A welding fixing process method of a liner pipe fitting

Abstract

The application discloses a kind of welding fixing process methods of inner container pipe fittings, belong to water heater production technical field;The method comprises: S1, punching: pipe fitting installation hole is set up on the middle section of inner container, and punching direction is punched from inside to outside, forms the hole structure of outward flanging, so that smooth surface is located inside, burr is located outside;S2, butt welding: after coaxial compression positioning of pipe fitting and inner container punching place, butt welding is carried out using butt welding positioning tool, and high temperature of butt welding makes outside burr melt, while compression makes local annealing and flattening of inner container arc, and clearance is eliminated;S3, tight welding: sealing welding is carried out at connecting portion;The application is by changing punching direction and eliminating burr in the melting of butt welding, and is flattened by cooperating butt welding, to realize gapless connection, without subsequent chamfering treatment, not only save process, reduce cost, but also inside of inner container is smooth without sharp angle, significantly improve the adhesion quality of enamel layer and the anticorrosion life of inner container.

Description

Technical Field

[0001] This invention relates to the field of water heater manufacturing technology, and in particular to the improvement of the inner tank welding process. Background Technology

[0002] The enamel-lined inner tank is the most widely used core component in storage-type electric water heaters. Its manufacturing typically involves three stages: steel plate processing and forming, welding and assembly, and enamel sintering. Among these, the welding quality between the pipe fittings and the inner tank directly affects the adhesion of the enamel layer and the final corrosion resistance lifespan of the inner tank. Conventional enamel-lined inner tank processing methods often leave burrs on the inner wall during punching. During welding, gaps can easily form between workpieces due to these burrs, and the weld joints on the pipe walls lack beveling design. These issues can lead to defects such as sharp corners, incomplete enamel application, and enamel layer peeling during subsequent enamel finishing processes, severely impacting the corrosion resistance and service life of the inner tank.

[0003] Chinese patent document CN111043779B discloses a method for treating the root of the water pipe in the inner liner of an enamel water tank. After the water pipe and the inner liner end cap are assembled and welded, a chamfering drill bit is used to chamfer and smooth the welded joint along the radial direction of the water pipe. The chamfering structure gradually transitions in size from the side of the water pipe away from the end cap axis to the side closer to the end cap axis. The gap generated by the assembly of the two workpieces is eliminated by machining, and the surface of the workpiece joint is smoothly transitioned, thereby ensuring that the enamel layer is uniform and continuous after enamel treatment, without enamel defects and flaws.

[0004] However, although the above technical solution can eliminate the gaps in the workpiece assembly through chamfering after welding, it still has the following drawbacks: First, the above solution requires an additional machining process (chamfering) after welding, which not only increases the production steps and processing costs, but also requires high operational precision. Improper chamfering may damage the workpiece surface. Second, the above solution only addresses the post-construction "repair" of the weld gaps, and does not solve the root cause of the gaps caused by punching burrs. Since the punching direction still adopts the conventional outside-to-in punching method, burrs left inside the inner liner or easily lift the workpiece during welding. Even subsequent chamfering cannot eliminate the local stress concentration or welding defects caused by burrs. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, a welding and fixing process for inner tubing fittings is provided.

[0006] This invention is achieved through the following technical solution: a welding and fixing process for an inner tubing fitting, comprising the following steps:

[0007] S1. Punching: Pipe installation holes are made in the middle section of the inner liner. The punching direction of the pipe installation holes is from the inside of the inner liner to the outside, forming an outward-turned hole structure, so that the smooth surface of the punching edge is located on the inside of the inner liner and the punching burrs are located on the outside of the inner liner.

[0008] S2. Spot welding: After using spot welding positioning fixtures to coaxially press and position the pipe fitting and the punched part of the middle section of the inner liner, spot welding is performed. During the spot welding process, high temperature is used to melt the burrs on the outside of the punched part, and at the same time, the pressing action is used to locally anneal and flatten the arc of the middle section of the inner liner, eliminating the gap between the pipe fitting and the inner liner.

[0009] S3. Sealing weld: Sealing weld is performed at the connection between the pipe fitting and the middle section of the inner liner.

