Archive | January, 2008

6469

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January 1, 2008
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Screw Compressors: Types, Application Range And Control

Part I of II…

 

0208_screwcompress_fig1The point of this two-part article is to alert the reader to the (often considerable) merits of twin-screw rotary compressors and to set the record straight on wet screw machines. For both dry screw and wet screw compressors, typical rotor profiles are shown in Fig. 1. These machines represent a sub-set of the machinery group making up rotating positive-displacement compressors. Of the various machines available, twin rotary screw compressors are used primarily in higher pressure air and process gas services, the subject of this article, whereas certain other rotary piston blowers and single-screw compressors are often used in lower pressure, high-volume applications. They are not covered here.

Rotating positive-displacement machines (like the one shown in Fig. 2) offer the same advantage as reciprocating positive-displacement equipment with regard to flow vs. pressure relationships, i.e., nearly constant inlet flow volume under varying discharge pressure conditions. Unlike centrifugal and axial machines, screw compressors do not have a surge limitation. Thus, there is no minimum throughput requirement for rotating positive displacement compressors.

The rotor tip speeds on rotary screw and rotary piston blowers are low; this allows for liquid injection or liquid flooding, which facilitates handling of contaminated gases. By design, the rotors are self-cleaning during operation, but contaminants must be kept away from the bearings. Likewise, dirt in the compression space has to be removed by filtration or other means.

0208_screwcompress_fig2Oil-free vs. oil-flooded models 
Rotary screw compressors are available in oil-free or oilflooded construction. Technically speaking, oil-free refers to not having oil in the compression space, but bearings still require lubrication by a clean medium. This lubricant is typically clean oil, although clean pressurized water can also be used [Ref. 1]. In fact, while pressurized water represents less well-known advanced technology, it has nevertheless been applied for decades. In the hands of truly competent compressor manufacturers, water-flooded screw compressors have been remarkably effective and successful in some of the dirtiest services [Ref. 1].

While oil-free twin-screw compressors are widely called dry screw machines, at least one prominent manufacturer defines and designates as “dry screw” any screw compressor equipped with timing gears. Therefore, whether the compression space is dry, oil-flooded or water-injected makes no difference: With timing gears keeping the two screws synchronized, it should be labeled a dry screw machine. Without timing gears, it cannot function as a dry screw machine, because the resulting contact of mating rotors would destroy the machine. If there are no timing gears, a separating liquid must be used. Any separating liquid circulating in the compression space will make it a wet screw machine [Ref. 2].

Fields of application for oil-free machines include all processes that cannot tolerate contamination of the compressed gas or where the lubricating oil would be contaminated by the gas. Oil-flooded machines can achieve slightly higher efficiencies than “dry screw” machines and can utilize the oil for cooling as well [Ref. 3]. The same statements could be made for water-flooded machines. In some instances, the bearing lube circuit must be totally separate from the fluid circuit used in the compression space. Whenever this requirement is disregarded, the purchaser/user may end up with either high maintenance costs or low equipment reliability.

Properly designed rotary screw compressors are constructed with no metallic contact whatsoever inside the compression chambers, either between the rotors themselves or between these and the walls of the housing. Although originally intended for air compression, rotary screw compressors are now found in numerous services in the petrochemical and related industries. These include air separation plants, industrial refrigeration plants, evaporation plants, mining and metallurgical plants.

Practically all gases can be compressed: ammonia, argon, ethylene, acetylene, butadiene, chlorine gas, hydrochloric gas, natural gas, flare gas, blast furnace gas, swamp gas, helium, lime-kiln gas, coking-plant gas and carbon monoxide gas can be compressed with screw machines. The same is true for all hydrocarbon combinations; town gas, air/methane gas, propane, propylene, flue gas, crude gas, sulfur dioxide, oxide of nitrogen, nitrogen, styrene gas, vinyl chloride gas and hydrogen gas can be found on the reference tabulations of experienced manufacturers.

One manufacturer alone has at least 20 oil-flooded twinscrew compressors in successful service with three years between shutdowns. While process conditions vary widely, there are perhaps several manufacturers with similar experience. Their compressors may not be lowest installed cost, but they usually represent best value and lowest possible life cycle cost by wide margins.

Application ranges 
Application limits for rotary screw compressors are set by the pressure and temperature ranges and by the maximum allowable speeds of the machines. Oil-free rotary screw compressors can be mechanically loaded with pressure differences up to 12 bar, and oil-flooded compressors up to 20 bar. Higher pressure differences are possible in special cases. Flow volumes up to 60,000 m3/hr (~35,000 acfm) have been accommodated in these compressors.

The maximum allowable compression ratio for one twin-screw compressor stage is that which will not cause the final compression temperature to rise above the permitted value of 250 C (482 F). This compression ratio and the associated temperature will to a very large extent depend on the specific heat ratio (cP/cV) of the gas to be compressed. For example, where the specific heat ratio (cP/cV) equals 1.4, the maximum compression ratio would be approximately 4.5, and where the specific heat ratio (cP/cV) equals 1.2, the maximum compression ratio would be approximately 10 for an oil-free twin-screw compressor stage.

Multistage (multi-casing) arrangements are not uncommon and can result in pressure ranges from approximately 0.1 bar absolute to 40 bar. Even 100 bar has been reached in some instances. Interstage cooling is used in many of these applications. Depending on compressor size, speeds from 2000 to 20,000 rpm can be encountered. The limiting factor is often the circumferential speed of the male rotor, which typically ranges from 40 to approximately 120 m/sec, and up to a maximum of 150 m/sec for very light gases.

Volume control
In principle, it is necessary to consider the volume-control options for dry-running and for oil-injection-type screw compressors separately.

Controlling dry screw compressors…

  • Control by variable speed Because screw compressors displace the medium positively, the most advantageous volume control strategy is to vary the speed. This may be done by using variable speed electric motors, steam turbine drive, hydraulic or hydro-mechanical torque converters and other means. 

    Speed may typically be reduced to about 50 percent of the maximum permissible speed. Induced flow volume and power transmitted through the coupling are thus reduced in roughly the same proportion. The allowable turndown depends on the adequacy of bearing lubrication at low speed and on the compressor discharge temperature. Even a 70 percent flow reduction is possible in special cases. In other words, the throughput is curtailed to as low as 30 percent of normal. As mentioned earlier, there is no surge limit (a minimum flow below which the gas would alternate between forward and reverse flow) for these positive displacement machine.

  • Bypass Using this method, the surplus gas volume is allowed to flow back to the intake side by way of a compressor discharge pressure controller. An intermediate cooler brings the surplus gas volume down to intake temperature.
  • Full-load/idling-speed governor
    As soon as a predetermined final pressure is attained, a pressure controller operates a diaphragm valve that opens a bypass between the discharge and suction sides of the compressor. When this occurs, the compressor idles until pressure in the system drops to a predetermined minimum value. The valve will close once again on receiving an impulse from a pressure sensor. This brings the compressor back to full load.
  • Suction throttle control 
    This method of control is suitable for air compressors only. As in the case of the full-load/idling-speed control method, a predetermined maximum pressure in the system, for example in a compressed air receiver, causes pressure on the discharge side to be relieved down to atmospheric pressure. Simultaneously, the suction side of the system is throttled down to about 0.15 bar absolute pressure. When pressure in the entire system has dropped to the permissible minimum value, full load is once again restored.

Controlling oil-injected screw compressors…

  • Suction throttle control 
    Since the final compression temperature is governed by the injected oil, a greater range of compression ratios can be accommodated. This permits the main flow volume to be varied within wide limits.
  • Built-in volume governor
    Large compressors are frequently equipped with an internal volume-regulating device. A slide valve that is shaped to match the contours of the housing is built into the lower part of the housing. It is designed to move in a direction parallel to the rotors, whereby the effective length of the rotors can be shortened. The range of this control mode is typically between about 10% and 100%. Compared with suction throttling, this type of control offers more efficient operation.

