JP7551247B2 - Surface treatment equipment - Google Patents

Description

The present invention relates to a surface preparation method and surface preparation treatment device for removing adhesions from an object by laser irradiation, and in particular to a surface preparation treatment device for removing part of a two-layer oxide coating of hematite and magnetite adhering to the surface of a steel material, which is the object to be treated.

Here, the process of removing the oxide film adhering to the surface of an object is called scraping.

Conventionally, when removing rust or paint from the surface of an object, a paint remover or shot blasting has been used. However, this not only creates a poor working environment and is inefficient, but also poses problems with the collection and disposal of the large amount of material removed. For this reason, a method of removing rust or removing paint using laser irradiation has been proposed.

For example, a method for generating metal nanocolloids has been proposed in which a target placed in a liquid is scanned and irradiated with pulsed laser processing with a laser spot at a distance of at least a certain distance from the target (see, for example, Patent Document 1).

Patent document 1 describes how the distance from the water surface to the target is kept constant, the water surface and the target surface are made parallel, and pulsed laser processing is applied at a constant speed.

In addition, a laser processing device and method capable of cutting brittle materials with high residual stress without causing cracks has been proposed, which includes a laser light irradiation mechanism that pulsates a laser light to irradiate and scan the workpiece at a constant repetition frequency, and the irradiation mechanism is provided with a laser light irradiation speed S of the laser light, where H is the repetition frequency, a is the beam diameter of the laser light, n is the number of scans of the laser light on the same processing line, and n/2×a is the moving distance L per irradiation of the pulsed laser light. The scanning speed S of the laser light is set to L/(1/H), and the irradiation start position of the laser light for the first scan is set to L1, and the irradiation start position Ln of the laser light for the nth scan is set to L1+(L/n)×(n-1), so that the irradiation start position is shifted for each scan (see, for example, Patent Document 2).

In addition, when manufacturing thin steel plates, the steel plate that is hot-rolled from a heated slab forms an oxide film (scale) on the surface of the steel plate as it cools naturally, so in the pickling process, the steel plate is passed through a pickling tank to remove the oxide film.

In order to efficiently and reliably remove the oxide film in the pickling process, it has been proposed to irradiate the magnetite-containing oxide film with laser light before the pickling process to transform the magnetite into wustite of approximately the same thickness as the magnetite, and then irradiate the oxide film with terahertz waves and determine the thickness of the oxide film using the signal of the reflected wave of the irradiated terahertz waves (see, for example, Patent Document 3).

JP 2018-40033 A JP 2011-177781 A JP 2009-186333 A

As mentioned above, when painting or welding steel materials, it is necessary to remove the scale (iron oxides formed during manufacturing) from the surface of the area before carrying out the work. Typically, shot blasting is used, in which tiny iron balls are struck against the surface of the steel material, and the kinetic energy is used to remove the scale (or a handheld grinder is used on a smaller scale), but this has environmental issues such as dust, noise, and vibration, as well as the high costs of disposing of the shot balls used and the waste material after removal.

As a result, surface preparation work using lasers has traditionally been carried out as a method that can improve both the environment and costs.

In the coating removal process using laser irradiation, the coating on the surface of the object to be treated can be removed by laser ablation without using chemicals.

However, the technology disclosed in Patent Document 1 is a metal nanocolloid production method in which a pulsed laser is irradiated onto a target placed in a liquid by scanning the target with the laser spot at a distance of at least a certain distance from the target, and the laser irradiation pitch for each pulse is set at a distance of at least 10 times the spot diameter, which is unique to the field of metal nanocolloid production. In normal cases, it is clear that unirradiated areas will occur if the distance between the spot diameters is set too far, and there is a problem that these areas cannot be treated.

The technology disclosed in Patent Document 2 is a cutting method that suppresses the thermal effects of the laser, but by setting the irradiation pitch per pulse to 1.5 times the spot diameter, overlapping irradiation is avoided, and any unirradiated areas that occur are filled in by the next and subsequent irradiations. This method requires multiple irradiations, which reduces work efficiency.

