A method for repairing a wear-resistant layer of a hollow shaft of a ball mill

Abstract

This invention discloses a method for repairing the wear-resistant layer of a hollow shaft in a ball mill, comprising the following steps: pretreatment of the surface of the hollow shaft to be repaired by high-pressure water washing, graded grinding, and wiping with anhydrous ethanol; preparation of a wear-resistant coating slurry according to the mass ratio of epoxy resin:silicon carbide:curing agent of 1:(0.5-1.5):(0.01-0.1), and forming a uniform mixture by mechanical stirring; uniformly coating the slurry onto the surface of the hollow shaft, and increasing the density by rolling, patting, and layer-by-layer compaction, controlling the coating thickness within the range of 5-50 mm; adopting a stepped heating heat treatment process, first holding at 40-60℃ for 2-3 hours, then raising the temperature to 80-120℃ and holding for 1-2 hours, and finally naturally cooling to room temperature to form a wear-resistant protective layer. The wear-resistant layer prepared by this method has a dense structure and a Rockwell hardness of not less than HRC60, which can improve the service life of the hollow shaft, reduce equipment maintenance costs, reduce the consumption of grease in the lubrication system, and improve the operational stability and production efficiency of the equipment.

Description

Technical Field

[0001] This invention relates to the field of surface coating and repair technology, and in particular to a method for repairing the wear-resistant layer of a hollow shaft in a ball mill. Background Technology

[0002] Ball mills are crucial equipment for further pulverizing materials after initial crushing, and are widely used in industries such as cement, silicate products, new building materials, refractory materials, fertilizers, ferrous and non-ferrous metal ore beneficiation, and glass and ceramics production. The hollow shaft of the ball mill is the core component responsible for the equipment's operation and material transport, and is typically made of cast steel. Due to its long-term operation at high speeds and under heavy loads, and continuous exposure to the scouring, friction, and mechanical vibration of materials (such as slurry), the surface of the hollow shaft is highly susceptible to wear grooves, scratches, and other damage. Particularly at the inlet and outlet ends, the wear on the inner bore of the hollow shaft can reach 6-10 mm, severely impacting the normal operation and production efficiency of the equipment.

[0003] Currently, the industry mainly uses two solutions for repairing and strengthening the worn hollow shafts of ball mills: traditional welding or direct replacement with a new shaft. Welding repair suffers from significant stress concentration, making the repaired hollow shaft prone to deformation. Furthermore, the wear resistance of the weld layer is limited, resulting in a short service life for the repaired equipment and requiring frequent maintenance. Replacing the shaft with a new one, on the other hand, incurs high procurement costs and leads to prolonged equipment downtime, severely impacting the continuity of mineral processing production.

[0004] The aforementioned traditional repair methods generally suffer from insufficient bonding strength between the repair layer and the substrate, leading to risks of detachment or cracking. They fail to effectively improve friction conditions, resulting in high grease consumption in the lubrication system and potentially increasing equipment failure rates due to component instability. Therefore, there is a need to develop a method for forming a wear-resistant layer for the hollow shaft of a ball mill, achieving a high-strength bond between the coating and the substrate, exhibiting excellent wear resistance, while also being cost-effective and easy to implement on-site. Summary of the Invention

[0006] The purpose of this invention is to provide a method for repairing the wear-resistant layer of the hollow shaft of a ball mill, solving the problems of short life, high cost, and easy failure in existing repair technologies.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for repairing the wear-resistant layer of a hollow shaft in a ball mill includes the following steps: Step 1: Hollow Shaft Surface Pretreatment: The surface of the hollow shaft of the ball mill to be repaired is sequentially subjected to high-pressure water washing, mechanical grinding, and solvent wiping. Mechanical grinding begins with coarse grinding using 80-120 grit sandpaper, followed by fine grinding with 240-400 grit sandpaper, achieving a surface roughness of Ra3.2-Ra6.3μm to enhance the mechanical adhesion between the coating and the substrate. Solvent wiping is preferably performed with anhydrous ethanol to remove oil and residual dust.