Coming in Part II 
The concluding installment in this series will discuss oilfree vs. oil-flooded rotary screw compressors and available seal design options.

Contributing editor Heinz Bloch is the author of 17 comprehensive textbooks and over 340 other publications on machinery reliability and lubrication. He can be contacted at: hpbloch@mchsi.com

References

1. Bloch, Heinz P., A Practical Guide to Compressor Technology, (2nd Edition, 2006) John Wiley & Sons, (ISBN 0-471-727930-8). [See also 1st Spanish Edition, (1998) McGraw-Hill, New York and Mexico City, ISBN 970-10- 1825-7].

2. Bloch, Heinz P., and Noack, Pierre, “Recent Experience With Large Liquid-Injected Rotary Screw Process Gas Compressors,” (Proceedings of 20th Turbomachinery Symposium, Texas A & M University, Dallas, TX).

3. Bloch, Heinz P., and Soares, Claire, Process Plant Machinery, 2nd Edition, 1998, Elsevier Publishing, London-New York-Amsterdam, ISBN 0-7506-7081-9.

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162

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January 1, 2008
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Problem Solvers

Lubricant-Free Bearings

0208_probsolvers_bearingsThe NA Poly-Round® bearings from EDT Corp have a plane bearing surface, thus eliminating the need for lubrication. More so, they will not fail catastrophically. With a 12-plus month life cycle, the amount of wear of the observable bearings can be determined through visual inspection. Once worn, the bearings will not cause damage to the shaft or contaminate the environment. They operate at temperatures up to 200 F, loads up to 2000 PSI and speeds up to 1000 RPM on a 1-inch shaft.

 

 

EDT Corp 

Vancouver, WA

0208_probsolvers_rfidRFID For Tool Tracking

The Storage+™ smart cabinet from Advanced Research Company uses RFID technology to track critical tools. Providing automatic accountability for company assets, the cabinet knows in real time what is inside, as well as what has been removed and by whom. Incorporating a touch screen interface, it is Ethernet ready and wireless capable. Other features include auto-checkout, autonotification of calibration dates and custom interfaces available to link to existing inventory systems.

Advanced Research Company
Orion, MI

0208_um_whatshot_static

Wireless Fluid Control

Balcrank’s fusion wireless fluid inventory control and management system tracks all fluid within a facility and does not allow dispersal without authorization. Each keypad wirelessly controls and manages up to 8 fluids and 48 handles. Additional capacity and capabilities can be added at the company’s pace. Up to 50 operators can use the system, each with their own pin. With no unauthorized oil changes, all dispersals are recorded and bulk deliveries verified.

Balcrank Products, Inc. 
Weaverville, NC

0208_probsolvers_duckNewly Launched SS Duck Motors

LEESON says its new Extreme Duck motors are unique to the stainless steel motor industry. Their revolutionary design makes them especially well-suited for food processing, pharmaceutical, packaging and beverage operations. They meet EPACT mandates for efficiency and feature LEESON’s exclusive IRIS™ Inverter-Rated Insulation System for extra protection and long life, especially in applications driven by an inverter. Among other things, these Extreme Ducks also incorporate LEESON’s Hydro Sealed System “HS2” that reduces the points of entry for contaminants and eliminates the need for drain plugs and breathers.

LEESON Electric/Lincoln Motors 
Grafton, WI

0208_probsolvers_pumpsHigh-Pressure Coolant Pumps

The MP-B series of high-pressure coolant pumps from MP Systems use Hydra-Cell® diaphragm pumps. The series handles abrasive particles found in machine tool coolant and, by eliminating packings, cups and seals, it reduces maintenance costs. Flow rate can be changed by adjusting the pump shaft speed. Designed for turning, milling and grinding use, the MPB series features specific attributes for each application.

MP Systems
Granby, CT

0208_probsolvers_shaftseal

Shaft-Sealing Solutions

Optimize Lube Retention SKF® low-friction Waveseal® shaft-sealing solutions feature a specially molded lip to form a sinusoidal or wave pattern around the shaft surface. This unique pattern enables lubricant to be pumped back to the bearing for optimized lubricant retention while pushing dirt away from the lip/shaft surface (regardless which way the shaft is turning) to protect against contamination. Seals with a Waveseal sealing lip are suitable for many applications, including gearboxes, speed reducers, transmissions, motors, drive systems, and pumps, among others.

SKF 
Kulpsville, PA

0208_probsolvers_collarsMounting Shaft Collars

Amounting shaft collar for securing gears, pulleys, sprockets and related components onto a shaft has been introduced by Stafford Manufacturing. The Stafford Accu-Mount™ Collars boast a split design, easy adjustability and slippage and vibration prevention. Providing a centering hub and rigid mounting method for a variety of drive components, the steel collars also feature a smooth bore to protect shafts. The collars are available in 11 sizes, ranging from 0.5” to 2.0”.

Stafford Manufacturing Corp.
Wilmington, MA

0208_probsolvers_couplings

Flat Face Couplings

When there is a risk of contamination of hydraulic circuits, the new line of flat face, hydraulic, quick connect couplings from Tuthill Coupling Group is applicable. These couplings feature a double shut-off valve configuration for a dry break connection, which eliminates fluid loss and minimizes air entry into the hydraulic circuit. Other capabilities consist of a 5075 PSI maximum operating pressure; automatic connection and sleeve lock; available NPT, BS and SAE threads; deeper knurling for an improved grip and optional colored rings for identification. The couplings meet or exceed ISO 16028.

Tuthill Coupling Group 
Berea, OH

0208_probsolvers_barrierHigh-Performance Barrier Fluids

Royal Purple has added two new barrier fluids to its line of products. Barrier Fluid FDA is a pure, non-reactive, synthetic fluid that provides superior lubrication and cooling for double and tandem mechanical seals. The fluid offers stable seal performance over a wide temperature range. Likewise, the Barrier Fluid GT is a non-reactive, synthetic fluid that provides superior lubrication and cooling for double and tandem mechanical seals. Recommended for high temperatures where FDA purity is not required, it is also chemically inert and can be used with most nonoxidizing gases and liquids. Both products are offered in the same grades and meet the same physical specifications.

Royal Purple 
Porter, TX

0208_probsolvers_pressure

Pressure Measuring Film

Sensor Products Inc.’s Pressurex® is a thin, flexible film that helps determine compression, magnitude and distribution between two mating or contacting surfaces. It is applicable for multiple industrial applications, such as assessing surface contact inconsistencies in gaskets, clamps, bolted joints, connectors and heat sealing elements, among others. When placed between two contacting services, the film changes color proportional to the actual pressure applied. A color correlation chart is used to verify the exact pressure magnitude.

Sensor Products Inc. 
Madison, NJ

0208_probsolvers_splitringSplit-Ring Bearing Protection

Electro Static Technology is offering a split-ring version of its AEGIS SGR Bearing Protection Ring™. According to the company, the ring is maintenancefree and lasts for the life of the motor. Its conductive microfibers work with no friction or wear and are unaffected by dirt, grease or other contaminants. It is available from stock with mounting hardware in sizes for motor shafts up to 6” in diameter. Larger rings can be specially ordered.

Electro Static Technology
Mechanic Falls, ME

0208_probsolvers_vacuumLiquid/Solid Industrial Vacuum

The VAC-U-MAX 55MW industrial vacuum cleans fluids and removes metal chips and swarf at one to two gallons per second. Working with any combination of liquids and solids, by turning a lever drum contents are pumped out through the discharge hose to a central filtration system. The unit is easy to move with dual swivel casters and a compact size of 26” wide. Smoothbore hoses prevent accumulation of liquids and chips and slotted holes in the case base prevent pooling of fluid.

