Bearings are critical components of machines and with proper performance
monitoring, imminent failures can be identified and corrected. However,
without a monitoring program in place, and subsequent corrective
actions taken, a single bearing failure can result in full machine
shutdown and countless hours of lost production.
Bearing monitoring is guided by three main senses: sight, sound and
touch. Basic monitoring is conducted through elemental observations.
However, many highly sensitive tools are available that amplify these
observations so they are more noticeable, recordable, and include basic
logic to assist with warning identification.
Visual Monitoring
Monitoring bearings visually through classical methods include observing
lubricant condition, corrosion, and deterioration. Mounted bearings
that are lubricated properly will purge grease from their seals. The
condition of the grease upon purging can indicate improper relubrication
intervals and/or contamination. Dark, cakey or milky grease are visual
signs that relubrication intervals and procedures may be improved.
Evidence of corrosion is a valuable monitoring tool as well. High levels
of corrosion can degrade material strength and performance.
Deterioration of the surface, seals, or obvious physical dimensional
characteristics should also warrant further investigation. These
observations are often signals of wear, heat and other abnormal
performance prior to total bearing failure.
Several monitoring tools commonly available to leverage visual
observations include site gauges for oil lubricated bearings, and
thermal imaging guns. Bearings that are lubricated by oil rather than
grease are often fitted with site gauges, which will give an indication
of the presence of oil and the quantity of oil available to the bearing.
These gauges are practical and inexpensive.
Audible Monitoring
Traditionally, audible monitoring is one of the most common methods of
monitoring machinery because odd noises are obvious indicators of
improper operation, even to the untrained user. It is conducted quickly
through an operator’s daily routines. After all, if a bearing within the
machine doesn’t sound well it usually isn’t well.
The main problems with bystander audible observations is that (1) it
usually identifies the later stages of bearing failure, when planning
downtime for bearing replacement is impractical and (2) when audible
feedback of a single bearing is masked by the overall noise of its
environment. That’s when instruments such as stethoscopes (with
amplification) and decibel level meters are advantageous. Both tools are
available with a wide range of features that include quantified
readings and recording features so bearing performance can be trended.
These tools are also more useful at identifying improper operation at a
less threatening stage of failure.
Bearings should run quiet and smooth; anything different will likely
reflect a flaw or a problem with the bearing itself. Noises such as
grinding or banging should be investigated quickly. These noises may
indicate complete bearing failure and continued use may lead to
catastrophic failure and/or damage to neighboring equipment. Bearing
noises such as light clicking and squealing may indicate looseness,
faults or skidding and should be inspected for cause and remedy.
Audible evaluation is not as sensitive as other monitoring techniques.
It is primarily a method of identifying a failure more so than
identifying poor performance. Additionally, audible monitoring in the
early stages of failure is more noticeable at higher operating speeds
than lower speeds.
Physical (Touch) Monitoring
Monitoring bearings by touch, and then trending the observations against
historical performance is by far the most useful and accurate means for
assessing bearing condition and predicting bearing failure. The touch
method can be used to monitor temperature, vibration, and lubrication.
Operating temperature is the most practical and beneficial monitoring
method for bearings because expensive tools are not required and is
appropriate to all types of applications; slow to high speeds, light to
heavy loads. For example, the average threshold of pain for humans is
approximately 130°F. If it is difficult to maintain hand-to-bearing
contact for several seconds then the temperature is likely above 130°F.
Furthermore, water droplets placed on a bearing housing that quickly
boil will indicate that the bearing temperature will have easily
exceeded 212°F.
There are also many useful tools available to measure and monitor
bearing temperatures. The most common include thermocouples and
resistance temperature detectors (RTDs), both of which can be
permanently mounted to locations on the bearing housing for continuous
real-time monitoring. Temperature switches are also available that can
be utilized for warning and/or shutdown at dangerous operating
temperatures. Many bearing manufacturers offer various permanently
mounted sensors pre-installed in bearing housings in areas that will
most accurately reflect the true bearing temperature, rather than the
housing skin temperature.
Portable thermal imaging tools are also a quick and efficient means to
monitor bearing performance. These tools use infrared thermography to
visually identify variations in temperature over a broad area. However,
the most common portable temperature measurement tool is the infrared
thermometer. Although it does not measure temperatures over a broad
area, they are inexpensive and easy to use.
Monitoring and trending bearing temperature is important because as a
bearing fails, the temperature will continually increase. Trending
temperature over time will help identify a failing bearing in the early
stages of failure.
Vibration analysis is the most information-rich method available for
bearing analysis, and touch can help identify smooth versus rough
operation. As safety permits, feel the housing during operation. Rough
operation, jostling, or grinding may indicate a bearing problem.
You may also consider vibration measurement instruments to not only
identify stages of bearing failure, but also identify overall machine
performance and problems. Sensors mounted to the bearing may include
permanently mounted or portable magnetic base accelerometers,
displacement probes, or velocity pickups. Sensor selection is dependent
upon the bearing speed, sensitivity requirements and the application.
Although vibration feedback is highly beneficial, proper training is
important due to the complexity in data collection and interpretation.
Simple tests can also be conducted on purged grease to detect hard
particle contaminants. Upon relubrication, rub some of the freshly
purged grease between fingertips. Gritty grease may indicate a need to
lubricate more often or wear from a failing bearing.
Many traditional and advanced options are available to monitor and
evaluate bearing performance. Leveraging instrumentation to support
traditional observations is a valuable practice in support of a
predictive maintenance program.
Galen Burdeshaw is Baldor’s customer order engineering manager for DODGE
bearings and power transmission components. For more information, visit
www.baldor.com.
Rolling bearings are high-precision machine elements whose service life
directly determines the performance of machines. However, the actual
service life is determined by many factors. Premature bearing failures
cause costly equipment downtime, sometimes even with very serious
consequences. Bearing experts provide some simple yet practical tips to
optimize bearing performance.
