On-line repairing method for cracks of lower cross beam of large free forging press

Abstract

The invention relates to an on-line repair method for cracks of a lower cross beam of a large free forging press, which comprises the following steps of: performing on-line welding repair and removing welding force according to the characteristics of the cracks of the lower cross beam of the large free forging press; the method specifically comprises the following steps of formulating and implementing safety measures before online repair of cracks of the lower cross beam of the large-scale free forging press and a treatment method of facade cracks of the lower cross beam of the large-scale free forging press to realize online intelligent heat treatment of a weld joint and stress relief after welding; the welding stress peak value of the lower cross beam is further reduced by adopting a multi-frequency repeated pressurization vibration method, so that the stress of each part of the lower cross beam is redistributed, and the method is efficient, convenient and capable of greatly shortening the operation time and reducing the operation cost.

Description

Technical Field

[0001] This invention belongs to the field of maintenance technology for large free forging presses, specifically relating to an online repair method for cracks in the lower crossbeam of a large free forging press. Background Technology

[0002] The lower crossbeam is a key component of a large free forging press, primarily bearing the reverse forces of all forging pressures during the forging process. In eccentric forging, it also bears eccentric moments or lateral thrust. Under the repeated action of these forces, the lower crossbeam is prone to fatigue and cracking. In such cases, the machine must be stopped for maintenance.

[0003] The traditional technical solution involves removing the lower crossbeam from the equipment and then welding or replacing it with a new one. The drawback of this traditional solution is the long maintenance time required for disassembling and reassembling the lower crossbeam and other components, approximately nine months, which significantly impacts production and operations. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide an online repair method for cracks in the lower crossbeam of a large free forging press. During the welding process and after welding, various methods are used to redistribute the stress in each part of the crossbeam to achieve a normal service state, which greatly reduces maintenance time and maintenance costs.

[0005] The technical solution of this invention is implemented as follows: A method for online repair of cracks in the lower crossbeam of a large free forging press is proposed. Based on the crack form of the lower crossbeam of the large free forging press, a method is developed that includes monitoring the balance of the main structure of the equipment, online welding repair, and stress removal during welding. The specific details are as follows: Step 1) Main structure balance monitoring of equipment: During the welding process, the balance of the main structure of the equipment is monitored. The deformation of the lower crossbeam is monitored using a deformation dimension dial gauge to control the changes of the main body of the equipment in real time. The welding repair strength is adjusted in a timely manner according to the deformation, and the deformation of the lower crossbeam is controlled to not exceed 10mm. Step 2) Online welding repair: Online cutting and grinding to remove cracks in the lower crossbeam, grinding the bevel, and welding to repair the lower crossbeam; among them, for large-area, complex, scattered, and radial cracks in the lower crossbeam, a directional cutting method is used to remove the most complex crack part of the main body as a whole, and the whole embedding method is used to treat it, that is, to make a repair material mold according to the shape of the cutting hole, make the repair material according to the mold, embed the repair material and weld it, reducing the amount of crack cleaning and welding repair work, and significantly reducing the difficulty of operation; Step 3) Achieve online intelligent heat treatment of weld seams: By using intelligent temperature-controlled welding heating equipment, the tracked electric heating belt is fixed in a 200mm area on both sides of the weld seam for preheating before welding, heat preservation during welding, and overall stress removal of the lower crossbeam after welding. Step 4) Removing post-weld stress: After welding, the stress of the lower crossbeam is removed by a combination of layered stress removal and overall stress removal. First, after each layer is welded, the weld is stress-removed by hammering and heating with an oxy-acetylene flame. Second, after all cracks have been repaired by welding, the weld is subjected to an overall stress removal treatment. Step 5) Remove welding stress by gradually increasing the pressure and vibrating the press at multiple frequencies: Gradually increase the pressure of the press from low pressure and use repeated vibration at multiple frequencies to further reduce the peak welding stress of the lower crossbeam, so that the stress in each part of the lower crossbeam is redistributed.