VAC-U-MAX 
Belleville, NJ

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228

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January 1, 2008
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Our Perspective: Primary Sense Is Common Sense

ken_bannister

Ken Bannister, Contributing Editor

During a five-hour flight to the West Coast, I had depleted the battery life of my laptop computer. Needing some type of diversion, I was forced to delve into the marsupial wonders of my front seat pocket. Settling on the airline’s in-flight magazine, I was delighted to find an article discussing the neglect of basic communication skills in today’s workplace.

The premise of the article was about how our educational system focuses primarily on only three of the four human interaction skills required for effective communication. The author went on to explore and quantify the time spent on the development and honing of reading, writing and speaking skills, at the expense and virtual total neglect of listening skills. Surprisingly, the article further claimed that listening skills are believed to contribute approximately 40% of the skill required to achieve effective communication!

Reflecting on my own education, I was surprised to realize I had never received any formal instruction on effective listening. I have, however, benefited from learning how to listen effectively during some industrial training in which I was taught how to use a mechanic’s stethoscope to listen for bearing wear and the “whirling” effects of over-lubrication.

Auditory, or hearing, is the primary sense we use to develop listening skills—listening being the effective interpretation of what we hear. Until a couple of hundred years ago, listening was an essential life skill used in hunting and for alerting us to danger. On the other hand, listening has been poorly exploited within the industrial environment.

Perhaps one of the most effective examples of how our primary senses are used to communicate effectively can be found in the automotive repair industry.

What typically happens when an automotive service advisor asks you to describe exactly what is happening to your vehicle? As an operator, you know instinctively when your vehicle is not running as it should by sensing small differences in its behavior. A good advisor will get you to articulate those differences by asking you to describe and emulate any noises, smells, vibrations and visuals. By listening carefully and understanding the context in which these observations occurred (at what speed, under acceleration or braking, etc.) an experienced advisor usually can accurately diagnose the problem and formulate an immediate repair strategy. This same common-sense approach to problem-diagnosing using listening and primary sense evaluation is fundamental to effective communication between operations and maintenance.

Like the car driver, an equipment operator understands exactly when his or her equipment is not running in the “sweet zone.” If we, as maintainers, are to respond effectively to machine failure, we must learn to listen effectively to the operator instead of just blindly pulling the machine apart. Using similar tactics to the automotive service advisor, we can question what noises they heard (Auditory); what they saw; (Visual); what they smelled (Olfactory); what vibrations they felt (Tactile); what they tasted (Taste); and what they perceived (Intuition, the sixth sense). Understanding the context of a failure and knowing that over 70% of mechanical problems are directly or indirectly caused by ineffective lubrication, a maintainer is already well on his/her way to diagnosing the repair, and also understanding the root cause of the failure.

How well are you listening? Good Luck!

Ken Bannister is lead partner and principal consultant for Engtech Industries, Inc. Telephone: (519) 469-9173; e-mail: kbannister@engtechindustries.com

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826

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January 1, 2008
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Oil Cleanliness: The Key To Equipment Reliability

Part I of this three-part series covered basic filtration principles and how to measure fluid cleanliness using the ISO 4406 chart. Part II focused on filter placement and setting cleanliness codes to maximize equipment reliability. In this concluding installment, the author discusses setting up a cleanliness program to maximize equipment reliability.

 

As noted in the two prior installments of this series, we most often think of the importance of fluid cleanliness in the context of hydraulic systems and their very sensitive components. Referring to Fig. 1, it’s clear to see there are many ways that solid contaminants can enter a typical hydraulic system:

  • Built-in contaminants, which occur in all new systems, are caused by debris from the construction of the equipment. The removal of these contaminants is through flushing until an ISO Cleanliness Code two levels below the established code for the equipment is achieved. (See Part II of this series, pgs. 8-12, LUBRICATION MANAGEMENT & TECHNOLOGY, November/December 2007, to learn how cleanliness codes are established.)
  • Generated contaminants occur primarily from the wearing of components in the hydraulic pump, but also can occur from cylinder and valve wear. These contaminants are removed through proper filtration.
  • Ingression of contaminants occurs when contaminants enter from the outside. This begins with the addition of new oil, which, if unfiltered, is not clean enough for the system. Most new oils introduced in bulk from steel drums normally exceed the cleanliness requirements of the system.
  • The cleanliness range of new oils is highly variable, but normally they have an ISO Cleanliness Code exceeding 22/20/18. The only exception is the introduction of oil filtered in a plastic drum to a certain cleanliness code, such as 15/13/11, and added in a way to minimize ingression from the outside. Therefore, if hydraulic oils are not purchased to a guaranteed cleanliness, they must be filtered during addition. A good practice is to filter all oils with the use of a filter cart.
  • The primary ingression of particles is from the outside through vents and cylinder rod packing. The key to fluid cleanliness is to be proactive by keeping ingression to a minimum by adding clean oil with the use of best practices to keep outside particles from entering, utilizing good desiccant breathers on vents that can filter down to 2 microns and maintaining proper sealing and packing in cylinder rods.

Remaining particles need to be removed with an effective filtration system. Remember, it has been estimated that the cost to remove particles by filtration is five to 10 times greater than proactively keeping the contaminants from entering.

0208_oilclean_fig1

Steps in a fluid cleanliness program 
A best-of-class fluid cleanliness program involves the following steps:

1. Analyze the system… 
Gather data on the specific equipment, such as operating conditions, criticality, OEM recommendations, type of fluid and usage, downtime and repair costs and historical and current data on fluid cleanliness and wear particles. Utilize both onsite testing, such as the patch test, and outside oil analysis for particle counts and wear debris along with fluid condition.

2. Establish performance and operational targets…
Utilize OEM recommendations and industry standards to establish ISO Cleanliness Targets for each piece of equipment in the program. Compare target ISO cleanliness codes with current ISO fluid cleanliness.

3. Implement plan for target achievement…
Consult with filter manufacturer for the most cost effective program utilizing optimum filtration equipment and placement to achieve established objectives.

Proactively implement the program to minimize particle ingression in the system. Estimate return on investment by comparing current program costs with proposed future costs, by evaluating current and future fluid costs, production downtime costs and repair costs (including parts and labor).

Establish a monitoring program in both frequency and types of tests. Implement oil analysis monitoring of fluid cleanliness, wear debris and fluid condition. Utilize, where appropriate, onsite testing, such as online and portable particle counters and filter patch testing. Work closely with the selected oil analysis laboratory and filter supplier to achieve the optimum monitoring program.

4. Monitor and adjust the program… 
Once the program is implemented, utilize the monitoring techniques to evaluate the results. Analyze data and compare to program objectives. Make adjustments, if necessary, to achieve objectives. Continue monitoring to keep the program on track and recalculate return on investment to demonstrate program success to management.

Real-world successes 
Until now, the discussion in this installment of our cleanliness series has focused on hydraulic systems. There are, however, benefits for all lubricating systems where fluid cleanliness principles are followed. For example, circulating systems can utilize full-flow filtration on the fluid circulating line. Moreover, offline filtration can be utilized on reservoirs.

There is a misconception that clean oil is not important in gearboxes. While the cleanliness level is more stringent for hydraulic systems, clean oil in gearboxes is very important in the life extension of equipment.

The following case histories, on both static and mobile hydraulic systems and two gearboxes, show the importance of clean oil in equipment reliability.

Case history #1: hydraulic shear

Overview…
A 1300-ton hydraulic shear used in a metal scrap yard in a harsh environment was experiencing severe pump problems. This dramatically affected production and led to the running of two shifts to meet production demands.

The system consisted of two 2400-gallon hydraulic oil reservoirs feeding 12 vane pumps at 3000 psig with solenoid control valves. Low quality remanufactured pumps were used and frequent pump failures occurred. Poor maintenance practices were a fact of life here, including: inadequate filtration utilizing a return line spin on 25µ nominal filter; recycling of leaked fluid without proper conditioning; the permitting of excessive leaks; use of low-quality hydraulic fluid; and no effective preventive maintenance.

