Multilobe Bearings High Performance Hydrodynamic Bearings
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fis M ULTI LOBE BEARINGS John Crane multilobe bearings (MGF) are hydrodynamic bearings whose characteristic high level of performance in high speed rotating equipment has been made possible by the optimisation of manufacturing quality. Precision processing spindles equipped with MGF bearings are characterised by their accurate and vibration-free operation, minimum operating bearing clearance, and high stiffness and damping coefficients. Such spindles are capable of producing a part with an accuracy of 0.001 mm. The characteristic of the multilobe bearing, is the non- cylindrical bearing bore. This deviates from conventional, cylindrical, hydrodynamic bearings by having two or more lobes. The lobe radius (R) is larger than the shaft radius (r) by a specific amount. This difference in the radius of the shaft and the lobe results in the formation of a wedge gap in each arc. This gap begins at the oil inlet groove, "a" axially positioned at the widest point of the respective arc. As a rule, the narrowest point of the gap lies in the centre of the lobe. When the shaft begins rotating, basic theory dictates that the lubricant's adhesive effect on the shaft and lobes acts to pull the lubricant into this gap, which narrows in the Peak pressure develops between the shaft and the bearing. Once this pressure reaches a certain level, it lifts the shaft off the bearing. Thus, the shaft and the bearing are separated by the lubricant gap. In other words, the shaft operates hydrodynamically with no metal to metal contact. Bore Geometry

Multilobe Bearings Theory Distributed across the entire shaft diameter, there are as many individual hydrodynamic carrying forces directed at the center of the shaft as there are lobes. The strength of the individual hydrodynamic force is, among other things, dependent on the width of the wedge gap. The vector total of all the individual carrying forces represents the effective load capacity of the MGF bearing towards the outside. This results in a strong centering effect being applied to the shaft which produces good concentricity and generates a defined shaft position. By matching the...

fis M ULTI LOBE BEARINGS Offset Halves - Bearing Calculation Program ALP3T calculation results: Results of geometry data: Bore type: Offset Halves 2 x 150 ° Bearing diameter Shaft diameter (Sartorius suggestion) Mean bearing clearance (cold) Mean relative clearance (cold/warm) profile factor (warm) Results of operational data: Specific load Load angle Maximum hydrodynamic pressure Maximum oil film temperature Maximum babbit temperature Average bearing temperature Average viscosity Minimum film thickness Minimum permitted film thickness Oil pressure before bearing Power loss Shaft...

Bearing Bore Configuration Selection Table Values shown in parentheses represent maximum values. In individual applications and after consultation with our design and technical support team, these may be permitted.

fis M ULTI LOBE BEARINGS Reference Codes For Ordering In order to provide clear identification, the products are coded Thrust part Journal part Examples of John Crane bearing reference codes Tilting pad journal bearing with five journal pads, split design for both directions of rotation, Series 6 catalogue type with L/D = 0.6, bearing bore diameter 050 mm, max. external diameter Double tilting pad thrust bearing, Series 8 catalogue type with 8 thrust pads, split design for both directions of rotation, directed lubrication with spacer and shims, inner diameter 0103 mm, outer diameter 0215.85...

Advantages, Applications, Assembly Information ■ Virtually no metal to metal contact between shaft and bearing while the machine is operating ■ Dampened, low-oscillation, noise and wear-free shaft operation. If the oil supply is operating properly, virtually unlimited bearing service life ■ Several supportive lubrication films distributed around the shaft circumference guarantee that the shaft is generally centered, thus significantly improving ■ Permits high continuous loading ■ Shock loads of several times the level of the continuous ■ Good lubricant flushing and cooling effects ■...

fis M ULTI LOBE BEARINGS Lubrication Grooves, Lubricants, Shaft Surface Finish Lubrication Grooves If necessary, the calculated oil flow through the bearing can be Increased by opening the sides of the lubricant grooves while maintaining a specified feed pressure. As long as all lubricant grooves are completely filled with oil during operation, and a minimum volume of oil flows through the bearing, correct operation of the hydrodynamlc lubrication Is guaranteed. These conditions are met If, when the lubricant grooves are opened, an adequate amount of oil can still be retained and prevent...

Offset-Halves Journal Bearings Offset-halves bearings represent a form that is gaining increasing significance, particularly by the gear manufacturers. Due to its improved dynamic properties, this type of bearing offers advantages over lemon-bore bearings. The bore shape of an offset-halves bearing can be described by the horizontal offset, "eh," of two, cylindrical half-shells with respect to the bore radius, RB. The shaft radius, R,, is smaller by one-half the bearing clearance, CR than the remaining half of the bore diameter, D. In this way, all the ratios according to DIN 31657...

MULTILOBE BEARINGS Offset-Halves Bearing Application For Turbine Gear Boxes: Load Direction: Centre Of Bearing Half 20-25° Pinion shaft driven (turbine speed) Main shaft driven (generator speed) 0° 12 0- Temperatu re probe bore 10 h m in ( T m ax ) 20-25° F Gearbox split line Bea ring split line Antirotation pin 9

Offset-Halves Journal Bearing - Bearing Clearances Speed Relative bearing Peripheral speed: Bearing clearance values in urn Relative bearing clearance: 0,0002 x Vnmax or relative clearance %<>: 0,2 x VW„ Definitions in accordance with DIN 31657 The following applies to the gap height ratio: With RB = Rj + CR + eh the following applies Radial bearing clearance = one-half the diameter clearance In addition, the term profiling is also generally understood