Method for cutting steel materials, and apparatus for cutting steel materials.
By forming a cut hole tangent to the cutting line and controlling the cutting torch's speed and position, the method addresses inefficiencies in cutting thick steel materials, reducing melted notches and enhancing cutting efficiency.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- JFE STEEL CORP
- Filing Date
- 2024-11-19
- Publication Date
- 2026-05-29
AI Technical Summary
The inefficiency in cutting thick steel materials due to the need to move the cutting torch from a pre-formed cut hole to the planned cutting line, leading to increased cutting time and the formation of excessive melted notches.
Forming a cut hole tangent to the planned cutting line, preheating the steel material with a preheating flame positioned at the point of contact between the cut hole and the cutting line, and moving the cutting torch along the cutting line while maintaining a controlled cutting speed to prevent excessive heat input.
Suppresses the occurrence of melted notches and improves cutting efficiency by eliminating the need to move the torch from the cut hole to the cutting line, ensuring uniform preheating and controlled cutting.
Smart Images
Figure 2026088599000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method for cutting steel materials and a steel material cutting device.
Background Art
[0002] When cutting a steel material, for example, a thick steel plate with a plate thickness of 40 mm or more, gas cutting is widely used. When starting gas cutting of the thick steel plate from a portion inside the end rather than at the end of the thick steel plate, a hole penetrating in the plate thickness direction of the thick steel plate (hereinafter referred to as a cut hole) is formed in advance in the inner portion where the gas cutting is started, for example, by a drill. A torch is arranged in the cut hole, and gas cutting of the thick steel plate is started from the cut hole.
[0003] An example of such gas cutting is disclosed in Patent Document 1. In the steel material cutting method disclosed in Patent Document 1, a cut hole for starting gas cutting is formed in the steel material by a laser beam, and gas cutting is started from the cut hole.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] When forming a notch in a thick steel plate to be cut, the notch is usually formed using a drill or a laser beam as disclosed in Patent Document 1, at a position a few millimeters away from the planned cutting line, in the part of the plate that will not become part of the product, known as the crop. This is to avoid forming holes or defects in the part that will become part of the product when forming the notch. When starting gas cutting, for example, a torch is placed in the center of the notch from above the thick steel plate. The torch is ignited to generate a preheating flame, and the thick steel plate is preheated by the preheating flame. Oxygen gas is injected from the torch onto the preheated thick steel plate to oxidize it, and the torch is moved so that it approaches the planned cutting line from the notch. In this way, the part of the thick steel plate between the notch and the planned cutting line is melted and cut by the heat of oxidation. When the outer edge of the preheating flame of the torch and the planned cutting line are approximately aligned in a top view, the torch is moved along the planned cutting line, and the thick steel plate is gas cut along the planned cutting line. However, when performing gas cutting in this manner, the torch must be moved from the cutting hole to approach the cutting line, as described above, before gas cutting begins along the planned cutting line. As a result, the cutting time becomes longer and the efficiency of the cutting work decreases.
[0006] Therefore, in order to suppress the increase in cutting time and decrease in cutting efficiency caused by moving the torch from the cut hole towards the cutting line, it is conceivable to position the torch off-center towards the cutting line within the cut hole, rather than in the center. That is, the cutting torch is positioned so that the preheating flame of the torch hits the area between the cut hole and the cutting line when viewed from above. By positioning the torch in this way, after preheating, the torch can be immediately moved along the cutting line to start gas cutting, thereby suppressing the increase in cutting time and the decrease in cutting efficiency. However, the area between the cut hole and the cutting line is excessively preheated by the preheating flame. Therefore, when gas cutting is started by injecting oxygen gas from the torch, the area that was hit by the preheating flame during preheating may be excessively melted by oxidation heat, potentially resulting in a large melted notch.
[0007] On the other hand, recent improvements in the positioning accuracy of drills and laser beams when forming cut holes have made it possible to stably form cut holes in contact with the planned cutting line. This is expected to suppress the increase in cutting time and decrease in cutting efficiency caused by gas cutting from the cut hole towards the planned cutting line, but there was still room for improvement in suppressing melting notches.
