ANTIFRICTION METALS, a group of alloys used in the manufacture of machine bearings to minimize friction. The theoreti cally ideal bearing would be composed of the hardest metal available. Practically, in spite of the highest skill in forming both the journal and its bearing, there are minute inequalities which have the effect of reducing the area of actual contact to a few isolated patches, result ing in the heating and eventual destruction of the shaft. To obviate this difficulty the bear ing metals have been developed by so alloying their components that a very large series of plastic metals has been produced with the two essential properties of being soft enough to adapt their form to the journal for which they are intended, and hard enough to hold their form against the pressure upon them.
Two general classes of these antifriction alloys are in common use: the first consisting of a soft matrix in which are embedded small particles of a hard alloy which has crystallized in the cooling of the molten mixture (see ALLOYS) ; the second, in which the hard con stituent of the alloy forms a sort of network, in the meshes of which is contained the soft metal which reduces the friction. Four metals are in use as components of the antifriction or bearing metals, tin, lead, antimony and cop per. Some special formulas call for zinc in addition, but it is generally argued that no benefit can be thus secured which cannot be better obtained by increasing the percentage of antimony in the mixture.
By far the larger number of the antifric tion metals have a basis of tin as the soft matrix, the hard constituent being particles of tin-antimony and tin-copper alloys distributed throughout the matrix. Tin has the advantage of taking a high polish and this in itself serves to reduce friction. A cheaper class of these metals has a matrix of lead, or tin-lead, with tin-antimony as the hard constituent. Both of these are known as white-metal alloys. The class of bearing metals having a hard matrix with soft metal filling is known as plastic bronzes. They consist of a tin-copper alloy with sometimes a little zinc• and occasionally nickel added, and may contain up to 30 per cent of lead. They are not as plastic as the white
metals, but are more durable and better adapted for heavy pressures.
The original antifriction metal was in vented by Isaac Babbitt in 1839, and was com posed of tin 24 parts; antimony 8 parts; and copper 4 parts. A softer variety had 2 parts of antimony and 2 parts of copper to 24 parts of tin. The market was at once flooded with other combinations, good and bad, and all went under the title of Babbitt metal, and the name still remains in some markets, although the original Babbitt metal was long ago supplanted by more scientifically combined. alloys.
For light-work bearings the formulas vary from 73 parts tin, 9 parts copper, and 18 parts antimony; to 85 parts tin, 5 parts copper, and 10 parts antimony.
For heavily loaded bearings: from tin 87 parts, copper 6 parts, and antimony 7 parts; to tin 90 parts, copper 2 parts, and antimony 8 parts.
For bearings of railway car axles: from tin 67 parts, copper 11 parts, and antimony 22 parts; to tin 83 parts, copper 6 parts and anti mony 11 parts. The Pennsylvania Railroad uses a special plastic bronze, composed of cop per 76.8 parts, tin 8 parts, lead 15 parts, and phosphorus 0.2 part. Another bronze highly recommended for railway bearings is composed of copper 64 parts, nickel 1 part, tin 5 parts, and lead 30 parts.
For locomotive axles a plastic brass is used: copper 5.5 parts, zinc 80 parts, and tin 14.5 parts.
For propeller shafts a plastic brass is com posed of copper 57 parts, zinc 29 parts and tin 14 parts.
Ajax bronze, a plastic antifriction metal, has the composition: copper 81.2 parts, in 10.7 parts, lead 7.2 parts, and phosphorus 0.4 part.
The lead-antimony bearing-metals range in composition from: lead 65 parts, antimony 25 parts, and copper 10 parts; to lead 80 parts, antimony 15 parts, and copper 5 parts.
''Universal" bearing metal is composed of tin 6 parts, lead 77.75 parts, antimony 16 parts and bismuth 0.25 part. Consult Buchanan, J. F., 'Practical Alloying' (Cleveland, Ohio 1910) ; Gulliver, G. H., 'Metallic Alloys: Their Structure and Constitution' (London 1913) ; Law, E. F., 'Alloys and Their. Industrial Ap plication' (London 1909).