. The Street railway journal . derable importance. The stressesin the material of the wheel must, throughout the whole section ofthe wheel, be kept within the limits permitted for the material. The wheel is made as a solid disc, on the circumference of whichthe buckets are dovetailed in, each bucket being made and fixedseparately to the wheel. The buckets consequently load the cir-cumference of the wheel with a radial force when the wheel is re-volving. The amount of this force may be understood when it ismentioned that the centrifugal force on the bucket of a 300-hpturbine wheel, which bucket
. The Street railway journal . derable importance. The stressesin the material of the wheel must, throughout the whole section ofthe wheel, be kept within the limits permitted for the material. The wheel is made as a solid disc, on the circumference of whichthe buckets are dovetailed in, each bucket being made and fixedseparately to the wheel. The buckets consequently load the cir-cumference of the wheel with a radial force when the wheel is re-volving. The amount of this force may be understood when it ismentioned that the centrifugal force on the bucket of a 300-hpturbine wheel, which bucket weighs 250 grains, is 15 cwts. whenthe wheel is running at its standard speed. The stresses in the wheel are tangential and radial, and if wecall the radial stress P and the tangential stresses S, it is evidentthat both P and S vary with the radius R. Further, these stressesdepend on the axial thickness of the wheel in each place, and theyalso affect one another. Fig. 2 shows the stresses in a wheel for a 50-hp steam Street Railway Journal FIG. 2.—STRESSES IN MATERIAL OF TURBINE WHEEL As may be seen by this diagram the wheel is so constructedthat both P and S have their largest value at the circumferenceof the wheel, just where the buckets are fixed. Consequentlythe wheel is not made of uniform strength, but is strongest at theheaviest part, that is, in the center. It will be seen from Fig. 2 that the tangential stresses S in theboss of the wheel increase as they approach the hole in the centerof the wheel. These stresses would be still greater on the largersizes of wheels, and in order to avoid these greater stresses thelarger wheels are made without any hole through the center, butthe shaft is made in two pieces fixed to the wheel by flanges andscrews. The part of the turbine which makes it possible to run theturbine wheel at its enormous speed, is the flexible shaft. Theshaft on which the turbine wheel is mounted has bearings on each side of the wheel at a good
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectstreetr, bookyear1884