[0006] The specific methods for monitoring the balance of the main structure, online welding repair, and relieving welding stress are as follows: Step 1) First, prepare for welding and install safety measurement facilities. Remove the peripheral accessories of the lower crossbeam and the internal guide wedge assembly of the movable crossbeam. Weld a positioning block on the base of the lower crossbeam on the side where the high-pressure pipe is installed to prevent the high-pressure pipe connected to the valve block of the upper crossbeam on this side from being damaged due to the heat expansion of the lower crossbeam. Remove the anchor bolts on the base of the other side of the lower crossbeam and install a deformation dimension dial indicator on this side to monitor the deformation of the lower crossbeam throughout the preheating, welding and heat treatment process. Step 2) Clean the lower beam and use dye penetrant to determine the extent and form of the cracks. The cracks are mainly large-area, complex, dispersed radial cracks on the vertical surface of the lower beam and transverse straight cracks on the bottom surface of the lower beam. Step 3) According to the extent of the cracks on the facade, use a steel ruler to draw lines, and then use an oxy-acetylene flame for directional cutting to remove all the cracked parts. Then use a carbon arc gouging tool to flatten the cut, straighten the cutting line, and clean and grind to form a U-shaped bevel with a depth equal to the thickness of the lower crossbeam wall. Since the shape and size of the cutting hole are irregular, a repair material mold is made by directly welding channel steel at the cutting hole. The repair material is made according to this mold, which is more accurate and convenient than direct measurement. During the mold making process, steel bars are used to pave a 10mm space between the repair material mold and the cutting hole to facilitate the subsequent installation and welding of the repair material. Step 4) According to the range of the transverse straight crack on the bottom surface of the lower crossbeam, mark the line with a steel ruler, and then use oxy-acetylene flame directional cutting to cut off all the cracked parts. Then use carbon arc gouging to flatten the cut. Since the bottom surface thickness exceeds the working depth of the carbon gouging rod, the slag cannot be blown out. To avoid the problem of poor gouging quality, beveling is done on the top and bottom surfaces of the bottom surface. The beveling depth of the upper surface is opened to ⅔ of the thickness, and the beveling depth of the lower surface is opened to ⅓ of the thickness. The purpose is to reduce the amount of overhead welding, improve welding efficiency, and ensure welding quality. Step 5) Install tracked electric heating belts within a 200mm range on both sides of the weld between the lower crossbeam vertical surface and the repair material. Use intelligent temperature-controlled welding heating equipment for preheating at 100-150℃. After holding the temperature for 2 hours, proceed to the welding stage. Step 6) Divide the area to be welded into 12 areas, and weld the transition layer between the lower crossbeam facade and the repair material in sequence. Use shielded metal arc welding (SMAW) with J507 low-hydrogen sodium alkaline welding rods with a diameter of 4mm. After the transition layer welding is completed, hammer the weld bead. Hammering time should be more than 15 minutes for every 100mm of weld bead. After hammering, use an oxy-acetylene flame cutting torch to heat the weld bead to relieve stress. After the flame heating stress relief is completed, grind the transition layer weld and perform flaw detection. After confirming that there are no defects in the transition layer, then perform overlay welding. Step 7) Divide the area to be welded into 12 zones. Sequentially weld the weld seams between the lower beam facade and the repair material, starting with the two sides and then the middle. Each layer should not exceed 5mm in thickness. Use argon-rich mixed gas (Ar 80% + Co 20%) + gas metal arc welding (MIG) with 1.2mm diameter ER50-6 solid welding wire. After each zone is welded, hammer the weld bead. Depending on the zone length, hammer for at least 15 minutes per 100mm weld bead, ensuring all parts of the weld bead are deformed to eliminate welding stress. After hammering, use an oxy-acetylene torch to heat the weld bead until it turns gray, ensuring all parts of the weld bead are deformed to eliminate welding stress. During welding, maintain the temperature of the lower beam facade and the repair material between 150-200℃. Continue welding until completion. Step 8) The welding of the bottom surface weld of the lower crossbeam shall be consistent with the welding scheme and stress relief requirements of Steps 6) and 7) and the welding of the vertical repair material in Steps 6) and 7). Step 9) Post-weld overall stress relief heat treatment: The intelligent temperature-controlled welding heating equipment is set to a heating temperature of 200℃ and preheated for 4 hours; then the temperature is set to rise to 350℃ and held for 12 hours; then the temperature is controlled to drop, with a drop of no more than 15℃ per hour. When the temperature drops to 150℃, the equipment heating is stopped and the temperature is allowed to cool naturally to room temperature. Step 10) Monitor the value of the deformation dimension dial gauge throughout the entire preheating, welding and heat treatment process, and control the deformation within 10mm; Step 11) Remove the tracked electric heating belt and insulation device, grind the weld until the surface has a metallic luster, remove the lower crossbeam positioning block and deformation dimension dial indicator, and install the anchor bolts and wedge iron assembly. Step 12) After the above steps are completed, the press is gradually increased from low pressure, and the peak welding stress of the lower crossbeam is further reduced by using a method of repeated high-frequency pressure and vibration, so that the stress in each part of the lower crossbeam is redistributed.

