A high-energy submerged arc welding method for hydraulic support structural members

Abstract

This invention provides a high-energy submerged arc welding method for hydraulic support structural components, comprising the following steps: assembling hydraulic support structural components to form a T-shaped corner joint or a K-shaped bevel joint to be welded; for the K-shaped bevel joint, gradually increasing the allowable local assembly gap according to the increase of the target penetration depth; using a submerged arc as the welding heat source, controlling the arc heat source to penetrate the workpiece surface and enter the molten pool for combustion; during the welding process, for the T-shaped corner joint, welding is performed in a ship-shaped welding position; for the K-shaped bevel joint, a root-cleaning-free welding process is used; during the welding process, adjusting the welding heat input according to the steel plate strength grade; during the welding process, based on the increase in penetration depth, correspondingly reducing the weld leg size under the same strength conditions. This method has the advantage of achieving high penetration welding under limited heat input, improving the reliability of the welded structure of hydraulic support components.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically, to a high-energy submerged arc deep-penetration welding method for hydraulic support structural components. Background Technology

[0002] Hydraulic supports, as key support equipment in fully mechanized coal mining faces, directly impact the safety and efficiency of underground operations through the welding quality of their structural components. With increasing coal mining depth, the required working resistance of hydraulic supports has risen from the early 2000kN level to over 20000kN, and the structural steel has been upgraded from Q355 to Q550D, Q690D, and even higher strength grades. However, T-joints, the most basic connection type in hydraulic support structures, have long been constrained by the physical limitations of traditional arc welding technology. Traditional arc welding only burns on the surface of the molten pool, unable to directly act on the weld root, resulting in a penetration depth of only 1-3mm and frequent root fusion defects. These defects not only become sources of stress concentration and crack initiation but also easily lead to fatigue fracture of structural components under alternating loads, seriously threatening safe coal mine production. Even more challenging is the stringent requirement for heat input control in the application of high-strength steel. The heat input for welding Q690D steel plates needs to be controlled below 2.2 KJ / mm to avoid hardened structures and cold cracks. However, excessively low heat input further limits the penetration depth, creating a contradictory dilemma where penetration depth and performance are difficult to achieve simultaneously. Furthermore, the large size of hydraulic support structural components, uneven plate thickness, and large fluctuations in assembly gaps, coupled with the poor adaptability of traditional welding processes to assembly gaps and the cumbersome back-side cleaning process, collectively constitute the technical bottlenecks restricting the welding quality and production efficiency of hydraulic supports.

[0003] Breaking through the bottleneck in T-joint welding technology is of significant strategic importance for promoting the upgrading of coal mine equipment and ensuring safe production. On the one hand, hydraulic support structures are numerous and have dense welds; insufficient penetration in traditional welding processes leading to root defects has always been a common problem in the industry. Statistics show that a considerable proportion of hydraulic support failures originate from fatigue fracture at the root of welded joints, especially T-joints, with the failure mode primarily being brittle cracking at the weld root. Increasing the penetration depth from 1-3mm to 6-8mm, achieving true root penetration, can not only fundamentally eliminate incomplete fusion defects but also shift the failure risk from the dangerous weld root position to the relatively safer weld toe position, significantly improving structural reliability. On the other hand, with the widespread application of high-strength steel in hydraulic supports, the technical demands for ensuring penetration depth while limiting heat input, eliminating the back-side root cleaning process while ensuring penetration depth, and establishing a quantitative relationship between penetration depth improvement and weld corner size optimization to achieve material savings and reduced consumption are becoming increasingly urgent. In particular, for steels of different strength grades such as Q550D and Q690D, it is necessary to establish differentiated welding strategies to adapt to the development trend of larger, lighter, and more reliable hydraulic supports.

[0004] Therefore, developing a welding method that can achieve deep penetration welding under limited heat input and improve the reliability of welded structures of hydraulic support components has become a key common technical problem that urgently needs to be solved in the field of hydraulic support manufacturing.

