JPH0461078B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a chrome-plated dull roll used mainly for rolling metal materials. (Prior Art) For example, so-called cold-rolled steel plates that are finished by cold rolling include bright steel plates that have a smooth surface and dull steel plates that have a moderately roughened surface by dull finishing. Dull steel sheets are manufactured by using dull finishing rolls (dull rolls) as rolling rolls that are normally used in the final step of cold rolling, and by imparting minute irregularities on the surface of the rolls to the steel sheet surface. As the dull roll is repeatedly used, the dull peak portion is worn out, and the surface roughness of the rolled material decreases, causing the product to no longer meet product specifications. 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 such cases, the cost of roll repair becomes significantly high. Therefore, increasing the wear resistance of dull rolls can reduce roll costs,
Furthermore, this is an extremely important issue for those skilled in the art in order to reduce the cost of manufacturing steel sheets. 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 uneven surfaces, 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 initial stage 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, uneven dull patterns and indentation defects will occur on the surface of the product steel sheet, resulting in product defects, so the rolls will eventually have to be replaced, and the effect of extending the life of the rolls will be poor. In addition to the above-mentioned chrome plating, measures to extend the life of the roll include making the roll itself of high-alloy, wear-resistant cast steel, hardening the roll by surface hardening, or using tungsten carbide or certain types of ceramics. There is a method of thermal spray overlay. However, these methods can only extend the life of the roll by about twice as much, and there are problems such as increased material costs, cracking of the hardened layer and overlay layer, and peeling, so it is difficult to say that it is a practical countermeasure. . (Problems to be Solved by the Invention) An object of the present invention is to extend the life of a roll by using chrome plating, which is currently the most practical method. As a method for plating rolling rolls with chrome, there have already been proposals in JP-A-61-201800 and JP-A-61-202707. However, the method proposed therein, that is, the method of reducing the roughness (Rz) of the underlying roll surface before plating,
In experiments conducted by the present inventors, no significant roll life extension effect was obtained. The present invention significantly extends the service life of the plated rolls, particularly in chrome plating of dull rolls used for rolling metal materials, and streamlines the plating process to reduce roll manufacturing or repair costs. The purpose is to lower the (Means for Solving the Problems) The present inventor has discovered that if the surface of a dulled roll is treated under appropriate conditions prior to chrome plating to increase its roughness, the adhesion of the plating film will be improved. It was confirmed that the cracking and peeling of the plating film caused by the high load during rolling was reduced. The present invention is based on the following technology: ``In a chromium electroplating bath with a bath temperature of 45 to 55 degrees Celsius, a dull-finished forged steel roll is used as an anode, and the cumulative current (current density x time) is 75 to 55 degrees Celsius.
Electrolytic treatment was performed under conditions of 250A/dm ²・min.
A method for manufacturing a chromium-plated roll, which comprises increasing the number of ridges on the roll surface represented by PPI by 3 to 50% compared to the number before electrolysis, and then applying chromium plating using the roll as a cathode. ” is the gist. In the above method, the surface of the roll before electrolytic treatment is given 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. FIG. 1 shows an enlarged cross section of the surface of a roll that has been dulled by shot blasting. For convenience of explanation, the figure is approximately 50 mm vertically from the horizontal direction.
It has been enlarged twice. As mentioned above, if chrome plating is directly applied to a roll with such an uneven surface, the adhesion of the plating film will be insufficient and the effect of extending the life of the roll will be small. In the present invention, prior to plating, the roll is electrolytically treated to modify (roughen) the uneven shape of the roll surface shown in FIG. 1 as shown in FIG. 2. FIG. 2 is an enlarged sectional view of the roll surface similar to FIG. 1. As shown in the figure, the initial uneven pattern created by dulling is further eroded by the electrolytic treatment, and the number of fine unevenness increases. The present invention uses PPI (Peak
