Improved Michell Thrust Blocks
Improved understanding of the theory of lubrication films (initially by Reynolds) allowed the development of much more efficient bearing surfaces. This allowed the replacement of multiple collars in a thrust box by a single thrust block.
Fluid-film thrust bearings were invented by Australian engineer George Michell who patented his invention in 1905. Michell bearings contain a number of sector-shaped pads, arranged in a circle around the shaft, and which are free to pivot. These create wedge-shaped films of oil between the pads and a rotating disk on the shaft. Each lubricant "wedge" can only be of a limited length (in the direction of travel, i.e. circumferential) so multiple pads are needed rather than a single ring. No lubrication pump is needed, the rotation of the shaft itself is sufficient.
The need for an efficient thrust block became even more important with the advent of steam turbines and their higher propeller speeds. Despite this, there was some reluctance to adopt them in their homeland, until the discovery that World War I U-boats were using them. After this they were soon adopted widely. The large single pad illustrated is a model of one used in the battlecruiser HMS Hood, the pride of the Royal Navy.
Michell Bearings continue in production today under the same name, now as part of Rolls-Royce marine systems.
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