We hear that connecting rods in Formula 1 engines no longer employ the steel-backed shell bearings we are familiar with, but now consist of copper-lead bearing material deposited directly onto the inner diameter of the rod’s big-end. The reason for this? To eliminate the heat barrier of a separate bearing shell, enabling heat from the bearing material to flow directly into the material of the surrounding rod. In a way, this brings engine bearing technology full circle from the early days, when soft “Babbitt” or white metal was poured into rods or engine blocks, with a “form” or dummy journal taking the place of the crankshaft. Such thick poured white metal proved vulnerable to fatigue cracking as engines became more powerful in the 1920s, so thinner Babbitt was found to be more resistant to cracking, or “picking-out,” as it was then called. Poured bearings were also labor-intensive, so a next step was to plate a thin layer of white metal onto brass inserts, which could simply be replaced with new ones when their bearing material wore. The modern form of replaceable bearing insert is the familiar semi-circular steel-backed three-layer bearing. For heavier duty than white metal can carry, so-called copper-lead bearing material is used, consisting of a strong, hard matrix of copper impregnated with soft lead. The copper structure carries the load, while the soft lead allows wear particles or contaminants in the oil to harmlessly embed in the lead, rendering them harmless. The three layers are the bearing material, topped with a thin layer of lead for break-in, topped by a very thin layer of indium for corrosion protection. For exceptional duty, the bearing material can be silver. In this recent F1 process, a very thin layer of copper-lead is deposited into F1 connecting rods by PVD, or physical vapor deposition. This is a “sputtering” process that moves atoms from a target onto a destination surface by ion bombardment. As you might suspect, this is not an inexpensive affair. Because the resulting layer of bearing material is very thin, it is unusually resistant to fatigue and can carry unit loads up to 17,000 psi, a substantial improvement over usual insert-bearing load capacity. Also interesting: I just learned that this process is also used to deposit bearing material directly into the bores of the five “star gears” in the fan-drive reduction gearboxes of Pratt & Whitney’s new Geared Turbo-Fan (GTF) aircraft engines. Such gearboxes will transmit 15,000 to 20,000 horsepower from a fast-spinning turbine to a much slower-turning propulsion fan, enabling both to turn at their most efficient speeds.Gadget Reviews: mamaktalk.com
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