A lot of applications in the marine industry are still making use of white metal bearings. White metal alloys are made of tin (Sn) and lead (Pb), with traces of antimony (Sb) and zinc (Zn) to give it better wear and lubrication properties.
Bearings of this type can be found in crossheads of large 2-stroke marine propulsion engines, generators, and stern tube arrangements. When these bearings wear out, the old white metal is first molten away and collected. The bearing shell or stern tube is then throroughly cleaned, and made ready to cast a new layer of white metal in.
For most bearings and stern tubes we use a centrifugal casting machine, as in the picture below. We just commissioned our machine 2 weeks ago, and did a few test pieces. The bearing or stern tube is placed in the machine, which keeps it rotating. Molten white metal is cast into the rotating bearing shell or tube assembly, and the centrifugal force ensures an even distribution across the surface.
After cooling, the bearing is pre-machined to almost the nominal size. With an ultrasonic testing device checks are being done to ensure a good bonding between the bearing shell surface and the white metal. Finally the bearing is machined to its correct size.
The machine in the picture is capable of casting bearings up to a length of 2.20 meters. The equipment in the top right corner consists of melting ovens, to prepare the white metal for casting.