[0008] The present invention was made to solve the above problems and aims to provide a method for cutting steel materials and a steel material cutting apparatus that can suppress the occurrence of erosion notches. [Means for solving the problem]
[0009] The means to solve the above problems are as follows: [1] A method for cutting steel, wherein a cutting hole is formed through the steel material in the thickness direction with the cutting line as the tangent, the steel material is preheated by generating a preheating flame, and a cutting torch is moved along the cutting line to cut the steel material by injecting a gas that oxidizes the preheated steel material and melting the steel material with the heat of oxidation of the steel material, the method comprising: a positioning step of positioning the outer edge of the preheating flame at the point of contact between the cutting hole and the cutting line; and a cutting step of moving the cutting torch along the cutting line while the outer edge is in contact with the cutting line, cutting the steel material from the cutting hole to a length of at least three times the inner diameter of the cutting hole at the starting cutting speed of the cutting torch when cutting the steel material is started, wherein in the cutting step, the starting cutting speed is 60% or more and 70% or less of a predetermined steady cutting speed. [2] The method for cutting steel materials according to [1], wherein in the cutting step, the cutting speed of the cutting torch when it exits the steel material on the front side of the steel material in the direction of movement of the cutting torch along the planned cutting line and the cutting of the steel material is completed is 20% or less of the steady cutting speed. [3] A steel cutting apparatus comprising: a cutting torch that generates a preheating flame to preheat the steel material and injects a gas that oxidizes the steel material to melt and cut the steel material by the heat of oxidation of the steel material; a notch forming device that forms a notch in the steel material through the thickness direction of the steel material with the planned cutting line as the tangent; and a moving device that positions the outer edge of the preheating flame at the point of contact between the notch and the planned cutting line, and moves the cutting torch along the planned cutting line while the outer edge remains in contact with the planned cutting line, cutting the steel material from the notch to a length of at least three times the inner diameter of the notch at the starting cutting speed of the cutting torch when cutting the steel material begins. [Effects of the Invention]
[0010] According to the present invention, the occurrence of melted notches when cutting steel can be suppressed. Furthermore, since the cutting hole is formed in the steel so as to be tangent to the planned cutting line, the cutting torch does not need to be moved from the cutting hole towards the planned cutting line when starting to cut the steel, thus preventing the cutting of the steel between them. Therefore, the efficiency of the cutting work can be improved. [Brief explanation of the drawing]
[0011] [Figure 1] This figure shows the configuration of the steel cutting device according to this embodiment. [Figure 2] This is a perspective view showing a steel material with cut holes formed in it. [Figure 3] This is a flowchart illustrating the method for cutting steel materials according to this embodiment. [Figure 4] This diagram shows the state where the outer edge of the preheating flame of the cutting torch is positioned at the point of contact between the planned cutting line and the cutting hole. [Modes for carrying out the invention]
[0012] The following describes embodiments of the present invention (hereinafter referred to as "this embodiment"). This embodiment is a preferred example of the present invention and is not limiting in any way to the present invention.
[0013] (Steel cutting device) Figure 1 shows the configuration of a steel cutting device according to this embodiment. The cutting device 1 shown in Figure 1 is a gantry-type cutting machine that cuts steel material S to predetermined product dimensions. The cutting device 1 also cuts off the portion of the steel material S that will not become the product, called the crop. The cutting device 1 includes a pair of rails 2, a gantry-type frame 3, a base plate 4, a cutting torch 5, a notch forming device 6, a slider 7, and a control device 8. Examples of steel material S include metal materials made from iron-based materials, such as thick steel plates, with a plate thickness of approximately 40 mm to 150 mm.
[0014] A pair of rails 2 extend in the y-direction in Figure 1 and are laid on a predetermined mounting surface with a predetermined width in the x-direction in Figure 1. A gantry frame 3 is installed on the rails 2 so as to be movable along the rails 2. The gantry frame 3 is equipped with a movable actuator (not shown). The gantry frame 3 is made movable along the rails 2 in the y-direction in Figure 1 by the movable actuator.
[0015] The surface plate 4 is on which the steel material S is placed. In the example shown in Figure 1, the surface plate 4 extends in the x-direction of Figure 1. The surface plate 4 is installed between a pair of rails 2 at regular intervals in the y-direction of Figure 1.
