JP2005193248A - Dull roll for cold-rolling metallic sheet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dull roll for cold-rolling a metallic sheet with which the desired surface property of the roll is obtained in a short time and simply, besides, the variation in the surface roughness of the roll caused by the rolling distance is small and the basic unit of the roll is improved. <P>SOLUTION: This dull roll for cold rolling has chromium plated layer composed of an upper layer and a lower layer on the surface of a base roll the Vickers hardness of which is ≥ 600, the Vickers hardness HV 0.025 of the upper layer and the lower layer of the chromium plated layer are respectively ≥ 850 and 650-950 and the surface of the chromium plated layer is ≥ 0.3μm in arithmetic mean roughness Ra and ≥ 200 in the number PPI of peaks per the length of 1 in.. By this manufacturing method of the dull roll for cold rolling, a first plated layer which is ≥ 0.35 in the arithmetic mean roughness Ra and ≥ 230 in the number PPI of peaks per the length of 1 in. is formed on the surface of the base roll which is ≥ 0.05-2.0 μm in the arithmetic mean roughness Ra and a second plated layer which is ≥ 0.3 μm in the arithmetic mean roughness Ra and ≥ 200 in the number PPI of peaks per the length of 1 in. is further formed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a cold rolling dull roll for a metal plate suitable for cold rolling (including temper rolling) of a metal plate such as a cold rolled steel plate such as a tin plate or a steel plate for automobiles, and its production. Regarding the method.

  In recent years, for cold-rolled steel sheets such as tin plate and automobile steel sheets, requirements regarding surface properties and shapes have become very strict. The surface properties of the cold-rolled steel sheet are mainly adjusted by a dull roll installed in a final stand of a cold tandem rolling mill, a final pass of a reverse rolling mill, and a temper rolling mill after annealing. For this reason, it is important to suitably control the surface properties of the dull roll.

Normally, when creating a dull roll with a predetermined target surface roughness (usually measured in the roll axis direction) indicated by the arithmetic average roughness Ra (Ra ( ³ ) specified in JIS B0601-2001), the dull roll is generally used. The greater the number of peaks per surface evaluation length, the better the surface condition of the steel sheet rolled with this dull roll.

  FIG. 1 shows an example of a method for measuring the surface roughness of a roll in the axial direction and evaluating the number of peaks per evaluation length L from the measurement result. The number of peaks per evaluation length L is not particularly specified by JIS, but is an index that is always mounted on a general two-dimensional contact roughness meter.

  The method for evaluating the number of peaks per evaluation length L is to draw a mean line on the roughness curve as shown in FIG. A threshold called level is provided. Next, the line segment of the roughness curve where the roughness curve is located between two points crossing the lower count level from top to bottom crossed the upper count level more than once (from top to bottom, down From the top to the top, each case counts as one)) and counted as one peak, and this number of peaks was taken as the number of peaks per evaluation length L. In the example of FIG. 1, the line segment of the roughness curve located between two points in the section II crosses the upper count level four times. In this case, it is also counted as one peak. Further, the line segment of the roughness curve located between two points in the section IV does not cross the upper count level even once, so in this case, it is not included in the number of peaks. Therefore, FIG. 1 shows a case where there are a total of six peaks Pk1 to Pk6 per evaluation length L of the roughness curve.

  That is, in the dull roll, if the number of peaks per evaluation length is large, a large number of micro-projections come into contact with the steel plate surface, so that a large number of transfer marks are formed on the steel plate surface and exist on the steel plate surface before rolling. It has the effect of making scratches and irregularities and defects in appearance invisible. Also, if there are many minute projections on the surface of the dull roll, the rolling load is dispersed, so that each transfer mark is shallow, and the surface appearance is beautiful.

  As a roll surface dull processing method, a shot dull processing method has been generally used so far. For example, as described in Patent Document 1, a processing method using a laser beam (hereinafter simply referred to as “laser dull processing method”). Is also used.

  Also, the surface of the dull roll always changes its roughness as the rolling distance corresponding to the length of the metal plate rolled by the dull roll increases, and the wear progresses from the projections of minute irregularities on the dull surface. However, as the dull roll, the slower the progress of the wear, the more preferable the surface of the rolled steel sheet is stably maintained in a desired state.