Start with the right choice
Right from the very beginning, design engineers could enhance the
bearing service life by selecting the right bearings for the
application. Many factors — such as loads, rigidity, bearing life
expectation, operating environment, etc. — need to be considered.
Renowned bearing manufacturers have years of experience in different
industrial applications. Developing bearing solutions with their
assistance can contribute to optimal bearing and equipment service life.
Bearings from renowned manufacturers are produced with the latest
technology and undergo stringent quality assurance procedures.
Nevertheless, to guarantee the optimum bearing service life, special
attention should be made in the following aspects: proper storage,
careful mounting and dismounting, adequate lubrication and
re-lubrication, appropriate condition monitoring, timely maintenance,
and sound personnel training.
Appropriate storage
In principal, all bearings should be stored in their original packaging
until being mounted. They should be kept in a clean, non-humid
environment at a fairly stable room temperature. Rolling bearings should
be stored away from dust, water and aggressive chemicals. Vibrations
and shocks could permanently damage the bearings mechanically and
therefore must be avoided during handling and storage.
Basically all bearings must be stored flat. Particularly larger and thus
heavier bearings might be deformed by their own weight if they are left
standing vertically for a long period.
Special care should be taken for the storage of pre-greased (sealed or
shielded) bearings. Such grease could change in consistence over a long
storage period. This could raise the running noise to a certain extent
when put in operation for the first time. Therefore the shelf life of
such bearings should be controlled by an FIFO-system (First In First
Out).
Cleanliness
Cleanliness is paramount when dealing with rolling bearings. The running
surfaces and rolling elements usually have a surface finish roughness
of tenths of microns (1/10 µm or 0.0001 mm). Such smooth surfaces are
very sensitive to damages by contaminants. The lubrication layer between
the running surfaces has usually a thickness between 0.2 to 1.0 µm.
Impurities with particle size larger than the lubricants could get over
rolled by the rolling elements and thus build up localized stresses in
the bearing steel and eventually cause premature material fatigue.
Normal environment dust has a grain size of up to 10 µm, which could
already damage the bearings.
Therefore, a clean, dust-free environment is extremely important for bearing storage and mounting.
Thorough preparation for mounting
Bearings should be mounted and dismounted carefully by means of
appropriate tools. Industry experts estimate that improper fitting
causes 16 percent of all premature bearing failures.
For volume mounting in the production assembly the conditions are
usually strictly controlled, and the suitable equipment is available for
bearing installation. However, for maintenance or replacement work, the
environments could vary. Therefore, thorough preparation for bearing
fitting is necessary in order to ensure the optimum bearing service
life. First of all, the relevant documentation, such as drawings,
maintenance manuals, specifications, etc., should be carefully studied.
All components, such as shafts, distance rings, housings, cups, flanges,
etc., must be thoroughly cleaned and protected from contaminants. The
conditions of such adjacent components should also be checked carefully.
Careful mounting and dismounting
Depending on the application, size and type of the bearing, an
appropriate mounting method — mechanical, thermal or hydraulic — and
tools should be selected. Here are some basic rules for bearing
mounting:
Mounting forces should never be applied through rolling elements. This
could easily lead to localized overloading in the contact area between
the rolling elements and raceways which in turn causes premature bearing
failures.
The bearing surfaces should never be hit directly with any hardened
tools such as hammers, cotter pin drives, etc. This could cause a
breakage or fragmenting of the bearing rings.
The instructions from the respective mounting equipment supplier should always be followed.
About 90 percent of rolling bearings are never removed from the
equipment where they are built in. Usually only the larger bearings
would be removed as part of the scheduled preventive maintenance
programs. Same as mounting a bearing, dismounting should also be
thoroughly prepared. During the dismounting, ensure the adjacent
components such as the shaft or housing are not damaged. Appropriate
methods and tools should be used for dismounting, depending on the
bearing type, size and application.
Appropriate lubrication
The lubricant separates the metallic bearing surfaces such as rolling
elements, rings, and cages and thereby reduces friction, preserves the
metal parts and guards off contaminants and impurities. A wide range of
lubricants — including grease, oil, and solid — is available for
different operating conditions. The correct selection of lubricant is
crucial to ensure optimal bearing and equipment service life.
Bearing lubricants undergo permanent mechanical stressing caused by the
over-rolling of rolling elements. Moreover, lubricants change their
chemical properties over time, particularly at high operating
temperatures and in humid or polluted environments. All these lead to a
gradual loss of lubricating quality.
Therefore bearings have to be re-lubricated at regular intervals to
ensure maximum service life. The re-lubrication interval depends on
operating conditions such as temperatures, running speeds, loads,
environment, etc.
Only in case of pre-greased bearings (shielded or sealed bearings), i.e.
“greased-for-life” bearings, the bearing service life is determined by
the lubricant service life span.
Lubricants must be stored properly according to manufacturers’
instructions. Particular attention must be paid to keep the lubricant
clean from any contamination. Prior to each application, the condition
of the lubricant should be checked carefully.
Condition monitoring and maintenance
Generally rolling bearings are extremely reliable although they do not
have an indefinite life. Like all other important components in the
machinery, they should be inspected and maintained regularly. How often
the inspections and maintenance should be carried out depends on the
importance of the particular application and operating conditions of the
individual equipment.
For bearing arrangements with critical functions, it is advisable to
incorporate a condition monitoring feature at the design stage.
Important parameters of the machine operation such as vibration and
noise can be monitored continuously. Preventive measures could be
planned before breakdowns.
Training
Practice makes perfect. But proper training provides the basis for the
practice. Reputable bearing manufacturers offer various training
programs for commercial, technical and workshop staff. Costly human
errors can be avoided if maintenance technicians possess fundamental
knowledge in handling bearings. Design and product development engineers
can maximize the equipment performance and minimize life-cycle costs by
optimal design of bearing locations.
