Worm gearing . y gearat which a constant temperature may be maintained, the otherpressures and speeds can always be calculated, lower speedspermitting higher pressures and conversely. THE TEMPERATURE COEFFICIENT 61 It is profitable to investigate the effect on the quantity ofheat generated by varying the pressure and the velocity. pV 60 H=v 778 Case 1.—Assume p constant at 3500 lb. then ^^ 3500X.002X60 ,,H = v ^^3 ^..54. TABLE V V f.p.s. B.T.U. per minute 5 2.70 10 5.4 15 8.1 20 10.8 25 13.5 30 16.2 35 18.9 40 21.6 45 24.3 Here the difference = 2.7 B.T.U. per increment of 5 f.p.s.Case 2.—Assum
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Worm gearing . y gearat which a constant temperature may be maintained, the otherpressures and speeds can always be calculated, lower speedspermitting higher pressures and conversely. THE TEMPERATURE COEFFICIENT 61 It is profitable to investigate the effect on the quantity ofheat generated by varying the pressure and the velocity. pV 60 H=v 778 Case 1.—Assume p constant at 3500 lb. then ^^ 3500X.002X60 , , H = v ^^3 ^..54. TABLE V V f.p.s. B.T.U. per minute 5 2.70 10 5.4 15 8.1 20 10.8 25 13.5 30 16.2 35 18.9 40 21.6 45 24.3 Here the difference = 2.7 B.T.U. per increment of 5 f.p.s.Case 2.—Assume v constant at 45 ft. per second H^2^ .002X45X60 778 .00694 / TABLE VI V B.T.U. per minute 1500 10.41 1750 12.14 2000 13.88 2250 15.62 2500 17.35 2750 19.09 3000 20.81 3250 22.55 3500 24.30 3750 26.05 4000 27.75 62 WORM GEARS Here the difference = 7.4 B.T.U. per increment of 250 lb. Fig.26 shows these increments of H plotted against pressures andvelocities respectively, and the results show that for a com-. 2500 §2250 ^2000 g1750 o1500 ^ 10 12 14 16 18B.T.U. per Minute Fig. 23. paratively small increase in the normal tooth pressure, the, heating effect is increased at a greater rate than with relativelylarger increments of the velocity. CHAPTER X EFFICIENCY OF WORM GEARING The efficiency of worm gearing has been discussed by severalwriters and it will be dealt with next, because closely bound upwith it is the coefficient of friction between the worm andwheel, and the determination of the latter is a necessarypreliminary. The most complete investigation of mechanical friction thatthe author is familiar with, is that conducted by BeauchampTower, and published by him in various numbers of the Proceed-ings of the Institution of Mechanical Engineers. Taking thematerials most nearly corresponding to those employed forworm gears, viz., steel rubbing against bronze in a bath ofmineral oil, we find the lowest value he obtained for /i was .0008.No doubt these conditions were ideal,