[0010] In a preferred embodiment of the present invention, before the pipe fitting is welded tightly in step S3, a bevel is made at the weldable part of the pipe wall of the pipe fitting.

[0011] In a preferred embodiment of the present invention, the weld surface between the pipe fitting and the punched section of the inner liner is a plane to ensure that the arc of the inner liner is evenly flattened during the weld.

[0012] In a preferred embodiment of the present invention, in step S2, the high-temperature pressing action during the welding of the pipe fittings causes local annealing at the arc section of the inner liner, which is then used for subsequent flattening.

[0013] In a preferred embodiment of the present invention, punching, spot welding and tight welding are performed sequentially and continuously. During the spot welding process, burrs are melted and gaps are eliminated simultaneously, eliminating the need for subsequent mechanical chamfering.

[0014] In a preferred embodiment of the present invention, in step S1, the punching is performed by punching from the inside of the inner liner outward using a stamping die to form an outward flange structure, the length of which matches the wall thickness of the pipe to be welded.

[0015] In a preferred embodiment of the present invention, during the pipe fitting welding step, the applied current and pressure completely melt the burrs and form a local metallurgical bond, while the arc section of the inner liner is flattened to be flush with the pipe fitting welding surface.

[0016] In a preferred embodiment of the present invention, the spot welding positioning fixture includes a spot welding copper electrode, a push rod, a positioning post, a return spring, and a spot welding copper base; the push rod is drivenly connected to the spot welding copper electrode; the spot welding copper base is provided with an axially extending guide groove, the return spring is accommodated in the guide groove, and the opening of the guide groove is opposite to the pipe fitting mounting hole in the middle section of the inner liner; the positioning post is axially slidably inserted into the guide groove; in the pre-welding assembled state, the pipe fitting, the positioning post, and the pipe fitting mounting hole are coaxially arranged.

[0017] In a preferred embodiment of the present invention, in step S2, during spot welding, the welding copper electrode drives the push rod to move downward, the front end of the push rod extends into the inside of the pipe fitting and abuts against the positioning post, pushing the positioning post back into the guide groove and compressing the reset spring, so that the positioning post disengages from the pipe fitting mounting hole. At this time, the positioning function is switched from the positioning post to the push rod. Subsequently, the push rod presses the pipe fitting and the middle section of the inner liner and applies welding current for spot welding. After the spot welding is completed, the push rod resets upward and moves out of the pipe fitting. The reset spring rebounds and drives the positioning post to slide upward and reset, which is used to realize the quick disassembly of the workpiece.

[0018] In a preferred embodiment of the present invention, the inner liner is an enamel liner, and the welding and fixing process is completed before the enamel sintering, so that the smooth inner surface of the inner liner is easy to cover with enamel glaze later.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] A welding and fixing process for inner liner fittings is proposed. By limiting the punching direction to punching from the inside of the inner liner outward, burrs are left on the outside and smooth surfaces are left on the inside, providing ideal inner surface conditions for subsequent enamel sintering. At the same time, the burrs are melted and local annealing and gap elimination are achieved during the spot welding process. A gapless welded joint can be obtained without additional processes, significantly improving welding quality and enamel layer adhesion.

[0021] Furthermore, before sealing welding, a bevel is made on the pipe wall to allow the weld material to fully penetrate into the molten pool formed by the bevel during sealing welding, resulting in a full weld filler, improved joint mechanical strength and sealing performance, and reduced welding defects.

[0022] Furthermore, the weld surface between the fitting and the inner liner at the punched hole is designed as a plane to ensure that a uniform clamping force is applied to the arc section of the inner liner during welding, avoiding insufficient clamping or deformation due to poor contact of the curved surface, which is conducive to achieving gapless welding in the entire circumferential direction.

[0023] Furthermore, the high-temperature pressing effect during spot welding allows for localized annealing of the arc section in the middle of the inner liner, reducing the hardness and yield strength of this area, making it easier to flatten and less prone to springback, thus ensuring the permanent elimination of gaps after spot welding and long-term joint stability.