[0007] The present invention has the following positive effects: 1. During the welding process, the main structure of the equipment is balanced and monitored. A deformation dimension dial gauge is used to monitor the deformation of the lower crossbeam and to control the changes in the main body of the equipment in real time. The advantages are: real-time monitoring of the deformation of the lower crossbeam, timely adjustment of the welding process according to the deformation, and control of the deformation of the lower crossbeam to not exceed 10mm. This effectively ensures the overall stability of the equipment during the repair of the main load-bearing component (lower crossbeam) and avoids structural imbalance caused by deformation, thermal stress and other factors, which could lead to secondary equipment structural safety accidents such as sudden fracture, collapse and deformation of the main body of the equipment.

[0008] 2. For large-area, complex, dispersed, and radiating cracks, a directional cutting method is used to remove the most complex part of the main crack as a whole. The whole embedding method is then used, which involves making a repair material mold according to the shape of the cut hole, making the repair material according to the mold, and embedding the repair material for welding. The advantages are that it can reduce the amount of crack cleaning and welding repair work and significantly reduce the difficulty of the operation.

[0009] 3. This method uses a multi-frequency repeated pressure vibration method, which has the advantage of reducing the peak welding stress of the lower crossbeam and redistributing the stress in various parts of the lower crossbeam.

[0010] 4. This method is efficient and convenient. Compared with traditional solutions, it is expected to save 6 months of maintenance time, which can significantly shorten maintenance time and reduce operating costs. Attached Figure Description

[0011] Figure 1 This is a schematic diagram illustrating the preparation and installation of safety measurement facilities before repairing cracks in the lower beam according to the present invention.

[0012] Figure 2 This is a schematic diagram of the crack path on the lower beam of the present invention.

[0013] Figure 3 This is a schematic diagram showing the direction of the cracks on the bottom surface of the lower beam in this invention.

[0014] Figure 4 This is a schematic diagram of the crossbeam cutting hole mold of the present invention.

[0015] Figure 5 This is a schematic diagram of the welding bevel on the bottom surface of the lower crossbeam of the present invention.

[0016] Figure 6 This is a schematic diagram of preheating before welding the lower crossbeam of the present invention.

[0017] Figure 7 This is a schematic diagram of the welding of the transition layer on the lower beam of the present invention.

[0018] Figure 8 This is a schematic diagram of the welding sequence of the lower crossbeam of the present invention.

[0019] Figure 9 This is a schematic diagram of the welding sequence on the bottom surface of the lower crossbeam of the present invention.

[0020] Figure 10 This invention provides a table outlining the requirements for repeated high-frequency vibration after the crossbeam is repaired, starting with gradually increasing pressure from a low level. Detailed Implementation

[0021] like Figure 1 As shown, the preparations for repairing the crack in the lower crossbeam and the installation of safety measurement facilities are as follows: Remove the peripheral accessories 4 of the lower crossbeam 3 and the internal guide wedge assembly 6 of the movable crossbeam 5; weld the positioning block 2 on the base 1 on the side of the lower crossbeam where the high-pressure pipe 7 is installed to prevent the high-pressure pipe connected to the valve block 8 of the upper crossbeam on this side from being damaged by the heat extension of the lower crossbeam; remove the anchor bolts 9 on the base on the other side and install the deformation dimension dial gauge 10 on this side to monitor the deformation of the lower crossbeam throughout the preheating, welding and heat treatment process.

