LGDX lateral gear drive for ball mills

Lateral gear drives for ball mills are widespread in cement and minerals plants all over the world. They are known for their compact design and the ingenious mechanical torque split reduces the tooth wide of girth gears. With the latest redesign of our FLSmidth MAAG LGDX Gear Unit we improve the longevity and flexibility of this well-proven ball mill drive.

Ball mills are known worldwide as straightforward and a reliable comminution system, used in cement and mining application. 

Two fundamentally different philosophies exist to drive horizonal mills: While the gear unit and the electric motor of a central drive are located at the front of the mill and take up a lot of space, the lateral drive is placed at the side of the mill. The three-stage spur gear unit includes a mechanical torque split and contributes significantly to the extremely compact setup. The design principle of this specific gearbox has been known for decades and many gear units from different suppliers are in operation around the globe. However, we have redesigned our own lateral gear unit - inventing the impossible: A highly standardised and extremely flexible drive system with increase longevity fitting into every mill setup. No matter whether it is a new comminutions lines or you need to replace an old and worn-out drive unit.

IMPROVING A GOOD SOLUTION
Redesigning a well-proven system is a difficult task for engineers. But our product specialists checked the strengths and weaknesses of the initial design and combined the benefit with new requirements to build the unique three-stage spur gear MAAG LGDX Gear Unit.

The gearing and bearing arrangement are the most important components, which was taken over from the existing design. The driving torque is transmitted via a flexible coupling from the motor shaft to the input shaft of the gear unit. The first gear stage transmits the power into the intermediate shaft, the centre piece of the mechanical torque split. Two helical gearings with opposite helix angels are located on both side of the first gear stage and mesh the output shafts containing self-aligning pinions. Due to girth gear misalignment, unbalanced torque on the two output pinions will cause uneven axial loads in the helical gearings of the intermediate shaft and it moves in the direction of the less loaded side, restoring the balance of torque. The special toroidal bearings installed in the intermediate shaft support the large capacity of axial movements. With this feature our MAAG LGDX gear unit can compensate larger misalignments than any other comparable gearboxes.

FLEXIBILITY AND INCREASED LONGEVITY BY DESIGN
The redesign is also used to increase the installation flexibility of this unique gearbox to almost every imaginable position and setup. Our engineers solved this challenge with a simple but smart solution. We decoupled the gear casing from the foundation frame and used the opportunity to configure the casing symmetrical to the horizontal as well as to the vertical. Now, the very same MAAG LGDX Gear Unit can be installed at the centre line or 40? below your ball mill. The latter reduces construction costs by cutting down on foundation height. In addition, the low, compact foundation is less sensitive to vibration, which contributes to the continued smooth operation of your ball mill. As the foundation frame is not an integrated part of the gear housing, design adaption to existing foundations are very easy to be implemented and support one-to-one replacements of existing gears of varying types and brands.

Finally, our gear unit comes with teeth grounded on both flanks, simplifying spare part management. In case of dual arrangement, where two gear units are installed on both side of large ball mills, one spare unit fits for both sides. And in case of worn- out teeth you can simply turn the MAAG LGDX upside down and operate on the back flank of the gearing, thanks to the symmetricity of the housing. In simple terms, it means that the spare gearing is already included in the original gearbox.

AUXILIARY SYSTEM ROUNDS UP THE PROVEN DESIGN
Based on two decades of operating experience and valuable customer feedbacks, we know that the most limiting factor for bearing and gearing lifetime is related to dusty environment around a ball mill. Clean and fresh lubricants are essential to ensure high reliability and durability, especial for the highspeed bearings and gearing.

For this, our engineers found the perfect solution. Key feature is the sealing of gearbox internals from the dusty environment. A sheet metal covering separates the highspeed gearing and bearings from the girth gear and keeps the internals in a clean and dust-free area. Finally, with two lube oil units we provide a closed lubrication circuit for the gearbox and an open circuit for the girth gear.

In case of replacement projects, we use the existing oil unit to lubricate the girth gear and in addition we supply a new small lubrication unit to feed the gear internals.

Our redesigned lateral gear drive for ball mills, the MAAG LGDX Gear Unit boost your ball mill to the next level of performance. Technical key features like the mechanical torque split, the large capacity to compensate girth gear misalignment and the sealed lubrication system provide the highest available reliability. The symmetrical casing with separated base frame supports every possible setup, including a dual arrangement for large horizontal mills. Together with the grounded back flank of toothing this gear unit includes a built-in spare gear set.

The compact and clever design makes the new MAAG LGDX Gear Unit the perfect solution for replacement of old worn-out gearboxes of almost every type and brand. With a simple adapter flange and the separated and adaptable base frame we can guarantee a one-to-one replacement fitting to the existing mill foundation and girth gear guard. In most cases driving motor, auxiliary drive and the girth gear are still fit for the use together with our redesigned gear unit. With the MAAG LGDX Gear Unit and a minimum of effort and down time for the gear exchange you bring your old mill drive system back to state of the art.

ABOUT THE AUTHOR: Martin Baechler Product Manager, MAAG Gears FLSmidth

(Communication provided by the management of the company)