Bimetal composite pipe for biomass boiler and powder-wire additive manufacturing method

Abstract

The invention is suitable for the technical field of pipe manufacturing, and provides a bimetal composite pipe for a biomass boiler and a powder-wire additive manufacturing method, a common carbon steel or alloy steel pipe is used as a base material, and a stainless steel or nickel-based alloy protective layer is prepared on the outer wall of a base material pipeline by adopting a powder-wire synergistic electric arc additive manufacturing method. A powder feeding pipe and a welding gun cooperatively act through a designed special clamp, Co-Mo-W metal powder and a welding wire are synchronously molten through an electric arc heat source and are evenly mixed in a molten pool, a novel alloy protective layer is formed after solidification, and the novel alloy protective layer and a pipeline base material are in tight metallurgical bonding. The texture of the additive manufacturing layer is fine isometric crystals and cellular grains, uniformly dispersed precipitated phase particles are distributed on the grain boundary, and the defects of cracks and air holes are avoided; the tensile strength of the composite pipe reaches 620 MPa, the percentage elongation after fracture reaches 38%, and the composite pipe is suitable for high-temperature oxidation resistance and corrosion resistance of the service environment of the heating surface of the biomass boiler.

Description

Technical Field

[0001] The present invention relates to the technical field of pipe manufacturing, and more specifically, it relates to a bimetallic composite pipe for a biomass boiler and a powder-wire additive manufacturing method. Background Art

[0002] A biomass boiler is an energy-saving and environment-friendly thermal energy device. It generates heat energy by burning biomass fuels such as straw and wood, and can be used to produce industrial steam, generate electricity, supply heat, etc. Since the carbon dioxide absorbed by biomass fuels during growth is approximately equal to the carbon dioxide released during their combustion, the carbon emissions of biomass boilers are close to zero emissions, and there are no sulfur oxide emissions, which is beneficial to environmental protection. Biomass fuels are cheaper than traditional boiler fuels such as coal and natural gas, so they have the advantage of cost savings. The reserves of biomass energy in China are relatively rich, which can meet the fuel demand of biomass boilers and have the characteristics of renewability and sustainability.

[0003] The internal superheater of a biomass boiler is a component that uses the heat of high-temperature flue gas to heat saturated steam. When saturated steam enters the superheater, the pipes of the superheater will absorb the heat of the high-temperature flue gas, increasing the temperature of the steam. The working conditions of the internal superheater of a biomass boiler are relatively harsh. Inside the superheater pipes is high-pressure steam, and outside is the high-temperature flue gas in the furnace. The outer wall of the superheater pipes is in contact with the high-temperature flue gas. Due to the temperature difference between the flue gas and the steam inside the pipes, the heat of the flue gas will be transferred to the pipe wall and then to the steam through the pipe wall, increasing the steam temperature. The high-temperature flames and flue gas in the furnace will emit thermal radiation to surrounding objects, and the outer wall of the superheater pipes absorbs this radiant heat to increase the steam temperature inside the pipes.

[0004] In the practical application of biomass power generation units, the safety operation problems caused by high-temperature corrosion and oxidation failure of boiler superheater pipes have become the key bottleneck problems faced by the popularization and application of current biomass boilers. Compared with fossil fuels, the content of alkali metals and chlorine in biomass fuels has increased significantly, making the problem of failure of boiler superheater pipes due to oxidation and corrosion increasingly prominent. Biomass fuels represented by straw and wood contain a large amount of alkali metals. During the combustion process, the alkali metals condense on the tube walls of the heating surfaces in the form of chlorides along with the flue gas flow and react with the oxide film on the tube wall surface to cause high-temperature corrosion. Components such as gaseous HCl and Cl2 in the flue gas have extremely strong penetrability, can penetrate the protective film on the metal surface and directly react with the internal metal, and the corrosion rate increases with the increase in temperature. Therefore, the heating surface pipes inside the biomass boiler furnace are prone to severe high-temperature oxidation and corrosion during operation, resulting in the thinning of the wall thickness of the heating surface pipes. When the pressure limit is exceeded, even tube burst accidents may occur, affecting the safe and stable operation of the boiler unit.

