Seal for a joint or juncture – Seal between relatively movable parts – Close proximity seal
Reexamination Certificate
2000-02-28
2002-10-29
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Close proximity seal
C277S418000, C277S419000, C277S420000, C277S421000
Reexamination Certificate
active
06471215
ABSTRACT:
BACKGROUND OF THE INVENTION
The present application, as presently envisioned, relates to mechanical joint packing devices, and more particularly, to a labyrinth sealing device for providing a dynamic seal between a rotating shaft and a bearing housing and, most particularly, to a grease purgeable labyrinth sealing device that is designed to eliminate the failure problems caused by applying excessive grease to the bearings being protected by the labyrinth sealing device.
Before May 1977, rubber lip seals protected the bearings in most industrial process pumps. Only those pumps that were designed for API service—petroleum refinery duty specifications—were fitted with labyrinth seals. Those labyrinth seals were designed primarily to keep the lubricant inside the bearing frame. They were ineffective in preventing contaminants from entering the bearing.
A failed lip seal in an HVAC pump prevented occupancy of the Sears Tower in Chicago shortly after it was built. Chilled water was needed to temper the sun load on the south side of the building. Water spray from a leaking mechanical seal entered the bearing housing and the pump shut down. Consequently, the southern windows on the top floors were popping out, making the building uninhabitable. Special labyrinth seals were installed to replace the lip seals and the pump was again in operation.
Because of the lack of reliable bearing protection, pump bearings were short-lived and considered expendable. Contamination by moisture, dust, dirt and the liquid being pumped, even loss of lubricant through the lip seals, was commonplace. Lip seals either grooved the shaft or “carbonized” at the contact point, allowing free movement of contaminant and lubricant in or out of the bearing housing.
Clearly, a better method of protecting pump bearings were sorely needed, one that would be permanent and effective, and, in effect, “isolate” the bearing environment. In 1977, no such device existed in the world. An all-out effort to solve the problem and satisfy the performance gap resulted in the first “bearing isolators.” These isolators were compound labyrinth seals, non-contacting, non-wearing and absolute in nature. Field trials proved the effectiveness of the new device, where all other methods of bearing protection had failed.
After quick rejections by nearly every major pump manufacturer in the U.S., the manufacturer of the isolator contacted the pump users in the process industries. After field installation of the new device, it was almost immediately apparent to the users that the enhanced reliability of the pumping equipment would prove to be an economical investment. Pump manufacturers rapidly responded to the customers and installed bearing isolators on new equipment whenever they were specified by users, but only then.
Today, almost every process pump produced in the U.S. is fitted with some sort of labyrinth sealing device. Enlightened pump users are retrofitting most of their repaired pumps and motors. Long-term cost savings and productivity improvements in the process industries are the results.
Shortly after the introduction of the bearing isolator, many competitors entered the niche market. Most offered similar products, but others were made of lightweight PTFE derivatives. Even magnetic face seals were successfully applied as bearing isolators in pumps and gears.
The most common form of rotating equipment in use in the process industries is the three-phase AC electric motor, varying in size for one through 500 horsepower. It is believed that more than 40 million motors are installed in the U.S. alone. Combined, they consume approximately 70 percent of the electrical power generated for industrial use. Motors have been manufactured in essentially their present form for nearly 100 years, without regard to effective bearing protection.
Since the days of Edison and Steinmetz, only rubber flingers or slingers inhibited direct ingress of contamination into the exposed bearing compartment. Therefore, mechanical—not electrical—failure is the overwhelming cause of motor outage. Users in the process industries recognized the obvious faults in motor design and rated bearing failure as the No. 1 cause of failures in NEMA frame drivers.
The reliability of pumps and motors has vastly improved over the past 20 plus years, due primarily to enhancement of bearing integrity. If a rolling element bearing is kept clean and well lubricated, it will conceivably perform for 150,000 hours (17 years) or more. ANSI pump manufacturers are warranting their pump bearing frames for three years. Motor manufacturers are typically warranting their bearing-protected motors for five years.
Typically, a bearing isolator is a mechanical device that permanently isolates a bearing from its environment. It should be non-contacting and non-wearing and must prevent humidity and moisture from entering the bearing enclosure during start and stop cycles.
Bearing isolators are easy to install, most have an interference fit with the bearing cap or end-bell, so they should be pressed into place with an arbor press, although the user sometimes prefers to tap them with a soft hammer.
Ideally, “maintenance” is the act of keeping equipment in running order. Maintenance is not a “fix it when it breaks down” function, as it may have been considered in the past. Reactive maintenance is disruptive of the manufacturing process and therefore an expensive luxury for the manufacturer. Pumps and motors are the most common forms of rotating equipment and require the most attention by the maintenance activity.
Preventive maintenance is also expensive and usually excessive for the job at, hand. Preventive maintenance is usually performed based on elapsed time, whether or not the equipment needs attention. The theory was to prevent catastrophic failures of process equipment by anticipating the weak links in the equipment design and replacing the weak link equipment before the failure thereof.
Predictive maintenance is now the methodology of choice for a majority of process industry professionals. Vibration analysis, thermography usually infrared technology and lubricant condition inspection are commonly used tools that predict a breakdown before it actually occurs.
If a rotating equipment maintenance cycle is less than the ideal design life of the component parts (bearing, mechanical seals or, in the case of electric motors, the electrical insulation), an effort should be made to design maintenance out of the equipment. Instead of spending the entire maintenance effort on condition-based, fixed time, or reactionary maintenance, a good maintenance organization should invest a significant portion of the budget toward cost-avoidance and equipment design enhancements.
Replacing the lip seals in pumps and the flingers and slingers on motor shafts has been proven to increase the mean time between planned maintenance by a factor of two. If the maintenance activity directed to pumps and motors is cut in half each year for three years, such activity will be reduced to 12.5 percent of the current benchmark. A return on investment as high as 400 percent is commonly attainable.
Historically, process pumps have had a useful service life of 2.8 years before being repaired in some way or another. Industrial motors fare much better, averaging 5.7 years until their first repair or replacement. Company personnel usually repair pumps on-site, while motors typically are sent off-site to a repair facility.
To minimize disruption to the maintenance department, pump repairs and bearing isolator upgrades are done in chronological order, according to specific instructional assistance provided by the isolator manufacturer's field personnel. Motors are sent to the repair facility along with specific instructions and specifications to install bearing isolators on the shaft and fan ends. Manufacturer's personnel will be on hand, as required, to assist and educate the repair facility employees as to the application and installation of bearing isolators.
Recent reliability enhancements to pumps and motors have had a
Drago James
Grudzien Jeffrey M.
Shaw Joel R.
Garlock Sealing Technologies LLC
Harrington John M.
Kilpatrick & Stockton LLP
Knight Anthony
Rodgers Matthew E.
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