JPS61149502A - Turbine rotor - Google Patents

Abstract

PURPOSE:To prevent the shrinkage-fitted section of a shrinkage-fitted turbine rotor having a rotor shaft onto which a cylindrical member such as a sleeve or the like is fitted, from being cracked due to fretting fatigue, by applying a surface hardening treatment to the section of the rotor shaft onto which the cylinder is shrinkage-fitted. CONSTITUTION:In a turbine rotor in which a sleeve 3 ad a coupling 6 are shrinkage-fitted onto a rotor shaft 1 and a bearing 5 lined with a white metal 4 is fitted in the sleeve 3, the sections of the rotor shaft 1 onto which the sleeve 3 and the coupling 6 are fitted, is subjected to a surface hardening treatment. This treatment is carried out such that the rotor shaft 1 is rotated at a constant speed by means of a drive motor 12 supported on a support bed 10 and a carrier bed 11 while a CO2 gas laser beam is irradiated to the shrinkage-fitted sections from a CO2 gas laser source 13. With this arrangement it is possible to enhance the residual compression stress and wear-resistance of shrinkage-fitted sections of the rotor shaft, and further it is possible to greatly enhance the fretting fatigue resistant ability of the rotor shaft.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a turbine rotor used at high temperatures, for example in a high pressure section or an intermediate pressure section of a steam turbine rotor.

[Technical background of the invention and its problems] In a conventional steam turbine, the turbine rotor in the high pressure section is
As shown in FIG. 6, a sleeve 3 made of low alloy steel such as Or-MO-V material is shrink-fitted into the journal portion 2 of the rotor shaft 1 made of high Cr alloy steel. This sleeve 3 is supported by a bearing 5 lined with white metal 4. A low alloy steel coupling 6 similar to the sleeve 3 is shrink-fitted to the end of the journal portion 2, and a key 7 is provided between the coupling 6 and the journal portion 2.

During operation of this turbine, lubricating oil is continuously injected into the bearing 5. However, if hard foreign matter mixed in this lubricating oil enters the journal moving part 8, the thermal conductivity of the journal part 2 made of high Cr alloy steel is lower than that of the low alloy steel sleeve 3 and coupling 6, so the above-mentioned problem occurs. The foreign material injection part is locally heated due to friction. This may cause local galling or welding phenomena in the surrounding portion 8, resulting in damage to the journal portion 2.

On the other hand, the surface of the journal portion 2 of the rotor shaft 1 is repeatedly subjected to bending stress during rotation of the rotor due to deflection due to the rotor's own weight and minute alignment errors, and also due to the firing of the sleeve 3 and coupling 6. Surface pressure is also at play. Due to such causes, a fretting fatigue phenomenon occurs in the journal portion 2 on which tensile stress is applied. This fretting fatigue phenomenon refers to a phenomenon in which fatigue damage accumulates when repeated stress is present due to repeated frictional force or external force on the firing contact surface where relative repeated microslips occur.

This fretting fatigue may cause cracks 9 to occur in the journal portion 2 of the rotor shaft 1, as shown in FIG. Especially due to foreign substances in the lubricating oil. Journal section 2
The damage is further aggravated by the fretting fatigue and promotes cracks 9. Shrink-fit rotor 1 with cracks 9 like this
There is a problem in that the turbine requires replacement from a safety point of view, resulting in the shutdown of the turbine.

[Object of the Invention] The object of the present invention is to reduce fretting fatigue on the fired joint surface by incorporating compressive residual stress in the surface layer at the site of the fired joint surface and further improving the wear resistance of the surface layer. It is an object of the present invention to provide a turbine rotor that prevents cracks from occurring due to

[Summary of the Invention] A turbine rotor according to the present invention is characterized in that a portion of the rotor shaft into which a cylindrical member such as a sleeve or a coupling is shrink-fitted is subjected to a surface hardening treatment.

[Embodiments of the Invention] As is well known, the phenomenon of fretting refers to the repeated relative movement of metals that are in contact with each other in a minute range, and a repeated frictional force is generated at the contact surface where fretting occurs. Fretting fatigue is a condition in which fatigue damage accumulates due to repeated stress caused by external forces.

It is known that the fretting fatigue durability limit of metal materials is significantly lower than that of ordinary smooth materials. Figure 5 shows the results of a rotating bending fatigue test using a specimen made of high Cr alloy steel with a parallel section of 8φl.
It is shown by a curve. In the figure, characteristic A is the result of a fatigue test of a normal smooth material, and characteristic B is a result of a fretting fatigue test. The fatigue endurance limit of the latter is approximately 40% lower than that of the former.

The reason why the fretting fatigue durability limit is significantly lower than that of normal smooth materials is because the shear force or friction force generated at the contact surfaces of two metals that are in contact with each other is in the area where relative slip occurs. This is because the relative slip reaches its maximum at the boundary of the region where no relative slip occurs, and cracks occur at lower stress than the stress generated by external force, although it looks good.

