Abstract
First Aid Treatment
for Machine Vibration
Problems
Excessive vibration in industrial machines often leads to reduced
output and eventual loss of overall plant effectiveness. Simple
vibration measurement, even with a limited in-house capability, can
often significantly enhance machine performance — and reduce the
impact of lost production — prior to the engagement of the services
of a vibration expert. This is demonstrated via a typical case study,
in which only the measured vibration spectrum was used to detect
the rotor unbalance resulting from the deposition of scale on the
impeller of an induced-draught fan of a critical rotary cement kiln.
Akilu Yunusa-Kaltungo and Jyoti K Sinha
School of Mechanical, Aerospace and Civil
Engineering, The University of Manchester
Introduction
Sometimes, the reduction or elimination
of faults on critical industrial machines
can be achieved through the accurate
trending of measured vibration data. These
trends often provide good indication of the
slightest deviations from normal operating
conditions, and hence response times
that are adequate for taking appropriate
maintenance decisions. Because most
machine faults possess their own unique
vibration signatures experts in monitoring
the condition of rotating machines have
described vibration-based condition
monitoring (VCM) techniques as being
capable of providing significant lead
times to machine failure, The proper
understanding and utilisation of these
unique signatures can greatly enhance
overall plant effectiveness, through the
implementation of simple first -level
maintenance tasks.
The case study reported here
demonstrates how vibration spectrum
analysis, on its own, was used to detect
unbalance (due to limestone deposits) in
an induced-draught (ID) fan, in a critical
cement process. The unbalance had
caused an excessive vibration, which
reduced hourly cement output, by
approximately 18%, over a period of 53
of measured vibration data and spectrum
analysis, prior to a comprehensive analysis
by an expert.
ROTARY KILN ID FAN UNIT
The kiln ID fan (see Figure 1 and Table 1)
is a critical part of the cement process,
providing the draught, through the rotary
kiln, which is needed for fuel combustion
and eventual production of clinker, which
is later ground with gypsum in the mills to
form cement.
The performance of a cement plant
is most often judged by the output from
its rotary kiln, which is highly dependent
on the performance of the kiln ID fan.
There is a direct
Type
Keith Blackman Gepol exhaust fan
proportionality
(Centrifugal fan)
between ID fan
Size
105 type – 12 double inlet
speed, draught
through the kiln and
Serial number
VW5/39231-02-01 & 02-02
output (the higher
Shaft length
4650mm
the speed, the higher
Impeller diameter
2697mm
the draught and the
higher the amount
Fan weight
5350Kg
of raw feed that can
Number of impeller blades 11
be burnt in the kiln,
Motor manufacturer
VEM Sachsenwerk
which eventually
translates into clinker
Motor speed
993RPM
produced). Optimum
Power
656kW
performance of the
Voltage/current/frequency 690V/674A/50Hz
ID fan is therefore
of great importance
Fan bearings
Cooper self-aligning journal sleeve
to any cement
Table 1: Technical details of the kiln ID fan
manufacturing plant.
days. Upon the
suspicion of
unbalance a visual
inspection and
cleaning of the
fan impeller was
recommended
as a first aid
treatment before
detailed vibration
analysis and rotor
balancing was
carried out by the
experts. The first
aid treatment itself
instantly restored
the fan operation
and cement
output to near
optimum. This
experience supports the belief that major
benefits are achievable through the trending
Figure 1: kiln ID fan and its drive motor
Continued on page 50 maintenance & asset management vol 29 no 2 ME | Mar/Apr 2014 | 49
Continued from page 49
Table 2: Lost sales due to kiln ID fan vibration
ROTARY KILN ID FAN
VIBRATION PROBLEMS
In normal operation the ID fan runs at a
speed of 860 RPM, corresponding to a
kiln feed rate of 80 tons/hour. On the 13th
of June 2013, high vibration readings were
constantly recorded on the fan bearings,
which led to the reduction of the fan speed
to 600 RPM (corresponding to a kiln feed
rate of 70 tons/hour). Table 2 summarises
the lost production and approximate loss
of cement sales as a result of this speed
reduction
Table 2 shows that approximately
11 TPH of clinker (i.e. approximately 12
TPH of cement) production was being
lost due to the reduction of the ID fan
speed, and for a period of 53 days (1272
hours) - corresponding to production and
sales losses of approximately 13,992 tons
of clinker (or approximately 18750 tons of
cement) and £2,756,250 respectively.
Figure 2 Vibration amplitude spectra: (a) at 600 RPM, and before cleaning deposits, (b) at 770 RPM, after
cleaning.
VIBRATION MEASUREMENT
AND DIAGNOSIS
Vibration spectra were then measured at
the fan and motor bearings, and showed a
peak at the rotational speed (1×). Without
further analysis, the detection of this peak
(see Figure 2(a)) triggered an immediate
suspicion of unbalance, which could have
been due to build-up of moist limestone
material from the rotary kiln exit gas
conditioning unit.
In order to reduce the further losses
that would be incurred in preparing for full
fan balancing by an expert, an immediate
visual inspection and cleaning of the fan
impeller blades was recommended. Upon
opening the fan casing, considerable buildups were found on the blades (see Figure
3). After cleaning and restarting the fan, a
second round of vibration measurement
was conducted; this showed a significant
drop in vibration amplitude, even at a much
higher fan speed of 770 RPM (see Figure
2(b)).
The cleaning enabled the fan speed
to be increased from 600 RPM to 770
RPM, which brought a gain in production
of approximately 7 TPH of cement - which,
had it been applied to the previous 53 days
of reduced speed operation, would have
brought a loss reduction of £1,308,888
(8904 tons of cement).
Figure 3: Limestone build-ups on kiln ID fan impeller blades.
CONCLUDING REMARKS
REFERENCE
This case study has demonstrated
the use of simple analysis of vibration
spectra to detect an ID fan unbalance.
Visual inspection and cleaning of the
fan impeller was then conducted,
which immediately enhanced fan
operation, and cement production
rate, by approximately 11%. The
experience highlights the fact that the
limited vibration measurement and
analysis capability often available at
a plant site can provide a ‘first aid’
diagnosis and treatment – to reduce
the level of vibration (temporarily, at
least) and hence increase safety and
reduce production losses before the
intervention of vibration experts.
Kaltungo Y A and Sinha J K (2012). Condition
monitoring: a simple and practical approach
(First Edition) Lambert Academic Publishing,
ISBN 978-3-8473-7807-5. Available on-line at
www.get-morebooks.com.
50 | Mar/Apr 2014 | ME | maintenance & asset management vol 29 no 2
ACKNOWLEDGEMENT
The authors wish to thank the management of
AshakaCem PLC (a subsidiary of Lafarge Cement
PLC) for granting access to the machine used
for the current study, which forms part of Akilu
Yunusa-Kaltungo’s PhD research at the School of
Mechanical, Aerospace and Civil Engineering of
the University of Manchester.
Authors’ email:
[email protected] and
[email protected]