Published: Jan 1937
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For the purpose of this discussion, wear of metal is taken to mean only that caused by friction and abrasion. Also for the purpose of this discussion, a treatment of the theoretical aspects of the wear problem is not considered necessary. It is well known that the results of wear manifest themselves not only in changing the dimensions of parts subjected to wear, thus rendering them unsafe or useless, but other surface conditions are often present. These surface conditions, in lay language, are referred to as pitting and galling. In more technical language the terms of erosion or corrosion are applied. These manifestations must not be forgotten or underrated. C. F. Kettering has said: “In metals there seems to be a connection between friction and corrosion. The cause of corrosion is not known, but it is coupled with the same thing as friction.” It is well known, of course, that there is a very direct relationship between friction and the wear of metals. The present-day problems relating to the wear of metals in railroad service are a concomitant of such changes in operating conditions as: 1. Formerly four locomotives were used to move a passenger train from Chicago to Memphis—a distance of approximately 500 miles. Today only one locomotive is used for the same run. 2. Formerly the fastest passenger train time between Chicago and the Twin Cities was slightly over 10 hr.—a distance of 410 miles, the average start to stop speed being 41.7 m.p.h. Today this run is made in 6 1/2 hr.—average start to stop speed being 63.1 m.p.h. This schedule requires running above 100 m.p.h. for extended distances. 3. Formerly freight trains were slow; today many operate on scheduled speeds equivalent to crack passenger trains of a few years ago. Today the average speed of freight trains between terminals, including all delays encountered en route, is approximately 55 per cent higher than in 1920. Today there are scheduled freight trains like the following: The “Merchandiser” from New York to Buffalo—438 miles—scheduled 10 hr. and 15 min.—average speed 42.7 m.p.h. The “Blue Streak“ from East St. Louis to Pine Bluff, Ark.—403 miles—scheduled slightly over 10 hr.—average speed 40 m.p.h. 4. The increase in piston speeds resulting from the foregoing accelerated passenger and freight train speeds are: Passenger locomotives—80-in. drivers, 28-in. stroke— (a) Average speed 41.7 m.p.h.— 838.5 ft. per min. (b) Average speed 63.1 m.p.h.— 1228.5 ft. per min. (c) Average speed 100 m.p.h.— 1950.0 ft. per min. Freight locomotives— (a) 63-in. drivers, 30-in. stroke— average speed of 30 m.p.h.—801 ft. per min. (b) 70-in. drivers, 30-in. stroke— average speed of 42.7 m.p.h.— 1032 ft. per min. 5. Formerly the surface speed of main locomotive driving wheel journals was 500 ft. per min. at 40 m.p.h. Today this surface speed is 750 ft. per min. at 70 m.p.h. 6. Recent tests have shown that the temperature near the center of locomotive bearings ranges from 320 to 535 F. 7. Formerly average locomotive boiler pressure was 180 to 200 lb. per sq. in. Today the range is from 225 to 255 lb. per sq. in. Today pressures as high as 500 lb. per sq. in. are being employed in high-pressure boilers equipped with watertube fireboxes. Today steam turbine — electric-drive locomotives are being built with a flash type of boiler with 1200 lb. pressure. 8. Formerly the degree of superheat used in locomotives ranged from 100 to 200 F. Today 300 F. of superheat is not uncommon. In the steam turbine locomotives being built temperatures in the order of 800 F. will be experienced. 9: Formerly metals and lubricants had to withstand relatively low temperatures. Today they confront in the higher brackets a temperature range of from 600 to 800 F. 10. Formerly rails, brake shoes, wheels and other parts had to withstand the wear induced by relatively slow speeds. Today they must resist the inherent wear associated with speeds of more than 100 m.p.h.
Wallace, L. W.
Director of Equipment Research, Association of American Railroads, Chicago, Ill.