Reliability

Exam-type questions on Thrust Bearing design 1. You have been asked to design a minimum power-loss, uni-directional, thrust bearing for an horizontally-mounted, axial, ammonia compressor in a nitric acid plant. The compressor has a shaft diameter of 100 mm and generates a thrust of 15kN when operating at 6,000 rpm. The thrust is negligible at zero speed. a. What type of thrust bearing would you recommend and why? b. What are the physical reasons why a dry, PTFE bearing would be unacceptable? c. With the bearing type recommended in (a), produce a detailed, professional design report for the bearing. The report should include a table of the performance characteristics of the bearing, indicating clearly the reasons for all the design choices made, along with a fully dimensioned sketch of the bearing assembly, and a dimensioned cross-section of one of the pads. Any other commentary you consider to be appropriate should be included. A proof of why this is the lowest possible power loss is required. (the attached Guide may be used) 2. A tilting-pad thrust bearing on the 100mm dia shaft of a merchant ship is examined during a shutdown, and all of the pads are found to have wear patterns as shown in the picture. It is known that the assembly has 6 ‘square’ pads (width 72.7mm and inner diameter 115 mm), and is designed to support a load of 90,000 N at 180 rpm. The lubricant is an ISO 46 oil, and the inlet oil temperature is normally 50C. The runner has a ground finish. You are told that misalignment is negligible. The filtration system filters down to 10 microns. What is the likely cause and why? What is the most cost-effective remedy?

3. A tilting-pad thrust bearing on a drilling rig has failed, and it is found that three of the 12 pads on one side of the bearing have worn, but all the other the pads are in perfect condition. What do you think is the likely cause of this problem? Explain your reasoning.

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