[0008] Step 2: Preparation of the wear-resistant coating slurry: Weigh the epoxy resin, silicon carbide, and curing agent according to the following mass ratio: epoxy resin: silicon carbide: curing agent = 1:(0.5-1.5):(0.01-0.1). The preferred silicon carbide particle size is 400-800 mesh, and the preferred curing agent is an amine-based curing agent. First, mix and stir the epoxy resin and silicon carbide for 5-10 minutes at a stirring speed of 300-500 r / min to ensure the silicon carbide particles are evenly dispersed in the resin. Then, add the curing agent and continue stirring for 15-20 minutes to obtain a uniform slurry.

[0009] Step 3: Coating Application: The slurry is evenly applied to the surface of the hollow shaft. The coating is then densified using a rolling, patting, and layer-by-layer compaction process. Specifically, after each 5-15mm thick layer of slurry is applied, rolling and patting are alternately performed 2-4 times. The next layer is applied only after no obvious air bubbles are visible on the surface, controlling the total coating thickness to be 5-50mm. This process effectively removes internal gas from the coating, reduces porosity, and improves the coating density and bonding strength with the substrate.

[0010] Step 4: Heat Treatment and Curing: The coating undergoes a stepped heating process at a rate of 0.5-1.5℃ / min. First, hold the coating at 40-60℃ for 2-3 hours to allow initial cross-linking of the slurry and slow release of internal stress. Then, raise the temperature to 80-120℃ and hold for 1-2 hours to promote full resin curing. Finally, allow it to cool naturally to room temperature. This stepped heating avoids thermal stress cracks within the coating caused by single-stage high-temperature curing, ensuring the integrity and mechanical properties of the thick coating.

[0011] Compared with the prior art, the present invention has the following advantages: (1) The wear-resistant protective layer formed by epoxy resin and silicon carbide composite of the present invention has a dense structure and a Rockwell hardness of not less than HRC60, which can effectively resist material erosion and mechanical friction. Practical application shows that the service life of hollow shafts repaired by this method is 5 to 8 times longer than that of traditional welding repair, reducing the frequency of maintenance and replacement.

[0012] (2) Compared with directly replacing the shaft, the repair method provided by this invention can save 70% to 80% of the procurement cost. The formed wear-resistant protective layer has a smooth surface and low frictional resistance, which can reduce the grease consumption of the lubrication system by 30% to 50%, bringing significant economic benefits.

[0013] (3) In this invention, the wear-resistant layer is firmly bonded to the hollow shaft substrate and has strong adhesion. Under long-term high-speed and heavy-load conditions, it is not prone to problems such as detachment and cracking, which enhances the reliability of equipment operation, reduces the risk of downtime caused by hollow shaft wear, and ensures the continuity of the mineral processing production process. Attached Figure Description

[0014] Figure 1 This is a flowchart of the process flow of the present invention. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to specific embodiments.

[0016] Example 1 A method for repairing the wear-resistant layer of a hollow shaft in a ball mill includes the following steps: Step 1: Surface pretreatment of the hollow shaft: The wear depth of the hollow shaft of a ball mill in a mineral processing plant is about 5mm. First, the surface is washed with a high-pressure water gun, then coarsely sanded with 80-grit sandpaper to remove rust, then finely sanded with 240-grit sandpaper to a surface roughness Ra3.2μm, and finally wiped clean with anhydrous ethanol and dried.

[0017] Step 2: Preparation of the wear-resistant coating slurry: Weigh out 10 kg of epoxy resin, 5 kg of silicon carbide (600 mesh particle size), and 0.1 kg of amine curing agent according to the mass ratio of epoxy resin:silicon carbide:curing agent = 1:0.5:0.01. First, stir the epoxy resin and silicon carbide at 300 r / min for 10 minutes, then add the curing agent and continue stirring for 15 minutes to obtain the slurry.

[0018] Step 3, Coating Application: Apply the slurry evenly to the surface of the hollow shaft. After each layer is about 5mm thick, use roller pressing and patting alternately twice. After there are no obvious bubbles on the surface, apply the next layer. Apply a total of 1 layer with a total thickness of 5mm.

[0019] Step 4, heat treatment and curing: Use an electric heating rod to raise the ambient temperature to 40℃ at a heating rate of 0.5℃ / min and hold for 3 hours; then raise the temperature to 80℃ at a rate of 1℃ / min and hold for 2 hours; finally, allow it to cool naturally to room temperature.

