JPH01123094A - Production of chromium plated roll - Google Patents

Abstract

PURPOSE:To produce a roll having a long service life for rolling a bright steel sheet having high sharpness by electrolytically treating a bright-finished roll as the anode in a Cr plating soln. to properly increase the number of peaks on the surface and by plating the roll with Cr. CONSTITUTION:A roll bright-finished to about 0.1-0.3mum surface roughness is electrolytically treated as the anode in a Cr plating soln. to carry out etching. By this etching, the number of peaks expressed by PPI on the surface of the roll is increased by 1.3-15 times the initial number of peaks. The polarity is then reversed, the surface of the roll is plated with Cr in about 5-20mum thickness and the plated surface is finish-polished by buffing or other method. A Cr plated roll not causing the exfoliation of the plating or abnormal wear such as the occurrence of edge marks, having a satisfactory surface state and suitably for the bright rolling of a cold rolled steel sheet is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing rolling rolls, particularly chromium-plated rolls with excellent wear resistance used for bright rolling of cold-rolled steel sheets.

(Prior Art) Cold-rolled steel sheets include so-called bright steel sheets with smooth surfaces and dull steel sheets whose surfaces are moderately 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 plate has a surface roughness of approximately 0.1 to
It is rolled with a so-called bride roll finished to about 0.3 μm Ra to make the surface smooth and bright.

Conventionally, forged steel type bride rolls have been used as such bride rolls. In addition to wear on the entire roll, edge marks on the edges of the steel plate (wear on both ends of the roll where the edge of the rolled material comes into contact) and scratches on the entire roll surface are easily noticeable, and the bright, beautiful surface is easily noticeable. In order to produce steel sheets, rolls must be changed frequently. That is, the roll life is short. In order to extend the life of this roll, high chromium alloy cast iron containing about 10 to 20% chromium is sometimes used, but even so, the extension of the life of the roll is only about 1.1 to 1.2 times. .

Another way to extend the life of a roll is to apply a wear-resistant coating to its surface. For example, ceramics such as tungsten carbide are sometimes applied by thermal spray overlay, but such overlay is not only difficult to apply, but the overlay itself can crack under high rolling load or impact, resulting in t! 11al is likely to occur, and abnormal wear may occur in the so-called bead mark portion where the build-up layers overlap, so an extension of the average roll life cannot be expected.

The most practical measure to extend roll life is chromium plating on the roll surface. Chrome plating technology itself is a technology that has been put to practical use in many fields, and it is relatively easy to apply a uniform film with excellent wear resistance. However, in order to apply chromium plating with predetermined characteristics to a special article such as a bride roll for rolling steel sheets, a certain amount of effort is required.

As a method for chromium plating rolling rolls, there have already been proposals in JP-A-61-201800 and JP-A-61-202707. However, according to the method proposed therein, that is, the method of reducing the roughness of the underlying roll surface before plating, in the tests conducted by the present inventors,
The effect of significantly extending the roll life cannot be obtained.

(Problems to be Solved by the Invention) In order to extend the life of rolling rolls, the present inventors roughened the surface of the base roll when applying chromium plating, and
He has already made an invention with the purpose of increasing the
The application was filed as No. 2-29409.

As clarified in the above-mentioned prior invention, if the roll surface is electrolytically treated to give an appropriate roughness to the roll surface as a plating base before chromium plating is applied to the roll surface, the adhesion of the plating film can be improved. This is a significant improvement and the roll life can be significantly extended. However, if the electrolytic treatment is strengthened to roughen the base surface in order to improve this adhesion, this effect will appear on the surface after chromium plating.

FIG. 1 is an enlarged cross-sectional view of the roll surface to explain this phenomenon.As shown in FIG. As a result, minute roughness 3 appears. Such roughness on the surface of the plating film has a roughness of 0.1 to 0.7μ.
Since it is as small as mRa, it does not have much of an adverse effect on rolling by boat. However, in order to manufacture high-quality bright steel sheets in order to improve the sharpness of steel sheets, which has often been a problem in recent years, such minute visibility is not desirable.

