Re-design results in high torque-low weight gearbox

Written by: Tom Shelley | Published:

After re-designing its range of planetary gearboxes, Brevini can now offer its customers a gearbox with fewer components, better torque ratings and improved reliability. Dean Palmer reports

A power transmission company has completely re-designed its range of high torque planetary gearboxes, resulting in a more reliable product that has fewer parts and much improved torque ratings across the range. Not only is the gearbox technically superior to its predecessor, but it has also helped to slash the company's manufacturing and logistics costs too.

The company is Brevini, an Italian power transmission specialist firm with a UK office in Warrington. The new gearbox range is the 'S' series high torque gear unit that supercedes the PDL range. The S series now incorporates a new epicyclic gear design that increases the power available from the unit without affecting the overall weight of the design, enabling an improvement of up to 60% over the PDL range.

The new gearbox is available in eight sizes - the PDL range consisted of 12 sizes - with up to four reduction stages, offering customers maximum nominal torque outputs from 34,000Nm of up to 370,000Nm. The type of applications these gearboxes are used in include mixers, winches, cranes, apron feeders, filters, extruders, conveyors and thickeners. Industries range from materials handling to mining, sugar, ship loading, cement, offshore oil and gas and chemicals.

Jon Snaith, sales manager at Brevini UK, told Eureka: "The S series really starts where our popular PDL range left off. The PDL units were used in heavy plant and process machinery applications and the design was so efficient it remained largely unchanged for 30 years.

"On a technological level, the design and launch of the S series enables us to offer clients a more complete and technologically advanced range that ensures vast application options and much improved product performance, with a drastic cut in production times and costs," he added.

The re-design didn't come cheap though. Snaith said the company had to fork out six million euros as part of a corporate strategy to "focus on the complex needs of large industry around the globe". Most of the investment went towards a completely new manufacturing facility based in Italy, which, contrary to the growing trend of manufacturers outsourcing their work, fulfils almost the entire manufacturing process, from raw materials through machining, assembly and test.
Because the S series has fewer parts than the PDL range, assembly times have been reduced, delivery times have also fallen from eight to 12 weeks down to five weeks and product quality has improved dramatically.

To improve the cooling characteristics of the new gearbox, the design now incorporates a special roller bearing rather than a needle bearing. Planetary gears can rotate at high speeds therefore oil ways are crucial. New ring gear has been added too. The PDL series had a double-sided spigot that is located with both sides of the casing. The S series has an outer centering ring gear that not only eliminates machining of the spigot, but also increases the diameter of the gearbox and improves the torque rating.

The new design increases the contact area of the planet gears on the central gear, increasing both rigidity and accuracy of the gearbox. This broadens the range of machines and applications that can benefit from a reduced weight and size planetary gearing solution.

The key is the design of the new planet carrier. It is a unique mono-bloc design that is machined from cast iron. The carrier used to consist of a plate on the underside and a plate on the topside, bolted together with a planet pin. This is now a single piece design, machined in only 17 operations. The oil ports (breather, level and drain plugs) have also been made larger, to enable easier and faster filling.

Rather than a single bearing, each stage of the S series gearbox now has a double bearing assembly to cope with the larger torque.

By being able to reduce the size and weight of the gearbox, the new products can be easily integrated into a hydraulic drive system used on mobile machinery and the increased torque available enables the S series units to be used with smaller motors in applications such as mixing.

And for those customers that already have a PDL gearbox, Brevini has designed a whole new range of input shafts, flanges and brakes that enable full interchangeability.

In bench tests, the S series has surprised even Brevini's own design engineers. Comparing the old PDL series gearbox with the S series, test have shown that pitting of the gears and bearing life have been significantly extended. The pitting tests indicated an improvement of nine times the life expectancy of the PDL gears, from 11,380 hours to 102,000 hours. The bearing life also improved from 51,300 hours to 71,400 hours.

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