JPS59115128A - Shrink-fitted rotor - Google Patents

Abstract

PURPOSE:To improve the resisting limit for the fretting fatigue of a rotor shaft and prevent generation of cracks by applying from the tempering temperature, the low-temperature quenching treatment onto the parts of the rotor shaft which is applied with shrink fit, and allowing a compression residual stress to internally exist on the surface layer at the above-described part of the rotor. CONSTITUTION:A rotor shaft 10 is applied with a series of heat treatment consisting of normalizing, quenching, and tempering, and then heated up to about 630 deg.C. As the final tempering treatment at a temperature rising speed of 40 deg.C per hour by coils 12 and 13, and kept at this temperature for 24hr, and then applied with low-temperature quenching by oil cooling. Each compression residual stress internally exists on each surface of the predetermined range 11a for shrink fit to sleeve and the predetermined range 11b for shrink fit of coupling because of the temperature difference between the inner part and the surface layer in the above-described low-temperature quenching. The structure of the surface layer is the same to the quenching structure of the inner part. With such a constitution, the resisting limit for fretting fatigue of the rotor shaft is improved, and the generation of cracks can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a shrink-fit rotor, and more particularly to a shrink-fit rotor that prevents cracking caused by fretting fatigue at a shrink-fit joint surface.

[Technical background and problems of the invention]

As shown in FIG. 1, in a conventional turbine rotor for the medium and high pressure section of a steam turbine, a sleeve 3 made of low alloy steel such as Cr-Mo-V material is attached to a journal part 2 of a rotor shaft 1 made of high Cr alloy copper. It is fitted. 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. When the turbine is in operation, the bearing 5 is continuously filled with lubricating oil. However, when hard foreign matter mixed in this lubricating oil enters the journal sliding part 8, the thermal conductivity of the journal part 2 made of high Cr alloy copper becomes lower than the sleeve 3 made of low alloy steel.
Since the foreign matter injection section is smaller than that of the coupling 6 and the coupling 6, the foreign matter injection section is locally heated due to friction. As a result, local galling or welding may occur in the sliding portion 8, and the journal portion 2 may be damaged.

On the other hand, bending stress is repeatedly applied to the surface of the journal portion 20 of the four-way shaft 1 during rotation of the rotor due to deflection due to the rotor's own weight, minute alignment errors, etc. Shrink fit 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 contact surfaces 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. In particular, damage to the journal portion caused by foreign matter in the lubricating oil is further aggravated by the fretting fatigue and promotes cracks 9. A shrink-fitted rotor with such cracks needs to be replaced from a safety point of view, and there is a problem in that the steam turbine will stop operating.

[Purpose of the invention]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a shrink-fit rotor that prevents cracks from occurring due to fretting fatigue at the shrink-fit joint surface.

[Summary of the Invention] In order to achieve this object, the present invention focuses on the fact that fretting fatigue phenomenon occurs when tensile stress is applied to the surface of the rotor shaft, and shrink fitting is performed. The rotor shaft portion is subjected to a low-temperature quenching treatment from the tempering temperature to create compressive residual stress in the rotor surface layer at the above-mentioned portion, and this compressive residual stress reduces the tensile stress applied from the outside.

[Embodiments of the invention]

An embodiment of a shrink-fit rotor according to the present invention will be described below with reference to the drawings.

In FIG. 3 showing the rotor heat treatment method according to the present invention, the journal portion 11 of the rotor shaft 10 is arranged in areas 11a and llb where the sleeve 3 and the coupling 6 shown in FIG. 1 are to be shrink-fitted, respectively. High frequency coils 12 and 13 are wound around. Area 11 other than the above two areas 11a and 11b
c is coated with anticementite 14. This rotor shaft 10 is subjected to a series of heat treatments of normalizing, hardening, and quenching, and as the final tempering treatment of this series of heat treatments, the coils 12 and 13 are heated at 40°C per hour.
After heating to approximately 630° C. at a temperature increase rate of 100° C. and holding at this temperature for a certain period of time, a low-temperature quenching treatment by oil cooling is performed. Due to this low-temperature quenching, compressive residual stress exists in the surface layer of the sleeve shrink-fit area 11a and the coupling shrink-fit area 11b due to the temperature difference between the inside and the surface layer. In addition,
The structure of the surface layer is the same as the internal tempered structure. In addition, a region 11 covered with anticementite 14
c has no inherent compressive residual stress. The journal portion 11 of the rotor 10, which has been locally low-temperature hardened in this way, is shrink-fitted with a sleeve and a coupling that are heated to 250° to 300°C at a heating rate of 20°C per hour and held for 3 to 10 hours. Ru. As described above, the shrink fit area of the journal portion 11 of the rotor shaft 1o, that is, the shrink fit joint surface 11a,
Since the compressive residual stress is built into the surface layer of the ILB, even if tensile stress is applied to the rotor journal portion 11 due to turbine operation, this tensile stress is offset by the compressive residual stress and is reduced, resulting in fretting fatigue. It can prevent the occurrence of cracks.

