A gray cast iron interface flange and low carbon steel transition flange connecting welding process

Abstract

This invention discloses a welding process for connecting a gray cast iron interface flange and a low-carbon steel transition flange. By creating a bevel on one side of the gray cast iron interface flange, and using a combination of manual argon arc welding and shielded metal arc welding with φ3.2mm Z116 welding rods and φ3.2mm and φ4.0mm E5015 welding rods, an optimized welding process is employed to sequentially complete the welding of the transition layer, the root pass, the filler layer, and the capping layer. This effectively solves the production problems of leakage and the inability to replace parts in the bolted connection between the gray cast iron interface flange and the low-carbon steel transition flange of the blast furnace top residual pressure energy recovery power equipment reducer box. The process not only provides stable welding quality and high work efficiency, but also ensures safety, ease of operation, and low maintenance costs, effectively meeting the actual needs of the site and reducing operation and maintenance costs.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, specifically relating to a welding process for connecting a gray cast iron interface flange and a low carbon steel transition flange. Background Technology

[0002] Blast furnace top residual pressure energy recovery power equipment is an auxiliary device used in blast furnace smelting to recover secondary energy from the residual pressure and heat of the by-product generated during blast furnace smelting—the top gas. Currently, the reducer housing interface flange and recovery pipeline flange of stable blast furnace top residual pressure energy recovery power equipment are generally connected by transition flanges, such as… Figure 1 and 2 As shown, the reducer housing interface flange is gray cast iron interface flange 1, and the transition flange 2 and the recovery pipe flange 3 are both made of low carbon steel. The gray cast iron interface flange 1 and the recovery pipe flange 3 are respectively connected and fixed to both sides of the low carbon steel filter flange 2 by connecting bolts 4. After long-term use, because the gray cast iron interface flange 1 and the low carbon steel filter flange 2 are fixed by connecting bolts 4, air leakage and water leakage often occur. Considering that the equipment parts cannot be replaced and the requirements of rapid production are met, the best solution is to directly weld the original bolt connection on site with guaranteed quality and quantity, and ensure that there are no welding defects in MT and PT penetrant testing. However, the gray cast iron interface flange 1 and the low carbon steel transition flange 2 are dissimilar steel materials with poor weldability. The following problems will exist when welding: (1) Cast iron is prone to white cast iron structure, cold cracks and pores. The thermal expansion coefficients of the two materials are very different, and the residual stress of welding is prone to joint cracking. (2) On-site welding is done in situ without preheating or slow cooling after welding. The operating space is small and the process control is extremely difficult. (3) At the same time, it is necessary to meet the requirements of MT and PT flaw detection without defects. It is necessary to eradicate leakage and ensure the strength and sealing of the joint. The prevention and control of welding defects and quality management are extremely challenging. Summary of the Invention

[0003] This invention provides a welding process for connecting a gray cast iron interface flange and a low-carbon steel transition flange, which effectively solves the production problems of leakage and inability to replace parts in the bolted connection between the gray cast iron interface flange and the low-carbon steel transition flange of the gearbox of the existing blast furnace top residual pressure energy recovery power equipment. By optimizing the welding scheme, welding defects are eliminated, the problem of air and water leakage at the flange connection is completely solved, and equipment production can be quickly restored.

[0004] The technical solution of this invention to solve the technical problem is as follows:

[0005] This invention provides a welding process for connecting a gray cast iron interface flange and a low-carbon steel transition flange. The gray cast iron interface flange and the low-carbon steel transition flange are vertically arranged and fixed together by multiple connecting bolts. The welding process steps are as follows:

[0006] S1. A bevel is prepared along the edge of the gray cast iron interface flange on the side corresponding to the low carbon steel transition flange. The bevel is heated to remove oil and moisture, and then polished to remove rust, so that the bevel reveals a metallic luster.

