JPH0520166B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method of manufacturing a chromium-plated cast iron roll mainly used for rolling metal materials. (Prior Art) Rolls for rolling metal materials can be broadly classified into steel and cast iron rolls based on their material, and on the other hand, they are classified into bright rolls and dull rolls based on roll surface properties. Here, the dull roll is used to produce a dull steel plate having an appropriately roughened surface by transferring minute irregularities on the roll surface to the steel plate surface. However, as the dull roll is repeatedly used, the dull peak portion is worn out and the surface roughness of the rolled material decreases, making it impossible to meet the product plan. In this case, the rolls are replaced, and the replaced rolls are repaired and refurbished and reused, but the interruption of rolling operations and the number of man-hours for roll repair associated with this roll replacement increase the manufacturing cost of the steel sheet. In particular, recently there has been a demand for steel sheets with finely adjusted surface roughness, and the surface dulling of the rolls used to manufacture them may be highly controlled using, for example, a laser beam. In that case,
The cost of roll repair can be significantly high. Therefore, increasing the wear resistance of dull rolls is an extremely important issue for those skilled in the art in order to reduce the cost of rolls and, by extension, the cost of manufacturing steel sheets. This situation is the same whether it is a steel-based roll or a cast iron-based roll, but in particular, a cast iron-based roll has dispersion of carbides and a non-uniform structure, so the surface roughness tends to deteriorate. 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, with dull rolls that have an uneven surface, even if chrome is plated, cracks will occur in the plating layer due to the high load of rolling, especially at the dull peaks in the early stages of rolling, and this will become a starting point for the plating film to peel off and fall off. invite. If rolling is continued with such rolls, dull pattern irregularities and indentation defects will occur on the surface of the product steel sheet, resulting in product defects, so replacing the rolls is inevitable.
The effect of extending roll life is poor. In addition to the above-mentioned chrome plating, measures to extend the life of the rolls include making the rolls themselves of high-alloy, wear-resistant cast steel, increasing the hardness of the rolls by surface hardening, or spraying tungsten carbide or some types of ceramics. There is a way to fill it up. However, the life of the roll that can be extended by these methods is only about twice as long at most, and there are problems such as increased material costs, cracking and peeling of the hardened layer and built-up layer, and it is difficult to say that it is a practical countermeasure. (Problems to be Solved by the Invention) The present inventor filed a patent application as Japanese Patent Application No. 1983-9405 regarding a method for manufacturing a chrome-plated dull roll mainly used for rolling metal materials, the gist of which is as follows: Electrolytic treatment is performed in an electrolytic solution using a dull-finished roll as an anode to increase the number of ridges on the roll surface indicated by PPI by 1 to 50% compared to the number before electrolysis, and then chrome plating is performed using the roll as a cathode. This is a method for producing a chrome-plated roll, which is characterized by subjecting the roll to chrome plating. This method increased the roughness of the roll base material, improved the adhesion of the plating film, eliminated cracking and peeling of the plating film even during high-load rolling, and increased the life of the roll by 13 times. In this method, the roll base material is a steel roll such as cast steel, as shown in the examples, and in that case, it is possible to certainly obtain good results. However, when the roll base material is cast iron, when plated using the above technique, the roll surface may not be plated or may have uneven plating. In addition, even if the plating appears to be clean on the surface of the roll, there is a problem in that the plating peels off early during high-load rolling, making it unusable. As mentioned above, the roll base material is cast iron (carbon content is
2.0% by weight or more), electrolytic treatment is performed in an electrolytic solution to increase the number of peaks indicated by PPI by 1 to 50%,
When chrome plating is applied afterwards, the electrolytically treated roll surface is covered with smut, which causes problems such as the plating film not being formed or the adhesion being reduced in the subsequent chrome plating process, which is expected to extend the life of the roll. Can not. Particularly during high load rolling, plating peeling tends to occur early. Unless the number of peaks indicated by PPI is increased by 1 to 50% by electrolytic treatment to ensure adhesion, smuts will not occur and it is possible to apply chrome plating uniformly. However, in the case of light-load rolls such as conveyor rolls such as bridles, almost good results can be obtained with this method, but in high-load rolling such as skin pass rolling and cold rolling, plating adhesion is weak and plating occurs early. Peeling occurs and no improvement in service life can be expected. If the roll surface is dulled, there will be point contact during rolling, which will be more severe (higher load).
Significant peeling of plating. Note that "smut" means "dirt" and refers to carbon, silicon, etc. in iron that are not dissolved by electrolytic treatment and adhere to the roll surface. Thus, when applying chromium plating to the surface of a cast iron roll with a carbon content of 2.0% or more, the present invention provides good adhesion between the roll base material and the chrome plating, and is suitable for high-load rolling such as skin pass rolling and cold rolling. The purpose of the present invention is to provide a method for manufacturing a chrome-plated roll that can exhibit a long service life. (Means for Solving the Problems) The inventor of the present invention has conducted various studies in order to achieve the above-mentioned problems, and found that, prior to chromium plating the surface of a cast iron roll, electrolytic treatment was performed using the roll as an anode in an electrolytic solution. By increasing the roughness of the surface, and then cleaning the obtained highly rough surface by electrolytic treatment in an alkaline solution, the adhesion between the roll base material and the chrome plating film is improved, and the skin pass is improved. The present invention was completed based on the finding that cracking and peeling of the plating film is reduced during high loads such as rolling and cold rolling. Therefore, the gist of the present invention is that when applying chromium plating to the surface of a cast iron roll having a carbon content of 2.0% by weight or more, electrolytic treatment is performed in advance using the roll as an anode in an electrolytic solution, and PPI The number of ridges on the roll surface shown by is 1 to 1 more than the number of ridges before electrolytic treatment.