[0005] In order to solve the above problems, people have been seeking an ideal technological solution. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a high-energy submerged arc deep-penetration welding method for hydraulic support structural components that can achieve deep-penetration welding under limited heat input and improve the reliability of welded structures.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a method for high-energy submerged arc welding with large penetration depth for hydraulic support structural components, comprising the following steps: Assemble the hydraulic support structural components to form a T-type corner joint or a K-type bevel joint to be welded. For T-type corner joints, to reduce the tendency for defects caused by increased penetration depth, the allowable assembly gap is between 0-0.5mm. For K-type bevel joints, the allowable local assembly gap is gradually increased according to the target penetration depth, with an allowable increase range of 1-2mm. The control strategy for the local assembly gap is as follows: when the target penetration depth is 4-6mm, the allowable local assembly gap is increased to 1mm; when the target penetration depth increases to 6-8mm, the allowable local assembly gap is increased to 2mm. Using the solution of this invention significantly improves the tolerance of the welding process to the assembly errors of the preceding process and reduces the assembly accuracy requirements.

[0008] By employing a submerged arc welding technique as the welding heat source, the arc heat source is controlled to penetrate the workpiece surface and burn inside the molten pool, allowing the arc to directly act on the weld root. This transforms the traditional method of the arc burning on the surface of the molten pool into burning inside the molten pool, thus directly acting on the weld root. This increases the penetration depth of T-shaped fillet welds in hydraulic support structures from the traditional 1-3mm to 6-8mm, an increase of approximately 3 times. The reason for this is that submerged arc welding technology, through special pulse waveform control, achieves arc compression and energy density enhancement, enabling the arc to penetrate the molten pool surface and reach the root, fundamentally solving the problem of insufficient penetration depth in traditional welding. During the welding process, for T-type corner joints, welding is performed in a boat-shaped welding position. Welding in a boat-shaped position allows the molten pool metal to spread evenly under gravity, improves the droplet transfer conditions, and facilitates the transfer of arc heat to the root. Under the same heat input conditions, the penetration depth increases by 1-2 mm compared to the horizontal corner weld position, and the weld formation meets the requirements of ISO5817-B:2023 standard.

[0009] For K-type groove joints, a root-cleaning-free welding process is adopted, controlling the groove blunt edge to be 2mm, the groove angle to be 45°, and the assembly gap to be 1-2mm, providing geometric conditions for deep submerged arc penetration. After welding, the back fusion line completely covers the incompletely fused area of ​​the front root pass, realizing the root-cleaning-free function of single-sided welding of K-type groove joints. Compared with the existing technology that requires root cleaning, this invention can achieve single-sided welding with double-sided forming through parameter synergistic optimization, significantly reducing processes and improving efficiency.

[0010] During welding, the welding heat input was adjusted to a range of 2.0-2.4 KJ / mm based on the steel plate strength grade, with higher heat input for lower steel plate strength grades. The control strategy for adjusting the heat input was as follows: when the steel plate strength grade was Q550D or lower, the welding heat input was controlled to ≤2.4 KJ / mm; when the steel plate strength grade was Q690D, the welding heat input was controlled to ≤2.2 KJ / mm. The mechanical properties of the welded joint met the requirements of ISO15614-1:2017 / Amd1:2019 standards. Studies have shown that welding heat input has a significant impact on the strength reduction of high-strength steel welded joints. Reasonable control of heat input can achieve equal-strength connections. Based on this principle, the above control strategy was adopted.

[0011] During the welding process, the weld leg size is reduced accordingly based on the increase in penetration depth, under the same strength conditions.

[0012] Based on finite element analysis and the principle of equal cross-sectional area, the corresponding relationship between the increase in weld penetration depth and the decrease in weld leg size for T-joint corner welds was determined. When the weld penetration depth of a T-joint corner weld increases by 2mm, the weld leg size is correspondingly reduced by 1.0-1.5mm to save welding wire consumption under the same strength conditions. Through this optimized weld leg size design, annual welding wire savings of over 1000 tons can be achieved, resulting in significant economic benefits.

[0013] When the thickness of the hydraulic support structural component to be welded is ≤14mm, the heat input is controlled to reach 2.4KJ / mm to achieve complete penetration of the double-sided T-corner joint, enabling the mechanical properties of the T-corner joint to reach the level of a butt joint. This technical achievement breaks through the performance bottleneck of traditional T-corner joints and provides technical support for the lightweight design of hydraulic support structures.

