GIRTH GEARS Girth gears are used to drive large, rotating systems such as dryers, rotary kilns or horizontal mills
A flexible range of girth gears, used to assist in the transfer of drive torque from a gear motor to a rotary cylinder, has been developed by drive engineering company SEW-Eurodrive.
The range of girth gears was launched onto the South African market in September 2014.
SEW-Eurodrive sales and engineering GM Conrad Pilger notes that the company also provides entire drive packages, including girth gears. These include the basic gear units, as well as the drive pinions, a base, housing, and any other parts that are required.
“When supplying girth gears, the process involves machine designers and users to determine the best technical and economic solution for the desired application. SEW-Eurodrive specialists support the process from the consulting stage through to the assembly and start-up,” he explains.
Girth gears are used to drive large, rotating systems such as dryers, rotary kilns or horizontal mills. They are installed around the circumference of these systems and transfer the drive torque from the gear motor to the rotary cylinder.
Pilger states that traditional girth gears generally consist of two to four segments that are assembled together for processing. “This requires large and expensive machines for production, handling and heat treatment. The size of component parts also creates disadvantages with regard to casting and heat treatment.”
In contrast, girth gears from SEW-Eurodrive are split into several identical segments to keep the component parts short and easy to handle.
SEW-Eurodrive uses austempered ductile iron (ADI) for girth gears, which Pilger says boasts unmatched tensile strength, compared with other materials.
The decreased size of the girth gear segments reduces the cost for the scrapping of blanks. These blanks can be used without additional welding or oversizing. In addition, the use of ADI lowers the weight of the girth gears and features an above-average contact fatigue strength, owing to its cold work hardening properties.
“These cold work hardening properties, when combined with an appropriate girth gear size, allow for a more compact and lighter gear design than traditional solutions. This low weight is important for the handling and assembly of the girth gear, as well as for achieving circumferential velocity,” he says.
The segmented design simplifies handling at the construction site. Owing to this design, there is no need for special transportation. The segmented design also guarantees an initial pitch accuracy of ISO 8, which reduces the vibrations of the girth gears.
Pilger points out that a benefit of the segmented design is that, if a segment or part is damaged, it can easily be replaced without the need for dismantling the entire ring. In addition, with the correct dimensioning, alignment, load and lubrication, an ADI girth gear is almost wear-free.
“SEW-Eurodrive girth gears are suitable for use in a variety of sectors, including the energy sector, the pulp and paper industry, mining, the steel sector and the cement industry,” concludes Pilger.