The roll surface with such roughness loses luster and luster and becomes milky white, resulting in a rolled steel sheet with poor image clarity.

The present invention further develops the above-mentioned prior invention and provides a new method for manufacturing chrome-plated rolls used particularly for rolling bright steel sheets with high image clarity.

(Means for Solving the Problems) The present invention performs electrolytic treatment using a brightly finished roll as an anode in a chromium plating solution, and increases the number of ridges on the roll surface indicated by PPI from 1.3 to the initial number of ridges. The gist thereof is a method for producing a chrome-plated roll, which is characterized by increasing the number of rolls by 15 times, then reversing the polarity, applying chrome plating, and then polishing the plated roll surface.

In the above method, the surface of the roll before electrolytic treatment is polished to a surface roughness equivalent to that of a roll normally used for finishing bright steel sheets, that is, about 0.1 to 0.3 μm Ra. Electrolytic etching) is then carried out in the same bath as the chrome plating.

However, it goes without saying that the roll side is used as the anode, contrary to the case of plating. By this electrolytic etching, PPI
The number of peaks on the roll surface, expressed as (Peak Count per Inch), is increased by 1.3 to 15 times the initial number of peaks. Note that PPI is a surface roughness evaluation method widely used in the industry. (For details, please refer to "Supervised by Naoji Kinoshita"
“Surface polishing and finishing technology collection” Nikkei Technical Books aIP, 233
(Reference) Here, the reason why the PPT is increased by 1.3 times or more is to ensure the improvement of the adhesion of the plating film and to further extend the life of the roll. The more the electrolytic etching is strengthened and the PPT is increased, the more the adhesion of the plating film is improved. However, excessive etching makes the surface of the roll too uneven, which also affects the surface after plating.

In the method of the present invention, since there is a step of polishing the surface of the plated film after plating, the degree of etching can be increased and the increase in PPI can be up to 15 times the initial value. However, if excessive etching exceeding 15 times is performed, a resin-like crystal structure will increase on the surface and the adhesion of the plating film will deteriorate.

In short, the conditions for the electrolytic treatment can be determined to increase the PPI as described above.However, considering that the next plating step will be performed in the same treatment solution, the desirable conditions are as follows. It is something.

Electrolyte...Chromic acid 100-300g#! Sulfuric acid 1~
5g/l aqueous solution.

Temperature: 20~60℃ Current density...20~60 A/da+''hours...
The roll whose surface has been roughened (activated) by the electrolytic etching for 2 to 15 minutes is chromium plated in the same bath with the polarity reversed and the roll side used as the cathode. The thickness of the plating is determined in consideration of the usage conditions of the roll, the required lifespan, 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 20 μm, the plating film tends to separate.

As mentioned above, the surface of the plating film applied to the electrolytically treated base has minute roughness. Therefore, in the method of the present invention, the surface of the film is polished after plating. This final polishing is sufficient to remove minute irregularities (surface roughness) on the surface as shown by reference numeral 3 in Figure 1, and the polishing is to the extent that it does not further grind the plating film or apply polishing pressure. .

Puff polishing is suitable as a polishing method, and commonly used materials such as cotton cloth, felt, and leather can be used as the base material of the puff body, and alumina, chromium oxide, cerium oxide, and hydroxide can be used as polishing agents. Chrome or other conventional abrasives can be used. This polishing removes surface roughness of the plating film and makes the roll smooth and glossy.

(Example) The surface of a forged steel roll (Hv850) for cold temper rolling with a diameter of 600 mm and a diameter of 1700 wz was polished with a grindstone, and processed into a bright finished roll with a center line average roughness Ra = 0.2 In and PPI = 50.

Electrolytic etching was performed under the following conditions using the above roll as an anode.

Bath composition: Chromic acid 225g/1 Sulfuric acid 2.5g/l Bath temperature: 50°C Cumulative current: 30A/da" x 4 minutes After this treatment, the roll surface has a Ra = 0.5μ clear, PPI = 20
It was 0.

Next, in the same bath, plating was performed for 30 minutes at a current density of 30^/dm'' with the polarity reversed and the roll used as a cathode.
Chrome plating with a thickness of 2 μm was applied. After washing with water and drying, it was confirmed that there was no abnormality in appearance, and the hardness was measured, and it was found to be Hv = 1100.