[0005] At present, thermal spraying technology can be used to spray high-temperature resistant coating materials on the surface of the pipeline to increase its service life. However, the thermal spray coating has a high porosity, and a sealing process is required later. The construction process is relatively complicated, and it is difficult to completely solve the problems of low coating adhesion and continued oxidation and corrosion of the pipeline after the coating pores are exposed. Document CN 118188889A proposes a double-layer seamless composite pipe based on induction heating quenching and a preparation method thereof. The two pipes are sleeved together by induction heating and then welded together to achieve the goal of manufacturing a double-layer composite pipe. The composite pipe manufactured by this process is a combination of two pipes of fixed materials, and the pipe specifications and composition are difficult to adjust. Document CN 117921142 A proposes a composite pipe for a thermal power generation cleaning system and a preparation method thereof. Using 316L stainless steel as the base alloy steel pipe material, Fe-Cr-Mn alloy welding wire is arc-coated to the inside of the stainless steel base pipe using the melting inert gas shielded welding technology. The composite pipe mainly prepares the protective layer inside the pipe to solve the corrosion and wear problems of the inner wall of the desulfurization pipe and the ash and flue gas conveying pipe. It is not suitable for the high-temperature oxidation and high-temperature corrosion environment of the heating surface. Therefore, new material pipes are developed for important components such as superheaters inside biomass boilers to enhance the resistance of biomass boiler heating surface components to high-temperature oxidation and corrosion, which can improve the overall operation safety and stability of biomass boilers. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a bimetallic composite pipe for a biomass boiler and a powder-wire additive manufacturing method, which uses a low-cost alloy steel pipe as a substrate, and uses a CMT arc as a heat source to melt the nickel-based alloy welding wire and the metal powder with adjustable composition. After solidification, a protective layer with excellent performance is formed on the outside of the alloy steel pipe, and finally a bimetallic composite pipe is formed to achieve the service conditions suitable for the heating surface of the combustion chamber of a biomass boiler and improve the pipe's resistance to oxidation corrosion.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A bimetallic composite pipe for a biomass boiler comprises an alloy steel pipe; a protective layer is arranged on the outside of the alloy steel pipe; the protective layer is formed by melting a nickel-based alloy welding wire and metal powder with adjustable composition.

[0009] A powder-wire additive manufacturing method for a bimetallic composite tube for a biomass boiler comprises the following steps:

[0010] T1. Select alloy steel or carbon steel of a certain diameter as the base material of the composite pipe, mechanically break and remove the oxide layer and oil stains on the outer wall of the pipe; select nickel-based alloy welding wire, stainless steel welding wire and Co-Mo-W powder of a certain ratio as the protective layer material of the composite pipe, ball-mill and mix the Co-Mo-W powder, and dry it after fully mixing for standby use;

[0011] T2. Clamp and fix both ends of the alloy steel pipe through the clamping mechanism on the positioner; assemble the powder feeding pipe and the welding torch together through the fixture, and adjust the angles of the powder feeding pipe, the welding torch and the position of the composite pipe substrate; put the Co-Mo-W powder into the powder feeder, and set the powder feeding speed and the carrier gas flow rate; set process parameters such as welding current, welding voltage, welding speed, and shielding gas flow rate on the CMT welding power source, set the wire feeding speed of the welding wire on the wire feeder, synchronously start wire feeding and powder feeding, and turn on the power supply to start the arc additive manufacturing process;

[0012] T3. Perform single-layer or multi-layer cladding to obtain an additive manufacturing layer with the required thickness, remove slag and spatter particles by mechanical grinding, and conduct microstructure and mechanical property inspections after cooling to room temperature.

[0013] The present invention is further configured as: in step T1, materials such as alloy steel and carbon steel with a certain diameter are used as the substrate of the composite pipe, and its outer diameter is 20 - 800 mm, and the thickness is 4 mm - 50 mm.

[0014] The present invention is further configured as: the nickel-based alloy welding wire and the stainless steel welding wire in step T1, characterized in that the diameter of the solid welding wire is 0.6 - 1.6 mm, and the composition of the nickel-based alloy welding wire by mass percentage is: Ni 56 - 75%, Cr 18 - 28%, Mo 6 - 12%, Nb 2.5 - 8.5%, Al 0.4 - 1.8%, Ti 0.4 - 1.8%, Mn 0.5%. The composition of the stainless steel welding wire by mass percentage is: C 0 - 0.03%, Si 0.1 - 0.95%, Mn 1.0% - 3.5%, Cr 18.0% - 26.0%, Ni 11.00% - 18.00%, Mo 2.0% - 6.0%.