Bearings are often critical components in all machines. Proper storage,
careful mounting and dismounting, adequate lubrication and
re-lubrication, appropriate condition monitoring, timely maintenance
and, last but not least, sound personnel training are essential to
improve bearing service life, and therefore enhance equipment
performance.
This is an edited article provided by NKE, which is distributed in Canada through Global Bear Inc. For more information, visit www.globalbear.ca.
Most
businesses typically put their energy, resources and investment into
things like product design, sales and marketing, production efficiency,
process control, IT and supply-chain management. With so many important
priorities vying for attention, managing a company’s MRO supply chain
has typically been neglected.
Capital equipment downtime costs huge dollar losses per day, especially
in asset-intensive industries like mining and oil & gas companies.
One of the challenges this sector faces is the complexity and diverse
configurations of the equipment. Often, the technical information
needed to complete a repair of equipment (especially unscheduled
services) is spread across multiple manuals and databases, resulting in
longer downtimes, which impacts maintenance efficiency and in turn
profits.
Maintenance management details procedures that define manpower
scheduling, equipment and tool control, quality control, reporting,
cost control, inventory control, training, loss prevention and
inspection/work status. The maintenance team holds the key to
maximizing assets, minimizing downtime and controlling costs. CMMS
software provides the foundation to deliver efficient, effective
maintenance regardless of the size and complexity of a maintenance team.
Sometimes knowing what not to do is helpful, so the following are seven don’t-dos in MRO master data management (MDM).
1. Free-for-all MRO text descriptions: Unleashing
peoples’ inner Shakespeare by letting each one choose their own words
and styles to describe MRO items results in item descriptions that are
cryptic, differently abbreviated and often unintelligible to anyone
other than the person who created them (and even to them if enough time
passes). For example, is a ball bearing a “ball bearing,” a “brg,” a
“ball brg,” a “bb,” a “b bear,” etc.
2. Taxonomy-free MRO: Having no discernible
taxonomy forces search and analysis activities into labour intensity
and failure. Simple, high-level taxonomies may help somewhat with
search but leave detailed drill-down-type analyses virtually impossible
to accomplish without ad hoc manual or external classification
exercises.
Solution for 1 & 2: Deploy an MDM
solution layer for MRO that automatically generates standardized short
and long item descriptions from key item attribute fields. UNSPSC
taxonomy has become the standard for classifying spending data and B2B
e-commerce transactions; adopting the same standard for MRO item master
classification enables transaction, inventory and consumption data to
be viewed through a single, powerful lens.
3. No ownership: Giving people direct access to create
item and supplier masters in ERP without a master data management
solution layer primed for data validation is just asking for
incomplete, inconsistent and inaccurate data.
4. No workflow for MRO: Workflow makes certain the
right people pay attention and participate in the process. Most
importantly, though, workflow makes it as easy as possible for a person
to comply with policy.
Solution for 3 & 4: Establish clear
owners of MRO item master data. There is no getting around the fact
that enterprises need people with responsibility for item master
stewardship and policies to support them. Niche MDM solutions for MRO
enable just a few data stewards to manage and enforce policies easily
even in large, complex organizations.
5. Improper cash management: Cash tied up in inventory
or spent on non- or negative-value-adding work is not earning returns,
hampering investment in innovation, capital expansion, future business
and growth. It also forces enterprises to finance more working capital
for longer periods than necessary. Solution for 5: Create clean, enterprise-level views
of MRO stockpiles for better visibility and inventory optimization,
thus ensuring better cash management and liquidity scenario.
6. Unknown PM parameters: While preventative
maintenance is typically triggered by testing, visual inspection,
electronic sensors or OEM recommendations for scheduling, dirty MRO
master data makes such a scenario impossible to contemplate.
7. Tying poor MDM to performance: Systematic problems
like poor MRO master data management can affect many people’s
job-performance metrics negatively — in ways that are not under their
direct control. This corrupts the company’s performance management
system, leading to great personal frustration and low morale.
Solution for 6 & 7: Insight into real parts
consumption as it relates to particular machines might go a long way to
making preventative maintenance more science than art. This would also
go a long way in reducing breakdowns.
These failures provide a picture of the vast duplication,
misclassification, inconsistency and inaccuracy that permeates typical
industrial enterprises’ ERP ecosystems related to MRO.
Nupur Agrawal is the analyst and public relations lead with Zynapse. For more information, visit www.zynapse.com.
Custom Made: Custom bearings may be the solution to difficult applications
Have
you ever been in a situation where you knew exactly what bearing you
needed for a troublesome application only to be told that a specific
design or feature was no longer available? Or maybe you’ve changed the
way some of your equipment is loaded and now a shorter bearing life is
driving your maintenance expenses through the roof. Perhaps you’re
discovering that the latest catalogue designs don’t perform as well as
what was previously available and there doesn’t seem to be an
alternative.
These are some of the reasons why there is a growing demand for custom bearings today.
Digging deep
For an example of a custom bearing application, Edmonton-based QA Bearing Technologies Ltd.
assisted a customer that had large pumps removing ground water from a
number of their mine locations. The problem was that as the volume of
water and the depth of the mines increased, they began to experience
reduced life in the fixed bearing location of the pump housing. They
believed if they could separate the thrust load from the existing
spherical bearing, by mating it up with an independent thrust bearing
in the same housing, they could solve their growing maintenance
problem. However, they were having trouble finding a catalogue bearing
with (1) the capacity required within the space available and (2) an
alignment feature to accept the possible shaft and housing alignment
issues.
QA Bearing was contacted by a local bearing distributor, and through
them, they had a number of discussions with the mine engineers to
clearly define the application and the issues. A solution involving
ideas from a number of sources emerged.