Evaluate by Counter Inch). PPI is included in the SAE standard as one of the notation methods for surface roughness. For more details, please refer to "Surface Polishing and Finishing Techniques Collection" supervised by Naoji Kinoshita, Nikkei Gijutsu Tosho Co., Ltd., p. 233.
The principle of measurement will be explained with reference to FIG. For example, stylus tip angle 90 degrees, tip curvature radius 5μ
The cross-sectional curve of the roll surface is determined by a stylus-type roughness measuring device using a diamond of m. A peak count level and a peak count level are set parallel to the average line of this cross-sectional curve and at positions 1 μm below and above the average line, respectively. Between two points where the cross-sectional curve and the lower peak count level intersect (for example, between points A and B, between points B and C), the point where the upper peak count level and the cross-sectional curve intersect ( If there is one or more points (X, X ₂ , X ₃ . . . in the figure), these are considered as one peak, and the number of peaks within the measurement length of 1 inch is defined as PPI. In Figure 3, if the distance from point A to point E is 1 inch, the PPI in this figure is 3. Now, in the present invention, the first
A roll having a surface shape as shown in the figure is placed in an electrolytic solution and subjected to electrolytic treatment (electrolytic etching) using the roll as an anode to increase the number of irregularities as shown in FIG. The PPI after this processing is also counted as described above, as shown in FIG. In the present invention, this
The number of peaks after electrolytic treatment, as indicated by PPI, is increased by 3 to 50% compared to the number before. The electrolytic treatment method may be any method as long as the above-mentioned increase in PPI can be obtained. For example, when using a solution with the same composition as that used for chrome plating (regardless of whether a separate bath is used), the temperature is usually 45 to 55.
°C, as an integrated current expressed in current density x time
25A/dm ² × 3 minutes (75A/dm ²・min) to 35A/
The conditions are approximately dm ² × 8 minutes (280A/dm ² · minutes). However, if the integrated current exceeds 250 A/dm ² ·min, the dendritic crystal structure will increase on the roll surface and the surface gloss will decrease, so the integrated current will be 75 to 250 A/dm2/min.
It is best to choose a range of dm ² minutes. In addition, in electrolytic etching, which is sometimes performed to remove the inactive layer on the surface as an activation treatment for the base of normal chrome plating, the integrated current is
Although the electrolytic treatment is about 30 A/dm ² ×1 to 2 minutes, no increase in PPI is observed with this level of electrolytic treatment. In the present invention, the increase in PPI is set to 3 to 50% because if the number of peaks increases by less than 3%, the effect of improving the adhesion of the plating film will not be noticeable, and if it exceeds 50%, the gloss of the roll surface will decrease. This is because the dendritic crystal structure increases on the surface and the adhesion of plating applied thereon deteriorates. Normally, when plating, the base material is degreased and cleaned. When implementing the method of the present invention, it is desirable to degrease and wash the roll after dulling prior to electrolytic treatment. However, this degreasing and cleaning treatment is not essential. An alkaline solution such as caustic soda is used for degreasing, but if this solution is carried into the electrolysis or plating solution in the next step, it will cause many problems due to deterioration of the solution, so sufficient washing with water is necessary.
That is, in order to perform resin treatment, a degreasing tank and a washing tank must be provided. Therefore, if this degreasing and cleaning process can be omitted, equipment and materials can be saved and the process can be simplified. According to the present invention, when electrolytic treatment is performed after dulling to increase the number of surface irregularities, chrome plating with sufficient adhesion can be achieved even if degreasing and cleaning before electrolytic treatment are omitted. can be applied. To confirm this, we conducted the following experiment. 30mmφ test roll (material: 0.8%C forged steel)
After dulling with PPI160 by shot blasting, electrolytic chrome plating was applied to the parts with degreasing and water washing and without washing. The treatment liquid and treatment conditions are shown in Table 1 below.