Lasers allow for processing with high energy density due to their focusing properties, but they must be used under optimal conditions in terms of equipment capacity (cost) and work efficiency. Naturally, work with high laser density and high laser focusing rate (small spot diameter) will have excellent quality (scale removal performance in surface preparation work), but the work time will be longer and work efficiency will decrease. On the other hand, work with low laser density and low laser focusing rate (large spot diameter) will have lower quality but shorter irradiation time. Therefore, it is necessary to set optimal conditions in terms of the quality and work efficiency of the work.

As mentioned above, surface preparation work is carried out when painting or gluing components in order to improve the paint and adhesive performance. There are ISO and other standards for evaluating the performance of the surface preparation work, but all of these are qualitative judgments made by the installer at the work site through visual inspection.

Surface preparation using a laser (hereafter referred to as laser cleaning) was developed as a new surface preparation method, and the quality evaluation standards for the blasting method described above may not be able to evaluate it correctly. In response to this, JIS Z2358 has established a method for quantitatively judging the quality of laser surface preparation using a colorimeter. In contrast to the conventional qualitative evaluation standards for the blasting method, this method evaluates the performance of laser cleaning by measuring the color saturation of the surface after laser cleaning (visual inspection is also possible) and comparing it with an existing color sample. However, although this method measures color saturation, there is a problem in that the measurement is strongly affected by external disturbances such as the amount of external light hitting the surface, making it difficult to evaluate correctly. In addition, the comparison with the color sample is done visually, so in this case the evaluation is qualitative.

On the other hand, one of the important quality performance factors for paint and adhesives is the adhesion to the component, and for existing materials, especially steel materials, the degree to which surface oxide scale is removed is an important factor.

The technology disclosed in Patent Document 3 is to measure the oxide film thickness and optimize the steel sheet transport speed in the pickling line based on the measurement results in order to improve the efficiency of the pickling process that removes surface scale from hot-rolled steel sheets. In measuring the oxide film thickness, the hematite on the outermost surface is removed by irradiating the oxide film, which has a two-layer structure of hematite and magnetite, from the surface with laser light, and the remaining magnetite is transformed into wustite, after which the thickness of the wustite is measured. Patent Document 3 describes the removal of hematite by laser irradiation, but its purpose is to measure the oxide film thickness, not to improve pretreatment (surface treatment) such as painting or bonding. There is also no description of the feed speed of the laser irradiation.

SUMMARY OF THE PRESENT EMBODIMENT In view of the above-mentioned conventional circumstances, an object of the present invention is to provide a surface treatment device capable of qualitatively removing surface oxide scale from steel materials.

Another object of the present invention is to improve the quality of the surface preparation of steel materials to be supplied to processing processes in which objects are attached or bonded to each other using coating materials (paints and lining materials) or adhesives, such as painting, gluing, and lining.

Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the description of the embodiments described below.

As a result of closely observing the surface condition after laser scraping, the present inventors discovered that the surface preparation performance can be improved by removing hematite (Fe ₂ O ₃ ), which is one of the main components constituting the oxide scale on the steel surface.

In the present invention, hematite (Fe ₂ O ₃ ) on the surface side, which is part of an oxide film having a two-layer structure of hematite (Fe ₂ O ₃ ) and magnetite (Fe ₃ O ₄ ) adhering to the surface of a steel material that is the object of treatment, is removed.