[0024] Furthermore, punching, spot welding, and tight welding are carried out sequentially. During the spot welding process, burrs are melted and gaps are eliminated simultaneously, eliminating the need for mechanical chamfering after welding. This saves on process and equipment costs, improves production efficiency, and avoids potential damage caused by secondary processing.

[0025] Furthermore, by matching the length of the outer flange formed by the punching with the wall thickness of the pipe fitting, it is ensured that the pipe fitting and the flange form a proper fit after insertion, which facilitates stable positioning before spot welding, and will not affect the welding quality or cause stress concentration due to the flange being too long or too short.

[0026] Furthermore, during the spot welding process, applying appropriate current and pressure completely melts the burrs and forms a local metallurgical bond. At the same time, the inner liner's arc is flattened to be flush with the spot welding surface of the pipe fitting, achieving atomic-level bonding of the welding surface, eliminating physical gaps, and improving the tensile strength and fatigue resistance of the joint.

[0027] Furthermore, by setting the spot welding positioning fixture as a combination of spot welding copper electrode, push rod, return spring, positioning post and spot welding copper base, and by making the pipe fitting, positioning post and pipe fitting mounting hole coaxial before welding, the precise alignment and positioning stability of the assembly before welding are ensured, thereby avoiding welding defects caused by misalignment and creating good conditions for the uniform coverage of the subsequent enamel layer.

[0028] Furthermore, during the spot welding process, the welding copper electrode drives the push rod downwards. The front end of the push rod extends into the pipe fitting and abuts against the positioning pin, pushing it back into the guide groove and compressing the return spring. This causes the positioning pin to actively disengage from the pipe fitting's mounting hole, and the positioning function switches from the positioning pin to the push rod. This design effectively prevents the positioning pin from being mistakenly welded between the pipe fitting and the inner liner due to high temperature or current during welding, protecting the tooling itself and avoiding welding defects. After the spot welding is completed, the push rod returns to its original position and moves out of the pipe fitting. The return spring rebounds, driving the positioning pin to slide upwards and return to its original position, achieving rapid disassembly of the workpiece. This automatic reset function requires no additional operation or external force, significantly improving the efficiency and ease of operation of the welding operation, while avoiding secondary damage to the workpiece caused by improper disassembly.

[0029] Furthermore, it is clarified that this welding and fixing process is applied before the enamel sintering of the enamel inner liner. The smooth surface of the inner side of the liner facilitates the uniform coverage of the enamel slurry, improves the adhesion strength and corrosion resistance of the enamel layer, and extends the service life of the liner.

[0030] Other features and advantages of the present invention will be disclosed in detail in the following detailed description and accompanying drawings. Attached Figure Description

[0031] The invention will be further described below with reference to the accompanying drawings:

[0032] Figure 1 This is a schematic diagram of a welding and fixing process for an inner tubular component according to the present invention.

[0033] Figure 2 for Figure 1 Enlarged structural diagram at point A in the middle;

[0034] Figure 3 This is a schematic diagram of the structure of the spot welding positioning fixture of the present invention before spot welding;

[0035] Figure 4This is a schematic diagram of the welding positioning fixture of the present invention during welding.

[0036] Figure 5 This is a schematic diagram of the tight welding method of the present invention.

[0037] The annotations in the attached figures are explained as follows:

[0038] Inner liner 1, pipe mounting hole 2, spot welding positioning fixture 3, pipe fitting 4, spot welding copper pole 31, top rod 32, positioning column 33, reset spring 34, spot welding copper base 35, guide groove 351. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be explained and described below with reference to the accompanying drawings. However, the following embodiments are only preferred embodiments of the present invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments in the implementation methods without creative effort are all within the protection scope of the present invention.

[0040] In the following description, terms such as “inner,” “outer,” “upper,” “lower,” “left,” and “right” are used only to indicate orientation or positional relationship for the convenience of describing the embodiments and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0041] like Figures 1 to 4 As shown, taking the production of an enamel-lined inner liner as an example, the welding and fixing process of an inner liner fitting according to the present invention is as follows: The middle section of the inner liner 1 is made of a special enamel-lined steel plate (such as DC04 or BTC1 cold-rolled steel plate) with a thickness of 1.8mm to 2.5mm, which is rolled and welded with straight seams to form a cylinder. This cylinder is the middle section of the inner liner 1, and fittings 4 need to be welded on it for water inlet / outlet or installation of other functional components.