[0015] The present invention is further configured as: the Co-Mo-W powder with a certain ratio in step T1, characterized in that elemental metal powders with a purity ≥ 99.95% and a particle size of 250 - 400 mesh are used for mechanical ball milling and mixing, and according to the mass fraction, Co powder is 0 - 80%; Mo powder is 0 - 48%; W powder is 0 - 28%. The rotation speed of the ball mill is 200 r / min, the ball-to-material ratio is 4:1, and the ball milling time is 60 - 200 min. The drying temperature is 60 - 150 °C, and the drying time is 30 - 120 min.

[0016] The present invention is further configured as: the fixture in step T2 includes a first clamping ring for fixing the powder feeding pipe and a second clamping ring for fixing the welding torch; rectangular long handles are respectively fixed on the first clamping ring A and the second clamping ring B; a plurality of positioning screw holes are evenly distributed on the rectangular long handles; positioning screws are rotationally arranged in threads in the two corresponding positioning screw holes on the two rectangular long handles.

[0017] The present invention is further configured as follows: the adjustment ranges of the powder feeding tube angle, the welding torch angle, and the position of the composite tube base material in step T2 are as follows: the included angle between the axis of the powder feeding tube and the horizontal line of the base material is between 0° and 65°; the included angle between the axis of the welding torch and the horizontal line of the base material is between 40° and 90°. The distance between the intersection point of the axis of the powder feeding tube and the axis of the welding torch and the outer wall of the alloy steel pipe is 0 to 2.0 mm.

[0018] The present invention is further configured as follows: in step T2, the welding current is 80 - 220 A, the welding voltage is 17 - 22 V, and the welding speed is 0.18 - 1.25 m / min; during the welding process, the combined device of the welding torch and the powder feeding tube is controlled to move left and right by an external mechanical component, and the adjustment of the welding speed is achieved by changing the rotation speed of the pipe by a positioner; the powder feeding speed is 2.0 - 35 g / min, the wire feeding speed is 3.1 - 13.0 m / min, the shielding gas is Ar gas with a purity of 99.9%, and the flow rate is 12.0 - 28 L / min.

[0019] The present invention is further configured as follows: in step T3, the number of layers of the multi-layer cladding is 1 - 10 layers, and the thickness of the additive manufacturing layer on the outer wall of the composite tube is 2.0 - 20.0 mm.

[0020] The advantages of the present invention are as follows:

[0021] 1. In the present invention, the inner wall of the composite tube uses a mature alloy steel single-layer tube as the base body, and a nickel-based alloy or stainless steel protective layer is prepared on the outside through the powder-wire combined additive manufacturing process, which can significantly increase the anti-oxidation and corrosion resistance of the biomass boiler heating surface pipeline while maintaining a low cost, and solve the problems such as high porosity and low coating bonding strength existing in the traditional thermal spraying pipeline protective coating.

[0022] 2. In the process of arc additive manufacturing of the protective layer in the present invention, the process of synchronous powder feeding and wire feeding is adopted, which significantly improves the manufacturing efficiency; by directly introducing high-temperature-resistant elements Co, Mo, and W into the arc molten pool in the form of metal powder, the anti-oxidation and corrosion resistance of the protective coating during service in the biomass boiler heating surface is significantly improved; by adding metal powder into the arc molten pool through the powder feeding tube, the contents of Co, Mo, and W in the protective coating can be conveniently adjusted, so that the high-temperature-resistant elements act synergistically to improve the anti-chloride corrosion ability of the protective coating.

[0023] 3. The present invention adopts the designed tooling fixture to quickly position the powder feeding tube and the welding torch, and conveniently and quickly adjust the angles and distances among the powder feeding tube, the welding torch, and the pipe parts, realizing the functions of adjusting the penetration depth, width, reinforcement height, contact angle, and forming morphology of the cladding layer, and further improving the quality of the protective coating.