Program implementation… 
The following changes were made systematically:

  • Existing oil was replaced with a higherquality ISO 68 hydraulic fluid.
  • Recycling of used oil was discontinued.
  • An oil analysis program was implemented to monitor fluid and equipment condition.
  • A fluid cleanliness target was changed from ISO 27/23/21 to ISO 17/15/12.
  • OEM-approved pump replacements were used.
  • Reservoirs were drained and cleaned.
  • Reservoirs were sealed to prevent particle ingression.
  • Practices to minimize leaks were implemented.
  • Proper filtration was implemented by replacing the return line filter with an offline ß3 = 200 absolute filter.

Results and conclusions…

  • ISO cleanliness level went from 27/23/21 to 14/12/10 in 24 hours after system was started with all the major changes.
  • Maintenance and operating costs dropped from $80,000/month to $20,000/month over an eightmonth period.
  • Production increased over the same eight-month period from 800 tons/day to 3200 tons/day. This resulted in elimination of one of the shifts, yet still allowed for the meeting of production demands.
  • Pumps were examined after a twoyear period and exhibited negligible wear.
  • This project demonstrated that significant results can be achieved quickly with the right program.
  • The project also demonstrated that an effective program involves more than just installing a filtration system. A total systems approach is important.

Case history 2: coal pulverizer gearbox

Overview… 
Coal fired power plants typically operate ball or coal pulverizers (as shown in Fig. 2) to crush coal to an optimum size for combustion. The crushers have gearboxes that run these mills, which are usually worm gears. Normally, they are lubricated with an ISO compounded mineral oil or a synthetic PAO or PAG.

The plant in this case study had six ball mills. None of the gearbox oil was filtered. Each gearbox contained 250 gallons of oil. This oil was changed on a time basis—usually every eight months—resulting in a total cost of $25,000/yr. for all six pulverizers. The major cost, though, was with equipment failure. A worm gear rebuild could cost $600,000.

0208_oilclean_fig2Program implementation…

  • Desiccant breathers were installed on all vents in the gearboxes to eliminate the ingression of coal dust.
  • An oil analysis program was implemented to monitor oil and equipment condition.
  • Oil change intervals based on oil condition as opposed to the previously time-based intervals were developed.
  • Mineral oil was replaced with a synthetic PAO.
  • A dedicated offline filter system that would run continuously during operation was installed for each individual gearbox. Auxiliary fill ports were added to the gearboxes, allowing for the filtering of new oil through the filtration system. Oil collection ports were installed before and after the filters to measure filter performance.
  • Testing was conducted on several units to monitor effectiveness of routinely using a filter cart for oil conditioning.
  • An ISO fluid cleanliness code of 16/13 was established; only a two-number code was used, measuring particles = 6µ and =14µ.

Results and conclusions…

  • Synthetic oil was added and initial readings on oil cleanliness showed an average of 21/16 for all gearboxes. After 22 hours, the cleanliness level dropped to 16/11. After 76 days the cleanliness level was 13/11.
  • Filter carts were used to clean two gearboxes for two days. The oil achieved a cleanliness level of 18/12. Fortyeight hours after the filter cart was removed, the fluid cleanliness was measured at 20/15. This demonstrated that a permanent offline system is more effective and easier to monitor than intermittently using filter carts.
  • Based on conservative numbers, with minimal operating and investment costs, savings well in excess of $100,000/yr. on each gearbox could be projected. ? The project demonstrated that gear oils don’t need to be dirty. Equipment life is greatly extended by running clean oil.
  • The project also demonstrated that high-viscosity oils can be effectively filtered with the right system.

Case history 3: hydraulic excavating shovel

Overview… 
Mobile equipment in the mining industry operates in a very harsh environment where premature component failure due to contamination is common. This was the case with a hydraulic excavating shovel like the one shown in Fig. 3. In 27 months, four variable speed piston pumps on this shovel failed at a cost of $20,000 each, along with associated hose, drive motor and servo failures. The oil life as a result of oxidation and contamination was only 2250 hours. Shovel downtime over the period was 39 hours valued at $26,000 per hour. Fluid cleanliness was typically at an ISO cleanliness code of 22/20/17. The goal was to increase equipment reliability through contamination control.

Program implementation…

  • Maintenance practices were implemented to minimize contamination ingression by cleaning and capping all the hoses during storage and installation.
  • Original hydraulic fluid rated at 4000 hours and showing signs of oxidation at 1000 hours was replaced with a higher quality fluid.
  • A cleanliness target of 15/13/10 was established. The strategy was to flush the system and filter with a ß12[c] > 1000 glass media filter replacing the original 10 micron nominally rated cellulose filter (ß10 = 1.4) to achieve the target cleanliness level and stabilize the system. This filter was replaced with a ß7[c] >1000 filter to maintain the target cleanliness code.
  • Improvements were made in applying better sealing for the elements and a flow deflector was installed to protect the element during service.

0208_oilclean_fig3Oil analysis sampling was standardized to the proper techniques and frequency. Training was provided to implement these new procedures.

Results and conclusions…

  • The cleanliness level of 15/12/9 exceeded the target cleanliness level.
  • Copper levels indicative of piston pump shoe dropped 70% along with other wear component metals.
  • After the cleanliness of the system equilibrated, the filter element replacement level increased from 500 to 1000 hours.
  • Over the next four years, there were no pump failures and shovel unplanned downtime was eliminated. Savings of nearly $350,000 vs. the initial failures over a 27-month initial period were achieved.
  • The fluid life was extended to 17,000 hours, greatly exceeding the OEM-rated fluid life of 4000 hours.
  • Practices were implemented to reduce particle ingression through the hoses, improving the filtration system. This resulted in significantly improved shovel reliability.

Conclusion

Before embarking on an oil cleanliness program, thoroughly evaluate your present situation and set reasonable objectives. Utilize filter companies and outside consultants to assist when needed. Be committed to the program long-term and the economic rewards will be significant. This was illustrated with the three case histories in this article. These are just the tip of the iceberg, however. There are many more real-world success stories that could have been presented to show the economic and reliability benefits of an oil cleanliness program

Do not expect to enhance equipment reliability through clean oil by merely improving filtration equipment. True and lasting success involves a total systems approach, starting with identifying sources of particle ingression and correcting the sources of entry.

Gearboxes don’t need to be dirty. There is a great economic incentive to filter oil in gearboxes, especially in harsh environments. Filtration is not limited to oils with ISO viscosities less than 100. High-viscosity gearbox oils (ISO 460) can be effectively filtered with present technology.

Acknowledgements

The author wishes to thank Aaron Hoeg of HY-PRO and Mike Boyd of Fluid Solutions for providing case history information and ongoing support in the research and preparation of this article.

Contributing editor Ray Thibault is based in Cypress (Houston), TX. An STLE-Certified Lubrication Specialist and Oil Monitoring Analyst, he conducts extensive training in a number of industries. E-mail: rlthibault@msn.com; or telephone: (281) 257-1526.

 

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604

6:00 am
January 1, 2008
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Oil Analysis Showcase

What’s in your oil? Contaminants unseen by the human eye can significantly affect a plant’s overall output. Thus, oil analysis is a crucial component in oil and machinery health. Regular oil analysis can reduce downtime and extend equipment life—helping save both money and resources. Sampling products for in-house analysis, as well as outside laboratory services and training, are among the offerings of the companies showcased here.

HYDAC Technology Corporation
HYDAC Technology Corporation offers a Fluid Analysis Set that provides the tools to determine levels of solid particulate contamination present in a particular fluid sample. Using the vacuum pump contained in the kit, the fluid sample is drawn through a membrane patch. The residual dirt left on the patch is viewed under a microscope and compared to photos of known contamination levels in the HYDAC Contamination Handbook for visual assessment. Items included in the kit are a molded carry case, microscope, vampire pump, funnel, forceps, rubber tubing hose, plastic petri dish, sample bottles, pen light for microscope, Millipore patches, solvent filters, syringes and the HYDAC Contamination Handbook.

