Archive | 2008

249

1:48 am
December 2, 2008
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Solution Spotlight: New High-Performance Compact VFDs

Upgrading from a winner to a winner…

Mitsubishi Electric Automation has introduced the D700, its latest compact variable frequency drive (VFD). Replacing the corporation’s popular S500E VFD, this “new-from-the-ground-up” model offers a host of benefits for users—even for existing S500E customers who will find it easy to move over to the D700.

mitsubishi-vfdAccording to the manufacturer, the S500E and D700 have the same ‘footprint,’ which means mounting arrangements will be unchanged. All the terminal markings and parameter numbers that the two drives share will be the same. Moreover, while the D700 provides superior dynamic performance to the S500E, it can copy the very same performance characteristics of the S500E. Thus, machines that have been tuned over the years to work with the S500E will not see the difference. Moreover, the D700 will still be able to operate with any programming originally developed for the S500E.

Among other things, the D700 features:

  • Improved speed range… 150% or more motor torque is now possible at 1 Hz using General Purpose Magnetic Flux Vector control, giving a smooth open loop speed range of 60:1.
  • More interoperability… Communications include Modbus RTU as well as Mitsubishi Electric’s own RS 485 programming protocol (supported as standard).
  • Remote operation… Drive I/O can be remotely operated over any supported network, regardless of what the drive is doing.
  • Easy mounting… In smaller panel spaces, the D700 can be “bookshelf ‘ mounted without a gap in between; DIN Rail mounting also is possible.
  • 100kA fault-withstand rating… This simplifies panel construction.
  • Safety stop function… The D700 comes standard with a safety stop circuit allowing the removal of a previously required external contactor and is EN951-1 Category 3 and IEC60204-1 Stop Category 0 compliant.
  • RoHS compliance… This means that the D700 is approved for installation on Europe-bound machines.
  • High accuracy… Analog inputs/outputs provide master/ slave control.
  • Maintenance-free operation… Intelligent fan control, fewer moving parts, more robust bus capacitors and custom-made intelligent power modules are all designed to have a 10-year operating life so that users can install the D700 and forget it.

The D700 is covered throughout North America by Mitsubishi Electric’s five-year limited warranty program. MT

Mitsubishi Electric Automation, Inc.
Vernon Hills, IL

For more info, enter 30 at www.MT-freeinfo.com

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326

1:44 am
December 2, 2008
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Viewpoint: Evidence-Based Asset Management

andrew-jardine

Andrew K.S. Jardine, Director Centre for Maintenance Optimization and Reliability Engineering, University of Toronto

Coronary artery disease is a leading cause of death in the world. A substantial amount of effort is spent preventing, diagnosing and treating this disease, with treatments including a variety of drugs and surgeries.

Common sense suggests an effective treatment for a restricted artery would be to expand the artery and support it with a tube to prevent further blockage. The tube is medicated with the same drugs taken orally that also help to prevent restricted blood flow.

The procedure, called “angioplasty and coronary stent implantation” is expensive, but nevertheless proved to be a popular choice made by patients and physicians for the preventive treatment of stable, long-term heart disease.

There was only one problem with this common sense preventive solution: it is inefficient.

The evidence says stents are no better than the cheaper and safer option of medication alone. The evidence in this case consisted of properly collected and analyzed data on groups of patients who underwent the two treatments. The process by which medical decisions are based on the best available research is called evidence-based medicine and is considered the gold standard in modern medical practice.

What does this have to do with asset management? Common sense and expert judgment play a role in maintenance and replacement decisions, but the underlying assumptions should be tested with data that has been properly collected and analyzed. We call this process Evidence-Based Asset Management, or EBAM.

Four key asset management decision areas are:

  1. Preventive maintenance strategies;
  2. Inspection decisions;
  3. Capital equipment replacement decisions;
  4. Resource requirements.

The value of EBAM to each decision area is easy to see. Consider preventive maintenance. A reliability engineer communicated to me the case of a piece of equipment whose components were being preventively replaced according to manufacturer recommendations. The engineer kept careful records of component lifetimes and failure causes. He concluded:

“I found that the hazard rates obtained were decreasing…due to poor quality components and questionable maintenance practices. Overhaul on these components has been suspended… Quality issues are also being addressed.”

The asset management decision was based on the best available evidence.

Consider the following capital equipment replacement decision. A fleet operator I met from a large marine cargo handling firm in the U.S. with approximately 2400 pieces of powered lift equipment. He said:

“We have no corporate strategy on equipment repair/replacement, lease/buy, economic service life, etc. These decisions are based often on strength of personalities and number of mechanics’ complaints, not objective analysis… On the plus side, we do have a CMMS and 4 years of ‘pretty good’ equipment information and cost history.”

Conclusion: the available data should be used to implement an EBAM approach.

I feel very fortunate to be linked with the blue-chip organizations that support the Centre for Maintenance Optimization and Reliability Engineering (C-MORE). They have made it their goal to adopt EBAM, from training right through to the support for development of evidence-based decision-making software tools. I encourage all organizations to do the same. MT


jardine@mie.utoronto.ca

The opinions expressed in this Viewpoint section are those of the author, and don’t necessarily reflect those of the staff and management of MAINTENANCE TECHNOLOGY magazine.

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246

1:40 am
December 2, 2008
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Connecting With Safety And Savings In The Pickle Industry

This Wisconsin-based pickle processor has seen significant payback from its new approach to connecting and disconnecting pumps, conveyors and other equipment.

Van Holten’s Pickles certainly knows its stuff. Founded in 1898, the company has been producing individually wrapped Pickle-in-a-Pouch products since 1939. Originally based in Milwaukee, Van Holten’s moved to a larger plant in Waterloo, WI in 1956. That’s where it recently opened a new 53,000 square foot facility—and where it now produces approximately 18 million individually pouched pickles annually.

These days, Van Holten’s is finding that connecting and disconnecting pumps, conveyors and other equipment in its operations has become much easier and safer than in the past, simply by using combination plug/receptacle and disconnect switches. The company has turned to Meltric Decontactor™ Series switch-rated plugs and receptacles that allow workers to safely make and break electrical equipment connections, even under full load. And, because they are UL switch and horsepower rated, the Decontactors meet NEC requirements for a motor “line of sight” disconnect. These devices also cost less than conventional connectors over the longterm.