[0024] 4. The microstructure inspection of the composite pipe of the present invention shows that the bonding in the interface area of the additive manufacturing layer is tight. The microstructure consists of fine columnar crystals and equiaxed crystals, and there are no defects such as cracks and pores. Most of the introduced Co, Mo, and W elements enter the additive manufacturing layer in a solid solution form, playing a role in solid solution strengthening. A small amount exists in the form of precipitated phases such as carbides and Laves phases at the grain boundaries, playing a role in grain refinement and precipitation strengthening. The comprehensive mechanical properties of the composite pipe are good. The tensile strength of the composite pipe can reach 380 - 620 MPa, and the elongation after fracture reaches 20 - 38%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 FIG. is a schematic diagram of the powder - wire synchronous additive manufacturing equipment used in Example 1 of the present invention.

[0026] Figure 2 FIG. is the morphology diagram of Co, Mo, and W powders used in Example 1 of the present invention.

[0027] Figure 3 FIG. is the microstructure diagram of the additive manufacturing composite pipe prepared in Example 1 of the present invention. (a) FIG. is the microstructure of the 12Cr1MoVG alloy steel base material; (b) FIG. is the microstructure of the heat - affected zone of the 12Cr1MoVG alloy steel; (c) FIG. is the microstructure of the interface area between 12Cr1MoVG and the additive manufacturing layer; (d) is the microstructure of the additive manufacturing layer.

[0028] Figure 4 FIG. is the mechanical property test result of the composite pipe prepared in Example 1 of the present invention. (a) FIG. is the engineering stress - strain curve; (b) FIG. is the measured tensile strength of 443.05 MPa and elongation of 29.32%.

[0029] In the figure: 1. Clamp; 2. Powder feeding pipe; 3. Welding torch; 4. Alloy steel pipe; 5. Positioner; 1 - A. First clamping ring; 1 - B. Second clamping ring; 1 - C. Positioning screw hole; 1 - D. Positioning screw. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0031] It should be pointed out that unless otherwise specified, all technical and scientific terms used in the present application have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0032] In the present invention, unless otherwise specified, the orientations such as "upper" and "lower" generally refer to the directions shown in the drawings, or to the vertical, perpendicular or gravitational directions; similarly, for the convenience of understanding and description, "left" and "right" generally refer to the left and right shown in the drawings; "inner" and "outer" refer to the inner and outer of the contours of the respective components themselves, but the above orientation terms are not used to limit the present invention.

[0033] Example 1, please refer to Figures 1-4 , the present invention provides the following technical solutions:

[0034] A bimetal composite pipe for a biomass boiler and a powder-wire additive manufacturing method. Specifically, a 12Cr1MoVG alloy steel pipe 4 is used as the substrate of the composite pipe. The outer diameter of the alloy pipe is 50 mm, the wall thickness is 8 mm, and the length is 1000 mm. The composite pipe is horizontally placed on a positioner 5 and clamped.

[0035] A stainless steel welding wire with a diameter of 1.2 mm is selected as the wire material for additive manufacturing the outer wall of the composite pipe. The composition of the stainless steel welding wire is as follows by mass fraction: C 0.02%, Cr 18.5%, Ni 16.0%, Mo 3.0%, Si 1.2%, Mn 2.0%, and the balance is Fe.

[0036] 500 g of elemental metal Co powder with a purity ≥ 99.95% and a particle size of 250 mesh, 500 g of elemental metal Mo powder with a purity ≥ 99.95% and a particle size of 300 mesh, and 500 g of elemental metal W powder with a purity ≥ 99.95% and a particle size of 400 mesh are selected for mechanical ball milling and mixing. According to the mass fraction, Co powder is 60%, Mo powder is 28%, and W powder is 22%. The rotation speed of the ball mill is 200 r / min, the ball-to-material ratio is 4:1, and the ball milling time is 200 min. The mixed powder after ball milling is dried. The drying temperature is 80 °C and the drying time is 120 min.

[0037] The composite powder is put into a powder feeder, and the powder feeding rate is set at 15 g / min. The stainless steel welding wire is put into a wire feeder. In the CMT welding power source, the welding current is set at 120 A, the welding voltage is 18.5 V, the wire feeding speed is 7.0 m / min, the shielding gas is Ar gas with a purity of 99.9%, and the gas flow rate is 26 L / min.

