A tower top roller surface coating resistant to high-temperature zinc slag adhesion and a preparation process thereof

Abstract

The application discloses a tower top roller surface coating resistant to high-temperature zinc slag adhesion and a preparation process thereof, and belongs to the technical field of surface modification of hot galvanizing equipment. In view of the problems of weak high-temperature zinc slag adhesion resistance, easy cracking and falling, and short service life of the existing tower top roller coating, the coating adopts a composite gradient structure, and from the inside to the outside of the base body, the coating is sequentially a bonding bottom layer, a transition layer and a functional surface layer, each layer is synergized through specific component allocation, wherein the bonding bottom layer guarantees high bonding strength, the transition layer relieves thermal stress, and the functional surface layer realizes the effects of low surface energy, high-temperature resistance and zinc slag adhesion resistance; the preparation process comprises base body pretreatment, coating material pretreatment and plasma spraying of three layers of coating treatment. The coating has a zinc slag adhesion resistance rate of greater than or equal to 95%, a bonding strength with the base body of greater than or equal to 80 MPa, and a service life, which is more than 2 times that of the existing coating, under a high-temperature environment of 450-550 DEG C. The application can reduce production and maintenance costs, guarantee the quality of hot galvanizing products, and is easy to be popularized in industry.

Description

Technical Field

[0001] This invention belongs to the field of surface modification technology for hot-dip galvanizing equipment, specifically relating to a coating on the surface of a tower top roller that resists high-temperature zinc slag adhesion and its preparation process. Background Technology

[0002] In continuous hot-dip galvanizing production, the tower top roller is a key steering component located at the top of the cooling tower above the zinc pot, primarily used to reverse the direction of the hot-dip galvanized steel strip. After the strip has fully reacted with the molten zinc to complete the galvanizing process, it enters the post-galvanizing cooling tower at a high temperature of 460±5℃. This causes the strip to run on the tower top roller at a temperature exceeding 300℃, transferring heat from the tower top roller to temperatures above 300℃. This results in incompletely solidified zinc layers adhering to the surface of the tower top roller, forming zinc dross. Over time, this zinc dross accumulates and forms protrusions, leading to surface defects on the strip.

[0003] Currently, most existing tower top rollers use a single tungsten carbide coating or a cloth-wrapped method, which has significant technical drawbacks. While a single tungsten carbide coating has a certain degree of wear resistance, its high surface energy at high temperatures makes it prone to zinc dross adhesion and difficult to clean. After long-term use, zinc dross will become embedded in the coating surface, leading to increased surface roughness of the tower top roller, which in turn scratches the steel strip surface and affects the quality of galvanized products. Some tower top rollers using a cloth-wrapped structure can reduce zinc dross adhesion to some extent, but the cloth wrapping has problems such as seam marks, easy damage, and the need for frequent replacement, increasing production and maintenance costs and downtime.

[0004] The existing surface protection of tower top rollers in this field still has the following technical difficulties: 1. Poor thermal stress matching between the coating and the substrate under high temperature conditions, which easily leads to cracking and peeling. Tower top rollers are in a high-temperature service environment of more than 300°C for a long time, and the temperature changes caused by the start-up and shutdown of the production line are also significant. The thermal expansion coefficient of the existing single coating (such as tungsten carbide coating) is significantly different from that of the metal substrate of the tower top roller. Under high temperature, internal stress concentration is easily generated, which leads to micro-cracks and local peeling of the coating. The peeled area will not only quickly adhere to zinc dross, but also directly scratch the steel strip, becoming the core cause of product quality defects. 2. Existing protective layers lack sufficient surface energy regulation, failing to meet the core requirement of resisting high-temperature zinc dross adhesion in hot-dip galvanizing production. In this process, the unsolidified zinc layer carried by the strip steel is molten at high temperatures, exhibiting strong wettability on solid surfaces. Existing single-coating materials such as tungsten carbide have high high-temperature surface energy and strong interfacial bonding with molten zinc dross, leading to easy adhesion and difficulty in cleaning. While fabric-covered structures can reduce surface energy, the uncoated structure cannot solve the wettability problem, only temporarily reducing adhesion through physical isolation, and cannot fundamentally achieve resistance to zinc dross adhesion. Therefore, a method is urgently needed to address the poor adhesion of the coating on the top roller surface in hot-dip galvanizing production. Summary of the Invention

