Long-life anti-corrosion and wear-resistant coating on the surface of a cast iron drying cylinder for fruit bag paper and a preparation method thereof

Abstract

This invention provides a long-life anti-corrosion and wear-resistant mirror coating for the surface of a cast iron drying cylinder for fruit bags and its preparation method, belonging to the field of surface coating technology. This invention prepares a mirror coating with high anti-corrosion and wear-resistant properties on the surface of the cast iron drying cylinder for fruit bags through thermal spraying, significantly improving the lifespan of the drying cylinder while maintaining the smoothness and gloss of the cylinder surface over a long period, thereby ensuring the surface gloss of the fruit bag paper.

Description

Technical Field

[0001] This invention relates to the field of surface coating technology, and in particular to a long-life anti-corrosion and wear-resistant mirror coating for the surface of a cast iron drying cylinder for fruit bags and its preparation method. Background Technology

[0002] The drying cylinder is a key mechanical component in a paper production line, playing a crucial role in drying and finishing the paper surface during the paper processing. Cast iron is one of the main materials for drying cylinders, offering high cost-effectiveness, but it suffers from poor corrosion resistance. In actual use, prolonged contact with water, acidic / alkaline chemical slurries, and other media can cause a certain degree of corrosion on the drying cylinder surface. Simultaneously, the friction from high-hardness steel doctor blades and occasional abnormal contact can lead to severe frictional damage on the drying cylinder surface. To ensure the papermaking process meets the requirements for the surface finish (smoothness and flatness) of the drying cylinder, the damaged surfaces need to be regularly ground. This process is time-consuming and labor-intensive, and the resulting thinning of the drying cylinder wall inevitably weakens its strength. Repeated machining can lead to significant variations in the thickness of the drying cylinder wall, resulting in insufficient minimum thickness safety margin.

[0003] Currently, there are two main methods for improving the surface properties of cast iron drying cylinders:

[0004] 1. Using arc spraying to apply a Fe-based alloy coating with certain corrosion resistance (commonly using materials such as 304, 316L, 4Cr13, 5Cr13, 7Cr13, FeCr-based amorphous materials, etc.) to obtain a coating of about 1 mm, the coating has good smoothness and corrosion resistance, but the hardness is low, only HV 300-HV 500, and the service life is short. It cannot effectively solve the problem of reduced surface smoothness or even serious friction damage when the drying cylinder is used together with a high-hardness steel scraper.

[0005] 2. The electroplating method of hard chrome plating is used to obtain an electroplated layer with a surface hardness greater than HV 800. It has high hardness and good smoothness. However, due to the sand hole defects on the cast iron surface, the electroplated layer is often incomplete and there are omissions, which become sources of corrosion, resulting in local peeling of the electroplated layer after 1-2 years of use. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention prepares a mirror coating with high corrosion resistance and wear resistance on the surface of the cast iron drying cylinder of fruit bag paper by thermal spraying, which significantly improves the coating life and achieves long-term maintenance of the surface smoothness and gloss of the drying cylinder, thereby ensuring that the surface gloss of the fruit bag paper continuously meets the requirements.

[0007] Fruit bag paper is a specialty paper with high requirements for surface gloss (single-sided gloss). The surface gloss of the paper is closely related to the smoothness of the drying cylinder surface; the higher the surface smoothness of the drying cylinder, the better its corrosion resistance and wear resistance, and thus the higher the gloss of the paper. Therefore, this invention uses thermal spraying to prepare a mirror-like coating with high corrosion resistance and wear resistance on the surface of the cast iron drying cylinder for fruit bag paper, significantly improving the coating life and maintaining the surface smoothness of the drying cylinder for a long time, thereby ensuring that the surface gloss of the fruit bag paper continuously meets the requirements.

[0008] The present invention determines the final spraying process as follows:

[0009] 1. Arc spraying primer. Arc spraying is a technique that uses an electric arc generated between two continuously fed metal wires as a heat source to melt the metal. High-pressure, high-flow-rate compressed air atomizes the molten metal and accelerates the atomized metal droplets to spray them onto the workpiece to form a coating. Figure 2 This is a diagram illustrating the working principle of arc spraying. As shown, two continuously fed metal wires, positioned at a certain angle at their ends, are connected to the positive and negative terminals of a DC power supply (18~40V). An electric arc is generated the instant the ends of the metal wires are short-circuited. The arc melts the metal wires, and a high-speed airflow ejected from a nozzle behind the arc point atomizes the molten metal into particles, which are then accelerated by the high-speed airflow and sprayed onto the surface of the workpiece.

