JPH0667557B2 - Roll roughening method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for roughening a surface of a rolling roll, and more specifically, the shape and size of a micro crater formed by a pulse laser beam on the surface of a roll for metal rolling. On how to control.

[Conventional technology]

Rolls for metal rolling are often used after roughening. Shot blasting and electric discharge machining are known as methods that have been widely used as a method for roughening the roll surface.

On the other hand, recently, a new roughening processing method using a laser has been attempted. As an example, by irradiating the surface of a rotating roll with a pulsed laser beam, one minute crater is generated for each pulse, and the craters are arranged innumerably on the surface of the roll. There is a method of producing a rough surface having a uniform profile.

The rough surface generated by shot blasting or electric discharge machining is composed of irregular peaks and valleys, and the same rough surface is also formed on the surface of the metal plate rolled by the roll having the rough surface. It is a well-known fact that if such a steel sheet is pressed, lubricating oil will be stored in the recesses of the rough surface, facilitating the pressing work, while irregular rough surfaces will also result in poor finish quality after painting. It is also a well known fact that they have the contradictory effects of reducing so-called glossiness and image clarity.

On the other hand, a metal plate rolled by a roll that has been given a regular roughness profile using a laser may have the property of satisfying the above-mentioned two contradictory requirements for lubricity and gloss. It became clear that the importance of the roughening processing method by laser has come to the fore.

By the way, as a concrete laser roughening method,
For example, there is a method disclosed in JP-A-55-94790. This publication describes in detail a method of arranging holes perforated by a pulse beam on a roll surface according to a predetermined arrangement. However, it does not mention the means for controlling the individual hole shapes.

The method disclosed in Japanese Patent Publication No. 60-2156 discloses a method in which the hole diameter is adjusted by adjusting the beam diameter and the hole depth is adjusted by the beam irradiation time (Q switching times) for the same hole. There is. However, this does not mention that the shape of the hole, that is, the molten metal is controlled to generate a crater having a desired shape.

As will be described later, the present invention aims to control the flow of the molten metal at the time of beam irradiation with respect to each crater generated by the pulse beam, and to make the hole shape a desired shape.

As a result of detailed studies on the control of the hole shape of the crater generated by the laser beam, the present inventors have adjusted the energy density of the laser beam irradiated on the surface to be processed in order to control the flow of the molten metal. Found that it is necessary to do. A technique for controlling the energy density of a laser beam is generally used in techniques such as laser heat treatment. For example, as a first example, the spot diameter on the surface to be processed disclosed in JP-A-54-5809 is used. There is a method of obtaining a desired energy density by changing the processing lens position by moving it. However, this method is for keeping the temperature of the work piece constant without melting the work piece, and is different from the laser irradiation condition for melting the metal.

Further, as a second example, the method disclosed in Japanese Patent Laid-Open No. 55-82724 is also a similar method, but this is also a method for widening the quench-hardened area without melting the workpiece. As a third example, JP-A-54-76405 describes the energy density of a beam for preventing melting of a workpiece by the same method, and as a fourth example, JP-A-54-76454. The publication also discloses a method of setting the lower limit of the beam energy density in laser welding to the limit above which the work piece melts, and the same to the upper limit above the limit at which molten metal becomes a splash and scatters.

In any case, it is not mentioned that the flow of the molten metal is controlled by controlling the energy density of the laser beam.

In order to form craters on the surface of the rolling roll by the pulsed laser beam, it goes without saying that the beam energy density must be set within the limit of melting of the workpiece and splashing of the molten metal. is there. However, laser welding is a process of irradiating a workpiece with a continuous beam, and the roughening method of the roll is a process of irradiating a pulse beam. It goes without saying that can not be applied as is, but in addition to that, in discontinuous machining, it is possible to control fluidized metal by irradiating within the upper and lower limits of the above energy density and at a specific energy density. It was unknown.

[Problems to be solved by the invention]

The crater shape generated on the rolling roll surface by the pulsed laser beam has a great influence on the surface texture of the metal sheet rolled by using this roll, and at the same time, the roughness of the rolling surface caused by rolling or plastic deformation It has a great effect on durability against deterioration.

When the moving roll surface is irradiated with a pulsed laser beam, the crater shape generally becomes a shape with uneven ridges as shown in FIG. This is because the heat source moves during irradiation. FIG. 5 is a partial cross-sectional view of the workpiece 6 showing the crater generation process for explaining this. As shown in FIG. 5, the metal 9 melted by the laser beam 7 is shown.
There is a part that evaporates, and this evaporation reaction force is generated by moving the molten metal 9 in the direction opposite to the movement of the heat source 7 shown by arrow 10, that is, the direction of arrow 11.