HYDAC Technology Corp. 
Bethlehem, PA
www.hydacusa.com

PdMA Corporation
PdMA’s full service, independent lubricant analysis laboratory offers a wide range of tests on oil, grease, coolant, fuel and transformer oil. The company’s laboratory is ISO 9001 Certified, and operates under the 10 CFR50 Appendix B QA Program. It is also licensed to receive radioactive oil samples. All reports provide accurate data interpretations and recommended actions coupled with a quick turnaround time, and reports can be generated in various electronic formats.

PdMA Corporation
Tampa, FL 
www.pdma.com

0208_oilanalysis_palA2 Technologies 
A2 Technologies offers a powerful analytical method of lube testing—Fourier transform infrared spectroscopy (FTIR)—available for the on-site lab. A2’s PAL™ FTIR Spectrometer is capable of measuring water in oil at levels that are critical to the reliable operation of your turbine equipment. The self-contained system detects water at the necessary warning levels and alerts users when the water reaches 100 ppm. If it reaches 200 ppm, the system issues a critical warning. This convenient, on-site capability eliminates the issues associated with Karl Fischer measurements, including the need for expensive and hazardous consumables and the time required for the KF measurement, not to mention dependency on the skill of the operator and the operating condition of the KF equipment.

A2 Technologies 
Danbury, CT 
www.a2technologies.com

Bently Tribology 
Services Bently Tribology Services (BTS) is an independent laboratory that tests lubricants, fuels (petroleum and bio-based), synthetic machine fluids and coolants. The company’s laboratories are certified to ISO 9001 and compliant with ISO/IEC Guide 25 and 10 CFR 50 App. B (Nuclear Power Quality Assurance) standards. Testing packages are designed with several factors in mind. Every sample receives a set of required tests that may vary depending on the equipment application. In addition to the required tests, a set of advisable tests are available to perform on any sample deemed to be abnormal. This second set of tests provides two functions: It serves as corroborators to the initial screen tests and it serves as root cause analysis indicators. BTS also can also test for machinery wear and/or contamination problems via its DoublecheckSM technique.

Bently Tribology Services 
Peabody, MA 
www.bentlytribology.com

Spectro Inc.
Spectro Inc. supplies condition monitoring instrumentation for oil analysis. The Spectro Industrial Tribology Laboratory (ITL) is an instrument package that makes the necessary measurements to effectively monitor all the oil lubricated equipment in a plant or fleet. The instruments included in the package are: 1) a Spectro optical emission spectrometer for analysis of wear metals, additives and contaminants; 2) a Fourier Transform Infrared (FT-IR) spectrometer for analysis of organic components; 3) an automatic viscometer; 4) a particle shape classifier and particle counter; and 5) a computer network for data storage, processing and retrieval. Spectro installs and provides training for all instruments. Since the Industrial Tribology Laboratory is a turnkey system, supplied and installed by one vendor, the worry and learning curve errors associated with new methods and equipment are minimized during the startup process.

Spectro Inc. 
Littleton, MA 
www.spectroinc.com

0208_oilanalysis_stavelyStaveley Services Fluids Analysis
Staveley Services Fluids Analysis (Staveley) has been providing oil, fuel, coolant and metalworking testing procedures since 1961. Today, Staveley has expanded throughout the United States and Canada, serving a diverse customer base. As a core business unit of Staveley Services North America Inc., a provider of testing services including nondestructive examination, Staveley offers standardized analysis packages and more than 100 specialized ASTM tests that cover any combination of conditions, fluids and applications to complement all types of predictive maintenance programs. The company also provides innovative new test procedures, advanced online data management tools and technical experts available to consult with clients to develop an effective testing program.

Staveley Services Fluids Analysis
Glendale Heights, IL 
www.staveleyfa.com

Emerson Process Management 
Emerson Process Management offers a number of CSI oil analysis options to help customers achieve an up to 500% return on their investment in this technology. Emerson offers an on site minilab for industrial oil analysis. Accurate measurement of wear, contamination and chemistry can be accomplished in less than seven minutes using the CSI 5200 Machinery Health® Analyzer. Oilview® software modules are fully integrated with each other and with other technologies through AMS® Suite: Machinery Health Manager software. These modules are also effective as standalone programs. The CSI Oil Lab delivers easy-to-interpret oil analysis reports in both PDF format and as an electronic file, which is easily imported into AMS Machinery Manager.

Emerson Process Management 
Knoxville, TN 
www.assetweb.com/mhm

POLARIS 
POLARIS—Performance Oil Analysis Laboratories and Reliable Information Services—specializes in testing oils, fuels and coolants for the mining, construction, industrial, oil and gas, power generation and marine industries. The company’s testing facilities are all ISO 17025 A2LA accredited, and more than 80% of the fluid samples tested on a daily basis are returned to the customers within 24 hours. POLARIS also offers extensive field services and practical training with nine classes available annually in five cities across the country. Headquartered in Indianapolis, POLARIS also has laboratories in Houston and Salt Lake City, all of which are within 48 hours ground transit from anywhere in the continental United States.

POLARIS
Indianapolis, IN 
www.polarislabs.com

0208_oilanalysis_insightInsight Services
Insight Services has guaranteed same-day oil analysis services to its industrial customers for more than 18 years. Insight’s Web-based reporting tool gives customers complete control of their program management and tracks actions taken on abnormal samples. The tool provides monthly management reports that monitor the overall success of a customer’s program. The company’s expertise in the power industry has led to its varnish potential report, EHC fluid report and turbine analysis report. Insight Services is in the process of developing technology in filter debris analysis. Insight also offers a free book on the fundamentals of oil analysis on its Website.

Insight Services 
Cleveland, OH 
www.testoil.com

0208_oilanalysis_timkenThe Timken Company 
The Timken Company’s knowledge in tribology, friction management and lubrication provides a foundation for oil analysis. Timken field engineers collect oil samples and analyze particles in lubricants to identify the type and amount of contamination reaching internal machine components. Analysis of these particles can determine the operating condition of the lubricant, as well as reveal the source of any contamination, such as dirt, coolant, moisture, improper usage and overloading. Oil and wear particle analysis often detects worn or defective bearings, cutting and rubbing wear, excessive gear wear and excessive contamination. Monitoring and trending wear particles in lubricant are two ways to detect abnormal component wear, and results from field testing can help determine whether a machine teardown is necessary to prevent further damage.

The Timken Company
Canton, OH 
www.timken.com

Vectron International 
The ViSmart™ viscosity sensor from Vectron International’s SenGenuity division correlates to data acquired from lab instrumentation for real-time, in-line oil condition monitoring applications. According to the company, the product will save time and money while providing lab quality viscosity sensing data in a mechanically active environment. The sensor requires no customer calibration and only 100 micro-liters of fluid are needed for measurement. The unit is unaffected by shock, orientation, flow or vibration conditions.

Vectron International SenGenuity
Hudson, NY
www.sengenuity.com

0208_oilanalysis_tricoTrico Corporation
Trico offers the latest sampling supplies and accessories— including sample ports and collection devices—designed to extract system and component specific samples that are both representative and repeatable from the best diagnostic locations in the most effective ways possible. Access to systems is done through the use of a mating sample port adapter. The sample port adapter screws onto the sample port. Oil samples can then be drawn from the system and placed into a clean sampling bottle for analysis. To guard against contaminating the sample and for superior leak protection, Trico sampling ports all feature a check valve and viton o-ring seal cap. Trico sample ports are available in several types and sizes to match the varying requirements of manufacturers.

Trico Corporation 
Pewaukee, WI 
www.tricocorp.com

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Cleaning Up A Maintenance Nightmare

About The Kruger Organization

The Kruger Organization is a 100-year-old global company operating under five business units. It manufactures and markets a variety of products related to pulp and paper, including: newsprint, specialty grades, lightweight coated paper, directory paper, tissue, recycled linerboard, corrugated containers, lumber and other wood products.

