: Progress of Practical and Theoretical Mechanics and Chemistry. On the Strength and other Properties of Cast Iron obtained from the Hot and Cold Blast. By WILLIAM FAIRBAIRN, Esq. [CONCLUDED FROM VOL. XXIV, PAGE 397.] There cannot be a doubt that the phenomenon of cohesive force is strongly developed in the preceding tables; the minute crystalline particles of the bars are acted upon by loads, which, in the heavier weights, are almost sufficient to produce fracture: yet fracture is not (except in one instance) produced, and to what extent the power of resistance may yet be carried is left for time to determine. It nevertheless appears from the present state of the bars (which indicate a slow but progressive increase in the deflections) that we must at some period arrive at a point beyond their bearing powers; or otherwise to that position which indicates a correct adjustment of the particles in equilibrium with the load. Which of the two points we have in this instance attained is difficult to determine: sufficient data are however adduced to show that the weights are considerably beyond the elastic limit,* and that cast iron will support loads to a much greater extent than what has usually been considered safe, or beyond that point where a permanent set takes place. But in whatever way this may be determined, it is obvious the preceding experiments give greater indications of strength than has generally been supposed cast iron would do; and should the bars continue to support the loads for a few years longer, there cannot exist a doubt as to the security of this metal under applications hitherto unknown; and the same may be said of other materials. In the 14th Table we shall find inch square bars loaded on the middle, within a few pounds of weights sufficient to break them; we shall also find the bars considerably bent, and the resisting powers in full operation to sustain the load. Now the question to be determined by this experiment is, the nature of this resistance; and to show in the first instance whether the resisting power of the extended particles below, and the powers of the condensed ones operating above, are sufficient at all times ad infinitum to support the load; or whether those particles, instead of being united (as we suppose) with a permanent force, nicely balanced at all points of resistance, are not absolutely giving way; and by slow, though imperceptible degrees, becoming hourly weaker, until the cohesive power is entirely destroyed and rupture takes place. It is not my intention in this place to offer any opinion upon the cohesive properties of matter, but simply to inquire how far the bearing powers of cast iron can be depended upon. It is evident from these experiments that both sorts of hot and cold blast iron possess that power in a high degree; and we need only refer to the experiments for examples to show the patient tenacity with which so heavy a load is supported. At first sight it would appear, that the heavier loaded bars were progressively giving way, as the deflections continue to increase since the loads were permanently fixed; this defect is however not more conspicuous in the bars supporting 448 lbs., than in those supporting 392 lbs.; * The elastic limit is that point where bodies under strain lose the power to restore themselves when the load is removed; a property which is strongly exemplified in cast iron. It has been considered by many that materials cannot be loaded with safety beyond that point. the deflection is even greater in the latter, arising in all probability from a greater degree of ductility in the bars. I hope shortly to induce my friend Mr. Hodgkinson, Professor Barlow, or some other able mathematician, to investigate this subject, and by close analysis to demonstrate those truths, so essential to the interests of all engaged in the use of the metals, but more particularly in reference to the security of the public at large. Effects of Temperature. When the multiplicity of objects to which cast iron is applied, and the innumerable situations in which it is placed, is considered, I may venture to state, that in every work of which cast iron forms the whole or a part of the structure, it is more or less liable to change. The rapidity with which it imbibes, and the facility with which it parts with caloric, is in itself a sufficient consideration for the labour I have bestowed upon these inquiries. The present investigation would have been less satisfactory had the experiments on the effects of temperature been omitted; and I trust, the annexed Tables, which exhibit hot and cold blast iron under various gradations of heat, will not be without their uses in the future application of this material. Rondelet, in his " Traite de Bâtir," has given and collected results from experiments, made by himself and others, on the expansion of bodies under the effects of heat; but I am not aware of any that have been made to ascertain the transverse strength of metallic substances under the various changes of temperature. It is well known that the effects of heat upon iron