Sleeve bearing

Pump vibration measurements and analysis of the ampHtude—frequency spectmm have led to the deterrnination of possible equipment ailments. Examples of frequency relationships to particular pump vibration problems are available (62). Eor example, a one-time (lx) frequency corresponding to a mnning speed usually indicates the presence of rotor unbalance, a 2 x peak may mean a bent shaft, and a - O.dx may be a symptom of an oil whip at the sleeve bearing. 

As a generahty, porous metal sleeve bearings tolerate Pp levels up to 1.8 MN/(m-s) (50, 000 psift/min). Pp levels for thmst bearings should not exceed about 20% of the sleeve bearing limit. Variations of oil viscosity, oil content, graphite content, and other material and property details also influence the approximate operating limits given in Table 7. 

The sleeve bearing has the further advantage that it func tions as a lubricated, pressurized shaft seal to contain the pressure on the process gas (see subsec tion Shaft Seals ). 

These pumps normally use sleeve bearings lubricated with oil, grease, or even the pumped liquid (except for abrasives). 

Motor sleeve bearings require limiting the axial play. 

Sleeve bearings on some older, slower, larger pump shafts can withstand dirt contamination better than ball and roller bearings. This is because the tolerances are not so strict with sleeve bearings, the surface area of contact is greater, and the lubricant flushing action is better. The sleeve bearing material of construction is... 

When selecting a high-speed gear unit, the possibility of using an AGMA No. 2 oil should be considered. In most cases, the sleeve bearings in the system can use this oil and, if not, a compromise 200 SSU at 100°F (38°C) oil should be considered. 

Both rolling element and split sleeve bearings are used. Normalh. packing is used for shaft sealing or for special services. Mechanical con tact seals can be used. 

Figure 5-37. Dam type sleeve bearing. (Courtesy of Elliott Company...

F(ir axial compressors, the journal bearings are of the plain sleeve type for the larger, slower speed compressors. They are of the tilting pad type for the smaller, higher speed machines. The sleeve bearing is normally housed io a spherically seated carrier. The bearings require pressure lubrication as do most of the other compressors. 

B. Bearings. See catalog only as to options and manufacturer s standard as to grease and oil-lubricated ball and sleeve bearings, also force-feed. Do not specify size and make of bearing or factory-filled lubricant. 

In normal operation, a sleeve bearing provides a uniform oil film around the supported shaft. Because the shaft is centered in the bearing, all forces generated by the rotating shaft, and all forces acting on the shaft, are equal. Figure 44.47 shows the balanced forces on a normal bearing. 

Lubricating-film instability is the dominant failure mode for sleeve bearings. This instability is typically caused by eccentric, or off-center, rotation of the machine shaft resulting from imbalance, misalignment, or other machine or process-related problems. Figure 44.48 shows a Babbitt bearing that exhibits instability. 

It is not always incorrect to over-grease. With a sleeve bearing, for instance, gun pressure may be maintained until old grease exudes from the ends of the bearing, and the same is tme of spring shackles. For the sake of economy and cleanliness, however, this should never be overdone. 

The four-axial groove bearing is the most commonly used oil-lubricated sleeve bearing. The oil is supplied at a nominal gage pressure that ensures an adequate oil flow and some cooling capability. Figure 60.3 illustrates this type of bearing. 

Machine-trains that use sleeve bearings are designed based on the assumption that rotating elements and shafts operate in a balanced and, therefore, centered position. Under this assumption, the machine-train shaft will operate with an even, concentric oil film between the shaft and sleeve bearing. 

Oil whirl In an abnormal mode of operation, the rotating shaft may not hold the centerline of the sleeve bearing. When this happens, an instability called oil whirl occurs. Oil whirl is an imbalance in the hydraulic forces within a sleeve bearing. Under normal operation, the hydraulic forces such as velocity and pressure are balanced. If the rotating shaft is offset from the true centerline of the bearing, instability occurs. 

Oil whip The most severe damage results if the oil whirl is allowed to degrade into oil whip. Oil whip occurs when the clearance between the rotating shaft and sleeve bearing is allowed to close to a point approaching actual metal-to-metal contact. When the clearance between the shaft and... 

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