A casting process to eliminate shrinkage in large bearings

Abstract

The application relates to a casting process for eliminating shrinkage of a large bearing and belongs to the technical field of bearing casting. The application uses an electric arc spraying molybdenum carbide coating to enhance wear resistance and corrosion resistance, sand blasting treatment provides a good adhesion basis for the coating, and the molybdenum carbide coating significantly improves the wear resistance and corrosion resistance of the bearing and prolongs the service life; the application combines four heat treatment modes of annealing, normalizing, quenching and tempering, so that the material organization is more uniform, the brittleness is reduced while the hardness is maintained, the plasticity and toughness are improved, the strength and toughness are better, meanwhile, the expansion tendency of defects such as shrinkage is reduced, the bearing has more balanced mechanical properties, and the use requirements under complex working conditions are met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of bearing casting and relates to a casting process for eliminating shrinkage of large bearings. BACKGROUND

[0002] In the casting process of a large bearing, due to the inconsistent cooling speed of each part of the casting, heat is concentrated in the thick center part or geometric hot spot, and finally, shrinkage is formed when solidification is not fully compensated. Shrinkage can lead to internal organization of the bearing being not dense, reducing its mechanical strength, hardness and wear resistance, affecting the service life and reliability of the bearing; the voids produced by shrinkage may become stress concentration points during the operation of the bearing, aggravating vibration and noise, and reducing the running stability of the equipment; for bearings that need to be sealed, shrinkage can cause the seal to be not tight, causing lubricating oil or grease to leak, affecting the lubrication effect and running stability of the bearing; in extreme working conditions, shrinkage can cause the bearing to break or fail, causing the equipment to stop and even safety accidents, posing a threat to personnel and property.

[0003] In the preparation process, improper riser setting and unreasonable pouring system are artificially created, which increases the risk of shrinkage, in addition, the solidification characteristics of the material, gas content and oxides can also cause the formation of shrinkage. SUMMARY

[0004] The application aims to provide a casting process for eliminating shrinkage of large bearings, which has the characteristics of high hardness and long service life of the prepared bearing.

[0005] The purpose of the application can be achieved by the following technical solutions:

[0006] A casting process for eliminating shrinkage of large bearings, the specific process of the casting process is as follows,

[0007] S1: Put the bearing raw material into a high-temperature smelting furnace for smelting treatment, the smelting temperature is 1350-1400 DEG C, the smelting time is 20-30 min, put the smelted raw material into a mold, and get a bearing blank after cooling;

[0008] S2: Heat the bearing blank to 820-850 DEG C, and anneal for 3-4 h, and cool to room temperature;

[0009] S3: Surface sand blasting treatment is performed on the annealed bearing blank, a layer of molybdenum carbide coating is sprayed on the surface of the bearing blank after sand blasting treatment, and surface polishing treatment is performed;

[0010] The sand blasting material used for sand blasting is prepared by the following method,

[0011] S3.1: Brown corundum, steel sand and glass beads are mixed in a mass ratio of 1:3:0.5, and are put into a ball mill to be ground at a rotating speed of 400-500 r / min for 3-5 h;

[0012] S3.2: The mixture obtained in S3.1 is washed with deionized water, and is dried at 110°C for 24 h after washing to obtain the sandblasting material;

[0013] S4: The bearing blank after polishing treatment is heated to 900-960°C for normalizing treatment, the constant temperature treatment time is 4-6 h, nitrogen is used to purge the bearing blank, and the bearing blank is slowly cooled to room temperature;

[0014] S5: The bearing blank after normalizing treatment is heated to 860-880°C for quenching treatment, the constant temperature treatment time is 1-2 h, the bearing blank is rapidly cooled in cooling water, and the bearing blank is dried on the surface by purging with nitrogen at 70°C after cooling, and the purging flow rate of nitrogen is 10 m / s;

[0015] S6: The bearing blank after quenching treatment is heated to 300-380°C for tempering treatment, the constant temperature treatment time is 1-2 h, and the bearing blank is slowly cooled to room temperature by uniformly purging the surface of the bearing blank with nitrogen to obtain the bearing.