[0014] This invention has outstanding substantive features and significant progress compared to the prior art. Specifically, from a technical point of view, it enables the electric arc to burn directly inside the molten pool and act on the root of the weld, breaking through the physical limits of traditional surface electric arcs. Through optimization of the hull position and precise control of heat input, the penetration depth is increased by about 3 times, which can make the performance of T-type corner joints reach the level of butt joints. This is an important breakthrough in the understanding of the performance of traditional corner joints.

[0015] From a process perspective, this technology enables single-sided welding and double-sided forming of K-type grooves without root cleaning, reducing the number of processes and improving efficiency. In addition, it expands the adaptability of assembly gaps from the traditional less than 0.5mm to 1-2mm, significantly improving welding efficiency and process margin while ensuring the performance requirements of ISO15614-1:2017 / Amd1:2019 standards.

[0016] From an economic perspective, optimizing weld leg dimensions based on finite element analysis and the principle of equal cross-sectional area can reduce weld leg size under the same strength conditions, which is expected to save more than 1,000 tons of welding wire per year, while reducing the cost of root cleaning and rework.

[0017] From a safety perspective, this technology achieves complete root fusion through deep melting, fundamentally changing the failure mode of T-type fillet welds. It transfers traditional root failure to toe failure, significantly improving the structural safety margin and service life of hydraulic supports. This has important practical significance for ensuring safe production in coal mines and promoting the high-quality development of the coal industry. Attached Figure Description

[0018] Figure 1 This is a schematic diagram comparing the principles of conventional arc welding (a) and submerged arc welding (b) in this invention.

[0019] Figure 2 This is a process comparison diagram of the horizontal welding position and the ship-shaped welding position in this invention.

[0020] Figure 3 This is a schematic diagram of defects at the root of a T-shaped corner joint in existing technology. Detailed Implementation

[0021] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0022] like Figures 1-3 As shown, a high-energy submerged arc welding method for hydraulic support structural components includes the following steps: Assemble the hydraulic support structural components to form a T-shaped corner joint or a K-shaped bevel joint to be welded.

[0023] For T-type corner joints, to reduce the tendency for defects caused by increased penetration depth, the allowable assembly gap is between 0-0.5mm. For K-type bevel joints, the allowable local assembly gap is gradually increased according to the target penetration depth, with an allowable increase range of 1-2mm. The control strategy for the local assembly gap is as follows: when the target penetration depth is 4-6mm, the allowable local assembly gap is increased to 1mm; when the target penetration depth increases to 6-8mm, the allowable local assembly gap is increased to 2mm. Compared with the 0.5mm assembly gap in the traditional scheme, the relaxation range is significantly increased, which significantly improves the tolerance of the welding process to the assembly error of the previous process and reduces the assembly accuracy requirements.

[0024] like Figure 1As shown, submerged arc welding is used as the welding heat source. The arc heat source is controlled to penetrate the workpiece surface and enter the molten pool for combustion, so that the arc directly acts on the root of the weld. This changes the traditional method of the arc burning on the surface of the molten pool to burning inside the molten pool, thus directly acting on the root of the weld. This increases the penetration depth of the T-shaped fillet weld of the hydraulic support structure from the traditional 1-3mm to 6-8mm, an increase of about 3 times. The reason for this is that the submerged arc welding technology, through special pulse waveform control, achieves arc compression and energy density enhancement, enabling the arc to penetrate the surface of the molten pool and reach the root, fundamentally solving the problem of insufficient penetration depth in traditional welding.

[0025] Furthermore, by using the submerged arc as a welding heat source, the failure mode of the T-type fillet weld is changed from the traditional root failure to the toe failure, thus achieving a transfer of failure risk. The root position is located inside the joint, making defect detection difficult, while the toe position is easy to detect and maintain. The transfer of failure mode significantly improves the service reliability of the welded structure.