[0016] The cutting torch 5 is used to gas-cut steel material S. In the example shown in Figure 1, the cutting torch 5 is attached to the beam 3a of the gantry frame 3 via a slider 7. The cutting torch 5 generates a preheating flame to preheat the steel material S, and then injects oxygen gas into the preheated steel material S to cause an oxidation reaction, melting the steel material S with the heat of oxidation and cutting it. For this reason, the cutting torch 5 is connected to a combustion gas supply source (not shown) that supplies combustion gas to generate the preheating flame to the cutting torch 5, and an oxygen gas supply source (not shown) that supplies oxygen gas to the cutting torch 5. The slider 7 is configured to be movable in the width direction (x direction in Figure 1) of the gantry frame 3.
[0017] The cutting torch 5 moves in the y-direction or x-direction shown in FIG. 1 along with the movement of the gantry frame 3 and the slider 7 to cut the steel material S. The gantry frame 3 and the slider 7 correspond to the moving device in the steel material cutting device according to the present embodiment. When the steel material S is cut by the cutting torch 5, a cutting groove along the moving direction of the cutting torch 5 is formed in the steel material S. Note that the position information of the cutting torch 5 during the cutting operation of the steel material S is sequentially detected as position information (x, y coordinates) on the surface plate 4 or on the steel material S using a position measuring device (not shown) attached to the cutting device 1 as the cutting torch 5 moves. Further, the detected position information is stored in a storage unit (not shown) of the control device 8.
[0018] The cut hole forming device 6 is a device that forms a cut hole, which is the cutting start position of the steel material S, in the steel material S. Examples of the cut hole forming device 6 include a laser drilling machine, a ball mill, or NC machining equipment. In the laser drilling machine, a laser is irradiated onto the steel material S to form a cut hole. In the ball mill or NC machining equipment, the steel material S is fixed and a drill attached to a rotating chuck is used to form a cut hole in the steel material S. In the example shown in FIG. 1, the cut hole forming device 6 is attached to the gantry frame 3 via the slider 7 in the same manner as the cutting torch 5. The cut hole forming device 6 may be made movable via a separately installed moving device instead of being made movable via the same slider 7 as the cutting torch 5. Note that when forming a cut hole in a thick steel plate, it is preferable to use the ball mill or NC machining equipment among the laser drilling machine, the ball mill, and the NC machining equipment in terms of hole drilling accuracy. In order to preheat the steel material S substantially uniformly in the plate thickness direction and start gas cutting, the cut hole is preferably formed to penetrate in the plate thickness direction of the steel material S.
[0019] The slider 7 is configured to move the cutting torch 5 and the cut hole forming device 6 in the x direction in FIG. 1. The slider 7 is attached to a beam 3a extending in the width direction of the cutting device 1 (the x direction in FIG. 1) of the portal frame 3 so as to be movable in the x direction of FIG. 1. Further, the slider 7 has an actuator (not shown). By operating the actuator, the cutting torch 5 and the cut hole forming device 6 are moved in the x direction in FIG. 1.
[0020] Further, the slider 7 has a lifting device 9 for moving the cutting torch 5 and the cut hole forming device 6 in the z direction in FIG. 1. The lifting device 9 has a movable part (not shown) movable in the z direction in FIG. 1 and a lifting actuator (not shown) for moving the movable part in the z direction in FIG. 1. The cutting torch 5 and the cut hole forming device 6 are connected to the movable part. When the lifting actuator of the lifting device 9 is operated and the movable part moves in the z direction in FIG. 1, the cutting torch 5 and the cut hole forming device 6 move in the z direction in FIG. 1 accordingly.
[0021] The control device 8 controls the operations of the cutting torch 5, the slider 7, and the lifting device 9 based on sensor information acquired from various sensors provided in the cutting device 1, information input to the control device 8, and information stored in a storage unit (not shown) of the control device 8. The control device 8 may be, for example, a configuration in which peripheral devices are added as necessary to a general-purpose programmable logic controller (PLG), a personal computer, or the like. Alternatively, it may be a control device terminal connected to a main control device (not shown) by wire or wirelessly. Examples of the sensor information include a signal from a combustion gas flow sensor that detects the supply amount of combustion gas to the cutting torch 5, a signal from an oxygen gas flow sensor that detects the supply amount of oxygen gas, and a signal from a position measuring device that detects the position of the cutting torch 5.