Yesterday and today
Previously, Van Holten’s connected its many pumps and conveyors with twist type or pin-and-sleeve connectors partnered with separate disconnect switches. The combination of salt, moisture, acid and heat used in the pickling process caused the switches and plugs to fail regularly. Safety also was an issue because of the potential for a worker to insert or remove a plug without first verifying deenergization at the local disconnect switch.

decontactor

Decontactor plugs feature an OFF switch/pawl that can be used as an emergency disconnect switch for conveyors.

Project Engineer Arland Wingate points out that the company does not hard wire most pumps and conveyors because being able to quickly disconnect and reconnect equipment for repair or replacement helps to minimize downtime. Electrical safety during equipment change-outs used to be a concern but is less so now because the Decontactors’ safety shutter and internal arc chambers prevent exposure to live parts and arc flash. The new plant provided an opportunity to upgrade and standardize on the Decontactor plugs and receptacles. Wingate explains: “When I first saw them, I thought they would work well for us, but we weren’t ready to change everything over. The new plant gave us an opportunity to include the conversion in the budget, so we made it our standard.”

According to Wingate, the heat and harsh atmosphere ruined the previous plugs because the brass contacts often corroded together.

He points out that the long-term operating cost was a big factor in selecting the Decontactors, which feature more corrosion resistant solid silver-nickel contacts. “Our company has been in business for 100 years, and I try to look at the long term when I buy things for the plant. We had been buying a lot of the previous plugs for replacements. When we designed the new facility, we looked at ways to keep the cost down without sacrificing safety or our other needs,” he says.

In addition to the long-term cost savings in replacement plugs, Wingate liked the Decontactors’ integrated disconnect switch, which meant there was no need for a separate plug and disconnect box. “It not only costs less,” he notes, “it eliminates one more thing to go wrong in our environment. Before, it was too easy for someone to disconnect something and forget to lock it out properly.” That’s not a problem with the Decontactor plugs. They can be locked out just by inserting a lock through a hole in the plug shroud.

Going forward
While moisture and other harsh conditions are prevalent in many areas, some of the NEMA 4X rated Decontactors are located in areas where they regularly are subject to being splashed with brine. According to Wingate, there have been no problems during the year they have been installed. “We’ve not had any scoring of the contacts because of the quick break, and we don’t have to worry about arcing or corrosion buildup.”

Most of the applications at Van Holten’s are on 440-volt power, with some on 230-volt equipment. In addition to the production equipment, the company also uses some Decontactors on maintenance equipment such as welders and saws. Several have even been installed along one exterior wall, where they are used to provide power to a large cucumber-loading machine when it needs to be moved along the back of the building.

Wingate reports that the company is planning to triple the size of its tank yard soon and will convert it to the Decontactors as part of the project. “We will use them on pumps and conveyors, and also on the low-pressure blowers we use to help move product along,” he adds. MT

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3507

1:35 am
December 2, 2008
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Solving Electrical Problems with Thermal Imaging

Today’s thermal imagers, which produce live images of the heat emitted from equipment, are rugged, easy to use and much more affordable than just a few years ago. This makes them highly practical and cost-effective solutions for everyday electrical maintenance. To use one, a qualified technician or electrician points the imager at the equipment in question, scans the immediate area for unexpected hot spots, then squeezes the trigger to capture a specific image. When the inspection is complete, the saved images can be uploaded to a computer for closer analysis, reporting and future trending.

fluke-thermalAlthough thermal imagers may be simple to operate, they are most effective in the hands of a qualified technician who understands electrical measurement and the equipment to be inspected. For anyone using this type of imager, the following three points are especially important.

• Point 1: Loading
The electrical equipment being inspected must be under at least 40% of nominal load in order to detect problems with a thermal imager. Maximum load conditions are ideal, if possible.

• Point 2: Safety
Electrical measurement safety standards still apply under NFPA 70E[1]. Standing in front of an open, live electrical panel requires personal protective equipment (PPE). Depending upon the situation and the incident energy level (Bolted Fault Current) of the equipment being scanned, this may include:
– Flame resistant clothing
– Leather-over-rubber gloves
– Leather work boots
– Arc flash rated face shield, hard hat and hearing protection, or a full flash suit

• Point 3: Emissivity
Emissivity describes how well an object emits infrared energy or heat. This affects how well a thermal imager can accurately measure the object’s surface temperature. Different materials emit infrared energy in different ways. Every object and material has a specific emissivity that is rated on a scale of 0 to 1.0. The higher emissivity the better it is for thermal imagers to report accurate temperatures.

Objects that have high emissivity emit thermal energy well and usually are not very reflective. Materials that have low emissivity are usually fairly reflective and do not emit thermal energy well. This can cause confusion and incorrect analysis of the situation if the user is not careful. A thermal imager can only accurately calculate the surface temperature of an object if the emissivity of the material is relatively high, and/or the emissivity level on the imager is set close to the emissivity of the object.

Most painted objects have a high emissivity of about 0.90 to 0.98. Ceramic, rubber and most electrical tape and conductor insulation have relatively high emissivities as well. Aluminum bus, copper and some kinds of stainless steel, however, are very reflective.

The good news is that most thermal imaging performed for electrical inspection purposes is a comparative—or qualitative—process. Users typically do not need a specific temperature measurement. Instead they should look for a spot that is hotter than similar equipment under the same load conditions—spots that are unexpected.

troubleshooting-electrical-systemsTroubleshooting electrical systems
There are specific things to check when chasing breaker problems or load performance issues. Once repairs are complete, another thermal scan should be obtained. If the repair was successful, the previously detected hot spot should have disappeared. (Note: Not all electrical hot spots are loose connections. For a correct diagnosis, it’s smart to have a qualified electrician either perform the thermal scan or be present while it’s completed.)

