The present invention relates to a method and to an apparatus for calibrating tubular articles consisting of a pulverulent metallic material which has undergone isostatic compression and a subsequent sintering operation. It is to be noted that while the invention is considered to be of special value in connection with the calibration of linings for the cylinders of internal combustion engines, its general field of use is much broader and covers all tubular articles manufactured as stated above.
In the prior art, a tubular article of the type above specified, including cylinder linings, are calibrated by placing the lining around a cylindrical mandrel. For obvious reasons it is then necessary that the internal diameter of the lining exceeds the diameter of the mandrel by an amount sufficient to permit convenient mounting of the lining thereon. The calibration process involves subjecting the lining to radially inwardly acting forces striving at bringing the internal surface of the lining into intimate and accurate contact with the cylindrical surface of the mandrel. As is understood, this means that the internal diameter of the lining must be reduced by an amount corresponding to the initial clearance between the mandrel and the lining. This forced deformation of the lining generates inside its material reactional forces in the form of tensions tending to counteract the deformation. The tangible result of the presence of such internal stresses in the material may occur in two different forms which may be present separately or in combination.