[0010] Because the particle velocity of arc spraying is lower than that of supersonic flame spraying (50-150 m / s), the atomized particle size is larger (in the hundreds of micrometers). After spraying, the particles spread out over a large area, which can effectively cover pinholes and form a protective layer with good corrosion resistance. The specific process steps and parameters are as follows:

[0011] 1) Turning

[0012] Remove rust and damage layers from the surface of the drying cylinder by turning.

[0013] 2) Repairing large-sized sand holes

[0014] For pinholes deeper than 0.5 mm, repair them with pins made of the same or similar materials with a similar coefficient of expansion.

[0015] 3) Polishing

[0016] Polishing was performed using a belt sander, and the surface roughness of the drying cylinder was controlled to be Ra 1.6 μm.

[0017] 4) Degreasing

[0018] Clean the surface of the drying cylinder to remove oil and impurities.

[0019] 5) Sandblasting

[0020] The surface of the drying cylinder is sandblasted using a sandblasting machine, and the surface roughness is controlled to be Ra 8-12 μm.

[0021] 6) Arc spraying

[0022] The spraying parameters are as follows:

[0023] Wire materials: φ1.6 metal wire, φ2.0 metal wire, φ3.0 metal wire; made of Fe-based alloy material with certain corrosion resistance;

[0024] Voltage: 28-36 V;

[0025] Current: 100-200A;

[0026] Spraying distance: 100-200 mm;

[0027] Wire feeding rate: 75-150 g / min.

[0028] A base layer with a porosity of <1%, a bonding strength of >35 MPa, and a thickness between 1-1.5 mm is obtained.

[0029] 2. High Velocity Oxygen Fuel (HVOF) or High Velocity Air Fuel (HVAF) technology refers to a process that utilizes gaseous or liquid fuels to form a high-intensity combustion flame under high pressure and high flow rate of oxygen or air. This high-intensity flame is then further compressed and accelerated through a specially structured nozzle to achieve a supersonic flame flow. This supersonic flame flow is then used as a heat source to heat and accelerate the sprayed material, forming a coating.

[0030] The specific process parameters and steps for using supersonic flame spraying are as follows:

[0031] 1) Polishing

[0032] Polishing is performed using a belt sander, controlling the surface roughness of the drying cylinder to not exceed Ra 1.0 μm, the straightness to be within 10 microns, and the circumferential runout to be within 5 microns.

[0033] 2) Degreasing

[0034] Clean the polished surface to remove oil and impurities.

[0035] 2) Sandblasting

[0036] The surface of the drying cylinder was sandblasted using a sandblasting machine, with the surface roughness controlled at Ra 6-8 μm. The sandblasting parameters are as follows:

[0037] Material: Single-crystal corundum, between 46 and 80 mesh;

[0038] Pressure: 0.5-0.7 MPa

[0039] 3) HVOF / HVAF spraying

[0040] The spraying parameters are as follows:

[0041] Material: WC-Cr3C2-M (M is a single metal or alloy of Fe, Co, Cr, and Ni);

[0042] WC-M (where M is a single metal or alloy of Fe, Co, Cr, or Ni);

[0043] Cr3C2-M (where M is a single metal or alloy of Fe, Co, Cr, or Ni);

[0044] Coating thickness: 0.3mm or more;

[0045] Coating hardness: ≥HV1000;

[0046] Coating porosity: <1.0%.

[0047] 4) Polishing

[0048] The coated surface is polished using diamond abrasive belts to control the surface roughness between Ra 0.2 and 0.6.

[0049] This results in a long-life cast iron drying cylinder for fruit bags with a service life of over 5 years, an anti-corrosion and wear-resistant coating on the surface, excellent paper quality from the mirror drying cylinder, and a good gloss effect for the fruit bag paper produced. Attached Figure Description

[0050] Figure 1 For arc-assisted undercoating;

[0051] Figure 2 This is a schematic diagram of the principle of electric arc spraying; in the diagram, 1 - workpiece; 2 - coating; 3 - spray beam; 4 - electric arc; 5 - spray wire; 6 - conductive nozzle; 7 - compressed air nozzle;

[0052] Figure 3 The cross-sectional microstructure of the arc-sprayed 5Cr13 coating;

[0053] Figure 4 Polishing of the bottom layer of the electric arc with abrasive belt;

[0054] Figure 5 For HVAF drying cylinder spraying (WC-10Co4Cr);

[0055] Figure 6 Diamond belt polishing was performed on the WC-10Co4Cr coating sprayed onto the HVAF drying cylinder.

