Selection of the right material can play an important role in the reduction of noise. Design engineers either re-design the gear or specify tighter dimensional tolerances in order to reduce noise. But these two methods can only add to the cost of the finished product; not to mention an unsatisfied end user. The only alternative is to go for Cast Iron that can bring down the cost significantly. Cast Iron, however, is often overlooked as an engineering material though it has higher machining properties. The general misconception is that Cast Iron is brittle and weak. While ductile iron is robust, grey iron is comparatively brittle. Graphite in grey iron is shaped like a flake, but in ductile iron, it is shaped in the form of small rounded nodules.
Ductile, Gray to all types of Cast Iron possess intrinsic sound damping properties and can lower noise. The graphite content of Cast Iron is attributed to the noise reducing property. Precipitated graphite particles absorb noise vibration; therefore ductile iron shows greater damping capacity compared to steel. It is precisely for this reason that cast iron is selected to make gears. Cast iron, in this case, has the much required mechanical properties in the gear tooth as well as the quantity of damping. Cast Iron, in the area of automobile manufacturing, goes into the manufacture of a four-cylinder engine that is used as the balance shaft. The result showed comparatively reduced noise characteristics. Earlier, gear was manufactured using steel. The noise reduction was achieved without any alterations made to the gear’s design or dimensional tolerances. The change of gear material to ductile iron was a key factor in cost reduction
In cases where extra strength is needed, switching to ductile iron is not advisable due to fatigue failures. Further, ductile iron does not go into the manufacture of gears that are usually subjected to high impact forces. Before making a switch to ductile iron, any manufacturer needs to know about the safety factors as well as the impact of forces on the gear.
However, many gear manufacturers go with Cast Iron. This is because manufacturers who set up to machine steel bar stock are concerned about the initial pattern cost. Sand moulds are required to make castings, and mould cavity patterns are used to produce the shape of the mould. To form cast iron, the part iron is poured into the cavity. Besides, they require machining centres and bar feeders designed to handlebars. Therefore, it is required to retool the machining centre if they are looking to switch to iron castings. Some of the general problems when switching to cast iron are shrine, slag and sand porosity and inclusions. Due to the graphite content, it can also dirty the machine. Whatever be the drawback, cast iron, undoubtedly, is the preferred material for the reduction of gear noise.