By modifying existing equipment (using current inventory) and designing
a custom thrust bearing, all their objectives were realized. The mine
would modify the shaft and produce a special mounting sleeve to accept
both the existing spherical roller bearing and the shaft race of a
custom cylindrical roller thrust bearing. The custom thrust bearing
would have the alignment feature in the housing race and dimensions to
fit within their existing housing with only slight modifications.
During the exchange of design ideas, it was determined that a special
flange should be added to one of the self-aligning housing race
components to assist in holding everything in position during the
horizontal installation. This is the type of value-added feature often
offered at no added expense.
The initial prototype operated for a number of months before suffering
a failure, so the bearing was returned to QA Bearing’s engineering
department for inspection. A complete analysis determined the thrust
bearing had been starved of lubrication. After presenting this to the
customer, they decided to add grease ports to the housing so the thrust
bearing would be assured fresh grease rather than the overflow from the
radial spherical bearing’s grease. Since then, the performance of the
pumps has returned to their initial, acceptable levels.
Cost considerations
It is always prudent to investigate the use of any standard catalogue
product before considering a custom bearing as standard bearings are
more economical and inventory is usually available. Sometimes standard
product can be modified or combined with an additional custom component
to solve smaller problems, such as installation, packaging or
field-retrofit situations.
However, when major dimensional, material or geometric issues are
involved, a completely new bearing needs to be designed and
manufactured. The higher price of low to medium-quantity custom
bearings will require justification from existing high maintenance
costs, downtime expenses or when a priority design project cannot move
forward without finding a solution for a bearing requirement.
Although custom bearings have been around for some time, they have
traditionally required higher production requirements before the
popular bearing manufacturers would consider the expense of designing
and manufacturing them. Tooling charges alone often prohibited requests
for smaller quantities.
Today, however, with 3D modeling design programs and numerically
controlled machining centres, customized bearings can be provided in
low to medium volumes with local engineering support. This is good news
for those who deal with bearings in difficult applications and are
looking for something outside of the normal bearing product lines.
Stephen Thompson, P.Eng., is the vice-president of engineering and
sales with QA Bearing Technologies Ltd., based in Edmonton. For more
information, visit www.qabearing.com.
It seemed as though nothing could stop the squealing.
Not that the Monarch Cement Co.’s huge ball mill wasn’t already loud.
Powered by a 5,000-HP motor, it pulverizes 100 tons of clinker (a
burned mixture of limestone and shale) per hour. But the squealing was
not what Randy Riebel wanted to hear. As electrical supervisor at
Monarch’s plant in Humboldt, Kan., he knew the noise meant the motor’s
bearings were going — again.
In fact, the sound of chronic bearing damage was all too familiar at
the plant, which has the capacity to produce 1,300,000 tons of cement a
year. Since 2001, when the ball mill was new, its motor bearings had
been replaced three times.
“We kept greasing those bearings, but they kept on squealing,” Riebel
recalls. “We knew that if we waited too long, the bearing race walls
would become fluted like they had in the past, and we weren’t looking
forward to another replacement because of all the expense and downtime.
It takes at least 10 days to pull that motor — it’s a major production.
Sometimes we have to hire help, rent a hoist to put it on a truck, and
take it away to be rebuilt. So [in summer of 2009] I decided to try
something else.”
The “something else” was the AEGIS iPRO bearing protection ring, manufactured by Electro Static Technology
(EST). By safely channeling harmful electrical currents away from
bearings to the ground, the company says it extends the lives of
medium-voltage motors and generators, thus improving the reliability of
entire systems. It is available in a range of sizes to accommodate
generator/motor shafts up to 30 inches in diameter.
The ring is suited for medium-voltage motors that drive pumps,
compressors, mixers, conveyors and other machinery used in mining,
wastewater treatment, petrochemical refining and many other
high-current applications. It also protects the bearings of generators
in both utility and on-site power generation systems.
Riebel had been discussing electrical bearing damage with Scott
Wilkins, manager of motor-shop operations for Independent Electric
Machinery Co. (IEMCO), a local motor and equipment repair shop. Wilkins
recommended the iPRO, and Riebel had IEMCO install two of them on the
ball mill motor. While for most large motors EST recommends installing
one in the drive end and insulation on the non-drive end, for some
large motors — especially those that do not have insulation designed
into them or where insulation cannot be easily installed — EST
recommends installing rings at both the drive end and the non-drive end
of the motor.
Riebel and Wilkins chose the iPRO split-ring model, which is designed
to facilitate field retrofits. The mating halves of each iPRO were
installed around the motor shaft without the need to decouple the motor
from the mill. Because IEMCO deal with large motors routinely, its
personnel are well aware of the severe damage shaft currents can cause
to motor bearings.
Mitigating electrical bearing damage
If not diverted, shaft voltages can discharge through bearings, pitting
the balls and race walls. Without long-term bearing protection,
concentrated pitting at regular intervals along a race wall can cause
washboard-like ridges called fluting, a source of noise and vibration.
The eventual result is motor failure.
Ironically, the company says, some products designed to protect
bearings, such as conventional spring-loaded grounding brushes, require
extensive maintenance themselves. Others, such as insulation and
ceramic bearings, can shift damage to connected equipment.
To boost the electron-transfer rate, the iPRO’s entire inner
circumference is lined with multiple rows of specially engineered,
conductive micro fibers. Locked securely in the ring’s patented AEGIS
FiberLock channel, these micro fibers surround the motor shaft,
providing millions of discharge points for harmful shaft currents and
creating the path of least resistance that effectively diverts these
currents away from bearings to ground.
A widespread problem
Contractors and retail home-improvement stores in six states depend on
the Monarch plant. Some of the cement is sold in bulk, some in bags.
And some of it is further processed by the subsidiaries, which
fabricate building products or add stone and sand to produce ready-mix
concrete.
When Monarch was founded in 1908, chunks of blasted limestone (“shot
rock”) up to four feet across were loaded by hand into mule-drawn
carts. Now this limestone is moved by huge front-end loaders, 50-ton
dump trucks and conveyors to be processed by a series of
computer-controlled crushers, kilns and mills until it is as fine as
face powder.
