Flame cutting method for slender and thick plates in hot environment

Abstract

A flame cutting method for slender, thick plate in a muggy environment involves key processes and parameters: using a cutting torch to synchronously flame cut a wide, thick steel plate lengthwise into multiple, identically sized, slender, thick plate pieces, with edge margins ranging from 10 to 50 mm. One cutting torch is used for the edge slits, while two torches are used for the center slits. The leading and edge torches are controlled to have identical cutting parameters for simultaneous cutting of the slender pieces, while the trailing torch acts as a heating element, providing additional heat to the center slit after cutting, thereby reducing thermal stress caused by the temperature drop difference between the edge and center slits. This method can effectively mitigate side bending when flame cutting thick steel plates with a thickness of 50 to 100 mm into slender pieces in an ambient temperature ≥30°C and a relative humidity ≥70%.

Description

Technical Field

[0001] The invention belongs to the technical field of steel plate processing and relates to a flame cutting method for a slender thick plate in a hot and humid environment. Background Art

[0002] When using flame to cut steel plates into long, thin strips, uneven thermal stress often causes the strips to bend sideways. Chinese patent CN105728886 discloses a symmetrical flame cutting method using multiple torches, which improves the sideways bending problem for thin strips. However, the heat dissipation conditions of the workpiece after flame cutting the edges and the middle of the steel plate are different. This symmetrical flame cutting method has its limitations, especially for thicker steel plates, under high ambient temperature and humidity conditions. Chinese patent CN105252127 proposes a "point-retention" cutting method, which leaves some areas uncut along the cutting path. This allows the workpiece to be subjected to rigid forces during the gas cutting process without deformation. After the remaining areas are gas-cut and a new internal stress balance is achieved, the reserved uncut areas are cut off. This effectively reduces deformation; however, for thick steel plates, re-igniting the flame after leaving the points uncut can easily form large scars at the junction, reducing the size of the area and easily causing stress concentration and microcracks, which can become the source of cracking. Summary of the Invention

[0003] In view of the shortcomings of the above-mentioned existing technologies, the purpose of the present invention is to provide a flame cutting method for slender thick plate parts in a hot and humid environment. By using this method, when thick steel plates with a thickness of 50~100mm are flame cut into slender parts under an ambient temperature ≥30℃ and a relative humidity ≥70%, the side bending problem of the slender parts can be effectively alleviated.

[0004] The technical solution of the present invention:

[0005] A flame cutting method for slender thick plates in a muggy environment, wherein the muggy environment refers to an ambient temperature ≥30°C and a relative humidity ≥70%. The slender thick plates have a thickness of 50-100 mm and an aspect ratio ≥20. The key processes and parameters of the flame cutting method include:

[0006] (1) Use a cutting torch to flame cut the thick steel plate synchronously along the length direction into multiple slender thick plates of the same size, with the edge allowance of the steel plate being 10~50mm;

[0007] (2) For edge cutting, a cutting torch is set up, so that it is perpendicular to the surface of the steel plate and the length of the air flow ejected during cutting exceeds the thickness of the steel plate by 8 to 12 mm; the edge cutting refers to the cutting seam formed for cutting the edge allowance;

[0008] (3) For the middle slit, two cutting torches are set up, both of which are perpendicular to the surface of the steel plate and ensure that the front cutting torch and the rear cutting torch are on the same cutting path. At the same time, the front cutting torch and the side cutting torch are arranged in a row in the width direction of the steel plate and use the same cutting parameters such as cutting nozzle model, flame intensity, cutting speed, etc. The rear cutting torch uses a neutral flame to heat the slit. The middle slit refers to the slit that is much farther away from the edge than the edge margin.

[0009] (4) Control the cutting speed during cutting v (mm / min)=320-(1.1~1.3) t ,in t is the thickness of the steel plate (mm); at the same time, set the relative distance between the front cutting torch and the rear cutting torch h The flame intensity of the rear cutting torch and other heating parameters are adjusted to make the two slits of the slender workpiece measured synchronously have a distance from the edge cutting torch and the front cutting torch to be 50~300mm. h The temperature difference at the distance of / 2 is within 20℃, and the two cutting surfaces of the slender piece measured synchronously are both h + t The temperature difference at the distance is also within 20℃;

[0010] (5) After cutting and heating by the cutting torch, the cut seam is cooled naturally in the air.

