Modern Machine-Shop Practice, Volumes I and II - Joshua Rose

“Experiment No. 3.—Wrought-iron bar, 1¹⁄₈ inches square by 30 inches long heated to a dull red and cooled gradually in air.

			Contraction.	Percentage on original length.	Remarks.
After	1st	cooling	No change.	——	——
„	2nd	„	„	——	——
„	3rd	„	„	——	——
„	4th	„	„	——	——
„	5th	„	„	——	——

Wrought iron rectangular plate. 14” thick × 11” 995 × 598 planed on both surface and edges. Heated to redness, and cooled in water 50 times. The dotted lines show original form, the black lines the form after the eperiment.

(Two-ninths of full size.)

Fig. 1430.

The plate was subjected to fifty heatings to redness and subsequent coolings in water of ordinary temperature. At every tenth cooling accurate measurements were taken of the contraction in superficial dimensions, and [Fig. 1430] shows the final form after fifty coolings. The intermediate measurements at every tenth cooling showed a uniform and gradual decrease in the superficial dimensions, but the thicknesses were only measured after the fifty coolings had been completed. The thickness appears to have varied considerably; in some places, notably towards the centre and outside edges, being much reduced. Between the centre and outside edges the thickness appears to have increased, and in some few places the plate has been split open. The average dimensions in inches before and after the experiment were as follows (dimensions of cracks being allowed for):—

		Average length.		Average breadth.	Average thickness.		Cubic inches capacity.
		Inches.		Inches.	Inches.
Original		11.99	5	5.98	.74		53.08
After 50 coolings		11.25		5.59	.77	4	48.72
Per cent. variation from original	-	Decrease		Decrease	Increase		Decrease
		of		of	of		of
		6.2 p. c.		6.52 p. c.	4.6 p. c.		8.2 p. c.

“Three triangular pieces of iron were then cut out of the plate from positions indicated on the diagram; No. 1a from the part most reduced in thickness, No. 3a from the part most increased in thickness, and No. 2a from a part where the thickness was a mean between the thickest and thinnest part. The specific gravities were accurately determined as follows:—

No. 1a	7.552 thinnest part.
No. 2a	7.574 average thickness.
No. 3a	7.560 thickest part.