[0022] Information input to the control device 8 includes the planned cutting line CL when cutting the steel material S, the cutting start position, and the movement speed of the cutting torch 5, i.e., the cutting speed of the steel material S. This information is input to the control device 8 by an input unit (not shown) and stored in the memory unit of the control device 8. The planned cutting line CL, the cutting start position, and the cutting speed are predetermined based on the size of the crop of the steel material S, the thickness of the steel material S, and the size of the product to be manufactured by cutting the steel material S.
[0023] The cutting start position of the steel material S is the aforementioned cutting hole where the cutting torch 5 is positioned. Figure 2 is a perspective view showing the steel material S with the cutting hole 10 formed therein. As shown in Figure 2, the cutting hole 10 is formed tangent to the cutting line CL at one end of the steel material S in the length direction, penetrating in the thickness direction of the steel material S. The cutting torch 5 is positioned above the cutting hole 10, and a preheating flame is generated above the cutting hole 10. Therefore, the inner diameter of the cutting hole 10 is preferably about 3 to 4 times the outer diameter of the nozzle and preheating flame of the cutting torch 5 (not shown). If the outer diameter of the preheating flame is 3 mm, the inner diameter of the cutting hole 10 is preferably about 10 mm. As described above, the cutting line CL is predetermined according to the size of the crop of the steel material S and the size of the product to be manufactured by cutting the steel material S. The cutting line CL is shown as a dashed line in Figure 2.
[0024] The cutting end position of the steel material S is set at the point where the cutting torch 5 exits the steel material S in the direction of movement of the cutting torch 5 along the planned cutting line CL. In other words, the cutting end position of the steel material S is set on the outside of the steel material S and on the forward side in the aforementioned direction of movement. In gas cutting, the lower part of the steel material S is cut slightly after the upper part in the thickness direction of the steel material S. To ensure that the lower part of the steel material is cut, the movement of the cutting torch 5 is stopped when the cutting torch 5 has cut through the steel material S and exited it on the forward side of the steel material S in the direction of movement of the cutting torch 5 along the planned cutting line CL.
[0025] (Method of cutting steel materials) Figure 3 is a flowchart illustrating the steel cutting method according to this embodiment. In the example shown in Figure 3, the outer edge of the preheating flame of the cutting torch 5 is positioned at the contact point P between the notch 10 and the planned cutting line CL (positioning step, step S101). For example, a steel material S with a pre-formed notch 10 tangent to the planned cutting line CL is prepared, and the steel material S is placed on the base plate 4 of the cutting device 1 shown in Figure 1. Position information of the planned cutting line CL and the notch 10 of the steel material S on the base plate 4 is input to the control device 8, and the movement of the gantry frame 3 and the cutting torch 5 by the slider 7 is controlled by the control device 8 based on this position information. In this way, the position of the cutting torch 5 in the y-direction and x-direction in Figure 1 is controlled to position the outer edge 11a of the preheating flame 11 of the cutting torch 5 at the contact point P between the notch 10 and the planned cutting line CL. Figure 4 shows this state. The outer edge 11a of the preheating flame 11 refers to the boundary between the preheating flame 11 and the surrounding air. When the preheating flame 11 is arranged concentrically around an oxygen gas (cutting oxygen) injection hole (not shown) located in the center of the cutting torch 5, it refers to the enveloping surface of the boundary between the concentrically arranged preheating flame and the surrounding air.
[0026] Next, the process proceeds to step S102 (cutting process), where the steel material S is preheated for a predetermined time (hereinafter referred to as preheating time) by the preheating flame 11 of the cutting torch 5. For example, when the outer edge 11a of the preheating flame 11 is positioned at the contact point P, the measurement of the preheating time is started by a timer (not shown). After the preheating time has elapsed, oxygen gas is injected from the cutting torch 5 onto the steel material S. The control device 8 also operates the actuator of the slider 7 and the moving actuator of the gantry frame 3. In this way, oxygen gas is injected from the cutting torch 5 onto the steel material S, and the cutting torch 5 is moved along the planned cutting line CL while the outer edge 11a of the preheating flame 11 remains in contact with the planned cutting line CL.
