Bearing ring for rolling bearing and method of manufacturing the same

Abstract

The present invention provides a raceway ring for rolling bearings and a method for producing the raceway ring, the raceway ring being capable of forming an insulating oxide layer (oxide film) on a steel alloy while maintaining a hardness exceeding the 58HRC (Rockwell hardness C scale) by containing predetermined components.SOLUTION: A bearing ring for a rolling bearing is made of alloy steel containing, by weight%, C:0.01 to 1.0%, Si: 0.2 to 4.0%, Mn: 0.2 to 2.0%, Cr: 1.0 to 9.0%, Mo: 1.5 to 6.0%, Al: 0.01 to 5.0%, V: 0.01 to 1.2%, and a balance of Fe and inevitable impurities, and a surface of the bearing ring for a rolling bearing is coated with a ceramic film.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a race for a rolling bearing that is applied to a rolling bearing, and a method for manufacturing the same. [Background technology]

[0002] Conventionally, for rolling bearing components, particularly rolling bearing raceways, some alloy steels manufactured with specified components have been given insulating properties by forming an insulating oxide layer or resin film on the surface of the component through high-temperature heating (see Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-236259 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-199674 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-84767 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when some of the parts disclosed in Patent Document 1 were replaced with resin and added, there were problems with the wear resistance and strength being insufficient compared to steel. Furthermore, ceramics lacked the toughness of steel and also had problems with workability. Additionally, the cost of these materials was higher than steel, which increased the overall cost of the part.

[0005] On the other hand, as disclosed in Patent Document 2, although oxidizing the surface of steel to impart insulating properties to parts is advantageous in terms of cost, the hardness of conventional alloy steel is below 50HRC (HRC: Rockwell hardness C scale), making it difficult to use such steel for long periods of time as parts in high-load environments that require wear resistance, fatigue strength, etc.

[0006] This is because the carbon content, which contributes greatly to the hardness of alloy steel, is extremely low. In addition, the temperature required to form the oxide layer is in the high range of 980 to 1220°C, so even if the steel was highly hard before treatment, it could soften.

[0007] Even if high hardness could be achieved by combining quenching and oxidation treatment at around 1200°C, the dimensions would vary significantly before and after treatment. Therefore, to manufacture high-precision parts, grinding or other processes would be required after oxidation treatment, which would remove the oxide layer that had been so carefully formed.

[0008] Furthermore, the material disclosed in Patent Document 3 also describes a method of oxidizing the surface of steel to provide insulating properties to the parts, but does not disclose any information on the hardness or strength of the material, nor does it state any particular consideration.In addition, the method of forming the oxide layer involves immersion in an acid solution, which raises issues of reduced material strength due to hydrogen embrittlement and a burden on the natural environment.

[0009] Therefore, an object of the present invention is to provide a raceway for a rolling bearing that can maintain high strength (or hardness) while having electrical insulation between itself and adjacent metal products, and a method for manufacturing the same. [Means for solving the problem]

[0010] To achieve the above-mentioned object, a rolling bearing raceway is provided, made of an alloy steel containing, by weight, 0.01-1.0% C, 0.2-4.0% Si, 0.2-2.0% Mn, 1.0-9.0% Cr, 1.5-6.0% Mo, 0.01-5.0% Al, and 0.01-1.2% V, with the remainder being Fe and unavoidable impurities. The surface of the rolling bearing raceway is coated with a ceramic coating. The ceramic coating may contain any of Fe2O3, SiO2, and Al2O3 compounds. The alloy steel may further contain, by weight, 0.01-2.0% W and 0.1-4.0% Co. The surface hardness of the alloy steel may be 58 HRC or higher on the Rockwell C scale.

[0011] Furthermore, the invention relates to a method for manufacturing a bearing ring, which comprises a coating step of coating a gel film on the surface of the base material of the rolling bearing ring by immersing the base material of the rolling bearing ring in an alcohol solution containing an organometallic compound; a drying step of drying the bearing ring with the gel film after the coating step in an atmosphere of 100°C or higher; a pre-firing step of pre-firing the bearing ring with the gel film after the drying step to obtain a fired film; and a main-firing step of firing the bearing ring with the fired film in an atmosphere of 500°C or higher after the pre-firing step to obtain a bearing ring with a ceramic film, with the coating step to the pre-firing step being considered as unit steps and the method for manufacturing a rolling bearing ring comprising repeating these unit steps two or more times. [Effects of the Invention]

[0012] The rolling bearing raceway of the present invention has the effect of forming an insulating oxide layer (oxide film) on the surface of the steel material while maintaining a hardness of over 58HRC (Rockwell hardness C scale) by containing the specified components. In addition, the invention of the method for manufacturing the rolling bearing raceway has the effect of reducing the manufacturing costs of the rolling bearing raceway. DETAILED DESCRIPTION OF THE INVENTION

[0013] Regarding the raceway for a rolling bearing, which is one embodiment of the present invention, we will explain the content of each element contained in the alloy steel that is the base material of the raceway for a rolling bearing, and the ceramic coating, or so-called ceramic film, that is coated on the surface of the raceway for a rolling bearing.