Most of the processing machinery is powered by electric motors, and the
problem of chronic bearing damage is by no means limited to the plant’s
ball mills. Many of the motors are controlled by variable frequency
drives (VFDs), which induce additional high-frequency currents on motor
shafts. A fan or pump motor tends to use less power if the input is
modulated by a VFD, but the benefits of improved efficiency are lost if
the motor keeps breaking down.
Such breakdowns were recurring headaches for Riebel, but because the
two rings installed in 2009 appear to be protecting the bearings of the
ball-mill motor, he has since had IEMCO install the iPRO on nine more
motors that had to be removed from service.
A case in point is a VFD-controlled cooler-vent fan where the 300-HP
motor had to be replaced frequently for almost eight years. Every time,
the kiln had to be shut down for at least a day.
“We’d send the pulled motor out to be rebuilt, but then three to six
months later, we’d have to do the same thing all over again,” Riebel
says. “We didn’t really realize what the problem was. There wasn’t much
information available about electrical bearing damage. We just knew
that bearings would fail and the motor would overheat, but we were not
looking to see why. Again and again, we just sent the motor out, got it
rebuilt and put it back in service. We didn’t know the root cause.”
It is now Monarch policy to have IEMCO add the iPRO ring in the shop
whenever a VFD-controlled Monarch fan motor is overhauled. Another such
installation was on the 2,250-HP motor for an induced-draft (ID) fan
that pulls kiln-heated air through a roller mill to dry the limestone
and shale during the raw grinding process. Other motors include four at
the plant’s kilns, where air is forced in and out: two 2,000-HP ID fan
motors and two 1,000-HP dust-collecting fan motors.
Also, because a cement plant is a very dusty place and many motors are
outdoors, Monarch has begun to specify that some of its new motors must
come equipped with the AEGIS Severe-Duty SGR bearing isolator shaft
grounding ring, another EST product, which has a built-in IP56
non-contact isolation seal to provide extra protection from dust, water
and other contaminants.
Monarch maintenance manager Mark Pily authorized the purchase of the
plant’s first motor with a factory-installed Severe-Duty SGR after
consulting IEMCO’s Wilkins. As of this writing, a 200-HP air-compressor
motor is the only such motor in operation at the plant.
“We want to keep the bearings clean because we push that motor really
hard,” Riebel explains. “We usually lose that motor because of winding
failure. I think most of that is caused by the bearings starting to
fail, which causes the motor to overload.”
An ounce of prevention …
Using a voltage probe and oscilloscope, Riebel periodically takes shaft
voltage readings on all the plant’s motors with grounding rings. He is
pleased with the results because the readings are low, indicating that
the rings have reduced potentially damaging shaft voltages. Riebel also
gives a high grade to the service the plant has received from IEMCO:
“In my opinion, they are by far the best shop we’ve worked with, and
we’ve worked with most every shop in the area.”
Time will tell exactly how much money the rings will save Monarch
overall, but Riebel is convinced the iPRO provides effective, long-term
bearing protection that reduces the costs of downtime and motor
maintenance.
“So far, so good,” he says. “On the 5,000-HP, since the last set of
bearings only lasted a year, chances are we would have noticed problems
by now, but we haven’t had any — no squealing.”
This is an edited article provided by Electro Static Technology. For more information, visit www.est-aegis.com.
Source of Energy: How to select generator sets for todays oil & gas drill rigs
Modern
horizontal drilling techniques used in oil and gas exploration require
reliable and fuel-efficient on-site generator sets to supply electric
power for the draw works, drilling, mud pumping and camp loads. Today’s
oil and gas drill rigs have to drill deeper and faster than ever
before. In addition, they have to use unconventional drilling
techniques such as horizontal drilling and fracturing to improve
petroleum extraction from less permeable geologic structures, such as
oil and gas-bearing shale.
Today’s new drilling realities require more power than conventional
wells and have given rise to the development of the AC/DC silicon
controlled rectifier (SCR) drill rig powered by multiple generator sets.
While AC/DC electric rigs with SCR controls dominate petroleum
exploration today, operators are constantly looking for ways to
increase total power availability, reliability and fuel efficiency,
requiring generator sets to deliver high specific power, low fuel
consumption and less maintenance.
AC/DC rigs with SCR
Oil and gas drill rigs tend to be classified by the type of power used to operate the equipment on the rig.
Mechanical rigs use dedicated diesel engines to provide
motive force for the mud pumps, draw works, rotary drill table and
other loads through a system of clutches and transmissions.
Hydraulic rigs have dedicated diesel engines running hydraulic pumps, which, in turn, provide power to the necessary equipment.
DC/DC electric rigs use dedicated diesel-electric direct-current generators to power DC motors that run the equipment.
While mechanical, hydraulic and DC/DC systems are still used for
conventional and shallower wells, they can be costly to operate and
maintain and lack flexibility. In addition, these older systems are
less reliable. Since individual engines are dedicated to single
functions such as driving the mud pump or operating the draw works, a
failure on any one engine can halt drilling altogether.
Today,
the majority of the new oil and gas drill rigs are AC/DC electric rigs
with SCR controls. These rigs use multiple diesel-electric generator
sets running in parallel to produce the two to four megawatts of power
needed at the drill site, including the power needed for camp loads
such as lighting, heating and air conditioning for crew quarters. Power
is generated as alternating current (AC) and then converted to direct
current (DC) by a unit called an SCR (so called for the banks of
silicon-controlled rectifier semiconductors that it contains). The SCR
unit allows precise control of the flow of power to any of the rig’s DC
motor loads while the generators run at a constant speed.
The number of generator sets running at any one time can be varied,
depending on total load, to save fuel. This configuration is also more
reliable because a failure of one of the generator sets does not
necessarily cause a shutdown of drilling operations even though it may
reduce the total amount of power available. An additional advantage of
paralleled generator sets is that individual units can be taken offline
for maintenance without greatly affecting the drilling operation.
