A method for making an alloy anti-corrosion coating on the surface of boiler pipes using powder metallurgy technology

Abstract

The present invention discloses a method for fabricating an alloy anti-corrosion coating on the surface of boiler pipes by powder metallurgy process, which should be divided into the following four steps: (1) Alloy powder coating prefabrication: adding a certain proportion of additives to the metallurgical powder with anti-corrosion properties to make it a coating alloy powder with good fluidity; (2) Coating of alloy coating on the surface of boiler pipes: coating the alloy powder coating completed in the first step on the surface of boiler pipes; (3) Degreasing of coating additives: performing degreasing treatment on the coated boiler pipes to remove the additives in the alloy mixed coating; (4) Cladding of alloy coating: performing cladding treatment on the boiler pipe coating after degreasing of the alloy powder coating to form an anti-corrosion coating with metallurgical bonding with the substrate. This method can customize the coating composition, and by mixing materials such as organic binders, the coating after coating and cladding is more uniform, improving the production efficiency of its anti-corrosion coating.

Description

Technical Field

[0001] The present invention relates to the field of anti-corrosion coatings for boiler pipes, and in particular to a method for fabricating an alloy anti-corrosion coating on the surface of boiler pipes using powder metallurgy technology. Background Art

[0002] Generally, coatings for boiler pipes are prepared by spraying alloy wires using thermal spraying technology. Different alloy wires can be selected according to needs to obtain properties such as wear resistance, corrosion resistance, oxidation resistance, and high temperature resistance. However, for the coatings prepared by this method, the bonding with the substrate is mainly mechanical, with low bonding strength and certain porosity in the coating. This results in that in the process of using boiler pipes in a high-strength corrosion environment, ordinary sprayed coatings are difficult to cope with, the coatings are prone to damage and peeling, posing potential hazards to the use and production safety of boilers. Moreover, the replacement operation of boiler pipes is complex, and once some pipes are corroded, the economic losses to users are huge.

[0003] The present invention provides a method for fabricating an alloy anti-corrosion coating on the surface of boiler pipes using powder metallurgy technology, which is made through four technological steps, namely (1) prefabrication of alloy powder coatings; (2) coating of alloy coatings on the surface of boiler pipes; (3) degreasing of coating additives; and (4) cladding of alloy coatings.

[0004] The surface coating material of the boiler pipes fabricated by this method adopts powder metallurgy technology, where extremely fine alloy powders with high anti-corrosion and certain wear resistance are formulated to address compatibility issues under different materials. At the same time, additives meeting coating performance requirements, including binders, plasticizers, and dispersants, are added to make a mixed alloy coating that can be coated on the surface of boiler pipes. The formulation of the additives can ensure that the coated coating is not easily deformed and has a uniform thickness. After degreasing the solvent of the mixed alloy coating, impurity residues are reduced. After coating, various cladding methods are adopted and selected according to different materials, greatly improving the cladding efficiency of the anti-corrosion coating on the surface of boiler pipes. The cladded coating is uniform, with a low dilution rate, and the coating and the substrate have good metallurgical bonding, having good anti-corrosion performance. Summary of the Invention

[0005] Based on the traditional manufacturing process of boiler pipe coatings, the present invention uses the following four-step process to fabricate a method for making an anti-corrosion coating on the surface of boiler pipes that is easier to control the composition and has higher efficiency. The specific steps are as follows.

[0006] First step: Prefabrication of alloy powder coatings.

[0007] Second step: Coating of alloy coatings on the surface of boiler pipes.

[0008] Third step: Degreasing of coating additives.

[0009] Fourth step: Cladding of alloy coatings.

[0010] Specifically, in the first step: prefabrication of alloy powder coating, the process is to mix metallurgical coating powder with anti-corrosion properties and alloy powder coating additives to form a mixed alloy powder coating with good fluidity, uniformity and certain plasticity.

[0011] Preferably, the so-called additives refer to substances that endow the blank with properties such as fluidity. According to their different functions in different working conditions, they can be divided into three categories: binders, plasticizers and solvents.

[0012] Preferably, common binders usually include polyvinyl alcohol, polyethylene glycol and paraffin, etc., which bond alloy powder coating particles together at room temperature, endow the blank with forming properties and certain strength, and the binder can oxidize, decompose and volatilize at high temperature.

[0013] Preferably, common plasticizers usually include glycerin, oxalic acid, etc., which are dissolved in organic binders to form a liquid layer between alloy powder coatings, improving the plasticity of the blank.

[0014] Preferably, common solvents usually include water, kerosene, absolute alcohol, acetone, benzene, ethyl acetate, etc., which are liquids that can dissolve binders and plasticizers and can form plastic substances with materials.