[0007] S2. Using a combination of manual argon arc welding and shielded metal arc welding (SMAW) with a welding machine and φ3.2 Z116 welding rods, employing DC reverse polarity, low current, and short arc welding, and controlling the penetration depth to ≤2mm, a transition layer is welded on one side of the bevel of the gray cast iron interface flange. The transition layer is welded in multiple layers and passes, each ≤3mm, with each subsequent pass covering 2 / 3 of the previous pass. After welding, the weld surface is cleaned to ensure the weld is smooth and free of any welding defects. Each weld pass employs intermittent welding and short-segment welding. The intermittent welding consists of skip welding and symmetrical welding. Two symmetrical points are set along the edge of the gray cast iron interface flange, and skip welding is performed symmetrically from these two points simultaneously. Each segment of the short-segment welding is 10–30mm long, stopping once the length is reached, and the weld is immediately hammered.

[0008] S3. Using a combination of manual argon arc welding and shielded metal arc welding machine with φ3.2mm and φ4.0mm E5015 welding electrodes, and employing a straight-line welding method, DC reverse polarity, low current, and narrow-channel welding, the welding of the root pass, filler pass, and cover pass is completed sequentially from the inside to the outside at the bevel between the transition layer and the low-carbon steel transition flange.

[0009] S4. After all welding is completed, wrap the weld with insulating cotton and let it cool slowly to room temperature. Then, use MT and PT for flaw detection to ensure that there are no welding defects in the weld.

[0010] Furthermore, the combined manual argon arc welding and shielded metal arc welding machine is a Panasonic YC-400TX4 combined manual argon arc welding and shielded metal arc welding machine.

[0011] Furthermore, the bevel is heated with an oxy-acetylene flame to remove oil and moisture, and then polished with carbon arc gouging and plasma gouging to expose a metallic luster.

[0012] Furthermore, the φ3.2mm and φ4.0mm E5015 welding electrodes are dried at 350℃ for 1 hour and placed in an insulated container for immediate use.

[0013] Furthermore, during the welding of the transition layer, the welding temperature is controlled to be ≤250℃.

[0014] Furthermore, when welding the underlayer, filler layer and cover layer, after each weld layer reaches 10mm, local welding stress is further eliminated by hammering to ensure that there are no welding defects before welding the next layer. The cover layer must maintain a smooth transition.

[0015] Furthermore, during the welding of the transition layer, the welding current is 90-120A, the arc voltage is 22±1V, and the welding speed is 15±1cm·min. -1 For the root pass welding, use φ3.2mm E5015 welding rods, welding current of 100-120A, arc voltage of 22±1V, and welding speed of 15±1cm·min. -1 When welding the filler layer and the cover layer, use φ4.0mm E5015 welding rods, welding current of 140-180A, arc voltage of 24±1V, and welding speed of 17±1cm·min. -1 .

[0016] Compared with existing technologies, the welding process for connecting gray cast iron interface flanges and low carbon steel transition flanges described in this invention, through the optimization of welding equipment, welding materials, and welding processes, can be directly implemented on-site. This not only ensures stable welding quality and high work efficiency, but also ensures safety, ease of operation, and low maintenance costs, effectively meeting actual on-site needs and reducing operation and maintenance costs. Attached Figure Description

[0017] Figure 1 This is a three-dimensional schematic diagram of the connection between the gray cast iron interface flange and the recycling pipeline flange in this invention via a low-carbon steel transition flange.

[0018] Figure 2 This is a front view of the connection between the gray cast iron interface flange and the recycling pipeline flange in this invention via a low-carbon steel transition flange.

[0019] Figure 3 This is a schematic diagram of the welding of the gray cast iron interface flange and the low carbon steel transition flange at the bevel in this invention.

[0020] In the diagram: 1. Gray cast iron interface flange; 2. Low carbon steel transition flange; 3. Recycling pipe flange; 4. Connecting bolts; 5. Bevel; 6. Transition layer; 7. Underlayment; 8. Filler layer; 9. Topcoat layer. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this disclosure pertains. The terms "upper," "lower," "left," "right," "front," and "back" used in the present patent application specification and claims are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship also changes accordingly. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Any aspects not detailed in this invention are well-known to those skilled in the art.

[0022] like Figure 1-3 As shown, the present invention provides a welding process for connecting a gray cast iron interface flange and a low carbon steel transition flange. The gray cast iron interface flange 1 and the low carbon steel transition flange 2 are vertically arranged and fixed by multiple connecting bolts 4. The gray cast iron interface flange 1 and the low carbon steel transition flange 2 are now connected and fixed by welding.