[0038] Adopt as Figure 1The designed fixture 1 assembles the powder feeding tube 2 and the welding torch 3 together. The powder feeding tube 2 is fixed by the clamping ring 1-A, and the height of the powder feeding tube 2 can be appropriately adjusted; the welding torch 3 is fixed by the clamping ring 1-B, and the height of the welding torch 3 can be appropriately adjusted; the rectangular long handles of the first clamping ring 1-A and the second clamping ring 1-B are cross-assembled, and the distance between the powder feeding tube 2 and the welding torch 3 is adjusted through the positioning screw hole 1-C and the positioning screw 1-D; the fixture 1 is adjusted so that the included angle between the axis of the powder feeding tube 2 and the horizontal line of the outer wall of the alloy steel pipe 4 is 60°; the fixture 1 is adjusted so that the included angle between the axis of the welding torch 3 and the horizontal line of the outer wall of the alloy steel pipe 4 is 80°; the intersection point of the axis of the powder feeding tube 2 and the axis of the welding torch 3 is 1.0 mm away from the outer wall of the alloy steel pipe 4.

[0039] The rotation speed of the pipe is set to 4.0 r / min through the positioner 5, and the welding speed of the outer wall of the pipe is obtained as 0.628 m / min. The horizontal movement speed of the welding torch 3 is set to 20 mm / min through the external manipulator, and the bead overlap rate is obtained as 37.5%.

[0040] Start the positioner 5 to rotate the pipe. First, turn on the powder feeder to evenly send out the powder beam. After 30 s, turn on the wire feeder and at the same time turn on the welding power supply according to the set parameters to start the additive manufacturing of the outer wall of the composite pipe.

[0041] After the single-layer welding layer is completed, first turn off the wire feeder, then turn off the powder feeder, and finally turn off the shielding gas. After the composite pipe cools to room temperature, use a angle grinder to polish the spatter and oxides on the outside of the weld bead.

[0042] The composite pipe finally obtained in this embodiment is as Figure 2 shown. The thickness of the additive manufacturing layer of the composite pipe is 5 mm. Cut the metallographic specimen and mechanical property specimen according to the standard for testing. The final obtained microstructure is as Figure 3 shown in a. The inner wall layer of the composite pipe is the base material of 12Cr1MoVG alloy steel, and the microstructure is a uniform mixture of ferrite and pearlite grains; Figure 3 b is the microstructure of the heat affected zone below the additive manufacturing layer, which is a mixed structure of lath martensite and a certain amount of bainite. Figure 3 c is the interface between the inner wall layer and the additive manufacturing layer of the composite pipe. It can be observed that the interface is tightly bonded without porosity and crack defects; Figure 3 d is the microstructure of the additive manufacturing layer. It can be observed that the additive manufacturing layer is a uniform and fine columnar crystal and equiaxed crystal structure, and granular precipitates are distributed between the grains; the measured mechanical properties of the composite pipe are as shown in the appendix Figure 4 shown. The tensile strength is 443.05 MPa, and the elongation after fracture is 29.32%.

[0043] Example two, please refer to Figures 1-4, the present invention provides the following technical solutions: Specifically, a 20G carbon steel pipe is used as the base material of the composite pipe. The alloy pipe has an outer diameter of 70 mm, a wall thickness of 10 mm, and a length of 1000 mm. The composite pipe is placed horizontally on the positioner 5 and clamped.

[0044] A nickel-based alloy welding wire with a diameter of 1.2 mm is selected as the wire material for additive manufacturing of the outer wall of the composite pipe. The composition of the nickel-based alloy welding wire is as follows by mass fraction: Cr 19.0%, Mo 8.0%, Nb 6.5%, Al 1.5%, Ti 0.8%, Mn 0.8%, and the balance is Ni.