[0056] Figure 7 Finished product of fruit bag drying cylinder;

[0057] Figure 8 For the roughness of the finished product of the fruit bag drying cylinder;

[0058] Figure 9 Paper is dispensed from the mirror-finish drying cylinder;

[0059] Figure 10 To enhance the gloss and shine of the fruit bag paper;

[0060] Figure 11 A schematic diagram illustrating the drawbacks of "direct supersonic flame spraying WC" at sand holes with large depth-to-depth ratio on the surface of the drying cylinder (inability to effectively fill sand hole defects);

[0061] Figure 12 The morphology of WC-10Co4Cr particles;

[0062] Figure 13 The microstructure is WC-10Co4Cr coating;

[0063] Figure 14 Photos showing the failure of the "direct HVOF spray WC coating" for the cast iron fruit bag drying cylinder;

[0064] Figure 15 Stainless steel-based metal alloy wire for arc spraying of fruit bag drying cylinder;

[0065] Figure 16 The drying cylinder is sprayed with a stainless steel coating and then polished.

[0066] Figure 17 This refers to scratches that appear after a period of use in traditional arc spraying drying cylinders.

[0067] Figure 18 Photo of an electroplating drying cylinder;

[0068] Figure 19 This refers to sand hole defects on the surface of cast iron drying cylinders;

[0069] Figure 20 Photos showing failures of traditional electroplating drying cylinders after 1-2 years of use. Detailed Implementation

[0070] Example 1

[0071] 1. Arc spraying primer (e.g.) Figure 1 Arc spraying is a technique that uses an electric arc generated between two continuously fed metal wires as a heat source to melt the metal. High-pressure, high-flow-rate compressed air atomizes the molten metal and accelerates the atomized metal droplets to spray them onto the workpiece to form a coating. Figure 2This is a diagram illustrating the working principle of arc spraying. As shown, two continuously fed metal wires, positioned at a certain angle at their ends, are connected to the positive and negative terminals of a DC power supply (18~40V). An electric arc is generated the instant the ends of the metal wires are short-circuited. The arc melts the metal wires, and a high-speed airflow ejected from a nozzle behind the arc point atomizes the molten metal into particles, which are then accelerated by the high-speed airflow and sprayed onto the surface of the workpiece.

[0072] Because the spraying speed of arc spraying is lower than that of supersonic flame spraying (50-150 m / s), the atomized particle size is larger (in the hundreds of micrometers), and the particle flattening and spreading area after spraying is larger (e.g., Figure 3 This process can effectively cover pinholes and form a protective layer with good corrosion resistance. The specific process steps and parameters are as follows:

[0073] 1) Turning

[0074] Remove the surface rust layer by turning.

[0075] 2) Repairing large-sized sand holes

[0076] For pinholes deeper than 0.5 mm, repair them with pins made of the same or similar materials with a similar coefficient of expansion.

[0077] 3) Polishing

[0078] Polishing is performed using a belt sander (e.g.) Figure 4 The surface roughness of the drying cylinder is controlled to be Ra 1.6 μm.

[0079] 4) Degreasing

[0080] Clean the surface of the drying cylinder to remove oil and impurities.

[0081] 5) Sandblasting

[0082] The surface of the drying cylinder is sandblasted using a sandblasting machine, and the surface roughness is controlled to be Ra 8-12 μm.

[0083] 6) Arc spraying

[0084] The spraying parameters are as follows:

[0085] Wire materials: φ1.6 metal wire, φ2.0 metal wire, φ3.0 metal wire;

[0086] Voltage: 28-36 V;

[0087] Current: 100-200A;

[0088] Spraying distance: 100-200 mm;

[0089] Wire feeding rate: 75-150 g / min.

[0090] A base layer with a porosity of <1%, a bonding strength of >35 MPa, and a thickness between 1-1.5 mm is obtained.