[0023] Preparation before welding:

[0024] 1) Welding equipment: Panasonic YC-400TX4 manual TIG welding and shielded metal arc welding combined welding machine; welding materials: Z116 welding rods φ3.2mm, E5015 welding rods φ3.2mm and φ4.0mm; dried at 350°C for 1 hour, then placed in an insulated container for use as needed.

[0025] 2) Heating and beveling equipment: Oxy-acetylene flame (to remove moisture and oil), carbon arc gouging ZX5-630 and plasma gouging LGK-100MA;

[0026] 3) Auxiliary equipment: angle grinder, file, hammer, chisel, face mask, template, thermometer, magnifying glass, insulation cotton, sandpaper, etc.;

[0027] 4) Welding materials: gray cast iron, Q235 steel (low carbon steel);

[0028] 5) Pre-welding requirements: The welding area and welding materials must be free of oil, oxide layer, moisture, etc., and the metal luster must be exposed; use an oxyacetylene flame to remove rust, grease, moisture, etc., and then grind with sandpaper or a grinding wheel to remove rust.

[0029] 6) Welding position: Horizontal fixed welding 2G;

[0030] 7) Welding requirements: The dissimilar metal overlay layer must be fused with the base metal, the weld must be free of any welding defects and meet the design dimensions;

[0031] Welding process parameters

[0032] Welding electrode type weld layer Electrode diameter / mm Welding current A Arc voltage / V <![CDATA[Welding speed / (cm`min -1 )]]> Z116 Transition layer on one side of cast iron 3.2 90-120 22±1 15±1 E5015 Start from the bottom 3.2 100-120 22±1 15±1 E5015 Filler, cover layer 4.0 140-180 24±1 17±1

[0033] The connection and welding process steps are as follows:

[0034] S1. Along the edge of the gray cast iron interface flange 1, a bevel 5 is prepared on the side corresponding to the low carbon steel transition flange 2. Oil and moisture are removed at the bevel 5 by heating with an oxy-acetylene flame, and rust is removed by carbon arc gouging and plasma gouging, so that the bevel 5 exposes a metallic luster.

[0035] S2. Using a Panasonic YC-400TX4 manual TIG welding and shielded metal arc welding combined welding machine and φ3.2mm Z116 welding rod, with DC reverse polarity (workpiece negative, welding torch positive), low current, short arc (φ3.2mm, 90–120A) welding, stabilize the arc, reduce spatter, and control the penetration depth ≤2mm, weld the transition layer 6 on the bevel 5 side of the gray cast iron interface flange 1. When welding the transition layer 6, multiple layers and multiple passes are used, each layer ≤3mm. Each pass covers about 2 / 3 of the previous pass. After welding, the weld surface is cleaned to ensure that the weld is flat and free of any welding defects, which facilitates the subsequent welding of the root layer 7, filler layer 8 and cover layer 9. Each weld uses intermittent welding and short-segment welding. Intermittent welding is skip welding and symmetrical welding. Two symmetrical points are set along the edge of the gray cast iron interface flange 1. Skip welding is performed symmetrically from the two symmetrical points at the same time. At the same time, the welding layer temperature is controlled to ≤250℃ to avoid uneven local temperature. Each segment of the short-segment welding is 10-30mm. Stop when the length is reached and immediately hammer the weld to eliminate stress and refine the grain.

[0036] S3. Using a Panasonic YC-400TX4 manual TIG welding and shielded metal arc welding combined welding machine and φ3.2mm and φ4.0mm E5015 welding electrodes, employing a straight-line welding method, DC reverse polarity, low current, and narrow-channel welding, the root pass 7, filler pass 8, and capping pass 9 are welded sequentially from the inside out at the bevel 5 between the transition layer 6 and the low-carbon steel transition flange 2. The weld surface is cleaned layer by layer. When the weld layer reaches 10mm, it must be hammered to further eliminate local welding stress. After ensuring that there are no welding defects, the next layer is welded. The capping pass maintains a smooth transition.

