1849.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



377 



properly balanced; and I have no doubt tbat a great portion of the 

 constant vibration to which they are subject may be traced to the 

 knocking action of the wheel upon the rail, owing to a want of 

 balance. The question of deterioration of axles arising from the 

 various causes which I have enumerated, is a very important one 

 to all railway companies: that some change in the nature of the 

 iron does take place is a well-established fact, and the investiga- 

 tion of this is most deserving of careful attention. 



I believe it will be found that the change from the fibrous to the 

 crystalline character is dependent upon a variety of circumstances. 

 I have collected a few specimens of fractured axles from different 

 points, which clearly establish the view I have stated. It is im- 

 possible to embrace in the present paper an exposition of all the facts 

 on this branch of the subject; but so valuable is the clear under- 

 standing of the nature of the deterioration of axles, that I am 

 now registering each axle as it goes from the workshops, and will 

 endeavour to have such returns of their performances and appear- 

 ances at different periods as will enable me to judge respecting 

 their treatment. When it is considered that on the railways of 

 Great Britain there are about 200,000 axles employed, the advan- 

 tage of having the best proportions, the best qualities, and the 

 best treatment for such an important and vital element of the 

 rolling stock, must be universally acknowledged. 



Remarks. — The President said, that Mr. McConnell had expressed a 

 strong opinion, that a change took place from a fibrous structure in iron to 

 a crystalline one during the time of its being in use : and it would be satis- 

 factory if an instance could be pointed out where this change had occurred, 

 owing to vibration or any other treatment, for he had not been able to 

 satisfy himself, from many experiments, that any such molecular change took 

 place. Hammering a piece of hot iron till it is cold produced a hardness 

 called crystalline ; but the question for consideration was, supposing an iron 

 axle were annealed by heating to a dull red heat and being allowed to cool 

 slowly, would the " texture" of that iron undergo any alteration afterwards, 

 from the vibration of the railway or any piece of machinery they were in 

 the habit of employing ? He had not been able to detect an instance of the 

 kind; and in giving evidence before the Iron Girder Bridge Commission, he 

 mentioned cases of vibration going on from year to year without any sensi- 

 ble change occurring in wrought or cast-iron. For instance, they hail the 

 Cornish engine-beam with a strain of 50 1b. per inch, working 8 or 10 

 strokes per minute for more than 20 years ; and certainly if a molecular 

 change was introduced by vibration, it ought to be by that continual con- 

 cussion and vibration, but none was perceived. Again, the connecting-rod 

 of a locomotive was a piece of iron in a most perplexing situation, for one 

 having more to do and having the strain changed more frequently it was 

 difficult to conceive ; and yet he had known the connecting-rod of a loco- 

 motive engine to vibrate 8 times in a second for several years' regular work, 

 making more than 200 million times altoj;ether, but the iron retained its 

 fibrous structure ; and he thought axles could not be suliject to so much 

 vibration. When, therefore, he found that a connecting-rod did not cliange 

 its molecular texture, he must say there were good grounds for douliting that 

 iron changes its state in axles. Then with regard to the experiments made 

 by Mr. McConnell with a view to ascertain where axles were most exposed 

 to tension, he could not quite agree with him ; for he subjected tlie wheels 

 and axles to a slow, steadily increasing pressure, till he bent the axles iu dif- 

 ferent positions. The results were correct as far as regarded the slow pressure 

 on the flanches of the wheel under the circumstances of the experiments re- 

 corded by him, but they were not a faithful representation of what takes 

 place in practice, for it would be found tbat when the wheels of a carriage 

 jarred, a violent blow was inflicted on the rail, and the strain on the axle 

 was toially distinct from a slow prrssurc. He would refer to the experi- 

 ments made some years ago by Mr. John Gray, on the Hull and Selby Itail- 

 way, and which were published in the Civil Engineer and Architect s Journalj 

 or the Mechanics* Magazine, to show how important is the element of time 

 in the fracture of an axle. He took a round bar of iron 3 feet long and 

 2 inches diameter, and turned it down in the middle to 1 inch in diameter 

 for 2 inches in length. He then took another bar, 1 inch in diameter uni- 

 formly throughout, and he tried the strength of these bars under coiicusnion 

 and not mere pressure. Now the severest point of strain would evidently 

 be the middle of the bars where the diameter was the same in both, and 

 consequently if weights were gradually and quietly laid on, the results would 

 be alike in both bars ; but when small weights were let fall on them, the bar 

 1 inch in diameter throughout its whole length was found to be much 

 stronger than that which was in the main 2 inches and 1 in the middle. 