That is, the present invention is a surface treatment device that removes a part of an oxide film having a two-layer structure of hematite (Fe ₂ O ₃ ) and magnetite (Fe ₃ O ₄ ) adhering to the surface of a steel material, which is a processing object, by pulsed irradiation of laser light, and the device is provided with an irradiation distance variable setting means that variably sets a laser irradiation distance for irradiating a processing object area of the steel material, which is the processing object, with pulsed laser light, a scanning means that moves the irradiation position of the pulsed laser light within a working area including the processing object area, a pulsed laser light irradiation device that irradiates the processing object area of the steel material, which is the processing object, with pulsed laser light, and a control device that controls the operation of the pulsed laser light irradiation device, and the control device controls the pulsed laser light irradiation device to set a laser density per pulse of the laser light irradiated in pulses, based on a spot diameter d _p of the pulsed laser light based on the laser irradiation distance and a movement distance d _m of the irradiation position _per pulse _, The present invention is characterized in that the operation of the pulsed laser light irradiation device is controlled so that a laser density effective for removing hematite (Fe 2 O 3 ) from the surface layer of the oxide coating is initially set to a laser density that is effective for removing the hematite (Fe ₂ O ₃ ) from the surface layer of the oxide coating, the irradiation position of the pulsed laser light is moved by the scanning means within a working area including the area to be treated, and the pulsed laser light having the initially set laser density is irradiated to perform a scraping process.
Here, the laser projection distance is the distance between the lens that focuses the laser light and the surface of the target object. Therefore, when the laser projection distance is equal to the focal length of the lens, the spot diameter is minimized.

In the surface treatment device according to the present invention, the control device can control the operation of the pulsed laser light irradiation device so that the proportion of hematite (Fe ₂ O ₃ ) removed by the scraping process is 78.5% or more in terms of area ratio on the surface of the oxide coating after the scraping process.

Furthermore, in the surface treatment device of the present invention, the control device can be configured to control the operation of the pulsed laser light irradiation device so that the scanning means moves the irradiation position of the pulsed laser light per pulse at a moving speed such that the moving distance d _m is within the range of the spot diameter d _p × (1/2 to 1).

Furthermore, in the surface treatment device of the present invention, the control device can set the spot diameter dp to an optimum value by defocusing the pulsed laser light irradiated to the treatment target area of the steel material, which is the treatment target, using the irradiation _distance variable setting means.
Here, defocusing refers to making the laser irradiation distance longer or shorter than the focal distance of the lens, which makes the spot diameter of the laser light larger than the minimum spot diameter.

In the present invention, the laser density per pulse of the pulsed laser light is initially set to a laser density effective for removing hematite (Fe ₂ O ₃ ) in the surface layer of the oxide film, based on the spot diameter _dp of the pulsed laser light based on the laser irradiation distance and the movement distance _dm of the irradiation position per pulse, and by irradiating the pulsed laser light of the initially set laser density to remove the hematite (Fe ₂ O ₃ ) in the surface layer of the oxide film, the hematite (Fe ₂ O ₃ ) with low adhesion is removed from the steel plate surface after laser scraping, and magnetite (Fe ₃ O ₄ ) with high adhesion accounts for the majority, thereby improving the adhesion of the paint.

Therefore, according to the present invention, it is possible to improve the quality of the surface preparation of steel materials to be supplied to processing processes in which objects are attached or bonded to each other using coating materials (paints and lining materials) or adhesives, such as painting, bonding, and lining.

Furthermore, in the present invention, the proportion of hematite (Fe ₂ O ₃ ) removed in the scraping process is set to 78.5% or more in terms of area ratio on the surface of the oxide film after the scraping process, thereby making it possible to provide a surface treatment device that is qualitatively capable of removing surface oxide scale of steel materials.

Furthermore, in the present invention, when performing scraping treatment, the movement distance d _m of the irradiation position of the pulsed laser light per pulse is moved at a movement speed within the range of the spot diameter d _p × (1/2 to 1), thereby providing a surface treatment device that is qualitatively capable of removing surface oxide scale of steel materials.

