Application of the hottest vibration treatment tec

Application of vibration treatment technology in steam turbine production

Abstract: vibration to eliminate residual stress is a process to adjust residual stress by mechanical method. The main characteristics of this process are low cost, high efficiency, low energy consumption, short production cycle, clean production, low noise, wide range of application and widely used. The use of graphene is still too expensive and impractical. This paper introduces the application of this technology in steam turbine and other components

key words: vibratory stress relief technology; Turbine components; Since the introduction of vibration treatment technology in China in the 1970s, it has not only been accepted by more and more people, but also made gratifying achievements in machine tools, heavy machinery, engineering machinery, aviation, metallurgy, chemical industry and other departments, and played an increasingly important role in the development of the machinery industry. Vibration treatment technology not only because of its low cost, low energy consumption and high efficiency, but also because of its simple process, short production cycle and pollution-free clean production, it overcomes the problems of surface oxidation and decarburization that some heat treatment processes cannot get rid of, so as to make up for the shortcomings of natural aging and thermal aging. Therefore, vibration treatment technology has been widely used at home and abroad

the vibration treatment technology has been proved by a large number of tests that it can make the welding residual stress, especially the size of the welding structure with extremely uneven distribution, so as to improve the retention of component accuracy, especially for castings

the principle of vibration treatment technology is to apply its dynamic stress to the component in the form of mechanical vibration. When this additional stress is superimposed with the residual stress inside the component, the total stress reaches or exceeds a certain value. At this time, at the place where the component stress is concentrated, the micro and macro plastic deformation occurs because the stress exceeds the yield strength of the material, reducing the peak value of the residual stress, The distribution of residual stress of the component is adjusted, so as to achieve the purpose of residual stress homogenization

the mechanism of vibration treatment technology, domestic and foreign scholars have carried out a large number of studies and experiments with dislocation theory, elastic deformation theory, plastic deformation theory, internal friction theory and other theories from the macro, micro, mechanical, material and other perspectives. It is shown that the essence of vibration treatment technology is a process in which the elastic strain energy stored in materials is gradually released through local or micro plastic deformation; From the perspective of microstructure, it is related to the change of dislocation substructure and its configuration. By increasing the vibration energy of lattice atoms, the lattice atoms with dislocations return to the low dislocation state, which is very similar to the mechanism of heat treatment, which makes the lattice atoms with dislocations return to the low dislocation state with low potential energy by increasing the thermal kinetic energy of lattice atoms; The relaxation of residual stress in the component caused by vibration aging technology is the result of the overall adjustment of plastic deformation in the micro area inside the component, which not only reduces the performance of the plastic; Because the existence of residual stress is characterized by overall balance, when the local residual stress peak changes, it will inevitably cause the redistribution (homogenization) of residual stress in the component; The reduction of residual stress is related to the amplitude of applied stress. Aging under appropriate dynamic stress can achieve the purpose of secondary load exercise without fatigue damage

in a word, although there are some limitations and differences in the understanding of the objective fact of vibration treatment technology, it has been widely used in aerospace, aviation industry, military industry, automobile and machinery industry in foreign industrial developed countries since the 1950s. Since the introduction of vibration treatment technology in China, it has not only been widely used in various fields, but also many scholars and scientific and technological workers have carried out a lot of experimental work on the ability to eliminate residual stress, dimensional stability, fatigue life and other effects on practical components, which have proved the feasibility of this technology. Vibration aging is also known as a revolution of aging technology

2 application examples of vibration treatment technology

⑴ vacuum chamber of dynamic balance testing machine

at the end of the 1970s, the largest dynamic balance testing machine in Asia was introduced from abroad. The vacuum chamber was processed in China. The vacuum chamber is a welded structural cylinder with a length of 13 meters and a diameter of 7 meters, which was rolled in sections. After welding according to the technical requirements, vibration treatment was carried out. Up to now, it still maintains dimensional accuracy

⑵ vacuum chamber of electron beam welder

large electron beam welder was introduced from abroad in 2001. The vacuum chamber is processed in China. The vacuum chamber is a welded structure, 7 meters long, 6.3 meters high, 5 meters wide, and weighs more than 110 tons. It is divided into three parts, namely, the front and rear chambers and the gate for vibration treatment. Near the main weld, the residual stress before and after vibration treatment is tested by the magnetic stress distribution tester jointly developed by Xi'an Jiaotong University and Harbin automobile, The test results of two welds are shown in the following table:

the elimination rate of residual stress is more than 50%. The vacuum chamber has been put into operation for three years