According to company literature, Kruger is the only manufacturer in the world to offer cellulose-based specialty products made from both wood and cotton.

K.T.G. (USA) LP– Memphis 
The Kruger facility in Memphis, TN, the setting for the accompanying article, was once part of Scott Paper. When Scott eventually merged with Kimberly-Clark, the mill was idled. In 2002, when Kruger acquired the operation, it became known as K.T.G. (USA) LP, part of the Kruger Tissue Group (KTG), which manufactures premium tissue products, under its own brand names and private labels, for retail, industrial, business and institutional use.

The Memphis mill was restarted in 2003 and a major modernization plan was implemented. Today, with over 40 acres under roof, it is the largest structure in the city of Memphis and employs some 175 people. Main products manufactured here are bath and facial tissue. Equipment includes four paper machines and 10 converting lines.

A hydropulper is an industrial blender used in the pulp and paper industry to process fibrous materials into a useable slurry. As shown in Fig. 1, the main parts include: a vessel, a lower chamber containing an agitator or impeller, a rotary drive, motor, gearbox, a tube to re-circulate the slurry and some type of sealing system work to prevent water and other kinds of contamination from damaging the equipment.

In simplest terms, a hydropulper’s tanks are filled with water where agitators mix material into homogenous slurry. Sensors gauge the slurry consistency and make adjustments by adjusting the water to thin or thicken the mix. A rotor or agitator inside the chamber vigorously pulps the fiber while an impeller moves the flow through an outlet and tube back to the vessel. Once the desired consistency is reached, it is pumped out, while a de-watering screen saves the water for re-use.

Hydropulper sealing
During the pulping process, material comes in contact with the rotor, a tremendous shock load is transferred to the shaft and it flexes the shaft of whatever sealing system is being used (contact, lip, labyrinth, etc.). To maintain the integrity of the seal, and keep contamination out, among other things, it must be able to accommodate shaft movement. Over time this action can break down even the best of seals. When a seal breakdown occurs, water runs past the component and down the shaft where it enters and contaminates the gearbox housing. Sealing options that have been tried on hydropulpers include [Ref 1]:

  • Lip seals—these dry running devices can wear out, break down or fall apart. Their short service life can be as little as 1800 hours. They actually can do damage by cutting into the shaft at the sealing point. Double lip seals can do twice the damage.
  • Sealed bearings—so-called (lubricated-for-life) bearings do not seal out moisture or water.
  • Fibrous packing—degrades and can fret the shaft.
  • Close clearance designs—still allow for humidity egress/ingress.
  • Contact face seals—stop contacting, produce gaps that allow for the movement of air and water across the bearing.
  • Flingers—rings that deflect leakage away from packed or sealed equipment are basically ineffective.

In time, using any of these methods, water will be sufficient enough to get past the seal and into the gearbox bearings and cause the bearings to fail. In other words, the root cause of the failure was not addressed.

The hydropulper’s problem 
KTG’s Memphis plant operates five (Voith) hydropulpers that have been in service for approximately 40 years. The units were all retrofitted and modernized in the 1990s, including the gearboxes and motors. Still, they continued to experience ongoing breakdowns—and it was never a pretty sight (see Fig. 2 and Fig. 3).

According to Dave Knox, KTG maintenance planner who oversees maintenance on the plants, refiners, pulpers and paper machines, the main cause of the failure was water contamination in the gearbox. Mounted directly under the hydropulper tank, water entered through the output shaft, entered the bearing housing, contaminated the bearings and the gearbox failed. The problem had been recurring for years and had not been solved by the previous owners.

0208_nightmare_fig1When the mill restarted in 2003, so did the equipment failures. Although the maintenance team knew that the root cause of the failure was water contamination in the bearing housing, it felt that it just had to live with it. To complicate matters even further, because of the hard-toaccess nature of the components, it was difficult to determine exactly when a contact seal might fail.

The problem continued because the standard overhaul procedure included the use of lip seals. While these components might have been brand new, right out of the box, the gearboxes would be doomed to fail again—it was just a matter of time. In fact, the problem of water contamination hindering the entire system was to continue until the true root cause of the failure was attacked two years ago—when the Memphis facility began to install bearing isolators in its hydropulpers.

Why lip seals fail
To understand the problem at KTG, one has to look at the history of lip seals. At the time they were first made available some 70 years ago, they were the only choice when it came to general-use sealing devices. Because of their inexpensive cost, over the years they became the number one choice for sealing industrial rotating equipment.

Today, according to their own manufacturers, even the best lip seals have a mean life to failure of only 1844 hours—or 77 days of operation. Half last longer than that and half last less than the mean time hours to leakage. This means that lip seals have a guaranteed failure rate of 100%.

As was experienced at KTG, no one can determine when the time is up for a lip seal. There simply is no advance warning. The only way to tell is after the equipment stops working and the lip seal has burned to a crisp and probably grooved the shaft.

0208_nightmare_fig2_3

Contact vs. non-contact 
While a lip seal or contact seal operates with contact, the bearing isolator, a non-contacting labyrinth-type seal, makes no contact. It never wears out and can be used over and over for many years. With this in mind, it may not make sense to protect rotating equipment that is designed to run uninterrupted for years, with a product that could experience a 100% failure rate in a relatively short period of time.

Bearing isolators
In the late 1970s, an alternative to contact/lip seals was made available with the invention of the Bearing Isolator, a noncontact, non-wearing, permanent bearing protection device [Ref. 2].

The bearing isolator consists of two parts, a rotor and stator, which are unitized so they don’t separate from one another while in use. Typically, the rotor turns with a rotating shaft, while the stator is pressed into a bearing housing. The two components interact to keep contamination out of the bearing enclosure and the lubricant in—permanently.

Today, bearing isolators are used to protect motor and pump bearings, machine tool spindles, turbines, fans, gearboxes, paper machine rolls and many other types of rotating and related equipment. Though the end-user has a choice, the best bearing isolators are made of metal, usually bronze, manufactured to specification, with a vapor-blocking feature to inhibit the free transfer of contamination (see Fig. 4).

0208_nightmare_fig4

The hydropulper solution 
When Dave Knox approached Mike Perkins, his Chesterton distributor, about the Memphis mill’s ongoing hydropulper breakdown problem, Perkins suggested trying Inpro/Seal branded bearing isolators. Following this recommendation, Knox met with Joe Klein, Inpro/Seal’s regional manager. Working together, Knox and Klein developed a plan of attack.

Bearing isolators were engineered and manufactured to the hydropulper drives’ exact needs and specifications. Between 2005 and 2006, these new devices were installed on two of the five hydropulpers as part of the overhaul program. For the last two years, the Memphis KTG site has not experienced a single hydropulper failure. That’s because the reason for their previous ongoing failures— water entering the gearbox housing—was totally eliminated. In the future, this type of bearing protection is expected to be applied to the remaining three hydropulpers.

The rest of the story
In addition to bearing isolators on its hydropulper drives, KTG also uses PMR bearing isolators on its paper machines. The PMR (an acronym for paper machine roll) bearing isolator was specially engineered for the size, speed, alignment and operating conditions of wet and dry ends of machine rolls.

As with the hydropulpers, before the availability of bearing isolators, end users had to contend with sealing methods that allowed roll bearings to fail. The leading cause of this failure also was contamination entering the bearing housing—contamination from heat, humidity, paper stock, water and oil leakage.

The bottom line 
K.T.G. (USA) LP – Memphis cleaned up the problem with its hydropulper breakdowns by keeping water out of the units’ bearing housings—the root cause of the failures. Key to this was replacing outdated sealing methods with state-of-the-art non-contacting technology.