On the other hand, as shown in characteristic C in Figure 5, fretting increases by approximately 70 to 90% in high C alloy steels subjected to surface hardening treatment using carbon dioxide laser light, compared to those in which fretting occurs. It was found that the surface hardening treatment increases the compressive residual stress in the surface layer, reduces the tensile stress acting on the inner and outer surfaces, and contributes to improving the fretting fatigue durability limit. For example, carburizing and quenching is a method of internalization, but there are many problems because the surface texture is rough and firing precision is required, and it is not possible to obtain an even compressive residual stress distribution.Furthermore, it takes a long time. However, there are drawbacks such as poor economic efficiency.

The surface hardening treatment method using carbon dioxide laser light of the present invention provides an extremely good finish on the rotor surface, has sufficient fatigue resistance, and can be said to be the most effective method for preventing fretting fatigue. Therefore, the present invention has been made based on the fatigue test results detailed above, and examples of the shrink-fitted rotor according to the present invention will be described below with reference to the drawings. High Cr alloy steel rotor material has C: 0.15-0.23%, Cr: 10
It consists of a high Cr alloy steel rotor material which has a main component of ~12% and has been subjected to a series of heat treatments of normalizing, quenching and tempering.

As shown in FIG. 1, the rotor surface hardening method according to the present invention involves supporting the rotor shaft 1 on a support base 10 and a support receiver 11, and attaching the rotor shaft 1 to a drive motor so that the surface hardening layer becomes uniform. The laser beam 14 oscillated by the laser light source 13 while rotating at a constant speed by the rotor 12 is irradiated over a range sufficient to cover the position where the sleeve 3 and the coupling 6 are shrink-fitted to the rotor shaft 1 in FIG. Laser light 1
4 continuously rotates the rotor shaft 1. The surface of the journal portion 2 is heated to a predetermined temperature, e.g.
Heat to 0°C and perform surface hardening treatment. In this case, as a light guide path for the laser beam 14, the laser beam 14 oscillated by the laser light source 13 passes through a lens 15, is reflected by mirrors 16a and 16b, and reaches the rotor shaft 1.

Further, as for the laser surface hardening treatment mechanism, when the rotor shaft 1 is irradiated with a laser, the absorbed optical energy is relaxed and converted into heat, resulting in a surface hardening effect. The area irradiated with laser light is rapidly heated, and after the irradiation is stopped, the heat quickly diffuses into the base steel, which occupies a much larger volume than the heated area, so the heated area cools down quickly. Ru.

The turbine rotor obtained by the above method has various features such as low distortion and no need for refinishing, distortion correction, etc. Figure 3 shows the wear resistance of the bearing obtained by the above-mentioned surface hardening treatment, in which iron powder (equivalent to ~325 mesh) was mixed into the lubricating oil, and a laboratory test was conducted to determine whether or not scratches would occur on the journal. This is what was investigated. High Cr alloy steel 17
In this case, it wears out over time and causes galling and welding phenomena, but the surface hardened layer 18 wears only a small amount and does not cause any scratches. Further, FIG. 4 shows the stress state of the surface hardened layer. As is clear from the figure, the compressive residual stress is distributed from the surface toward the deep part, and exhibits the highest value in the middle region of the hardened layer.

[Effects of the Invention] As described above, according to the present invention, the sleeve and coupling firing portion of a high Cr alloy steel turbine rotor are treated with carbon dioxide laser light to improve compressive residual stress generated during surface hardening treatment and wear resistance. This is superimposed on the bending stress and frictional force during rotor rotation, substantially improving the fretting fatigue durability limit and preventing the occurrence of cracks due to fretting fatigue, which was a concern in the past.

Here, a rotor made of high Or alloy steel and a Cr-Mo-
Although the embodiment has been explained using a combination of a sleeve and a coupling made of V-low alloy steel, it is also effective in the case of a combination of a sleeve and a coupling made of other steel types.

[Brief explanation of drawings]

FIG. 1 is a front view showing a method of surface hardening a turbine rotor according to the present invention, FIG. 2 is a front view showing an end portion of a turbine rotor according to the present invention, and FIG. 3 is a front view showing a method for surface hardening a turbine rotor according to the present invention. Characteristic diagram showing the wear characteristics results of the treated layer and high-Or alloy steel rotor material. Figure 4 is a characteristic diagram showing the compressive residual stress distribution caused by surface hardening treatment. Figure 5 shows the fatigue test results of high Cr alloy steel. The S-N curve diagram, FIG. 6 is a sectional view showing the end of a conventional fired rotor, and FIG. 7 is a sectional view showing the site where fretting fatigue occurs. 1... Rotor shaft, 2... Journal portion 3
... Sleeve 6 ... Low alloy steel coupling 13 ... Laser light source, 14 ... Laser light (8733
) Agent Patent attorney Yoshiaki Inomata (and 1 other person) Figure 1 D Figure 2

Claims (2)

[Claims] (1) In a shrink-fit rotor in which a cylindrical member such as a sleeve or a coupling is shrink-fitted onto the rotor shaft, a surface hardening treatment is applied to the portion of the rotor shaft where the cylindrical member is shrink-fitted. A turbine rotor featuring: (2) The turbine rotor according to claim 1, wherein the surface hardening treatment for the portion of the rotor shaft into which the cylindrical member is shrink-fitted is performed by a surface hardening treatment method using carbon dioxide laser light.