[0022] like Figure 2 , 3 As shown, the lower crossbeam was cleaned and dye penetrant was used to determine the extent and form of the cracks. The cracks were mainly large-area, complex, dispersed radial cracks on the lower crossbeam facade 11 and transverse straight cracks on the lower crossbeam bottom surface 13 14.

[0023] like Figure 4 As shown, according to the extent of the cracks on the facade, lines were drawn with a steel ruler, and then oxy-acetylene flame directional cutting was used to cut away all the cracked parts. Then, carbon arc gouging was used to flatten the cut, straighten the cutting line, and clean and grind to form a U-shaped bevel with a depth equal to the thickness of the lower crossbeam wall. Since the dimensions of the cutting hole 15 are irregular, a repair material mold 16 was made by directly welding channel steel at the cutting hole. The repair material was made according to this mold, which is more accurate and convenient than direct measurement. During the mold making process, a 10mm space was created between the repair material mold and the cutting hole using steel bars 17 to facilitate the subsequent installation and welding of the repair material.

[0024] like Figure 5As shown, based on the range of the transverse straight crack on the bottom surface of the lower crossbeam, a line was drawn with a steel ruler. Then, oxy-acetylene flame directional cutting was used to cut away the entire cracked part. Next, carbon arc gouging was used to smooth the cut. Since the bottom surface thickness exceeded the working depth of the carbon gouging rod, the slag could not be blown out. To avoid the problem of poor gouging quality, beveling was done on both the top and bottom surfaces. The upper surface beveling depth was 18 to ⅔ of the thickness, and the lower surface beveling depth was 19 to ⅓ of the thickness. The purpose was to reduce the amount of overhead welding work, improve welding efficiency, and ensure welding quality.

[0025] like Figure 6 As shown, tracked electric heating belts 20 are installed within a 200mm range on both sides of the weld 22 between the lower crossbeam vertical surface 11 and the repair material 21. The intelligent temperature-controlled welding heating equipment is used for preheating at a temperature of 100-150℃. After holding the temperature for 2 hours, the welding stage begins.

[0026] like Figure 7 As shown, the area to be welded is divided into 12 zones. Following the sequence ①-⑫ in the diagram, the transition layer 23 is welded sequentially between the lower crossbeam facade 11 and the repair material 21. Shielded metal arc welding (SMAW) is used, employing J507 electrodes with a diameter of 4mm. After completing the transition layer welding, the weld bead is hammered, with each 100mm section hammered for more than 15 minutes. After hammering, the weld bead is stress-relieved using an oxy-acetylene flame. After stress relief via flame heating, the transition layer weld is ground and inspected for defects. Once the transition layer is confirmed to be free of defects, the overlay welding is then performed.

[0027] like Figure 8 As shown, the area to be welded is divided into 12 zones. Following the sequence ①-⑫ in the diagram, the weld 22 between the lower crossbeam facade 11 and the repair material 21 is welded sequentially. The welding sequence for each layer follows the requirements of diagrams Ⅰ-Ⅳ: weld the two sides first, then the middle, with each layer not exceeding 5mm in thickness. A mixed gas (Ar 80% + Co 20%) gas metal arc welding (MIG) method is used, employing 1.2mm diameter ER50-6 solid core welding wire. After each zone is welded, the weld bead is hammered. Depending on the zone length, hammering time is greater than 15 minutes per 100mm weld bead to ensure complete deformation of all weld bead parts, thus eliminating welding stress. After hammering, the weld bead is heated using an oxy-acetylene flame to relieve stress, requiring the weld bead to turn gray. During the welding process, the temperature of the lower crossbeam facade and the repair material is maintained at 150-200℃ until welding is completed.

[0028] like Figure 9As shown, the surfacing welding of weld 13 on the bottom surface of the lower crossbeam is carried out in the order shown a-a'-b-b'. The welding scheme and stress relief requirements are basically the same as those for the facade repair material welding. Post-weld overall stress relief heat treatment: The intelligent temperature-controlled welding heating equipment is set to a heating temperature of 200℃ and preheated for 4 hours; then the temperature is set to rise to 350℃ and held for 12 hours; subsequently, the temperature is controlled to drop, with a drop of no more than 15℃ per hour. When the temperature drops to 150℃, the equipment heating is stopped, and the temperature is allowed to cool naturally to room temperature. The tracked electric heating belt and heat preservation device are removed, and the weld is ground until the surface has a metallic luster. The lower crossbeam positioning block and deformation dimension dial indicator are removed, and the anchor bolts and wedge iron assembly are installed.

