JPS62144543A - Cold working type non-magnetic retaining ring - Google Patents

Abstract

PURPOSE:To increase cold draft while reducing stress corrosion cracking by final-finishing and working a non-magnetic retaining ring having high strength through cold working and high-frequency heating only both inner and outer surfaces. CONSTITUTION:A material for a non-magnetic retaining ring 1 consists of high manganese steel having austenite texture composed of 18% Mn, 5% Cr and Fe as the remainder, and is made up of high strength steel, yield strength thereof reaches 1,150N/mm through cold working. The retaining ring is finished and worked in predetermined size, a high-frequency coil capable of simultaneously heating an outer circumferential surface including the end surfaces of the retaining ring and an inner circumferential surface is set and these regions are kept constant at 750 deg.C, and the outer circumferential surface and the inner circumferential surface are high-frequency heated, and held for 0.3hr. The currents of the high-frequency coil are interrupted, heating is stopped and the whole is left as it is and cooled. A softened layer having 0.3mm depth and the small sensitivity of stress corrosion cracking is formed to the inner and outer surfaces of the retaining ring through the surface heat-treatment.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention is a turbo all in one! This invention relates to a retaining ring used to protect the end of a field winding of a machine.

[Prior art and its problems]

A retaining ring is used in a turbo generator to prevent the field winding attached to the rotor shaft from flying out due to the centrifugal force of rotation. Fig. 1 shows an external view of the rotor shaft of a turbo generator, and a retaining ring 1 is attached to both sides of the body end of the rotor shaft 2 to hold field windings pulled out from the rotor (not shown). The end of the is fixed. In addition, in order to explain the structure in the vicinity of the retaining ring 1, a partial cross-sectional view of the area A indicated by the broken line circle in FIG. 1 is shown in FIG. 2, and the parts common to those in FIG. It is a representation. In Fig. 2, the retaining ring 1 has one end shrink-fitted to the rotor shaft 2, and is prevented from being removed by a ring key 3, and the intermediate heating part covers the outer periphery of the end of the field winding 4, The winding a4 is fixed, and the other end of the retaining ring 1 is fastened to the retaining ring support 5. Reference numeral 6 indicates insulation under the retaining ring, and a wind cylinder for cooling is provided between the field winding 4 and the rotor shaft 2.

The retaining ring generates a stray current due to leakage magnetic flux from the stator winding of the generator, and the winding is damaged due to the heat generated by this 5"5" current, so the material of the retainer ring is not affected by the surface leakage flux. It is necessary to use a non-magnetic material with a small magnetic field. In addition, the retaining ring must also serve as a high-strength member to which tensile stress is applied by centrifugal force during operation in addition to the tensile residual stress caused by shrink fitting.

Therefore, austenitic copper, which is a non-magnetic material, is used as the material for the retaining ring.
For this purpose, high manganese steel, such as 18Mn-5Cr steel, which maintains a stable austenitic structure even after cold working, is often used as the retaining ring.

On the other hand, as turbo generators have become thicker and cleaner in recent years, the rotor shaft has become larger and the diameter of the attached retaining ring has also increased.

As the diameter increases, the circumferential speed of the retaining ring during continuous rotation also increases, so the retaining ring must be subjected to higher tensile stress and a large shrinkage fit commensurate with the stress. Therefore, even when the generator σ) is stationary, a high tensile residual stress exists in the retaining ring. Therefore, a material with even higher strength is required for the retaining ring.

However, since the non-magnetic retaining ring of high manganese steel with an austenitic structure imparts high material strength through cold working, the higher the degree of cold working and the higher the material strength, the better the resistance to stress corrosion cracking. There is a problem with being sensitive. To solve this problem, during generator factory assembly, transportation, post-installation maintenance, etc., the generator must be exposed to corrosive substances that can induce stress corrosion cracking in the retaining ring. It is even more important to take care to prevent moisture from adhering, but this is actually quite difficult. No effective method has yet been established to treat the retaining ring, for example by coating the entire surface of the retaining ring with a corrosion-resistant material.

In view of the above, a high-strength, non-magnetic retaining ring that has been subjected to cold working that prevents the occurrence of stress corrosion cracking through appropriate material treatment is desired.

- [Object of the Invention] The present invention has been made in view of the above points, and its object is to provide a high-strength non-magnetic retaining ring made of austenitic steel that reduces stress corrosion cracking susceptibility without impairing material strength. It's about doing.