Therefore, the conventional dull roll manufacturing method generally forms a hard plating layer of chromium on the surface layer after dulling the surface of the base roll to a desired state.
JP-A-5-65686

  As described above, in order to make the surface property of the dull roll suitable, it is preferable to form a surface state with a large number of peaks by processing by the laser dull processing method, and then apply hard chrome plating. In the processing method, there is a problem that it takes a very long processing time to form minute irregularities.

  Further, as described in Patent Document 1, the laser dull processing method performs processing by once melting the surface, so that the roll surface layer is softened. Therefore, even if hard chrome plating is applied to this softened surface, the surface of the underlying roll itself is deformed under the plating layer at the time of rolling, so that the roughness changes greatly as if it were worn. There is also a problem.

  In view of this point, Patent Document 1 discloses a method of performing chrome plating after removing a softened convex portion after processing by a laser dull processing method by electrolytic etching. In this method, a step of performing electrolytic etching is disclosed. Requires extra time and cost.

  Furthermore, in the method of Patent Document 1, when a dull roll whose surface has worn away from the desired surface properties due to rolling distance is used again, it is necessary to rework the roll surface by a laser dull processing method. The roll surface layer must be removed by polishing or the like in advance for each processing, and the roll diameter becomes smaller each time reprocessing is performed. As a result, the number of rolls used is limited, resulting in a problem that the roll basic unit deteriorates.

  The object of the present invention is to obtain a desired surface property of a roll having a peak number that is the same as that of the laser dull processing method or more easily in a short time. Provided are a dull roll for cold rolling of a metal plate and a method for producing the same, which can improve the basic unit.

  Some chrome plating, for example, decorative chrome plating, is called gray plating in which reflected light diffuses and appears gray in appearance. The plating method is as described in “Plating Technology” (Nikkan Kogyo Shimbun, page 273, Fig. 3.3.1), in the same plating bath as in the case of applying hard plating, for example, in the plating bath of chromic acid and sulfuric acid. Is carried out by lowering the plating bath temperature and increasing the current density.

  The inventors conducted a detailed investigation focusing on this plating method. As for gray plating, the precipitation of chrome plating grows, and minute irregularities are formed on the surface, thereby realizing diffusion of reflected light. I found out.

  The inventors have found that the micro unevenness has a sufficiently large arithmetic average roughness Ra to form a desired dull roll surface, is very fine, and is further formed by a laser dull processing method. It was also found that the number of peaks per evaluation length was equal to or greater than.

  Therefore, the inventors think that a dull roll having a desired surface property can be formed by using gray plating, which has been conventionally used only for adjusting the plating appearance for decoration, as a dull roll for cold rolling of a metal plate. It was.

  However, as described in “Plating Technology” (page 281, Figure 3.3.12), the plating conditions range for gray plating is the bath temperature from the so-called hard chromium plating condition range where the Vickers hardness HV is 1000 or more. Further, since the value of the Vickers hardness HV is smaller than that of the hard chrome plating, it is not preferable to form the surface layer of the dull roll for cold rolling of the metal plate only by the gray plating.

  Then, the inventors next formed a chromium plating layer composed of a first plating layer that is gray plating and a second plating layer that is hard plating on the first plating layer on the surface of the base roll. By doing so, the second plating layer, which is the hard plating, is made to follow the minute irregularities of the first plating layer, which is the gray plating, and the high number of peaks per evaluation length specific to the gray plating is maintained, while the high unique to the hard plating It was thought that it could have surface hardness.

  As described above, in the present invention, the chromium plating layer is formed of two types of chromium plating layers having different physical properties. As described above, only in the same plating bath, only by changing the bath temperature plating conditions, Two types of chromium plating layers can be formed in an extremely short time. Further, as a secondary effect, the formation of the second plating layer has an effect of filling unnecessary concave portions in the micro unevenness on the surface of the first plating layer, thereby preventing so-called clogging during rolling.

  In the present invention, since the laser dull processing method is not used, the surface hardness of the base roll can be maintained at 600 or more, and the appropriate surface hardness is ensured by the two types of chromium plating layers having different physical properties as described above. Therefore, there is no deformation of the roll surface due to the softening of the surface layer of the base roll as mentioned as a problem in the case of the laser dull processing method. The change in the number of peaks is very small.