[0029] like Figure 10 As shown, although layered stress relief and overall stress relief were adopted during the welding process of the lower crossbeam, considerable welding stress inevitably remained due to the large number and width of welds, the large amount of welding, and the high strength of the lower crossbeam. A method of gradually increasing pressure from low pressure and repeatedly applying pressure and vibration at multiple frequencies was used to further reduce the peak welding stress, thereby redistributing the stress in various parts of the lower crossbeam.

Claims

1. A method for online repair of cracks in the lower crossbeam of a large free forging press, characterized in that: Based on the crack pattern of the lower crossbeam of a large free forging press, a method for balancing and monitoring the main structure of the equipment, online welding repair, and stress removal is proposed as follows: Step 1) Main structure balance monitoring of equipment: During the welding process, the balance of the main structure of the equipment is monitored. The deformation of the lower crossbeam is monitored using a deformation dimension dial gauge to control the changes of the main body of the equipment in real time. The welding repair strength is adjusted in a timely manner according to the deformation, and the deformation of the lower crossbeam is controlled to not exceed 10mm. Step 2) Online welding repair: Online cutting and grinding to remove cracks in the lower crossbeam, grinding the bevel, and welding to repair the lower crossbeam; for large-area, complex, scattered, and radial cracks in the lower crossbeam, directional cutting is used to remove the most complex crack part of the main body as a whole, and the whole embedding method is used to treat it, that is, a repair material mold is made according to the shape of the cutting hole, the repair material is made according to the mold, and the repair material is embedded and welded, which reduces the amount of crack cleaning and welding repair work and significantly reduces the difficulty of operation; Step 3) Achieve online intelligent heat treatment of weld seams: By using intelligent temperature-controlled welding heating equipment, the tracked electric heating belt is fixed in a 200mm area on both sides of the weld seam for preheating before welding, heat preservation during welding, and overall stress removal of the lower crossbeam after welding. Step 4) Removing post-weld stress: The overall stress removal of the lower crossbeam after welding adopts a combination of layered stress removal and overall stress removal. First, after each layer is welded, the weld is stress-removed by hammering and heating with an oxy-acetylene flame. Second, after all cracks have been repaired by welding, the weld is subjected to an overall stress removal treatment. Step 5) Remove welding stress by gradually increasing the pressure and vibrating the press at multiple frequencies: Gradually increase the pressure of the press from low pressure and use repeated vibration at multiple frequencies to further reduce the peak welding stress of the lower crossbeam, so that the stress in each part of the lower crossbeam is redistributed.