[Key points of the invention]

In the present invention, after final finishing a non-magnetic retaining ring with high strength by cold working, high-frequency heating is applied to only both the inner and outer surfaces to remove stress and form a softened layer of a predetermined depth. The entire surface of the ring is covered with a thin softened layer without reducing the strength of the entire retaining ring (the softened surface layer reduces the susceptibility of the material to stress corrosion cracking in a corrosive environment).

[Embodiments of the invention]

The present invention will be explained below based on examples.

The material of the non-magnetic retaining ring used in the present invention was 18% Mn.

It is a high manganese steel with an austenitic structure consisting of 5% Cr and balance Fe, and the yield strength has been increased to 11 by cold working.
It is a high strength steel that reaches 5ON/+ns.

After finishing the retaining ring to the predetermined dimensions, a high-frequency coil that can simultaneously heat the outer and inner circumferential surfaces, including the end faces of the retaining ring, is installed, and these areas are high-frequency heated at a constant temperature of 750°C. .Hold for 3 hours.

Next, the current to the high frequency coil is cut off to stop heating and allow cooling. By this surface heat treatment, a softened layer with a depth of 0.3 mm is formed on the inner and outer surfaces of the retaining ring.

(If left cold-worked, the wicker hardness Hv
380, but the surface softening layer decreases to lv310, but at this time, the area sandwiched between the surface softening layers of the thick part of the retaining ring has the original hardness Hv.
380 can be kept as is. Since the retaining ring is strengthened by cold working, it is easily recrystallized by heating and it is easy to form a softened layer, but if the depth of the softened layer is too deep, the effect will be lost, so 0.5 m
It is preferable to keep it within m, preferably within 0.3 mat, and it is preferable to select it so that the combination of the strength of the material, that is, the degree of processing, and the softening heating temperature is optimal.

In this way, the retaining ring is covered with either a surface that is directly exposed to a corrosive environment and is susceptible to stress corrosion cracking, or a softened layer that is less susceptible to stress corrosion cracking than the interior. The stress acting on the retaining ring is also shared by the strong interior, so even if a softened layer with the hardness and depth described above is formed on the surface, it will not reduce the required strength of the retaining ring as a whole. , the influence of the softened layer can be ignored regarding the strength. In addition, the above-mentioned high-frequency-applied PA material that forms a surface softening layer of this level has only slight oxidation on the surface, and there is no problem in practical use.

As described above, the retaining ring according to the present invention is composed of a thickened part with high strength and a skin covering it and directly exposed to a corrosive environment, each of which has the role of maintaining strength and preventing stress corrosion cracking. This solution solves the contradictory conditions of increasing the degree of machining and reducing stress corrosion cracking within the same material.

〔Effect of the invention〕

The retaining ring that fixes the field winding end of the rotating shaft of the turbo generator has an austenite structure that is stable even when subjected to cold working, in order to prevent the generation of thin current due to leakage magnetic flux from the stator winding. High manganese steel is used to hold the ring, and as the generator becomes larger, the strength of the holding ring must also be increased.
Increasing the degree of cold working and increasing the strength of the material also makes it more susceptible to stress corrosion cracking.In order to prevent this stress corrosion cracking from occurring, corrosion must be maintained in all environments such as generator assembly, transportation, and maintenance. In order to prevent corrosive effects such as the adhesion of harmful substances and moisture condensation from reaching the retaining ring, current technology requires coating the entire surface of the retaining ring with a corrosion-resistant material to completely suppress stress corrosion cracking. This is extremely difficult in practice, so in order to solve this problem, the present invention aims to create a final finish by cold-working the retaining ring to give it the necessary high strength, as described in the embodiment. By high-frequency heating the entire outer and inner circumferential surfaces including the end surfaces,
A thin, softened layer that relieves stress is provided on the entire surface, and this softened layer does not reduce the internal strength.The retaining ring as a whole maintains high strength, and the surface The softened layer can contribute to reducing stress corrosion cracking susceptibility. In other words, in the retaining ring of the present invention, regions that play different roles as a strength member and stress corrosion crack prevention are formed into a single material by simple heat treatment, which increases cold working strength and reduces stress corrosion cracking susceptibility. This method solves contradictory conditions for the same component all at once.

[Brief explanation of drawings]

Figure 1 is an external view of the rotor shaft of the generator, Figure 2 is Figure 1A
FIG. 1... Holding ring, 2... Rotor shaft, 4... Field winding, 5... Holding ring support.

Claims (1)

[Claims] 1) A non-magnetic retaining ring that is strengthened by cold working and that fixes the end of the field winding of the rotor shaft of a turbo generator,
A cold-worked nonmagnetic retaining ring characterized by having its surface subjected to heat treatment to form a softened layer after final finishing.