A large bearing cage copper / steel heterogeneous material welding process

Abstract

The application discloses a large bearing retainer copper / steel heterogeneous material welding process and belongs to the technical field of non-ferrous metal heterogeneous welding. The process steps are as follows: a welding flux is applied to the edge of the contact surface of an aluminum bronze pad and alloy steel, the pad is assembled and fixed on a steel body, after 80-150 DEG C preheating treatment, a tungsten inert gas welding is used for filling wire welding, and through suitable welding parameters, the filler metal and the two side base materials are fully intermelted to form a weld. The application can solve the problems of weld cracks and incomplete fusion of the aluminum bronze-alloy steel fillet weld and groove weld in the structure of the large bearing retainer, can effectively improve the root shape, greatly reduce the root stress concentration, finally significantly improve the toughness of the copper / steel heterogeneous weld, and improve the service safety and reliability of the retainer. The process disclosed by the application is not limited to the aluminum bronze-alloy steel composite retainer heterogeneous welding of the large bearing, and is also very suitable for solving the root defect problem of the aluminum bronze partial penetration joint.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal dissimilar welding technology, specifically to a welding process for large bearing cages made of copper / steel dissimilar materials. Background Technology

[0002] The main bearing is the "heart" of a large tunnel boring machine (TBM), primarily composed of an outer ring, an inner ring, rolling elements between the inner and outer rings, and a cage assembly. The cage, which encloses and moves with the rolling elements, plays a crucial role in isolating them, guiding their movement within the raceway, and providing lubrication space. Therefore, the cage material must possess high strength, high rigidity, good thermal conductivity, and low friction. Traditional TBM bearing cages use either steel or a single copper alloy. Steel has poor wear resistance and thermal conductivity, while copper alloys offer excellent wear resistance but are more expensive and have lower rigidity and toughness, neither of which meets the normal operating requirements of TBM bearings. Therefore, a copper / steel composite manufacturing technology is proposed, in which copper alloy pads are welded onto the steel body to leverage the advantages of both alloys. Figure 1 As shown. However, there are two main challenges in achieving good weld quality for the copper / steel cage structure: First, the mismatch in physicochemical properties between copper and steel can easily lead to problems such as incomplete fusion, steel side penetration cracks, and high residual welding stress if the process window is not selected properly. Second, the copper / steel cage weld structure is a partial penetration joint with gaps at the root, which not only easily causes oxidation of alloying elements Al and Mn in the molten pool, but also easily leads to stress concentration at the root.

[0003] This invention has conducted research on the dissimilar welding process of aluminum bronze / alloy steel for large bearing cages. Based on the research results, a dissimilar welding process of copper / steel for large bearing cages is proposed. By implementing this process, a well-formed aluminum bronze / alloy steel dissimilar weld with a good bond between the two side interfaces can be obtained. Summary of the Invention

[0004] The purpose of this invention is to provide a welding process for dissimilar copper / steel materials in large bearing cages. Using conventional tungsten inert gas (TIG) welding, without the need for complex and expensive protective measures, a well-formed aluminum bronze / alloy steel dissimilar weld with no root defects can be obtained. The weld has high strength and good toughness matching with the base material. This process is particularly suitable for assembly line processes in cage manufacturing.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A welding process for copper / steel dissimilar materials of a large bearing cage, wherein the bearing cage includes a steel cage body and a copper alloy pad, and the process involves welding the copper alloy pad to the steel cage body using tungsten inert gas welding.

[0007] The process includes the following steps:

[0008] (1) Before welding, apply flux to the bottom of the copper alloy pad to be welded, and then assemble the copper alloy pad onto the steel cage body according to the position requirements;

[0009] (2) Preheat the workpiece to be welded, and weld when the temperature of the part to be welded reaches between 80-150℃.

[0010] (3) Welding: The welding method is tungsten inert gas welding. Two welds are selected: root pass and fill pass. The welding current for the root pass is controlled at 125-150A, the welding current for the fill pass is controlled at 140-165A, and the interpass temperature is controlled between 80-150℃.

[0011] In step (1) above, the flux is cryolite, which can increase the fluidity of the weld in the molten pool, effectively improve the quality of the weld, and improve the purity of the weld. At the same time, the surface tension generated when the flux melts can improve the shape of the weld root, reduce the stress concentration at the root, and prevent cracks.