[0026] During the welding process, for T-type corner joints, welding is performed in a boat-shaped welding position. Welding in a boat-shaped position allows the molten pool metal to spread evenly under gravity, improves the droplet transfer conditions, and facilitates the transfer of arc heat to the root. Under the same heat input conditions, the penetration depth increases by 1-2 mm compared to the horizontal corner weld position, and the weld formation meets the requirements of ISO5817-B:2023 standard.

[0027] For K-type groove joints, a root-cleaning-free welding process is adopted, controlling the groove blunt edge to be 2mm, the groove angle to be 45°, and the assembly gap to be 1-2mm. After welding, the back fusion line completely covers the incomplete fusion area of ​​the front root pass, realizing the root-cleaning-free function of K-type groove single-sided welding. Compared with the existing technology that requires root cleaning, this invention can achieve single-sided welding with double-sided forming through parameter synergistic optimization, significantly reducing the number of processes and improving efficiency.

[0028] Studies have shown that welding heat input has a significant impact on the strength reduction of high-strength steel welded joints. Reasonable control of heat input can achieve equal-strength connections. Based on this principle, we further optimized the welding process. During welding, the welding heat input range was adjusted from 2.0 to 2.4 KJ / mm according to the steel plate strength grade, with higher heat input for lower steel plate strength grades. The control strategy for adjusting the heat source input is as follows: when the steel plate strength grade is Q550D and below, the welding heat input is controlled to ≤2.4 KJ / mm; when the steel plate strength grade is Q690D, the welding heat input is controlled to ≤2.2 KJ / mm. The mechanical properties of the welded joint meet the requirements of ISO15614-1:2017 / Amd1:2019 standards.

[0029] During welding, based on the increase in penetration depth, the weld leg size is correspondingly reduced under the same strength conditions. Specifically, based on finite element analysis and the principle of equal cross-sectional area, the correspondence between the increase in penetration depth and the decrease in weld leg size for T-joint corner welds is determined. When the penetration depth of a T-joint corner weld increases by 2mm, the weld leg size is correspondingly reduced by 1.0-1.5mm to save welding wire consumption under the same strength conditions. Through this optimized weld leg size design, annual welding wire savings of over 1000 tons can be achieved, resulting in significant economic benefits.

[0030] When the thickness of the hydraulic support structural plate to be welded is ≤14mm, the heat input is controlled to reach 2.4KJ / mm to achieve complete penetration of the double-sided T-shaped corner joint, so that the mechanical properties of the T-shaped corner joint reach the level of the butt joint. This technical effect breaks through the performance bottleneck of the traditional T-shaped corner joint and provides technical support for the lightweight design of hydraulic support structure.

[0031] Example 1: Welding of T-joints on Q690D high-strength steel plates Materials: The base material is Q690D high-strength low-alloy steel with a plate thickness of 20mm; the welding wire is a solid welding wire with matching strength (diameter 1.2mm).

[0032] Method and steps: Heat source and location: Use a deep penetration submerged arc welding machine with a current of 450A, a voltage of 34V, and a welding speed of 36cm / min. Place the T-joint in the boat-shaped welding position. Control the arc to penetrate the surface of the molten pool and burn internally (keyhole effect).

[0033] Beveling and assembly: Design a K-type bevel with a 2mm blunt edge and a 45° bevel angle. The assembly gap should be controlled within 1.5mm (locally relaxed to 1.8mm, within the range of 1-2mm).

[0034] Heat input control: Calculate heat input E = η × UI = 0.8 × (450 × 34 × 60) / (10 × 36) / 1000 = 2.04 KJ / mm. Since the base material is Q690D, E must be strictly controlled to ≤ 2.2 KJ / mm.

[0035] Weld radius optimization: Based on finite element analysis, the traditional process requires a weld radius of 10mm. In this embodiment, due to the increased penetration depth, the weld radius is optimized to 7mm.

[0036] Effect verification: Penetration depth: Post-weld dissection inspection showed that the weld penetration depth reached 7.2mm (within the range of 6-8mm), which is about 3.6 times higher than that of traditional electric arc (about 2mm).

[0037] No root cleaning required: The back weld is flat and the back fusion line completely covers the incomplete fusion area of ​​the front root pass, so no root cleaning is required.

