Development of Porous Steel Structures for Steam Turbines

Dilthey, Ulrich; Ghandehari, A.; Kopp, Reiner; Hohmeier, P.; Beiss, Paul; Figueredo, E. Iglesias; El-Magd, Essam; Kranz, Alexander

doi:10.1002/1527-2648(200103)3:3<111::aid-adem111>3.0.co;2-z

Cited by 15 publications

(5 citation statements)

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“…This paper will concentrate on these blanks, especially on TRBs and TRSs. Furthermore, weight minimisation can be incredibly realised by hollowed blanks without or with load adapted thicknesses [4,5].…”

Section: Introductionmentioning

confidence: 99%

Flexibly Rolled Sheet Metal and Its Use in Sheet Metal Forming

Kopp

Wiedner²,

Meyer³

2005

AMR

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Light weight construction is a construction philosophy which aims at maximum weight reduction. Reasons for light weight construction can be very diverse. One main cause can be to improve fuel efficiency. This can be achieved by use of load optimised sheet thicknesses. Another reason can be the increasing demands on crash performances by optimisation of local properties. This paper presents two production processes of flexibly rolled blanks, one with longitudinal and the other one with latitudinal thickness transitions. Both of them have been developed at the Institute of Metal Forming (IBF) and yet found their way into series production. The potential of these processes is already proved by a large range of products, especially in automotive industries. Some special deep drawing tests with flexibly rolled blanks have been conducted and their results are presented. Also process simulation has been carried out at the IBF and will be explained. One possibility with regard to optimise these products is shortly introduced. Completing this paper an outlook is given.

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Section: Introductionmentioning

confidence: 99%

Flexibly Rolled Sheet Metal and Its Use in Sheet Metal Forming

Kopp

Wiedner²,

Meyer³

2005

AMR

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“…Refinement of a microstructure is seen to be responsible for behaviours such as superplasticity, [2,3] enhanced flow stress [4,5] and Vickers microhardness, [6,7] significant enhancement of the fatigue limit and the fatigue life. [8] In the ECA technique, the sample is strained essentially by approximately simple shear, when pressed many times through a deviated die; this makes this procedure very anisotropic in nature. It should result that the microstructure and the related mechanical behaviour are anisotropic and are strongly dependant on the pressing cycles and routes.…”

Section: Methodsmentioning

confidence: 99%

“…Space holders can be removed in a number of ways, e.g. by electrochemical leaching [8] or by pyrolysis as in the so called hollow sphere-concept based on styrofoam cores. [9] A similar approach is to use carbamide (urea) which can be removed at temperatures below 200 C. [10] In this way, highly porous Tias well as Ni-base components have been produced, although sintering of Ni-base-superalloys remained incomplete, as the authors point out.…”

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confidence: 99%

Superalloy IN625 with Cellular Microstructure – Fabrication Route and Mechanical Properties

Quadbeck¹,

Kaschta

Singer

2004

Adv Eng Mater

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In a number of studies in the last years, solid metallic foams have demonstrated their remarkable properties and their potential for a variety of applications. Predominantly light metals have been the subject of investigations, because of the relative ease of manufacturing and the interest of the automotive industry in light weight construction. [1±3] If cellular metal structures shall be exposed to very demanding corrosive or high temperature environments, superalloys rather than light metals must be employed. Such conditions are encountered in heat exchangers for use in chemical processes, acoustic absorption of turbine generated sound, or high temperature filtering of exhaust gas. In these particular examples open-porous structures are needed. Open-porous structures from superalloys will be the focus of the present paper.The main manufacturing routes for high temperature metal foams involve either casting techniques or powder metallurgy. Gas expansion methods, e.g. by addition of a foaming agent such as SrCO 3 that will decompose at a suitable temperature, lead to closed cell structures. [4] For open cell structures, removable internal structures or ªspace holdersº are necessary. Precision steel casting techniques make use of space holders in the form of polyurethane fugitive patterns [5] or agglomerated pit-iron sand. [6] Space holder techniques are particularly common in powder-metallurgy. They can involve either the coating of a template with a slurry [7] or the filling of the open spaces in a template with powder. Space holders can be removed in a number of ways, e.g. by electrochemical leaching [8] or by pyrolysis as in the so called hollow sphere-concept based on styrofoam cores. [9] A similar approach is to use carbamide (urea) which can be removed at temperatures below 200 C. [10] In this way, highly porous Tias well as Ni-base components have been produced, although sintering of Ni-base-superalloys remained incomplete, as the authors point out.In the present work a new approach to the fabrication of cellular structures from the superalloy Inconel 625 will be introduced. It is shown schematically in Figure 1. As in the literature a P/M space holder technique is applied, i.e. space holder particles and metal powder particles are mixed together and cold compacted. After removal of the space holders by thermal treatment, densification is achieved by sintering. In contrast to the literature, however, polyoxymethylene (POM) is employed as a removable internal structure in our approach. Furthermore, supersolidus liquid phase sintering (SLPS) is used for consolidation rather than standard sintering. The reasoning behind this will be explained in the following.Use of polyoxymethylene (POM) brings essentially two advantages. POM is a material that is injection-moldable, hence it can be brought into almost any user-defined shape. There is a potential that extremely complex cellular superalloy structures can be produced based on this space holder, i.e. sandwich type geometries with dense outer layers and cellula...