2. The method for online repair of cracks in the lower crossbeam of a large free forging press according to claim 1, characterized in that: The specific methods for monitoring the balance of the main structure, online welding repair, and relieving welding stress are as follows: Step 1) First, prepare for welding and install safety measurement facilities. Remove the peripheral accessories of the lower crossbeam (3) and the internal guide wedge group (6) of the movable crossbeam (5). Weld a positioning block (2) on the base (1) on the side of the lower crossbeam where the high pressure pipe (7) is installed to prevent the high pressure pipe connected to the valve block (8) of the upper crossbeam from being damaged by the heat extension of the lower crossbeam. Remove the anchor bolts (9) on the base on the other side of the lower crossbeam and install a deformation dimension dial gauge (10) on that side to monitor the deformation of the lower crossbeam throughout the preheating, welding and heat treatment process. Step 2) Clean the lower beam and use dye penetrant to determine the extent and form of the cracks. The cracks are mainly large-area, complex, dispersed radial cracks on the vertical surface (11) of the lower beam (12) and transverse linear cracks on the bottom surface (13) of the lower beam (14). Step 3) According to the extent of the cracks on the facade, use a steel ruler to draw lines, and then use an oxygen-acetylene flame for directional cutting to cut off all the cracked parts. Then use a carbon arc gouging to flatten the cut, straighten the cutting line, clean and grind to form a U-shaped bevel with a depth equal to the thickness of the lower crossbeam wall. Since the dimensions of the cutting hole (15) are irregular, a repair material mold (16) is made by directly welding channel steel at the cutting hole. The repair material is made according to this mold, which is more accurate and convenient than direct measurement. During the mold making process, a 10mm space is created between the repair material mold and the cutting hole using steel bars (17) to facilitate the subsequent installation and welding of the repair material. Step 4) According to the range of the horizontal straight crack on the bottom surface of the lower crossbeam, use a steel ruler to draw lines, and then use oxygen-acetylene flame directional cutting to cut off all the cracked parts. Then use carbon arc gouging to flatten the cut. Since the bottom surface thickness exceeds the working depth of the carbon rod gouging, the slag cannot be blown out. In order to avoid the problem of poor gouging quality, bevels are made on the bottom surface and the top and bottom surfaces respectively. The depth of the upper plane bevel (18) is opened to ⅔ of the thickness, and the depth of the lower plane bevel (19) is opened to ⅓ of the thickness. The purpose is to reduce the workload of overhead welding, improve welding efficiency, and ensure welding quality. Step 5) Install tracked electric heating belts (20) within a 200mm range on both sides of the weld (22) between the lower crossbeam vertical surface (11) and the repair material (21). Use intelligent temperature control welding heating equipment for preheating. The preheating temperature is 100-150℃. After holding the temperature for 2 hours, enter the welding stage. Step 6) Divide the area to be welded into 12 areas, and weld the transition layer (23) between the weld seam (22) between the lower beam vertical surface (11) and the repair material (21) in sequence. Welding is carried out by shielded metal arc welding. The welding rod is a J507 low-hydrogen sodium type alkaline welding rod with a diameter of 4mm. After the transition layer welding is completed, the weld is hammered. The hammering time for each 100mm length of weld seam is more than 15 minutes. After the hammering is completed, the weld seam is heated with an oxy-acetylene flame cutting torch to relieve stress. After the flame heating stress relief is completed, the transition layer (23) weld is ground and inspected for defects. After confirming that the transition layer (23) is free of defects, the overlay welding is carried out. Step 7) Divide the area to be welded into 12 areas, and weld the weld (22) between the lower beam facade (11) and the repair material (21) in sequence. The welding sequence of each layer is to weld the two sides first, and then weld the middle. The thickness of each layer does not exceed 5mm. Welding is carried out using argon-rich mixed gas (Ar 80% + Co 20%) + gas metal arc welding (MIG). The welding material is ER50-6 solid core welding wire with a diameter of 1.2mm. After each area is welded, the weld bead is hammered. According to the length of the area, the hammering time for each 100mm weld bead is more than 15 minutes to ensure that all parts of the weld bead are hammered and deformed to eliminate welding stress. After hammering, use an oxygen-acetylene flame cutting torch to heat the weld bead to remove stress. The weld bead is required to be heated to gray color to ensure that all parts of the weld bead are hammered and deformed to eliminate welding stress. During the welding process, the temperature of the lower beam facade and the repair material is kept at 150-200℃. Continue until the welding is completed. Step 8) The welding of the bottom surface (13) weld of the lower crossbeam shall be consistent with the welding scheme and stress relief requirements of Step 6) and 7) and the welding of the vertical repair material in Step 6) and 7); Step 9) Post-weld overall stress relief heat treatment: The intelligent temperature-controlled welding heating equipment is set to a heating temperature of 200℃ and preheated for 4 hours; then the temperature is set to rise to 350℃ and held for 12 hours; then the temperature is controlled to drop, with a drop of no more than 15℃ per hour. When the temperature drops to 150℃, the equipment heating is stopped and the temperature is allowed to cool naturally to room temperature. Step 10) Monitor the value of the deformation dimension dial gauge throughout the entire preheating, welding and heat treatment process, and control the deformation within 10mm; Step 11) Remove the tracked electric heating belt (20) and the heat preservation device, grind the weld until the surface has a metallic luster, remove the lower crossbeam positioning block (2) and dial indicator (10), and install the anchor bolts (9) and wedge iron group (6). Step 12) After the above steps are completed, the press is gradually increased from low pressure, and the peak welding stress of the lower crossbeam is further reduced by using a method of repeated high-frequency pressure and vibration, so that the stress in each part of the lower crossbeam is redistributed.

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