[0027] The operator may initiate the timer-based measurement of the preheating time. Alternatively, the control device 8 calculates the point in time when the outer edge 11a of the preheating flame 11 is positioned at the contact point P, based on the positional information of the planned cutting line CL and cutting hole 10 of the steel material S on the surface plate 4, and the respective movement amounts of the gantry frame 3 and slider 7. At this calculated point, the control device 8 may activate the timer to begin measuring the preheating time. The preheating time is determined by the type of combustion gas, the ignition temperature of the steel material S, and the specific heat of the steel material S, and can be determined in advance. Conventional acetylene gas and propane gas can be used as combustion gases. High-purity oxygen gas, conventionally used in gas cutting, can be used as the oxygen gas. The preheating temperature of the steel material may be 900°C, which is the ignition temperature of iron, or higher.
[0028] Then, the cutting torch 5 is moved along the planned cutting line CL, and when the cutting torch 5 cuts through the steel material S on the front side in the direction of movement of the cutting torch 5, the movement of the cutting torch 5 is stopped. At the same time, the supply of combustion gas and oxygen gas to the cutting torch 5 is stopped, and the cutting is completed (cutting completion process, step S103).
[0029] Here, we will explain the movement speed of the cutting torch 5, that is, the cutting speed of the steel material S. In step S102 of Figure 2, the cutting speed at the time the movement of the cutting torch 5 begins (hereinafter referred to as the starting cutting speed) is preferably 60% to 70% of the steady cutting speed. The steady cutting speed is predetermined considering the material of the steel material S, the plate thickness, and whether the quality of the cut surface produced by gas cutting is of a quality that can be shipped as a product. For example, the steady cutting speed may be determined by conducting a preliminary gas cutting test on the steel material S, or it may be determined based on past gas cutting results. In other words, the steady cutting speed means the maximum cutting speed at which the steel material S can be cut while maintaining the desired quality.
[0030] The reason for setting the initial cutting speed to 60% to 70% of the steady cutting speed is explained below. If the initial cutting speed is less than 60% of the steady cutting speed, it means that the movement speed of the cutting torch 5 is slower than the optimal range. As a result, excessive heat input from the cutting torch 5 to the steel material S may occur, potentially leading to the formation of melted notches. The optimal range for the movement speed of the cutting torch 5 refers to the movement speed of the cutting torch 5 that allows for the cutting of the steel material S while suppressing the formation of melted notches.
[0031] When the initial cutting speed exceeds 70% of the steady-state cutting speed, it means that the cutting torch 5 is moving faster than the optimal range. Also, at the start of gas cutting of the steel material S, the steel material S is at a low temperature or nearly room temperature, and preheating may take time. Therefore, the high speed of the cutting torch 5 and the low temperature of the steel material S can suppress excessive heat input from the cutting torch 5 to the steel material S, thereby suppressing the occurrence of melted notches. However, because the cutting torch 5 moves at a high speed, there is a possibility that the cutting torch 5 will move forward in the direction of travel before the steel material S is cut along its entire length in the thickness direction. As a result, the upper side of the steel material S is cut in the thickness direction, but the lower side is not cut. In the following explanation, the uncut areas will be referred to as uncut areas.
[0032] If uncut areas occur, oxygen gas cannot pass linearly through the entire length of the cut hole 10 in the thickness direction of the steel material S, causing oxygen gas to accumulate in the uncut areas. This can lead to excessive oxidation of the steel material S in the uncut areas, potentially causing melting due to oxidation heat and resulting in large erosion notches. Large erosion notches necessitate extensive grinding of the cut surface after cutting the steel material S. For these reasons, it is preferable that the initial cutting speed be 60% to 70% of the steady cutting speed. In this case, erosion notches can be reduced or their occurrence can be suppressed, and the effort required for post-processing such as grinding of the cut surface after cutting the steel material S can be reduced. To further reduce the occurrence of erosion notches and the effort required for post-processing, it is even more preferable that the initial cutting speed be 63% to 67% of the steady cutting speed.
