Abstract: In a process for the production of half-tubes or tubes of a recuperative waste gas heat exchanger using a precision casting process, the half-tubes or tubes consisting of a high-temperature-resistant metallic material have a plurality of elliptical openings passing through their surface.

Abstract: A ceramic heat insulation layer applied to a metal structural part or to an intermediate adherent layer thereon, has the surfaces of its inner, open pore structure coated with a passivating ceramic material or a metal deposition material for improving the properties of the heat insulation layer.

Abstract: A ceramic heat insulation layer applied to a metal structural part or to an intermediate adherent layer thereon, has the surfaces of its inner, open pore structure coated with a passivating ceramic material or a metal deposition material for improving the properties of the heat insulation layer.

Abstract: A process for testing the tolerances of bores made by laser pulses records a matrix image of the bore region during each laser pulse and evaluates the matrix image to determine the average bore diameter. Compliance with the required tolerances can thereby be achieved during the boring operation. The evaluation of the matrix image is made by optically forming a half tone, dot matrix, mosaic image of the bore and its surrounding region, adding gray scale values of the dots in the columns and rows and differentiating the column and row totals to produce spaced maxima for the rows and columns. The distance between the spaced maxima in the rows and columns represents the diameter of the bore in the direction of the rows and columns respectively.

Abstract: An article comprising a component of ceramic material and a metal component has a metal felt located between opposed faces of the two components, the metal felt being permanently joined to both the ceramic face and the metal face to join the two components together. The metal felt may be brazed to both components, the brazing alloy being one which chemically combines with the ceramic material. The brazing alloy may be in the form of a foil placed between the metal felt and each of the components, and the brazing may take place in a vacuum.