Three-phase imbalance
Capture thermal images of all electrical panels and other high-load connection points such as drives, disconnects, controls and so on. Wherever higher temperatures are discovered, follow that circuit and examine associated branches and loads.

Compare all three phases side-by-side and check for temperature differences. A cooler-than-normal circuit or leg might signal a failed component. More heavily loaded phases will appear warmer. Hot conductors may be undersized or overloaded. However, since an unbalanced load, an overload, a bad connection and harmonics all can create a similar pattern, it is important to follow up with electrical or power quality measurements to accurately diagnose the problem. (Note: Voltage drops across the fuses and switches also can show up as unbalance at the motor and excess heat at the root trouble spot. Before it is assumed the cause has been found, double-check with both the thermal imager and a multimeter or clamp meter current measurements.)

Connections and wiring
Look for connections that have higher temperatures than other similar connections under similar loads. That could indicate a loose, over-tightened or corroded connection with increased resistance. Connection-related hot spots usually—but not always—appear warmest at the spot of resistance, cooling with distance from that spot. In some cases, a cold component is abnormal due to the current being shunted away from the high-resistance connection. Broken or undersized wires or defective insulation also may be found. The NETA (Inter-National Electrical Testing Association) guidelines say that when the difference in temperature (DT) between similar components under similar loads exceeds 15 C (~25 F), immediate repairs should be undertaken.

Fuses
If a fuse shows up hot on a thermal scan, it may be at or near its current capacity. Not all problems are hot, however. A blown fuse, for example, would produce a cooler than normal temperature.

Motor control centers (MCC)
To evaluate an MCC under load, open each compartment and compare the relative temperatures of key components: bus bars, controllers, starters, contactors, relays, fuses, breakers, disconnects, feeders and transformers. Incorporate the foregoing guidelines for inspecting connections and fuses and identifying phase imbalance.

Transformers
For oil-filled transformers, use a thermal imager to look at high- and low-voltage external bushing connections, cooling tubes, and cooling fans and pumps, as well as the surfaces of critical transformers. (Dry transformers have coil temperatures so much higher than ambient, it’s difficult to detect problems with thermal imagery.) Incorporate the previously noted guidelines for connections and imbalances. The cooling tubes should appear warm. If one or more tubes are comparatively cool, oil flow is probably restricted. Remember: like an electric motor, a transformer has a minimum operating temperature that represents the maximum allowable rise in temperature above ambient (typically 40 C). A 10 C rise above the nameplate operating temperature will probably reduce the transformer’s life by 50%. (Note: For a thermal imager to detect an internal transformer problem, the malfunction must generate enough heat to be detectable on the outside. That means that a malfunctioning bushing connection, for example, will be much hotter than the surface temperatures read by the imager.) MT


Reference
1. For PPE guidelines, reference NFPA (National Fire Protection Association) Standard 70E Tables 130.7 (c)(9) (a), (c)(10), (c)(11).

Michael Stuart manages thermography products for the Fluke Corporation and has previous experience in electrical and insulation resistance testing. Telephone: (800) 760-4523; e-mail: michael.stuart@fluke.com

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407

12:55 am
December 2, 2008
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Reliability Business Case: Conversion Costs

Need a better way to show the contributions of a reliability effort to your bottom line?

Most people in the reliability profession probably have heard the saying that the maintenance of today is the capacity assurance of tomorrow. Many in our field would agree that business trends already have taken the industry to that day of the future. Our teams no longer maintain the status quo. What we do is strive to assure our assets’ capacity by constantly optimizing equipment availability to make the product when it is scheduled to be made. We work hard to make sure that machines don’t generate scrap. And we ensure that the equipment runs as close to the expected productions speeds as possible. For today’s capacity assurance managers, overall equipment effectiveness (OEE) works very well as the key performance indicator of our success.

Our business leaders understand the importance of the reliability effort, too. But, they also understand the need to control manufacturing overhead. As a result, they must clearly see how a reliability effort contributes to the bottom line. What’s the best way to make this type of business case?

Keep it simple
A reliability effort does contribute to an increase in the return on assets. The most direct and easy-to-understand impact resides in the expenses section of the income statement. There, it is apparent that the greatest part of the reliability financial benefit lies in the conversion costs reduction.

Let’s think in simple terms. We expect a machine to be available for a certain period of time to make a specific number of product units. When the hard work of our maintenance teams leads to higher machine reliability, the company spends less time making those expected units of product. The machine is operational and the operators are standing by. Their labor costs in dollars per unit already are accounted for.

1208-reliability-case-table1

Table 1. Basic Conventions Used To Translate Logic Into Dollars

Given this scenario, we now have three choices: send the operators home, reassign them to do something else or make more units of product by running the machine and incurring related material costs and all other conversion costs but the labor. In other words we achieved a reduction in labor costs per unit of product or generated additional capacity to make more units of product without having to account for the labor.

Is that simple enough? Let’s see if we can translate that logic into dollars and cents. The basic conventions that we will start with are shown in Table I.

Suppose that a business needed to make X number of product units and scheduled N number of hours to do it. In actuality, however, the equipment only ran at UT1 uptime. So, to make the intended units of product the number of run hours was:

N + (1 – UT1) • N = (2 – UT1) – N (1)

Similarly, at improved UT2 uptime the time to make needed number of units would be:

(2 – UT2) • N

We can express the Total Direct Labor Costs without Uptime Improvemetn in two different ways by using either hourly wage or the labor costs per unit:

TLC1 = W • (2 – UT1) • N = VL1 • X (2)

Solving for W:

W = (VL1 • X) / ([2 – UT1] • N) (3)

Applying the same reasoning:

W = (VL2 • X) / ([2 – UT2] • N) (4)

Therefore:

([VL1 • X] / [(2 – UT1) • N]) = ([VL2 • X] / [(2 – UT2) • N]) (5)

VL2 = VL1 • ([2 – UT2] / [2 – UT1]) (6)

Plugging in the above findings to derive the conversion costs per unit of product we will get:

CCU1 = V + VL1 (7)

CCU2 = V + VL2 = V + VL1 • ([2 – UT2] / [2 – UT1]) (8)

And now, if we apply some more basic algebra, we easily come to the conclusion for the reduction in conversion costs per unit:

= CCU1 – CCU2 = VL1 • (UT2 – UT1) / 2 – UT1

1208-reliability-case-fig1

Fig. 1. Conversion costs variance due to uptime change (copyright Mike Shekhtman 2008)

Formula 9 can be expressed in a verbal statement shown in Fig 1.