[0011] Principle of the Invention: This invention addresses the problem of lateral deflection during symmetrical flame cutting of slender, thick plate parts in muggy environments. Using thermometers, the temperature drop at two symmetrical kerfs on the slender part was measured simultaneously. The results revealed a slower temperature drop at the edge kerfs, while a significantly faster temperature drop at the center kerf. From a heat transfer perspective, due to the narrow edge margin, heat dissipation from the flame-cut kerfs is primarily conducted inward, but outward heat conduction becomes dominant after a very short distance, with radiation dominating. In contrast, heat dissipation from the center kerfs is primarily conducted on both sides. This difference in heat dissipation leads to different temperature drop rates at the edge and center kerfs. To address this issue, the present invention proposes adding a post-cutting torch to the center kerf path, where the temperature drop is greater. The torch then uses a neutral flame to heat the cut kerf, minimizing the temperature drop. Furthermore, by controlling cutting and heating parameters such as flame intensity, cutting speed, and the distance between the cutting and heating torches, the two kerfs on the slender part maintain a substantially equivalent temperature field within the higher temperature range, thereby reducing the thermal stress caused by the temperature difference and effectively alleviating the lateral deflection problem.

[0012] Beneficial Effects of the Invention: This invention addresses the fact that the side slits dissipate heat more slowly than the center slits during symmetrical flame cutting of slender thick plates in a muggy environment. By heating the cutting torch to supplement the heat in the center slit after cutting, the thermal stress between the side slits and the center slits is reduced, thereby effectively alleviating the lateral bend problem that occurs when flame cutting thick steel plates with a thickness of 50-100 mm into slender parts at ambient temperatures ≥30°C and relative humidity ≥70%. This meets the requirements for slender thick plates to prevent slender plate bend when welded or bolted together into steel structures such as steel box girders. Compared to conventional processes, the method proposed by the present invention not only reduces the labor and time involved in correcting the lateral bend of slender thick plates, thereby reducing processing costs and improving processing efficiency, but also reduces stress concentration in steel structures assembled from slender thick plates, thereby increasing the safe lifespan of the steel structures. DETAILED DESCRIPTION

[0013] The present invention will be further described with reference to the following examples. Example 1

[0014] A flame cutting method for a slender thick plate in a muggy environment, wherein the muggy environment is an environment with a temperature of 35°C and a relative humidity of 75%. The slender thick plate has a thickness of 50 mm, a length of 12,000 mm, a width of 500 mm, and an aspect ratio of 24. The key process steps include:

[0015] (1) Using a cutting torch, a thick steel plate with a width of 3600 mm is synchronously flame cut along the length direction into 7 slender thick plates of the same size, with a steel plate edge allowance of 45 mm;

[0016] (2) For edge cutting, a cutting torch is set up so that it is perpendicular to the surface of the steel plate and the length of the air flow ejected during cutting exceeds the thickness of the steel plate by about 10 mm; the edge cutting refers to the cutting seam formed for cutting the edge allowance;

[0017] (3) For the middle slit, two cutting torches are set up, both of which are perpendicular to the surface of the steel plate and ensure that the front cutting torch and the rear cutting torch are on the same cutting path. At the same time, the front cutting torch and the side cutting torch are arranged in a row in the width direction of the steel plate and use the same cutting parameters such as cutting nozzle model, flame intensity, cutting speed, etc. The rear cutting torch uses a neutral flame to heat the slit. The middle slit refers to the slit that is much farther away from the edge than the edge margin.

[0018] (4) Control the cutting speed during cutting v 260mm / min; set the relative distance between the front cutting torch and the rear cutting torch at the same time hThe maximum temperature difference between the two slit surfaces of the slender workpiece measured synchronously at a distance of 100 mm from the side cutting torch and the front cutting torch is 10°C, and the maximum temperature difference between the two slit surfaces of the slender workpiece measured synchronously at a distance of 250 mm from the side cutting torch or the front cutting torch is 12°C.