[0038] Performance: The mechanical properties of the joint meet the ISO15614-1:2017 / Amd1:2019 standard, and the impact energy at -20℃ reaches 95J (far exceeding the standard requirement of 47J).

[0039] Failure mode: Fatigue tests showed that the crack originated at the weld toe, and no weld root cracks were found, thus achieving failure mode transfer.

[0040] Example 2: Full penetration welding of Q550D thin plate structure Material: The base material is Q550D, and the plate thickness is 12mm (≤14mm).

[0041] Method and steps: Heat source and heat input: Deep melting submerged arc is used to control the heat input to 2.4KJ / mm (Q550D upper limit).

[0042] Assembly and Position: T-joint, welded at the ship-shaped position.

[0043] Melt depth control: The target melt depth is set to 6mm or more.

[0044] Effect verification: Full penetration: Ultrasonic testing and metallographic analysis show that the weld achieves complete penetration of the double-sided T-shaped corner joint, with no incomplete fusion defects.

[0045] Performance breakthrough: Tensile properties and fatigue tests show that the static load strength and fatigue life of this T-joint reach the level of butt joints, breaking through the performance limitations of thin plate T-joints.

[0046] Formation: The weld surface has a beautiful appearance and meets the requirements of ISO5817-B:2023 standard.

[0047] Example 3: Verification of Material Saving in Deep Penetration Submerged Arc Welding Materials: Base material is Q550D, plate thickness is 20mm, weld length is 1000m.

[0048] Method and steps: Weld leg optimization: Utilizing the "principle of equal cross-sectional area," the weld leg is reduced by 1.5mm for every 2mm increase in penetration depth. Traditionally, a 9mm weld leg is required; this embodiment uses a 6mm weld leg.

[0049] Heat source and heat input: Deep melting submerged arc is used, with a heat input of 2.3 KJ / mm.

[0050] Assembly and Position: T-joint, welded at the ship-shaped position.

[0051] Effect verification: Economic benefits: The cross-sectional area of ​​a single weld is reduced by approximately 30%. Calculations show that approximately 1.13 kg of welding wire is saved per weld. Based on an annual production of 1000 such welds, the annual welding wire savings reach 1130 tons, exceeding the 1000 tons described in claim 8.

[0052] Example 4: Comparison of melting depth between ship-shaped and horizontal positions.

[0053] Material: The base material is Q550D steel, and the plate thickness is 20mm.

[0054] Method and steps: Group comparison: Group A (this invention): Ship-shaped welding position, heat input 2.2KJ / mm.

[0055] Group B (Comparison): Horizontal fillet weld position, heat input 2.2KJ / mm (equal heat input).

[0056] Process: T-type joints are all welded by submerged arc welding with a gap of 0.5mm.

[0057] Effect verification: Melt depth gain: Group A (ship-shaped) average melt depth 7.8mm; Group B (horizontal) average melt depth 5.5mm. The melt depth increased by 2.3mm in the ship-shaped position compared to the horizontal position. This is slightly higher than the 1-2mm increase due to parameter optimization, but it demonstrates a significant gain trend.

[0058] Forming quality: Group A welds are full and without undercut; Group B welds have slight sagging and poor forming coefficient.

[0059] Comparative Example 1: Conventional surface arc welding (non-submerged arc, heat input not optimized) Material: The base material is Q690D steel, and the plate thickness is 20mm.

[0060] Deviation parameters: MAG (80%Ar+20%CO2) gas shielded welding (surface combustion arc, non-submerged arc) is used.

[0061] Heat input is controlled at 1.8 KJ / mm (non-submerged arc, unable to increase penetration depth).

[0062] Beveling and assembly: Design a K-type bevel with a 2mm blunt edge and a 45° bevel angle. The assembly gap should be controlled within 1.5mm.

[0063] result: Insufficient penetration depth: Due to the "right-angle blocking effect", the electric arc only burns on the surface, and the measured penetration depth is only 1.8mm (far below the requirement of 6-8mm).

[0064] Root cleaning is necessary: ​​There is severe lack of fusion at the root, so carbon arc gouging is required to clean the root, which introduces the risk of carbon inclusion and increases the working time.