[0016] Further, the bearing raw material in S1 is one of chromium-molybdenum steel and nickel-chromium-molybdenum steel.

[0017] Further, the parameters of sandblasting treatment in S3 are that the sandblasting distance is 50-70 mm, and the sandblasting angle is 60-80°.

[0018] Further, the particle size of the sandblasting material in S3 is 200 mesh.

[0019] Further, the parameters of electric arc spraying in S3 are that the diameter of the molybdenum carbide nanowire wire is 200 nm, the spraying voltage is 30 V, the spraying current is 200 A, the spraying distance is 150 mm, and the compressed air pressure is 0.4 MPa.

[0020] Further, the parameters of polishing treatment in S3 are that first, a 1000-mesh elastic module is used to treat for 0.5-1 h at 0.3-0.5 MPa, and then a 2000-mesh elastic module is used to treat for 0.5 h at 0.5 MPa.

[0021] Further, the flow rate of nitrogen purging in S4 is 10 m / s.

[0022] Further, the slow cooling rate in S4 is 3°C / min.

[0023] Further, the purging flow rate of nitrogen in S6 is 20 m / s.

[0024] Further, the rate of slow cooling to room temperature in S6 is 5℃ / min.

[0025] The application first eliminates casting stress, refines grains, improves the processing performance and use performance of the material by annealing after getting the blank, and the annealing treatment helps to improve the plasticity and toughness of the bearing blank, and reduces the risk of deformation and cracking caused by casting stress. Then the bearing blank after annealing treatment is subjected to surface sand blasting treatment, followed by arc spraying a layer of molybdenum carbide coating, and then surface polishing treatment. The sand blasting treatment increases the surface roughness and improves the coating adhesion; the arc spraying molybdenum carbide coating enhances the wear resistance and corrosion resistance, and the sand blasting treatment provides a good adhesion basis for the coating, and the molybdenum carbide coating significantly improves the wear resistance and corrosion resistance of the bearing, prolonging the service life; the bearing blank after polishing treatment is heated to 900-960℃ for normalizing treatment, which can refine the grains, improve the strength and hardness of the material, and improve the cutting performance, further improving the mechanical properties of the bearing, making it more suitable for high load and complex working conditions; the bearing blank after normalizing treatment is heated to 860-880℃ for quenching treatment, which can obtain high hardness and high wear resistance of martensite organization, significantly improving the hardness and wear resistance of the bearing, making it better adapt to high load and high speed working conditions; finally, the bearing blank after quenching treatment is heated to 300-380℃ for tempering treatment, which can eliminate the quenching stress, stabilize the organization, obtain good comprehensive mechanical properties, avoid the deformation and cracking problem caused by quenching stress, and at the same time maintain high hardness and wear resistance, ensuring the stability and reliability of the bearing. The bearing prepared by the casting process is not prone to shrinkage, and has a longer service life.

[0026] The sand blasting treatment can form a uniform roughness on the surface of the bearing blank, which is crucial for the subsequent coating adhesion. The molybdenum carbide coating needs to be attached to a surface with a certain roughness to ensure stronger bonding force between the coating and the substrate, thereby improving the durability of the coating; the sand blasting treatment can completely remove impurities such as oil, dirt, and scale on the surface of the bearing blank, making the surface cleaner and providing a good base for subsequent coating spraying. A clean surface helps to reduce bubbles and defects in the coating and improve the quality of the coating; the increased surface roughness through sand blasting treatment can significantly improve the mechanical interlocking force between the molybdenum carbide coating and the bearing blank, thereby making the coating more firmly attached to the substrate. This helps to prevent the coating from peeling or falling off during use, prolonging the service life of the bearing.

[0027] The mixed use of brown corundum, steel sand and glass beads can comprehensively play the advantages of each other and improve the comprehensive performance of the sand blasting treatment. The high hardness and good cutting ability of the brown corundum can remove stubborn dirt; the moderate hardness and toughness of the steel sand can maintain the cleaning effect while avoiding excessive damage; and the lightness, smallness and environmental protection of the glass beads can form a high smoothness surface. Through the grinding treatment of the ball mill, the particle size of the mixed sand blasting material is uniform, so that uniform impact effect can be formed in the sand blasting process, and the uniformity and consistency of the surface treatment are improved.