[0045] 500 g of elemental metal Co powder with a purity ≥ 99.95% and a particle size of 400 mesh, 500 g of elemental metal Mo powder with a purity ≥ 99.95% and a particle size of 300 mesh, and 500 g of elemental metal W powder with a purity ≥ 99.95% and a particle size of 400 mesh are selected for mechanical ball milling and mixing. According to the mass fraction, Co powder is 50%, Mo powder is 32%, and W powder is 18%. The rotation speed of the ball mill is 200 r / min, the ball-to-powder ratio is 4:1, and the ball milling time is 200 min. The mixed powder after ball milling is dried. The drying temperature is 120 °C and the drying time is 100 min.

[0046] The composite powder is put into the powder feeder, and the powder feeding rate is set at 10 g / min. The stainless steel welding wire is put into the wire feeder. In the CMT welding power source, the welding current is set at 140 A, the welding voltage is 19.0 V, the wire feeding speed is 8.0 m / min, the shielding gas is Ar gas with a purity of 99.9%, and the gas flow rate is 22 L / min.

[0047] The powder feeding tube 2 and the welding torch 3 are assembled together by using the designed fixture 1. The powder feeding tube 2 is fixed by the first clamping ring 1-A, and the height of the powder feeding tube 2 is adjusted; the welding torch 3 is fixed by the second clamping ring 1-B, and the height of the welding torch 3 is adjusted; the rectangular long handles of the first clamping ring 1-A and the second clamping ring 1-B are cross-assembled, and the distance between the powder feeding tube 2 and the welding torch 3 is adjusted through the positioning screw hole 1-C and the positioning screw 1-D; the fixture 1 is adjusted so that the included angle between the axis of the powder feeding tube 2 and the horizontal line of the outer wall of the alloy steel pipe 4 is 45°; the fixture 1 is adjusted so that the included angle between the axis of the welding torch 3 and the horizontal line of the outer wall of the alloy steel pipe 4 is 90°; the intersection point of the axis of the powder feeding tube 2 and the axis of the welding torch 3 is 1.5 mm away from the outer wall of the alloy steel pipe 4.

[0048] The rotation speed of the pipe is set at 2.5 r / min through the positioner 5, and the welding speed of the outer wall of the pipe is obtained as 0.55 m / min. The horizontal moving speed of the welding torch 3 is set at 10 mm / min through the external manipulator, and the bead overlap rate is obtained as 42.9%.

[0049] Start the positioner 5 to rotate the pipe. First, turn on the powder feeder to evenly send out the powder beam. After 30 s, turn on the wire feeder and simultaneously turn on the CMT welding power supply according to the set parameters to start additive manufacturing of the outer wall of the composite pipe.

[0050] After the first welding layer is completed, first turn off the wire feeder, then turn off the powder feeder, and finally turn off the shielding gas. After the composite pipe cools to room temperature, use a angle grinder to grind the spatter and oxides on the outside of the weld bead.

[0051] Repeat the above steps for the 2nd - 3rd layer welding. In this embodiment, the additive manufacturing layer with a thickness of 10 mm is finally obtained. After the composite pipe is manufactured, cut the metallographic specimen and mechanical property specimen according to the standard for testing.

[0052] Example 3, please refer to Figures 1-4 , the present invention provides the following technical solutions: Specifically, use the Q345 low - alloy steel pipe 4 as the composite pipe substrate. The outer diameter of the alloy pipe is 48 mm, the wall thickness is 5 mm, and the length is 1000 mm. Place the composite pipe horizontally on the positioner 5 and clamp it.

[0053] Select a stainless - steel welding wire with a diameter of 1.6 mm as the wire material for additive manufacturing of the outer wall of the composite pipe. The composition of the nickel - based alloy welding wire is as follows by mass fraction: C 0.02%, Cr 20%, Ni 8.0%, Mo 3.0%, Si 1.5%, Mn 2.5%, and the balance is Fe.

[0054] Select 500 g of elemental metal Co powder with a purity ≥99.95% and a particle size of 300 mesh, 500 g of elemental metal Mo powder with a purity ≥99.95% and a particle size of 400 mesh, and 500 g of elemental metal W powder with a purity ≥99.95% and a particle size of 300 mesh for mechanical ball - milling and mixing. According to the mass fraction, Co powder is 40%, Mo powder is 36%, and W powder is 24%. The rotation speed of the ball mill is 200 r / min, the ball - to - powder ratio is 4:1, and the ball - milling time is 200 min. After ball - milling, the mixed powder is dried. The drying temperature is 100 °C and the drying time is 120 min.