[Table] As shown in Figure 5, the test roll A obtained above and the mating material (JIS S45C) B of the same size.
In combination, surface pressure 75Kg/mm ² , rotation speed 5×10 ⁴ ,
A rolling test was carried out under the conditions of a pressure regulating oil supply rate of 80 c.c./min, and the surface of test roll A was observed to check for peeling of the plating layer. Degreasing results - with or without water washing and with electrolysis
Table 2 is organized by PPI increase rate.

[Table] From the results in Table 2, if the PPI on the roll surface is increased by 3% or more through electrolytic treatment, the degreasing and water washing steps before electrolytic treatment can be omitted since the chrome film has good adhesion. I know that I can make a connection. The electrolytic treatment can be carried out using the same solution as the chromium plating solution as described above. Therefore, it is possible to first increase the surface roughness by electrolytic treatment and then perform chromium plating by changing the polarity in the same liquid bath (using the roll as a cathode). In this case, there is no need to separately provide an electrolytic treatment tank and a plating tank, which is preferable from the standpoint of equipment. However, as the electrolytic treatment progresses, a portion of the roll surface is eluted into the solution and trivalent iron ions (Fe ³⁺ ) increase. If chrome plating is performed in a solution with increased Fe ³⁺ , the electrical resistance will increase and high voltage will be required, the coverage of the plating will deteriorate, and the plated surface will become rough and lose its luster. Problems with plating quality arise. Figure 6 shows the current density of 30A/ ^dm2 in 14 chromium plating solution (composition: chromic acid 225g/, sulfuric acid 2.5g/) using a forged steel ring of 30mmφ x 8mm width as an anode. This shows the change in the amount of Fe ³⁺ in the liquid. When the cumulative current (current density x current application time) of electrolytic treatment is 30000 A/dm ² ·min, Fe ³⁺ is 5 g/min. This increase in Fe ³⁺ does not pose much of a problem if only electrolytic treatment is used. but,
If chromium plating is performed using such a solution, the above-mentioned problems will occur, and the solution will have to be replaced. Therefore, if the efficiency and quality stability of chrome plating are particularly important, it is recommended to install an electrolytic treatment tank and a plating tank separately, and to perform plating by changing the tank after the electrolytic treatment. In this case, the electrolytic treatment solution can be used until the Fe ³⁺ content reaches approximately 50 g/. The conditions for chrome plating, for example, the thickness of the plating, are determined by taking into account the usage conditions of the roll, the required lifespan, and other factors. In the case of dull rolls used for temper rolling of cold-rolled steel sheets, the plating thickness may be approximately 5 to 25 μm. (Function) The effect of increasing the number of uneven peaks by the electrolytic treatment of the present invention will be explained in more detail. Generally, the surface of a roll that has been dulled by, for example, shot blasting is three-dimensionally irregular, as schematically shown in FIG. 4, and the peaks are two-dimensionally dispersed. On such a rough surface,
For example, when the number of ridges in one cross section increases due to electrolysis, the number of ridges increases significantly two-dimensionally compared to the rate of increase. As an example, for an experimental sample roll, the initial PPI160 was electrolyzed.
175 (increase rate of 9.1%), it was found that electrolytic treatment not only increases the number of peaks but also makes their distribution uniform. Such a roughened surface has a significantly increased surface area, which together with the anchoring effect due to the increased unevenness greatly improves the adhesion of the plating film.
Even if chrome plating is applied to the surface roughened in this way, the PPI hardly changes. During rolling, the many uniformly distributed peaks evenly bear the rolling load, reducing wear, cracking, and peeling of the surface chromium plating layer, significantly extending the life of the roll. Generally, when rolling using dull rolls,
The tip of the dull peak on the roll surface receives a strong concentrated load in the vertical direction, and at the same time receives a load in the tangential direction of the roll, that is, in a direction transverse to the peak, causing wear and breakage of the tip of the peak. However, in the roll manufactured by the method of the present invention and having a significantly increased number of peaks, the absolute value of the load on each peak is small, and therefore the peeling and falling off of the chromium-plated layer is reduced. Table 3 shows the rate of increase in PPI due to electrolytic treatment and qualitative evaluation of rolls plated with chrome. From this result, it is clear that the range of PPI to be increased by electrolytic treatment is suitably 1 to 50%. In addition, as shown in Table 2 above, PPI is 3%
If the PPI is increased by more than 3%, it becomes possible to omit the steps of degreasing and washing with water before electrolytic treatment, so it is more desirable that the increase in PPI be in the range of 3 to 50%.

[Table] Under electrolytic treatment conditions that increase PPI by 3 to 50% by the method of the present invention, the 10-point average roughness Rz does not change or increases. One of the key points of the present invention is not to reduce this Rz. For example, after dulling the surface of a forged steel roll by shot blasting, the initial PPI160 was increased to 170 (increase rate 6.25%) by electrolytic treatment at 30 A/dm ² × 5 minutes. The value was only changed from 25 μm to 25.1 μm (increase rate of 0.4%). Aspects of the present invention will be explained below with reference to Examples. Example 1 The surface of a 600 mmφ×1700 mm cold temper rolling forged steel roll (Hv850) was dulled by shot blasting. The properties of the obtained roll surface were as follows: PPI = 165, center line average roughness Ra = 2.5 μm, and 10 point average roughness Rz = 27.0 μm (all average measurements at 5 locations). After degreasing this roll with a caustic soda solution and washing it with water, electrolytic treatment was performed using the roll as an anode under the following conditions. Bath composition...Chromic acid: 225±25g/Sulfuric acid: 2.5±1g/Bath temperature...50℃ Integrated current...30A/ ^dm2 x 8 minutes The roll surface properties after this treatment are PPI=180 (9.1
% increase), Ra = 2.5μm (unchanged), Rz = 27.0μ
m (unchanged). Next, in the same liquid, using the roll as a cathode,
Plating was carried out under the conditions of 30A/dm ² × 32 minutes, and the thickness was 15μm.
After forming a chromium plating layer, it was washed with water and dried to confirm that there were no abnormalities in appearance, and the hardness was measured to be Hv1050. According to the above procedure, initial PPI and post-electrolytic treatment
Eight types of rolls with different PPI are prepared, each is installed in a temper rolling mill, and used for rolling cold rolled steel sheets. The amount of rolling was investigated. The steel plate to be rolled was an annealed material equivalent to JIS SPCC, and the rolling was temper rolling (reduction ratio: 1.0%) using the above rolls as upper and lower work rolls. The results are shown in Table 4. Bare (no chrome plating)
Compared to the rolling amount of 180 tons of dull rolls, the average rolling amount of rolls coated with chrome using the method of the present invention is 2345 tons, and the roll life is approximately 13 tons.
It has been doubled. No peeling of plating occurred in any of the rolls No. 1 to No. 8 in Table 4, and very stable operation with little variation was possible. In addition, width schedule rolling, which was previously impossible due to wear of the barrels in the steel plate passage area, became possible, and production increased dramatically from 250 tons/hour to 300 tons/hour.