[0005] This invention provides a coating for the surface of a tower top roller that resists high-temperature zinc slag adhesion and its preparation process. By optimizing the coating material ratio and preparation process, the coating achieves a synergistic improvement in high-temperature resistance, low surface energy, high bonding strength and anti-zinc slag adhesion performance, thereby extending the service life of the tower top roller, reducing production and maintenance costs, and ensuring the quality of hot-dip galvanized products.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a coating for the surface of a tower top roller that resists the adhesion of zinc slag at high temperatures, wherein the coating is a composite gradient coating, and from the inside to the outside of the tower top roller substrate surface are an adhesive underlayer, a transition layer and a functional surface layer; The bonding underlayer is composed of the following components by mass percentage: 75-85% NiCr alloy and 15-25% Al powder; in the NiCr alloy, the mass percentage of Ni is 80-90% and the mass percentage of Cr is 10-20%; the transition layer is composed of the following components by mass percentage: Ni: 30-35%, Cr: 16-18%, Al: 5-8%, Y: 0.5-1%, with the balance being Co; the functional surface layer is composed of the following components by mass percentage: ZrO2: 70-82%, MoSi2: 10-15%, WS2: 5-10%, BN: 3-5%.

[0007] The thickness of the adhesive underlayer of the present invention is 20-30 μm; the thickness of the transition layer is 20-30 μm; and the thickness of the functional surface layer is 60-90 μm.

[0008] The composite gradient coating of this invention has a total thickness of 100-150 μm, and the bonding strength between the coating and the substrate of the tower top roller is ≥80 MPa. It can be used for more than 2 years in a high-temperature environment of 450-550℃, with an anti-zinc slag adhesion rate of ≥95%, and its service life is more than twice that of existing coatings. The bonding strength testing method refers to "GB / T 8642-2025 Determination of Tensile Bond Strength of Thermal Spray Coating". The anti-zinc slag adhesion rate testing method involves measuring the area of ​​the zinc slag adhesion zone within a certain number of days of use (e.g., comparing the actual online use of the finished roller, measuring the zinc slag adhesion rate every three months). The anti-zinc slag adhesion rate is calculated as (1 - zinc slag adhesion area / total roller area) * 100%.

[0009] Another objective of this invention is to provide a method for preparing a coating on the surface of a tower top roller that resists high-temperature zinc slag adhesion, the method comprising the following steps: Step 1: Pre-treatment of the tower top roller substrate: First, grind the tower top roller substrate, then sandblast it, and blow off the surface sand and dust for later use. Step 2: Coating material pretreatment: Weigh the raw materials according to the mass percentage of each layer and dry them; Step 3: Preparation of the bonding underlayer: The bonding underlayer is prepared on the pretreated substrate surface using plasma spraying technology. The spraying power is 20-25kW, the powder feeding speed is 20-30g / min, and the spraying distance is 100-120mm. After spraying, the substrate is allowed to cool naturally to room temperature. Step 4: Transition layer preparation: A transition layer is prepared on the surface of the bonding substrate using plasma spraying technology. The spraying power is 20-25kW, the powder feeding speed is 20-30g / min, and the spraying distance is 100-120mm. After spraying, the substrate is allowed to cool naturally to room temperature. Step 5: Preparation of functional surface layer: The functional surface layer is prepared on the surface of the transition layer by plasma spraying process. The spraying power is 30-35kW, the powder feeding speed is 20-30g / min, the spraying distance is 80-100mm, and the coating is allowed to cool naturally to room temperature after spraying.

[0010] In step 1 of this invention, white corundum sand is used for sandblasting, the sandblasting pressure is 0.4-0.6 MPa, the sandblasting angle is 45°-60°, the sandblasting distance is 80-120 mm, and the sandblasting time is 10-15 min; after sandblasting, the surface roughness Ra of the substrate reaches 5-8 μm.

[0011] In step 3 of this invention, the plasma spraying parameters are: spraying voltage 30-40V, spraying current 500-600A, plasma gas is Ar+H2 mixed gas, and spray gun moving speed 50-80mm / s.

[0012] In step 4 of this invention, the plasma spraying parameters are: spraying voltage 30-40V, spraying current 500-600A, plasma gas is Ar+H2 mixed gas, and spray gun moving speed 50-80mm / s.

[0013] In step 5 of this invention, the plasma spraying parameters are: spraying voltage 50-60V, spraying current 700-800A, plasma gas is Ar+N2 mixed gas, and spray gun moving speed 30-50mm / s.

[0014] The design concept for the chemical composition is as follows: The role of the bonding underlayer is to improve the bonding strength between the coating and the substrate of the tower top roller, reduce the difference in the coefficient of thermal expansion between the coating and the substrate, and prevent the coating from cracking and peeling off due to thermal stress in a high-temperature environment. Among them, NiCr alloy provides good high-temperature oxidation resistance and basic bonding ability, while Al powder can form an alumina film at high temperature, further enhancing the bonding performance and high-temperature resistance.

