JPS63123586A - Surface roughing method for roll for cold rolling - Google Patents

Abstract

PURPOSE:To reduce the wear of a dull roll and to maintain a good roughness state for long time by combining a bearing reducing treatment and surface hardening treatment in case of executing a surface roughing by a laser dulling. CONSTITUTION:A roll 1 is fitted to the rotary supporting device 2 of a roll and rotated at the specified speed. On the other hand the laser beam outputted from a laser oscillator 3 is projected almost vertically on the roll surface via plural mirrors. A laser projecting head 4 is moved in the roll axial direction by the rotation of a driving screw 5 synchronized with the roll rotation. The pattern and depth of the roll surface roughness are controlled by the output of this frequency, the number of roll rotations and the moving speed of the laser projecting head. After the laser dulling, the unevenness of the roll on which a bearing reducing treatment is executed becomes uniform and by performing the hardening treatment of a subzero treatment surface hardening coating treatment, etc., thereafter the wear resistant effect can remarkably be displayed.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a method for roughening the surface of a roll for cold rolling, and more specifically, for roughening the surface of a roll for cold rolling of metal materials or for rolling 11 quality to a desired level. This invention relates to a method for roughening and maintaining a rough surface with a pattern and uneven depth.

[Conventional technology]

Surface quality is an important quality for rolled steel sheets, which are metal materials.6 Surface qualities include beauty, adhesion to paint and enamel, press workability, corrosion resistance, and gloss, but these characteristics include the geometry of the sheet. The physical shape, ie surface roughness, has an important influence.

The most common method of obtaining a metal surface with the desired surface roughness for each application is by cold rolling or/and
Another method is to process the surface of a temper rolling roll to a predetermined roughness, and then roll a steel plate with the roll at a predetermined pressure to transfer the roughness of the roll surface to the plate surface.

Conventionally widely used methods for roughening the roll surface include (1) shot blasting and (2) electrical discharge machining.

Shot blasting is very simple and has the advantage of work-hardening the roll surface and improving the wear resistance of the roll. The disadvantages of this method are that it requires a long processing time and that it is difficult to create deep roughness.

In electrical discharge machining, surface roughness is controlled by varying the applied voltage and frequency between a rotating Ronil and an axially moving electrode. Since the roughness is determined by the shape and dimensions of the electrode, it is difficult to obtain fine roughness with a small pitch beyond a certain limit, and convex portions caused by electrical discharge machining.

It is mechanically weak, the initial wear of the rolls during rolling is severe, and the roughness of the transferred plate surface changes drastically.

In contrast to the above two methods, a processing method using a laser beam (hereinafter referred to as laser dull processing) has recently been proposed.
For example, JP 56-160892, JP 58-255
57, JP-A-54-61043, JP-A-55-9479
0, etc.

All of these describe in detail how to irradiate the laser pulse, but do not mention the characteristics of the irradiated roll.

[Problem that the invention seeks to solve]

The inventors have conducted extensive research in order to commercialize roll surface roughening technology based on laser dulling. According to the research, when skin pass rolling is performed using a roll that has been roughened by laser dulling, the initial wear of the roll is quite large. As a result, it was found that the plating peeled off and the effect of this method could not be fully demonstrated.

Therefore, as a result of a detailed investigation of the temper rolling rolls, we found that there was a decrease in roughness in the part of the work roll that comes into contact with the rolled material, and a decrease in roughness in the part of the work roll that does not come into contact with the rolled material but only with the backup roll. It turns out that they are almost equal. From this, it has become clear that the wear of the dulled portion of the roll or the peeling of the plating is not related to the rolled material, but is caused by the transfer between the work roll and the backup roll.

In addition, as a result of cutting the rolling roll into rounds and examining the cross-sectional structure and hardness distribution near the roll surface, it was found that retained austenite phase, which is softer than the base material, was found near the very surface of the convex part of the roll surface caused by dulling with a laser beam. was found to exist.