Any reliability practitioner after looking at that statement and thinking for a few minutes would say: “I knew that!” There is no doubt that it is somewhat intuitive for the insiders. For maintenance and engineering managers, it is quite empowering in that it can be applied to any time interval and any area of the production process or piece of equipment to prioritize the allocation of resources. This statement also appears to be a straightforward tool for quantifying the reliability objectives for the business leadership and showing them the gains triggered by the improved uptime. Let’s demonstrate.

Say, for example, that last year a manufacturing area produced 100,000 widgets at $8.00 of labor costs per every widget and at 85% physical availability or uptime. This means that due to equipment reliability issues the machines ran only 85 out of every 100 scheduled hours. This year, our hypothetical maintenance organization has committed to increasing the uptime to 90% by improving reliability. Then:

VL1 = 8 ($/Widget)    UT1 = 0.85     UT2 = 0.90

If we plug in the numbers from Formula 9, the maintenance objective for the reduction in conversion costs per unit for this year is:

= 8 • ([0.90 – 0.85] / [2 – 0.85]) = 8 • (0.05 / 1.15) = 0.35 ($ / Widget)

reliability-case-table2

Table II. Semi-Random Examples of Calculated Conversion Costs Variances Related to Uptime Changes Caused by Increased or Decreased Reliability

Accordingly, the total commitment by maintenance for this year to reduce labor costs and consequently the overall conversion costs at the same production levels of 100,000 caused by either increased or decreased reliability. The widgets is:

0.35 ($ / Widget) • 100,000 = $35,000

Table II shows a few semi-random examples of calculated conversion costs variances related to uptime changes caused by either increased or decreased reliability. The numbers in Column 6 of this table result from plugging all values into Formula 9.

If absorption is a company’s costing method of choice, the fixed costs are treated as product costs just like labor. Since in that scenario fixed costs are assigned to each unit produced, the same uptime driven proportionality factor that is demonstrated in Fig. 1 can be utilized to derive the fixed costs variance. The improved uptime will demonstrate a favorable variance for the reporting period.

Crunch your own numbers
It may make for an interesting exercise to apply this approach to a few hypothetical scenarios for your own business—and crunch some numbers of your own. Some results may appear puzzling, though.

One important thing to keep in mind is that the numbers are not constant. What this means, more often than not, is that companies take advantage of improvements in reliability and uptime by making more units of product. That additional capacity without added labor costs translates into higher labor productivity, which prompts lowering the number for the labor costs per unit produced for the next round of calculations. So, ultimately, the model needs to be readjusted for every consecutive time period.

It is possible that such a model can be taken further to try to predict the impact of various reliability trends on the bottom line. It also is possible—especially when analyzed on a smaller scale—that the savings may never materialize into something measurable. But then the numbers can be reported to management as intangible labor productivity gains.

In its present form—with all other factors but uptime being irrelevant—the method seems to be surprisingly simple and elegant. We can choose to analyze a quarter or a month or even a week. We may decide to run the numbers for the separate machines or for the entire plant or multiple plants.

As long as the data being used are accurate, the numerical results will show what the business leadership really needs to know. Hopefully, this will help enable business teams to effectively rank priorities and make the right choices on funding and resource allocation. MT


Mike Shekhtman is a senior regional reliability engineer for the Goodyear tire manufacturing North American region, based at Goodyear Tire and Rubber corporate headquarters in Akron, OH. Prior to joining Goodyear earlier this year, he had spent 20 years in the manufacturing industry in various capacities in maintenance management and engineering. A licensed Professional Engineer and a Certified Maintenance and Reliability Professional, Shekhtman holds an MSME degree from St. Petersburg State Polytechnic University in Russia and an MBA from Cleveland State University. Telephone: (330) 796-7245; e-mail:mike_shekhtman@goodyear.com Continue Reading →

1390

8:06 pm
December 1, 2008
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Turning To Active Balancing To Enhance Fan Reliability

Continuous monitoring for and correction of centrifugal-fan imbalances during operation is an especially cost-effective way of eliminating vibration problems.

From the time centrifugal fans first entered the marketplace, they have been subject to vibration-related problems. These problems range from simple unbalance conditions caused by mass variations on the fan rotor to more complex issues related to shaft alignment, bearing fatigue and resonance. In many cases, excessive vibration levels in fans lead to unplanned outages to perform maintenance. While these outages are necessary, they also can be very costly from both a maintenance and lost-production standpoint.

vibration_frequency-cpm

Fig. 1. This vibration severity chart shows the commonly accepted criteria for vibration levels in most rotating equipment.

Some levels of vibration are acceptable—and standards have been established for these acceptable levels at corresponding operating speeds. The chart in Fig. 1 reflects commonly accepted criteria for vibration levels in most rotating equipment. To effectively deal with vibration issues in such equipment, however, it is necessary to implement a condition-based maintenance program that can identify problems before they turn catastrophic.

Condition-based maintenance
A condition-based maintenance program requires an initial review of the following common causes:

Shaft misalignment…
Proper alignment between a drive motor shaft and a fan shaft needs to be addressed during new fan installation or if a shaft/rotor assembly is replaced. Misalignment between a drive motor shaft and fan shaft typically results in a 1X and 2X harmonic component of vibration.

Often, misalignment conditions will lead to excessive levels of axial vibration. Because most fans are not equipped with axial vibration probes, this is often not detected unless the 2X vibration component exists. Misalignment can be caused by careless installation of new equipment, but is more commonly caused by bent shafts or improperly seated bearings.