[0033] The travel length of the cutting torch 5 that maintains the initial cutting speed will be explained below. This travel length is ensured for the following reasons: At the start of cutting, the steel material S is at a low temperature or nearly room temperature. Therefore, in order to ensure time for the steel material S to be heated by the heat of oxidation during gas cutting, and to shorten the preheating time when the speed is increased thereafter, it is necessary to maintain the initial cutting speed within a certain range of travel length of the cutting torch 5. The travel length of the cutting torch 5 that should maintain the initial cutting speed must be at least 3 times the inner diameter of the cutting hole from the cutting start position (cut hole), and preferably 3 to 4 times.
[0034] Then, when the cutting torch 5 reaches a position at least three times the length of the inner diameter of the cut hole 10 from the cutting start position (cut hole), the cutting speed is changed from the starting cutting speed to an intermediate cutting speed or a steady cutting speed. The intermediate cutting speed is higher than the starting cutting speed and lower than the steady cutting speed. From the viewpoint of suppressing the occurrence of melted notches after increasing the cutting speed from the starting cutting speed and the effort required for post-processing of the cut surface, it is preferable to change from the starting cutting speed to an intermediate cutting speed and then to a steady cutting speed.
[0035] It is preferable to change from an intermediate cutting speed to a steady cutting speed when the cutting torch 5 reaches a position 8 to 10 times the inner diameter of the cutting hole 10 from the cutting start position (cut hole). This is for the same reasons as when changing from the starting cutting speed to an intermediate cutting speed. In other words, it is to ensure time for the steel material S to be heated by the oxidation heat during gas cutting, thereby shortening the preheating time when the speed is increased afterward.
[0036] Furthermore, the cutting speed of the cutting torch 5 when the gas cutting of the steel material S is completed (hereinafter sometimes referred to as the cut-through speed or completion speed) is preferably lower than the steady-state cutting speed. The reason for this is explained below. For example, when gas cutting a steel material S by applying the cutting torch 5 to the top surface of the steel material S which is placed horizontally on a surface plate 4, heat is transferred from the top surface to the bottom surface of the steel material S. In other words, gas cutting proceeds from the top surface to the bottom surface in the thickness direction of the steel material S. If the cut-through speed when the gas cutting of the steel material S is completed is excessive, it is possible that at the end portion of the steel material S in the direction of travel of the cutting torch 5 along the planned cutting line CL, the top surface may be cut in the thickness direction, but the bottom surface may remain uncut. To avoid such a situation, it is preferable that the cut-through speed is lower than the steady-state cutting speed.
[0037] Specifically, the through-cutting speed is preferably 20% or less of the steady-state cutting speed. The point at which the steady-state cutting speed is changed to the through-cutting speed is preferably adjusted as appropriate according to the material of the steel material S, the plate thickness, and the operating conditions of the steel material cutting device shown in Figure 1 when gas cutting the steel material S at the steady-state cutting speed. As described above, the bottom side of the steel material S is cut slightly later than the top side in the plate thickness direction. Therefore, it is preferable to reduce the through-cutting speed from the steady-state cutting speed at a position upstream of the end portion of the steel material S in the direction of travel of the cutting torch 5 by the length of the bottom side that is cut later than the top side in the direction of movement of the cutting torch 5.
[0038] Furthermore, it is preferable that the stopping position of the cutting torch 5 be downstream of the steel material S in the direction of travel of the cutting torch 5 along the planned cutting line CL. In other words, it is preferable that the cutting torch 5 cuts through the steel material S and then moves and stops. This is to ensure that the steel material S is reliably gas-cut along the entire length of the planned cutting line CL.
[0039] According to the embodiment described above, gas cutting of the steel material S is started from a notch 10 tangent to the planned cutting line CL. Therefore, there is no portion to be cut between the notch 10 and the planned cutting line CL, thereby shortening the cutting time and improving the efficiency of the cutting work. In addition, the outer edge 11a of the preheating flame 11 is positioned at the contact point P between the notch 10 and the planned cutting line CL to preheat the steel material S. Since the preheating flame 11 is not applied directly to the steel material S, excessive heat input to the steel material S can be suppressed. Therefore, when oxygen gas is injected afterward to start gas cutting, it is possible to suppress the occurrence of large melting notches caused by excessive heat input. Furthermore, since the notch 10 is formed to penetrate the thickness direction of the steel material S, the steel material S can be preheated and gas cut along its entire length in the thickness direction. In other words, even thick steel plates of about 40 mm to 150 mm can be cut while suppressing the occurrence of melting notches and a decrease in cutting work efficiency.