[0055] Put the composite powder into the powder feeder and set the powder feeding rate at 8 g / min. Put the stainless - steel welding wire into the wire feeder. Set the welding current at 100 A, the welding voltage at 17.0 V, the wire feeding speed at 6.0 m / min in the CMT welding power supply. The shielding gas is Ar gas with a purity of 99.9%, and the gas flow rate is 18 L / min.

[0056] Assemble the powder feeding tube 2 and the welding torch 3 together using the designed fixture 1. Fix the powder feeding tube 2 through the clamping ring and adjust its height; fix the welding torch 3 through the first clamping ring 1-A and the second clamping ring 1-B and adjust its height; cross-assemble the rectangular long handles of the first clamping ring 1-A and the second clamping ring 1-B, and adjust the distance between the powder feeding tube 2 and the welding torch 3 through the positioning screw hole 1-C and the positioning screw 1-D; adjust the fixture 1 so that the angle between the axis of the powder feeding tube 2 and the horizontal line of the outer wall of the alloy steel pipe 4 is 30°; adjust the fixture 1 so that the angle between the axis of the welding torch 3 and the horizontal line of the outer wall of the alloy steel pipe 4 is 90°; the intersection point of the axis of the powder feeding tube 2 and the axis of the welding torch 3 is 1.5 mm away from the outer wall of the alloy steel pipe 4.

[0057] Set the rotation speed of the tube to 5.0 r / min through the positioner 5 to obtain a welding speed of 0.75 m / min on the outer wall of the tube. Set the horizontal movement speed of the welding torch 3 to 18 mm / min through the external manipulator to obtain a bead overlap rate of 40%.

[0058] Start the positioner 5 to rotate the tube. First, turn on the powder feeder to evenly send out the powder beam. After 30 s, turn on the wire feeder and simultaneously turn on the CMT welding power supply according to the set parameters to start the additive manufacturing of the outer wall of the composite pipe.

[0059] After the first welding layer is completed, first turn off the wire feeder, then turn off the powder feeder, and finally turn off the shielding gas. After the composite pipe cools to room temperature, use an angle grinder to polish the spatter and oxides on the outside of the weld bead.

[0060] Repeat the above steps for the 2nd to 5th layer welding. In this embodiment, the thickness of the additive manufacturing layer is finally obtained as 14 mm. After the composite pipe is manufactured, cut the metallographic specimen and mechanical property specimen according to the standard for testing.

[0061] Obviously, the above-described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0062] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0063] It should be noted that the terms "first", "second", etc. in the description, claims and the above-mentioned drawings of this application are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances so that the embodiments of the present application described here can be implemented in an order different from those illustrated or described here.

[0064] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0065] The above is only the preferred implementation mode of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art, several improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A bimetallic composite pipe for a biomass boiler, comprising an alloy steel pipe (4); characterized in that: The alloy steel pipe (4) is provided with a protective layer on the outside; the protective layer is formed by melting a nickel-based alloy welding wire and metal powder with adjustable composition.

2. The powder-wire additive manufacturing method for a bimetallic composite tube for a biomass boiler according to claim 1, characterized in that: The following steps are involved: T1. Select alloy steel or carbon steel of a certain diameter as the base material of the composite pipe, mechanically break and remove the oxide layer and oil stains on the outer wall of the pipe; select nickel-based alloy welding wire, stainless steel welding wire and Co-Mo-W powder of a certain ratio as the protective layer material of the composite pipe, ball-mill and mix the Co-Mo-W powder, and dry it after fully mixing for standby use; T2. Clamp and fix the two ends of the alloy steel pipe (4) by means of the clamping structure on the positioner (5); assemble the powder feeding pipe (2) and the welding gun (3) together by means of the clamp (1), adjust the angle of the powder feeding pipe (2), the angle of the welding gun (3) and the position of the composite pipe substrate; put the Co-Mo-W powder into the powder feeder, set the powder feeding speed and the carrier gas flow rate; set the welding current, welding voltage, welding speed, shielding gas flow rate and other process parameters on the CMT welding power source, set the wire feeding speed on the wire feeder, start wire feeding and powder feeding simultaneously, and start the arc additive manufacturing process on the welding power source; T3. Perform single-layer or multi-layer cladding to obtain the required thickness of the additive manufacturing layer, use mechanical grinding to remove slag and splash particles, and then cool to room temperature for microstructure and mechanical property inspection.