[0042] First, the punching step S1 is performed: the middle section of the inner liner 1 is fixed on the stamping die, and the pipe fitting mounting hole 2 is punched from the inside of the inner liner 1 outwards. During punching, the punch of the die moves from the inside of the inner liner 1 outwards, so that the smooth surface of the punched edge is naturally formed on the inside of the inner liner 1, while the burrs generated by punching are pushed to the outer welding surface. The core function of this punching direction is that the smooth inner surface provides an excellent surface condition for the subsequent enamel slurry coverage, avoiding sharp corners, scorching, or bubbles in the enamel layer caused by burrs; while the burrs left on the outside can be melted away by high temperature in the subsequent spot welding process, thus fundamentally solving the problem that burrs remain inside the inner liner and cannot be removed when punching from the outside in in conventional methods. At the same time, the punching forms an outwardly flanged hole structure, and the flange length needs to be designed to match the wall thickness of the pipe fitting 4 to be welded. For example, when the wall thickness of pipe fitting 4 is 1.2mm, the flange length is controlled between 1.0 and 1.5mm, so that after pipe fitting 4 is inserted, it forms a suitable interference fit or positioning fit with the root of the flange. If the flange is too short, the positioning will be unstable, and if the flange is too long, it will interfere with folding. After punching, the inner side of the inner liner 1 is smooth and burr-free, while the outer flange and burrs are located on the outer side.

[0043] Next, the spot welding step S2 is performed: Spot welding is a process that uses resistance heating to partially fuse the pipe fitting 4 to the inner liner 1. In order to achieve precise coaxial positioning and stable clamping, the present invention adopts a special spot welding positioning fixture 3. The spot welding positioning fixture 3 includes a spot welding copper electrode 31, a push rod 32, a positioning post 33, a return spring 34, and a spot welding copper base 35; the push rod 32 is connected to the spot welding copper electrode 31; the spot welding copper base 35 is provided with an axially extending guide groove 351, and the return spring 34 is housed in the guide groove 351. The groove opening of the guide groove 351 is opposite to the pipe fitting mounting hole 2 in the middle section of the inner liner 1; the positioning post 33 is axially slidably inserted into the guide groove 351; in the pre-welding assembled state, the pipe fitting 4, the positioning post 33, and the pipe fitting mounting hole 2 are coaxially arranged.

[0044] The lower end face (welding surface) of fitting 4 is pre-machined into a flat surface and contacts the arc surface of the middle section of inner liner 1. The reason for designing the welding surface of fitting 4 as a flat surface is that the middle section of inner liner 1 is an arc surface. If the welding surface of fitting 4 is also an arc surface, the two will be in line contact or even point contact. The pressure distribution during welding will be extremely uneven, which can easily lead to local incompatibility or overpressure deformation. When the flat surface contacts the arc surface, the arc surface will undergo plastic deformation under the action of clamping force, gradually fitting the entire flat surface, thereby achieving uniform contact in the entire circumferential direction.

[0045] During spot welding, the spot welding copper electrode 31 drives the push rod 32 to move downward. The front end of the push rod 32 extends into the inside of the pipe fitting 4 and abuts against the positioning post 33, pushing the positioning post 33 back into the guide groove 351 and compressing the reset spring 34, so that the positioning post 33 disengages from the pipe fitting mounting hole 2. At this time, the positioning function is switched from the positioning post 33 to the push rod 32. Then the push rod 32 presses the pipe fitting 4 and the middle section of the inner liner 1 and applies welding current to perform spot welding.