  Furthermore, when manufacturing the cold rolling dull roll of the present invention for the first time, the surface of the base roll may be polished, for example, which is often performed prior to the formation of the plating layer. After subjecting the cold rolling dull roll of the present invention to use once, when re-forming the micro unevenness on the roll surface, it is only necessary to remove the plating layer, and the underlying roll surface layer is inevitably polished when the plating layer is removed. Therefore, the roll diameter hardly changes, the number of times the roll can be reused increases, and the roll basic unit can be dramatically improved.

  In addition, since the surface of the base roll is a well-polished grinding wheel, factors that hinder plating adhesion, such as abrasive powder from the roll and falling abrasive grains from the grinding wheel, can be easily washed away with electrolytic degreasing or water. As a result, the plating layer is hardly peeled off.

The gist of the present invention is as follows.
(1) It has a chromium plating layer composed of an upper layer plating and a lower layer plating on the surface of the base roll having a Vickers hardness of 600 or more, and the upper layer plating and lower layer plating Vickers hardness HV0.025 of the chromium plating layer is 850 and 950, respectively, the surface of the chromium plating layer has an arithmetic average roughness Ra of 0.3 μm or more and a peak number PPI per inch of 200 or more. A dull roll for cold rolling of a metal sheet.

(2) On the surface of the base roll having an arithmetic average roughness Ra of 0.05 to 2.0 μm, the arithmetic average roughness Ra is 0.35 μm or more and the number of peaks PPI per inch is 230 or more. A first plating layer is formed, and further, a second plating layer having an arithmetic average roughness Ra of 0.3 μm or more and a peak number PPI per inch of 200 or more is formed. A method for producing a dull roll for cold rolling of a metal sheet.

(3) In both the first and second plating layers, the base roll is immersed in a chrome plating bath of chromic acid 200 to 500 g / l, sulfuric acid 2 to 5 g / l, pH 1.0 to 3.0, and electrochrome Formed by plating, the conditions for forming the first plating layer are as follows: bath temperature: 20 to 41 ° C., current density: 20 to 90 A / dm ² and plating time: 0.2 hour or more. The method for producing a dull roll for cold rolling of a metal sheet according to the above (2), wherein the bath temperature is 43 to 60 ° C., the current density is 30 to 90 A / dm ² and the plating time is 0.2 to 1.5 hours.

  According to the present invention, a desired surface property of a roll can be easily obtained in a short time, and a dull roll having a small change in roll surface roughness due to a rolling distance can be produced. Thereby, it becomes possible to stably manufacture a steel sheet having fine surface irregularities. Furthermore, the basic unit of the roll is also improved.

Embodiments of the present invention will be described below.
The dull roll for cold rolling of a metal plate according to the present invention is obtained by forming a chromium plating layer having a predetermined hardness and surface roughness (Ra and PPI) on the surface of a base roll.

  As the base roll used in the present invention, it is necessary to use a roll having a Vickers hardness of 600 or more in order to suppress deformation of the roll surface during rolling. For example, it is preferable to use a steel roll. The upper limit of the hardness of the base roll is not particularly limited, but since the roll that can be manufactured at present has a Vickers hardness of 900 or less, the upper limit of the base roll is set to 900. Is preferred.

  Moreover, the chromium plating formed on the surface of the base roll requires that the Vickers hardness HV0.025 of the upper plating portion and the lower plating portion of the chromium plating layer is 850 or more and 650 to 950, respectively.

Here, the upper layer plating, the lower layer plating, and the Vickers hardness of the base roll are assumed to be the values measured as described below.
Since the upper layer plating is the outermost layer of the roll, the value obtained by measuring the Vickers hardness of the outermost layer as it is is used.
The problem is the lower layer plating that is not the outermost layer and the Vickers hardness of the underlying roll.

  These rolls are first cut into a ring, and the surface layer is cut out as a sample, and only a few μm to several tens of μm of the extreme surface layer is seen in a cross-section of the ring. Even if there is an ambiguity of the boundary or an ambiguity of the starting point due to the unevenness, it is measured by several μm roughly due to the difference of First, estimate how many μm each in consideration of a margin sufficient to cover the maximum error.