Resonance…
Resonance problems are often two-fold on large fan assemblies. The first component to address is critical speed. Mapping of critical speed typically is handled during new fan design. Most fans operate below first critical speed. The factors in avoiding critical speed in fan design include overall rotating mass, span between bearings and necessary operating speed to produce the required airflow. If a fan operates above first critical speed, careful attention must be paid to vibration levels as the fan accelerates to operating speed and coasts down to a stop from operating speed. Excessive levels of vibration while passing through a critical speed can lead to severe damage to bearings, seals and other equipment.

The second factor to address is structural resonance, which can be quite challenging to predict. Every structure has a natural frequency at which it will resonate. If a fan operates at a structural resonance point that is not corrected, it can lead to component failures. Structural resonance can occur at 1X operating speed or at a harmonic frequency (2X, 3X, …). Structural resonance will vary, depending on operating speed. It can be identified through a signature plot that maps vibration amplitude versus frequency versus rotational speed.

Mechanically loose connections…
Looseness in any mechanical connection between bearing caps, bearing pedestals or foundations can cause excessive vibration levels or amplify an already existing unbalance problem. A mechanically loose connection will yield harmonic levels of vibration (2X, 3X, …) and may also yield sub-harmonic levels of vibration (X/2, X/3, …). Vibration caused by mechanically loose connections frequently is misdiagnosed due to the presence of sub-harmonic vibration levels.

A second type of vibration caused by mechanically loose connections can take place if there is looseness in the connection between the fan rotor and fan shaft. This will induce an extremely high unbalance-related vibration level that is not necessarily at 1X operating speed. In most cases, properly designed interference fits between the rotor hub and the fan shaft can be implemented to avoid this condition.

Cracked shafts or rotors…
Crack propagation in either a fan shaft or rotor can lead to one of the most dreaded failure modes in any type of rotating equipment: catastrophic failure. Luckily, early crack detection is possible if vibration trending and analysis is done on a piece of equipment.

The common symptoms of a crack propagating in a fan are an emergence and growth of a 2X component of vibration along with a change in the phase and amplitude of the 1X vibration component.

Rotor mass unbalance…
Rotor mass unbalance is the most common cause of excessive vibration in rotating equipment and fans. The primary symptom of rotor mass unbalance is a high 1X vibration level.

Rotor mass variation leading to an unbalanced condition usually stems from the following:

  1. Variations in manufacturing that lead to unevenly distributed mass in the fan rotor
  2. Exposure to high air stream temperatures that cause uneven growth of the fan rotor
  3. Deterioration of the fan rotor caused by either high-speed particle collisions or corrosive material passing through the fan
  4. Uneven material accumulation or fouling on the fan rotor. Large chunks of material flaking off and causing sudden, excessive vibration can compound this issue.

Excessive amounts of rotor mass unbalance can have two detrimental effects on fans. The primary concern is the excessive long-term, fatigue-inducing beating forces incurred by running at elevated vibration levels. The second (although uncommon) concern in fans is related to the equipment’s passing through critical speeds on startup or coastdown. Excessive amounts of rotor mass unbalance also can amplify other vibration conditions, such as a loose bearing cap or instability in a foundation.

Correcting unbalance in fans
Removing particulate build-up from the rotor or performing a mechanical balance of a fan are ways to reduce the amount of unbalance in these types of units. Both of these actions, however, require that the fan be stopped.

Two methods for making a mass unbalance correction to compensate for 1X vibration include using a manual balancing system, often portable, that can be deployed on multiple pieces of equipment, or using a dedicated active balancing system.

Manual balance corrections…
A manual balance correction—or off-line balancing procedure—is a common action that takes place during new equipment installation or during a maintenance procedure in a planned outage. This six-part process is as follows:

  1. Clean the impeller of any particulate build-up.
  2. Measure the initial vibration phase angle and magnitude.
  3. Stop the fan and add a known trial mass at a known location.
  4. Start the fan and measure the resultant vibration phase angle and magnitude. Use this information to compute the fan sensitivity or response to unbalance.
  5. After completing the foregoing calculation, stop the fan and determine the proper amount of mass for the balance weight and where to attach the weight.
  6. Attach the weight and restart the fan.

Steps three to six may be repeated multiple times depending on the operator experience level and the equipment sensitivity.

Although a manual balance correction typically is necessary for new equipment installation and during planned outages, it does have drawbacks—especially if there is a need to employ this technique regularly between planned maintenance intervals.

  • The amount of time required to perform a manual balance correction can be difficult to determine.
  • Multiple starts and stops may lead to shortened life expectancy of the motor and other associated equipment.
  • Variable-speed applications can result in different balance corrections needed for different operation speeds.
  • Although uncommon in most fan applications, the excessive vibration levels experienced while equipment passes through a critical speed can lead to excessive bearing and seal wear.
balance_ring

Fig. 2. The balance ring in an automatic or active balancing system is permanently attaced to the fan’s shaft, and contains internal weights that can be repositioned as needed to offset imbalance.

Automatic or active balancing systems allow users to continuously monitor fan vibration levels and make balance corrections without shutting down the fan. They consist of a control system, balance rings, actuators and vibration sensors. The balance ring, permanently attached to the fan’s shaft, contains internal weights that can be repositioned to offset the mass unbalance and compensate for excessive 1X vibration levels (Fig. 2).

Because active balancing systems continuously monitor fan vibration levels, the user must program a fixed tolerance range for the vibration level. When vibration levels reach the upper limit of the tolerance range, the control system determines the necessary magnitude and phase angle of the required balance correction. The control system sends power and data to a stationary actuator that communicates with the rotating balance ring. The actuator commands the internal weights in the balance ring to move to new positions to offset the unbalance and bring the 1X vibration level back within the tolerance range. Fig. 3 provides a schematic of a typical system configuration.

active-balance-configuration

Fig. 3. A typical active balancing configuration

Active balancing systems are used primarily on three types of induced draft (ID) fans: overhung single-inlet, center-hung single-inlet and center-hung double-inlet. The most important reason to use an active balancing system on these fans is that such a system allows the operator to maintain low levels of vibration as the fans continue to run. That can have an enormous impact on both production and maintenance.

