Work on crankshaft crankpins of a Niigata V18 diesel engine has recently been completed on-site by In-Situ Machining Solutions (UK) Ltd for a utilities company supplying electricity for a country in the southern hemisphere.
Removing the crankshaft from the engine due to its remote location from any local machine shop, the work was conducted in-place, in-situ at the power station.
The work consisted of repairing three crankpins/big end bearings in-place in the crank bay of a 6000 kw diesel generator set after the engine suffered a disastrous failure causing heat induced hardening into the three crankpins of the crankshaft and totally destroying the shell bearings and fillet radii of the crankpins.
As the orbital machining system that In-Situ Machining Solutions use rely on fillet radii of the crankpins being in an undamaged condition prior to machining, the damaged fillet radii had to be re-machined on the correct axis of the crankshaft. This is achieved by using a dummy journal or false ring which is clamped around the crankpin, set central and parallel to the axis of the crankshaft by means of an extremely accurate micro level.
Once this has been carried out the orbital turning machine is positioned, set and rotated around the stationary dummy journal via a variable speed arrangement. With radius tool in place the fillet radii at each end of the crankpin were re-machined to a minimum depth to remove the existing damage, these were to serve as reference diameters to machine the damaged crankpins to the requisite under sizes.
After the removal of dummy journal and machine, the same machine was positioned and set into the newly formed fillet radii and rotated around the stationary crankpin. Two of the three crankpins had to be reduced by 5mm and one by 9mm on diameter to make good the damaged surfaces and to remove all traces of induced hardening (up to 690 HB relating to 9mm under size crankpin) and surface cracking.
All new diameters were orbitally machined, superfinished and polished to design tolerances with 0.2 µm Ra surface finish. MPI and hardness checks were routinely carried out as the work progressed.
The fillet radii of all crankpins were re produced and polished to the new diameters and manufactures specification, so too the radii of the oil feed holes.
This contract was duly concluded to the complete satisfaction of In-Situ Machining Solutions (UK) Ltd’s customer.