Since it began installing Inpro/Seals two years ago, the Memphis operations have yet to experience a single breakdown on any bearing isolator-equipped hydropulper. Once the facility installs these devices on its other hydropulpers, breakdown due to water contamination should be totally eliminated.

One thing is certain—the installed bearing isolators will not experience unexpected breakdown [Ref. 3]. These well-engineered components should run maintenancefree throughout their intended design life, which could be 20 years or more.

Bearing Isolators Widely Accepted Worldwide

Almost three million Inpro/Seal-branded bearingisolator designs are in operation in process plants around the globe, where end users continue to report significantly reduced operating costs with increased productivity and reliability. Protected bearings have proven to run 150,000 hours or more (17+ years), eliminating the need for continual maintenance and repair. Documented cases show that a plant can easily double its mean-time-between failure (MTBF) and reduce its maintenance costs by at least half, with users reporting an extremely high Return On Investment (ROI).

Inpro/Seal Company (www.inpro-seal.com) the product’s originator, recently announced that its production capacity has increased to accommodate 40,000 bearing isolators per month, making it the largest producer of bearing isolators in the world [Ref. 4]. To supply this demand, the Rock Island, IL-based company’s campus, the largest of its kind, encompasses engineering, research, development, testing and manufacturing facilities operating on a 24/7 basis.

References
1. Before the advent of the bearing isolator 
2. David C. Orlowski holds the patent for the “bearing isolator,” a term he coined when he founded Inpro/Seal Company in 1976. 
3. The first bearing isolators, installed in a process plant in Iowa over 20 years ago, are still operating. In addition, Inpro/Seal offers a full no-questions-asked warranty. 
4. Based on available statistics.

Dave Orlowski is founder, president and CEO of Inpro/Seal Company. E-mail:dco@inpro-seal.com

(Editor’s Note: This article is based on one that first appeared in the December 2007 issue of Maintenance Technology magazine.)

The Tissue Making Process In Brief

Tissue paper is a nonwoven fabric made from cellulose fiber pulp. (The Memphis KTG plant uses northern softwood and eucalyptus as the main fibers.) In the manufacturing process, fibers are broken up in a hydropulper and mixed in a cooking liquor with water and chemicals usually consisting of either calcium, magnesium, ammonia or sodium bisulfate.

The mixture is cooked into a viscous slurry. To whiten and brighten the pulp, bleaching agents, such as chlorine, peroxides or hydrosulfates are added. The pulp is washed and filtered multiple times until the fibers are completely free from contaminants. This blend of water and pulp is called the “furnish” stage.

The slurry then flows into a head box that spreads it out on a continuous wire mesh belt or Fourdrinier. As the fibers travel down the Fourdrinier, much of the water is drained out through the holes in the wire mesh. A series of other steps further compress the fibers and continue to remove water to a point where the sheet is strong enough to be transferred to a specially adapted tissue or Yankee dryer.

The highly polished Yankee dryer takes the wet sheet over a series of rollers until it is adequately dried. Along the way, raised supports on the line create bumps and valleys on the now completed fabric or “web.” The web passes through a series of rotating knives that cut it to the desired widths that are folded and packaged in boxes or cellophane wrap.

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LMT News

News of people and events important to the Lubrication Management community

EMERSON ACQUIRES THE AUTOMATION GROUP
Emerson today announced that it has acquired The Automation Group (TAG) of Houston, TX. TAG becomes part of Emerson Process Management, expanding Emerson’s capabilities for providing technical and management services for the design, engineering and implementation of process automation systems for the refinery, petrochemical, oil and gas production and other industries. Terms of the deal were not announced. TAG has branches in Corpus Christi, TX, Bloomington, MN, Concord, CA and Baton Rouge, LA. It supports all of the leading process automation systems and will continue to do so.

SYCLO AND IBM EXPAND MARKETING PARTNERSHIP
Syclo has announced an updated and expanded marketing partnership with long-time alliance partner IBM. For the past decade, Syclo has had a strong relationship with MRO Software (MRO). With IBM’s acquisition of MRO, that relationship is expected to grow. The expansion will allow Syclo to maintain closer relationships with its customer base and give the company the ability to directly offer services and support. Current and prospective IBM Maximo users can purchase Syclo SMART for MAXIMO products either directly from Syclo or from IBM.

MRC BEGINS MATCHING UP SUMMER ENGINEERING INTERNS
The Maintenance and Reliability Center (MRC) of the College of Engineering at the University of Tennessee – Knoxville is actively seeking to match up engineering students with companies for its 2008 Summer Intern Program. According to the center’s director, Tom Byerley, MRC currently has 25 company applications on file. He encourages other organizations interested in participating in this year’s program to submit their applications ASAP. The earlier a company completes the application process, the better the chance for having its intern requirements met. Information on the program and applications (one per each intern a company is willing to place) are available from the MRC Website: www.engr.utk.edu/mrc

ASSOCIATION NEWS

HYDRAULIC INSTITUTE (HI) SEEKS COMMENTS ON STANDARDS
The Hydraulic Institute (HI), under the approval of the American National Standards Institute (ANSI), is seeking qualified individuals in North America to participate in the review process for the drafts of two updated standards: ANSI/HI 2.4, Rotodynamic (Vertical) Pumps for Installation, Operation, and Maintenance Manuals; and ANSI/HI 9.6.2, Rotodynamic (Centrifugal and Vertical) Pumps – Allowable Nozzle Loads. (Details on which equipment is covered by or excluded from the updated material can be found on www.pumps.org)

Individuals and organizations in North America directly and materially affected by these standards are asked to contact HI for details on how they might participate in the upcoming ANSI/HI canvasses. Such parties include pump users and specifiers, producers, standards developers, government agencies and general interest groups. E-mail Karen Anderson, Administrator, Technical Affairs, at kanderson@pumps.org, or call (973) 267-9700 x 23.

(EDITOR’S NOTE: HI periodically introduces new standards based on industry needs. The current Edition of ANSI/HI Standards comprises over 1500 pages and 27 documents.)

SMRP ASKS FOR INPUT ON BODY OF KNOWLEDGE
The SMRP Body of Knowledge—the basis for CMRP examination question specifications—must be reviewed periodically to ensure that it is current and complete. Your participation in an online survey is needed to help validate the new revised edition. Broad participation from SMRP members and the public will help strengthen SMRP’s ANSI-accredited certification program.

The survey asks you to rate the importance of various job tasks to success in maintenance and reliability operations. It also asks for anonymous demographic information that will help demonstrate breadth of industry representation and experience of survey respondents. Use the survey experience to help point out professional development opportunities that can help improve your performance and that of your organization. The survey is scheduled to remain active through March 2008. For more details, go to www.smrp.org

YOUR NEWS IS OUR NEWS! OUR READERS WANT TO KNOW ALL ABOUT IT. SEND LMT NEWS ITEMS TO: jalexander@atpnetwork.com

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Using Ultrananocrystalline Diamond To Improve Mechanical Seal Performance

Through extensive R&D and the advent of improved equipment and processes, nature’s hardest substance now appears to have a very bright future in the area of seal faces.

A mechanical seal is a critical component whose useful life significantly impacts the overall reliability and robustness of pump or centrifugal compressor. Unscheduled or premature failure of the seal leads to increased maintenance and increased overall equipment costs to the user. The overall performance of a mechanical seal often is most affected by the performance of the faces and the intervening lubricating film. This primary element of a mechanical seal represents a classic problem in the science of tribology, the study of friction, wear and lubrication.

The demands placed on seal faces require careful attention to the issues of wear resistance, chemical compatibility, mechanical and thermal properties—all of which are determined by the end use application and overall seal design. When a mechanical seal is used in a pump, the liquid in the pump is used to cool and lubricate the seal faces. The seal faces are in sliding contact and prevent the liquid in the pump from reaching atmosphere. This contact also generates frictional heat that must be removed from the seal faces. Failure to remove this unwanted heat often results in the boiling of the lubricating liquid film at the seal faces, usually leaving a deleterious residue and causing premature failure of elastomeric components in the seals (static-secondary seals). Both of these undesirable effects of elevated temperatures lead to premature seal failure.