The most visible benefit is the ability to improve fan reliability and availability. This leads to reductions in both scheduled and unscheduled maintenance outages used for more conventional means of correcting unbalance problems, as well as the potential for extensions in planned maintenance outages. Secondary benefits include extended equipment life—i.e., motors, bearings and seals last longer—and reduced fuel and power consumption from limiting the number of starts and stops of the process.

One of the most useful pieces of information obtained from an active balancing system is an event log that tracks use of the balancing system. The log will display beginning and ending vibration levels and phase angle, as well as the amount of time required to complete a balance correction. This information can be accessed through Windows-based control software.

The balancing system also can be accessed via a remote interface module that allows the system to be linked to a plant’s network through an Ethernet connection. This provides a secure connection for remote users to download history data, access and change parameters, and monitor vibration levels.

A vibrating fan solution
When running 121-in. diameter, 13-ton double-wide, double-inlet ID fans, it is particularly inefficient to have emergency shutdowns for unplanned maintenance.At U. S. Steel’s Fairfield Works in Fairfield, AL, the level of vibration on fans responsible for pulling air, gases and materials off the basic oxygen furnace would creep to unacceptable levels during operation. With furnaces heating steel to nearly 2800 F, these enormous fans are critical in successfully turning out product.

At this facility, imbalance and high vibration levels caused by excess build-up of particulate on the fan rotors resulted in chunks of build-up falling off the rotor. Maintenance team members had to clean and manually balance the fans at least every three months. Moreover, it took three to five balance attempts to successfully perform a manual fan balance. This often resulted in a violation of the time recommended between starts on the motor, creating a high potential for motor failure. And, when a fan was stopped due to high vibration, it would result in a production shutdown.

Since the installation of balancers, Fairfield Works has averaged one scheduled maintenance shutdown and one interim cleaning per year. Because a typical shutdown can last eight to 12 hours, savings are significant. Beyond saved revenue and time from reduced shutdowns, the online balancing technology continuously maintains the balance level of the fans below 0.8 mils, as compared with the previous 1.0 mils low-level field balance. Additionally, motor and bearing life was increased, resulting in fewer motor rebuilds at roughly $200,000 each.

What’s in it for you?
Active balancing systems can help solve one of the most common causes of excessive vibration in rotating equipment by compensating for rotor mass unbalance. These corrections, made while equipment remains in service, help a company avoid costly outages. Reductions in 1X vibration amplitudes, caused by rotor mass unbalance, also help minimize the effects of other vibration conditions, such as looseness in bearings or inadequate stiffness in bearing pedestals or foundations.

An active balancing system provides detailed trending information for outage planning and for identifying other vibration problems that are not strictly displayed at 1X operating speed. Proper use of these types of systems allows organizations to increase equipment availability, while running more stable production processes and safer, more reliable operations. MT


Andy Winzenz, a staff engineer for LORD Corporation based in Cary, NC, has spent 11 years in the balancing and vibration industry. Telephone: (919) 468-5981; e-mail: Andy_Winzenz@lord.com

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7:56 pm
December 1, 2008
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Uptime: We're Only As Strong As Our Weakest Link

bob_williamson

Bob Williamson, Contributing Editor

For want of a nail, the shoe was lost.
For want of a shoe, the horse was lost.
For want of a horse, the rider was lost.
For want of a rider, the battle was lost.
For want of a battle, the kingdom was lost,
And all for the want of a horseshoe nail…

This old proverb—which can be traced back to the 1390s—has been used countless times in a variety of ways over the centuries. Benjamin Franklin, for example, included a version of it, preceded by the words, “A little neglect may breed great mischief,” in Poor Richard’s Almanack in 1758. (That’s when the American colonies were tangling with the English Parliament.) Many years later, during World War II, the verse was framed and hung on the wall of the Anglo-American Supply Headquarters in London to remind everyone of the importance of seemingly trivial repair parts and inventory replenishment. I’m borrowing it here to make the same point to today’s capacity assurers: We’re only as strong as our weakest link.

Case in point
It is highly unlikely that anybody, upon seeing an unshod horse, ever thought a kingdom would actually fall because of a missing nail. In the heat of the battle, hardly anyone would have time to notice the work of the lowly blacksmith. Few would truly appreciate the value of a properly fitted horseshoe affixed with nails when the horse is in full gallop—except the smithy himself. When catastrophe strikes, however, 20/20 hindsight really brings the nail into a much sharper focus, and the smithy gets the blame. There are real-life historical examples of the truth behind this proverb.

Consider this: On the bloodiest day in American history—September 17, 1862—the Civil War Battle of Sharpsburg (also known as Antietam) resulted in nearly 23,000 casualties. After crossing the Potomac River into Maryland on September 9, 1862, Confederate General Robert E. Lee divided the 45,000-man Army of Northern Virginia and spelled out the location for each group on written dispatches (Special Order No. 191) sent to various commanders. All but one of these dispatches were delivered by couriers on horseback to the commanders. The one that didn’t make it accidentally dropped from the courier’s pocket when he he stopped along the way to relieve himself. Unfortunately for General Lee, this secret dispatch—in an envelope wrapped around three cigars—was found by a Union soldier a few days later. When it was delivered to Union Army Commander George B. McClellan, it gave him and his 90,000-man army the exact locations of their enemy, leading to a strategic Union victory—in other words, for the want of a rider…for the want of a message. (Of course, it is important to remember that such root-cause thinking is typically seen in hindsight. Who would have thought that cigars in a message envelope would have led to foiled military plans and to the loss of a Civil War battle.)

Take-aways for today
Horseshoe nails are not self-installing, so let’s go back to the original proverb and explore days gone by to see what happens before the “nail” is ever struck. (My apologies to Ben Franklin and others before him.)

For want of an apprentice, the blacksmith was lost.
For want of a blacksmith, the shop was lost.
For want of a shop, the hammer was lost.
For want of hammer, the nail was lost.
For want of a nail, the shoe was lost.
For want of a shoe, the horse was lost.
For want of a horse, the rider was lost.
For want of a rider, the message was lost.
For want of a message, the battle was lost.
For want of a battle, the war was lost.
For want of a war, the kingdom was lost,
All for the want of an apprentice…

The point here is that while the nail is truly important, the apprentice who is in training to properly shoe the horse with all the skills and knowledge of a blacksmith is by far the most important element of sustainable success. The success of a kingdom rests with apprentices in training! Think about that point a bit deeper—before the apprentice.