[0012] In step (1) above, the flux is first mixed with alcohol to form a paste before use. Specifically, 30-50 ml of anhydrous ethanol is added to every 100 g of cryolite and stirred until it becomes uniformly viscous. The paste form helps to control the amount applied, avoiding excessive application that could lead to inclusions in the weld and negatively impact performance. After preheating, the alcohol in the paste evaporates quickly, allowing the flux to adhere firmly. The flux does not fall off during flipping, handling, and transporting of the cage, making it very convenient for on-site assembly line operations of copper / steel cage welding.

[0013] During the welding process in step (3) above, the tungsten electrode is pointed vertically towards the root to ensure sufficient heat input for root welding. The upper limit of the current is specified to prevent excessive melting of the alloy steel side, which could lead to penetration cracks and solidification cracks.

[0014] In step (3) above, the current ranges used for the root pass and the fill pass are 125-145A and 146-165A, respectively.

[0015] Furthermore, the copper alloy pad is made of aluminum bronze, and nickel-aluminum bronze welding material of the same system as the aluminum bronze base material is selected for welding.

[0016] After welding using the process of this invention, the weld strength of the weld is better than that of the base material, and the impurity content of the weld is low.

[0017] The design concept and beneficial effects of this invention are as follows:

[0018] This invention utilizes cryolite as a flux for welding aluminum bronze, which increases weld fluidity in the molten pool, effectively improving weld quality and purity. Simultaneously, the molten flux protects the weld root, blocking oxygen, and the surface tension of the molten flux effectively improves the root shape, reducing root stress concentration. Based on a clear understanding of the crack formation mechanism in the weld, strict control of the process window ensures crack-free weld formation. The specific principles are as follows:

[0019] Because aluminum bronze contains 10% aluminum, a highly reactive element, special attention must be paid to weld oxidation during welding. The copper / steel cage welded structure is a partial penetration joint, and gaps at the root make it difficult to completely prevent oxygen intrusion. The flux used in this invention is cryolite, which melts under the high welding temperature, effectively preventing root air from causing oxidation of the molten pool.

[0020] This invention employs a double-layer welding process of root pass welding and filler weld welding. The welding currents must be greater than 125A and 140A respectively. This is achieved by limiting the minimum heat input to ensure that the aluminum bronze and steel substrate at the root melt and bond together.

[0021] One of the key factors affecting the microstructure and properties of welds is the amount of melting of the base metal on the alloy steel side. When the welding heat input is too high, the amount of melting in the steel matrix is ​​excessive, which easily leads to solidification shrinkage cracks. Simultaneously, excessive heat input can also cause liquid copper to penetrate along the heat-affected zone of the steel, resulting in penetration cracks. Therefore, this invention employs a double-layer welding method consisting of a root pass and a fill pass, with welding currents not exceeding 150A and 165A respectively, to ensure control of the upper limit of heat input, thereby limiting the amount of melting in the steel matrix and achieving the goal of avoiding solidification cracks and penetration cracks. Attached Figure Description

[0022] Figure 1 A schematic diagram of an aluminum bronze-alloy steel composite cage composed of copper alloy pads welded onto a steel bearing cage body.

[0023] Figure 2 The morphology and elemental analysis of the area near the root of the weld after welding according to the method in Example 1 are shown.

[0024] Figure 3 The specimen is a sample after tensile fracture of the welded joint following the welding method in Example 1.

[0025] Figure 4 The image shows a metallographic photograph of the weld root after welding using method 1 in Comparative Example 1.

[0026] Figure 5 This is a diagram showing the solidification crack defects inside the weld pool after welding using method 2, along with the corresponding elemental distribution. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0028] Example 1

[0029] Step 1: Clean the weld joint thoroughly, removing rust, oil, and moisture. Before welding, take an appropriate amount of cryolite powder and mix it with 40ml of anhydrous ethanol for every 100g of cryolite, stirring until a thick, uniform paste is formed. Apply the paste evenly to the edge of the aluminum bronze pad to be welded, then press the aluminum bronze pad down... Figure 1 The position requires assembly onto the steel cage body;

[0030] Step Two: After assembling the aluminum bronze spacers according to the required positions, preheat the welding area and surrounding area with an oxy-acetylene flame. Welding should commence when the welding temperature reaches 100℃ and the alcohol in the flux has completely evaporated. The base materials are aluminum bronze QAl10-5-5 and low-alloy steel Q355. The welding material is SCu6338 bare welding wire. The welding method is tungsten inert gas welding (TIG), using a two-pass weld: a root pass and a fill pass. The root pass welding current is 140A, and the fill pass welding current is 160A. The interpass temperature is 80-150℃.