[0014] 《C (Carbon)》 The C content (C amount) was set to a range of 0.01 to 1.0% by weight. If the C amount exceeds this range, the toughness of the alloy steel may decrease and the carbides in the matrix structure may become coarse. There is also a risk that the hot workability of the alloy steel may deteriorate. On the other hand, if the C amount is less than this range, the surface hardness of the alloy steel will be less than 58 HRC.

[0015] Silicon The Si content (Si amount) is set to the range of 0.2 to 4.0% by weight. If the Si amount exceeds this range, the toughness of the alloy steel may decrease or the hot workability may deteriorate. On the other hand, if the Si amount is below this range, the insulating property of the oxide layer formed on the surface may decrease or the machinability may deteriorate.

[0016] Manganese (Mn) The Mn content (Mn amount) is set to the range of 0.2 to 2.0% by weight. If this range is exceeded, there is a risk of deterioration in workability. On the other hand, if it is below this range, it is necessary to carefully select the raw materials, which will actually increase the material cost.

[0017] 《Cr (Chromium)》 The Cr content (Cr amount) is set to the range of 1.0 to 9.0% by weight. If it exceeds this range, the oxide layer of the alloy steel becomes thin and the insulating properties of the oxide layer deteriorate. If it falls below this range, the insulating properties of the oxide layer of the alloy steel deteriorate.

[0018] Mo (Molybdenum) The Mo content (Mo amount) is set to the range of 1.5 to 6.0% by weight. If it exceeds this range, the carbides may become coarse or the toughness of the alloy steel may decrease. On the other hand, if it is below this range, the surface hardness of the alloy steel after oxidation treatment may become less than 58 HRC.

[0019] Aluminum (Al) The Al content (Al amount) is set to the range of 0.01 to 5.0% by weight. If this range is exceeded, the surface hardness of the alloy steel after oxidation treatment may be less than 58 HRC, or nonmetallic inclusions may increase, resulting in reduced fatigue strength. On the other hand, if the Al content is below this range, the insulating properties of the oxide layer may be reduced.

[0020] "V (Vanadium)" The V content (V amount) can be in the range of 0.01 to 1.2% by weight. If this range is exceeded, the carbides may become coarse or the toughness of the alloy steel may decrease.

[0021] As other additive elements, W (tungsten) may be further contained in a range of 0.01 to 2.0% by weight, and Co (cobalt) may be further contained in a range of 0.1 to 4.0% by weight.

[0022] By adjusting the composition of the alloy steel to fall within the above range, it is possible to maintain a balance between the mechanical properties and workability of the alloy steel, thereby providing a rolling bearing raceway with excellent wear resistance and corrosion resistance.

[0023] Furthermore, ceramic coatings (ceramic films) mainly contain one of the following compounds: Fe2O3, SiO2, or Al2O3. These compounds have the effect of improving the wear resistance and corrosion resistance of bearing rings. In other words, the formation of a ceramic film can extend the life of rolling bearing rings and reduce maintenance intervals.

[0024] Next, the details of each step constituting the manufacturing method of the invention for a raceway ring for a rolling bearing will be described.

[0025] <Coating process> The coating process is the first step in forming a ceramic coating on the surface of a rolling bearing ring. In this process, the base material of the ring is immersed in an alcohol solution containing an organometallic compound. The organometallic compound to be used should contain at least one of the metal elements Fe, Si, or Al. These metals determine the properties of the ceramic coating formed in the subsequent process.

[0026] First, to prepare the solution, the organometallic compound is dissolved in an alcohol solution at an appropriate concentration. The type of alcohol used can be ethanol or methanol. The concentration and pH of the solution have a significant impact on the uniformity and quality of the coating film, so they are adjusted to the desired concentration and pH.

[0027] Next, the base material for the rolling bearing raceway is immersed in the solution. During this immersion process, a uniform gel film is formed on the surface of the base material. The immersion time and temperature affect the film thickness and adhesion, so optimal specified values ​​must be set in advance.

[0028] After immersion, the base material of the rolling bearing raceway is slowly pulled out of the solution. If the pulling speed is too fast, the film will become uneven, so it must be pulled out at an appropriate speed. After pulling out, the base material of the rolling bearing raceway is left to dry naturally, allowing the solution on the surface to dry naturally. This helps maintain the uniformity of the gel film.

[0029] <Drying process> The drying process is a process for hardening the gel film formed in the coating process. In this process, the base material of the rolling bearing raceway is dried in an atmosphere of 100°C or higher. In this process, if the atmosphere is suddenly heated to a high temperature, the gel film will be prone to cracking, so it is better to increase the temperature (raise the temperature) in stages.

