32
MODERN STEAM PRACTICE.
For double-rivetted joints, add two-thirds of the depth of thesingle lap. Where great strength is desirable this form of jointshould always be adopted. It will be seen from the following tablethat the double-rivetted joints retain their resisting power, while thesingle-rivetted joints lose about one-fifth of the actual strength oithe plates.
The figures 2, i‘5, 4-5, 6, 5, &c., given in the preceding table aremultipliers. These multipliers are considered as proportionals ofthe plates; thus, supposing we take of an inch as the thicknessof plates, we have simply to multiply the thickness by the numberto find the proportionate quantities to form the strongest joint:—
Inches.
*375 x 2 — ‘75° diameter of rivet.
•375 x 4-5 = 1 '687 length of rivet.
•375x5 =1*875 distance between rivets.
‘375 x 5*5 =2*062 quantity of lap, single rivetted.
*375 X9*i =3*412 quantity of lap, double rivetted.
It will be seen that the dimensions thus found nearly agree withthe dimensions in the preceding table, which are practically correct.
Boilers are now being made of Steel: as made by the Siemens orBessemer process, the tensile strength is about 29 tons per squareinch, and the elastic strength appears to lie within 11 to 16 tonsper square inch. Test pieces, 10 inches long, give an elongation of28 per cent., with a contraction of area of about 49 per cent.Punching the rivet holes weakens the metalby about 30 per cent.;the strength can, however, be restored by annealing. Drilling theholes does not seem to affect the strength. By the use of Steelthe weight of boilers has been reduced about 10 per cent. Forfurther reference to manufacture and strength of steel see article onShipbuilding.