1 is a block diagram showing an example of the configuration of a surface treatment device according to the present invention ; FIG. 2 is a perspective view showing a schematic structure of a two-axis galvanometer mirror mechanism provided in the substrate processing apparatus. 4 is a schematic diagram showing a feeding state of an irradiation position of a pulsed laser beam in the above-mentioned surface treatment device. FIG. 1A and 1B are schematic diagrams showing the movement trajectory of the laser spot by the two-axis galvanometer mirror mechanism, in which (A) is a schematic diagram showing the state of laser irradiation, and (B) is a schematic diagram showing the state of laser irradiation in which the second row and subsequent rows are irradiated at intermediate positions between the irradiation positions of the previous row when the laser is irradiated in a folded manner. 1A and 1B are diagrams showing schematic cross-sectional structures of objects to be processed by the above-mentioned base treatment device, in which (A) is a schematic cross-sectional view of the object to be processed before the base treatment, and (B) is a schematic cross-sectional view of the object to be processed after the base treatment. 3A to 3C are process diagrams showing a surface treatment method carried out by the surface treatment device. (A) shows the case where the moving speed is such that the moving distance _dm1 per pulse is equal to the spot diameter _dp , (B) shows the case where the moving speed is such that the moving distance _dm2 per pulse is equal to (1/√2) times the spot diameter _dp , and (C) shows the case where the moving distance _dm3 per pulse is equal to (1/2) times the spot diameter _dp . This figure shows the results of a tensile test (pull-off test) conducted to confirm the adhesion strength of a test piece coated with paint and dried and cured in order to evaluate the performance of a laser scraper with different laser intensities (energy densities).

The following describes in detail the embodiments of the present invention with reference to the drawings. Common components are described with common reference numerals in the drawings. Furthermore, the present invention is not limited to the following examples, and can be modified as desired without departing from the spirit of the present invention.

The present invention is embodied, for example, by a surface treatment apparatus 100 that performs surface treatment work using a robot, as shown in the block diagram of FIG.

In this substrate processing device 100, the robots used for substrate processing operations include manipulator robots made up of articulated links, three-axis robots made up of three axes (X, Y, Z), and transport devices using moving carts. This substrate processing device 100 employs a manipulator robot 40 consisting of a manipulator 20 (including a robot arm 21) and a robot control unit 30.

That is, this surface treatment device 100 is a device that performs surface treatment work by attaching a pulsed laser light irradiation device 10 to a manipulator robot 40 and removing adhesions from a treatment target 1 by irradiating the treatment target with pulsed laser light, and is composed of a pulsed laser light irradiation device 10, a manipulator robot 40, and an overall control device 50.

The pulsed laser light irradiation device 10 consists of a laser oscillator 11, an optical fiber 12 that transmits laser light from the laser oscillator 11, and a laser head 13 that irradiates the laser light.

In this pulsed laser light irradiation device 10, the laser light irradiation conditions are controlled by the overall control device 50, and pulsed laser light Lp is generated by the laser oscillator 11, emitted from the laser head unit 13, and irradiated onto the processing object 1.

As shown in FIG. 2, the laser head 13 of the pulsed laser light irradiation device 10 is provided with a two-axis galvanometer mirror mechanism 130 consisting of two motors 131X and 131Y and two mirrors 132X and 132Y.

This two-axis galvanometer mirror mechanism 130 is capable of scanning the pulsed laser light Lp supplied from the laser oscillator 11 via the optical fiber 12 by changing the laser reflection angle independently in the X-axis and Y-axis directions.

The two-axis galvanometer mirror mechanism 130 functions as a scanning means for moving the irradiation position of the pulsed laser light Lp within the processing target area of the processing target object 1.

That is, the mirror 132X is rotated around the Z axis by the motor 131X, thereby scanning the pulsed laser light Lp irradiated onto the processing object 1 in the X axis direction.

In addition, the mirror 132Y is rotated around the X-axis by the motor 131Y, thereby scanning the pulsed laser light Lp irradiated onto the processing object 1 in the Y-axis direction.

The two mirrors 132X and 132Y in the two-axis galvanometer mirror mechanism 130 can each be replaced with a polygon mirror.

In other words, it is possible to irradiate a specified range while keeping the position of the laser head unit 13 of the pulsed laser light irradiation device 10 fixed.

In addition, in scanning with a galvanometer mirror or polygon mirror, the optical axis coincides with the normal direction at only one point, and the focal position of the pulsed laser light Lp is located on an arc, so this two-axis galvanometer mirror mechanism 130 irradiates the processing object 1 with the pulsed laser light Lp via a telecentric f-θ lens (or a telecentric optical system having optical characteristics equivalent to a telecentric f-θ lens) 133. In other words, in laser irradiation by galvanometer mirror scanning, the focal length to the processing object 1 changes, so it is necessary to restrict the laser irradiation range so that the irradiation position of the pulsed laser light Lp is scanned within a range where the reduction in laser processing capacity is small.