Selection criteria
In response to the power needs of modern oil and gas drill rigs, rig
power manufacturers have developed special generating sets that are
designed to stand up to the rigors of the petroleum patch while
delivering maximum power and fuel economy with minimum maintenance.
When selecting generator sets to power a modern drill rig, look for
these key attributes:
1. Base frame stiffness, durability.
A prerequisite for any electric drill generator set is rugged
construction to take the often-severe operating environments and rough
handling that are typical in the field. The stiffness of the generator
set base is a critical factor in its longevity because any distortion
could affect the alignment of the coupling between the engine and
alternator, resulting in severe vibration and damage. Ordinary
structural steel does not have the necessary stiffness to prevent base
frame distortion under severe handling or if placed on uneven ground. A
base frame that uses high-strength, low-alloy steel withstands the
rigorous operating conditions. A three-point mounting system with
rubber vibration isolators provides the best stability of the engine
generator.
2. Ratings and performance characteristics.
Drill rig generator sets are designed for continuous operation, and
therefore are conservatively rated in terms of their kilowatt (kW)
output. A typical drill rig generator set has a nameplate rating of
about 1,100 kW, although there are both larger and smaller units
available. Since these units are likely to be subjected to severe
service, generator sets with a 10 percent overload capability beyond
their nameplate rating will meet most requirements. While engines on
typical commercial 60 Hz generator sets operate at 1,800 rpm, well
servicing companies have found that engines that operate at 1,200 rpm
have a better record of longevity in the field.
3. Overload capacity.
Due to the severity of the operating conditions in the field, generator
sets are often called upon to deliver their maximum output — and then
some. Generator sets should have at least a 10 percent overload
capability beyond their nameplate rating. For further assurance,
compare the ratio of cylinder displacement to rated horsepower of the
generator drive engine. Generally speaking, engines with a larger
displacement to horsepower ratio combined with a longer piston stroke
will have more built-in reserve horsepower and torque than smaller,
shorter stroke engines of the same horsepower rating. They will also
exhibit greater fuel economy and durability.
4. Fuel consumption.
Since drill rig generator sets operate continuously, fuel consumption
accounts for the largest operational cost. Just a few percentage points
of better fuel economy can add a significant number of dollars to the
bottom line at the completion of a well. Diesel engines tend to be most
fuel-efficient in proportion to their output when operated at 100
percent of their rated load. Engines are typically rated in terms of
their brake specific fuel consumption (BSFC), which varies with the
percentage of rated load. The BSFC rating allows specifiers to compare
the fuel economy of generator sets before the units are in the field.
For 1,200-rpm generators sets with a rating of about 1,100 kW, BSFC
should be less than 200 grams of fuel per kW-h generated. And, for
maximum fuel economy, always operate the generator sets as near their
nameplate rating as possible.
The
“Overload capacity” graph illustrates that different engine
manufacturers have different ratios of cylinder displacement to brake
horsepower (BHP). This ratio is an important factor in a generator
set’s ability to respond quickly to changes in load and maintain
voltage and frequency. Generator drive engines with the highest
displacement to BHP ratio have more reserve horsepower, the lowest fuel
consumption and the best durability.
The
“Fuel consumption” graph shows the fuel efficiency advantage that a
large displacement to BHP ratio confers for Brand X. Fuel is one of the
major operating costs on a drill rig and there are significant
differences in fuel consumption rates between brands of generator sets.
Since diesel engines are most fuel efficient at full power, it is
important to not oversize the generator sets for the job.
5. Oversized alternator.
While the SCR unit on AC/DC drill rigs allows for efficient and precise
control of power to the various DC motors loads, it causes the current
in the system to lag the voltage, resulting in a low 0.7 power factor
(PF) load on the generator sets. Ordinary generator sets are designed
to operate optimally at about a 0.8 PF. The 0.7 PF load on the
generator sets causes field heating in the alternator, and unless the
alternator is properly oversized, damage can result. For a 1,200-rpm
generator set with about 1,100 kW of capacity, look for its alternator
to be oversized to at least 1,750 kVA to meet the low PF requirements.
Also look for a 50-degree C ambient rating and minimum 80-degree C
temperature-rise capability.
6. Control and monitoring.
Precise control of the generator engine’s speed and operating
parameters yields good regulation of the power output and quick
response to changes in the load. Generator sets with engines that
feature an integrated electronic engine governor and electronic engine
management system provide the most accurate control, protection and
monitoring.
These systems will also monitor alarm conditions and protect the engine
from damage. They are also capable of communicating with external
control systems for remote monitoring and control of the generator
sets. This can be convenient when paralleled generator sets need to be
started or stopped to match the load conditions. Mechanical gauges on
the generator set skid should display variables such as lube oil
pressure, oil temperature, engine coolant temperature, engine speed and
operating hours. Also available are units that feature multi-page color
LCD display panels for various performance and status readouts.
7. Maintenance requirements.
All diesel engines require periodic maintenance to ensure good
performance and reliability. Besides regular inspections, the most
important maintenance procedure involves changing the engine oil
approximately every ten days or 250 hours of operation. Generator sets
that feature an engine-mounted lube oil centrifuge as standard
equipment reduce the downtime required for oil changes. This device can
significantly extend the lube oil change intervals, save money on oil
and filters and increase generator set availability.
8. Single-source supplier.
Generator sets from a single-source supplier that manufactures and
tests the complete drill modules in a factory setting provide assurance
of a higher quality product and faster repairs when they are necessary.
There are many drill rig generator sets that are assembled by
integrators using engines from one manufacturer, alternators from
another and controls from still another. If the generator set breaks
down for any reason, parts or service availability can be a serious
problem if an integrator assembled the unit. Drill rig downtime caused
by delays in getting repair parts can be very costly. n
Steve Besore deals with oil and gas applications at MTU Detroit Diesel. For more information, visit www.mtu-online.com. This was previously published in REM.