What if the society in the days of horse-mounted warriors had not really valued the work of the “lowly” blacksmiths. What if that society had not encouraged its younger generation(s) to become skilled at the blacksmith’s trade? How would horses have been properly shod? Could they have performed their tasks with ill-fitting, loose and missing shoes? Would riders be lost in battle? The deeper meaning of this proverb is simple: The end result depends entirely on the functional capability of every component, every element or preparation. A process is only as strong and reliable as its weakest link. That’s a powerful message for today’s business world.

Most of us recognize that the goal of any mechanized, capital-intensive business is to consistently and safely deliver highly valued goods or services to the customers at the lowest cost and the highest profits. Without reliable equipment and processes, competitive advantage is lost regardless of the type of capital-intensive business. So, let’s analyze this expanded age-old proverb and see how it fits in today’s business of maintenance and reliability.

The apprentice represents a dedicated, young, eager, able student—the assistant and trainee. The blacksmith represents a skilled journeyman mechanic or technician who also keeps the shop as a well-organized and stocked workplace. The hammer represents the proper tools used in working with the nail, or a bolt that holds the motor in alignment. The horseshoe represents the motor for a critical pump. The horse represents the machine or unit of equipment. The rider represents the in-control production line or manufacturing process. The message (or mission statement)—on time, high-quality, low-cost producer—guides us to success in a battle for on-time customer deliveries. The war most businesses are in is for market share. And, of course, the kingdom is the business of the company that supports investors and employees and benefits the community. Here’s the modern-day antithesis of the centuries-old nail proverb:

Because s/he was an apprentice, the journeyman mechanic was highly skilled.
Because of the journeyman mechanic, the shop was also efficient, well-organized and stocked.
Because of the efficient, well-organized and stocked shop, the tools and parts were available.
Because of the tools and parts, the bolts were torqued by the highly skilled mechanic.
Because of the torqued bolts, the motor was aligned.
Because of the aligned motor, the equipment remained reliable.
Because of the reliable equipment, the production process was effective. Because of the effective production process, the mission is possible. Because of the shared commitment to the mission, the customer deliveries were on time.
Because of the on-time customer deliveries, market share was won.
Because of the added market share, the business of the company was victorious,
All because of the apprentice.

Where we are now
The truth is we have neglected to encourage today’s younger generation’s active and purposeful pursuit of applied skills and knowledge for careers in industrial maintenance and reliability. In fact, most teachers, counselors, parents and students have no idea of how satisfying and financially rewarding careers in industrial maintenance and reliability could be with one to two years of technical education beyond high school graduation. Consequentially, shop classes, industrial arts, career education and career preparation classes are few and far between in our nation’s public schools—making us truly a kingdom at risk!

To highlight the worsening career education disconnect that began back in the 1960s, I will share one of my favorite and highly appropriate quotes from the 1964 Presidential Medal of Freedom recipient John W. Gardner as a point to ponder:

“The society which scorns excellence in plumbing as a humble activity and tolerates shoddiness in philosophy because it is an exalted activity will have neither good plumbing nor good philosophy. Neither its pipes nor its theories will hold water.”

And lastly, another of Gardner’s memorable quotes from more than 40 years ago:

“Much education today is monumentally ineffective. All too often, we are giving young people cut flowers when we should be teaching them to grow their own plants.”

We must do everything we can to help our youth, our executives, our leaders, our educators, our politicians and our governmental agencies appreciate the dead-end road that our nation is travelling. Capital-intensive businesses truly generate original wealth and are one of the most critical building blocks of our nation’s economy. Assuring the capacity to produce efficiently and effectively depends on reliable equipment. Reliable equipment depends on our people—their applied skills and knowledge—doing things right the first time.

Think about it. For the want of a nail, the kingdom was lost. For the want of an apprentice, an industry will be lost. MT


RobertMW2@cs.com

Want More?More of Bob Williamson, that is? He and many of our other great contributors will be at MARTS 2009. Come hear from them in person. For details, visit www.MARTSconference.com

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197

7:48 pm
December 1, 2008
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MT News

News of people and events important to the maintenance and reliability community

BLACHE JOINS MRC AS ASSOCIATE DIRECTOR

Klaus Blache has accepted the position of associate director with the Maintenance and Reliability Center (MRC) at the University of Tennessee. In making the announcement, MRC’s director Tom Byerley noted that Blache is a recently retired GM manger with a rich history of education,training and experiences, much of which is directly in the area of reliability and maintenance. He was an early chairman of the Society for Maintenance and Reliability Professionals (SMRP) and has championed reliability and maintenance initiatives within GM for years. He has numerous honors and awards, holds several certifications and has a MBA, an MS in Plant Engineering and a PhD in Civil-Mechanical Engineering. Working half time for now, he will be focusing on MRC’s Membership and Research programs and gradually taking over the UT-Monash Graduate Study program.

DINGO ANNOUNCES MANAGEMENT CHANGES

Dingo Maintenance Systems has announced the promotion of Steve Bradbury to chief operating officer and the naming of Bob Williams to vice president of sales. Williams will report to Bradbury, who joined Dingo in 2005 as vice president, Operations, following a distinguished career with Air Control Science where he served for eight years leading Alliances and Contracts and Business Development. Williams joins Dingo after leading business growth and operations in a variety of industries, including British Oxygen Company, Siemens Energy and Automation, Invensys and Leica Geosystems.

EMERSON & MITSUBISHI IN POWERFUL NEW ALLIANCE

Emerson Process Management has announced the formation of an alliance with Mitsubishi Power Systems Americas, Inc. (MPSA) of Orlando, FL. The alliance, which combines Emerson’s expertise in power plant automation and control with Mitsubishi’s experience in gas and steam turbine design and service, applies to North American and Latin American turbine retrofit projects supporting W251, W501D5, W501D5A and W501F gas turbines, as well as all models of Westinghouse technology steam turbines. MPSA has unique and valuable expertise on these turbines because they were involved in the design and development of the Westinghouse technology since the 1970s and continue to support and modernize the original Westinghouse technology platform.