3. The powder-wire additive manufacturing method for a bimetallic composite tube for a biomass boiler according to claim 2, characterized in that: The alloy steel, carbon steel or other materials of a certain diameter described in step T1 are used as the base material of the composite pipe, and the outer diameter thereof is 20 to 800 mm and the thickness is 4 to 50 mm.

4. The powder-wire additive manufacturing method for a bimetallic composite tube for a biomass boiler according to claim 3, characterized in that: The nickel-based alloy welding wire and the stainless steel welding wire described in step T1 are characterized in that the solid welding wire has a diameter of 0.6 to 1.6 mm, and the nickel-based alloy welding wire has the following components in mass percentage: Ni 56-75%, Cr 18-28%, Mo 6-12%, Nb 2.5-8.5%, Al 0.4-1.8%, Ti 0.4-1.8%, and Mn 0.5%. The stainless steel welding wire has the following components in mass percentage: C 0-0.03%, Si 0.1-0.95%, Mn 1.0%-3.5%, Cr18.0%-26.0%, Ni 11.00%-18.00%, and Mo2.0%-6.0%.

5. The powder-wire additive manufacturing method for a bimetallic composite tube for a biomass boiler according to claim 4, characterized in that: The Co-Mo-W powder of a certain ratio described in step T1 is characterized in that the pure metal powder with a purity of ≥99.95% and a particle size of 250-400 mesh is used for mechanical ball milling and mixing, and the mass fraction of Co powder is 0-80%; Mo powder is 0-48%; W powder is 0-28%. The speed of the ball mill is 200r / min, the ball-to-material ratio is 4:1, and the ball milling time is 60-200min. The drying temperature is 60-150°C and the drying time is 30-120min.

6. The powder-wire additive manufacturing method for a bimetallic composite tube for a biomass boiler according to claim 5, characterized in that: The clamp (1) in step T2 comprises a first clamping ring (1-A) for fixing the powder feeding tube (2) and a second clamping ring (1-B) for fixing the welding gun (3); a rectangular long handle is fixed on the first clamping ring (1-A) and the second clamping ring (1-B), respectively; a plurality of positioning screw holes (1-C) are evenly spaced on the rectangular long handle; and positioning screws (1-D) are threadedly arranged in two corresponding positioning screw holes (1-C) on the two rectangular long handles.

7. The powder-wire additive manufacturing method for a bimetallic composite tube for a biomass boiler according to claim 6, characterized in that: The adjustment ranges of the angle of the powder delivery pipe (2), the angle of the welding gun (3) and the position of the composite pipe substrate in step T2 are as follows: the angle between the axis of the powder delivery pipe (2) and the horizontal line of the substrate is between 0 and 65°; the angle between the axis of the welding gun (3) and the horizontal line of the substrate is between 40 and 90°; the intersection of the axis of the powder delivery pipe (2) and the axis of the welding gun (3) is 0 to 2.0 mm from the outer wall of the alloy steel pipe (4).

8. The powder-wire additive manufacturing method for a bimetallic composite tube for a biomass boiler according to claim 7, characterized in that: In step T2, the welding current is 80-220A, the welding voltage is 17-22V, and the welding speed is 0.18-1.25m / min. During the welding process, the combined device of the welding gun (3) and the powder feeding pipe (2) is controlled to move left and right by an external mechanical component, and the welding speed is adjusted by changing the rotation speed of the pipe by a positioner (5). The powder feeding speed is 2.0-35g / min, the wire feeding speed is 3.1-13.0m / min, and the shielding gas is Ar gas with a purity of 99.9% and a flow rate of 12.0-28L / min.

9. The powder-wire additive manufacturing method for a bimetallic composite tube for a biomass boiler according to claim 8, characterized in that: The number of layers of the multi-layer cladding in step T3 is 1 to 10 layers, and the thickness of the additive manufacturing layer of the outer wall of the composite pipe is 2.0 to 20.0 mm.

Images