(.’hap. XI.

MECHANICS.

9<I5

hammered, and afterwards filed into the true form : when iron wheels are under ten feetin diameter, they are cast entire ; when larger, the arms are cast in separate pieces, andthey are attached to the rims by flanches, and securely bolted together : these Blanchesshould be cast at right angles to the circumference, and the arms are secured to the bossby means of two projecting pieces cast upon it, and which fit into the nave or boss.

In the construction of fly-wheels the greatest quantity of cast-iron possible is given tothe rim and arms, in order that the momentum generated in the rim should not destroy it:they are usually cast in a number of pieces, and bolted together, using every means toresist the tendency they have to fracture.

Strength of Wheels. —We must first ascertain the weight which acts on the rim of thewheel, then the length of the arm or lever, and the part supported by each arm, must betaken as a fraction of the whole. Suppose, then,—

w = the weight, or straining power in pounds,r = the radius in feet.

b and d = the breadth and depth of the arms in inches.n = the number of arms.a = the quantity of allowable deflection.

w r 32656 na

The breadth or depth being given, the other dimensions may be found: — in a wheel 6feet radius the number of arms eight, the weight acting on its circumference 1600 pounds,and the allowed deflection a tenth of an inch : then —

1600 x 6 3

- = bd*.

bd* =

= 163.

2656 x 8 x 1Hence when the breadth is 2J inches, then —

d= 3/1^.= 4’03 inches in depth.

V 2-5

When a wheel is so strained that the arms break, the fracture takes place near the axle,and here then should the greatest strength be given.

Shafts or Axles are employed either in a horizontal or vertical position, and the arbour orspindle on which they turn is called a gudgeon. A horizontal shafthas a support between the first mover and the work to be per-formed ; the cylindrical portion revolving on this support is calledthe journal; that which supports it, or in which the journalrevolves, is called the carriage, but when it is not a part of theframework, it is called a plummer’s block ; the lower gudgeonsof upright shafts rest upon steps or bearings.

When shafts are made of cast-iron, their strength may be thuscalculated ; suppose r = to the radius of the wheel in feet, at thecircumference of which the power is applied, s = to the side of asquare, or d = to the diameter of the shaft in inches, £ = to thethickness of the metal in a hollow cylinder, u> = to the weight inpounds. In cast-iron shafts,

r w = 150 s 3rw= 125 d 3nv— 125 d s (1 — p*)

Fig. 1295.

'i.

Square

Solid cylindricalHollow cylindrical -In wrought-iron shafts,

Square

Solid cylindricalHollow cylindrical

Where

<

—X-

Fij. 1296.

P=-

d—2t

r it = 168 s 3r w = HO </ 3ri« = 160(/ 3 (l-

-P')

then for cast-iron shafts, where the length does not exceed one-fourth of e, we haveS= for a square shaft,

V 150 4 .

d= 3 /- ■ * for a solid cylinder,V 125 >

y.

V 1

for a hollow cylinder.

125 (1-p 4 )

The same formula answers for malleable iron, if we use the number 168 for the first,140 for the second, and 140 (1 —p 4 ) for the third divisors : when the shafts are cylindricaland of cast-iron of great length, multiply the weight in pounds by r in feet, and divide thoproduct by the cube of the length in feet, multiplied by 5-2 ; add 5148 to the quotient,

3 P