One of the last steps for the treatment of crankshafts is the sanding. The ultimate form and surface of the connecting rods, main bearings and the crankshaft ends can be fine-tuned. Thus, e.g., rounding-offs are possible between bearing surface and crank web. Also a certain roughness of this surface can be reached.
Centric clamping or pendular movements
There are machines that work on just one particular spot of the bearing (see picture), and there are others that take care of two or more spots at the same time. The first machines are usually employed for the change or repair of engines, the latter in the series production.Sanding the main bearing takes place by clamping the crankshaft along its main bearing axis. For sanding the connecting rod bearings the crankshaft can be reached round on its axis with a suitable eccentric tappet. Another method is to lead them along the grinding wheels with pendulum stroke movements. Discs from cubic drilling nitride (CBN) whose diameter remains relatively steady, are used.
Sanding with corundum, balance by drilling
Usual grinding discs consist of aluminum oxide (corundum), having a diameter of at least 600 mms, for large crankshafts clearly more. They are mostly thinner than the smallest bearing width to be sanded. During the treatment the crankshafts must be cooled down with pure oil or an oil water mixture (emulsion).
Before the crankshaft can be mounted, it must be balanced, polished, and washed. Before the balancing perhaps counterbalances (nowadays also with vibration dampers) and the blanking plugs for the external ends of the oil bores should be mounted. The balancer machine indicates where and how much material must be removed by drilling. There are also crankshafts (without counter weights) with which balancing takes place by adding material.
Polish, wash, mount, examine
After the buffing machine has refined the bearing spots, all treatment residues, especially in the oil bores, are removed during the washing phase. For mounting the cylinder block is turned around. Carefully, the crankshaft is placed into the cylinder block, prepared with half the bearing liners and perhaps axial bearing-half rings. Either now single main bearing lids or screwed on or they are put on in one complete component (mostly automated). The fast series production already now requires the first checks, before the completion of the single crank mechanisms and the assembly of the flywheel. 05/08