[0020] Post-repair testing: The wear-resistant layer hardness is HRC60, and after 6 months of operation, the wear amount is 0.08mm, and the grease consumption is reduced by 30%.

[0021] Example 2 A method for repairing the wear-resistant layer of a hollow shaft in a ball mill includes the following steps: Step 1: Surface pretreatment of the hollow shaft: The wear depth of the hollow shaft surface of a ball mill in a mineral processing plant is about 10mm. First, it is rinsed with high-pressure water, then coarsely polished with 120-grit sandpaper, and finely polished with 400-grit sandpaper to a roughness Ra of 6.3μm. Finally, it is wiped with anhydrous ethanol.

[0022] Step 2: Preparation of the wear-resistant coating slurry: Weigh out 10 kg of epoxy resin, 15 kg of silicon carbide (400 mesh particle size), and 1 kg of amine curing agent according to the mass ratio of epoxy resin: silicon carbide: curing agent = 1:1.5:0.1. First, stir the epoxy resin and silicon carbide at 500 r / min for 5 minutes, then add the curing agent and continue stirring for 20 minutes.

[0023] Step 3, Coating Application: After each layer is approximately 15mm thick, alternate between rolling and patting 4 times, for a total of 4 layers, with a total thickness of 50mm.

[0024] Step 4, heat treatment and curing: Heat to 60℃ at 1.5℃ / min and hold for 2 hours, then heat to 120℃ at 1℃ / min and hold for 1 hour, then let cool naturally.

[0025] Post-repair testing: The wear-resistant layer hardness is HRC65, and after 10 months of operation, the wear amount is 0.03mm, and the grease consumption is reduced by 50%.

[0026] Example 3 A method for repairing the wear-resistant layer of a hollow shaft in a ball mill includes the following steps: Step 1: Surface pretreatment of the hollow shaft: The wear depth of the hollow shaft surface of a ball mill in a mineral processing plant is about 8mm. First, it is rinsed with high-pressure water, then coarsely polished with 100-grit sandpaper, and finely polished with 320-grit sandpaper to a roughness of Ra4.8μm. Finally, it is wiped with anhydrous ethanol.

[0027] Step 2: Preparation of the wear-resistant coating slurry: Weigh out 10 kg of epoxy resin, 10 kg of silicon carbide (600 mesh particle size), and 0.5 kg of amine curing agent according to the mass ratio of epoxy resin: silicon carbide: curing agent = 1:1:0.05. First, stir the epoxy resin and silicon carbide at 400 r / min for 7 minutes, then add the curing agent and continue stirring for 18 minutes.

[0028] Step 3, Coating Application: After each layer is approximately 8mm thick, alternate between rolling and patting 3 times, applying a total of 3 layers with a total thickness of 25mm.

[0029] Step 4, heat treatment and curing: Heat to 50℃ at 1℃ / min and hold for 2.5 hours, then heat to 100℃ at 1℃ / min and hold for 1.5 hours, then let cool naturally.

[0030] Post-repair testing: The wear-resistant layer hardness is HRC63, and after 8 months of operation, the wear amount is 0.05mm, and the grease consumption is reduced by 40%.

[0031] Comparative Example 1 The same raw material ratio and pretreatment steps as in Example 3 were used, except that only a 25mm thick slurry was applied at once during coating construction, without rolling, patting, or layer-by-layer compaction; the surface was simply smoothed with a scraper. The heat treatment curing conditions were the same as in Example 3.

[0032] Post-repair testing: The wear-resistant layer has a hardness of HRC48, and obvious pores and microcracks are visible on the surface. After 2 months of operation, the coating peeled off locally, with a wear amount of 0.35mm and a reduction in grease consumption of only 8%.

[0033] Comparative Example 2 The same raw material ratio, pretreatment steps and coating construction process (compacted layer by layer to 25mm) as in Example 3 were used. The difference was that during heat treatment curing, the temperature was directly raised to 100℃ at 1℃ / min and kept at that temperature for 4 hours, without step-by-step heat preservation.

[0034] Post-repair inspection: The wear-resistant layer hardness is HRC52. Multiple through cracks appeared on the coating surface. After 3 months of operation, the cracks expanded, causing the coating to crack and fall off. The wear amount was 0.28mm, and the grease consumption decreased by 12%.