[0015] The transition layer serves to achieve a smooth transition between the substrate and the functional surface layer, alleviating performance differences and thermal stress between the substrate and the surface layer, while providing excellent oxidation resistance, corrosion resistance, and high-temperature service stability. The balance Co, as the alloy matrix, possesses good metallurgical bonding and mechanical support capabilities and is the core component of the transition layer. Ni optimizes the alloy lattice matching and enhances the bonding strength between the transition layer and the substrate and surface layer. Cr forms a dense oxide passivation film, giving the transition layer excellent oxidation resistance and corrosion resistance. Al assists Cr in forming a stable high-temperature oxide film, strengthening the high-temperature protection performance of the transition layer. Y refines the oxide film grains, optimizes the film density and adhesion, delays film peeling under high-temperature environments, and ensures the long-term service stability of the transition layer.

[0016] The functional surface layer is the core layer for achieving high-temperature zinc dross adhesion resistance. Its components work synergistically to endow the coating with low surface energy, excellent high-temperature resistance, resistance to zinc liquid erosion, and self-lubricating properties. Among them, ZrO2 has extremely high high-temperature resistance and good chemical stability, which can maintain structural stability in high-temperature environments and resist the erosion of zinc liquid and zinc dross. MoSi2 has excellent high-temperature oxidation resistance and low friction coefficient, which can reduce the surface energy of the coating and reduce the adhesion of zinc dross. WS2 and BN are solid lubricants that can further reduce the surface friction coefficient of the coating, making the adhered zinc dross easy to fall off during the operation of the tower top roller, while improving the self-lubricating properties of the coating and reducing wear between the coating and the steel strip.

[0017] The beneficial effects of adopting the above technical solution are as follows: 1. The coating of the present invention adopts a composite gradient structure design, which consists of an adhesive underlayer, a transition layer and a functional surface layer from the substrate to the surface. The material components of each layer work together to effectively solve the defect of single coating performance. The adhesive underlayer ensures high bonding strength between the coating and the substrate, the transition layer alleviates thermal stress and performance differences between the layers, and the functional surface layer gives the coating excellent resistance to high temperature zinc dross adhesion. It achieves a synergistic improvement in high temperature resistance, low surface energy, high bonding strength, wear resistance and resistance to zinc dross adhesion. The coating can be used for a long time in a high temperature environment of 450 to 550℃ with a zinc dross adhesion rate of ≥95%, effectively avoiding the impact of zinc dross adhesion on the surface quality of the tower top roller and steel belt. 2. The functional surface layer of this invention is composed of ZrO2, MoSi2, WS2, BN, and other components. ZrO2 solid solution possesses extremely high temperature resistance and chemical stability, resisting the erosion of high-temperature zinc liquid and zinc dross. MoSi2, WS2, and BN work synergistically to significantly reduce the surface energy and friction coefficient of the coating, making it difficult for zinc dross to adhere. Furthermore, any adhered zinc dross easily detaches during the operation of the tower top roller. It also possesses good self-lubricating properties, reducing wear between the coating and the steel strip. 3. The preparation process of this invention employs plasma spraying, combined with substrate pretreatment, material pretreatment, and high-temperature annealing post-treatment. The process is stable and controllable, resulting in a dense and uniform coating free of defects such as pores and cracks. The adhesion strength between the coating and the substrate is ≥80MPa, and the thickness is uniform and controllable. This further extends the service life of the tower top roller, more than doubling it compared to existing coatings and cloth-wrapped structures, significantly reducing production and maintenance costs and downtime. 4. The coating material of this invention is widely available, the preparation process is simple, no special and expensive equipment is required, and it is easy to promote and apply industrially. After subsequent grinding, the coating surface is smooth and flat, which will not cause scratches on the steel strip surface. It can effectively ensure the quality of hot-dip galvanized products, solve many technical problems existing in the coating and cloth wrapping structure of the tower top roller, and has significant economic benefits and practical value. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments.

[0019] A process for preparing a coating on the surface of a tower top roller that resists high-temperature zinc slag adhesion includes the following steps: Step 1: Pretreatment of the substrate for the tower top roller (1) First, grind the top roller substrate to remove the oxide scale and rust on the surface. After grinding, use anhydrous ethanol for ultrasonic cleaning to remove residual dust and oil on the surface.

[0020] (2) The surface of the dried tower top roller substrate is sandblasted. The sandblasting medium is white corundum sand, the sandblasting pressure is 0.4-0.6 MPa, the sandblasting angle is 45°-60°, and the surface roughness Ra of the substrate reaches 5-8 μm after sandblasting, forming a uniform and rough surface, increasing the contact area between the bonding substrate and the substrate, and improving the bonding strength. After sandblasting, compressed air is used to blow away the sand dust on the substrate surface to avoid the sand dust affecting the coating bonding effect.

