Innovation beyond magnetic bearings

Ask most people about innovation in bearings and they will mention magnetic bearings. Certainly, they deserve the spotlight. It seems that every turbine OEM and major bearing supplier has been eager to augment its arsenal with mag bearings.

Examples include Dresser-Rand acquiring Synchrony, MAN Diesel & Turbo buying Mecos Traxler, SKF picking up S2M and Waukesha Bearings taking over Glacier Rotating Plant Bearings. The large number of mergers tells a tale of fast-paced development and rapidly maturing technology.

“Mag bearings are crossing the chasm between highly specialized applications into more of a mainstream adoption by other machine builders,” said Lars Kahlman, Senior Application Specialist, SKF Fluid Machinery.

Yet magnetic bearing breakthroughs may not even be regarded as being on the forefront of bearing technology. Indeed, recent work on air bearings and the incorporation of advanced materials, such as ceramics can possibly stake a claim as being on the cutting edge.

Wherever you look, vendors, such as SKF, Dresser-Rand Synchrony (p. 30), Lufkin, Kingsbury, Waukesha Bearings, Mecos, GMN Bearing, Calnetix, LA Turbine, Capstone Turbine and New Way Air Bearings, are incorporating a host of new features into their wares, many of them squarely targeted at the turbomachinery market.

The traditional bearing field, if it can still be called that, is a hotbed of innovation.

Vendor after vendor has responded to the challenges posed by turbomachinery applications that drive the limits in terms of high temperatures, high pressures, harsh environments and faster machinery.

“The big push is to find bearings that can handle faster speeds and heavier loads,” said Joseph Hart, RMT Bearings Sales Manager for Lufkin (part of GE Oil and Gas). Lufkin-RMT has introduced Spray-Bar Blocker and By-Pass Cooling advancements to its tilting pad journal bearings and thrust bearings. The goal is to reduce operating temperatures while handling increased load capacities and surface velocities. This same technology is offered in its Ultra Pressure Dam Sleeve Bearings and Ultra Thrust Bearings.

Waukesha Bearings (WB) offers tilting pad thrust, journal, combination and fixed profile bearings, used in pumps, motors, compressors, turbines, generators and gear-boxes. Examples include: Maxalign bearings that reduce power loss and handle misalignment in large shaft turbomachinery; Flexure Pivot bearings that eliminate pivot wear, pad flutter, and tolerance stack up; and MLSF bearings that improve stability and lifespan when compared to conventional floating ring bearings.

In addition, WB supplies housed horizontal and vertical bearing assemblies. They include options such as cooling, electrical insulation, hydrostatic jacking, self-contained ring or disc lubrication, and instrumentation, for use in pumps, motors and generators in applications, such as nuclear power stations and air-cooled units for LNG pumps.

The company also employs advanced material bearings, such as Hiperax and Hidrax, to withstand high temperatures, high loads and abrasive materials, as well as axial and radial magnetic bearings, RDS auxiliary bearings, position sensors and control systems that increase reliability and availability and reduce the need for on-site maintenance.

“We are seeing more partnerships between OEMs, end users and bearing suppliers, which allow each expert to share their knowledge for improved technical collaboration and testing validation,” said Barry Blair, Chief Engineer for Fluid Film Bearings at WB. “There is higher market demand for directed lubrication, the use of synthetic oils and other lubricant options. We are also noticing lower power losses, lower oil flow rates and smaller oil tanks.”

For small diameter shafts operating at high speeds and high loads, Flexure Pivot bearings address problems such as pivot wear and vibration increase. They have an integral pad-pivot-retainer design, manufactured as one piece. WB’s ISFD technology for radial bearings ups the damping capability to combat sub-synchronous vibrations.

Additionally, WB is a presence in magnetic bearings. Its compact Zephyr controller can fit a redundant controller configuration in the same space envelope as older nonredundant controllers. The controllers for these magnetic bearing can measure and process all data required to commission the bearing system, eliminating the need for ancillary equipment such as signal analyzers.

These controllers can now be placed 500 meters away from the machine, said Richard Shultz, Chief Engineer at WB. Kingsbury specializes in tilting pad thrust and journal bearings, with applications in turbines, compressors, generators, motors, pumps, gearboxes and auxiliary equipment.

This includes tilting-pad thrust bearings, which incorporate leveling plates to equalize the load among the individual pads and accommodate misalignment between the collar and housing. The equalizing feature provides higher load capacity.

Non-equalizing tilting-pad thrust bearings, as the name implies, have no equalization system, which reduces the overall axial height of the bearing. These Kingsbury bearings are best for applications with axial space limitations. The design requires tighter bearing and casing manufacturing tolerances. A means for adjustment is sometimes required to align the bearings and rotor during assembly.

In addition, Kingsbury supplies tiltingpad journal bearings that have several design variables that are used to attain reliable and stable machine performance. Tilt-pad pivot designs accommodate shaft misalignment.

Both equalizing and non-equalizing tilting-pad thrust bearings and tilting-pad journal bearings are available in two styles:

• Flooded lubrication bearings that circulate oil around the pads are used for low-to-moderate bearing surface speeds

• Direct lubrication bearings that introduce cool, fresh oil at the leading edge of the bearing pad, and reduce oil flow requirements and power loss in high-speed applications.

“Bearing power loss and oil flow requirements increase exponentially with speed and significantly influence machine efficiency and oil lube system size,” said Scan DeCamillo, Kingsbury’s Manager of R&D. “Direct lubrication is a technology designed to lower bearing oil flow requirements and power loss as turbomachinery continues to increase in size and speed.”

Recent research, said DeCamillo, has been focused on a direct-lube design for journal bearings designated between-padgroove (BPG), which introduces direct lube technology in a more robust bearing design of simpler construction. SSV (subsynchronous vibration) grooves for use in direct lube journal bearings eliminate a low-amplitude, broadband, radial, sub-synchronous vibration.

Two further features — high-speed tapers and axial dampers — address high temperatures and axial SSV encountered in thrust bearing applications at high-speed and low-load conditions. “SSV grooves, highspeed tapers, and axial dampers are being incorporated in many high-speed turbomachinery applications,” said DeCamillo.

Read more in the November-December 2014 issue of Turbomachinery International