[0035] The product performance and analysis results are shown in Table 1.

[0036] Table 1 Product Performance and Analysis Results *Note: For Comparative Examples 1 and 2, the wear values ​​are the actual values ​​measured after 2 months and 3 months of operation, respectively, due to the premature failure of the coating, not the data after 6 months.

[0037] As shown in Table 1, the coatings formed using the layer-by-layer compaction process of this invention (Examples 1-3) all achieved a hardness of HRC60 or higher, with wear not exceeding 0.08 mm after 6 months of operation, grease consumption reduced by more than 30%, and the coatings remaining intact and defect-free. In contrast, Comparative Example 1, which did not undergo layer-by-layer compaction, had poor coating density and a hardness of only HRC48, resulting in peeling within a short period. Comparative Example 2, which used one-step temperature-curing, experienced stress concentration and cracking within the coating, resulting in a hardness below HRC53. These comparisons demonstrate that the combined layer-by-layer compaction and stepped temperature-curing process of this invention is key to obtaining thick coatings with high density, high hardness, and no defects.

[0038] The above embodiments and comparative examples show that the method of the present invention can stably form a high-performance wear-resistant coating under the conditions of the lower limit, intermediate value and upper limit of process parameters, which is significantly better than the existing repair technology.

Claims

1. A method for repairing the wear-resistant layer of a hollow shaft in a ball mill, characterized in that, Includes the following steps: Step 1: Surface pretreatment of hollow shaft: The surface of the hollow shaft of the ball mill to be repaired is sequentially subjected to high-pressure water washing, mechanical grinding and solvent wiping; Step 2: Preparation of wear-resistant coating slurry: Weigh epoxy resin, silicon carbide and curing agent according to the mass ratio, wherein epoxy resin: silicon carbide: curing agent = 1:(0.5-1.5):(0.01-0.1). First, mix epoxy resin and silicon carbide and stir for 5-10 minutes at a stirring speed of 300-500 r / min. Then add curing agent and continue stirring for 15-20 minutes to obtain a uniform slurry. Step 3, Coating Application: Apply the slurry evenly to the surface of the hollow shaft, and use roller pressing, patting and layer-by-layer compaction processes to densify the coating, controlling the total coating thickness to be 5-50mm; Step 4, heat treatment and curing: The coating is subjected to a stepped heating process. First, it is kept at 40-60℃ for 2-3 hours, then heated to 80-120℃ and kept at 80-120℃ for 1-2 hours, and finally cooled naturally to room temperature.

2. The method for repairing the wear-resistant layer of a hollow shaft in a ball mill according to claim 1, characterized in that, The mechanical polishing described in step one includes first using 80-120 grit sandpaper for coarse polishing, and then using 240-400 grit sandpaper for fine polishing, so that the surface roughness reaches Ra3.2-Ra6.3μm.

3. The method for repairing the wear-resistant layer of a hollow shaft in a ball mill according to claim 2, characterized in that, The solvent wiping in step one uses anhydrous ethanol.

4. The method for repairing the wear-resistant layer of a hollow shaft in a ball mill according to claim 3, characterized in that, The silicon carbide in step two has a particle size of 400-800 mesh.

5. The method for repairing the wear-resistant layer of a hollow shaft in a ball mill according to claim 4, characterized in that, The curing agent mentioned in step two is an amine curing agent, and its addition amount is calculated as 1%-10% of the epoxy resin mass.

6. The method for repairing the wear-resistant layer of a hollow shaft in a ball mill according to claim 5, characterized in that, The layer-by-layer compaction process described in step three is as follows: after each layer of slurry with a thickness of 5-15mm is applied, roller pressing and patting are alternately performed 2-4 times. The next layer is applied only after there are no obvious bubbles on the surface.

7. A method for repairing the wear-resistant layer of a hollow ball mill shaft according to claim 6, characterized in that, The heating rate of the stepped heating process described in step four is 0.5-1.5℃ / min.

8. The method for repairing the wear-resistant layer of a hollow shaft in a ball mill according to claim 7, characterized in that, The heat treatment described in step four uses an electric heating rod for on-site environmental heating.

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