“Leveraging the respective strengths of Emerson and MPSA results in a complete turbine solution, giving power generators an OEM alternative for gas and steam turbine retrofits, and long-term service and support,” said Bob Yeager, president of the Power & Water Solutions division of Emerson. “Together, these companies can offer customers a level of turbine reliability, durability and operability that they don’t always get from their existing suppliers.”

For decades, Emerson’s automation technology has been helping customers to control critical power generation processes, increase plant efficiencies and megawatt production, and realize long-term O&M savings. As a leading control systems supplier to the North American power market, Emerson has supplied more than 1200 steam and gas turbine control systems.

Mitsubishi is one of the largest OEM service providers for gas turbine outages in North America with a proactive turbine service program focused on enhanced performance, turbine life extension, protection against avoidable damage and prevention of unplanned outages. Mitsubishi brings a wealth of service support experience to the alliance including form-fit equivalent product modifications, long-term service agreements, gas and steam turbine outage services, and new and extended-life parts, as well as U.S.-based manufacturing, shop repair and engineering support.

Emerson and MPSA have already successfully collaborated on a number of turbine retrofit projects. These include performing mechanical upgrades and installing controls at the Termocandalaria power plant in Cartagena, Colombia and for the San Juan Repowering Project in Puerto Rico.

DANFOSS TURBOCOR OPS RECEIVES ISO CERTIFICATION

Danfoss Turbocor Compressors Inc. (DTC), a joint venture between Danfoss, Inc. and Turbocorp, has announced that its manufacturing facility in Tallahassee, FL has received ISO 9001:2000 certification. The certification applies to the design and manufacture of highly efficient, oil-free compressors for commercial air conditioning and refrigeration applications. DTC operates a 38,000 sq. ft., stage-one manufacturing plant in Tallahassee. It is designed for machining, sub-assembly, quality assurance and final assembly operations, including run testing prior to shipment. State-of-the-art automated assembly and computer-controlled, manufacturing work centers enable an annual plant capacity of more than 10,000 units.

VACON AND EATON MAKE NEWS IN DRIVES

AC drives manufacturer Vacon will build new office and factory premises in Chambersburg, PA, with completion expected by the end of 2009. According to Dan Isaksson, president of Vacon, Inc., the new facility will allow the Finnish company to expand its product portfolio in the local market and also offer shorter delivery times to all parts of North America. “We will also have our product development and test laboratory under the same roof. This will further help us to serve our North American customers with the commitment Vacon is famous for around the world.”

Vacon, Inc., a wholly owned subsidiary of Vacon Plc, was founded in December 2007. On January 1, 2008 it acquired the AC drives business of TB Wood’s. Its announcement that it will build a new U.S. factory came shortly after news of Vacon extending its supplier agreement with Eaton Corporation with regard to variable speed AC drive technology. Vacon will provide Eaton with its design expertise and latest VFD hardware. Eaton will promote its VFD offering throughout its global organization, including the recently acquired Moeller business, through which the corporation expanded its position as a worldwide supplier of electrical control products and power distribution, as well as power quality equipment and systems.

Vacon has sales on all continents and R&D and production on three continents.

ASSOCIATION NEWS: ASSE CAUTIONS AGAINST CUTS IN WORKPLACE SAFETY

The American Society of Safety Engineers (ASSE) cautions employers against cutting back on workplace safety in time of economic difficulty and encourages them to explore creative ways of generating temporary and long-term savings in safety and training expenses, while still ensuring that the safety needs of employees and safety regulations are met.

Laura Comstock, president-elect of the ASSE South Carolina Chapter, cites the possibility that employers seeking to cut expenses in a down economy may target variable operating costs such as travel, training and safety. She notes that while some safety-related purchases and testing can be deferred, other purchases, including those for employee personal protective equipment like hardhats, safety glasses and respirators, are critical to operations. She also notes that it is especially important for companies to show support for their employee safety during challenging economic times. Employee morale may be low and employees may be carrying additional workloads, including working additional hours or doing unfamiliar tasks due to cutbacks, which can make them more prone to injury and accidents than in the past.

Comstock, who holds Masters Degrees in occupational safety and business, adds: “In order to remain viable long-term, a company must maintain a solid safety program and strong safety performance even through difficult times. The most successful companies in the long term also have the strongest safety performance.”

Employers should remember that some safety-related training is driven by regulation, is time sensitive and cannot be delayed. According to Comstock, however, savings can be generated through streamlining and implementing some simple solutions. Those types of solutions include using online or electronic safety training services, rather than face-to-face classroom safety training, even if employees and employers prefer classroom settings.

“Even if a company doesn’t have a high-tech system, having employees view a simple presentation may meet the company’s need for safety training,” Comstock said. “Employers that have safety and training professionals on staff can save on costs related to training by conducting training on-shift and at the jobsite to prevent overtime or taking employees off the job for extended periods.”

ASSE Region VI vice president Jim Morris agrees with Comstock. “Money cut from safety programs now could have an enormous cost later; this can be from fines, employee morale, or worst of all, employee injury or even death.” As he puts it, there are better and smarter ways to protect the bottom line. Good safety is good business.

(EDITOR’S NOTE: In recent remarks to occupational safety and health students from Oklahoma State University and the surrounding area, ASSE President Warren K. Brown emphasized the fact that investing in safety pays and contributes positively not only to a great working environment, but to a business’ bottom line. Brown reported that businesses spend about $170 billion a year on costs associated with workplace injuries and illnesses and pay almost $1 billion every week to injured employees and their medical providers. He also referenced a recent Goldman Sachs study in Australia that showed valuation links between workplace safety and health factors and investment performance. That research revealed that companies who did not adequately manage workplace safety issues underperformed those that did and that workplace safety and health factors have potentially greater effectiveness at identifying underperforming stocks.) MT

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