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


Figure 5-37. Dam type sleeve bearing. (Courtesy of Elliott Company inserts are used. The inserts are lined with a thin layer of babbitt on a steel backing. Precise manufacturing assures interchangeability. Babbitt thickness is a compromise, balancing enough depth for particle imbed-ability against keeping the strength up by staying close to the steel liner. This form of journal bearing is also referred to as a liner bearing.

The bearing most often found in centrifugal compressors is the tilting pad bearing, shown in Figure 5-38, which is inherently stable. The individual pads break up the rotating oil film and discourage the tendency for the oil to whirl. Each pad also acts as a separate force to keep the bearing loaded and thereby stabilized. The bearing, also known as the tilting shoe bearing, has grown in popularity in recent years and is found in most process compressors in critical service. The bearing can be furnished with various numbers of pads, with five being the most common. Bearing dynamics can be altered by a variety of configuration changes, such as load on or between pads. The number of pads can be changed for alternative dynamic parameters, with the four-pad bearing the most common alternative. Bearing clearance for a journal bearing is on the order of 1 to 1.5 mils per inch of journal diameter and is generally the same value for both the liner and the tilting pad bearings.

The pads are fabricated of steel with a babbitt coating, the thickness determined by the same argument as stated for the liner bearing. The

Figure 5-38. Five-pad tilting pad bearing. (Courtesy of Turbocare, a Division of Demag Delavel Turbomachinery Corp., Houston facility

backside of the pad is fitted with some form of rocker, the exact shape varying from one maker to the next. The pads are contained by a hori zontally split base ring assembly.

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