. Railroad construction. Theory and practice. A textbook for the use of students in colleges and technical schools . to thelower temperature of the journal-boxes, is very marked andcostly. It has been suggested that a jacketing of the journal-boxes, which would prevent rapid radiation of heat and enablethem to retain some of the heat developed by friction, wouldresult in a saving amply repaying the cost of the device. Roller journals for cars have been frequently suggested, andexperiments have been made with them. It is found that theyare very effective at low velocities, greatly reducing the
. Railroad construction. Theory and practice. A textbook for the use of students in colleges and technical schools . to thelower temperature of the journal-boxes, is very marked andcostly. It has been suggested that a jacketing of the journal-boxes, which would prevent rapid radiation of heat and enablethem to retain some of the heat developed by friction, wouldresult in a saving amply repaying the cost of the device. Roller journals for cars have been frequently suggested, andexperiments have been made with them. It is found that theyare very effective at low velocities, greatly reducing the start-ing resistance, which is very high with the ordinary forms ofjournals. But the advantages disappear as the velocity in-creases. The advantages also decrease as the load is increased,so that with heavily loaded cars the gain is small. The excessof cost for construction and maintenance has been found to bemore than the gain from power saved. 344. Grade resistance. The amount of this may be com-puted with mathematical exactness. Assume that the bailor cylinder (see Fig. 206) is being drawn up the plane. If W. Fig. 206. is the weight, N the normal pressure against the rail, and G the force required to hold it or to draw it up the plane with uniform velocity, the rolling resistances being considered zero or considered as provided for by other forces, then WhG:W::h:d, or G=-^) but for all ordinary railroad grades, c? = c to wdthin a tenth of Wh1%, , G = = TT Xrate of grade. In order that the student may appreciate the exact amount of this approximation the per-centage of slope distance to its horizontal projection is given inthe following tabular form: 414 RAILROAD CONSTRUCTION. §344. Grade in per cent. 1 2 3 1 5 Slope dist.^jQp nor. dist. Grade in per cent. 6 7 8 9 10 Slonedist.^^Qp nor. disi. This shows also the error on various grades of measuring withthe tape on the ground rather than held
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