Patent Application
20080053578
In the following, embodiment of the present invention will be described based on the drawings.
Referring to
Referring to
After quenching bearing ring 1, bearing ring 1 may be tempered in the state constrained by molds 12a, 12b. In this case, molds 12a, 12b serve as tempering media in tempering bearing ring 1.
Through the aforementioned method, bearing ring 1 can be manufactured, which has an even hardness distribution, does not have defects such as oxidation or decarburization on the surface layer face, has very few warping and deformation, and has a long life.
As compared to a conventional bearing ring manufactured using air or gas as a quenching medium, rolling bearing ring 1 manufactured as above has low and aligned flatness, and also has stabilized hardness.
It should be noted that, when quenching bearing ring 1, there is a method to substantially increase the heat capacity of molds 12a, 12b as compared to that of bearing ring 1, as molds 12a, 12b are used as quenching media. For example, in order to suppress the temperature increase of molds 12a, 12b by at most 5 C.° for lowering the temperature of bearing ring 1 by 900 C.°, the heat capacity of molds 12a, 12b must be at least 180 times as great as that of bearing ring 1. As bearing ring 1 is interposed between upper and lower molds 12a, 12b, the heat capacity of either upper mold 12a or lower mold 12b must be at least 90 times as great as that of bearing ring 1. Accordingly, provided that bearing ring 1 and molds 12a, 12b are formed of the same material (for example, steel) and have the same specific heat, then the mass of either upper mold 12a or lower mold 12b must be at least 90 times as great as that of bearing ring 1. If a substance of great heat capacity, for example water, is allowed to flow through the molds, the molds themselves may be small.
If heating/quenching is performed in the air, even for a short period of time, a thin component may be oxidized. Thus, an oxide film may be formed, the surface hardness may be decreased due to decarburization, or precipitation of troostite may occur. A product such as a ring of a thrust needle roller bearing, which is not subjected to finishing (polishing, super finishing) by a machine process after heat treatment, requires heat treatment (quenching) for suppressing oxidation/decarburization. Such heat treatment can be addressed by using an inert gas in the atmosphere.
As quenching or isothermal transformation, in which molds are employed as cooling media as in the present embodiment, is a heat treatment of piece-by-piece, it is not necessary to separate the heat treatment process from a production line as in a conventional manner, but instead it may be incorporated into the production line of a machine process. Further, if tempering is performed by high-frequency induction heating or high-frequency heating while performing pressing with molds (high-frequency press-tempering), there is an advantage of integrating the whole processes from material input to product completion into a line.
In light of improving a processing speed, an efficient continuous quenching is possible by performing quenching while constantly cooling inside of the molds or the pressing surface with water, oil, air or the like. To this end, it is preferable to provide cooling means for introducing medium such as water, oil, air or the like into the molds.
It should be noted that, while tests were conducted in examples described below with plate-like products of l mm thickness, the method of the present invention is applicable to a thick plate (a 5-6 mm thickness plate) if the pressure when pressing is increased, though the thickness for quench-hardening at the cooling rate by the molds may be limited.
The molding process of a flange or a collar can simultaneously be performed when quenching, by controlling the shape of the mold or the pressing pressure.
Using bearing ring 1 manufactured by the aforementioned method, a thrust needle roller bearing, for example as shown in
Additionally, using bearing ring 1 manufactured by the aforementioned method, a drawn cup radial needle roller bearing, for example as shown in
As bearing ring 1 shown in
While the case in which a thin component is a bearing ring of a thrust needle roller bearing has been described in the foregoing, the present invention is not limited thereto and it may be a washer or a leaf spring that is employed in a wearing portion.
In the following, examples of the present invention will be described.
Mid-carbon steel S53C was used as a material, and a thrust needle roller bearing ring (NTN product name: AS1112) having an outer shape of inner diameter 60 mm, outer diameter 85 mm, and thickness 1 mm was manufactured by punching from a plate-like product.
Using a high-frequency induction heating apparatus (80 kHz) and rotating the ring, induction heating was performed by allowing prescribed current to flow through an induction coil arranged closely to one end panel (
Table 1 shows relationship among mold temperature and constraint time (holding time) by molds, pressing pressure, warping deformation, hardness after heat treatment, and microstructure.
Table 1 also shows relationship among warping deformation, hardness after heat treatment, and microstructure of a sample that was high-frequency heated and thereafter water quenched, a sample that was wholly heated and thereafter air-blow quenched, and a sample that was high-frequency heated and air-cooled.