[0015] Preferably, the additives used in the alloy powder coating prefabrication process meet the following requirements: they should have sufficient viscosity to ensure good formability and strength; they can all volatilize after high-temperature forging, with a simple process, no corrosiveness, and no adverse effects on the coating performance.

[0016] Specifically, in the second step: coating the alloy coating on the surface of boiler pipes, the process is to coat the alloy powder coating mixed in the first step on the surface of boiler pipes, and the coating methods should include airless spraying and press coating. The alloy powder coating after coating should be tightly combined with the substrate and not easily deformed.

[0017] Preferably, for the airless spraying, the process is to coat the mixed alloy powder coating completed in the first step of alloy powder coating on the surface of the workpiece by brushing. The mixed alloy powder coating should have certain fluidity and plasticity, and the thickness of the alloy powder coating after coating on the surface of the workpiece should be uniform.

[0018] Preferably, for the press coating process, the general method is to use mechanical high-speed extrusion coating, usually hydraulic press coating and spiral press coating. The uniformity of the alloy powder coating after press coating on the workpiece has no obvious difference and the thickness is the same.

[0019] Specifically, for the degreasing of the coating additive, the process is generally thermal degreasing. It is a method of volatilizing or decomposing the binder component by heating the workpiece after coating, so as to remove it from the green body. Selecting appropriate holding temperature and holding time can effectively control carbon content. After degreasing, the alloy powder coating on the workpiece surface can effectively remove all the binder components.

[0020] Specifically, for the fourth step of alloy coating cladding, the process is to perform cladding treatment on the surface coating of the boiler pipeline after degreasing with alloy powder coating. The cladded coating should form a dense metallurgical bond with the substrate. The cladding methods should include induction cladding and laser cladding.

[0021] Preferably, the induction cladding should be high-frequency induction surface cladding. The process is to rely on the inductor to transfer electrical energy to the heated metal through electromagnetic induction, and use the eddy current generated by the electromagnetic induction effect to heat the alloy powder coated on the surface of the substrate to make it reach the molten state and form an anti-corrosion coating with metallurgical bond on the surface of the workpiece substrate.

[0022] Preferably, for the laser cladding, the process is that the molten pool formed after irradiating the workpiece coated with alloy powder coating by laser causes the two to solidify rapidly together to form an anti-corrosion coating with metallurgical bond covering the surface of the workpiece.

[0023] Compared with the prior art, the present invention has the following advantages.

[0024] In the production of traditional boiler anti-corrosion coatings, airless spraying and pressing coating methods are used for the surfaces and shaped surfaces of different workpieces. Usually, thermal spraying is used for coating production. However, due to its special method, it is very difficult to control the thickness and uniformity of the coating. Most of the spraying processes are manual operations, and it is difficult to make the thickness uniform. Even after spraying, the coating thickness in some parts is difficult to meet the use requirements.

[0025] The present invention uses airless spraying or mechanical pressing coating methods for coating before cladding, which can reasonably control the coating thickness and quality, and avoid most of the disadvantages of thermal spraying, such as uneven coating and many surface pores.

[0026] Applying multiple cladding methods for different composite materials, the cladding methods of the present invention include induction cladding and laser cladding. The two cladding methods select the best method according to the characteristics of the workpiece, effectively improving the cladding efficiency and cladding quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 . Schematic diagram of hydraulic pressing coating.

[0028] Figure 2 . Schematic diagram of airless spraying.

[0029] Figure 3 . Schematic diagram of laser cladding.

[0030] Figure 4 . Schematic diagram of high-frequency induction cladding. Specific implementation manners

[0031] The present invention will be further described in detail below with reference to the accompanying drawings.

[0032] Example 1

[0033] Manufacture of an anti-corrosion coating with a thickness of 0.5 mm by laser cladding on the boiler membrane water wall with a specification of φ51*6.5 mm.

[0034] 1. Preparation of alloy powder coating: Before adding the binder, the prepared alloy powder coating is first mixed evenly, usually in an alloy powder coating prefabrication machine. After the dry mixing of the alloy powder coating is uniform, the binder is added for wet mixing. In this example, the dry alloy powder coating uses a high-temperature oxidation-resistant alloy powder coating SOR (45% Cr, 1.2% Ti, 0.8% B, with the balance being Fe) with a screening particle size of about 400 mesh. It has high-temperature oxidation and corrosion resistance, resistance to S hot corrosion, and good wear resistance. The binder uses polyethylene to bond the alloy powder coating particles at room temperature, making the alloy powder coating have forming properties and a certain strength. At the same time, the plasticizer glycerol is used to form a liquid layer between the alloy powder coatings to improve the plasticity of the alloy powder coating. Adding anhydrous alcohol or kerosene solvent can dissolve the binder and plasticizer and form a plastic liquid with the material. A double "S" shaft mixer is selected to mix the alloy powder coating prefabrication. The powder cylinder has a volume of 500 L. The main quality requirements for the alloy powder coating prefabrication are to make the composition components of the coating uniform, the dry and wet states uniform, and suitable for the needs of coating. After the alloy powder coating is applied, it should be uniform and smooth, with stable eccentricity, no impurities, fermentation and deterioration, etc.