50%, the roll surface is washed in an alkaline solution, and then chromium plating is applied in a chromium plating solution using the roll as a cathode. be. (Function) Next, the reason why each manufacturing condition is limited as described above in the present invention will be explained in detail. The base material of the chromium-plated roll obtained by the method of the present invention is a cast iron roll with a carbon content of 2.0% or more. This is because smut does not occur and there is no need to wait for the application of the present invention. There are no particular restrictions on the composition of other cast irons, but it is preferable to add appropriate alloy components to form an alloy cast iron roll. For example, there are high alloy grain cast iron rolls and high chromium cast iron rolls to which Ni, Cr, etc. are added. Applications include rolls for scale breaking mills for rolling black-skinned steel sheets as a pretreatment for pickling and descaling, rolls for skin passes for rolling black-skinned steel sheets, and rolls for cold rolling of pickled steel sheets. FIG. 1 shows an enlarged schematic cross-sectional view of a cast iron roll surface subjected to dull processing. This is an example of the surface form of the base material to be chromium plated. In the present invention, the surface of the cast iron roll before electrolytic treatment is not particularly limited, but preferably has a dull finish with a roughness depending on the intended use of the roll. The dull processing method may be any of the general shot blasting method, electric discharge machining method, etc., as well as processing methods using electron beams or laser beams, which are becoming popular recently. Next, the cast iron roll thus prepared is electrolytically treated in an electrolytic solution such as a chromic acid bath using the cast iron roll as an anode to increase the number of ridges on the roll surface by 1 to 50% compared to before the electrolytic treatment. If the increase rate is less than 1%, even if the surface is subsequently cleaned and plated, the plating adhesion will be weak, and it cannot be used for high-load skin pass rolling, cold rolling, etc.
Furthermore, if it exceeds 50%, the initial shape will be distorted, so it should be kept below 50%. An enlarged schematic cross-sectional view of the electrolytically treated roll surface is shown in FIG. 2. The cross-sectional shape is almost the same as that in FIG. 1 showing the shape of the dull roll base material, but minute irregularities are generated. In addition, adhesion of Smut 1 can be seen on the surface. In the present invention, such increase in unevenness can be solved by PPI (Peak
Evaluate by Count per Inch). PPI is a method specified in the SAE standard as one of the notation methods for surface roughness. For details, see "Surface Polishing and Finishing Techniques Collection" supervised by Naoji Kinoshita, Nikkei Gijutsu Tosho Co., Ltd., p. 233. The purpose of the anodic electrolytic treatment in this case is arbitrary as long as it increases the above PPI, but for example, when using a chrome plating solution, the temperature is usually 45
~55℃, as integrated current (current density x time)
The conditions are approximately 25A/dm ² x 3 minutes to 35A/dm ² x 8 minutes. Here, an example of a method for increasing PPI by electrolytic treatment in an electrolytic solution is as follows. Electrolyte: The same solution used for chromium plating CrO ₃ : 200-250g/, H ₂ SO ₄ : 2-2.5
g/ Liquid temperature: 40 to 60℃ Current density x time: 25A/dm ² x 3 minutes to 25A/d
m ² × 8 minutes In addition, electrolytic etching, which is sometimes performed to remove the passivation layer on the surface as an activation treatment for the base of normal chrome plating, has an integrated current value of 30 A/dm ² × 1 to 2 The increase in PPI is not observed with this level of electrolytic treatment. Cast iron rolls whose PPI has been increased through anodic electrolytic treatment are further subjected to alkaline cleaning. Alkaline cleaning may be combined with electrolytic cleaning or simply immersed in an alkaline cleaning solution. However, in order to fully exhibit the effect of alkaline cleaning in a short time, it is preferable to perform it in combination with electrolytic treatment. This is so-called electrolytic alkaline cleaning. FIG. 3 is an enlarged schematic cross-sectional view of the cast iron roll surface seen when the roll surface is washed in an alkaline solution. A typical example of operation when performing electrolytic alkaline cleaning using a cast iron roll as an anode is shown below. Alkaline liquid: 20 to 120 g of sodium cyanide/Current density: 1.5 to 10 A/dm ² Liquid temperature: Room temperature to 60°C Processing time: 30 to 60 sec Caustic soda, soda carbonate, etc. can also be used as the alkaline liquid. After the alkaline cleaning is completed, the roll is thoroughly washed with water, and chrome plating is applied in a chrome plating solution using the roll as a cathode. Such chrome plating can be performed under the following conditions, for example. . Chromium plating solution: Chromic acid CrO ₃ , 200-250g/
Sulfuric acid H ₂ SO ₄ , 2 to 2.5 g/Liquid temperature: 40 to 60° C. Current density: 20 to 40 A/dm ² FIG. 4 is an enlarged schematic cross-sectional view of the chromium-plated roll surface. As can be seen from the figure, the chrome-plated layer 2 is in close contact with the dulled roll surface. The thickness of the chromium plating layer thus obtained is determined by taking into account the usage conditions of the cast iron roll, the required life span, and other factors. For example, in the case of cast iron dull rolls used for scale breaking, 5~
A thickness of about 20 μm is sufficient. Next, the effects of the present invention will be explained in more detail with reference to Examples. Example 1 This example is a method for manufacturing a cast iron roll for a scale-breaking mill for rolling black-skinned steel sheets as a pretreatment for pickling and descaling. Table 1 shows the specifications of the cast iron roll of this example. This roll had been dulled in advance by shot blasting.