Shoring up Power: Power-quality solution controls flicker and sag at Port of Sept-Iles
The Port of Sept-Îles is the largest ore handling port in Canada. Open year-round, the port is characterized by its deep waters and 10 km wide semi-circular bay.
The port is composed of 12 docks, six of which belong to it. Each year, nearly 23 million tons of merchandise is handled, composed mainly of iron ore. Alumina, aluminum, petroleum coke, limestone and other material also transit through the port, as well as more than 400,000 tons of petroleum products.
Alumina and coke are offloaded, stored and shipped via conveyors to the nearby Aluminerie Alouette smelter. The seaport equipment used to handle this raw material has 21 motors, varying form 50 to 2,000 HP. Two of the 800-HP motors and the single 2,000-HP motor are required to offload the alumina and coke from the ships and stored in existing silos; this equipment is operated and maintained by Aluminerie Alouette.
Motors at Port of Sept-Îles
• One 2,000-HP motor powers a giant, 4.16-KV suction pump. This pump removes the alumina and coke from the ships and deposits it on conveyors leading to the storage silos. This motor is started with an autotransformer starter at 65 percent of its nominal rated voltage.
• Three 800-HP motors activate the silo blowers. These motors are started across the line.
• Several 400 and 900-HP motors activate blowers used to transport the alumina and coke from the storage silo to the plant. These motors start three to four times daily.
When these large motors start, they draw an inrush current that significantly exceeds their full load current. This occurrence often causes the supply voltage to sag.
To reduce these voltage sags, Schneider Electric had initially looked at the feasibility of using soft starters to accelerate the large motors in conjunction with fixed and automatic capacitor banks. The soft starters would start the motors, the fixed capacitors would help support the voltage during the start, and the automatic capacitor bank would correct the Power Factor during the normal seaport operation. This solution was not considered feasible because:
The voltage sags would exceed the required three-percent limit; and
Trying to further limit the inrush current with a lower voltage and starting current would exceed the motors’ thermal limits.
The most feasible solution, proposed and implemented by Schneider Electric, was a medium-voltage hybrid VAR compensator (HVC) rated at 3,950 MVAR. This solution injects real-time capacitive reactive power during the motor start-up to support the voltage.The medium-voltage HVC is a mix of active harmonic filter technology (AccuSine) with a fixed or automatic de-tuned capacitor bank (MV6000) that can inject reactive power into a network with a one-cycle response time. The AccuSine can inject lagging or leading VARs within 16.6 ms. The MV6000 supplies a fixed amount of VARs to the system and the AccuSine either cancels these VARs when there is no load, or adds to these VARs when there is an increased amount of VARs required by the load.
The primary sizing calculation done by Schneider for this project was based on the motor lock rotor amps. The company collected real-time measurements on site during the motor start-ups, including current, voltage, real power (kW), reactive power (kVAR) and apparent power (kVA). With this data, Schneider constructed a computer model with which they could simulate the effect of real time VAR injection in the electrical network at 4.16 KV.
“We liked this solution for several reasons,” says Richard Lapierre of Alouette. “First and foremost, this cost-effective solution meets Hydro-Québec’s voltage sag limit of three percent at the PCC, and corrects the power factor during our seaport operations. Second, it is compact enough to fit in the electrical room, thereby avoiding contact with airborne contaminants (coke and alumina). Third, we appreciated being able to run the motors while the HVC was being installed, thereby minimizing production stoppage.”
This is an edited article provided by Schneider Electric Canada.
From All Directions: Pros and cons of tapered roller bearings
Tapered
roller bearings have been in existence since the early 20th century and
remain an ideal, versatile roller bearing for many applications, can
tolerate multi-directional loads and operate well at high speeds.
The nomenclature and load ratings differ slightly for tapered roller
bearings compared to ball bearings or other types of roller bearings.
Instead of an outer ring, tapered roller bearings have a cup; and
instead of an inner ring, tapered roller bearings have a cone. The
remaining bearing components, the cages and rollers, are referred to
similarly in other bearings. The tapered roller bearing’s rollers have
a distinct shape; a tapered shape, hence the name. This tapered roller
has a line contact between the raceways of the cups and cone(s), as
opposed to oval or circular contacts with spherical roller and ball
bearings respectively.
Another primary difference between tapered roller bearings and other
bearings is the difference in capacity definitions. Dynamic capacity is
often the ideal method for defining a bearing’s loading ability as it
resists fatigue. Dynamic capacity (C) is the load at which 90 percent
of a given group of bearings will meet or exceed one million
revolutions. For tapered roller bearings the dynamic capacity (C90) is
defined at ninety million revolutions. At first glance the lower values
of the tapered roller bearing’s published dynamic capacities appear
deficient to the dynamic capacities of other roller bearings due to the
different base of comparison. To compare C90 to C on the same base,
multiply C by 0.259.
Advantages
There are many advantages of tapered roller bearings. For starters,
since the roller is tapered and angled between cups and cones, it can
easily support a variety of directional loading. Its ability to support
combined heavy thrust and radial loads surpasses spherical, cylindrical
or needle roller bearings. Most standard mounted tapered roller
bearings can support pure radial, pure axial and any combination of
those two types of loading scenarios without modifications.
The tapered roller bearing’s geometry allows true rolling motion of the
roller between the raceways, which means the rollers are unlikely to
skid or slide when unloaded. Other roller bearings have minimal load
requirements to insure the roller actually rolls and does not slide
between the raceways. Skidding or sliding is harmful because it sweeps
the lubrication away from the surfaces, which will lead to wear and
premature failure.
Tapered roller bearings have high load capacities. These capacities far
exceed ball bearing limitations and rival similar spherical roller
bearing capacities.