  Next, when measuring the Vickers hardness of lower layer plating, the said sample surface layer is ground by the value estimated as thickness of upper layer plating, and Vickers hardness is measured about the surface layer after grinding.

  And when measuring the Vickers hardness of a foundation roll, the sample surface layer after the grinding is further ground by the value estimated as the thickness of the lower layer plating, and the Vickers hardness is measured for the surface layer after grinding.

  Since both the upper layer plating and the lower layer plating have a thickness of only a few μm to several tens of μm, it is preferable to perform a so-called micro Vickers measurement.

  In addition, because there are variations in the Vickers hardness of the upper layer plating, lower layer plating and under roll, there are 6 or more locations on one surface, and in the case of upper layer plating and lower layer plating, the measurable range may be used, but the thickness direction In addition, it is preferable to measure several surfaces (by grinding naturally) at a pitch of 2 to 3 μm and take an average value.

  The lower layer plating is the so-called gray plating described above, but in the present invention, when the lower layer plating has a Vickers hardness HV of 650 to 950, the surface property of the lower layer plating can be made appropriate. As a result, the surface properties of the lower layer plating are reflected in the surface properties of the upper layer plating formed on the upper layer plating so that the upper layer plating follows the minute unevenness of the chrome roll. The property can be controlled.

  In addition, the upper layer plating is the so-called hard plating described above, but in the present invention, the Vickers hardness HV measured by the upper layer plating is required to be 850 or more in order to suppress wear on the dull roll surface during rolling. . The upper limit of the upper layer plating hardness is not particularly limited, but since the hardness that can be manufactured at present is 1150 or less in Vickers hardness, the upper limit of the upper layer plating Vickers hardness may be 1150 preferable.

  In the present invention, the lower plating of the chromium plating layer mainly plays a role of making the surface of the chromium plating layer a desired surface property, and the upper plating of the chromium plating layer plays a role of mainly suppressing the wear of the dull roll surface layer during rolling. Let's bear.

  In order to sufficiently exhibit the above-described roles of the lower layer plating and the upper layer plating of the chromium plating layer, in the present invention, it is preferable that the Vickers hardness of the upper layer plating is 50 or more higher than the Vickers hardness of the lower layer plating.

  In the dull roll of the present invention, the surface of the chromium plating layer needs to have an arithmetic average roughness Ra of 0.3 μm or more and a peak number PPI per inch of 200 or more. Ra is a value measured with a standard (evaluation) length (cutoff value) of 0.8 mm and a measurement length of 4 mm, and PPI is a value obtained by converting a value measured in the same manner per inch.

  This is because if the arithmetic average roughness Ra of the chromium plating layer surface is less than 0.3 μm, the performance normally required for a dull roll (for example, unevenness elimination existing before rolling) cannot be satisfied. The upper limit of the arithmetic average roughness Ra of the chrome plating layer surface is not particularly limited. However, since the upper limit of the specification of the arithmetic average roughness Ra of existing dull rolls is 6.5 μm, the arithmetic average roughness Ra is not limited. The upper limit is preferably 6.5 μm.

  Further, the surface of the chromium plating layer needs to have a peak number PPI per inch of 200 or more. This is because if the number of peaks PPI per inch is less than 200, the performance as a dull roll is not satisfied as in the case of Ra. The upper limit of the number of peaks PPI per inch of the chrome plating layer surface is not particularly limited, but because the specification upper limit of the number of peaks PPI per inch of existing dull rolls is 500. The upper limit of the number of peaks PPI per inch is preferably 500.

  Fig. 2 (a) shows the surface profile when a new dull roll surface according to the present invention was measured with a laser microscope, and Fig. 2 (b) shows the cold rolled steel sheet with the dull roll of Fig. 2 (a). Fig. 2 (c) shows the surface profile when rolled (rolling distance: 53.3km) and then the surface of this dull roll was measured with a laser microscope. Fig. 2 (c) was rolled with the dull roll shown in Fig. 2 (a). The surface profile when the cold-rolled steel plate surface immediately after that is measured with a laser microscope is shown. The Vickers hardness of the base roll is 800, the Vickers hardness HV of the upper plating and the lower plating of the chromium plating layer is 700 and 1050, respectively, and the arithmetic average roughness Ra and length 1 of the chromium plating layer surface are 1 The initial number of peaks per inch PPI was 0.8 μm and 350, respectively.