[0028] Molybdenum carbide (MoC) has extremely high hardness and good wear resistance. Spraying a molybdenum carbide coating on the bearing surface can significantly enhance the wear resistance of the bearing surface and prolong the service life of the bearing; the molybdenum carbide coating also has good corrosion resistance, can resist the erosion of various corrosive media, and protect the bearing matrix from corrosion damage, thereby maintaining the stability and reliability of the bearing. The hardness and wear resistance of the molybdenum carbide coating improve the overall structural stability of the bearing, so that the bearing is less likely to deform or be damaged during operation, thereby reducing the possibility of expansion or new shrinkage caused by structural problems. By improving the wear resistance and corrosion resistance, the molybdenum carbide coating significantly prolongs the service life of the bearing. During long-term use, the bearing can better maintain its original size and shape accuracy, reducing the size change and performance degradation caused by wear and corrosion.

[0029] The present application combines the four heat treatment methods of annealing, normalizing, quenching and tempering. Annealing helps to eliminate or reduce the internal stress and organizational defects of the bearing blank generated during casting, making the material organization more uniform and laying a good foundation for subsequent processing and heat treatment; normalizing can further refine the grains, improve the strength and toughness of the material, and reduce the expansion tendency of defects such as shrinkage; quenching makes the bearing blank obtain high-hardness martensite structure through rapid cooling, significantly improving the hardness and wear resistance of the bearing; tempering reduces brittleness while maintaining a certain hardness, improves plasticity and toughness, so that the bearing has more balanced mechanical properties to meet the use requirements under complex working conditions.

[0030] The beneficial effects of the present application are:

[0031] (1) The present application uses electric arc spraying molybdenum carbide coating to enhance wear resistance and corrosion resistance, sand blasting treatment provides a good adhesion basis for the coating, and the molybdenum carbide coating significantly improves the wear resistance and corrosion resistance of the bearing and prolongs the service life;

[0032] (2) The four heat treatment methods of annealing, normalizing, quenching and tempering are combined to make the material structure more uniform, reduce brittleness while maintaining certain hardness, improve plasticity and toughness, have better strength and toughness, and reduce the expansion tendency of defects such as shrinkage, so that the bearing has more balanced mechanical properties and meets the use requirements under complex working conditions. DETAILED DESCRIPTION

[0033] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined object of the application, the specific embodiments, structures, features and effects according to the present application are described in detail as follows in combination with examples.

[0034] Example 1

[0035] S1: Put the bearing raw material chromium-molybdenum steel into a high-temperature smelting furnace for smelting treatment, the smelting temperature is 1350℃, the smelting time is 25min, and the smelted raw material is put into a mold, and the bearing blank is obtained after cooling;

[0036] S2: The bearing blank is heated to 830℃, and the annealing treatment is carried out for 4h, and then cooled to room temperature;

[0037] S3: The surface of the bearing blank after annealing treatment is sandblasted, the sandblasting distance is 60mm, and the sandblasting angle is 70°. After sandblasting, a layer of molybdenum carbide coating is arc sprayed on the surface of the bearing blank, the parameters of arc spraying are that the diameter of molybdenum carbide nanowire is 200nm, the spraying voltage is 30V, the spraying current is 200A, the spraying distance is 150mm, and the compressed air pressure is 0.4MPa. Then, the surface is polished, and the parameters of polishing are that first, a 1000-mesh elastic module is used at 0.4MPa for 0.5h, and then a 2000-mesh elastic module is used at 0.5MPa for 0.5h;

[0038] The sandblasting material used for sandblasting is prepared by the following method,

[0039] S3.1: Brown corundum, steel sand and glass beads are mixed in a mass ratio of 1:3:0.5, and put into a ball mill for grinding at a speed of 500r / min for 3h;

