Manufacturing process of porous tubular members

Process for making porous tubular elements having two superposed coaxial layers, an external layer of rough texture and of high mechanical strength, and an internal layer of small radial thickness and fine texture, the steps of preparing a tubular shape of rough texture agglomerated by an organic binder, forming a thin layer of fine texture on a rigid core having a smaller external diameter than the internal diameter of the tubular shape, isostatically compressing the tubular shape for radial compression of the shape onto the rigid core, releasing the isostatic compression on the resulting assembly with radial expansion of the tubular shape and of the thin layer adhered thereto away from the rigid core, withdrawing the rigid core from the assembled tubular shape and thin layer and then baking the assembly.