The roll described above was attached to a roll grinder, and the roll surface was polished with a cotton cloth puff while an oil-based liquid polishing agent containing chromium hydroxide powder was applied to the roll surface.

In each of the above steps, the gloss of the roll surface is measured using a Murakami Color Technology Research Institute type gloss meter (portable gloss meter, GMX-
100), if the gloss before electrolytic etching is 1, then it was 0.8 after electrolytic etching and chrome plating, and 1.3 after puff polishing. Electrolytic etching roughens the roll surface, and plating maintains the roughness up to the plated surface, but it was confirmed that polishing after plating resulted in a roll with extremely good surface gloss.

A steel plate rolling test was conducted using the roll obtained above, and the life of the roll was investigated.

The rolled steel plate was an annealed material equivalent to JIS SP (:C).

The rolling was temper rolling (reduction ratio: 1.0%) using the above rolls as upper and lower work rolls.

The limit of roll life was determined based on changes in the surface gloss of the steel sheet and the presence or absence of edge marks.

The test results are shown in Table 1. Comparative Example 1 is a bare roll that is not plated, and Comparative Example 2 is a roll that was treated in the same manner as the present invention example up to plating, but was not polished at the end.

The unplated bare roll of Comparative Example 1 in Table 1 was rolled at -1f.
Edge marks occurred at t100 tons, whereas the roll manufactured by the method of the present invention showed no plating I! even after rolling 5 times as much as the roll of Comparative Example 1. There was no abnormal wear such as JJ separation or edge marks, and the gloss of the finished steel sheet was significantly improved compared to Comparative Example 1.

Comparative example 2 is a roll that was treated in the same way as the inventive example up to plating, but without the final polishing, but like comparative example 1, there was no problem with the rolling amount up to 500 tons without peeling of the plating or edge marks, etc. Since the roll surface was roughened, the steel sheet gloss was also inferior to Comparative Example 1. Comparative Example 2 is not suitable for steel plates that require high gloss, and requires polishing after plating.

(Effect of the invention) As is clear from the results of the examples, the roll manufactured by the method of the present invention still maintains a high gloss level of the finished steel sheet even after rolling 5 times the amount of steel sheet as the roll of the comparative example. . Even with the roll of Comparative Example 2, it is possible to roll 500 tons until edge marks occur, but the gloss of the finished steel sheet is poor. This is because the roll surface condition is significantly improved by performing appropriate polishing after plating.

The roll produced by the method of the present invention does not suffer from peeling of plating or abnormal wear such as the edge marks mentioned above, and therefore,
Width schedule-free rolling, which was not possible using conventional rolls, is also possible with this roll. Extending the life of the rolls reduces the number of interruptions in rolling operations due to roll replacement, lowers the cost of repairing the rolls, and ultimately greatly contributes to reducing the cost of manufacturing steel sheets.

[Brief explanation of the drawing]

FIG. 1 is an enlarged schematic cross-sectional view of the plated roll surface. 1: Roll base 2: Plating film 3: Surface roughness Applicant: Sumitomo Metal Industries, Ltd. (1 other person) Agent: Patent attorney Akira Hirose - (1 other person) Cleaning of drawings (B…21) (None) Figure 1 Procedural amendment Labor side February 29, 1988 Director General of the Patent Office Kunio Ogawa 1, Indication of the case 1988 Patent Application No. 278571 2, Name of the invention Method for manufacturing chrome-plated rolls 3 , Person making the amendment Relationship to the case Patent applicant Address 5-15-6 Kitahama, Higashi-ku, Osaka City Subject of amendment Drawings

Claims (1)

[Claims] Electrolytic treatment is performed in a chrome plating solution using a roll with a bright finish as an anode to increase the number of ridges on the roll surface indicated by PPI by 1.3 to 15 times the initial number of ridges, and then reverse the polarity and chrome plate it. A method for producing a chrome-plated roll, which comprises applying chromium-plated rolls and then polishing the plated roll surface.