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“…Compared with the conventional resistance welding process, [2] this joining method is characterized by a low thermal effect on the weld spots of the joints between wire mesh and sheet. Before discharging the capacitor, the sheets and the woven wire mesh were fixed between two CuCrZr electrodes with a contact area of 25 cm 2 by a pressure force of 30 kN.…”

Section: Layout Of the Cooling Structurementioning

confidence: 99%

Flow Behavior of Sandwich Structures for Cooling Thermally Highly Loaded Steam Turbine Components

2009

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Within the release of the latest climate report, the discussion about global warming has gained importance. Industry and power plants, which cause 68% of all CO 2 emissions, are requested by policy to react to the situation. To reduce the emission quantity of combined cycle power plants, it is essential to improve thermal efficiency. In the case of modern steam turbines, this improvement can be achieved by increasing steam temperature and pressure. Since typical power plant materials will reach their operation limit with higher steam temperature, the application of a new cooling system could reduce the material temperature to tolerable conditions. In the context of the collaborative research program SFB 561, a new sandwich structure ( Fig. 1) was developed comprising a woven wire mesh interlayer between two plane sheets. Cooling steam is fed into the interlayer, where it can flow without severe losses. This sandwich structure is planned to be applied to the steam turbine casing as a wall cladding. Owing to constant overpressure of cooling steam in combination with high temperature loads during operation, the structures are primarily subjected to creep deformation. Furthermore, steam temperature fluctuations as well as starts and shutdowns of the steam turbine cause a superimposed fatigue process. Overall, the structures are stressed during operation by a combined creep-fatigue interaction with loads perpendicular and parallel to the intermediate layer. Results of creep tests showed shortest lifetimes in case of loading normal to the sheets, where the strength of the structure basically depends on the strength of the weld spots of the wire mesh sheet joints. The flow behavior under static loading was investigated to characterize completely the mechanical high-temperature behavior of the cooling structure in this critical direction. Tensile tests on the constituent wire and sheet were carried out at temperatures from room temperature up to 800 8C to determine constitutive equations required for a subsequent finite element method (FEM) simulation. The flow behavior of the constituents was described by the material law of Swift [1] and implemented in an adequate user subroutine of the commercial FEM software Abaqus. For the tensile tests of the structure with loads perpendicular to the intermediate layer two new types of test specimens (see Fig. 5a,c) were developed. Layout of the Cooling StructureThe constituent wire mesh and face sheets were joined by capacitor discharge resistance welding. Compared with the conventional resistance welding process, [2] this joining method is characterized by a low thermal effect on the weld spots of the joints between wire mesh and sheet. Before discharging the capacitor, the sheets and the woven wire mesh were fixed between two CuCrZr electrodes with a contact area of 25 cm 2 by a pressure force of 30 kN. As a result of the weaving process, the wire mesh was divided into warp and weft wires. In the case of structures manufactured of the midsize wire mesh (wire diameter d w ¼ 1.2 m...

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Development of Porous Steel Structures for Steam Turbines

Cited by 15 publications

References 0 publications

Flexibly Rolled Sheet Metal and Its Use in Sheet Metal Forming

Flexibly Rolled Sheet Metal and Its Use in Sheet Metal Forming

Superalloy IN625 with Cellular Microstructure – Fabrication Route and Mechanical Properties

Flow Behavior of Sandwich Structures for Cooling Thermally Highly Loaded Steam Turbine Components

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