To find the weight of any forging the volume may first be found in cubic inches and this multiplied by .2779, the weight of wrought iron per cubic inch. If the forging be made of steel, the figures .2835 should be used in place of .2779. This gives the weight in pounds. Below is given the weight of wrought iron, cast iron, and steel, both in pounds per cubic inch and per cubic foot.
Cast iron 450 per cu. ft. .2604 per cu. inch Wrought iron 480 per cu. ft. .2779 per cu. inch Steel 490 per cu. ft. .2835 per cu. inch.
Fig. 87. Diagram for Calculating Stock in Special Forging.
Fig. 89. Diagram of Connecting Rod.
Suppose it were required to find the weight of the forging shown in Fig. 87. A has a volume of 11/14 cubic inch, C 3/4 cubic inch, and B 1 cubic inch, making a total of 2 15/38 cubic inches. If the forging were made of wrought iron it would weigh 215/28X.2779 =.7 pound. The forging in Fig. 89 has a total volume of 171 3/7 cubic inches and would weigh, if made of wrought iron, 47.64 pounds.
A much easier way to calculate weights is to use tables such as II and III given herewith. Table II gives the weights per foot of flat iron bars. In Table III is given the weights for each foot of length of round and square bars.
When using Table II to ascertain the weight of any size of flat iron per foot of length, look in the first column at the left for the thickness. Then follow out in a horizontal line to the column giving the width. The number given will be the weight in pounds of one foot of the desired size.
To use the table for calculating weights, the procedure would be as follows:
Taking Fig. 89 as an example, each end is 2 inches by 4 inches and 6 inches long, and, as far as the weight is concerned, the two ends would be equal to a bar 2 inches by 4 inches and 1 foot long. From the table it will be seen that a bar 2 inches by 2 inches weighs 13.33 pounds, and a bar 2 inches by 4 inches, being twice as thick would weigh twice that, or 26.66 pounds. A bar 2 inches in diameter weighs 10.47 pounds per foot and, as the central part of the forging is 2 feet long, it will weigh 20.94 pounds, making the total weight of the forging 47.6 pounds.