ENGINEERING CONCEPTS,
LLC
|
These numbers are very conservative
in the actual savings achieved through a predictive maintenance
program. They are significantly greater when downtime and reduced
production are calculated into the equation to obtain the actual
total saving.
Which program would you prefer? The maintenance costs per year
for each of the different programs are as follows:
• $163,900/year under a reactive maintenance program.
• $119,800/year under a preventive maintenance program.
• $69,300/year under a predictive maintenance program.
(Typical savings for a plant with 200 motors of various horsepower
sizes.)
It should be relatively easy to see that using predictive maintenance
is very beneficial for improving facility standards and profits.
How do you start a predictive maintenance program? First, solicit
management's support. You will need to define goals for this program.
Determine what is the present acceptable failure rate or downtime
allowed compared to where you would like to be. Also, you may
consider what is the value added for your customers in better
delivery and quality products. The question should then be asked,
how much time and effort are you going to invest in this?
The cost and time for establishing your own vibration analysis
may prove to be more than you are willing to spend. The very basic
vibration equipment and accessories start at around $8,000-$10,000
and can exceed $50,000. Then add software at $20,000, plus training
at $5,000. In addition, it usually takes a dedicated individual
approximately three to five years to gain sufficient hands-on
experience to use this equipment effectively.
The other way is to hire a consultant familiar with various predictive
maintenance techniques in order to initiate a predictive maintenance
program at your facility. This will save on the startup costs
and time to acquire the necessary experience if your own maintenance
staff did not have the familiarity with this type of equipment.
Once you have identified the areas of concern you can effectively
schedule and implement a plan of action. The plan of action should
include but is not limited to gathering as much information about
the equipment from the manufacturer or equipment supplier as possible.
This information relates to such things as equipment cross sectional
views number of gear teeth, pump vanes, seats, materials of construction,
bearings (size, style, manufacturer etc.), and process flow diagrams.
Next, establish what the facility's critical equipment is and
then prioritize that equipment in a list that can be accommodated
in a regular schedule biweekly, monthly or quarterly. The frequency
of monitoring is dependent on equipment application, surrounding
environment, horsepower, rpm, available spares and how critical
it is to the operation.
SHOCK PULSE METER
Vibration monitoring is applicable to all types of rotating
equipment. I use two different types of vibration equipment
in monitoring the machine's condition. One is the Shock Pulse
Meter (SPM), which is designed to filter out all machine noise
except noise generated by bearings going over imperfect bearing
surfaces. This was one of the first pieces of testing equipment
that I used over 18 years ago in determining bearing condition.
If there was any bearing damage it would, indicate so. This
piece of equipment in experienced hands can be very reliable
method of detecting roller bearing damage. I have achieved a
99.999 percent reliability rating with this -equipment and could
even predict when catastrophic failure would occur within a
specific time frame with surprising accuracy. Roller bearings
may be at the heart of most equipment, but there are other factors
and conditions that can, cause catastrophic failure.
FAST FOURIER TRANSFORM
The other piece of vibration equipment is the full spectrum
vibration analyzer - fast fourier transform (FFT). This equipmentt
is relatively (10-15 years) new to the general industry and
is ideal for picking up low-frequency vibration that usually
occurrs in industrial applications. The newer analyzers are
very portable, battery operated and easier to use than older
frequency analyzers that were either permanently installed or
not sufficiently rugged enough to be used in industrial environments.
This piece of equipment is used to identify imbalance, misalignment,
journal bearing damage, gear damage, cracking, mechanical looseness,
ball bearing damage, bent shafts, some electrical conditions,
noise, mechanical rubbing and structural resonance frequency.
Obviously this equipment is considerably more sophisticated and
requires more training plus hands-on experience in the field.
The FFT and SPM equipment is what I consider the necessary edge
needed to bring up standards needed for maintaining facilities
in the 21st Century. Other test equipment such as thermography,
thickness measurement meters, along with voltage frequency analyzers
also help to define root cause of the problem.
Vibration analysis is used to perform mechanical diagnostics.
Using SPM and FFT instrumentation the analysis can identify most
mechanical problems. The other methods of temperature, pressure,
flow, and oil analyses were used prior to vibration analysis and
still can be effective today in providing additional. information
to define the root cause of a problem.
The PdM cycle begins with periodic monitoring if the measurement
exceeds the limit; further analysis is required and a recommendation
for repair is discussed with facility's staff. Once the repair
is completed the equipment is tested again to make sure the repair
was successful. This is usually the case and the equipment is
then periodically measured. If not, further analysis is done to
identify the problem and corrective action is taken until measurement
limit is satisfied. In my 20 years of experience, this is where
the real savings are made. and a significant improvement to equipment
reliability is achieved. In other words, paying attention to details
counts.
DOCUMENTATION
Documentation of PdM findings and savings is a very useful management
tool. This is where we identify the actual value of predictive
maintenance programs and it can occur within the first year. However,
greater benefits are usually realized after two years.
This is where I identify predicted machine faults through trend
and analysis charts, the problem severity and list the recommended
actions in order of priority. In addition, a list of actual
faults along with maintenance costs is provided. This is used
to determine maintenance savings.
The following examples are typical results achieved using vibration
analysis in predictive maintenance programs:
Example 1:
Equipment: (3) 25 HP Paper Cutter Blowers
Problem: Hot bearings caused paper dust to catch on fire
on an average frequency of twice per year.
Solution: Provide a continuous bearing monitoring system
and constant lubrication to bearings.
Results: No fires for 16 years and $115,000 per year in
savings and increased production.
Cost to Benefit Analysis of Example 1
• Anticipated savings per chart (Maint. Costs To General Industrial
Machin ery) = $2,160/year
• Realized savings = $115,000/year
• Implementation cost = $10,000 one-time charge
• Monitoring cost = $400/year
Example 2
Equipment: (6) 50 HP Hammer Mills
Problem: Short bearing life -Three months average. Lubrication
failure thought to be the cause.
Solution: Specified bearing fit to shaft. Replace shaft
if bearing surface did not meet specifications.
Results: Improved bearing life from three months to two-plus
years savings = $7,000/year.
Cost to Benefit Analysis of Example 2
• Anticipated savings per chart (Maint. Costs to General Industrial.
Machinery) = $3,600/year
• Realized savings = $7,000/year
• Implementation cost = $150/unit or $600 total
• Monitoring cost = $400/year
SUMMARY
The key benefits of a predictive maintenance program is:
Plant reliability is improved so that unplanned shutdowns are
a very rare occurrence. This is especially true after two years
with this type of program.
Reduced maintenance costs are achieved because labor and material
are scheduled as machine condition indicates. This reduces overtime
and material inventory requirements.
Improved production efficiency by operating production equipment
without unplanned shutdowns. Scheduling of equipment repairs when
it has the least effect on production and shipping schedules.
Improved equipment life cycle cost by scheduling equipment replacement
when machine condition indicates that replacement is needed. Increased
profits are achieved through better utilization of facility resources
and smoother running operation.
William E. Johnson is a consultant at Engineering Concepts,
LLC, a maintenance consulting firm in West Hartford, Connecticut,
that provides creative solutions to today's problems.
Top of Page
|
|