[0065] Performance not up to standard: Although the heat input is low, the joint fatigue strength is extremely low due to the lack of fusion defects.

[0066] Failure mode: Fracture surface analysis shows that the crack originated at the non-fusion point of the weld root, which is a hidden fatal defect and the failure mode transfer was not achieved.

[0067] Comparative Example 2: The blunt edge of the K-type bevel is too large and the assembly gap is out of control. Material: The base material is Q550D steel, and the plate thickness is 20mm.

[0068] Deviation parameters: It adopts a traditional thick plate bevel design with a blunt edge of 4mm (>2mm).

[0069] The assembly gap was artificially increased to 3mm (>2mm).

[0070] Heat source: submerged arc welding, heat input 2.4KJ / mm.

[0071] result: Root defects: Due to the excessive thickness of the blunt edge (4mm), although the deep-melting arc has high energy, it forms a "dead zone" at the root of the blunt edge, resulting in severe lack of fusion on the back side.

[0072] Risk of burn-through: The assembly gap of 3mm exceeds the adaptive limit of deep arc (6-8mm penetration depth only allows a 2mm gap), resulting in liquid metal loss, burn-through at the weld root, and extremely irregular formation.

[0073] Root cleaning is unavoidable: The back of the plant is poorly formed and root cleaning is necessary.

[0074] Conclusion: This study proves that the specific combination of "2mm blunt edge + 45° + 1-2mm gap" for the K-type bevel is a necessary condition for achieving "the back fusion line encompassing the unfused area on the front side", thus eliminating the need for root cleaning. Deviation of these parameters will lead to process failure.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A method for high-energy submerged arc welding with deep penetration for hydraulic support structural components, characterized in that, Includes the following steps: Assemble the hydraulic support structural components to form a T-type corner joint or a K-type bevel joint to be welded. For T-type corner joints, in order to reduce the tendency of defects caused by the increase in weld penetration value, the allowable assembly gap is between 0-0.5mm; For K-type bevel joints, the allowable local assembly gap is gradually increased according to the increase of the target weld depth value, and the allowable increase range is between 1-2mm; Using a submerged arc as the welding heat source, the arc heat source is controlled to penetrate the workpiece surface and enter the molten pool for combustion, so that the arc directly acts on the root of the weld. During the welding process, for T-type corner joints, welding is performed in the ship-shaped welding position, with an assembly gap of 0-0.5mm; for K-type bevel joints, a root-cleaning-free welding process is adopted, controlling the bevel blunt edge to be 2mm, the bevel angle to be 45°, and the assembly gap to be 1-2mm. Depending on the strength grade of the steel plate, the optimal welding heat input range is adjusted to 1.8-2.4 KJ / mm, and the lower the strength grade of the steel plate, the higher the welding heat input. During the welding process, the weld leg size is reduced accordingly based on the increase in penetration depth, under the same strength conditions.

2. The high-energy submerged arc deep penetration welding method for hydraulic support structural components according to claim 1, characterized in that, The control strategy for the local assembly gap of the K-type bevel joint is as follows: When the target melt depth is 4-6mm, the permissible local assembly gap is increased to 1mm; When the target melting depth is increased to 6-8mm, the allowable local assembly gap is increased to 2mm.

3. The high-energy submerged arc deep penetration welding method for hydraulic support structural components according to claim 1, characterized in that, The control strategy for adjusting the heat source input is as follows: When the steel plate strength grade is Q550D or below, the welding heat input should be controlled to ≤2.4KJ / mm. When the steel plate strength grade is Q690D, the welding heat input should be controlled to be ≤2.2KJ / mm.

4. The high-energy submerged arc deep penetration welding method for hydraulic support structural components according to claim 1, characterized in that, For T-type corner joints, for every 2mm increase in the weld penetration, the weld leg size should be reduced by 1.0-1.5mm.

5. The high-energy submerged arc deep penetration welding method for hydraulic support structural components according to claim 1, characterized in that, For steel with strength grades of Q550D and below, T-type corner joints are used. When the thickness of the hydraulic support structural component to be welded is ≤14mm, the heat input is controlled to reach 2.4KJ / mm.

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