[0021] Step 2: Pretreatment of coating materials According to the above-mentioned mass percentage ratio of the bonding underlayer, transition layer and functional surface layer, accurately weigh each component raw material; place the coating powder in an oven at 100-120℃ for 60-80 minutes to remove moisture from the powder and prevent defects such as pores and cracks in the coating caused by moisture during the preparation process.

[0022] Step 3: Preparation of the bonding underlayer A bonding underlayer was prepared on the pretreated surface of the tower top roller substrate using plasma spraying. The spraying parameters were as follows: spraying power of 20-25kW, spraying voltage of 30-40V, spraying current of 500-600A, plasma gas of Ar+H2 mixture, powder feeding speed of 20-30g / min, and spray gun moving speed of 50-80mm / s. After spraying, the substrate was allowed to cool naturally to room temperature to obtain the bonding underlayer.

[0023] Step 4: Preparation of the transition layer A transition layer was prepared on the surface of the bonding substrate using a plasma spraying process. The spraying parameters were as follows: spraying power of 20–25 kW, spraying voltage of 30–40 V, spraying current of 500–600 A, plasma gas of Ar + H2 mixture, powder feed rate of 20–30 g / min, spraying distance of 90–110 mm, and spray gun movement speed of 50–80 mm / s. After spraying, the mixture was allowed to cool naturally to room temperature to obtain the transition layer.

[0024] Step 5: Preparation of Functional Surface Layer A functional surface layer was prepared on the transition layer surface using a plasma spraying process. The spraying parameters were as follows: spraying power of 30–35 kW, spraying voltage of 50–60 V, spraying current of 700–800 A, plasma gas of Ar+N2 mixture, powder feed rate of 20–30 g / min, spraying distance of 80–100 mm, and spray gun moving speed of 30–50 mm / s. After spraying, the surface layer was allowed to cool naturally to room temperature to obtain the functional surface layer. Example 1

[0025] A coating for the surface of a tower top roller that resists high-temperature zinc slag adhesion is a composite gradient coating. From the inside to the outside of the tower top roller substrate surface, it consists of an adhesive underlayer, a transition layer, and a functional surface layer. The total coating thickness is 100 μm. The material ratio, thickness, and preparation process of each layer are as follows: (1) Parameters of each layer of coating Bonding substrate: NiCr alloy: 75% (Ni: 80%, Cr: 20% in NiCr alloy), Al powder: 25%, thickness 20μm; Transition layer: Ni: 30%, Cr: 16%, Al: 5%, Y: 0.5%, balance Co, thickness 20μm; Functional surface layer: ZrO2: 70%, MoSi2: 15%, WS2: 10%, BN: 5%, thickness 60μm.

[0026] (2) Preparation process Step 1: Pretreatment of the substrate for the tower top roller ① The top roller of the tower is machined to remove surface oxide scale, rust, oil and impurities. After grinding, it is ultrasonically cleaned with anhydrous ethanol to remove residual dust and oil. ② The dried substrate surface is sandblasted with white corundum sand as the sandblasting medium, sandblasting pressure of 0.4MPa, sandblasting angle of 45°, sandblasting distance of 80mm and sandblasting time of 10min. After sandblasting, the surface roughness of the substrate Ra=5.0μm, and the surface dust is blown away with compressed air.

[0027] Step 2: Pretreatment of coating materials Weigh the raw materials according to the above-mentioned mass percentage ratio for each layer, and dry the coating powder in a 100℃ oven for 60 minutes to remove moisture and prevent the coating from developing pores and cracks.

[0028] Step 3: Preparation of the bonding underlayer A bonding underlayer was prepared on the pretreated surface of the tower top roller substrate using plasma spraying. Spraying parameters: spraying power 20kW, spraying voltage 30V, spraying current 500A, plasma gas Ar+H2 (Ar gas flow rate 30L / min, H2 gas flow rate 5L / min), powder feeding speed 20g / min, spraying distance 100mm, and spray gun moving speed 50mm / s. After spraying, the material was allowed to cool naturally to room temperature.

[0029] Step 4: Preparation of the transition layer A transition layer was prepared on the surface of the bonding substrate using plasma spraying. The spraying parameters were as follows: spraying power 20kW, spraying voltage 30V, spraying current 500A, plasma gas Ar+H2 (Ar gas flow rate 30L / min, H2 gas flow rate 5L / min), powder feeding speed 20g / min, spraying distance 100mm, and spray gun moving speed 50mm / s. After spraying, the material was allowed to cool naturally to room temperature.

[0030] Step 5: Preparation of Functional Surface Layer A functional surface layer was prepared on the transition layer using plasma spraying. The spraying parameters were as follows: spraying power 30kW, spraying voltage 50V, spraying current 700A, plasma gas Ar+N2 (Ar gas flow rate 40L / min, N2 gas flow rate 8L / min), powder feeding speed 20g / min, spraying distance 80mm, and spray gun moving speed 30mm / s. The substrate temperature was maintained at 200℃ during the spraying process, and the substrate was allowed to cool naturally to room temperature after spraying.