⑶ ring diaphragm

ring diaphragm is an important part of the turbine body, which is used to fix the guide vane. The heat energy is converted into kinetic energy in the steam passage composed of guide vanes to make the turbine work. The ring diaphragm adopts a welded structure, and the total length of the weld is tens of meters. In order to eliminate the residual stress generated during welding, tempering heat treatment is generally used to eliminate the stress, and at the same time, sandblasting process is also carried out to remove the oxide skin caused by tempering. Secondly, the body and outer ring of the diaphragm are made of different materials with the blades welded therein. Therefore, during the thermal aging process, new thermal stress will be generated due to the different thermal expansion coefficients of the two materials. If the vibration treatment technology is used instead of thermal aging, it will not only shorten the production cycle, reduce the sand blasting process, reduce the production cost, but also overcome the adverse effects of thermal aging on the components

according to the inspection standard for thermal aging of ring diaphragms, 30 pairs of ring diaphragms were inspected. Before and after the vibratory aging process, the maximum change of the end face distance between the inner and outer rings was + 3.1mm ~ -2.5mm, and the average change was 0.35mm. The maximum change of diaphragm with outer ring diameter is ± 3mm, and the average change is 0.7mm, which does not exceed the standard and is better than thermal aging

in addition, X-ray stress meter was used to detect the stress changes around the last ring diaphragm weld before and after vibration aging, and magnetic stress distribution tester was used to detect the stress distribution changes around the inner and outer welds before and after vibration aging. The test results showed that obvious stress homogenization effect was produced after vibration time effect

at present, the vibration aging process of ring diaphragms has replaced the thermal aging process, and hundreds of ring diaphragms have been treated, saving millions of production costs

⑷ cylinder

the function of the cylinder is to contain steam in the cylinder to expand and do work. The cylinder is equipped with nozzles, diaphragms, steam seals, etc., which are collectively referred to as stators. The cylinder shall bear the self weight of the above parts, the installation tension of the pipeline, the pressure difference inside and outside the cylinder during operation and other forces. Due to different working conditions, cylinders are divided into high-pressure, medium pressure and low-pressure cylinders

the cylinder adopts the vibration aging process, which is currently limited to the low-pressure cylinder and repair welding cylinder, because the low-pressure cylinder is mostly welded structure, and the repair welding cylinder is often repaired when defects are found during finishing. The thermal aging is used to eliminate the repair welding stress, and if there is deformation, it cannot be repaired. The vibration aging process is the best choice

the following is the test results of the dimensional stability of the lower half of the middle part of the low-pressure cylinder of the air-cooled unit treated by the vibration aging process:

according to the above test results, the cylinder weighing 26 tons after vibration aging, after nearly ten processes of movement, its main dimensional change is ± 12mm left and right, and the standard for controlling the abnormal noise or short circuit of the equipment found by everyone is not more than 30mm. It is superior to thermal aging, which requires a large heat treatment furnace, and the heat source is generally coal gas, which often causes new deformation of the cylinder due to uneven furnace temperature; Due to the reduction of strength, the cylinder will produce greater deformation when moving; High energy consumption is not conducive to cleaner production; High cost and long production cycle

(5) water chamber of condenser

in the thermal system of steam turbine unit, condenser is an auxiliary equipment to meet the thermal cycle of steam turbine. Its function is to improve the thermal efficiency of the cycle and turn the exhaust steam into condensate for use in the cycle. The cooling water flows out of the water inlet chamber through the cooling pipe group and then through the water outlet chamber. Therefore, the condenser is required to have good tightness and dimensional stability

the water chamber and the end cover of the water chamber are of welded structure, and the weight ranges from a few tons to dozens of tons. Due to the complex structure, the dual aging method of spectrum aging and standard aging is adopted. Some of the water chambers treated by vibration aging have been working in power plants for more than three years

generally, the volume of the water chamber is large, and a large heat treatment furnace is required for thermal aging, and the treatment cost is more than 10000 yuan per piece. In addition, the production costs such as transportation and treatment cycle are high. Vibration aging can be carried out on the original processing site and then transferred to the next process. Not only the production cycle is very short, but also the treatment cost is very low

(6) other bearing boxes, scoring platforms, radial plates, spring supports, cushion boxes, noise elimination chambers, missile transport boxes, etc. after rough machining. Its weight ranges from hundreds of kilograms to tens of tons. According to the requirements and structure of components, sub resonance aging, standard aging and spectrum aging are adopted respectively

3 conclusion

in a word, there are many advantages of adjusting the residual stress by applying dynamic load to the component, which is beyond doubt. Its technical and economic benefits are very considerable, especially some incalculable benefits. Due to the homogenization effect of vibratory stress relief on the residual stress of the member, the body of the member has a certain hardening effect. Therefore, it not only homogenizes the stress, but also increases the deformation resistance and relative dimensional stability of the member. In particular, the steam turbine unit operates at 3000 rpm, and the aging frequency of spectrum aging is mostly around this range, which can be considered as the purpose of secondary load forging, and some potential defects can be found, which is a matter of killing two birds with one stone

references

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[3] machinery industry standard of the people's Republic of China Selection of vibration aging process parameters and technical requirements Jb/t.

[4] machinery industry standard of the people's Republic of China Selection of vibration aging process parameters and technical requirements for welded components Jb/t.

[5] Zhuang Tongxin, etc Development and application of magnetic stress detector [j] Modern instruments 2002.5:.

[6] Zhuang Tongxin et al Application of residual stress testing technology in steam turbine production and quality control [j] Physical and chemical inspection Physical volume 2003.10:.

[7] Zhuang Tongxin et al Application of vibration aging technology in ring diaphragm [j] mechanical engineer 2005.8.. (end)