[0091] 2. Supersonic flame spraying (e.g.) Figure 5 High Velocity Oxygen Fuel (HVOF) or High Velocity Air Fuel (HVAF) technology refers to a process that utilizes gaseous or liquid fuels to form a high-intensity combustion flame under high pressure and high flow rate of oxygen or air. This high-intensity flame is then further compressed and accelerated through a specially structured nozzle to achieve a supersonic flame flow. This supersonic flame flow is then used as a heat source to heat and accelerate the sprayed material to form a coating.

[0092] The specific process parameters and steps for using supersonic flame spraying are as follows:

[0093] 1) Polishing

[0094] Polishing is performed using a belt sander (e.g.) Figure 6 The surface roughness of the drying cylinder should not exceed Ra 1.0 μm, the straightness should be within 10 mils, and the circumferential runout should be within 5 mils.

[0095] 2) Degreasing

[0096] Clean the polished surface to remove oil and impurities.

[0097] 2) Sandblasting

[0098] The surface of the drying cylinder was sandblasted using a sandblasting machine, with the surface roughness controlled at Ra 6-8 μm. The sandblasting parameters are as follows:

[0099] Material: Single-crystal corundum, between 46 and 80 mesh;

[0100] Pressure: 0.5-0.7 MPa

[0101] 3) HVOF / HVAF spraying

[0102] The spraying parameters are as follows:

[0103] Material: WC-Cr3C2-M (M is a single metal or alloy of Fe, Co, Cr, and Ni);

[0104] WC-M (where M is a single metal or alloy of Fe, Co, Cr, or Ni);

[0105] Cr3C2-M (where M is a single metal or alloy of Fe, Co, Cr, or Ni);

[0106] Coating thickness: 0.3mm or more

[0107] Coating hardness: ≥HV1000;

[0108] Coating porosity: <1.0%.

[0109] 4) Polishing

[0110] The coated surface is polished using diamond abrasive belts to control the surface roughness between Ra 0.2 and 0.6. Figure 7 , Figure 8 .

[0111] This results in a long-life cast iron drying cylinder for fruit bags with a service life of over 5 years, featuring an anti-corrosion and wear-resistant coating, and a mirror-finish drying cylinder producing excellent paper quality (such as...). Figure 9 The resulting fruit bag paper has a better gloss effect (e.g. Figure 10 ).

[0112] Comparative Example 1

[0113] Referring to existing literature (Yang, M., Song, P., Kong, D., et al. (2024). Wear and corrosion properties of HVOF sprayed WC-Cr3C2 composite coating for application in polysilicon cyclone separator. Journal of Materials Research and Technology, 29, 78-89.), a WC-Cr3C2 base coating was prepared by supersonic flame spraying (fuel: propane, propylene, natural gas, kerosene, etc. + oxygen HVOF / air HVAF), with a hardness between HV 1000-1400, to obtain a coating with high corrosion resistance and wear resistance. Coatings obtained by direct HVOF / HVAF spraying have poor corrosion and wear resistance because the powder particles used in supersonic flame spraying are small, typically 5-25 μm, 5-30 μm, or 15-45 μm in size, and the spraying speed is high (500-1000 m / s) with a large airflow. This results in insufficient penetration depth in areas with large pinholes on the drying cylinder surface (such as...). Figure 11 After the powder collides with the substrate surface, it forms carbide particles with a size of 1-3 μm (e.g. Figure 12 ), relying on adhesives to form concrete-like structures (such as Figure 13 It is difficult to effectively deposit and cover the pinholes, requiring increased spray thickness to achieve complete coverage, but failure still occurs after two years of use (e.g. Figure 14 ).

[0114] Comparative Example 2

[0115] Referring to existing literature (Matikainen, V. (2022). Modern HVAF Spray Process and Cr3C2-Based Coatings: Exploring the process, structure, properties and performance (Tampere University Dissertations, Vol. 600). Tampere University.), the method of arc spraying stainless steel alloys (304, 316, 5Cr13, 7Cr13, etc.) was adopted (e.g. Figure 15 ), to obtain a coating of about 1 mm (e.g. Figure 16 Its gloss and corrosion resistance are good, but its hardness is low, only HV 300-HV 500, resulting in a short service life. It cannot effectively solve the problem of decreased surface smoothness or even severe friction damage when the drying cylinder and high-hardness steel scraper are used together (e.g., Figure 17 ).

