Ten Reasons to go with planetary gearboxes

Planetary gearboxes are hardly new, but for some reason a surprising number of designers regard them with suspicion. Here then are Ten Reasons to go Planetary...

Getting more performance from a smaller working envelope and saving weight and cost in the process are objectives shared by most design engineers.

Certainly those who design mobile plant, machine tools, handling systems, conveyor systems, sugar processing plant, steel rolling mills, agitators, industrial robots et al.

Why these in particular? Well all of these and more are areas where planetary gearboxes are demonstrating the benefits of alternative gearing technology.

Planetary gearboxes are hardly new, but for some reason a surprising number of designers regard them with suspicion.

Why this is so is still a mystery, but one theory is that prejudice against their use could result from the innovative design that makes them so successful.

The traditional (and erroneous) thinking is that older, more conventional, gearing layouts are more reliable.

Also, in a failure situation they can be brought back into service quicker (albeit temporarily) by welding or hand dressing of gears.

If this is indeed the line of thinking then it overlooks certain crucial facts.

Firstly, computerised selection as used by Brevini, can ensure that a planetary gearbox will last the lifetime of the machine.

Secondly, planetary gearboxes are perfectly balanced units and are extremely reliable in service.

Finally, other than routine oil changes, no maintenance is required on Brevini planetary gearboxes throughout their design life.

One application that proves conclusively the reliability aspects of planetary technology is the long-term use of Brevini gearboxes to provide high torque and low speed operation on the drive heads of scrapers and thickeners in the water treatment industry.

In this extremely arduous application the Brevini gearbox rotates a drive head mechanism at speeds of as low at 0.05rpm, 24 hours a day, 365 days a year.

The torque required for this operation, to drive the rakes through the settled solids, could be anywhere 1000Nm to 50,000Nm depending upon tank size and other factors.

The planetary drive is around 90% efficient and, critically is able to provide the extremely low speeds required without any loss of efficiency.

Set against worm gears with a rating of less than 50%, this enables smaller motors to be used, for the same torque output and thus produces measurable energy savings.

Apart from the efficiency and cost savings it provides, the drive is also comfortably able to last the 100,000 hours, or even 150,000 hours working life, required by the water companies.

Nor are there any lubrication problems arising from the drive operating at low speeds, conditions which can reduce the reliability of conventional gear units.

Reliability apart, what are the other major considerations that a designer or engineer takes into account when selecting one type of gearbox in preference to another? Certainly, in terms of planetary technology, the task of the designer has, until now, been complicated by the fact that, no formalised list of the advantages of the technology has been produced.

In an effort to rectify this situation, and to make the case for planetary technology, Brevini has now produced such a list (see below).

It compares planetary gearboxes with conventional gear units and highlights ten areas where the planetary can provide real advantages to the OEM and user, both in specifying and using the unit.

Ten Reasons to go Planetary - 1 Compact size - Planetary gearboxes can be half the size of conventional gear units.

They also fit where others will not, which translates into easier installation and neater design solutions.

2 Weight - Weight savings can be as much as 60%, which can mean lighter and smaller support structures.

3 Superior Efficiency - While some transmissions can be less than 50% efficient, planetary units are 90% plus.

This enables a smaller motor gearbox combination, and lower running costs.

4 Low Maintenance - Other than routine oil changes, no maintenance is required through the design life, not even replacement bearings.

This eliminates the need to hold costly stocks of spares.

5 Extended Life - Using computerised selection, Brevini technical staff are able to select planetary units to last the machines total design life.

6 Design Flexibility - The modular construction of Brevini planetary units allows standard modules to be combined to 'customise' the gear unit for non-standard applications.

This reduces the requirement for specialised components.

7 Cost Effective - Volume production of standard planetary stages enables significant economies of scale and highly competitive pricing.

8 Fully Reversible - The construction of a planetary gear stage allows it to be equally efficient in either direction.

This is an advantage if the machinery regularly runs in clockwise and anti-clock wise cycles.

9 Coaxial Arrangement - The coaxial configuration of the input and output shafts of planetary gear units to be installed in line with the motor and machine.

Brevini's universal adapter system allows almost any type of motor to be direct mounted to the gear unit.

10 Short Deliveries - The modular construction means that standard parts can be held in UK stock to allow a large number of different units to be compiled virtually off the shelf.

Even the larger gear units (output torques greater than 100 KNm) can be supplied within 12 weeks..

(This was Engineeringtalk's Top Story on 9 January 2002).

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