[0031] The coating prepared in this embodiment has an adhesion strength of 85 MPa to the substrate and a zinc slag adhesion rate of 97% under high temperature conditions of 450-550℃. Example 2

[0032] A coating for the surface of a tower top roller that resists high-temperature zinc slag adhesion is a composite gradient coating. From the inside to the outside of the tower top roller substrate surface, it consists of an adhesive underlayer, a transition layer, and a functional surface layer. The total coating thickness is 150 μm. The material ratio, thickness, and preparation process of each layer are as follows: (1) Parameters of each layer of coating Bonding substrate: NiCr alloy: 85% (Ni: 90% Ni, Cr: 10% in NiCr alloy), Al powder: 15%, thickness 30μm; Transition layer: Ni: 35%, Cr: 18%, Al: 8%, Y: 1%, balance Co, thickness 30μm; Functional surface layer: ZrO2: 82%, MoSi2: 10%, WS2: 5%, BN: 3%, thickness 90μm.

[0033] (2) Preparation process Step 1: Pretreatment of the substrate for the tower top roller ① The top roller of the tower is machined to remove surface oxide scale, rust, oil and impurities. After grinding, it is ultrasonically cleaned with anhydrous ethanol to remove residual dust and oil. ② The dried substrate surface is sandblasted with white corundum sand as the sandblasting medium, sandblasting pressure of 0.6MPa, sandblasting angle of 60°, sandblasting distance of 120mm and sandblasting time of 15min. After sandblasting, the surface roughness of the substrate Ra=8.0μm, and the surface dust is blown away with compressed air.

[0034] Step 2: Pretreatment of coating materials Weigh the raw materials according to the above-mentioned mass percentage ratio for each layer, and dry the coating powder in a 120℃ oven for 80 minutes to remove moisture and prevent the coating from developing pores and cracks.

[0035] Step 3: Preparation of the bonding underlayer A bonding underlayer was prepared on the pretreated surface of the tower top roller substrate using plasma spraying. The spraying parameters were as follows: spraying power 25kW, spraying voltage 40V, spraying current 600A, plasma gas Ar+H2 (Ar gas flow rate 40L / min, H2 gas flow rate 7L / min), powder feeding speed 30g / min, spraying distance 120mm, and spray gun moving speed 80mm / s. After spraying, the material was allowed to cool naturally to room temperature.

[0036] Step 4: Preparation of the transition layer A transition layer was prepared on the surface of the bonding substrate using plasma spraying. The spraying parameters were as follows: spraying power 25kW, spraying voltage 40V, spraying current 600A, plasma gas Ar+H2 (Ar gas flow rate 40L / min, H2 gas flow rate 7L / min), powder feeding speed 30g / min, spraying distance 120mm, and spray gun moving speed 80mm / s. After spraying, the material was allowed to cool naturally to room temperature.

[0037] Step 5: Preparation of Functional Surface Layer A functional surface layer was prepared on the transition layer using plasma spraying. The spraying parameters were as follows: spraying power 35kW, spraying voltage 60V, spraying current 800A, plasma gas Ar+N2 (Ar gas flow rate 50L / min, N2 gas flow rate 12L / min), powder feeding speed 30g / min, spraying distance 100mm, and spray gun moving speed 50mm / s. The substrate temperature was maintained at 250℃ during the spraying process, and the substrate was allowed to cool naturally to room temperature after spraying.

[0038] The coating prepared in this embodiment has a bonding strength of 92 MPa with the substrate and a zinc slag adhesion rate of 95% under high temperature conditions of 450-550℃. Example 3

[0039] A coating for the surface of a tower top roller that resists high-temperature zinc slag adhesion is a composite gradient coating. From the inside to the outside of the tower top roller substrate surface, it consists of an adhesive underlayer, a transition layer, and a functional surface layer. The total coating thickness is 125 μm. The material ratio, thickness, and preparation process of each layer are as follows: (1) Parameters of each layer of coating Bonding substrate: NiCr alloy: 80% (Ni: 85% Ni, Cr: 15% in NiCr alloy), Al powder: 20%, thickness 25μm; Transition layer: Ni: 32%, Cr: 17%, Al: 6.5%, Y: 0.7%, balance Co, thickness 25μm; Functional surface layer: ZrO2: 76%, MoSi2: 12%, WS2: 7%, BN: 4%, thickness 75μm.