[0116] Comparative Example 3

[0117] Referring to existing literature (Xiong Wenying, Liu Junquan, Luo Weiyin. Several new processes to replace hard chromium plating [J]. Electroplating and Finishing, 2006, (04): 50-53. DOI: 10.19289 / j.1004-227x.2006.04.016. / [2] Gawne, DT (1984). Failure of electrodeposited chromium coatings on cast ironsubstrates. Thin Solid Films, 118(3), 385-393.), an electroplating layer with a surface hardness greater than HV 800 (such as) was obtained by electroplating hard chromium. Figure 18 It has high hardness and good gloss, but due to sand hole defects on the surface of cast iron (such as...), it is difficult to achieve high hardness and good gloss. Figure 19 The electroplated layer is often incomplete, with omissions, and after 1-2 years of use, localized peeling of the electroplated layer may occur (e.g.) Figure 20 ).

[0118] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A corrosion-resistant and wear-resistant mirror coating on the surface of a cast iron drying cylinder for fruit bags, characterized in that, It includes an arc spraying primer and a supersonic flame spraying topcoat; wherein the spraying wire for the arc spraying primer includes φ1.6 metal wire, φ2.0 metal wire and / or φ3.0 metal wire; the spraying material for the supersonic flame spraying topcoat includes at least one of the following: WC-Cr3C2-M, WC-M and Cr3C2-M, wherein M is a single metal of Fe, Co, Cr or Ni or an alloy formed by two or more of the above elements.

2. The anti-corrosion and wear-resistant mirror coating on the surface of the cast iron drying cylinder for fruit bags according to claim 1, characterized in that, The porosity of the arc-sprayed undercoat is <1%, the bonding strength is >35 MPa, and the thickness is 1-1.5 mm.

3. The anti-corrosion and wear-resistant mirror coating on the surface of the cast iron drying cylinder for fruit bags according to claim 1, characterized in that, The coating thickness of the supersonic flame spraying surface layer is above 0.3mm.

4. The method for preparing the anti-corrosion and wear-resistant mirror coating on the surface of the cast iron drying cylinder for fruit bags according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Apply an electric arc spray coating to the surface of the cast iron drying cylinder for fruit bag paper. The spraying parameters include: selecting φ1.6 metal wire, φ2.0 metal wire and / or φ3.0 metal wire; voltage of 28-36 V, current of 100-200 A, spraying distance of 100-200 mm, and wire feeding rate of 75-150 g / min. (2) After the arc spraying primer, supersonic flame spraying is performed. The spraying material includes at least one of the following: WC-Cr3C2-M, WC-M and Cr3C2-M, wherein M is a single metal of Fe, Co, Cr or Ni or an alloy formed by two or more of the above elements; the spraying thickness is more than 0.3 mm, the coating hardness is ≥ HV1000, and the coating porosity is < 1.0%.

5. The preparation method according to claim 4, characterized in that, Before the arc spraying primer in step (1), the process also includes turning, repairing sand holes, polishing, degreasing and sandblasting.

6. The preparation method according to claim 5, characterized in that, The repair of sand holes includes using pins made of the same or similar materials with a depth of 0.5 mm or more for repair.

7. The preparation method according to claim 5, characterized in that, The polishing includes polishing using a belt sander, controlling the surface roughness of the drying cylinder to be Ra 1.6 μm.

8. The preparation method according to claim 5, characterized in that, The sandblasting includes using a sandblasting machine to sandblast the surface of the drying cylinder, controlling the surface roughness to be Ra 8-12 μm.

9. The preparation method according to claim 4, characterized in that, Before the supersonic flame spraying in step (2), polishing, degreasing and sandblasting are also included; after the supersonic flame spraying, polishing is also included again.

10. The preparation method according to claim 9, characterized in that, The polishing includes polishing until the surface roughness of the drying cylinder does not exceed Ra 1.0 μm, the straightness is within 10 mils, and the circumferential runout is within 5 mils; The material used for sandblasting includes 46-80 mesh single-crystal corundum, and after sandblasting, the surface roughness is Ra 6-8 μm; After the second polishing, the surface roughness of the anti-corrosion and wear-resistant mirror coating on the surface of the finished fruit bag drying cylinder is between Ra 0.2 and 0.6.

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