A specific example of the compressive residual stress generated by the above-mentioned low-temperature quenching treatment is shown below.

Figure 4 shows the stress state of the surface layer when a cylindrical high Cr alloy steel specimen with a parallel part diameter of 8.0 mm was subjected to low-temperature hardening treatment at a tempering temperature of 630°C. . As is clear from the figure, compressive residual stress is distributed in the surface layer up to about 0.25 mm from the surface, and the compressive residual stress is 0.25 mm.
It exhibits a maximum value of about 50'/- at a depth of around 1 mm.

Next, the results of a comparison experiment between fretting fatigue of the rotor according to the present invention and fretting fatigue of a conventional rotor will be shown.

This experiment was conducted using (5) a conventional rotor material without fretting, a conventional rotor material (which caused fretting by applying 81 surface pressure), and (a conventional rotor material which caused fretting by applying 0 surface pressure). For the rotor material according to the present invention, that is, the rotor material subjected to the above-mentioned low-temperature quenching treatment, the fatigue durability limit (-) was measured by a rotating bending fatigue test.The results of this experiment are shown in the table below. .

In the above table, the stress ratio is ((B) or (fatigue endurance limit of Q)/(fatigue endurance limit of prisoner), and the rate of increase is (
(Fatigue endurance limit of C1 - (seasonal fatigue endurance limit)/(fatigue endurance limit of (B)).

As is clear from the above table, the fatigue durability limit when fretting occurs in the conventional rotor material decreases to 0.36 in the case without fretting, whereas it decreases to 0.6 in the rotor material according to the present invention. This is a 66% increase compared to when fretting occurs in conventional rotor material.

In this example, a rotor made of high Cr alloy steel and a sleeve and coupling made of Cr-Mo-V made of low alloy steel were used.
Other steel types may be used, and the low temperature quenching treatment of the present invention is also effective in preventing stress corrosion cracking in the keyway portion of nuclear rotor wheels.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the portion of the rotor shaft to which the shrink fit is performed is subjected to low-temperature quenching treatment from the tempering temperature, and compressive residual stress is created in the rotor surface layer at the above-mentioned portion. Since tensile stress is reduced by compressive residual stress, fretting fatigue durability can be improved and cracking can be prevented even if repeated bending stress and frictional force are superimposed on the rotor surface during rotation of the rotor shaft. Therefore, the reliability of the shrink-fit rotor can be improved.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view showing a conventional shrink-fit rotor, Fig. 2 is a longitudinal sectional view showing a fretting fatigue crack occurrence site in the shrink-fit rotor, and Fig. 3 is a longitudinal sectional view showing a shrink-fit rotor according to the present invention. FIG. 4, which is a front view showing the method of heat treatment, is a graph showing the distribution of compressive residual stress caused by the low temperature quenching treatment. 10... Rotor, 11... Journal section, lla.
... Sleeve shrink fit area, llb... Coupling shrink fit area, 12, 13... High frequency coil.

Claims (1)

[Claims] In a shrink-fit rotor in which a cylindrical member such as a sleeve or a compression stop is shrink-fitted onto the rotor shaft, the portion of the rotor shaft to which the cylindrical member is shrink-fitted is quenched at a low temperature from the tempering temperature. A shrink-fit rotor characterized by having compressive residual stress built into the surface layer of the rotor shaft.