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The Effect of Shell Thickness, Insulation and Casting Temperature on Defects Formation During Investment Casting of Ni-base Turbine Blades

Raza M., Irwin M., Fagerström B.

Archives of Foundry Engineering

2015

Vol. 15, iss. 4

115--123

Turbine blades have complex geometries with free form surface. Blades have different thickness at the trailing and leading edges as well as sharp bends at the chord-tip shroud junction and sharp fins at the tip shroud. In investment casting of blades, shrinkage at the tip-shroud and cord junction is a common casting problem. Because of high temperature applications, grain structure is also critical in these castings in order to avoid creep. The aim of this work is to evaluate the effect of different process parameters, such as, shell thickness, insulation and casting temperature on shrinkage porosity and grain size. The test geometry used in this study was a thin-walled air-foil structure which is representative of a typical hot-gas-path rotating turbine component. It was observed that, in thin sections, increased shell thickness helps to increase the feeding distance and thus avoid interdendritic shrinkage. It was also observed that grain size is not significantly affected by shell thickness in thin sections. Slower cooling rate due to the added insulation and steeper thermal gradient at metal mold interface induced by the thicker shell not only helps to avoid shrinkage porosity but also increases fill-ability in thinner sections.

Scanning of Magnetic Field as a Method of Irwestigations of the Structure of Magnetic Materials

Tumański S.

Przegląd Elektrotechniczny

2007

R. 83, nr 1

108-112

The measuring system designer for 3D magnetic field scanning is presented. As a sensor of magnetic field AMR magnetoresistive sensor has been used. The result of scanning can be presented in form o a colour map. Such map very well represents the grain structure of a material. This grain structure influences performances of the material, for example losses in the case of electrical steel. lnvestigations of the structure can be an usefui tool for controi of technoiogy of magnetic material manufacturing as well as a non-destructive testing of material.

Zaprezentowano system pomiarowy zaprojektowany do skanowania pola magnetycznego w przestrzeni trójwymiarowej. Jako czujnika pola magnetycznego użyto cienkowarstwowy czujniki magnetorezystancyjny AMR. Po przeprowadzeniu skanowania rozkład pola magnetycznego może być przedstawiany w postaci mapy. Wykazano, że mapa taka dobrze odwzorowuje strukturę ziarnistą materiału. Od struktury ziarnistej zależą parametry użytkowe materiału, na przykład straty w przypadku blach elektrotechnicznych. Badania struktury mogą być dobrym narzędziem do kontroli procesu technologicznego wytwarzania materiałów magnetycznych, a także nieniszczących metod defektoskopii.