With respect to such a shape, if it is possible to generate a donut-shaped crater that is evenly raised around the hole as shown in FIG. 3, it is possible to improve the surface texture of the above-mentioned rolled plate and to roll it. It can be easily estimated that the wear resistance of the can be improved. That is, the work roll receives a load from the rolling plate and the backup roll in general, but in the case of a roughened work roll, the load concentrates on the ridges on the surface, which causes plastic deformation of the ridges, and Deteriorate.

The crater with the shape shown in Fig. 3 is several times wider than the crater with the shape shown in Fig. 2 under the load around the crater, and as a result, the stress received by the ridge is much lower. This is because the progress of plastic deformation is less likely to occur. Further, since the shape shown in FIG. 3 has no directionality, it is possible to improve the mold galling resistance during pressing of the rolled plate.

The present invention is applied to a processing method of condensing and irradiating a pulsed laser beam on a rotating rolling roll surface to roughen the roll surface, in order to achieve the above object. In addition, the present invention is intended to provide a laser processing method capable of generating a symmetrical crater shape with no deviation as shown in FIG. 3 and also capable of arbitrarily controlling the hole diameter.

[Means for solving problems]

The technical means of the present invention for achieving the above object are as follows.

(1) O ₂ gas is injected as an assist gas in a direction coaxial with the laser beam and perpendicular to the processing surface.

(2) Laser irradiation conditions To do.

Where Δt: irradiation time per pulse of pulse beam (seconds) δ: distance that roll surface moves with respect to beam during Δt (m) W: output of laser oscillator (MW) r: laser beam on roll surface The radius of the spot (m).

[Action]

In order for the pulsed laser beam to generate a crater having a non-uniform shape as shown in FIG. 3 on the surface of the rolling roll, it is necessary that the force applied to the molten metal has no directionality. The above-mentioned evaporation reaction force always has a direction unless the movement of the heat source can be avoided. Therefore, metal evaporation must be minimized, and the energy density of the laser beam applied must be limited for this purpose. For this purpose, a method of controlling the laser output and a method of controlling the beam spot diameter on the roll surface, for example, a method of controlling the focal position of the laser beam can be considered.

According to a detailed study by the inventors, the laser output, the spot diameter, and the irradiation time per pulse (hereinafter simply referred to as irradiation time) are controlled, and an assist gas such as O ₂ is applied to the processed surface to form a beam. By spraying perpendicularly to the machined surface from the coaxial direction, it became possible to generate a crater having a required diameter while maintaining the shape shown in FIG.

The important point of the present invention is the action of the assist gas.
Without the action of this gas, due to the evaporation reaction force, which is generated only by controlling the laser output, spot diameter and irradiation time, and the surface tension of the molten metal,
A crater having a shape similar to that of FIG. 2 is also generated.

Further, when the assist gas is sprayed from a direction other than the above, for example, obliquely laterally, a crater having a nonuniformly raised shape around the hole is naturally generated as shown in FIG.

Generally, the beam mode (intensity distribution) of the stable laser oscillator exhibits a Gaussian distribution as shown in FIG. 6, which has a similar distribution even after being focused by a lens or the like. The peak power density at the center I _0, when the power density has a radius which becomes I = I ₀ / e ² is defined to be the spot radius r, the power density I at a position at a distance of ρ from the beam center, I = I ₀ exp (−2ρ ² / r ² ) ... (1) The total output remains unchanged even if d changes due to light collection by a lens or the like. Therefore, the output W of the laser oscillator
And the relationship between I ₀ Next to Is. Since the beam moves during irradiation on the roll surface, the average power density E ₀ that the roll surface receives during irradiation
(MW / m ² ) is different from the equation (2), and if the beam moves relative to the roll surface by the distance δ (m) during the irradiation time Δt (sec), it is calculated that at the crater center with the highest power density. Almost Becomes According to the research conducted by the present inventors, the condition for generating the symmetric crater having the symmetrical shape shown in FIG. 3 is that the assist gas is blown from the above direction at a flow velocity range of 10 to 500 m / s. E ₀ (MW / m ² ) of equation (3) and irradiation time Δt
Between (seconds) Then, it was confirmed that the craters having the symmetrical shape shown in FIG. 3 were formed. On the contrary, under the condition of E ₀ that does not satisfy the above equation (4), the crater has an asymmetric shape as shown in FIG. The reason for this is considered to be as described above. Expression (4) can be expressed using Expression (3). Becomes Also, within the E ₀ satisfies the equation (4) was confirmed to be capable of deep crater depth higher the E _0. As described above, the radius r of the beam spot is changed according to the output W of the laser oscillator, the distance δ, and the irradiation time Δt. By adjusting the beam spot radius r to satisfy the above condition, it is possible to always obtain a crater having a symmetrical shape shown in FIG.