Disadvantages
However, it is important to note that there are a few areas where
tapered roller bearings have disadvantages. Tapered roller bearings do
not tolerate dynamic misalignment well. Due to raceway and roller
geometry, spherical roller bearings support dynamic misalignment much
better. Tapered roller bearings also have static misalignment
limitations however, in some applications the bearing housings can be
designed so the bearing can self align properly.
One of the other disadvantages is with speed limitations. Although
tapered roller bearings can operate successfully at high speeds, ball
bearings can exceed the tapered bearing’s speed limitations and
generate less heat at the elevated speeds.
Many tapered roller bearings are available as mounted units such as
pillow blocks, flanges, piloted flanges, and take-up units. These
mounted units are often pre-lubricated and offered with a variety of
seals for a broad range of applications. The cones of these mounted
units are configured specifically for quick bearing-to-shaft
installation through setscrew, tapered adapter, eccentric locking or
clamp-style attachments.
Mounted tapered roller bearing units are typically offered with two
rows of opposing rollers. The rows can be oriented as either converging
or diverging orientations. Converging orientations are often provided
with two separate cups and have contact angles where the apexes of each
row of rollers converge near the centerline of the bearing assembly.
Diverging orientations are often provided with two separate cones and
have contact angles where the apexes of each row of rollers diverge
away from the centerline of the bearing assembly. Converging
orientations are the most common because the assembly is less involved
and provides slightly more forgiveness to misalignment. Diverging
orientations are considered to be more stable and resistive to moment
loading.
Unitized configurations are also common for tapered roller bearings and
allow for misalignment expansion capability. Unitized configurations
are tapered roller bearing assemblies mounted within a housing that has
a spherical outside diameter or rib. These units are then assembled
within a flange or pillow block. The assembly works similar to a
ball-and-socket joint where the unitized bearing assembly swivels
relative to the anchored bearing housing. Common configurations allow
for up to 4° of static angular misalignment. These unitized assemblies
are also available with expansion capability to prevent preload from
thermal shaft growth or contraction.
Tapered roller bearings are common in many applications. Gearboxes and
gear sets, particularly those utilizing helical gears, use tapered
roller bearings due superior performance with multi-directional
loading. Mounted tapered roller bearings are common with fans exposed
to high axial forces, agricultural equipment, mining and aggregate
machinery, aggressive machines used with wood products, forest and
paper products as well as general industrial applications.
Galen Burdeshaw is Baldor customer order engineering manager with Dodge bearings and PT components. For more information, visit www.baldor.com.
THE BUSINESS OF MAINTENANCE: Put power into your power transmissions
In today's competitive economy, there's even more pressure on oil and gas companies to justify asset fleet purchases and reduce maintenance costs. And getting the most out of heavy-duty vehicles working in the field is critical. If you're in the market for more power under the hood, Caterpillar recently launched the new CX31-P600 and CX35-P800 transmissions for petroleum applications.
Chicago - Connect with more than 400 distributors and manufacturers of power transmission/motion control products with the just-released Power Transmission Distributors Association (PTDA) 2009 Membership Directory.
Bearings are critical components of machines and with proper performance
monitoring, imminent failures can be identified and corrected. However,
without a monitoring program in place, and subsequent corrective
actions taken, a single bearing failure can result in full machine
shutdown and countless hours of lost production. 
Most
businesses typically put their energy, resources and investment into
things like product design, sales and marketing, production efficiency,
process control, IT and supply-chain management. With so many important
priorities vying for attention, managing a company’s MRO supply chain
has typically been neglected.
Have
you ever been in a situation where you knew exactly what bearing you
needed for a troublesome application only to be told that a specific
design or feature was no longer available? Or maybe you’ve changed the
way some of your equipment is loaded and now a shorter bearing life is
driving your maintenance expenses through the roof. Perhaps you’re
discovering that the latest catalogue designs don’t perform as well as
what was previously available and there doesn’t seem to be an
alternative.
It seemed as though nothing could stop the squealing.
Mitigating electrical bearing damage
Modern
horizontal drilling techniques used in oil and gas exploration require
reliable and fuel-efficient on-site generator sets to supply electric
power for the draw works, drilling, mud pumping and camp loads. Today’s
oil and gas drill rigs have to drill deeper and faster than ever
before. In addition, they have to use unconventional drilling
techniques such as horizontal drilling and fracturing to improve
petroleum extraction from less permeable geologic structures, such as
oil and gas-bearing shale.
Today,
the majority of the new oil and gas drill rigs are AC/DC electric rigs
with SCR controls. These rigs use multiple diesel-electric generator
sets running in parallel to produce the two to four megawatts of power
needed at the drill site, including the power needed for camp loads
such as lighting, heating and air conditioning for crew quarters. Power
is generated as alternating current (AC) and then converted to direct
current (DC) by a unit called an SCR (so called for the banks of
silicon-controlled rectifier semiconductors that it contains). The SCR
unit allows precise control of the flow of power to any of the rig’s DC
motor loads while the generators run at a constant speed.
The
“Overload capacity” graph illustrates that different engine
manufacturers have different ratios of cylinder displacement to brake
horsepower (BHP). This ratio is an important factor in a generator
set’s ability to respond quickly to changes in load and maintain
voltage and frequency. Generator drive engines with the highest
displacement to BHP ratio have more reserve horsepower, the lowest fuel
consumption and the best durability.
The
“Fuel consumption” graph shows the fuel efficiency advantage that a
large displacement to BHP ratio confers for Brand X. Fuel is one of the
major operating costs on a drill rig and there are significant
differences in fuel consumption rates between brands of generator sets.
Since diesel engines are most fuel efficient at full power, it is
important to not oversize the generator sets for the job.
Tapered
roller bearings have been in existence since the early 20th century and
remain an ideal, versatile roller bearing for many applications, can
tolerate multi-directional loads and operate well at high speeds.