[0040] S3.2: The mixture obtained by grinding in S3.1 is washed with deionized water, and then dried at 110℃ for 24h after washing to obtain the sandblasting material, and the particle size of the sandblasting material is 200 mesh;

[0041] S4: The polished bearing blank is heated to 930℃ for normalizing treatment, the constant temperature treatment time is 5h, nitrogen gas is used to blow the bearing blank, the flow rate of nitrogen gas blowing is 10m / s, and the temperature is slowly cooled to room temperature at a rate of 3℃ / min;

[0042] S5: heating the bearing blank after the normalizing treatment to 870 DEG C for quenching treatment, the constant temperature treatment time is 2h, put into the cooling water to rapidly reduce the temperature, after cooling, using 70 DEG C nitrogen gas to blow to the bearing blank surface dry, the nitrogen gas blowing flow rate is 10m / s;

[0043] S6: heating the bearing blank after the quenching treatment to 350 DEG C for tempering treatment, the constant temperature treatment time is 1.5h, then using nitrogen gas to uniformly blow the bearing blank surface to slowly reduce the temperature to room temperature at the rate of 5 DEG C / min, the nitrogen gas blowing flow rate is 20m / s, obtaining the bearing.

[0044] Example 2

[0045] S1: putting the bearing raw material chromium molybdenum steel into the high temperature smelting furnace for smelting treatment, the smelting temperature is 1400 DEG C, the smelting time is 20min, putting the smelted raw material into the mold, after cooling, obtaining the bearing blank;

[0046] S2: heating the bearing blank to 820 DEG C again, the constant temperature treatment time is 4h, for annealing treatment, cooling to room temperature;

[0047] S3: surface sand blasting treatment is carried out on the bearing blank after the annealing treatment, the sand blasting distance is 50mm, the sand blasting angle is 60 DEG, after the sand blasting treatment, arc spraying a layer of molybdenum carbide coating on the surface of the bearing blank, the parameters of the arc spraying are that the diameter of the molybdenum carbide nanowire wire is 200nm, the spraying voltage is 30V, the spraying current is 200A, the spraying distance is 150mm, the compressed air pressure is 0.4MPa, then surface polishing treatment is carried out, the parameters of the polishing treatment are that first using the elastic module of 1000 purposes to treat for 1h under 0.3MPa, then using the elastic module of 2000 purposes to treat for 0.5h under 0.5MPa;

[0048] The sand blasting material used for sand blasting is prepared by the following method,

[0049] S3.1: mixing brown corundum, steel sand and glass beads according to the mass ratio of 1:3:0.5, putting into the ball mill to grind at the speed of 400r / min for 5h;

[0050] S3.2: washing the mixture obtained by grinding in S3.1 with deionized water, drying at 110 DEG C for 24h after washing, obtaining the sand blasting material, the particle size of the sand blasting material is 200 meshes;

[0051] S4: heating the bearing blank after the polishing treatment to 900 DEG C for normalizing treatment, the constant temperature treatment time is 6h, using nitrogen gas to blow the bearing blank, the nitrogen gas blowing flow rate is 10m / s, slowly cooling to room temperature at the rate of 3 DEG C / min;

[0052] S5: heating the bearing blank after the normalizing treatment to 860 DEG C. for quenching treatment, the constant temperature treatment time is 2h, put into the cooling water to rapidly reduce the temperature, after cooling, using 70 DEG C. nitrogen gas to blow to the bearing blank surface dry, the nitrogen gas blowing flow rate is 10m / s;

[0053] S6: heating the bearing blank after the quenching treatment to 300 DEG C. for tempering treatment, the constant temperature treatment time is 2h, then using nitrogen gas to uniformly blow the bearing blank surface to slowly reduce the temperature to room temperature at the rate of 5 DEG C. / min, the nitrogen gas blowing flow rate is 20m / s, obtaining the bearing.