Next, a method of controlling the hole diameter (outer diameter) of the crater will be described.
The inventors have confirmed that there is almost no change in the crater hole diameter when the focal point of the condenser lens is moved and the beam spot radius r is changed under the same conditions of the output W of the laser oscillator and the irradiation time Δt. This is considered to be due to the following reasons. That is, the power density distribution of the laser beam is calculated by using equations (1) and (2), Becomes

This is the distribution of I calculated for W = 800 (W), r = 100 (μm), 200 (μm), and Δt = 125 × 10 ^{−6 under the} same conditions.
FIG. 7 shows the outer diameter (radius R) of the crater obtained under the above-mentioned assist gas blowing condition in (sec). Considering that a portion irradiated with a power density equal to or higher than a certain image Ic with respect to a certain irradiation time Δt melts and this is a factor that determines the crater diameter, under normal laser processing conditions, the laser oscillator If the output W and the irradiation time Δt are constant, the crater radius R does not change much even if the beam spot radius r is changed.

On the other hand, when the output W of the laser oscillator is increased, the distribution of E is increased as a whole, and the skirt is expanded, so that the crater diameter is increased. Further, if Δt increases, Ic may be small, so that the crater diameter increases.

According to the investigation by the inventors, the radius R (m) of the crater when the assist gas is sprayed under the above conditions is approximately R = 0.32 (WΔt) ^1/2 (6) where W: output of the laser oscillator (MW) Δt: Irradiation time (seconds) was found to be sorted.

According to the above knowledge, when the crater diameter and the hole pitch for obtaining the desired roughness pattern are given, when Δt (second) is determined from the machining efficiency and the like, the roll moving speed U
Δ = UΔt (7) is obtained from (m / sec), and the required output W is further obtained from the equation (6). Under this condition, if the focal point of the focusing lens is adjusted so as to obtain r satisfying the formula (4) and the assist gas is blown under the above condition, the symmetrical shape shown in FIG. It is possible to form a crater with the size of.

〔Example〕

FIG. 1 shows an example of an apparatus that enables a laser roughening method according to the present invention.

In FIG. 1, reference numeral 1 is a pulse laser oscillator or a continuous laser oscillator and an assembly of devices for pulsing a beam, and from here to the condenser lens 3, one or a plurality of optical paths of the laser beam 7 are changed as necessary. Insert the mirror 2 of. Reference numeral 4 is a device for adjusting the focus of the lens and a device for displaying the amount of movement of the focus or the spot diameter on the roll surface. Reference numeral 5 is a conical nozzle for blowing the assist gas 8, and the beam and the assist gas are emitted from the tip of the nozzle 5 in the coaxial direction and perpendicularly to the surface of the workpiece 6. The roll, which is the workpiece 6, has a structure that moves in the axial direction of the roll while being rotated by a lathe (not shown).

Next, Table 1 shows the shape of the generated crater and the measurement result of the crater radius under various irradiation conditions and assist gas conditions using this apparatus. In the shape column of Table 1, the shape shown in FIG. 2 is marked with x, and that in FIG. 3 is marked with ◯. The above results show the change in shape in the relationship between Δt and E ₀ in FIG. 8, and the case of processing under the above assist gas spraying conditions (No. 1 in Table 1) and the case of no spraying (Same No. ,) And the crater radius R are shown in FIG. The numbers attached to each plot point in FIGS. 8 to 9 correspond to the experiment numbers in Table 1. The symbols (◯ and ×) of the plotted points in FIG. 8 correspond to the symbols in the shape column of Table 1. In FIG. 8, each 1 / Δ
For the value of t, the area below the upper right solid line is (4) above.
A crater represented by a formula and having the shape shown in FIG. 3 is formed under the conditions of this region. However, in FIG.
The plot points of and mean that if there is no assist gas, the crater having the shape of FIG. 3 is not formed even under the condition of satisfying the equation (4). Similarly, the broken line in FIG. 8 represents the lower limit at which a crater is not generated when the value of E ₀ is smaller than this, and the boundary line equation at this time is equation (8).

Here, in order to form at least a crater, each Δt
The value of E _{0 for} the value of must be greater than the value of E ₀ in Eq. (8).

Between E ₀ (MW / m ² ) and Δt (seconds) Must have a relationship. This region is a region above the broken line in FIG. 8, and the plot point of is too small because the value of E ₀ does not fall within this region and a crater is not generated.

That is, the conditions for obtaining the target crater shape shown in FIG. 3 are calculated from the equations (4), (9) and (3). Becomes

Further, FIG. 9 shows that under the above-mentioned assist gas conditions, the crater radius R is arranged by W × Δt, and the relational expression is the expression (6).

