PLANETARY GEARS WELL SUITED FOR RETROFIT

Worm gears sets include the worm itself which is meshed with an ordinary looking gear wheel. They provide a simple and compact way to achieve a high torque, low speed gear ratio. However the downside is considerably lower efficiency, which can be as low as 50%.

The planetary gearbox consists of one or more outer gears (planets) revolving around a central (sun) gear. A large outer ring gear (annulus) meshes with all the planets. The axes of all gears are parallel, so input and output shaft will always be inline. Planetary gearboxes are highly efficient (96- 98% per stage of reduction) even at low speeds. They offer high gear ratios per stage, and are highly compact, able to transmit three times the torque of a similarly sized, conventional spur gearbox, because the load being transmitted is shared across multiple planets. Multi-stage planetary gearboxes can deliver extremely high ratios, and efficiencies losses are as little as 2% per stage.

Planetary gearboxes can also be combined with bevel and/or helical gears to offer the best of both worlds in terms of performance characteristics, while also allowing the input and output shafts to be turned through 90 degrees. An example of such a hybrid design can be found in Brevini’s Posiplan gearbox.

COMPACT NATURE

Planetary gearboxes are well suited for retrofit in older, obsolete gear designs, as their compact nature allows them to be designed into the available space envelope with relative ease in most applications.

Posiplan gearboxes can accommodate up to 80,000Nm of torque. Thanks to the inclusion of planetary stages, reduction ratios can reach in excess of 1:70,000 (starting at 1:12), making them suitable where medium/low speeds and high torque are required, such as mixers, conveyors and crushers.

Using the hybrid gearboxes in a shaft mounted configuration offers the flexibility of fitment in any orientation and here they can be used to replace high wearing, and therefore high maintenance, exposed transmission alternatives such as belts, chains and pulleys. It also helps to reduce costs when compared to worm and wheel transmissions, where the demanded input power is reduced in comparison.