have not escaped the notice of philosophers; but I believe no writers on this subject have conducted their experiments in any way analogous to those now under consideration. The celerity with which heat passes through the metals, and the frequent recurrence of iron being the medium of communication between fluids and this powerful agent, it is not surprising that the changes of temperature thus induced should cause such visible indications of deterioration in the material. Gas retorts, and all those vessels exposed to the alternate changes of the heating and cooling process, are considerably injured by the expansion and contraction of the parts; and no doubt the destruction of the metals is much accelerated when they are worked up to a high and excessive temperature. Probably steam-boilers are not so much injured as those above-mentioned, as the temperature is kept moderately low by the water they contain, which seldom exceeds 212°. The same causes are, nevertheless, in operation, and must continue to be so under the varied influences of calorific action. Had time permitted, it was my intention to have pursued the experiments on temperature under a much greater degree of form and change than is here exhibited. For example, it might have been desirable not only to load the bars until they were broken, but also to charge them with different weights, and, by alternate heating and cooling, to have ascertained how far the bars so charged were affected by the change. Such an extension of the experiments might have led to the development of some new feature in the actions thus produced, and that more particularly by the introduction, abstraction, re-introduction, &c. of the different increments of heat. As it is, the bars were all broken at the temperatures indicated in the tables. TABLE XV. Coed-Talon, Cold Blast. To determine the relative strengths of Coed-Talon Hot and Cold Blast Iron, to resist a transverse strain under different degrees of temperature. 114° Permanent set, : +8 inches. Deflection in Weight in lbs. Temp. Fahr. Permanent set. inches. Deflection in Temp. Fahr. Weight in lbs. Permanent Set. inches. Deflection in Weight in lbs. Set. Temp. Fahr. Weight in lbs. inches. Deflection in Temp. Fahr. Permanent Set. inches. Deflection in 32° 112.034 224.072 + 420.144.008 113° 784.274.028 1120 Weight in lbs. 26° 112.041 + 28° 112.040 +32° 112.035 336.132.011 224.074 448.151.007 560.204.012 672.244.024 672.252.021 This bar was broken Broken in water. 448.142 448.187 560.242.027 672.224.051 672 .310 .385. This bar was... Ultimate deflection air. The microscopic appearance of this iron will be found at No. I. Table, on the transverse strain. Results reduced to those of bars 1.00 in. square, and 2 ft. 3 in. between supports. Product Experiment 3rd, No. 2 Iron 32° 6.955 13506700 940.7 .383 360.3 Experiment 4th, No 2 Iron 32° 15148200 958.5 .422 404.5 Mean, 6.955 14327450 949.6 .402 382.4 Experiment 5th, No. 2 Iron 113° 6.955 14168000 812.9 .336 273.1 Breadth of do. 1.004 Breadth of do. ports, 2 ft. 3 in. ports, 2 ft. 3 in. ports, 2 ft. 3 in. ports, 2 ft. 3 in. ports, 2 ft. 3 in. 1.010 Breadth of do. 1.012 Breadth of do. 1.010 Breadth of do. 1.009 Distance between sup Distance between sup- Distance between sup- Distance between sup- Distance between sup (b). Modulus of Breaking Ultimate 6 x d, or weight deflection power of (d). resisting Results reduced to those of bars 1.00 in. Product Temp. gravity. Experiment 2nd, No. 2 Iron Experiment 1st, No. 2 Iron 16° 6.968 15538300 24° .. impact. 800.29 .3865 309.3 14267500 823-10 .4140 340.8 .4002 325.0 .436 406.9 .423 383.2 6.968 14003350 919.7 .429 395.0 84° 6.968 14500000 877.5 .421 369.4 of temperature. ble to a considerable extent in the experiments ranging from 26° up to 190° weaker, and less secure under the effects of heavy strain. This is observaand probably less rigid in its nature; and I apprehend it will be found The infusion of heat into a metallic substance may render it more ductile, for the hot blast, or 15 per cent. loss of strength in the cold blast, and 10 being a diminution in strength as 100: 85 for the cold blast, and 100 : 90 The hot blast at 21° and 190°, is in strength as 811 : 731; TABLE XVII. Coed-Talon Cold Blast. To determine the relative strengths of Coed-Talon hot and cold blast iron to No. 2 Iron. No. 3 Iron. No. 3 Iron. No. 2 Iron. No. 2 Iron. Experiment 6. Set. Fahrenheit. Weight in lbs. inches. Deflection in 112.034 224.069 :: supports, 2ft 3in Distance between 672 broke it, 784 broke. This 336.106 + .987 Breadth 997 448.144.009 1930 considerable. The measure the de- 560.185.011 Distance between Distance between on at once. This 672.231.016 191 supports, 2ft. 3in supports, 2ft 3in. 784.281.021 Weight in Tem Weight in Tem light. 812.293 broke lbs. lbs. 934 broke 212° 1124 broke 600° Broke in hot water. Broke in boiling Broke in melted water. lead. Coed-Talon No. 3 cold blast iron exhibits greater density in the arrangement of its crystalline texture than the No. 2. Colour a whitish gray, interspersed with a number of minute luminous crystals. |