  For comparison, the surface of a conventional new dull roll manufactured by forming a hard chrome plating after performing a shot dull process (Ra: 1.1 μm) on the surface of the base roll is similarly measured with a laser microscope. The surface profile is shown in Fig. 3 (a), and the steel plate is cold-rolled with this dull roll (rolling distance: 18.0km), and then the surface profile when the dull roll surface is measured with a laser microscope is shown in Fig. 3 (b). Shown in The Vickers hardness of the base roll is 800, the Vickers hardness HV of the chrome plating layer is 1050, and the initial value of the arithmetic average roughness Ra of the chrome plating layer surface and the peak number PPI per inch of length is They were 1.2 μm and 190 pieces, respectively.

  From the surface profiles shown in FIGS. 2 (a) to 2 (c), the surface of the dull roll of the present invention at the time of a new article is formed with a large number of granular projections with little variation in size (FIG. 2 (a)) and long. Even after rolling the rolling distance, most of the granular convex portions remain without being worn or crushed (FIG. 2 (b)), and on the surface of the cold rolled steel sheet rolled using the dull roll of the present invention. It can be seen that a plurality of uniform recesses are formed (FIG. 2 (c)).

  On the other hand, from the surface profiles shown in Fig. 3 (a) and (b), the conventional dull roll (shot dal + hard chrome plating roll) is sparse and has large convex portions scattered unevenly (Fig. 3 (a)). After rolling for a long rolling distance, it can be seen that the substantial convex portion disappears due to wear or crushing of the convex portion (FIG. 3 (b)).

Next, the manufacturing method of the dull roll for cold rolling of the metal plate according to this invention is demonstrated below.
Steel rolls used as the base roll, roll overturning equipment, plating current density control equipment and roll plating equipment including ancillary equipment such as an electrolytic degreasing bath, and chromium plating bath composition used in the present invention are conventional. You can use the same thing.

  However, as for the control of the temperature of the chrome plating bath, a low temperature plating bath suitable for gray plating conditions is used compared to the case where hard chrome plating is applied after dulling the surface of the roll for cold rolling as in the past. Must be feasible. Even in the conventional plating equipment, the control equipment for the plating bath temperature is always installed. Therefore, it is sufficient that these have a wider control range.

  The surface of the steel-based roll that becomes the base roll may be, for example, grindstone polishing that is often performed conventionally.

  And the manufacturing method of the dull roll for cold rolling according to the present invention, after that, the base roll is transported to the plating equipment without directly dulling the surface, and after degreasing, etc., the arithmetic average roughness Ra is 0.05. The first plating layer (lower plating part) with an arithmetic average roughness Ra of 0.35 μm or more and a peak number PPI per inch of 230 or more on the surface of the base roll of up to 2.0 μm Further, a second plating layer (upper layer plating) having an arithmetic average roughness Ra of 0.3 μm or more and a peak number PPI per inch of 200 or more is formed.

  The reason for limiting the arithmetic average roughness Ra of the surface of the base roll to 0.05 to 2.0 μm is that if it is less than 0.05 μm, it cannot be realized by normal grinding stone polishing, requires a separate polishing process, and adheres between the roll and the plating layer. This is because, when the thickness exceeds 2.0 μm, the unevenness of the polishing scratches is increased, and the adhesion of the plating layer is deteriorated.

  The first plating layer is formed under the above-described gray plating formation conditions, and corresponds to the lower plating of the chromium plating layer constituting the dull roll, and the second plating layer is formed under the above-described hard plating formation conditions. This corresponds to the upper plating of the chromium plating layer constituting the dull roll.

  The first plating layer may have an arithmetic average roughness Ra of 0.35 μm or more and a peak number PPI per inch of 230 or more. Thereafter, a second plating layer formed on the first plating layer. The arithmetic average roughness Ra of the plating layer is preferably 0.3 μm or more and the number of peaks PPI per inch of PPI is preferably 200 or more.