From the result shown in Table 1, it can be seen that, as in the example of the present invention, with the pressing pressure of 2.94N/cm2 (0.3 kgf/cm2), by setting the mold temperature to at least 250° C. and at most 320° C. and the constraint time (holding time) by molds to at least 30 seconds and at most 5 minutes, isothermal transformation occurs and a structure having lower bainite can be obtained. It can also be seen that, in the structure of the example of the present invention having lower bainite, warping deformation becomes at most 19 μm, and Vickers hardness HV becomes at least 685. Further, in part of the example of the present invention, a structure similar to tempered martensite that appears on tempering was observed, while tempering was not performed.
Additionally, it can be seen that, as in the example of the present invention, when continuous cooling was performed by setting the mold temperature to 30° C. and the constraint time (holding time) by molds to 1 minute, martensite transformation occurs and a structure having tempered martensite can be obtained. It can also be seen that, in this sample, warping deformation becomes 20 μm, and Vickers hardness HV becomes 750.
As above, it has been shown that, with all samples of the present invention, warping deformation becomes at most 20 μm, and Vickers hardness HV becomes at least 685.
On the other hand, samples of the comparative example were in a quality in which warping deformation was more than 20 μm and which cannot attain Vickers hardness of at least HV 685.
As to the representative of these bearing rings, result of performing life estimation with the condition shown in Table 2 is shown in Table 3.
Here, since the ring of the example of the present invention subjected to isothermal transformation is partially or wholly subjected to isothermal transformation, tempering was not performed.
The rings of the example of the present invention subjected to martensite transformation by continuous cooling quenching were subjected to tempering of 150° C.×120 minutes. The test was conducted under a scarce lubrication condition.
From the result of Table 3, it can be seen that L10 life of the samples of the example of the present invention was at least 15.2 hours, which was increased. The sample of the comparative example, which was high-frequency heated normally and thereafter water quenched, was so deformed that it could not be tested. The sample of the comparative example, which was wholly heated and thereafter air-blow quenched, exhibited 11.9 hours of L10 life, which was reduced. Despite being a thin component, the sample of the comparative example, which was high-frequency heated and thereafter air-cooled, was not quench-hardened.
From the result above, with the ring obtained by the present method (the example of the present invention), warping deformation can be suppressed, and hardness and life can be increased as compared to the comparative example.
As materials, mid-carbon steel S53C and steel of a composition that is improved in quenching property and that can attain sufficient hardness with slow cooling (0.7 mass % C-1.0 mass % Si-0.6 mass % Mn-1.5 mass % Cr-0.3 mass % Mo) were used.
From these materials, thrusts needle bearing ring (NTN product name: AS1112) having an outer shape of inner diameter 60 mm, outer diameter 85 mm, and thickness 1 mm was manufactured by cutting.
Using a high-frequency induction heating apparatus (80 kHz) and rotating the ring, induction heating was performed by allowing prescribed current to flow through an induction coil arranged closely to one end panel (
Table 4 shows deformation state of conventional various products and deformation state in the experiment conducted this time.
From the result of Table 4, while conventional air-blow quenching products show few warping, deformation or warping of the products according to the present method still show smaller degree than the air-blow quenching products, irrespective of the steel types. Accordingly, distortion correction or warping correction after heat treatment is not necessary. By setting pressing-pressure to at least a prescribed value, deformation was suppressed to at most a certain value. It should be noted that, as actual quenching is not quenching using water soluble cooling agent or oil, the periphery of the quenching mechanism can be maintained clean, eliminating waste liquid processes.
After performing the aforementioned quenching to the test rings, tempering at 150° C. for two hours was performed, and finishing process was performed on the surface thereof. Thus, the rings were subjected to life estimation. The test was conducted under a scarce lubrication condition. The rolling life test condition was the same as the condition shown in Table 2. The test result is shown in Table 5.
From the result of Table 5, in the rings according to the present method that provides less warping deformation, even S53C attained the life of the conventional carburized product level. 0.7 mass % C steel attained longer life than the carburized steel. This may be attributed to its higher content of C as compared to S53C, which facilitates attaining high hardness. Additionally, it is considered that much Si, Mo, and Cr content contributed to the long life. The thin races in the shape of the present case exhibited great warping deformation with free quenching by oil or water, and therefore life test could not be conducted.
From the result above, with the rings (example of the present invention) obtained through the present method, warping deformation was suppressed as compared to the comparative example, and the life thereof can be increased.
It should be understood that the embodiment and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the meaning and scope equivalent to the terms of the claims.
The manufacturing method of the present invention is advantageously applied to a manufacturing method of a thin component, such as a ring of a thrust needle roller bearing or a thin bearing ring, which tends to show great deformation in heat treatment and to which a polishing process after the heat treatment is not performed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-347095 | Oct 2003 | JP | national |
| 2003-414967 | Dec 2003 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP04/14501 | 10/1/2004 | WO | 00 | 4/6/2006 |