[0054] Example 3

[0055] S1: putting the bearing raw material nickel-chromium-molybdenum steel into a high-temperature smelting furnace for smelting treatment, the smelting temperature is 1350 DEG C., the smelting time is 30min, putting the smelted raw material into a mold, after cooling, obtaining a bearing blank;

[0056] S2: heating the bearing blank to 850 DEG C. again, the constant temperature treatment time is 3h, for annealing treatment, cooling to room temperature;

[0057] S3: surface sand blasting treatment is performed on the bearing blank after the annealing treatment, the sand blasting distance is 70mm, the sand blasting angle is 80 DEG, after the sand blasting treatment, arc spraying a layer of molybdenum carbide coating on the surface of the bearing blank, the parameters of the arc spraying are that the diameter of the molybdenum carbide nanowire wire is 200nm, the spraying voltage is 30V, the spraying current is 200A, the spraying distance is 150mm, and the compressed air pressure is 0.4MPa, then surface polishing treatment is performed, the parameters of the polishing treatment are that first using an elastic module of 1000 purposes to treat for 0.5h under 0.5MPa, and then using an elastic module of 2000 purposes to treat for 0.5h under 0.5MPa;

[0058] The sand blasting material used for sand blasting is prepared by the following method,

[0059] S3.1: mixing brown corundum, steel sand and glass beads according to the mass ratio of 1:3:0.5, putting into a ball mill to grind at the speed of 500r / min for 3h;

[0060] S3.2: washing the mixture obtained by grinding in S3.1 with deionized water, drying at 110 DEG C. for 24h after washing, obtaining the sand blasting material, the particle size of the sand blasting material is 200 meshes;

[0061] S4: heating the bearing blank after the polishing treatment to 960 DEG C. for normalizing treatment, the constant temperature treatment time is 4h, using nitrogen gas to blow the bearing blank, the nitrogen gas blowing flow rate is 10m / s, slowly cooling to room temperature at the rate of 3 DEG C. / min;

[0062] S5: heating the bearing blank after the normalizing treatment to 880℃ for quenching treatment, the constant temperature treatment time is 1h, rapidly cooling in the cooling water, after cooling, using 70℃ nitrogen to blow and dry the surface of the bearing blank, the blowing flow rate of the nitrogen is 10m / s;

[0063] S6: heating the bearing blank after the quenching treatment to 380℃ for tempering treatment, the constant temperature treatment time is 1h, then using nitrogen to uniformly blow the surface of the bearing blank to slowly cool to room temperature at a rate of 5℃ / min, the blowing flow rate of the nitrogen is 20m / s, obtaining the bearing.

[0064] Comparative Example 1

[0065] The comparative example does not perform sand blasting treatment on the surface in the preparation process, and the remaining steps are consistent with Example 1.

[0066] Comparative Example 2

[0067] The comparative example does not perform arc spraying a layer of molybdenum carbide coating on the surface in the preparation process, and the remaining steps are consistent with Example 1.

[0068] Comparative Example 3

[0069] The comparative example does not perform normalizing treatment in the preparation process, and the remaining steps are consistent with Example 1.

[0070] Comparative Example 4

[0071] The comparative example does not perform quenching treatment in the preparation process, and the remaining steps are consistent with Example 1.

[0072] The surface wear resistance of the examples and comparative examples is detected according to GB / T 12444.1-1990; the hardness is detected according to GB / T 230.1-2018, and the experimental results are arranged in the following table; the corrosion resistance is tested according to ISO 9227:2017, the sample is fixed, the concentration of sodium chloride is adjusted to 10% by using 3% hydrochloric acid to make the pH value to be 3, the brine is prepared, the sample is sprayed by a spraying device, the spraying amount is 20mL / s, the spraying frequency is 60min / time, each spraying time is 20s, after continuous spraying for 72h, the corrosion of the sample is observed,

[0073] 100 revolutions mass loss amount / mg hardness value HR corrosion resistance Example 1 32.4 120 No corrosion, no bubble generation Example 2 32.8 115 No corrosion, no bubble generation Example 3 32.7 115 No corrosion, no bubble generation Comparative Example 1 35.6 95 No corrosion, bubble generation Comparative Example 2 38.5 95 Corrosion Comparative Example 3 37.4 75 No corrosion, no bubble generation Comparative Example 4 42.5 70 No corrosion, no bubble generation

[0074] According to the experimental data, sand blasting treatment makes the coating and the blank more closely combined, and the increase of the coating effectively improves the corrosion resistance of the bearing, and the normalizing treatment and the quenching treatment effectively improve the wear resistance and the hardness of the bearing.