[0019] (5) After cutting and heating by the cutting torch, the cut seam is cooled naturally in the air.

[0020] The lateral bending degree of the 7 slender thick plates cut was tested, and the maximum lateral bending was 3mm. Example 2

[0021] A flame cutting method for a slender thick plate in a muggy environment, wherein the muggy environment is an ambient temperature of 32°C and a relative humidity of 80%. The slender thick plate has a thickness of 100 mm, a length of 11,000 mm, a width of 500 mm, and an aspect ratio of 22. The key process steps include:

[0022] (1) Using a cutting torch, a thick steel plate with a width of 3050 mm is synchronously flame cut along the length direction into 6 slender thick plates of the same size, with a steel plate edge allowance of 20 mm;

[0023] (2) For edge cutting, a cutting torch is set up so that it is perpendicular to the surface of the steel plate and the length of the air flow ejected during cutting exceeds the thickness of the steel plate by about 10 mm; the edge cutting refers to the cutting seam formed for cutting the edge allowance;

[0024] (3) For the middle slit, two cutting torches are set up, both of which are perpendicular to the surface of the steel plate and ensure that the front cutting torch and the rear cutting torch are on the same cutting path. At the same time, the front cutting torch and the side cutting torch are arranged in a row in the width direction of the steel plate and use the same cutting parameters such as cutting nozzle model, flame intensity, cutting speed, etc. The rear cutting torch uses a neutral flame to heat the slit. The middle slit refers to the slit that is much farther away from the edge than the edge margin.

[0025] (4) Control the cutting speed during cutting v 200mm / min; set the relative distance between the front cutting torch and the rear cutting torch at the same time h The maximum temperature difference between the two slit surfaces of the slender workpiece measured at a distance of 75 mm from the side cutting torch and the front cutting torch is 12°C by adjusting the flame intensity and other heating parameters of the rear cutting torch, and the maximum temperature difference between the two slit surfaces of the slender workpiece measured at a distance of 250 mm from the side cutting torch or the front cutting torch is 8°C;

[0026] (5) After cutting and heating by the cutting torch, the cut seam is cooled naturally in the air.

[0027] The lateral bending degree of the 6 slender thick plates cut was detected, and the maximum lateral bending was 2mm.

Claims

1. A flame cutting method for slender thick plates in a hot and humid environment, wherein the hot and humid environment refers to an ambient temperature ≥30°C and a relative humidity ≥70%; the slender thick plates have a thickness of 50-100 mm and an aspect ratio ≥20; characterized in that The key process steps include: (1) Use a cutting torch to flame cut the thick steel plate synchronously along the length direction into multiple slender thick plates of the same size, with the edge allowance of the steel plate being 10~50mm; (2) For edge cutting, a cutting torch is set up, so that it is perpendicular to the surface of the steel plate and the length of the air flow ejected during cutting exceeds the thickness of the steel plate by 8 to 12 mm; the edge cutting refers to the cutting seam formed for cutting the edge allowance; (3) For the middle slit, two cutting torches are set up, both of which are perpendicular to the surface of the steel plate and ensure that the front cutting torch and the rear cutting torch are on the same cutting path. At the same time, the front cutting torch and the side cutting torch are arranged in a row in the width direction of the steel plate and use the same cutting parameters such as cutting nozzle model, flame intensity, cutting speed, etc. The rear cutting torch uses a neutral flame to heat the slit. The middle slit refers to the slit that is much farther away from the edge than the edge margin. (4) During the cutting process of steps (1) to (3), control the cutting speed v=320-(1.1~1.3)t, where v is the cutting speed, mm / min; t is the thickness of the steel plate, mm; and at the same time set the relative distance between the front cutting torch and the rear cutting torch. h The flame intensity of the rear cutting torch and other heating parameters are adjusted to make the two slits of the slender workpiece measured synchronously have a distance from the edge cutting torch and the front cutting torch to be 50~300mm. h The temperature difference at the distance of / 2 is within 20℃, and the two cutting surfaces of the slender piece measured synchronously are both h + t The temperature difference at the distance is also within 20℃; (5) After cutting and heating by the cutting torch, the cut seam is cooled naturally in the air.