[0046] The current is set according to the wall thickness of pipe fitting 4 and the thickness of inner liner 1, typically 8000–12000A, with an energizing time of 3–6 cycles (approximately 0.06–0.12s). Under the resistance heat generated by the current passing through the contact surface, the temperature of the contact area rapidly rises to near the metal melting point. At this time, the burrs (tiny but sharp) on the outside of the punch first reach the melting state and disappear. Simultaneously, the arc section in the middle of inner liner 1 undergoes localized annealing due to high temperature. During the rapid heating and compression cooling process, the metal material undergoes grain refinement, dislocation density reduction, and a significant decrease in hardness and yield strength. Under the continuous clamping force (typically 2000–5000N) applied by the welding electrodes, the softened and annealed arc section in the middle of inner liner 1 is flattened and gradually adheres to the flat welding surface of pipe fitting 4. The tiny gaps originally caused by burr padding or steel plate warping are completely eliminated in this process. At the same time, the pure metal on the contact surface undergoes atomic diffusion and recrystallization under high temperature and pressure, forming a localized metallurgical bond. This step simultaneously achieves three effects: burr removal, gap elimination, and local flattening, and is the core innovation of the entire process. After the spot welding is completed, the push rod 32 returns to its original position and moves out of the pipe fitting 4. The return spring 34 rebounds and drives the positioning column 33 to slide upward and return to its original position, which enables the rapid disassembly of the workpiece without the need for hammering or prying, greatly improving work efficiency.

[0047] Then, perform the sealing welding step S3: Although spot welding achieves positioning and initial fixation, sealing welding is required to obtain a completely sealed joint with sufficient mechanical strength. Before sealing welding, it is preferable to pre-cut a bevel at the sealing welding location on the pipe wall of fitting 4. This bevel is usually located on the outer wall of fitting 4 near the end face, and is a V-shaped or Y-shaped bevel of 30° to 60°. The purpose of the bevel is to form a molten pool to accommodate the welding wire during sealing welding, allowing the molten metal to fully penetrate to the root of the joint and ensuring no incomplete penetration defects. If no bevel is provided, the weld metal will only adhere to the surface during sealing welding, resulting in insufficient penetration depth, poor mechanical strength after welding, and a tendency to produce porosity or cracks. After beveling, use argon arc welding (TIG) or carbon dioxide gas shielded welding (MAG / MIG) to perform a continuous sealing weld around the connection between fitting 4 and inner liner 1. The welding parameters are adjusted according to the material thickness, for example, welding current 90 to 130A, arc voltage 12 to 18V, and welding speed 15 to 25 cm / min. During welding, the welding wire melts and flows into the root along the bevel, fully fusing with the base metal to form a dense and full sealed weld. Since spot welding ensures no gaps between the workpieces, the tight welding process will not result in molten droplet seepage or burn-through. Moreover, the bevel improves the filling capacity of the molten pool, ultimately enabling the mechanical strength of the weld to reach or even exceed that of the base metal.

[0048] The entire process of punching, spot welding, and tight welding is carried out sequentially and continuously, without the need to transfer the workpiece for any mechanical chamfering or grinding. Compared to the prior art, which requires welding followed by chamfering with a chamfering drill, this method completely eliminates the secondary processing step, avoids scratches, dimensional deviations, or stress concentrations that may be caused by chamfering, and significantly improves production efficiency.

[0049] Because the inner surface of the inner liner 1 is kept smooth during punching, and no burrs or sharp corners are generated on the inner side during the spot welding and tight welding processes, the enamel slurry can be evenly coated and firmly adhered in the subsequent enamel sintering process. Enamel sintering typically includes: pretreatment (degreasing, pickling, neutralization, surface conditioning), enamel slurry spraying (wet spraying or electrostatic dry powder spraying), drying, and high-temperature sintering (approximately 800–900°C). During the sintering process, the smooth inner surface allows the glassy enamel slurry to spread evenly, forming a continuous and dense enamel layer after cooling; without sharp corners or gaps, the enamel layer will not crack, chip, or become incomplete due to uneven shrinkage. The welding and fixing process of this invention eliminates these structural factors that cause defects at the source, thus significantly improving the corrosion resistance and service life of the inner liner. Tests have shown that the enamel inner liner processed using this method has a hot water erosion resistance life (according to GB / T23150 standard) that is more than twice that of conventional processes.