[0075] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application in any form. Although the present application has been disclosed with the preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, as long as the changes or modifications do not deviate from the technical solution of the present application. Any modification, change, equivalent change and modification of the above embodiments made according to the technical essence of the present application still belong to the scope of the technical solution of the present application.

Claims

1. A casting process for eliminating shrinkage porosity in large bearings, characterized in that, The specific process of the casting procedure is as follows. S1: The bearing raw material is placed in a high-temperature melting furnace for melting treatment. The melting temperature is 1350-1400℃ and the melting time is 20-30 minutes. The melted raw material is placed in a mold and cooled to obtain the bearing blank. S2: Heat the bearing blank to 820-850℃, keep it at a constant temperature for 3-4 hours, anneal it, and then cool it to room temperature. S3: The annealed bearing blank is subjected to surface sandblasting. After sandblasting, a layer of molybdenum carbide coating is applied to the surface of the bearing blank by arc spraying, followed by surface polishing. The preparation method of the sandblasting material used for sandblasting is as follows. S3.1: Mix brown corundum, steel grit and glass beads in a mass ratio of 1:3:0.5, and grind them in a ball mill at a speed of 400-500 r / min for 3-5 hours; S3.2: The mixture obtained by grinding in S3.1 is washed with deionized water and then dried at 110°C for 24 hours to obtain the sandblasting material; S4: Heat the polished bearing blank to 900-960℃ for normalizing treatment, and maintain the temperature for 4-6 hours. Purge the bearing blank with nitrogen and slowly cool it to room temperature. S5: Heat the normalized bearing blank to 860-880℃ for quenching treatment. The constant temperature treatment time is 1-2 hours. Place it in cooling water to cool down quickly. After cooling, use 70℃ nitrogen gas to purge until the surface of the bearing blank is dry. The nitrogen purging flow rate is 10m / s. S6: Heat the quenched bearing blank to 300-380℃ for tempering treatment, and keep it at a constant temperature for 1-2 hours. Then, use nitrogen to evenly blow the surface of the bearing blank to slowly cool it down to room temperature to obtain the bearing. The bearing material in S1 is either chromium-molybdenum steel or nickel-chromium-molybdenum steel. The polishing parameters in S3 are as follows: first, use a 1000-mesh elastic module to process at 0.3-0.5 MPa for 0.5-1 h, and then use a 2000-mesh elastic module to process at 0.5 MPa for 0.5 h.

2. The casting process for eliminating shrinkage porosity in large bearings according to claim 1, characterized in that, The parameters for the sandblasting process in S3 are a sandblasting distance of 50-70 mm and a sandblasting angle of 60-80°.

3. The casting process for eliminating shrinkage porosity in large bearings according to claim 1, characterized in that, The particle size of the sandblasting material in S3 is 200 mesh.

4. The casting process for eliminating shrinkage porosity in large bearings according to claim 1, characterized in that, The parameters for arc spraying in S3 are: molybdenum carbide nanowire diameter 200nm, spraying voltage 30V, spraying current 200A, spraying distance 150mm, and compressed air pressure 0.4MPa.

5. The casting process for eliminating shrinkage porosity in large bearings according to claim 1, characterized in that, The nitrogen purging velocity in S4 is 10 m / s.

6. The casting process for eliminating shrinkage porosity in large bearings according to claim 1, characterized in that, The slow cooling rate in S4 is 3°C / min.

7. The casting process for eliminating shrinkage porosity in large bearings according to claim 1, characterized in that, The nitrogen purging velocity in S6 is 20 m / s.

8. The casting process for eliminating shrinkage porosity in large bearings according to claim 1, characterized in that, The rate at which the temperature is slowly reduced to room temperature in S6 is 5°C / min.