The present invention has been developed focusing on the above findings.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved method for roughening the surface of a rolling JA roll using a pulsed laser in order to obtain a cold rolling roll with less surface wear.

[Means for solving problems]

The present invention is characterized in that when roughening a cold rolling roll by laser dulling, the roll after dulling by a laser beam is subjected to roll surface pressure reduction treatment, and then the roll surface is hardened. This is a method for roughening the surface of a cold rolling roll.

Suitable methods for reducing the surface pressure of the roll include kiss rolling, polishing, spraying an assist gas nozzle at an angle of 60 degrees to 90 degrees with respect to the roll surface during surface roughening, or shot or sandblasting.

The surface hardening treatment method for the roll is preferably sub-zero treatment, surface hardening film treatment, or sub-zero treatment followed by surface hardening film treatment.These surface hardening treatments include any of the above surface pressure reduction treatments. May be used in combination with

[Effect]

The rolling roll processed according to the present invention has less wear force on the roll surface when subjected to rolling, and can maintain a good roughness state for a long time. It can be rolled over a period of time.

〔Example〕

A detailed explanation will be given below based on examples.

FIG. 3 shows an overall view of a roll surface roughening device using a laser beam.

The roll 1 is attached to a roll rotation support device 2 having a configuration similar to that of a machine tool such as a lathe or a grinder, and is rotated at a predetermined speed.

On the other hand, the laser beam output from the laser oscillator 3 is irradiated approximately perpendicularly onto the roll surface via a plurality of mirrors. The laser beam is adjusted to a predetermined beam by an optical device, and further focused on the roll surface. The laser irradiation head section 4 can be moved parallel to the roll axis direction by rotation of the drive screw 5 in synchronization with the roll rotation. The laser beam can be pulsed to a predetermined frequency by a Q-switch or by a mechanical chopper. The pattern and depth of the roll surface roughness can be controlled by setting the frequency and output of this pulse, the roll rotation speed, and the moving speed of the laser irradiation head. Further, assist gas (O2) is sprayed using a nozzle toward the laser beam irradiation position.

Figures 2(a) and 2(b) show the dull shape of the laser irradiation part.
Shown below.

It is known that the wear of the dulled portion of the laser dull roll is caused by transfer between backup rolls, and that the surface pressure during rolling is carried by the convex portion of the dulled portion. There is a problem in significantly lowering the roll rolling load during skin pass rolling from the viewpoint of ensuring a sufficient transfer rate of the dull portion to the rolled material.

The present inventors have found that there is a deep relationship between how to form the convex part of the barrel and how to lower blood pressure.

If the molten metal is locally raised as shown in FIG. 2(a), only this convex portion will support the load from the receiving backup roll, resulting in significantly increased surface pressure and increased wear. If the molten metal is evenly piled up around the hole as shown in FIG. 2(b), the contact area with the backup roll will increase, the surface pressure can be lowered, and the service life will be improved. As a result of detailed tempering, the ratio of the raised part to the circumference of the hole was 6.
It has been found that when the amount is 0% or more, wear is significantly reduced.

As a means of lowering the surface pressure, it is effective to eliminate particularly high convex portions in the crater portion and to flatten the highest portion of the convex portions.

One effective way to lower blood pressure is to kiss-roll the material after laser dulling and roll it under a surface pressure of 60 kg/mm" or less. At this time, the opposing roll surface is a polished surface with small roughness. It is preferable to roll with a surface pressure of more than 80 kg/mm, as it allows for a more even flattening process, and the reduction in the height of the convex portions increases, resulting in the desired performance on the surface of the rolled material after rolling. 1. For example, the surface pressure reduction treatment by kiss roll that cannot obtain
It is preferable to perform kiss rolling with a backup roll having a of 0.5 gm, and roll the roll at a speed of 50 m/min for 5 minutes under a load such that the surface pressure is 40 kg/mrrI'.

Another means of reducing surface pressure is polishing. This method involves scraping off the highest part of the crater convex part a little after laser dulling to make the height even.

