In some of my research, there are many types of plain or hydrodynamic bearings made which make their way into the engine market.
Thick Babbitt bearings, of which there are a couple of subgroups, consist of a metal backing material on which a layer of Babbitt is cast onto. The Babbitt can be thick, but the thin limits are approx ~.005” depending on who you read and what they are talking about. The Babbitt, usually a lead alloy, would allow conformability between the shaft and the bearing surface, and would allow particles to embed in the lead, protecting the shaft from poor oil filtration. The low strength of the Babbitt alloy which leads to poor fatigue resistance are some of the weaknesses of these bearings. The shells of these bearings can be very thick, limiting their usefulness in connecting rods. These are a step up from the old engines where the Babbitt would be cast directly into the block of the engine. The metal backing shells could be removed and new bearings installed with out all the clean up and machining needed to cast Babbitt into the block.
Thin Babbitt bearings start to take advantage of the relative strength of the thinner layers of Babbitt. These bearings tend to have thinner shells and thus were much nicer to use in connecting rods and other weight or size sensitive applications. Since the Babbitt is now thinner, more precise machine work is needed, as there is less conformability. The oil must be filtered better as there is less embedding ability. The upside is the increased strength of the bearing and improved fatigue resistance. As the Babbitt is thinner there is increased risk of wearing through the Babbitt so more attention is given to the different types of alloys used as the backing material. The material needs to be both strong for support to the Babbitt, and soft to protect the shaft if it should wear through the Babbitt. Bronze, lead and tin alloys of Bronze, lead and tin alloys of Aluminum are commonly useds. Steel is also used, and is preferable because of its strength and thermal growth characteristics. Sometimes a thin Bronze layer is rolled onto steel strip that is then formed into bearings. This bearing is then formed and Babbitt electroplated or cast onto the surface. As the backing material of these bearings tends to be formed, the appeal of bronze and aluminum is apparent. The engine block or Con-rod, must take more of the load than the previous bearings, however the bearing is still instrumental in distributing the loads it supports. There are several subgroups of this bearing, depending on the thickness and type of Babbitt alloy used, the backing material and the number of layers
Micro Babbitt bearings have some Babbitt Alloy electroplated onto the surface of the bearing material. These have the thinnest shells and rely on the strength of the block or con-rod for support. The shell is the wear material also and is formulated of alloys that have the desired anti-wear properties. The Babbitt coating is measured in tens of thousandths. The oil must be clean and the bearing support blocks and shaft perfectly true. These tend to be the strongest bearings.
I am looking for Mfg. of the thin Babbitt bearings and any references or recommendations you may have from your dealings with them. Thanks for all the replies. Also please comment if you question the accuracy of these descriptions as I am planning on using the info in a paper at work.
dwedel
Hotrod Big Engines!
For site policies and guidelines
see faq731-376
