4.5 BEARINGS

The journal and thrust bearings are plain type with pressure lubrication.

They are placed outside the compressor casing and can be inspected without releasing pressure from casing inside (see Figure 4.12).

Generally the thrust bearing is mounted out frm the journal bearings and on the side opposite to the coupling.

This_soluti0n aims at reducing the center distance, thus improving the flexural behaviour of the compressor.

For the machines constituing a compressor train having therefore two couplings, the above solution would result in having one of the shaft end loaded by the coupling and the thrust bearing weights, thus leading to flexural troubles, because masses concentrated outside the journal bearings produce the 2nd critical frequency. In this instance the thrust bearing-is mounted inboard as compared with the journal bearings.

4.5.1 gurnal bearings

At present all Nuovo Pignone compressors are e- quipped with tilting pad bearings (see Figure. 4.10) They result to be the most suitable for resisting to any unbalancing action of the oil film.

They are used according to the study electronically processed, including also the check of shaft vibration frequencies.

Carbon steel is the base material chosen for bearing manufacture. The working faces of the pad are besides coated with white, babbit metal(a tin alloy); the metal application is got by melting and centrifugation.

 4.5.2 Thrust bearings

The thrust bearings assembled on Nuovo Pignone compressors are tilting pad type, provided with supports to distribute load equally (see Figure 4.13). The pads act on the collar hydraulically fitted onto the shaft.

Although the compressor has been designed to run generally with a positive thrust, i.e. towards the thrust bearing outside, its bearings are double-acting type; they have, namely, pads also inside to face negative thrusts caused by e§ traordinary conditions (transient states, start ups etc.)

Outside the bearing a ring with a gauged hole is provided to control oil flow for lubrication Nuovo Pignone use thrust bearings with 4 to 12 inch diameters.

The tip speed of the collar that cannot exceed 190 m/s, and the load on bearing not over 50% of max. limit stated by the manufacturer, are the parameters adopted to chose the bearing to be mounted.

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