Gearbox replacement on a vertical roller mill by Cementos La Cruz Azul*)
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Gearbox replacement on a vertical roller mill by Cementos La Cruz Azul*) selves as well as on the ancillary equipment, such as the lubrication unit. As a result, the installation of a MAAG lubrication system is advantageous due to its higher level of operational reliability and lower maintenance requirements. � Fig. 2 shows a schematic representation of the MAAG lubrication system. An obvious and significant difference is that the gearboxes from MAAG cannot be misused as oil tanks. The lubrication units are mounted on a separate tank, thus forming a self-contained system. This lubrication unit can then be installed at a distance from the mill, preferably in an enclosed space, where it is protected from the dusty environment of the mill. The tank volume and design are chosen so that a sufficiently long outgassing time for the oil can be achieved. Heat exchanger, filter, pumps and control valves are mounted on top of the tank, creating a compact unit that is easy to install. Introduction Cementos La Cruz Azul is a company belonging to the co­ perative La Cruz Azul, a traditional Mexican cement proo ducer and owner of four cement factories with a total cement production of 8 million t/a of. Cementos La Cruz Azul (� Fig.1), situated in the state of Hidalgo, uses three gear units for driving cement and raw mills that had been delivered by FLSmidth MAAG Gear from Switzerland. The first ones replaced the gearboxes of a horizontal cement mill and a horizontal raw mill in 1993. Both new gearboxes were of CPU type. The latest installation was a WPU type gear unit for another vertical raw mill in 2005. The high-pressure pumps are among the critical components of the lubrication unit. They are necessary to raise the grinding table of the mill hydrostatically. Usually piston pumps are used for this task. However, the narrow tolerances of the delivery pistons make them highly sensitive for oil contamination. The lubrication system has been designed for optimum operating reliability and low maintenance in this regard, too. The high-pressure pumps do not suck in dirty and hot oil straight from the tank, but are purposely supplied with cool, filtered oil. Gearbox replacement Cementos La Cruz Azul also encountered problems with the Three years ago, these benefits led Cementos La Cruz Azul gearbox of a Polysius roller mill type RM/46/26 for raw grind- to the decision to replace the gear unit of raw mill No. 5 with ing, designated as mill No. 5. The gearbox of this mill had required major repairs Oil lines to gear box every five years since its start-up due to Oil lines to axial Heat exchanger problems with the lubrication unit. The bearing of gear box problems with the high-pressure lubrication system, supplying oil to the axial bearDouble oil filter ing, which supports the grinding table of the raw mill had even caused damage to the mill itself. Low pressure Description of the MAAG lubrication system MAAG Gear is familiar with problems regarding lubrication units. The harsh environment and rough operating conditions for vertical roller mills place the highest demands on the reduction gears them- High pressure oil pump Additional oil tank for HP supply Figure 2: Schematic representation of the MAAG lubrication system T. Quellmatz, M. Baechler, FLSmidth MAAG Gear AG, Winterthur, Switzerland Figure 1: View of Cementos La Cru

Figure 6: Preparation of a new foundation for the lubrication unit with new piping at site a MAAG gearbox. Following the positive experience with the first replacements, especially in 2005, the company ordered a gearbox with the product designation WPU and all the necessary ancillary equipment rated for the installed motor power of 2 100 kW with a ratio from 890 to 25.73 rpm. The WPU gear unit is a two-stage planetary gearbox (� Fig. 3). Maintaining the existing dimensions of the connections is a great challenge when replacing a reduction gear from Figure 4: Removing of the old gear unit...