[0031] After welding using the above method, the weld morphology photograph is as follows: Figure 2 As shown, the base materials on both sides are well fused with the weld, and there are no cracks or oxidation problems. Figure 3 The images show the transverse tensile test specimens of the weld after fracture. The fracture locations are all in the base metal, and the weld is intact, indicating that the weld strength is superior to that of the base metal. The corresponding fracture strengths are shown in Table 1. Table 2 shows the test results of the impurity element content in the weld, which shows that the impurity content in the weld is quite low.

[0032] This embodiment demonstrates that the method has excellent welding processability, stable and reliable weld performance, and is simple, efficient, and energy-saving to operate. It is suitable for copper / steel welding of large bearing copper-steel composite cage structures.

[0033] Table 1. Tensile strength of welded joints after welding according to Example 1.

[0034]

[0035]

[0036] Table 2. Elemental analysis of impurities in the weld seam after welding using the method in Example 1 (wt.%)

[0037]

[0038] Comparative Example 1

[0039] The base materials are aluminum bronze QAl10-5-5 and low-alloy steel Q355. The welding material is SCu6338 bare welding wire, and the welding method is tungsten inert gas welding (TIG). The welding method uses a root pass followed by a fill pass, with a root pass current of 140A and a fill pass current of 160A. The preheating temperature and interpass temperature are both 80-150℃. No flux is added before welding. A photograph of the welded root is shown below. Figure 4 As shown, a crack was found at the root, and the copper / steel interface was not fully welded.

[0040] Comparative Example 2

[0041] Step 1: Clean the weld joint of rust, oil, and moisture. Before welding, take an appropriate amount of cryolite powder and add 30-50ml of anhydrous ethanol per 100g of cryolite, stirring until it becomes a uniform and viscous consistency. Apply the flux evenly to the edge of the aluminum bronze block to be welded, and assemble the aluminum bronze block onto the steel retainer according to the positioning requirements.

[0042] Step Two: After assembling the copper blocks according to the required positions, preheat the welding area and surrounding area with an oxy-acetylene flame. Welding should proceed when the temperature reaches 80-150℃ and the alcohol in the flux has completely evaporated. The base materials are aluminum bronze QAl10-5-5 and low-alloy steel Q355, the welding material is SCu6338 bare welding wire, and the welding method is tungsten inert gas welding (TIG). Two weld passes are used: a root pass and a fill pass. The welding currents for the two passes are 180A and 190A respectively, and the interpass temperature is 80-150℃. Cracks appeared in the weld after welding. Upon dissection, it was found that the cracks were solidification cracks near the copper-steel interface. Figure 5 As shown.

[0043] It is worth emphasizing that although specific illustrative embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, those skilled in the art can make corresponding changes based on the above technical solutions and concepts, combined with practical considerations. All such changes should fall within the protection scope of the present invention as defined and determined by the appended claims.

Claims

1. A large bearing cage copper / steel dissimilar material welding process characterized by: The bearing cage comprises a steel cage body and a copper alloy pad, and the process is to weld the copper alloy pad to the steel cage body by using tungsten argon arc welding method; The process comprises the following steps: (1) before welding, the flux is applied on the bottom of the copper alloy pad to be welded, and then the copper alloy pad is assembled on the steel cage body according to the position requirement; The flux is first mixed with alcohol to form a paste before use, specifically, 30-50ml of anhydrous ethanol is added to 100g of cryolite and stirred until uniform and thick; (2) preheat the workpiece to be welded, and weld when the temperature of the welding part reaches 80-150℃; (3) welding: the welding method is tungsten argon arc welding, and two welds of backing welding and filling welding are selected to form a weld, wherein: the welding current of backing welding is controlled at 125-150A, the welding current of filling welding is controlled at 140-165A, and the interpass temperature is controlled at 80-150℃.

2. The large bearing retainer copper / steel dissimilar material welding process of claim 1, wherein: In step (3), the tungsten electrode is vertically directed to the root.

3. The large bearing retainer copper / steel dissimilar material welding process of claim 1, wherein: In step (3), the current ranges of the backing welding and the filling welding are 125-145A and 146-165A respectively.

4. The large bearing retainer copper / steel dissimilar material welding process of claim 1, wherein: The material of the copper alloy pad is aluminum bronze, and the nickel aluminum bronze welding material of the same system as the aluminum bronze base material is selected during welding.

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