The manipulator 20 of the manipulator robot 40 is equipped with a multi-joint robot arm 21, and the laser head 13 of the pulsed laser light irradiation device 10 is attached to the tip 21A of the robot arm 21.

In other words, the laser head unit 13 of the pulsed laser light irradiation device 10 attached to the tip 21A of the robot arm 21 is capable of irradiating pulsed laser light Lp in any direction at any position within the working range of the manipulator robot 40.

The manipulator robot 40 also functions as an irradiation distance variable setting means for variably setting the laser irradiation distance at which the pulsed laser light Lp is irradiated from the laser head unit 13 onto the processing target area of the processing target object 1.

The overall control device 50 transmits predetermined robot operating conditions to the robot control unit 30 so that the laser head unit 13 of the pulsed laser light irradiation device 10 attached to the tip 21A of the robot arm 21 passes through a pre-set surface treatment work trajectory by the manipulator robot 40, and the robot control unit 30 controls the robot based on this and transmits the laser irradiation conditions of the pulsed laser light irradiation device 10 to the laser oscillator unit 11, which emits the laser based on this and operates the galvanometer mirror mechanism 130, thereby automatically controlling a series of surface treatment work operations by this surface treatment device 100.

The manipulator robot 40 in this substrate processing device 100 is basically controlled by programming the movement trajectory in advance through teaching using the robot control unit 30.

The laser irradiation pattern determined by the overall control device 50 is instructed to the laser oscillator 11, and the laser oscillator 11 performs the laser irradiation as specified by driving the galvanometer mirror mechanism 130 built into the laser head unit 13 based on the instruction from the overall control device 50.

The overall control device 50 receives a signal from the robot control unit 30 that the robot has arrived at the specified position where the laser is to be emitted, and sends a command to the laser oscillation unit 11 to start laser emission. The overall control device 50 also receives a signal from the laser oscillation unit 11 that laser emission is complete, and sends a command to the robot control unit 30 to start moving to the next irradiation position. Here, the robot movement completion signal and the laser emission completion signal may be exchanged directly between the robot control unit 30 and the laser oscillation unit 11 without going through the overall control device 50. In this case, it is possible to shorten the signal transmission time, but if it is desired to send additional information during that time, the method will be via the overall control device 50 as described above.

The overall control device 50 repeats the above control operations from the start position to the end position of the laser irradiation, thereby carrying out the base treatment work for the entire treatment target area of the treatment target 1.

That is, as shown in FIG. 3, the scanning range of the irradiation position of the pulsed laser light Lp by the two-axis galvanometer mirror mechanism 130, i.e., the size of the laser irradiation range, is, for example, a square basic area of 50 mm x 50 mm, and the entire processing target area of the processing target 1 is divided into (n-1) in the X direction and (m-1) in the Y direction, with the upper left end point being (1, 1), the point 50 mm forward in the X-axis direction being (1, 2), and so on until the end in the right direction is (1, n).

Next, the point 50 mm downward in the Y direction is set to (2,n), then the point 50 mm to the left in the X direction is set to (2,n-1), and so on, moving forward until the end point to the left is (2,1).

Then, repeat this operation until you reach the final point (m, n) at the bottom right.

The method of moving the manipulator 40 is to start from the upper left point (1,1) based on the above points, scan the irradiation range _AR11 shown with diagonal lines using the two-axis galvanometer mirror mechanism 130 to perform the base treatment work, and then move the laser head unit 13 to the next point (1,2), and similarly scan the irradiation range _AR12 shown with dots using the two-axis galvanometer mirror mechanism 130 to perform the base treatment work.