Polishing is performed by rotating the roll at a speed of 5 ORPM or less and bringing sandpaper or a grindstone into contact with it at a surface pressure of 10 kg/mm" or less. If the surface pressure exceeds 10 kg/mm", it is 60 kg/mm in the case of a kiss roll. In the 0-roll method, where the height of the convex portion decreases too much and the surface quality of the material to be rolled becomes unfavorable, as in the case of a surface pressure exceeding To give an example of surface pressure reduction treatment by polishing, which may be performed by rotating a file or a grindstone, a roll after laser dulling is rotated at a speed of 30 m/min, and a strip of 6
This was carried out by bringing 00# emery paper into contact with a surface pressure of 5 kg/mm'' and moving it in the roll axis direction.

Furthermore, as another means of surface pressure reduction treatment, the height of local convexities can be reduced by performing light shot blasting on the roll surface after laser dulling, shot blasting with a 120# grid with a small particle size, or sandblasting. It is possible to lower the height and make the height the same. The surface pressure reduction treatment by blasting is performed, for example, by subjecting the roll after laser dulling to 120# grid shot blasting.

As another method for reducing the surface pressure of the roll, as shown in FIG. 4, an assist gas (for example, The object can also be achieved by maintaining the spray angle θ of the nozzle 14 of the gas 13 with respect to the roll surface 10 within a certain range.

In order to ensure that the percentage of the circumference occupied by the bulge of molten metal around the crater generated by the laser beam is 60% or more of the total circumference of the crater, it is necessary to aim at the position where the laser beam hits the roll. It is necessary to set the blowing angle θ of the assist gas to the roll surface of the nozzle to be 60 to 90 degrees. If assist gas is blown at an angle of less than 60 degrees, the molten metal at the laser beam irradiation position will swell in only one direction, making it impossible to ensure that the circumference of the bulge is more than 60% of the total circumference of the crater. Assist gas was sprayed at the nozzle at an angle of 65 degrees with respect to the roll surface. (The flow rate of the assist gas at this time was 40 i/min, and the pressure was 3 kg/c.) This treatment made it possible to make the height of the bulge of the molten metal more uniform, reducing the surface pressure. becomes possible.

It is advantageous for the roll surface to be hard in terms of roll wear. Therefore, in the present invention, a roll surface hardening treatment is performed.

The soft portion of the roll surface layer after laser dulling is caused by the metal being melted by the laser irradiation being rapidly cooled and not sufficiently transformed into martensite, leaving the austenite phase behind. One effective means of imparting hardness to this portion to exhibit sufficient abrasion resistance is to transform the roll surface into martensite by subjecting it to i-subzero treatment.

As a roll surface hardening treatment by sub-zero treatment, it is sufficient to spray liquid nitrogen onto the roll surface. In this example, liquid nitrogen liquid was sprayed as sub-zero treatment, but any means can be used to perform sub-zero treatment on the laser irradiated portion of the roll surface. For example, the roll may be soaked in a dry ice solution.

In addition, as another means of roll surface hardening treatment, there is a method of applying a surface hardening film treatment, such as applying a film such as chromium plating, composite plating, TEN film by ion blating, etc.
Such treatment can also reduce wear.

The thickness of the chrome plating and the plating conditions are as follows, showing an example in which the roll surface was plated with chrome as a roll surface hardening treatment using a surface hardening film treatment.

The plating bath was Sargent bath (Cr03: 200g/l
, H2S 04: 2 g/l) in a static bath at a bath temperature of 50°C and a current density of 30 A/drn'.
A chrome plating thickness of 10 pm was obtained. As other surface hardening coating treatment methods, for example, TiN ion plating treatment, composite plating, WC thermal spraying, etc. may be applied.Furthermore, if the surface hardening coating treatment is performed after subzero treatment, the effect will be further improved.