[0035] 2. Hydraulic pressure coating (see the attached Figure 1 ) : Use a hydraulic pressure coater to coat the workpiece. The specific operation is as follows: After cleaning the surface of the boiler membrane water wall, use a specific hydraulic pressure coater for the coating operation of the anti-corrosion layer. After loading the prefabricated alloy powder coating (104) to be coated into the pressure vessel (102) of the coater, place the boiler membrane water wall (105) into the coater for coating. Using the transmission device (101), under the action of the hydraulic pressure rod (103), a 0.5 cm thick coating adheres to the surface of the boiler membrane wall. The coating layer on the surface of the boiler membrane water wall after pressure coating should be uniform and have a consistent thickness, and at the same time, it should be firmly attached to the pipe surface and not easily fall off, without phenomena such as missing, uneven thickness, and instability.

[0036] 3. Degreasing of coating additives: Since the coating method requires mixing materials such as organic binders and solvents, the organic binders and other materials on the coated layer of the boiler membrane water wall should be removed before cladding to prevent the residual organic solvents from affecting the performance of the alloy coating. In this example, the degreasing is carried out by introducing an atmosphere into the heating furnace. The method is to put the boiler membrane water wall with the coated layer into the heating furnace for heat treatment, that is, put the coated boiler membrane water wall into nitrogen, heat it to 70 - 150 °C, and introduce nitric acid. The binder is catalytically cracked into gas by nitric acid. The residual amount of the organic binder and solvent in the coated layer after degreasing should be less than 1%, which does not affect the anti-corrosion effect of the alloy coating.

[0037] 4. Laser cladding (see attachment Figure 3 ): The laser (303) used is a semiconductor laser with a laser power of 6 kW. The laser beam wavelength is 1100 nm, and the spot shape is selected as a circular spot with a spot size of φ3 mm. During the cladding process, the spiral remelting method is adopted, that is, the laser (303) is fixed above the device, the laser beam is vertically downward. While starting the laser, the conveying device (301) advances the boiler membrane water wall (302) with the coated layer along the vertical direction of the laser and the boiler membrane water wall (302) rotates itself, so that the laser performs spiral remelting on the surface of the boiler membrane water wall (302) to form an anti-corrosion coating (304). After cladding, the surface of the boiler membrane water wall (302) should have good anti-corrosion performance and certain wear resistance at the same time. The dilution rate should be controlled below 3%, the thickness is about 0.5 mm uniformly, and the surface morphology of the cladding is neat and uniform.

[0038] Example 2

[0039] Manufacture of an anti-corrosion coating with a thickness of 1.5 mm by induction cladding on a boiler membrane water wall with a specification of φ51*6.5 mm.

[0040] 1. Preparation of dry alloy powder coating: Before adding the binder, the prepared alloy powder coating is first mixed evenly, usually in an alloy powder coating prefabricator. After the alloy powder coating is evenly dry-mixed, the binder is added for wet mixing. In this embodiment, the dry alloy powder coating uses a high-temperature antioxidant alloy powder coating 625 with a screening particle size of about 200 mesh, which has high-temperature oxidation and corrosion resistance, anti-S hot corrosion, and good wear resistance. The binder uses polyethylene to bond the alloy powder coating particles at room temperature, enabling the alloy powder coating to have forming properties and a certain strength. At the same time, the plasticizer glycerol is used to form a liquid layer between the alloy powder coatings to improve the plasticity of the alloy powder coating. Adding anhydrous alcohol or kerosene solvent can dissolve the binder and plasticizer and form a plastic liquid with the material. A double "S" shaft mixer is selected to mix the alloy powder coating prefabrication. The powder cylinder volume is 500L. The quality requirements for the preparation of the alloy powder coating are mainly to make the composition components of the coating uniform, the dry and wet states uniform, and suitable for coating needs, so that the alloy powder coating is uniform, smooth, eccentrically stable, and the coating has no impurities, fermentation, or deterioration after coating.