In addition, in scanning by the two-axis galvanometer mirror mechanism 130, as shown in _FIG. 4A (A), the galvanometer mirror 132X is moved back and forth in the X-axis direction while the galvanometer mirror 132Y is moved in the Y-axis direction, thereby irradiating in a zigzag pattern, or as shown in FIG. 4A (A), the irradiation locus RT _S2 is combined with the feed in the X-axis direction and the feed in the Y-axis direction to irradiate in a spiral pattern.

Furthermore, as shown in the irradiation locus RT _S3 in FIG. 4B, in the case of turning around and irradiating like the irradiation locus RT _S1 in FIG. 4A, the second and subsequent rows can be irradiated at intermediate positions between the irradiation positions of the previous row, and this can be continued up to the final bottom side.

Here, the substrate treatment device 100 treats, for example, hot-rolled steel sheets, etc., and the steel material that is the treatment object 1 is a steel material that is supplied to a treatment process in which the objects are attached and bonded to each other using coating materials (paints and lining materials) or adhesives, such as painting, bonding, and lining.

Figure 5 is a diagram showing a schematic cross-sectional structure of a steel material, which is the processing object 1 to be subjected to surface treatment by this surface treatment device 100, where (A) is a schematic cross-sectional view of the steel material before surface treatment, and (B) is a schematic cross-sectional view of the steel material after surface treatment.

As shown in Fig. 5A, in _an untreated state, a steel material which is a processing object 1 has an oxide film 2 of a two-layer structure with a thickness of t1, mainly composed of magnetite ( _Fe3O4 ) 2A and _hematite ( _Fe2O3 ) 2B _, attached to the surface of an Fe base material 1A. In the above-mentioned surface treatment device 100, the hematite ( _Fe2O3 ) 2B on the outermost surface of the processing object 1 is removed, and as shown in Fig. _5B , a surface treatment is performed to form a single-layer structure of only an oxide film 2A of a thickness of t2, mainly composed of highly adhesive magnetite ( _Fe3O4 ), on the surface of the Fe base material 1A.

In other words, the surface treatment method performed by this surface treatment device 100 is a surface treatment method that removes an oxide film 2 adhering to the surface of a steel material, which is a treatment object 1, by pulsed irradiation of laser light, and includes a scraping process step that removes hematite (Fe ₂ O ₃ ) from the surface layer of the oxide film 2, which has a two-layer structure of hematite (Fe ₂ O ₃ ) 2B and magnetite (Fe ₃ O ₄ ) 2A that constitutes the oxide film 2, by pulsed irradiation of laser light, as shown in Figure 6.

Specifically, the surface treatment method performed by the surface treatment device 100 consists of a laser density setting process ST1 and a scraping process ST2, as shown in the process diagram in Figure 6.

That is, in this substrate processing device 100, the overall control device 50 controls the operation of the pulsed laser light irradiation device 10 in the laser density setting process ST1 and the scraping process ST2 as follows.

First, in the laser density setting step ST1, the above-mentioned overall control device 50 initially sets the laser density per pulse of the laser light irradiated from the pulsed laser light irradiating device 10 to the steel material, which is the processing object 1, in the scraping processing step ST2 to a laser density effective for removing hematite (Fe ₂ O ₃ ) 2B from the surface layer of the above-mentioned oxide coating 2, based on the spot diameter d _p of the pulsed laser light based on the laser irradiation distance and the moving distance d _m of the irradiation position per pulse.

In the laser density setting step ST1, the initially set laser density is determined according to the required performance for the surface properties before and after processing of the object, and the spot diameter _dp can be set to an optimal value by defocusing the pulsed laser light irradiated in the scraping treatment step ST2.

Then, the above-mentioned overall control device 50 controls the operation of the pulsed laser light irradiation device 10 in the scraping treatment process ST2 so as to irradiate pulsed laser light having a laser density that is initially set based on the spot diameter _dp of the pulsed laser light based on the laser irradiation distance in the above-mentioned laser density setting process ST1 and the moving distance _dm of the irradiation position per pulse, thereby removing hematite (Fe ₂ O ₃ ) 2B from the surface layer of the above-mentioned oxide coating 2.