By carrying out the above-mentioned hardening treatments such as sub-zero treatment and surface hardening coating treatment after the above-mentioned surface pressure reduction treatment, a remarkable wear-resistant effect is exhibited. In other words, the unevenness of the roll that has been subjected to surface pressure reduction treatment after laser dulling is uniform and there are no sharp protrusions, so the current density at the protrusions does not increase during chrome plating, for example, and the microscopic A uniform ROM plating thickness can be ensured. As a result, peeling of plating, which has often been a problem in the past, can be completely eliminated.

The method of the present invention uses the above-mentioned technical means to provide a roll with much superior wear resistance compared to conventional methods by applying sub-zero treatment and surface hardening coating after surface pressure reduction treatment without deteriorating the dimensional accuracy of the roll. It is possible to significantly suppress changes in plate surface roughness of the rolled material.

If a roll after laser dulling is subjected to any of the surface pressure reduction treatments mentioned above, then subjected to sub-zero treatment, and then chrome plated, the sub-zero treatment hardens the base before plating, which reduces the plasticity of the roll surface due to rolling. Deformation is significantly reduced.

This is further covered with a hard chrome plating layer, which provides even better wear resistance.

Next, specific processing conditions will be shown based on more specific examples.

The rolling mill used in the experiment was a small laboratory-type rolling mill, and the hoop-shaped material was continuously rolled using zero rolls with a diameter of 70 mm to check for wear of the rolls and changes in the roughness of the material surface. Examined.

The chemical composition of the rolls used in the experiment was C: 0.85% by weight Si: 0.8 weight% Mn: 0.4 weight% Ni: 0.15% by weight Cr: 2.9 weight% Mo: 0.29% by weight V: 0.01% by weight It is a widely used component system.

The manufacturing process of the roll is as follows.

That is, after casting molten steel with the above components, the temperature is 1100.
It was forged at ℃ to a forging ratio of 3.5. Thereafter, a so-called norm treatment of heating to 950° C. and cooling with air was performed. This is heated to 800℃
After XIO time and carbide spheroidization treatment at 700°C x 10 hours, machined to the specified dimensions, heated at 900°C, quenched in oil, then tempered at 650°C, It was machined again to final dimensions. Further, the surface layer was heated to 900° C. by induction heating, quenched in water, tempered at a low temperature of 150° C., and then subjected to final surface polishing.

A roll subjected to such treatment exhibits a healthy structure in which spherical carbides are uniformly distributed in the martensitic matrix.

According to the method of the present invention, the surface of this roll was roughened to a predetermined roughness by irradiating it with a pulsed CO2 gas laser beam using a mechanical chopper.

The laser irradiation conditions are: Laser output: 2 kW Pulse frequency: 56 kHz Energy density: 6.4 x 10"W/c Irradiation time per pulse: 25 #Lsec Pitch of craters formed on the roll surface by irradiation: Roll circumferential direction , both in the axial direction are 220 lm, and the obtained roll roughness Rmax is about 20° lm
It is.

Let the beer surface roughened as in step 9 kiss the backup roll, and the surface pressure was 40 kg/m and the speed was 50 m.
A blood pressure lowering treatment was performed by transferring the mice at a speed of 5 min.

The obtained roll roughness is Rmax from 204 m to 17 m
It declined to .

Figure 5 shows the results of measuring the hardness distribution near the roll surface roughened in this way, and Figure 6 shows the results of measuring the hardness distribution near the roll surface after sub-zero treatment.Retained austenite in the molten zone is almost completely martensitic and exhibits higher hardness than the base metal.

After the sub-zero treatment, the roll surface was cleaned and chrome plated.

The hardness distribution on the roll surface is shown in FIG. 7, showing considerably high hardness over a depth of 10 pm from the roll surface.

After dulling into 4 sets of rolls under the above conditions, a) One set was chrome plated as described above.

b) One set was subjected to the surface pressure reduction treatment using the kiss roll described above, and then to the sub-zero treatment.

c) 1 set is the above-mentioned surface pressure reduction treatment by kiss roll,
Then it was chrome plated.

d) 1 set is the above-mentioned surface pressure reduction treatment 1 by kiss roll.
Next, it was subjected to sub-zero treatment and then -chrome plating treatment.

