Specialist drive engineering company SEW-EURODRIVE has developed a flexible range of girth gears to assist with the transfer
of drive torque from the gearmotor to the rotary cylinder, which simplifies manufacturing, transport and installation.
SEW-EURODRIVE general manager for sales and engineering Conrad Pilger notes that the company provides entire drive packages,
including girth gears. This includes the basic gear units, as well as the drive pin-ions, a base, housing, and any other parts
that are required.
"When supplying girth gears, the process involves machine designers and users, in order to determine the best technical and
economic solu-tion for the desired application. SEW-EURODRIVE specialists support the process from the consulting stage right
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 circumfer-ence 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 treat-ment. The size of component parts also
creates disadvantages with re-gard to casting and heat treatment."
In contrast, SEW-EURODRIVE girth gears are split into several identical segments in order to keep the component parts short
and easy to han-dle. "SEW-EURODRIVE uses Austempered Ductile Iron (ADI) for girth gears, which boasts unmatched tensile strength
compared to other ma-terials," he adds.
The decreased size of the girth gear segments reduces the cost for the scrapping of blanks. These blanks can be used without
additional weld-ing or oversizing. In addition, the use of ADI lowers the weight of the girth gears and features an above
average contact fatigue strength thanks to its cold work hardening properties.
Pilger observes: "These cold work hardening properties, when com-bined with an appropriate girth gear size, allows for a more
compact and lighter gear design than traditional solutions. This low weight is im-portant for the handling and assembly of
the girth gear, as well as for achieving circumferential velocity."
The segmented design simplifies handling at the construction site. Due to this design, there is no need for special transportation.
The segment-ed design also guarantees an initial pitch accuracy of ISO 8, which min-imises the vibrations of the girth gears.
Pilger points out that a benefit of the segmented design is that if a seg-ment 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.
"The SEW-EURODRIVE girth gears are suitable for use in a variety of sectors. These include; the energy sector, the pulp and
paper industry, mining, the steel sector, and the cement industry," concludes Pilger.
The girth gears was launched at Electra Mining, which was hosted at the Nasrec Expo Centre in Johannesburg in September 2014.
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