  In the inventors' investigation, the most dominant factor that determines the surface roughness of the dull roll is the thickness of the first plating layer that forms the basic unevenness, and this thickness is controlled by the plating time. It has been found that the second plating layer, which is a hard plating, protects the surface of the first plating layer, and at the same time plays a role of adjusting the roughness by filling an unnecessary large concave portion of the surface layer. .

  Therefore, the thickness of the first plating layer is 10 to 70 μm, the thickness of the second plating layer is 5 to 20 μm, and the total thickness of the first and second plating layers is 15 to 90 μm. It is preferable that

  Both the first and second plating layers may be formed by immersing the base roll in a chrome plating bath and electrochrome plating, and the first and second plating layers may be formed by different plating baths. However, it is preferable in terms of simplification of the process and the like to increase the bath temperature using the same plating bath and form the second plating layer subsequent to the formation of the first plating layer.

  Examples of the chromium plating bath include a chromium plating bath of chromic acid and sulfuric acid.

The formation conditions of the first plating layer are, for example, a common chromic acid 200-500 g / l, sulfuric acid 2-5 g / l, pH 1.0-3.0 plating bath, bath temperature: 20-41 ° C., current density : 20 to 90 A / dm ² and plating time: 0.2 hours or more are preferable. This is because if the bath temperature is less than 20 ° C., a large amount of electric power is required to control the bath temperature, and if it exceeds 41 ° C., good fine irregularities cannot be obtained. Further, if the current density is less than 20 A / dm ² or more than 90 A / dm ² , uniform micro unevenness cannot be obtained. Furthermore, if the plating time is less than 0.2 hours, it is difficult to grow sufficient fine irregularities.

The conditions for forming the second plating layer are, for example, a common chromic acid 200-500 g / l, sulfuric acid 2-5 g / l, pH 1.0-3.0 plating bath, bath temperature: 43-60 ° C., current density : 30 to 90 A / dm ² and plating time: 0.2 to 1.5 hours are preferable. This is because if the bath temperature is less than 43 ° C. or exceeds 60 ° C., the hardness required for wear resistance cannot be obtained. The same applies when the current density is less than 30 A / dm ² or more than 90 A / dm ² . Furthermore, if the plating time is less than 0.2 hours, a hard plating layer with a sufficient thickness cannot be formed. Cost increases unnecessarily.

  The surface of a work roll for cold rolling (more precisely, temper rolling) having a body diameter of 600 mm and a body length of 1500 mm was subjected to dull processing. The material of the base roll was 5% Cr forged steel, and the target arithmetic average roughness was Ra = 1.0 μm. In the dull roll of the present invention, the ground roll was finished to Ra = 0.2 μm by grinding with a grindstone, then carried into a plating facility, and subjected to alkali degreasing treatment and water washing. Thereafter, electrochromic plating was carried out under various plating conditions shown in Table 2 in a chromium plating bath having a composition of chromic acid and sulfuric acid shown in Table 1. Table 2 shows the Vickers hardness HV0.025 (measurement load 0.245 N), arithmetic average roughness Ra, and peak number PPI per inch of length of the first and second plating layers.

For comparison, a dull roll was also prototyped using the laser dull processing method described in Patent Document 1. That is, the ground roll was finished to Ra = 0.2 μm by grinding with a grindstone, and then laser dull processing was performed with a laser processing machine at a laser output of 50 W and a frequency of 8 kHz. The processing time was 3 hours. Then, it carried in to the plating equipment similarly to the said Example, and performed alkaline degreasing and water washing. Then, in the chromium plating bath shown in Table 1, the plating bath temperature is 50 ° C., the current density is 20 A / dm ² , the electrolysis time is 500 seconds, and the soft layer on the surface of the base roll is removed by electrolytic etching. A dull roll (conventional example) was prototyped by performing chromium plating under conditions of 50 ° C. and a current density of 50 A / dm ² and forming a plating layer having a thickness of 10 μm in a plating time of 1 hour.

  Next, the dull rolls of the invention examples and comparative examples shown in Table 2 are separately used as work rolls 1 (FIG. 4) of a four-stage temper rolling mill having a pair of work rolls and a pair of backup rolls 2. Built and temper rolled. The test material was an annealed low carbon steel plate 3 having a plate thickness of 0.2 mm and a plate width of 1200 mm, and rolled at 100 km with an elongation of 1.5%.