Using these four sets of rolls, a cold-rolled and annealed plate of low carbon AfL killed steel with a plate thickness of 0.8 mm was rolled at a rolling reduction rate of 0.8.
%, and the results of examining and comparing changes in plate surface roughness are shown in the first table.
The curves 11.12.13.14 in FIG.
Curve 11: Blood pressure lowering treatment followed by sub-zero treatment followed by chromium plating. Curve 12 Bilateral pressure lowering treatment followed by chrome plating. Curve 13: Surface pressure reduction. After processing, the curve 14 was treated with sub-zero and the one with nichrome plating was used. Also curves 21.22. ．． 23 and 24 show the average surface roughness Ra of the rolled plate materials, respectively.Curve 21: Surface pressure reduction treatment, sub-zero treatment, and chrome plating treatment.Curve 22: Surface pressure reduction treatment, then chrome plating treatment. Curve 23: Sub-zero treatment after bifacial pressure reduction treatment; Curve 14: Nichrome plating treatment. According to Figure 1, when chrome plating is performed without surface pressure reduction treatment, the plating layer peels off, the initial roughness decreases significantly, and the desired board performance cannot be achieved.0 The method of the present invention is applied. In the other three examples, the decrease in roughness can be significantly reduced, and the initial roughness can be maintained even with an actual machine equivalent pressure extension of 50 km.

〔Effect of the invention〕

According to the present invention, by combining surface pressure reduction treatment and surface hardening coating treatment after laser surface roughening processing, wear of dull rolls can be significantly reduced, and roughness reduction of the surface of the rolled material is significantly improved. be done.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between actual machine equivalent pressure extension and average surface roughness, Figures 2 (a) and 2 (b) are crater shapes formed by laser pulse beams, and Figure 3 is the rough surface of the roll. FIG. 4 is an explanatory diagram showing the relationship between the roll surface and the assist gas nozzle, and FIGS. 5, 6, and 7 are perspective views of the chemical processing equipment.
The figure is a graph showing the relationship between the depth from the surface of the roll and hardness. 1... Roll 2... Roll rotation support device 3... Laser oscillator 4... Laser irradiation head 5... Laser drive screw, applicant Kawasaki Steel Corporation

Claims (1)

[Claims] 1. On the surface of the cold rolling roll, 5×10^4 to 9×10
When roughening the roll surface by irradiating it with a laser beam with an energy density of ^6W/cm^2, there are two steps: a) applying surface pressure reduction treatment to the roll after dulling with the laser beam; b) then roughening the roll surface. 1. A method for roughening a cold rolling roll, the method comprising the step of subjecting a cold rolling roll to a hardening treatment. 2. The method for roughening the surface of a roll according to claim 1, wherein the surface pressure reduction treatment of the roll is a kiss roll. 3. The method for roughening the surface of a roll according to claim 1, wherein the treatment for reducing the surface pressure of the roll is a polishing treatment. 4 The angle of the assist gas nozzle with respect to the roll surface during surface roughening treatment of the roll is 60 degrees or more.
Claim 1 is to spray at 90 degrees.
The method for roughening the roll described in Section 1. 5. The method for roughening the surface of a roll according to claim 1, wherein the treatment for reducing the surface pressure of the roll is shot or sandblasting. 6. The method for roughening a roll surface according to any one of claims 1 to 5, wherein the hardening treatment of the roll surface is a sub-zero treatment. 7. The method for roughening a roll surface according to any one of claims 1 to 5, wherein the hardening treatment of the roll surface is a surface hardening coating treatment. 8. The method for roughening a roll surface according to any one of claims 1 to 5, wherein the hardening treatment for the roll surface is to perform a surface hardening film treatment after performing a sub-zero treatment.