Here, the overall control device 50 can be configured to move the irradiation position of the pulsed laser light per pulse in the cleaning treatment step ST2 at a moving speed such that the moving distance d _m is within the range of the spot diameter d _p ×(1/2 to 1).

By changing the intensity of the pulsed laser light to remove the oxide scale, the condition of the remaining scale after laser irradiation changes.

7A and 7B are diagrams showing irradiation conditions when the moving speed of the irradiation position of the pulsed laser light, i.e., the scanning speed of the laser spot LS, is changed in order to change the irradiation energy of the pulsed laser light in this substrate processing apparatus 100, where (A) shows the case of a moving speed where the moving distance d _m1 per pulse is equal to the spot diameter d _p , (B) shows the case of a moving speed where the moving distance d _m2 per pulse is equal to (1/√2) times the spot diameter d _p , and (C) shows the case of a moving speed where the moving distance d _m3 per pulse is equal to (1/2) times the spot diameter d _p .

Here, the laser spot diameter _dp is the spot diameter of the laser light at the focal position obtained by the optical system of the pulsed laser light irradiation device 10 used, and in the following description, it is assumed that the shape is circular.

In addition, in FIG. 7, the movement speed in the X direction (horizontal direction) and the Y direction (vertical direction) are set to the same value, but this is not limited to this, and the X direction (horizontal direction) and the Y direction (vertical direction) may be set separately.

For example, as shown in FIG. 7A, when scraping is performed by moving at a speed where the moving distance per pulse, _dm1 , is equal to the spot diameter, _dp , scale remains in the unirradiated portions where the laser light is not irradiated, so that the proportion of hematite ( _Fe2O3 )2B removed in the scraping process ST2 is 78.5 _% in terms of area ratio on the surface of the oxide film after scraping.

FIG. 6B shows a case where the hematite (Fe ₂ O ₃ ) 2B on the surface layer of the oxide film 2 has been completely removed. However, depending on the application, it may not be necessary to remove 100% of the hematite (Fe ₂ O ₃ ) 2B.

As shown in FIG. 7B, by setting the moving speed of the moving distance d _m2 per pulse to (1/√2) times the spot diameter d _p , the laser spots LS can be overlapped to eliminate unirradiated areas, making it possible to achieve the most efficient state.

As shown in FIG. 7C, in the case of a moving speed in which the moving distance _dm3 per pulse is set to ½ times the spot diameter _dp , there are no unirradiated areas, but the overlap rate of the laser spot LS increases, and the energy input efficiency is inferior to that in the case of FIG. 7B.

According to these methods, (Fe ₂ O ₃ ) 2B can be removed from the portion irradiated with the laser, and hematite (Fe ₂ O ₃ ) 2B remains in the portion not irradiated with the laser light.

In FIG. 7A, the removal rate of hematite (Fe ₂ O ₃ ) is (area of four circles)/(area of a square circumscribing the four circles)=π/4=0.785 (78.5%).

In (B) and (C) of FIG. 7, the laser spots LS overlap, so the removal rate of hematite (Fe ₂ O ₃ ) is 100%.

To evaluate the performance of the laser scraper with different laser intensities (energy densities), paint was applied to each test piece, which was then dried and cured, and the adhesion strength was confirmed by a tensile test (pull-off test). The results are shown in Figure 8.

In Figure 8, (o) shows the steel plate surface as is (black surface) without laser irradiation, (a) shows the case where the laser was irradiated using the irradiation method in Figure 7 (A) above, and (c) shows the case where the laser was irradiated using the irradiation method in Figure 7 (C) above. Two test pieces were prepared for each test, and the average value of the results was normalized to '1.0' for the case of an untreated black surface.

These results show that laser scraping improves the adhesion of the coating and improves its performance as a surface treatment.

Furthermore, the laser intensity changes by changing the scanning speed of the laser light, but it is necessary to set appropriate laser irradiation conditions (scanning speed) based on the required quality performance and processing efficiency of the base processing, with the lower limit being a moving speed where the moving distance per _{pulse dm1} shown in FIG. 7A is equal to the spot diameter _dp , and the upper limit being a moving distance _dm3 that is (1/2) times the spot diameter dp shown in FIG. 7C.