[0037] S4. After all welding is completed, wrap the weld with insulating cotton and let it cool slowly to room temperature. Then, use MT and PT for flaw detection to ensure that there are no welding defects. Once it fully meets the requirements, it can be put into use.

Claims

1. A welding process for connecting a gray cast iron interface flange and a low carbon steel transition flange, wherein the gray cast iron interface flange (1) and the low carbon steel transition flange (2) are vertically arranged and fixed together by a plurality of connecting bolts (4), characterized in that, The connection welding process steps are as follows: S1. Prepare a bevel (5) along the edge of the gray cast iron interface flange (1) on the side corresponding to the low carbon steel transition flange (2). Heat the bevel (5) to remove oil and moisture, and grind to remove rust, so that the bevel (5) exposes a metallic luster. S2. Using a combination of manual argon arc welding and shielded metal arc welding machine and φ3.2mm Z116 welding rod, DC reverse polarity, low current, and short arc welding are adopted to control the penetration depth ≤2mm. A transition layer (6) is welded on the bevel (5) side of the gray cast iron interface flange (1). When welding the transition layer (6), multiple layers and multiple passes are adopted, each layer ≤3mm, and the subsequent pass covers 2 / 3 of the previous pass. After welding, the weld surface is cleaned to confirm that the weld is flat and free of any welding defects. Each weld uses intermittent welding and short segment welding. The intermittent welding is skip welding and symmetrical welding. Two symmetrical points are set along the edge of the gray cast iron interface flange (1), and skip welding is performed symmetrically with the two symmetrical points as the starting point. Each segment of the short segment welding is 10-30mm. The welding stops when the length is reached, and the weld is hammered immediately. S3. Using a combination of manual argon arc welding and shielded metal arc welding machine and E5015 welding rods of φ3.2mm and φ4.0mm, the welding of the base layer (7), filler layer (8) and cover layer (9) is completed from the inside out at the bevel (5) between the transition layer (6) and the low carbon steel transition flange (2). S4. After all welding is completed, wrap the weld with insulating cotton and let it cool slowly to room temperature. Then, use MT and PT for flaw detection to ensure that there are no welding defects in the weld.

2. The welding process for connecting a gray cast iron interface flange and a low-carbon steel transition flange according to claim 1, characterized in that, The combined manual argon arc welding and shielded metal arc welding machine is a Panasonic YC-400TX4 combined manual argon arc welding and shielded metal arc welding machine.

3. The welding process for connecting a gray cast iron interface flange and a low-carbon steel transition flange according to claim 1, characterized in that, The bevel (5) is heated with an oxy-acetylene flame to remove oil and moisture, and then polished with a carbon arc gouging and a plasma gouging to expose a metallic luster.

4. The welding process for connecting a gray cast iron interface flange and a low-carbon steel transition flange according to claim 1, characterized in that, The φ3.2mm and φ4.0mm E5015 welding electrodes are dried at 350℃ for 1 hour and then placed in an insulated container for immediate use.

5. The welding process for connecting a gray cast iron interface flange and a low-carbon steel transition flange according to claim 1, characterized in that, When welding the transition layer (6), the welding layer temperature is controlled to be ≤250℃.

6. The welding process for connecting a gray cast iron interface flange and a low-carbon steel transition flange according to claim 1, characterized in that, When the base layer (7), filler layer (8) and cover layer (9) are welded, after each weld layer reaches 10mm, the local welding stress is further eliminated by hammering. After ensuring that there are no welding defects, the next layer is welded. The cover layer must maintain a smooth transition.

7. The welding process for connecting a gray cast iron interface flange and a low-carbon steel transition flange according to claim 1, characterized in that, When welding the transition layer (6), the welding current is 90-120A, the arc voltage is 22±1V, and the welding speed is 15±1cm·min. -1 When welding the root pass (7), use φ3.2mm E5015 welding rods, welding current 100-120A, arc voltage 22±1V, and welding speed 15±1cm·min. -1 When welding the filler layer (8) and the cover layer (9), use φ4.0mm E5015 welding rods, welding current 140-180A, arc voltage 24±1V, and welding speed 17±1cm·min. -1 .

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