[Table] Example 2 A roll of the same size and material as Example 1 was shot blasted, PPI = 170, Ra = 2.3 μm, Rz
= 25.0 μm dull roll. This is degreased and left in the electrolytic treatment tank without cleaning (the liquid composition is as follows:
Chromic acid (250g/2.5g/) and sulfuric acid (2.5g/) were used as an anode, and electrolytic treatment was performed for 6 minutes at a liquid temperature of 50°C and an electrolytic density of 30A/dm ² . The roll surface after this treatment is
PPI=183 (7.6% increase), Ra=2.3 μm (no change), and Rz=25.2 (0.8% increase). Next, a chromium plating tank (liquid composition: 230 g of chromic acid, 2.6 g of sulfuric acid) was installed separately from the electrolytic treatment tank.
g/) and use this as a cathode to adjust the liquid temperature.
Plating was performed for 25 minutes at 50° C. and a current density of 30 A/dm ² to provide 11 μm thick chrome plating. When this chrome-plated roll was installed in a temper rolling mill and tested in the same manner as in Example 1, the rolling amount reached 2,500 tons, which was similar to the results of Example 1 in which degreasing and cleaning were performed before electrolytic treatment. It was the same. In this example, the electrolytic treatment tank and the plating tank were separated as described above. As a result, the concentration of Fe ³⁺ in the electrolytically treated solution increased almost in proportion to the number of rolls treated, as shown in FIG. in this way
A solution with increased Fe ³⁺ cannot be used for chrome plating, so if one solution were to be used for both electrolytic treatment and plating, the solution would have to be replaced after about 1000 rolls were processed. However, if a separate tank is used as in this example, the electrolytic treatment will be 6,000 yen.
This can be done without changing the liquid. On the other hand, there was almost no increase in Fe ³⁺ in the plating solution, and because there was little deterioration of the solution, its service life was extended three times. (Effects of the Invention) The description has been made above using a dull roll mainly used for rolling cold rolled steel sheets as an example. However, the method for manufacturing chrome-plated rolls of the present invention is useful not only for manufacturing rolls used for rolling not only steel materials but also non-ferrous metal plates and other products, as well as rolls used for rolling other products such as pinch rolls for pickling lines. It can also be applied to the production of rollers, bridal rolls, conveyor line rollers, etc. In short, the present invention provides a method for applying chromium plating to a dull-finished roll (roll in a broad sense, including what is generally called a roller) with minute irregularities on its surface in order to improve its wear resistance and other properties. Covers everything. As described above, according to the present invention, it is possible to manufacture a roll with excellent durability in which the chrome plating bath hardly peels off or falls off. Furthermore, depending on the situation, we can degrease the base material dull roll,
It is also possible to omit water washing, and in that case, the effect of simplifying the process and equipment is significant. Further, the electrolytic treatment and plating may be carried out in the same solution in one tank, or if they are carried out in separate tanks, other advantages will also arise. Thus, one of the effects of the present invention is that the process can be modified as necessary.

[Brief explanation of the drawing]

Figure 1 is an enlarged schematic cross-sectional view of the surface of a dull roll, Figure 2 is a schematic enlarged cross-sectional view of the surface of a dull roll roughened by electrolytic treatment, and Figure 3 is a schematic enlarged cross-sectional view of the surface of a dull roll roughened by electrolytic treatment. FIG. 4 is an enlarged schematic cross-sectional view of the surface of the roll for explaining the roughness evaluation method, and FIG. 5 is an enlarged perspective view of the surface of the dull roll.
A schematic diagram illustrating a rolling test method for testing the durability of a chromium-plated layer; FIG. 6 is a diagram showing changes in the Fe ³⁺ concentration in the liquid due to electrolytic treatment of rolls; FIG.
FIG. 6 is a diagram similar to FIG. 6, which was measured in the example.

Claims (1)

[Claims] 1. A dull-finished forged steel roll is used as an anode in a chromium electroplating bath with a bath temperature of 45 to 55°C, and the cumulative current expressed as current density x time is 75 to 250 A/dm ² · min. Chromium, characterized by performing electrolytic treatment under the following conditions to increase the number of ridges on the roll surface indicated by PPI by 3 to 50% than the number before electrolysis, and then applying chromium plating using the roll as a cathode. Method for manufacturing plated rolls. 2. The method for manufacturing a chrome-plated roll according to claim 1, wherein the dull-finished forged steel roll is subjected to electrolytic treatment and chromium plating without degreasing or cleaning.