[0040] The notch-forming device 6 may be movable by the same moving mechanism as the cutting torch 5, or it may be movable via a separate moving mechanism from the cutting torch 5. In either case, it is possible to form the notch 10 in the steel material S while it is placed on the base plate 4 for gas cutting, and then proceed with gas cutting without moving or transporting the steel material S. This eliminates the time and effort required to move the steel material S from the notch-forming work area to the gas cutting area. [Examples]
[0041] This section describes examples of gas cutting of steel materials S by changing the distance between the cutting hole and the planned cutting line, and the cutting speed, in the steel material cutting method according to this embodiment. Table 1 summarizes the distance, cutting speed, and evaluation for Examples 1 to 3 and Comparative Examples 1 to 4.
[0042] [Table 1]
[0043] (Example 1) A carbon steel plate with a thickness of 110 mm was prepared, and a 10 mm inner diameter cut hole was drilled into the steel plate, tangential to the planned cutting line. LPG was used as the combustion gas for the preheating flame of the cutting torch, generating a preheating flame with an outer diameter of 3.2 mm. The steady cutting speed with the cutting torch was set to 165 mm / min, and the starting cutting speed was set to 60% of the steady cutting speed, which was maintained until 30 mm from the cut hole. After that, the speed was increased to the intermediate cutting speed. The intermediate cutting speed was set to 80% of the steady cutting speed, which was maintained until 100 mm from the cut hole. After that, the speed was increased to the steady cutting speed, and then decelerated to the cut-through cutting speed just before the end of the steel plate. The cut-through cutting speed was set to 20% of the steady cutting speed.
[0044] (Example 2) This is an example of gas cutting of carbon steel material in the same manner as in Example 1, except that the initial cutting speed was set to 65% of the steady cutting speed.
[0045] (Example 3) This is an example of gas cutting of carbon steel material in the same manner as in Example 1, except that the initial cutting speed was set to 70% of the steady cutting speed.
[0046] (Comparative Example 1) This is an example of gas cutting of carbon steel material in the same manner as in Example 1, except that the distance between the cutting hole and the planned cutting line was set to 2.0 mm and the starting cutting speed was set to 80% of the steady cutting speed.
[0047] (Comparative Example 2) This is an example of gas cutting of carbon steel material in the same manner as in Example 1, except that the distance between the cutting hole and the planned cutting line was set to 1.0 mm and the starting cutting speed was set to 80% of the steady cutting speed.
[0048] (Comparative Example 3) This is an example of gas cutting of carbon steel material in the same manner as in Example 1, except that the initial cutting speed was set to 80% of the steady cutting speed.
[0049] (Comparative Example 4) This is an example of gas cutting of carbon steel material in the same manner as in Example 1, except that the initial cutting speed was set to 25% of the steady cutting speed and the intermediate cutting speed was set to 70% of the steady cutting speed.
[0050] (Comparative Example 5) This is an example of gas cutting of carbon steel material in the same manner as in Example 1, except that the initial cutting speed was set to 50% of the steady cutting speed.
[0051] After gas cutting carbon steel material, the width and depth of the erosion notches formed on the cut surface of the product were compared with the width and depth of a predetermined standard sample of erosion notches. The width of the erosion notch refers to the size of the erosion notch in the direction of movement of the cutting torch, and the depth of the erosion notch refers to the size of the erosion notch in the direction perpendicular to the cut surface. If the width of the erosion notch formed on the cut surface of the product was narrower than the width of the standard sample, and the depth of the erosion notch formed on the cut surface of the product was shallower than the depth of the standard sample, the width and depth of the erosion notch were judged to be within the acceptable range. In such cases, "○" was marked in the evaluation column of Table 1. If the width or depth of the erosion notch was outside the acceptable range, "×" was marked in the evaluation column of Table 1. Among the examples where the width and depth of the erosion notch were judged to be within the acceptable range, the example with the largest difference from the standard sample was marked with "◎" in the evaluation column of Table 1.