In the case of the plot points, since there is no assist gas, the crater radius R does not satisfy the above equation (6).

The crater a having the shape shown in FIG. 2, the crater b having the shape shown in FIG. 3, and the shape shown in FIG. 4 obtained by obliquely blowing the assist gas using the apparatus of FIG. 1 under different conditions. Crater c of each is formed into a cold rolling roll of 560φ, and 4
Fig. 10 shows an example of changes in rolling length and roughness when cold-rolled steel sheets are rolled at a load of 280 tons in a heavy-duty skin-pass rolling mill. In Fig. 10, the sharp decrease in roughness that occurs at the initial stage of rolling is mainly plastic deformation of the crater rising portion due to the contact surface pressure with the backup roll. In this, the ridge portion is crushed by the deformation, and the deformation proceeds until the contact area becomes less than the plastic yield stress of this portion. The subsequent decrease in roughness is mainly wear due to friction with the rolled plate. Since the crater b manufactured according to the present invention can have a large contact area, the initial roughness reduction is very small. As a result, as shown in FIG. 10, the roll life is greatly extended.

Next, sliding of dull steel sheet (SPCC) skin-pass rolled using dull rolls in which a crater a having the shape shown in FIG. 2, a crater b having the shape shown in FIG. 3, and a crater c having the shape shown in FIG. A dynamic test was conducted. In this test method, as shown in FIG. 11, the steel plate 12 is sandwiched between the sandwiching pieces 13 and pressed with a constant pressing force P = 100 kgf to pull out the steel plate 13.
It can be judged that the smaller the pulling force 2F at this time is, the better the mold galling property is. The test is performed in a degreased state.

The experimental results are shown in FIG. The pulling force with equal roughness is 3rd
It becomes the smallest in the case of a steel plate rolled by a roll having a crater b having the shape shown in the figure. Therefore, by using the dull roll manufactured according to the present invention, it is possible to obtain a steel plate having the best resistance to galling.

(Effect of the invention) According to the present invention, it is possible to form a crater having a good hole shape in the dull working method by the pulse laser beam of the rolling roll, therefore, when performing the skin pass rolling using the roll, It is possible to significantly extend the roll life and improve the die galling resistance of the rolled steel sheet.

[Brief description of drawings]

FIG. 1 shows an apparatus 1 in which the present invention can be preferably implemented.
2 to 4 are perspective views showing a crater shape, FIG. 5 is an explanatory view of a mechanism generated by the crater having the shape shown in FIG. 2, and FIG. 6 is a laser oscillator. A curve showing the beam mode, FIG. 7 is an explanatory diagram showing the calculation of the power density distribution when W is constant and d is changed, and a comparison of the actual crater diameter. FIG. 8 shows the relationship between Δt and the crater shape by E ₀ . Fig. 9 is a diagram showing the relationship between WΔt and crater radius R, and Fig. 10 is a graph showing the relation between rolling length and roughness change in rolling using rolls having craters of three types. FIG. 11 is an explanatory view of the sliding test, and FIG. 12 is a graph showing the sliding test results. 1 ... Pulse laser oscillator 2 ... Mirror 3 ... Condensing lens 4 ... Lens focus adjusting device 5 ... Assist gas nozzle 6 ... Workpiece (roll) 7 ... Laser beam 8 ... Assist gas 9 ... … Molten metal 10, 11 …… Arrow 12 …… Dull steel plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Onda 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Inventor Takashi Kusaba 1 Kawasaki-cho, Chiba-shi Kawasaki Steel Co., Ltd. Research Headquarters (72) Inventor Hideo Abe 1 Kawasaki-cho, Chiba City, Chiba Prefecture Technical Research Headquarters, Kawasaki Steel Co., Ltd. (72) Inventor Takehiro Yokoyama 5-21-12 Bijogi, Toda City, Saitama Prefecture Miyamauchi Co., Ltd. 72) Inventor Masafumi Mitsuka 2-3-6 Ginza, Chuo-ku, Tokyo Okura Shoji Co., Ltd.

Claims (1)

[Claims] 1. In a processing method of condensing and irradiating a rotating rolling roll surface with a pulsed laser beam to roughen the roll surface, an assist gas is perpendicular to the processing surface from a direction coaxial with the laser beam. As well as spraying A method for roughening a surface of a roll, which comprises irradiating a laser under the conditions of. Where Δt: irradiation time per pulse of pulse beam (seconds) δ: distance that roll surface moves with respect to beam during Δt (m) W: output of laser oscillator (MW) r: laser beam on roll surface Spot radius (m)