Gearbox replacement on a vertical roller mill by Cementos La Cruz

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
co­operative La Cruz Azul, a traditional Mexican cement producer 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-
*)
oil pump
High pressure
oil pump
Additional oil tank
for HP supply
Oil tank
Figure 2: Schematic representation of the MAAG lubrication system
T. Quellmatz, M. Baechler, FLSmidth MAAG Gear AG, Winterthur, Switzerland
CEMENT INTERNATIONAL 4 2/2014 4 VOL. 12
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MAINTENANCE
Figure 1: View of Cementos La Cruz Azul
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 with chain blocks and rolls
Conversion work for gearbox and the ancillary lubrication system started in the middle of February 2013. When the ser­
vice engineer from MAAG arrived on site, the mill had already
been taken out of service and the old reduction gear
removed. Thus, the service engineer inspected the foundation straightaway, and the base plate for the reduction gear
could be cleaned. On the second day, the reduction gear was
already connected to the mill table. � Figs. 4 to 5 show the
gearbox replacement. At the same time, the best location
for the lubrication system was identified. The local conditions
made it impossible to install the tank exactly as originally
planned and the foundation had to be slightly adjusted
(� Fig. 6). However, that was relatively easy to do during the
first week of the replacement. At the same time as fitting
and aligning of the drive engine, the pipework between oil
tank and reduction gear was adjusted to the new conditions.
The pipes were adjusted, welded and cleaned in parallel with
the wiring of the instruments and the power supply of the
engine. After only two weeks, the oil tank could be filled,
and the first rotation direction tests of the lubrication drive
system were carried out. Simultaneously, the mill and its
equipment were also tested. These short tests thus served
as the launch of the commissioning phase in the last two
st
days of February. On 1 March 2013, the new drive system
ran for the first time at full load for approximately three hours.
Following the successful functional test of the instruments,
the mill went immediately into normal operation. One week
later, after being in operation for 40 hours, the service engineer was able to carry out the final on-site tests and check
the contact pattern of the bevel gear.
Final remarks
Figure 5: Installation of the MAAG WPU gear unit under the grinding
table of the mill
CEMENT INTERNATIONAL 4 2/2014 4 VOL. 12
The management of Cementos La Cruz Azul was completely
satisfied with the replacement work. Following the slogan
that a drive unit is only as good as its weakest piece of ancillary equipment, the management was not afraid to replace
the existing drive of the vertical roller mill No. 5. As Alejo
Cruz Salas, the responsible Chief of Service and Maintenance said, the investing of more money in new drive systems is a good way to improve operational reliability and
maintenance.3
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MAINTENANCE
Figure 3: 3D sectional drawing of the MAAG WPU gearbox for driving
the table of vertical roller mills
another manufacturer. The compact design of the MAAG
WPU series makes it easily adaptable to individual conditions
in a cement plant. The dimensions of the new gearbox were
built identically to those of the existing one. Therefore, there
was no need for any on-site adjustment either to the mill or
its foundations.