Mechanical (Rotary) Common Questions -6

EPC-School 2012

M for Mechanical  

Topic - Bearings

1. What are the different types of bearings used for rotating machines?
2. What are thrust bearings?
3. What are common causes of bearing failure in a centrifugal pump?
4. What are main sources of water or moisture contamination in a centrifugal pump?
5. What factors warrant the use of journal bearings instead of antifriction bearings?
6. Why are antifriction bearing temperatures high during starting? And does greasing play a role?
7.  What are the different types of antifriction bearings?
8. What material are journal bearings made of?
9. Why cant machines on journal bearings run at low speeds?
10. What is the protection to avoid serious damage on account of lubrication failure in centrifugal compressors?

Answers to Above Questions-

1. Antifriction, journal bearings

2. Thrust bearings are those which absorb axial thrust load generated on the rotor

3. Lack of lubrication, excessive loads/stresses, loosening of bearing in housing, excessive lubrication, high lube oil temperature (malfunction of cooler), equipment problems

4. During monsoon through pipe flanges, while cleaning the floor with pressurised water, when mechanical seals leak

5. Need for better heat carrying capacity, better load carrying capacity, reduce friction, carry away chippings etc

6. Over greasing causes friction in the bearings and the temperature goes high until excessive grease is squeezed out

7. Ball bearings, roller bearings, needle bearings

8. About 1-2 mm babbit metal coating over SS / Steel

9. At low speeds journal bearings cannot develop the thin/squeeze film lubrication and shaft rubs against the bearings

10. RTDs are installed in journal and thrust bearings to detect rise in bearing temperature (due to lubrication failure or any other reason)