By Miba AG |
If turbomachinery temperature problems occur or the bearings have to have an increased load carrying capacity, it is common practice to use features like directed lubrication and pad base materials with a high thermal conductivity. But especially pad base materials like Copper-Chromium are expensive and increase the bearing’s delivery time. At high sliding speeds, Miba engineered bearings with eddy groove technology clearly outperforms CuCr base material and thereby pushes the limits of bearings and applications considerably.
Tilting pad journal bearings
Tilting pad journal bearings are used in rotating equipment such as compressors, turbo gears, gas turbines and steam turbines. A prerequisite for the safe and reliable operation of bearings is a sufficient lubricant film thickness, which basically depends on the occurring load, speed, and the selected lubricant. The second parameter is the heat which is generated in the oil. The maximum temperatures of both the lubricant and the bearing can be a crucial parameter. The key to improved bearing performance is designing the product accordingly, so that even at high speeds and loads excessive heating of certain bearing areas as well as hot spots in the oil film are avoided.
To increase the heat dissipation, it is common practice to use features like directed lubrication and pad base materials with a high thermal conductivity. If this approach is still insufficient, there are geometric options like an increase of the axial length or the bore diameter of the bearing although such changes often increase oil demand, power loss and the space requirements.
Physically, robust grooves of a certain shape, arranged in a certain pattern, are machined into a specific area of the bearing material. The grooves are optimized to disturb the laminar lubricant flow and thus create the cooling effect, by improving temperature exchange between cooler oil near the shaft and warmer oil near the bearing surface. Compared to an identical bearing without whirling grooves, key operating parameters such as oil consumption, frictional power and dynamic properties remain practically unchanged.
A detailed article of the performance improvement by eddy grooves was published in 2021 (Schüler E, Berner O.)*. The investigation was conducted on a Miba 5-tilting pad journal bearing with a bore diameter of 120 mm at a speed range of 50 – 110 m/s and a load range of 0 – 4 MPa. Temperature sensors close to the sliding surface enabled the precise determination of maximum temperatures. These tests confirmed a significant surface temperature reduction.
To date, the technology has been experimentally verified on bearings with shaft diameter of 120 and 500 mm. In addition, a first Ø60 mm eddy groove tilting pad bearing was installed in January 2021 in an integrally-geared compressor. The machine is again in operation and the former temperature problem of the bearing was solved. The predicted temperature drop was recorded and is confirmed by the operator.
As a summery, the tested and verified eddy groove technology can be especially beneficial for highly loaded bearings in e.g. integrally-geared compressors, that operate near their performance limits to increase the reliability and availability of the machine. In some cases, the reduced maximum temperatures may also allow a reduction of the bearing size which would lead to reduced oil demands and power losses of the bearing, while keeping the temperatures at an acceptable level.
The reduced bearing temperatures, induced by eddy grooves, can be utilized to:
- Increase the operational reliability of the bearing and slow down the aging of the lubricating oil
- Operate bearings at higher loads without an increase of maximum temperatures
- Reduce the bearing diameter or the axial length with the aim of reducing the necessary oil supply and the power loss without having to accept an increase in the maximum bearing temperatures
- Economically better than using expensive pad materials with currently limited availability
Miba Industrial Bearings
Miba produces hydrodynamic bearings and labyrinth seals for use in critical rotating equipment, such as turbines, compressors, generators or industrial pumps. Our fluid film bearings are used in power generation as well as in the oil and gas industry and the petrochemical industry. Miba combines the former Orion, Sartorius Bearings, TCE and Zollern Plain Bearings, who all support the industry since decades. With OE manufacturing and aftermarket support, we partner with you for the life of the product and your equipment.
*Schüler, E.; Berner, O. Improvement of Tilting-Pad Journal Bearing Operating Characteristics by Application of Eddy Grooves. Lubricants 2021, 9, 18. https://doi.org/10.3390/lubricants9020018