[0050] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A welding and fixing process for an inner tubular fitting, characterized in that, Includes the following steps: S1. Punching: Pipe fitting installation hole (2) is opened in the middle section of the inner liner (1). The punching direction of the pipe fitting installation hole (2) is from the inside of the inner liner (1) outward to form an outward-turned hole structure, so that the smooth surface of the punching edge is located inside the inner liner (1) and the punching burr is located outside the inner liner (1). S2, Spot welding: After using the spot welding positioning fixture (3) to coaxially press and position the punched part of the pipe fitting (4) and the inner liner (1) in the middle section, spot welding is then performed; during the spot welding process, the burrs on the outside of the punched part are melted by high temperature, and at the same time, the arc of the middle section of the inner liner (1) is locally annealed and flattened by the pressing action to eliminate the gap between the pipe fitting (4) and the inner liner (1); S3, Sealing: Sealing welding is performed at the connection between the pipe fitting (4) and the middle section of the inner liner (1).

2. The welding and fixing process method for an inner tubular fitting according to claim 1, characterized in that, Before performing a tight weld on the pipe fitting (4) in step S3, a bevel is made at the tight weld location on the pipe wall of the pipe fitting (4).

3. The welding and fixing process method for an inner tubular fitting according to claim 1, characterized in that, The weld surface between the pipe fitting (4) and the punched section of the inner liner (1) is a plane to ensure that the arc section of the inner liner (1) is evenly flattened during welding.

4. The welding and fixing process method for an inner tubular fitting according to claim 1, characterized in that: In step S2, the high-temperature pressing action during the spot welding of the pipe fitting (4) causes local annealing at the arc section of the inner liner (1) for subsequent flattening.

5. The welding and fixing process method for an inner tubular fitting according to claim 1, characterized in that: The punching, spot welding, and tight welding are performed sequentially. During the spot welding process, burrs are melted and gaps are eliminated simultaneously, eliminating the need for subsequent mechanical chamfering.

6. The welding and fixing process method for an inner tubular fitting according to claim 1, characterized in that: In step S1, the punching is performed by punching from the inside of the inner liner (1) outward to form an outer flange structure. The length of the outer flange matches the wall thickness of the pipe fitting (4) to be welded.

7. The welding and fixing process method for an inner liner fitting according to claim 1, characterized in that: In the welding step of the pipe fitting (4), the applied current and pressure completely melt the burrs and form a local metallurgical bond, while flattening the arc of the middle section of the inner liner (1) to be flush with the welding surface of the pipe fitting (4).

8. The welding and fixing process method for an inner liner fitting according to claim 1, characterized in that: The spot welding positioning fixture (3) includes a spot welding copper electrode (31), a push rod (32), a positioning post (33), a return spring (34), and a spot welding copper base (35); the push rod (32) is connected to the spot welding copper electrode (31) in a transmission manner; the spot welding copper base (35) is provided with an axially extending guide groove (351), the return spring (34) is housed in the guide groove (351), and the groove opening of the guide groove (351) is opposite to the pipe fitting installation hole (2) in the middle section of the inner liner (1); the positioning post (33) is axially slidably inserted into the guide groove (351); in the pre-welding assembly state, the pipe fitting (4), the positioning post (33), and the pipe fitting installation hole (2) are coaxially arranged.

9. The welding and fixing process method for an inner tubular fitting according to claim 8, characterized in that: In step S2, during spot welding, the spot welding copper electrode (31) drives the push rod (32) to move downward. The front end of the push rod (32) extends into the inside of the pipe fitting (4) and abuts against the positioning post (33), pushing the positioning post (33) back into the guide groove (351) and compressing the reset spring (34), so that the positioning post (33) disengages from the pipe fitting mounting hole (2). At this time, the positioning function is switched from the positioning post (33) to the push rod (32). Subsequently, the push rod (32) presses the middle section of the pipe fitting (4) and the inner liner (1) and applies welding current for spot welding. After the spot welding is completed, the push rod (32) resets upward and moves out of the pipe fitting (4). The reset spring (34) rebounds and drives the positioning post (33) to slide upward and reset, which is used to realize the quick disassembly of the workpiece.

10. The welding and fixing process method for an inner tubular fitting according to claim 1, characterized in that: The inner liner (1) is an enamel inner liner (1). The welding and fixing process is completed before the enamel sintering so that the smooth inner surface of the inner liner (1) is easy to cover with enamel glaze later.

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