[0040] (2) Preparation process Step 1: Pretreatment of the substrate for the tower top roller ① The top roller of the tower is machined to remove surface oxide scale, rust, oil and impurities. After grinding, it is ultrasonically cleaned with anhydrous ethanol to remove residual dust and oil. ② The dried substrate surface is sandblasted with white corundum sand as the sandblasting medium, sandblasting pressure 0.5MPa, sandblasting angle 52°, sandblasting distance 100mm, and sandblasting time 12min. After sandblasting, the surface roughness of the substrate Ra=6.5μm. The surface dust is blown away with compressed air.

[0041] Step 2: Pretreatment of coating materials Weigh the raw materials according to the above-mentioned mass percentage ratio for each layer, and dry the coating powder in a 110℃ oven for 70 minutes to remove moisture and prevent the coating from developing pores and cracks.

[0042] Step 3: Preparation of the bonding underlayer A bonding underlayer was prepared on the pretreated surface of the tower top roller substrate using plasma spraying. The spraying parameters were as follows: spraying power 22kW, spraying voltage 35V, spraying current 550A, plasma gas Ar+H2 (Ar gas flow rate 35L / min, H2 gas flow rate 6L / min), powder feeding speed 25g / min, spraying distance 110mm, and spray gun moving speed 65mm / s. After spraying, the material was allowed to cool naturally to room temperature.

[0043] Step 4: Preparation of the transition layer A transition layer was prepared on the surface of the bonding substrate using plasma spraying. The spraying parameters were as follows: spraying power 22kW, spraying voltage 35V, spraying current 550A, plasma gas Ar+H2 (Ar gas flow rate 35L / min, H2 gas flow rate 6L / min), powder feeding speed 25g / min, spraying distance 110mm, and spray gun moving speed 65mm / s. After spraying, the material was allowed to cool naturally to room temperature.

[0044] Step 5: Preparation of Functional Surface Layer A functional surface layer was prepared on the transition layer using plasma spraying. The spraying parameters were as follows: spraying power 32kW, spraying voltage 55V, spraying current 750A, plasma gas Ar+N2 (Ar gas flow rate 45L / min, N2 gas flow rate 10L / min), powder feeding speed 25g / min, spraying distance 90mm, and spray gun moving speed 40mm / s. The substrate temperature was maintained at 220℃ during the spraying process, and the substrate was allowed to cool naturally to room temperature after spraying.

[0045] The coating prepared in this embodiment has a bonding strength of 90 MPa with the substrate and a zinc slag adhesion rate of 98% under high temperature conditions of 450-550℃. Example 4

[0046] A coating for the surface of a tower top roller that resists high-temperature zinc slag adhesion is a composite gradient coating. From the inside to the outside of the tower top roller substrate surface, it consists of an adhesive underlayer, a transition layer, and a functional surface layer. The total coating thickness is 110 μm. The material ratio, thickness, and preparation process of each layer are as follows: (1) Parameters of each layer of coating Bonding substrate: NiCr alloy: 77% (Ni: 82% and Cr: 18% in NiCr alloy), Al powder: 23%, thickness 22μm; Transition layer: Ni: 31%, Cr: 16.5%, Al: 5.5%, Y: 0.6%, balance Co, thickness 23μm; Functional surface layer: ZrO2: 73%, MoSi2: 14%, WS2: 8%, BN: 5%, thickness 65μm.

[0047] (2) Preparation process Step 1: Pretreatment of the substrate for the tower top roller ① The top roller of the tower is machined to remove surface oxide scale, rust, oil and impurities. After grinding, it is ultrasonically cleaned with anhydrous ethanol to remove residual dust and oil. ② The dried substrate surface is sandblasted with white corundum sand as the sandblasting medium. The sandblasting pressure is 0.45MPa, the sandblasting angle is 48°, the sandblasting distance is 90mm, and the sandblasting time is 11min. After sandblasting, the surface roughness of the substrate Ra=6.0μm. Compressed air is used to blow away the sand and dust on the surface.

[0048] Step 2: Pretreatment of coating materials Weigh the raw materials according to the above-mentioned mass percentage ratio for each layer, and dry the coating powder in a 105℃ oven for 65 minutes to remove moisture and prevent the coating from developing pores and cracks.

[0049] Step 3: Preparation of the bonding underlayer A bonding underlayer was prepared on the pretreated surface of the tower top roller substrate using plasma spraying. The spraying parameters were as follows: spraying power 21kW, spraying voltage 32V, spraying current 520A, plasma gas Ar+H2 (Ar gas flow rate 32L / min, H2 gas flow rate 5.5L / min), powder feeding speed 22g / min, spraying distance 105mm, and spray gun moving speed 60mm / s. After spraying, the material was allowed to cool naturally to room temperature.

[0050] Step 4: Preparation of the transition layer A transition layer was prepared on the surface of the bonding substrate using plasma spraying. The spraying parameters were as follows: spraying power 21kW, spraying voltage 32V, spraying current 520A, plasma gas Ar+H2 (Ar gas flow rate 32L / min, H2 gas flow rate 5.5L / min), powder feeding speed 22g / min, spraying distance 105mm, and spray gun moving speed 60mm / s. After spraying, the material was allowed to cool naturally to room temperature.