Among the above conditions, the method of moving the spot by a moving distance _dm2 that is (1/√2) times the spot diameter _dp shown in FIG. 7B is considered to be a desirable method in terms of performance and efficiency, since no portion is left unirradiated with the laser light and the overlap rate can be made small.

From these test results, it was found that performance as a base treatment can be obtained by setting the proportion of hematite (Fe ₂ O ₃ ) 2B removed in the scraping treatment step ST2 to 78.5% or more in terms of area ratio on the surface of the oxide film after scraping treatment.

In this way, by carrying out a surface treatment method consisting of _a laser density setting process ST1 and a scraping process ST2 using the surface treatment device 100 and removing a certain amount (78.5% or more) of the low-adhesion hematite ( _Fe2O3 ) 2B, the surface of the steel material (treatment object 1) after laser scraping will be dominated by highly adhesive magnetite _{( Fe3O4} ) 2A, improving the adhesion of paint.

When higher adhesion is required, the scraping work may be carried out by a laser irradiation method, which has a high removal rate of hematite (Fe ₂ O ₃ ) 2B.

In addition to using a robot, the laser can be irradiated by a person holding the laser head by hand, but to ensure uniformity of the laser irradiation, it is preferable to use a mechanical device such as a robot.

1 Processing object, 1A Base material (Fe), 2 Oxide film, 2A Magnetite (Fe ₃ O ₄ ), 2B Hematite (Fe ₂ O ₃ ), 10 Laser irradiation device, 11 Laser oscillation section, 12 Optical fiber, 13 Laser head section, 20 Manipulator, 21 Robot arm, 21A Tip section, 30 Robot control section, 40 Manipulator robot, 50 Overall control device, 100 Base treatment device, 130 Galvano mirror mechanism, 131X, 131Y Motor, 132X, 132Y Mirror, 133 Telecentric f-θ lens

Claims (4)

A surface treatment device that removes a part of an oxide film having a two-layer structure of hematite (Fe ₂ O ₃ ) and magnetite (Fe ₃ O ₄ ) adhering to the surface of a steel material, which is a treatment object, by irradiating the steel material with a pulse of laser light,
a pulsed laser light irradiating device including an irradiation distance variable setting means for variably setting a laser irradiation distance for irradiating a processing target area of the steel material, which is the processing target, with a pulsed laser light, and a scanning means for moving an irradiation position of the pulsed laser light within a working area including the processing target area, and for irradiating the processing target area of the steel material, which is the processing target, with the pulsed laser light;
A control device for controlling the operation of the pulsed laser light irradiation device,
The control device controls the operation of the pulsed laser light irradiation device so as to initially set the laser density per _pulse of the pulsed laser light irradiated by the pulsed laser light irradiation device to a laser density effective for removing hematite (Fe ₂ O ₃ ) on the surface of the oxide film based on a spot diameter _dp of the pulsed laser light based on the laser irradiation distance and a movement distance dm of the irradiation position per pulse, and to move the irradiation position of the pulsed laser light within a working area including the treatment target area using the scanning means, and irradiate the pulsed laser light at the initially set laser density to perform a scraping process to remove hematite (Fe ₂ O ₃ ) on the surface of the oxide film. The surface treatment device according to claim 1, characterized in that the control device controls the operation of the pulsed laser light irradiation device so that the proportion of hematite (Fe ₂ O ₃ ) removed by the scraping process is 78.5% or more in terms of area ratio on the surface of the oxide film after the scraping process . The surface treatment device according to claim 1, characterized in that the control device controls the operation of the pulsed laser light irradiation device so that the scanning means moves the irradiation position of the pulsed laser light per pulse by a moving distance d _m at a moving speed within a range of the spot diameter d _p × (1/2 to 1 ). The surface treatment device according to any one of claims 1 to 3, characterized in that the control device sets the spot diameter _dp to an optimal value by defocusing the pulsed laser light irradiated onto the treatment target area of the steel material , which is the treatment target, using the irradiation distance variable setting means.