[0030] The drying time varies depending on the thickness and material of the gel film, but allowing sufficient time for drying allows the solvent inside the gel film to completely evaporate and promotes uniform hardening. Furthermore, the drying atmosphere can be clean air or an inert gas such as nitrogen. This prevents oxidation and maintains the quality of the film. After drying, gradually returning the film to room temperature rather than rapidly cooling it can also prevent shrinkage and cracking of the film.

[0031] <Pre-firing process> The pre-firing process is a process for further hardening the gel film obtained in the drying process to form a fired film. In this process, the base material of the rolling bearing race is heated to a specific temperature. The pre-firing temperature is usually set in the range of 300°C to 500°C. In this application, "pre-firing" refers to firing performed before the main firing described below, and refers to a heat treatment process performed at a temperature lower than the main firing temperature to remove organic matter, moisture, and residual carbon from the film.

[0032] By heating within this temperature range, the organic components decompose and the inorganic components sinter, forming a strong film. The heating time depends on the thickness and material of the film. Therefore, a uniform fired film can be obtained by heating for an appropriate amount of time.

[0033] Furthermore, the pre-baking atmosphere can be inert gas to prevent oxidation, which can improve the quality of the film. After pre-baking, the film is cooled gradually to prevent cracking and peeling caused by film stress due to rapid cooling.

[0034] <Final firing process> The sintering process is a process for finishing the sintered film obtained in the pre-sintering process. In this process, the base material for the rolling bearing raceway is sintered at a high temperature of 500°C or higher. The sintering temperature is set in the range of 500°C to 800°C. Sintering at this high temperature increases the density of the film and improves its mechanical strength. The sintering time is also adjusted according to the properties of the film. In this application, "sintering" refers to the final heat treatment process performed to obtain ceramics, and is a heat treatment process for crystallizing and densifying the sintered film obtained in the previous pre-sintering process.

[0035] In other words, heating for an appropriate period of time is necessary, as excessive heating can cause film deterioration. Furthermore, like pre-firing, the final firing can be carried out in an inert gas atmosphere. Since the effects of oxidation are particularly pronounced at high temperatures, controlling the atmosphere significantly influences the film's properties. Finally, gradual cooling after the final firing stabilizes the film's crystalline structure, determining its final properties.

[0036] <Repetition of unit processes> The coating process through the pre-baking process is considered a unit process, and by repeating this at least twice, the thickness and uniformity of the film can be improved. After completing the first unit process, the substrate is again immersed in an alcohol solution to form a new gel film. The new gel film is then dried again in an atmosphere above 100°C.

[0037] After drying, the coating is pre-fired again, and finally fired to form the final ceramic coating. By repeating this series of steps, the coating becomes thicker and more durable.

Claims

1. A raceway for a rolling bearing made of alloy steel containing, by weight, C: 0.01 to 1.0%, Si: 0.2 to 4.0%, Mn: 0.2 to 2.0%, Cr: 1.0 to 9.0%, Mo: 1.5 to 6.0%, Al: 0.01 to 5.0%, V: 0.01 to 1.2%, and the balance being Fe and unavoidable impurities, wherein the surface of the raceway for a rolling bearing is coated with a ceramic coating.

2. The ceramic coating contains Fe. ２ O ３ , SiO ２ , Al ２ O ３ 2. The raceway ring for a rolling bearing according to claim 1, further comprising any one of the compounds above.

3. 3. The raceway for a rolling bearing according to claim 2, wherein the alloy steel further contains, by weight percent, W: 0.01 to 2.0%.

4. 4. The raceway for a rolling bearing according to claim 3, wherein the alloy steel further contains, by weight percent, Co: 0.1 to 4.0%.

5. 5. The raceway for a rolling bearing according to claim 4, wherein the surface hardness of said alloy steel is 58 HRC or more on the Rockwell C scale.

6. 6. A method for manufacturing a raceway for a rolling bearing according to claim 1, comprising: a coating step of coating a surface of the base material of the raceway for a rolling bearing with a gel film by immersing the base material of the raceway for a rolling bearing in an alcohol solution containing an organometallic compound; a drying step of drying the raceway for a rolling bearing with the gel film after the coating step in an atmosphere of 100°C or higher; a pre-firing step of pre-firing the raceway for a rolling bearing with the gel film after the drying step to obtain a fired film; and a main-firing step of firing the raceway for a rolling bearing with the fired film in an atmosphere of 500°C or higher after the pre-firing step to obtain a raceway for a rolling bearing with a ceramic film, wherein the coating step to the pre-firing step are unit processes, and the method for manufacturing a raceway for a rolling bearing comprises repeating the unit processes two or more times.

7. 7. A method for manufacturing a raceway ring for a rolling bearing according to claim 6, wherein the organometallic compound is an organometallic compound containing at least one of the metal elements Fe, Si, and Al.