of etching can be increased and the PPI can be increased up to 15 times the initial value. However, if the etching is excessively performed to exceed 15 times, the resin-like crystal structure increases on the surface and the adhesion of the plating film deteriorates.

The conditions of the electrolytic treatment may be determined so that the PPI can be increased as described above. However, considering that the next plating step is performed in the same treatment liquid, the desirable conditions are as follows.

Electrolyte solution: An aqueous solution of chromic acid 100-300g / sulfuric acid 1.5g /.

Temperature: 20 to 60 ° C Current density: 20 to 60 A / dm ² hours: ^{2 to} 15 minutes The roll whose surface is roughened (activated) by the above electrolytic etching is in the same bath. The polarity is reversed and the roll side is used as the cathode for chrome plating. The thickness of the plating is determined in consideration of the usage conditions of the roll, the required life, etc., but the practical range is 5 to 20 μm. If it is less than 5 μm, the effect of improving wear resistance is insufficient, and if it exceeds 21 μm, the plating film tends to peel off.

As described above, the surface of the plating film applied to the electrolytically treated base has fine roughness. Therefore, in the method of the present invention, the surface of the film is polished after plating. This finish polishing is sufficient to remove minute irregularities (roughness) on the surface as indicated by reference numeral 3 in FIG. 1, and to such a degree that the plating film is not further ground or polishing flaws are attached. . As a polishing method, buff polishing is suitable, and the base material constituting the buff body can be made of commonly used materials such as cotton cloth, felt, and leather, and the polishing agent can be alumina, chromium oxide, cerium oxide, or hydroxide. Chromium and other conventional abrasives can be used. By this polishing, the surface roughness of the plating film is removed, and the roll becomes smooth and has a good gloss.

(Example) 600 mmφ x 1700 mm forged steel roll for cold temper rolling (Hv85
The surface of (0) is polished with a grindstone, and the center line average roughness Ra = 0.2μ
Bright finish roll with m and PPI = 50.

Using the above roll as an anode, electrolytic etching was performed under the following conditions.

Bath composition ・ ・ ・ Chromic acid 225g / Sulfuric acid 2.5g / Bath temperature ・ ・ ・ ・ 50 ℃ Accumulated current ・ ・ 30A / dm ² × 4 minutes Roll surface after this treatment is Ra = 0.5μm, PPI = 200 It was

Next, in the same bath, the polarity was reversed and the roll was used as a cathode to carry out plating at a current density of 30 A / dm ² for 30 minutes, and then 12 μm thick chromium plating was performed. After washing this with water and drying, it was confirmed that there was no abnormality in the appearance, and the hardness was measured to find that Hv = 11
It was 00.

The above roll was attached to a roll grinder, and the surface of the roll was polished with a cotton cloth buff while applying an oily liquid abrasive containing chromium hydroxide powder.

In each of the above steps, the gloss of the roll surface was measured by Murakami Color Research Laboratory gloss meter (portable gloss meter, GMX-10
0), the gloss before electrolytic etching is 1, and after the electrolytic etching and chrome plating is 0.
8 and 1.3 after buffing. It was confirmed that the surface of the roll is roughened by electrolytic etching and the surface of the plated surface is maintained rough by plating, but polishing after plating results in a roll having an extremely good surface gloss.

Using the roll obtained as described above, a rolling test of a steel sheet was conducted to examine the roll life.

The rolled steel sheet was an annealed material equivalent to JIS SPCC. The rolling was temper rolling (rolling rate 1.0%) using the above rolls as upper and lower work rolls.

The roll life limit was judged by the change in the steel sheet surface glossiness and the presence or absence of the occurrence of edge marks.

Table 1 shows the test results. In addition, Comparative Example 1 is a bare roll which is not plated, and Comparative Example 2 is a roll which has been subjected to the same treatments as those of the present invention up to plating and which has not been finally polished.

The bare roll of Comparative Example 1, which is not plated, has a rolling amount of 100.
Although the edge mark was generated at a ton, the roll manufactured by the method of the present invention does not suffer from peeling of the plating and abnormal wear such as the edge mark even when rolled 5 times as much as the roll of Comparative Example 1. Further, the glossiness of the product steel sheet was also significantly improved as compared with Comparative Example 1.

Comparative Example 2 is a roll which has been treated in the same manner as the present invention example up to plating and not subjected to the final polishing, but like Comparative Example 1, up to a rolling amount of 500 tons, there is no problem such as plating peeling and edge marks. Since the roll surface is roughened, the steel plate gloss is inferior to Comparative Example 1. Comparative Example 2 is not suitable for a steel sheet that requires glossiness, and requires polishing after plating.

(Effects of the invention) As is clear from the results of the examples, the roll manufactured by the method of the present invention has a high gloss of the finished product steel sheet even after rolling five times as many steel sheets as the roll of Comparative Example 1. . Even with the roll of Comparative Example 2, 500 tons can be rolled until the generation of the edge mark, but the gloss of the product steel sheet is inferior. This is because the roll surface condition is remarkably improved by performing appropriate polishing after plating.

The roll according to the method of the present invention does not cause abnormal wear such as peeling of the plating or the edge mark described above, and therefore,
This roll also enables width schedule free rolling, which was not possible using conventional rolls. The extension of the roll life largely contributes to the reduction of the number of interruptions of the rolling work accompanying the roll replacement, the cost of roll repair, and the reduction of the steel plate manufacturing cost in the end.

[Brief description of drawings]

FIG. 1 is an enlarged schematic sectional view of a plated roll surface portion. 1: Roll base, 2: Plating film 3: Surface roughening

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akio Shinshiro 1-3, Nishi-Nagasumotodori, Amagasaki City, Hyogo Prefecture Sumitomo Metal Industries, Ltd. Research Institute (72) Inventor Takayuki Sato Higashikohama, Sumiyoshi-ku, Osaka City, Osaka Prefecture 1-10-7

Claims (1)

[Claims] 1. A chrome electroplating bath having a bath temperature of 20 to 60 ° C., in which a bright-finished forged steel roll is used as an anode and the cumulative current expressed by current density × time is 40 to 900 A / dm ² · min. Perform electrolytic treatment to increase the number of crests on the roll surface indicated by PPI by 1.3 to 15 times than the number of crests before electrolysis, then reverse polarity and perform chrome plating, and then polish the plated roll surface A method for manufacturing a chrome-plated roll characterized by the above.