By contrast with the usual process (rough-milling and finish-machining of the toothing by means of profile grinding), this large-scale spur gear was first rough-milled using a single-piece miller, rough-finished with a class B hob, and finally finish-machined with a high-precision, class A skiving hob. The result: the profile, tooth trace and surface quality achieved is outstanding, and the required toothing accuracy of 8 (according to ISO 1328) was surpassed by 1-2 classes. The toothing surface roughness (1.6 µm Ra) was also below the required value! All the necessary geometrical and surface measurements were performed on both the gear cutting machine itself and confirmed using a special gear measuring machine.
The throughout time and the machining costs were significantly reduced by comparison with the conventional machining strategy. However, special technical skills and expertise are required for this, as aligning the spur gear in special devices, handling the various milling tools, and fitting the tools into the toothing is a very demanding process. The gear manufacturing team in Hilchenbach was able to meet these requirements in every respect.
The spur gear itself is part of a new converter tilting gear unit for the basic oxygen steelmaking plant at TATA Steel UK in Port Talbot.