From an open gearing perspective, girth gears (or ring gears) may be supplied using either cast steel or cast ductile iron as the base material. With recent advancements in material properties, including Ferry-Capitain’s development of its proprietary FerryNod® ductile iron grades for girth gear applications, allowing for the use of a minimum design hardness of 340 BHN for both materials, most heavy duty gear applications can be serviced using either material with very few exceptions.
In general terms, cast ductile iron typically provides a cost and delivery advantage over cast steel due to a reduced number of intermediate manufacturing steps, lower processing energy consumption, and a reduced specific gravity compared to steel, resulting in lower weight for an equivalent gear design. Ultimately, the choice rests with the end customer, as the manufacturing facilities are equally adept in all phases of steel or ductile iron gear processing, including all required non-destructive testing and gear tooth verifications.
The girth gears are driven by shafted pinions, which are manufactured from forged steel, and supplied either through-hardened or case-carburized, depending upon application requirements. Pinion teeth are typically finish-ground to achieve high cutting quality and surface finish requirements for long service life.
Gear sets are designed in accordance with ISO, DIN and AGMA standards. A summary of open gearing offerings is as follows:
| Gear materials: | Cast steel, cast ductile iron |
| Maximum diameter: | 16 000 mm |
| Maximum facewidth: | 1500 mm |
| Max. tooth size (module): | 50 |
| Tooth types: | spur, helical, double-helical |
| Pinion materials: | Forged steel (through-hardened or case carburized) |
| Pinion configurations: | Bored, integral (solid-on-shaft) |
| Cutting quality: | AGMA Q10 (gears), Q12 (pinions) |
| Finish-grinding: | up to Ø 4500 mm |