Mechanics of engineeringComprising statics and dynamics of solids: and the mechanics of the materials of constructions, or strength and elasticity of beams, columns, arches, shafts, etc . ay bewritten F=fB, in which f is a coefficient of axle-friction derivable fromexperiments with axles, and JR, the resultant pressure on thebearing. In some cases B, may be partly due to the tightnessof the bolts with which the cap of the bearing is fastened. As before, the work lost in overcoming axle-friction perrevolution is =fP27tr, in which r is the radius of the , like f is an abstract number. As i
Mechanics of engineeringComprising statics and dynamics of solids: and the mechanics of the materials of constructions, or strength and elasticity of beams, columns, arches, shafts, etc . ay bewritten F=fB, in which f is a coefficient of axle-friction derivable fromexperiments with axles, and JR, the resultant pressure on thebearing. In some cases B, may be partly due to the tightnessof the bolts with which the cap of the bearing is fastened. As before, the work lost in overcoming axle-friction perrevolution is =fP27tr, in which r is the radius of the , like f is an abstract number. As in Fig. 176, a friction-circle, of radius =fr, may be considered as subtending the dead-angle. 166. Experiments with Axle-Friction.—Prominent amongrecent experiments have been thoseof Professor Thurston (1872-73),who invented a special instrumentfor that purpose, shown (in princi-ple only) in Fig. 178. By means ofan internal spring, the amount ofwhose compression is read on a scale,a weighted bar or pendulum is causedto exert pressure on a projecting axlefrom which it is suspended. Theaxle is made to rotate at any desiredTelocity by some source of power, the axle-friction causing. 176 MECHANICS OF ENGINEERING. the pendulum to remain at rest at some angle of deviationfrom the vertical. The figure shows the pendulum free, theaction of gravity upon it being G, that of the axle consistingof the two pressures, each = i?, and of the two frictions (eachbeing F —f R\ due to them. Taking moments about 0, wehave for equilibrium 2fjRr = Gb, in which all the quantities except f are known or temperature of the bearing is also noted, with referenceto its effect on the lubricant employed. Thus the instrumentcovers a wide range of relations. General Morins experiments as interpreted by Weisbachgive the following practical results: -> r for well-sustained For iron axles, in iron or i lubrication; brass bearings • ] to .08 for ordinary I lubrication. By pressure p
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectenginee, bookyear1888