[0051] Step 5: Preparation of Functional Surface Layer A functional surface layer was prepared on the transition layer using plasma spraying. The spraying parameters were as follows: spraying power 31kW, spraying voltage 52V, spraying current 720A, plasma gas Ar+N2 (Ar gas flow rate 42L / min, N2 gas flow rate 9L / min), powder feeding speed 22g / min, spraying distance 85mm, and spray gun moving speed 35mm / s. The substrate temperature was maintained at 210℃ during the spraying process, and the substrate was allowed to cool naturally to room temperature after spraying.

[0052] The coating prepared in this embodiment has an adhesion strength of 87 MPa to the substrate and a zinc slag adhesion rate of 97% under high temperature conditions of 450-550℃. Example 5

[0053] A coating for the surface of a tower top roller that resists high-temperature zinc slag adhesion is a composite gradient coating. From the inside to the outside of the tower top roller substrate surface, it consists of an adhesive underlayer, a transition layer, and a functional surface layer. The total coating thickness is 140 μm. The material ratio, thickness, and preparation process of each layer are as follows: (1) Parameters of each layer of coating Bonding substrate: 83% NiCr alloy (88% Ni and 12% Cr in NiCr alloy), 17% Al powder, 28μm thickness; Transition layer: Ni: 34%, Cr: 17.5%, Al: 7.5%, Y: 0.9%, balance Co, thickness 27μm; Functional surface layer: ZrO2: 79%, MoSi2: 11%, WS2: 6%, BN: 4%, thickness 85μm.

[0054] (2) Preparation process Step 1: Pretreatment of the substrate for the tower top roller ① The top roller of the tower is machined to remove surface oxide scale, rust, oil and impurities. After grinding, it is ultrasonically cleaned with anhydrous ethanol to remove residual dust and oil. ② The dried substrate surface is sandblasted with white corundum sand as the sandblasting medium. The sandblasting pressure is 0.55MPa, the sandblasting angle is 58°, the sandblasting distance is 110mm, and the sandblasting time is 14min. After sandblasting, the surface roughness of the substrate Ra=7.5μm. The surface dust is blown away with compressed air.

[0055] Step 2: Pretreatment of coating materials Weigh the raw materials according to the above-mentioned mass percentage ratio for each layer, and dry the coating powder in an oven at 115℃ for 75 minutes to remove moisture and prevent the coating from developing pores and cracks.

[0056] Step 3: Preparation of the bonding underlayer A bonding underlayer was prepared on the pretreated surface of the tower top roller substrate using plasma spraying. The spraying parameters were as follows: spraying power 24kW, spraying voltage 38V, spraying current 580A, plasma gas Ar+H2 (Ar gas flow rate 38L / min, H2 gas flow rate 6.5L / min), powder feeding speed 28g / min, spraying distance 115mm, and spray gun moving speed 75mm / s. After spraying, the material was allowed to cool naturally to room temperature.

[0057] Step 4: Preparation of the transition layer A transition layer was prepared on the surface of the bonding substrate using plasma spraying. The spraying parameters were as follows: spraying power 24kW, spraying voltage 38V, spraying current 580A, plasma gas Ar+H2 (Ar gas flow rate 38L / min, H2 gas flow rate 6.5L / min), powder feeding speed 28g / min, spraying distance 115mm, and spray gun moving speed 75mm / s. After spraying, the material was allowed to cool naturally to room temperature.

[0058] Step 5: Preparation of Functional Surface Layer A functional surface layer was prepared on the transition layer using plasma spraying. The spraying parameters were as follows: spraying power 34kW, spraying voltage 58V, spraying current 780A, plasma gas Ar+N2 (Ar gas flow rate 48L / min, N2 gas flow rate 11L / min), powder feeding speed 28g / min, spraying distance 95mm, and spray gun moving speed 45mm / s. The substrate temperature was maintained at 240℃ during the spraying process, and the substrate was allowed to cool naturally to room temperature after spraying.

[0059] The coating prepared in this embodiment has an adhesion strength of 89 MPa to the substrate and a zinc slag adhesion rate of 96% under high temperature conditions of 450-550℃.

[0060] Comparative Example: A tower top roller with an existing single tungsten carbide coating, 100-150 μm thick, was used, prepared by supersonic spraying. The finished tower top rollers prepared in Examples 1-5 of this invention and the comparative example tower top rollers were simultaneously placed on the same hot-dip galvanizing production line and continuously operated at a high temperature of 450-550℃. The zinc dross adhesion and service life of each tower top roller were recorded. The results are shown in the table below:

[0061] The test results above show that the composite gradient coating on the surface of the tower top roller prepared by the present invention has a significantly higher resistance to high-temperature zinc slag adhesion than the existing single tungsten carbide coating, and its service life is extended by more than 2 times. Moreover, the coating does not crack or peel off, which can effectively meet the usage requirements of the tower top roller in the hot-dip galvanizing production line and solve the technical problems existing in the prior art.