[0052] (evaluation) In Comparative Examples 1 and 2, after placing the cutting torch in the notch, the cutting torch is moved toward the planned cutting line until the outer edge of the preheating flame of the cutting torch touches the planned cutting line, and gas cutting is performed. After the outer edge of the preheating flame of the cutting torch touches the planned cutting line, the cutting torch is moved along the planned cutting line and gas cutting is performed. As a result, the cutting time is longer and the cutting work efficiency is reduced because the cutting torch placed in the notch is moved toward the planned cutting line and gas cutting is performed. In addition, because gas cutting is performed from the notch toward the planned cutting line, a larger erosion notch was formed at the point where the outer edge of the preheating flame of the cutting torch first touched the planned cutting line than in the standard sample. Furthermore, the starting cutting speed was 80% of the steady cutting speed, which is higher than in the other Comparative Examples 3 and 4, and Examples 1 to 3. As a result, a wider and deeper erosion notch was formed on the lower side in the thickness direction of the carbon steel material than on the upper side. As mentioned above, this is thought to be because the high initial cutting speed resulted in uncut areas, where oxygen gas accumulated, causing excessive oxidation and melting of the steel material S, leading to the formation of large erosion notches.
[0053] In Comparative Example 3, since the cutting hole was formed tangent to the planned cutting line, gas cutting was not performed from the cutting hole toward the planned cutting line, thus suppressing a decrease in cutting efficiency. However, the starting cutting speed was the same as in Comparative Examples 1 and 2, at 50% of the steady cutting speed, which resulted in a large melting notch.
[0054] In contrast to Comparative Examples 1-3, Comparative Examples 4 and 5 had a low initial cutting speed. As a result, excessive heat input from the cutting torch to the carbon steel material occurred, causing larger erosion notches in the carbon steel material of the product compared to the standard sample.
[0055] In Examples 1-3, the width of the eroded notch was narrower than that of the standard sample, and the depth of the eroded notch was also shallower than that of the standard sample. In Example 2, the width of the eroded notch was narrowest. These results are thought to be because, in Examples 1-3, the starting cutting speed was within the aforementioned numerical range, which suppressed excessive heat input to the carbon steel material and prevented the occurrence of uncut areas. [Explanation of symbols]
[0056] 1 cutting device 2 rails 3 Gate-type frame 3a beam 4. Surface plate 5 Cutting Torch 6 Cut hole forming device 7 Sliders 8 Control device 9. Lifting device 10 Cut holes 11 Preheating flame 11a Outer edge of preheating flame S steel material
Claims
1. A cutting method for steel is provided, wherein a cutting hole is formed through the steel material in the thickness direction with the cutting line as the tangent, the steel material is preheated by generating a preheating flame, and a gas that oxidizes the preheated steel material is injected to melt and cut the steel material by the heat of oxidation, and the cutting torch is moved along the cutting line to cut the steel material. A positioning step of positioning the outer edge of the preheating flame at the point of contact between the notch and the planned cutting line, The cutting process includes moving the cutting torch along the cutting line, with the outer edge portion in contact with the cutting line, from the cut hole to a length of at least three times the inner diameter of the cut hole, at the starting cutting speed of the cutting torch when cutting the steel material, thereby cutting the steel material. A method for cutting steel, wherein in the cutting step, the starting cutting speed is 60% or more and 70% or less of a predetermined steady cutting speed.
2. The method for cutting steel according to claim 1, wherein, in the cutting step, the cutting speed of the cutting torch when it exits the steel material on the front side of the steel material in the direction of movement of the cutting torch along the planned cutting line and the cutting of the steel material is completed is 20% or less of the steady cutting speed.
3. A cutting torch that generates a preheating flame to preheat the steel, then injects a gas that oxidizes the steel, melting and cutting the steel with the heat of oxidation, A cutting hole forming device for forming a cutting hole in the steel material that penetrates the steel material in the thickness direction, with the cutting line tangent to the cutting line, A steel cutting device comprising: a moving device that positions the outer edge of the preheating flame at the point of contact between the notch and the planned cutting line, and moves the cutting torch along the planned cutting line, with the outer edge in contact with the planned cutting line, from the notch to a length of at least three times the inner diameter of the notch, at the starting cutting speed of the cutting torch when cutting the steel material is started, thereby cutting the steel material.