Table 2 shows the rolling distance at which the Ra reduction rate is 6% in the dull rolls of the inventive example and the comparative example. In addition, when it did not fall 6% even after 100 km rolling, it displayed as 100 km.
From the results shown in Table 2, all of the inventive examples were excellent in wear resistance, and Ra did not decrease to 6% even at a rolling distance of 100 km. On the other hand, both the conventional examples and the comparative examples outside the appropriate range of the present invention have failed to meet the roll specifications, or have had problems with wear resistance and peeling resistance. And about the dull roll of the No. 1 invention example shown in Table 2 and the conventional dull roll, when the rolling distance is 0, 10, 50 and 100 km, the arithmetic average roughness Ra and the length per inch of the work roll surface Peak number PPI was measured. The measurement results are shown in FIG.

  From the results shown in FIG. 5, the dull roll of the invention example has a new value of the arithmetic average roughness Ra of the work roll surface at the time of a new article and the peak number PPI per inch of length compared to the conventional dull roll. It can be seen that the rate of change is small and the surface properties of the dull roll can be maintained even at a long rolling distance.

  In addition, after rolling, grinding of the roll was performed again, and when the influence of roll surface processing was removed and changes in the roll diameter were investigated, the roll of the present invention had a diameter of only 7 μm. The diameter of the conventional roll was significantly reduced to 50 μm.

  According to the present invention, a desired surface property of a roll can be easily obtained in a short time, and a dull roll having a small change in roll surface roughness due to a rolling distance can be produced. Thereby, it becomes possible to stably manufacture a steel sheet having fine surface irregularities. Furthermore, the basic unit of the roll is also improved.

It is a figure for demonstrating the method of evaluating the peak number PPI per evaluation length L. FIG. (a) is a surface profile when a new dull roll surface according to the present invention is measured with a laser microscope, and (b) is after cold rolling (rolling distance: 53.3 km) of a steel sheet with the dull roll of (a). (C) is the surface profile of a cold-rolled steel sheet rolled using the dull roll according to the present invention. (a) is a surface profile when a conventional new dull roll surface is measured with a laser microscope, and (b) is after cold rolling (rolling distance: 18.0 km) of a steel sheet with the dull roll of (a). It is a surface profile. It is a figure which shows the arrangement | positioning state of the work roll of a 4-stage temper rolling mill. FIG. 6 is a diagram in which the arithmetic average roughness Ra of the work roll surface and the number of peaks PPI per inch of length are plotted against the rolling distance.

Explanation of symbols

1 Work roll 2 Backup roll 3 Low carbon steel plate

Claims (3)

  On the surface of the base roll having a Vickers hardness of 600 or more, a chromium plating layer composed of an upper layer plating and a lower layer plating is provided, and the Vickers hardness HV0.025 of the upper layer plating and the lower layer plating is 850 or more respectively. 650 to 950, and the surface of the chromium plating layer has an arithmetic average roughness Ra of 0.3 μm or more, and a peak number PPI per inch of PPI of 200 or more. Dull roll for cold rolling.   First plating with arithmetic average roughness Ra of 0.35 μm or more and peak number PPI per inch of 230 or more on the surface of the base roll having arithmetic average roughness Ra of 0.05 to 2.0 μm And forming a second plating layer having an arithmetic average roughness Ra of 0.3 μm or more and a peak number PPI per inch of 200 or more. A manufacturing method of a dull roll for cold rolling. Both the first and second plating layers are subjected to electrochrome plating by immersing the base roll in a chrome plating bath of 200 to 500 g / l chromic acid, 2 to 5 g / l sulfuric acid, and pH 1.0 to 3.0. The formation conditions of the first plating layer are bath temperature: 20 to 41 ° C., current density: 20 to 90 A / dm ² and plating time: 0.2 hour or more, and the formation conditions of the second plating layer are bath The method for producing a dull roll for cold rolling of a metal sheet according to claim 2, wherein the temperature is 43 to 60 ° C, the current density is 30 to 90 A / dm ² and the plating time is 0.2 to 1.5 hours.

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