[0062] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A coating on the surface of a tower top roller that resists high-temperature zinc slag adhesion, characterized in that: The coating is a composite gradient coating, consisting of an adhesive underlayer, a transition layer, and a functional surface layer from the inside to the outside of the top roller substrate surface. The functional surface layer is composed of the following components by mass percentage: ZrO2: 70-82%, MoSi2: 10-15%, WS2: 5-10%, BN: 3-5%.

2. The coating on the surface of a tower top roller resistant to high-temperature zinc slag adhesion according to claim 1, characterized in that: The bonding underlayer is composed of the following components by mass percentage: 75-85% NiCr alloy and 15-25% Al powder; in the NiCr alloy, the mass percentage of Ni is 80-90% and the mass percentage of Cr is 10-20%; the transition layer is composed of the following components by mass percentage: Ni: 30-35%, Cr: 16-18%, Al: 5-8%, Y: 0.5-1%, with the balance being Co.

3. The coating on the surface of a tower top roller resistant to high-temperature zinc slag adhesion according to claim 1 or 2, characterized in that: The thickness of the bonding substrate is 20–30 μm; the thickness of the transition layer is 20–30 μm; and the thickness of the functional surface layer is 60–90 μm.

4. A coating for the surface of a tower top roller resistant to high-temperature zinc slag adhesion according to claim 1 or 2, characterized in that: The total thickness of the composite gradient coating is 100-150 μm, the bonding strength between the coating and the top roller substrate is ≥80 MPa, it can be used for more than 2 years in a high temperature environment of 450-550℃, and the anti-zinc slag adhesion rate is ≥95%.

5. A method for preparing a coating on the surface of a tower top roller that resists high-temperature zinc slag adhesion, based on any one of claims 1-4, characterized in that: The preparation method includes the following steps: Step 1: Pre-treatment of the tower top roller substrate: First, grind the tower top roller substrate, then sandblast it, and blow off the surface sand and dust for later use. Step 2: Coating material pretreatment: Weigh the raw materials according to the mass percentage of each layer and dry them; Step 3: Preparation of the bonding underlayer: The bonding underlayer is prepared on the pretreated substrate surface using plasma spraying technology. The spraying power is 20-25kW, the powder feeding speed is 20-30g / min, and the spraying distance is 100-120mm. After spraying, the substrate is allowed to cool naturally to room temperature. Step 4: Transition layer preparation: A transition layer is prepared on the surface of the bonding substrate using plasma spraying technology. The spraying power is 20-25kW, the powder feeding speed is 20-30g / min, and the spraying distance is 100-120mm. After spraying, the substrate is allowed to cool naturally to room temperature. Step 5: Preparation of functional surface layer: The functional surface layer is prepared on the surface of the transition layer by plasma spraying process. The spraying power is 30-35kW, the powder feeding speed is 20-30g / min, the spraying distance is 80-100mm, and the coating is allowed to cool naturally to room temperature after spraying.

6. The method for preparing a coating on the surface of a tower top roller that resists high-temperature zinc slag adhesion according to claim 5, characterized in that: In step 1, white corundum sand is used for sandblasting, the sandblasting pressure is 0.4-0.6 MPa, the sandblasting angle is 45°-60°, the sandblasting distance is 80-120 mm, and the sandblasting time is 10-15 min; after sandblasting, the surface roughness Ra of the substrate reaches 5-8 μm.

7. The method for preparing a coating on the surface of a tower top roller that resists high-temperature zinc slag adhesion according to claim 5, characterized in that: In step 3, the plasma spraying parameters are: spraying voltage 30-40V, spraying current 500-600A, plasma gas is Ar+H2 mixed gas, and spray gun moving speed 50-80mm / s.

8. A method for preparing a coating on the surface of a tower top roller that resists high-temperature zinc slag adhesion according to any one of claims 5-7, characterized in that: In step 4, the plasma spraying parameters are: spraying voltage 30-40V, spraying current 500-600A, plasma gas is Ar+H2 mixed gas, and spray gun moving speed 50-80mm / s.

9. A method for preparing a coating on the surface of a tower top roller that resists high-temperature zinc slag adhesion according to any one of claims 5-7, characterized in that: In step 5, the plasma spraying parameters are: spraying voltage 50-60V, spraying current 700-800A, plasma gas is Ar+N2 mixed gas, and spray gun moving speed 30-50mm / s.

Images