[0041] 2. Airless spraying coating (see attachment Figure 2 ): The alloy mixture slurry is sprayed by means of high-pressure airless spraying. The alloy coating (202) is sucked from the storage tank by a high-pressure pump (201) and then pressurized, usually to 11MPa - 25MPa. After passing through a pressure-holding filter (203), the coating is sprayed out from the nozzle (204). The alloy coating with a certain adhesiveness is sprayed on the surface of the boiler membrane water wall (205) in a high-speed atomized state, forming a coating layer of 2 - 2.5 cm. See attachment Figure 2 .

[0042] 3. Degreasing of coating additives: Since the airless spraying method requires mixing organic binders and solvents and other materials, the organic binders and other materials on the coating layer of the boiler membrane water wall should be removed before cladding to prevent the residual organic solvents from affecting the performance of the alloy coating. In this example, the degreasing is carried out by introducing an atmosphere into the heating furnace. The method is to put the boiler membrane water wall with the coating layer into the heating furnace for heat treatment, that is, placing the coated boiler membrane water wall in nitrogen, heating to 70 - 150 °C, and introducing nitric acid. The binder is catalytically cracked into gas by nitric acid. The residual amount of the organic binder and solvent in the degreased coating layer should be below 1%, which does not affect the anti-corrosion effect of the alloy coating.

[0043] 4. Induction cladding (see attachment Figure 4: The LH-15A series high-frequency induction equipment is adopted, with an input power of 100 kW, an output oscillation frequency of 30 - 80 kHz, and the induction coil (404) has a circular induction cross-section with a size of φ60*30 mm. The boiler membrane water wall (403) coated with the coating layer is subjected to cladding treatment. During cladding, the induction cladding equipment is placed in a vacuum environment, and the boiler membrane water wall (403) with the coating layer is preheated to 200 °C. The high-frequency power supply (401) is started, with an applied frequency of 50 kHz and an initial current of 500 A. The current is increased to the coating cladding target current of about 1000 A in 30 s to completely melt the coating in the induction coil (404). At the same time, the conveyor device (402) is used to move the boiler membrane water wall (403) in the vertical direction along the induction coil (404) so that the surface-coated coating is completely cladded on the surface of the boiler membrane water wall (403). After cladding, the surface of the boiler membrane water wall should have good anti-corrosion performance and certain wear resistance. The coating dilution rate should be controlled below 3%, the cladding thickness is 2 mm, and the cladding surface morphology is neat and uniform.

Claims

1. A method for making an alloy anti-corrosion coating on the surface of boiler pipes by using powder metallurgy technology, characterized in that, It is made through four technological steps, namely: the first step: prefabrication of alloy powder coating; the second step: coating of alloy coating on the surface of boiler pipes; the third step: degreasing of coating additives; the fourth step: cladding of alloy coating; In the second step: coating of alloy coating on the surface of boiler pipes, the alloy powder coating prepared in the first step is coated on the surface of boiler pipes. The coating methods should include two methods: airless spraying and pressure coating. After coating, the alloy powder coating should be closely attached to the substrate and not easy to fall off; For the airless spraying mentioned above, specifically high-pressure airless spraying, the prefabricated alloy powder coating to be coated in the previous step is pressurized to a pressure of 9.8 MPa - 29.4 MPa by a pressure pump, and then sprayed out through the small holes of a special nozzle, and the alloy powder coating is evenly coated on the surface of boiler pipes; For the hydraulic pressure coating mentioned above, specifically mechanical pressure coating with hydraulic power, the prefabricated alloy powder coating to be coated in the previous step is stored in a raw material tank. After applying pressure by a hydraulic piston, the membrane wall passes through a pressure vessel at the same time, so that its surface is evenly coated with the mixed alloy coating.

2. According to the first step described in claim 1: prefabrication of alloy powder coating, the process is to mix the metallurgical coating powder with anti-corrosion properties and alloy powder coating additives to make a mixed alloy powder coating with good fluidity, uniformity and certain plasticity.

3. According to the third step described in claim 1: degreasing of coating additives, in the form of thermal degreasing, the membrane wall with the mixed alloy coating coated on its surface is placed in a heating container, and after heating for a certain time and at a certain temperature, the additives in the alloy powder coating are removed from the alloy powder coating.

4. According to the fourth step described in claim 1: cladding of alloy coating, the surface coating of the boiler pipe after degreasing of the alloy powder coating is subjected to cladding treatment. The cladding methods should include high-frequency induction cladding and laser cladding. The cladding thickness of the coating is 0.5 - 4 mm, and the coating has good metallurgical bonding with the substrate.

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