Brake Tests

239 (G) The rate of wear of shoes as affected by clasp and standard brake conditions on the basis of wear per unit of work done. (H) The rate of wear under clasp brake conditions as affected by various types of standard and reduced area brake shoes on a basis of wear per unit of work done. (I) The effect of a difference in the relative hardness of the brake shoe metal. (J) The effect of the rate of cooling of brake shoes after test. (K) The effect of the difference in conditions of brake shoe machine and road tests. 454. A complete schedule of the tests is shown on the table on page 240 which indicates the number of tests made under each condition, with respect to braking power, speed, type of shoe and rigging con- ditions. The tests were made in two series. In the first series plain solid (type A), plain slotted (type B) and plain solid special hard (type H) shoes were tested under both standard and clasp brake conditions at 150 per cent, nominal braking power through the range of speeds (30, 60 and 80 m.p.h.) and at 60 m.p.h. through the range of nominal per cents, of braking power (50, 90, 113, 150 and 180). 455. The second series of tests was made, under clasp brake con- ditions only, on plain reduced area (types C and D) flanged solid (type E) flanged slotted (type F) and flanged reduced area (type G), all at the same ranges of speed and braking power. 456. The summaries of averages for the various tests are shown on pages 391 to 397. The detailed data of all the tests is on file in the office of the General Superintendent M. P. at Altoona. 457. All of the brake shoes were of the cast iron steel back type, selected from the shoes provided for the road tests. Two or more shoes of each type were tested. There was some variation between different shoes of the same type when tested under the same conditions, but this variation was not greater than that noted when making successive tests on the same shoe and under the same conditions. There is one ex- ception to this rule in the case of Shoe 97 after it had been reduced to one-half its original area. This shoe repeatedly failed to check with other similarly modified shoes of the same type. At the time the shoe was modified it was noted that this shoe was very hard and differed con- siderably in this respect from the other shoes. For this reason all the tests of Shoe 97 in its modified form were rejected from the averages.