Original Date: 07/09/2007
Revision Date: / /
Best Practice : Tool Spindle Protection Using Bearing Isolators
The Inpro/Seal Company has installed bearing isolators in its machine tooling spindles to virtually eliminate maintenance and increase reliability of the company’s production CNC machines. The longevity and ability of the bearing isolator to perform in an absolute manner with respect to complete and permanent bearing protection has been an invaluable asset to the Inpro/Seal production process.
In any machining operation, spindle repair and rebuilding to restore machine tool spindles to maximum efficiency is an ongoing process and interrupts valuable production time. Spindles are rotating mechanisms that drive the cutting tool in lathes, CNC machining centers, and milling machines. The spindle is either attached directly to the machine tool or attached via a spindle-mounted adaptor system. Spindles are typically cylindrical units comprised of a variety of smaller components that include the spindle housing, a spindle shaft, various fittings, and precision bearings. The bearings in a spindle are extremely important because they are the key component in the tooling spindle that allows the shaft to rotate without contact with other parts. Given extensive use and exposure to cutting coolants, even the most well-designed spindles require regular maintenance and eventual repair or possible replacement following prolonged use.
Recognizing the cost of spindle repair and expensive production downtime, Inpro/Seal installed its own invention and design of bearing isolators in two Mazak CNC machines tooling spindles and 12 Cincinnati Milacron CNC machine tooling spindles to virtually eliminate bearing maintenance and increase reliability of the company’s CNC machines that support a production rate of 400,000 bearing isolators per year. Inpro/Seal’s bearing isolators are sold around the world.
The Inpro/Seal bearing isolator is a non-contact, non-wearing, permanent bearing protective device containing a rotor and a stator; the two are unitized so they do not separate from one another while in use. The rotor typically turns with a rotating shaft while the stator is pressed into a bearing housing (Figure 2-2). The two components interact to keep coolant and other contamination out of the bearing enclosure and the lubricant in. Bearing isolators can be installed in virtually any type of rotating equipment that requires protection from hostile environments (e.g., pumps, electric motors, gear boxes, and mechanical drive steam turbines). Bearing isolators are made of metal, usually bronze, and utilize a vapor-blocking feature that inhibits the free transfer of vapor contamination when the rotating equipment is cycled on and off.
Before the introduction of bearing isolators, bearing protection for industrial and process equipment was generally limited to contact seals such as lip seals and face seals. A rubber lip seal with a maximum useful life of 3,000 hours (4 months) was used to protect bearings with a design life rating exceeding 150,000 hours (17 years). As a lip seal’s condition deteriorates, it grooves the shaft or carbonizes at the point of contact with the shaft and loses its ability to effectively seal the bearing enclosure. Face seals, whether spring-loaded or magnetically loaded, were found to have a finite life and were unpredictable as to the timing of their abrupt and certain failure.
Because of these inadequacies, rotating equipment in the process industries is quite unreliable and catastrophic failures due to bearing degradation are commonplace. Not only do they contribute to a large amount of maintenance and tear-down time, they interrupt production and greatly increase non-value-added time to the process.
At Inpro/Seal, bearing isolators have replaced lip seals in CNC tooling spindles and have proved to be an economic alternative to what was once conventional contact sealing methods. Their longevity and ability to perform in an absolute manner with respect to complete and permanent bearing protection has been a tremendous contribution and benefit to the Inpro/Seal production process.
Figure 2-2. Typical Bearing Isolator (3-D cutaway view)
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