[Table] The cast iron roll thus prepared was subjected to electrolytic treatment, alkaline cleaning, and chromium plating under the conditions shown in Table 2 to provide chrome plating with a thickness of 10 μm and a surface hardness of Hv1000. In addition, PPI is 180 due to electrolytic treatment.
increased by 20%.

[Table] The chrome-plated cast iron roll manufactured in this manner was installed in a scale breaking mill and used for scale breaking of black skin steel plate (JIS SPHC plate thickness 3.2 mm). The scale-breaking rolling capacity until the roll life reaches the end due to abrasion or peeling of the plated layer and requires replacement or repair is 50,000 tons, which is 10 times more than a non-plated roll. Example 2 This example is a method for manufacturing a cast iron roll for a skin pass mill for rolling black-skinned steel sheets. The third specification of the roll
Shown in the table. In this example, dull processing was not performed.

[Table] The cast iron roll prepared in this way was subjected to the same treatment as in Table 2, and the plating thickness was 15 μm and the surface hardness was
Finished with Hv1000 chrome plating. In addition, PPI increased by 25% to 125 due to electrolytic treatment. The resulting chrome-plated cast iron rolls were used in a skin pass mill and the life of the rolls was investigated. As a result, the rolling capacity was 25,000 tons, 13 times greater than that of non-plated rolls. (Effects of the Invention) As described in detail above, according to the present invention, rolls with good plating adhesion can be manufactured even with cast iron rolls having a carbon content of 2% or more. Not only can it be used for high loads such as skin pass rolling and cold rolling, but it can also achieve a long service life. Moreover, there have been no examples of cast iron rolls that have been plated with chrome, and according to the present invention, the use of cast iron rolls can be expanded even to the above-mentioned high-load applications, and the practical significance of the present invention is is big.

[Brief explanation of the drawing]

Fig. 1 is an enlarged schematic cross-sectional view of the roll surface that has been dulled; Fig. 2 is an enlarged schematic cross-sectional view of the roll surface after electrolytic treatment; Fig. 3 is an enlarged schematic cross-sectional view of the roll surface after washing with alkaline solution. and FIG. 4 is an enlarged schematic cross-sectional view of the chrome-plated roll surface. 1...Smart, 2...Chrome plated layer.

Claims (1)

[Claims] 1. When applying chromium plating to the surface of a cast iron roll with a carbon content of 2.0% by weight or more, electrolytic treatment is performed in advance in an electrolytic solution using the roll as an anode, and PPI
After increasing the number of ridges on the roll surface represented by 1 to 50% than the number before electrolytic treatment, the roll surface is washed in an alkaline solution, and then the roll is used as a cathode in a chrome plating solution. A method for manufacturing a chrome-plated cast iron roll, characterized by applying chrome plating.