The ability to maintain coolant on the seal face is even more critical when compounded by the demands associated with the pumping of abrasive media or a pump’s ability to withstand intermittent and unscheduled coolant loss. The ability to run two hard-faced seal materials such as SiC against each other often is desirable but not practical due to the premature failures that result from elevated temperatures caused by friction at the seal interface.

In the case of a centrifugal gas compressor, a noncontacting mechanical seal is used to contain the gas within the machine. A lift mechanism, such as spiral grooves, is included in the design of the seal. During operation the seal faces do not make contact except at startup and shutdown. The intense frictional heat occurring at this time must be controlled or face damage can occur.

Based on the benefits nature’s hardest substance would appear to offer for this application, the idea of using the diamond as a wear resistant face material in seals is not new. Diamond also possesses many other attractive properties, including extremely high thermal conductivity and chemical resistance. Unfortunately, previous attempts at integrating diamond into seal faces failed due to difficulties in ensuring that the diamond face presented the necessary surface finish required for such a demanding tribological application. Following extensive research and development and improvements in equipment and processes, those problems appear to have been solved.

Today, a new form of diamond with ultrananocrystalline grains has entered the industrial arena. Invented at Argonne National Laboratory and commercialized for seals by John Crane, Inc. and Advanced Diamond Technologies, Inc., UNCD®, as it is commercially known, provides the surface roughness typical of normal, unprocessed seal. UNCD has been dynamically tested and shown to signifi- cantly reduce the frictional heat and increase the life of the seal faces in accelerated wear. The work highlighted in this article was completed, in part, by funding from the National Science Foundation and the Department of Energy.

Manufacturing hurdles
One of the major obstacles in providing a diamond-treated surface for a mechanical seal is maintaining the surface flatness and roughness necessary to achieve sealing. Early work in diamond surfacing placed extreme demands on finishing and polishing the diamond to meet the required metrology and geometric specifications of a seal face. Surfaces were rough and had a high degree of waviness. Additional lapping of the diamond surface to achieve sealing could not be done cost-effectively due to the hardness of diamond. Consequently, many researchers abandoned the idea of using diamond as a surface for seals.

The development of ultrananocrystalline diamond (UNCD), though, generated renewed interest in diamondtreated seal faces. The process demonstrated that the base material could be treated with diamond without changing its original flatness. This was a major breakthrough in the manufacturing technology for diamond-structured surfaces. At last, diamond could be applied to a seal face without any further work to achieve the desired flatness for sealing fluids. Moreover, UNCD, unlike other diamond films, has nanometer-scale roughness that allows as-deposited UNCD to have sufficient smoothness so that it doesn’t degrade a soft counterface. In other words, UNCD works in both hard on hard and hard on soft sealing applications.

Still, there was an additional obstacle to overcome. Work to this point was done to transfer this laboratory-scale process to meet the demand of seal production. New equipment and processes had to be designed to handle a larger volume of seals at one time. Once this was done, the new equipment and processes had to be validated. Tests were run on production parts and compared to those run on the smaller scale equipment. Continuous testing confirmed that the production parts met the early results for friction and wear testing of parts manufactured on the smaller scale equipment.

0108_diamon_fig_1_2Friction testing
Friction plays an important part in the success or failure of a set of seal faces. Not all materials make good seal faces. Some materials have properties that hold heat in the seal face, while others wear too much. Applying diamond to a seal face reduces both friction and wear. One of the best substrate materials for diamond is silicon carbide. Silicon carbide and diamond have very similar material properties. Results of friction testing for UNCD on a SiC face are as follows:

  • Carbon running against UNCD on silicon carbide µ = 0.07
  • Silicon carbide running against UNCD on silicon carbide µ = 0.04

The results for carbon versus UNCD on silicon carbide were expected. This is a normal value for friction in seal design work. The results for silicon carbide versus UNCD on silicon carbide were very good. When silicon carbide runs against itself without any diamond treatment, the coefficient of friction is greater than 0.1. For those applications requiring hard-on-hard seal faces, the application of a diamond-treated seal face is a major improvement. Several groups of seal faces have been tested, resulting in the same friction values.

0108_diamond_fig_3_4Dynamic testing
An important step in qualifying materials for a mechanical seal is dynamic testing in hot water. This test involves running a 1.375” diameter seal in 250 F water at 100 psig and 3450 rpm. At these conditions, the pressure-velocity value for the seal is 170,000 psi x ft/min. This test in hot water is very demanding of the seal. Each test run consists of running a group of four pumps, three fi tted with seals treated with diamond and one without a treated surface. The results of hot-water testing were outstanding for the diamond-treated seals. Very minimal or no measureable wear occurred over the 100-hour test. The untreated silicon carbide seals in each case failed due to heavy wear across the entire seal face. The conditions for the untreated and treated seals are shown in Figs. 1, 2, 3 and 4. In each test, the seals were run against carbon.

These results (as depicted in Figs. 1, 2, 3 and 4) were typical for each test run. The UNCD-treated surfaces were in excellent condition with very little carbon wear. The untreated seal had high wear for both the carbon and silicon carbide seal faces.

An interesting measurement taken after testing was surface flatness. The diamond-treated seals had no change in surface flatness during testing. The untreated silicon carbide had an increase of 240 microinches. This is an indication that the untreated surface was running hotter than the diamond-treated surface. Continued increases in flatness or surface waviness will lead to unwanted seal leakage and wear.

Summary
The development of ultrananocrystalline diamond (UNCD) and the improvements in equipment and processes have resulted in an excellent material for seal faces. When applied to a base material such as silicon carbide that has been lapped flat, no further processing is required to achieve a working seal face. Results in friction testing also have been excellent. UNCD shows promise when run against carbon or silicon carbide. Tests in hot water demonstrate no visible wear occurring during the 100-hour tests. Untreated silicon carbide failed to pass the hot-water test. Tests have shown that diamondtreated seal faces will improve seal performance. MT


James P. (Jim) Netzel is director of Seals Engineering for Advanced Diamond Technologies, Inc. of Romeoville, IL. His 40+ years of experience in the design and application of mechanical seals includes 20 years of service as chief engineer at John Crane, in Morton Grove, IL. During his career, Netzel has authored (and presented) numerous technical papers through the International Pump Symposium, STLE, ASME, BHRA, AISE, SAE and various trade publications. He also has written chapters on seals and sealing systems for The Pump Handbook, The Centrifugal Pump Handbook and The Compressor Handbook. E-mail: netzel@thindiamond.com

Charles F. (Charlie) West, the VP of Engineering for Advanced Diamond Technologies, has been leading and working in product development of thin inorganic films for over 35 years. During that time, he has been directly responsible for the development of many vapor phase thin-film (primarily CVD) applications in the areas of electronic, biomedical, optics and wear and corrosion. Before joining ADT, West was one of the founders of QuesTek Innovations, LLC, another high-tech startup in the Chicago area. He had been the CVD Group leader and a research scientist at Northwestern University prior to starting QuesTek and a research scientist for 10 years at Battelle Columbus Laboratories in the Electronic and Optical Materials Group. Over the course of his career, West has been personally responsible for enabling and transferring new and unique CVD processing to NASA, universities, national laboratories and several industrial firms. E-mail: cfwest@thindiamond.com

Tom W. Lai is principal engineer at John Crane, stationed in Morton Grove, IL. Since joining the company in 1982, he has been involved in developing new products, maintaining seal analysis software and providing technical support to advanced seal applications. Lai holds four patents related to face seal designs. He received his B.S. from National Taiwan University and his M.S. and Ph.D. in Mechanical Engineering and Master of Management degree from Northwestern University. He is a registered Professional Engineer in the State of Illinois and a member of STLE. E-mail: TWLai@johncrane.com

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