 For as time is an element \\hen the resistance of material is concerned, re. 

 garding the axle as elastic like a piece of india-rubbber, the only particles 

 that could yield to percussion from the falling weight were tlmse between 

 the shoulders in the part of the axle that was turned down, but in the case 

 of the bar an inch in diameter throughout its whole length, the whole of 

 the particles would yield ; the one being a good spring and the other a very 

 bad one. It therefore appeared to him that the experiments recorded by 

 Mr. McConnell, though correct as regarded the position in which he put 

 them, were not correct as regarded concussion. The axles rarely if ever 

 broke in the middle, but generally at the end close to the boss of the wheel, 

 because of the sudden change in the elasticity of the axle at that point ; the 



portion of the axle fixed within the boss of the wheel being very rigid whilst 

 the rest remained elastic, which caused the vibrations to be suddenly checked 

 at that point. No doubt the plan of weakening axles in the middle had 

 done good because it made them spring, and in crank axles it relieved the 

 strain in the cranked part. 



Mr. Henry Smith suggested that in the case of bar-iron, the exterior 

 portion had greater tenacity than the interior or under part ; and the strength 

 would be more than proportionately diminished where the exterior portion 

 was cut through. He also referred to some experiments in which he had 

 cold-hammered fibrous iron till it became crystalline, and the effect produced 

 corresponded with the description given by Mr. McConnell of the fractured 

 axles. 



Mr. McConnell observed, that he had met with several cases of broken 

 axles in which a distinct annular space was observable all round the surface 

 of fracture, that was quite short.grained and appeared changed into a crys- 

 talline texture, whilst the centre of the axle remained fibrous. He admitted 

 that his experiments were only approximate, and that he had not put the 

 strain in the natural way ; but it was almost impossible to do so in conse- 

 quence of the great trouble and expense that would have accompanied it ; 

 at the same time the results were proportionate in each case, and the accu- 

 racy of the experimental results had been confirmed by calculation. With 

 regard to the axle fitting into the wheel, they now allowed only a very small 

 shoulder, not exceeding a sixteenth of an inch ; and this shoulder was not 

 square but tapered, and the boss of the wheel was slightly coned to fit the 

 shoulder. 



Mr. Cowper did not believe that any axle which when broken proved to 

 be crystalline had ever been filirous in its character. 



Mr. Uamsbottom considered that a change took place in the axle from 

 the effect of mere mechanical action, and his observations tended to confirm 

 him in that opinion. Some time ago he selected an axle which had not a 

 very good form of journal, and the end broke off with two blows of a 12 II). 

 hammer. This axle had for three years been subjict to a strain vertically, 

 which was reversed at every revolution, and it came off with a crystaUine 

 fracture. He then tried the part that had been within the boss of the 

 wheel, which had not been subject to this great strain, and found the 

 strength was very much greater than that of the journal, for it required 79 

 blows to break it off, and in that case the fracture was fibrous. A parallel 

 case might be observed with reference to an ash stick, which if doubled 

 would break with a fibrous fracture; but if subjected to vibration, however 

 slight, running through it a great number of times, it would break in a 

 different mode. He thought the strain on a locomotive connecting-rod was 

 by no means so great for the sectional area as upon an axle-journal ; and 

 the latter had two reversed strains for every revolution of the small wheels, 

 but the connecting-rod had only two for each revolution of the driving- 

 wheels. 



The President said, he was only desirous to put the members on their 

 guard against being satisfied with less than incontestiljle evidence as to a 

 molecular change in iron, for the subject was one of serious importance, and 

 the breaking of an axle had on one occasion rendered il questionable whether 

 or not the engineer and superintendent would have had a verdict of man- 

 slaughter returned against them. The investigation hence required the 

 greatest caution ; and in the present case there was not evidence to show 

 that the axle was filirous beforehand, but crystalline when it brcke. He 

 therefore wished the members of the Institution, connected as they were 

 with the manufacture of iron, to pause before they arrived at the conclusion 

 that iron is a substance liaide lo crystallise or to a molecular change from 

 vibration. For his own part, he was now induced to look upon wruught-iron 

 as literally elastic, l.ke a piece of india-rubl)er ; fur in the case of the 

 Britannia Tubular Bridge, where they had two lOinch square chains or bars, 

 each 100 feet in length, it was found that before the tube was raised, the 

 chains or bars strftc-hed nearly 2 inches in length at each time of lifting, but 

 resumed their original length when the strain was withdrawn; the same 

 action being repeated every time the tube was Jifted. He could therefore 

 only regard these 10-inch bars of iron as analogous to a piece of india- 

 rubber. 



Mr. McConnell said, he had one specimen of an axle which he thought 

 furnished nearly incontestible evidence of the truth of his position, that a 

 change took place in the texture of (he iron. One portion of this axle was 

 clearly fibrous iron, but the other end broke off as shoit as glass. The axle 

 was taken and hammered under a steam hauimer, then heated again and 

 I allowed to cool, after which they had to cut it nearly half through and to 

 hammer it a long time before they could break it. 



The President remarked, that this was a case of converse reasoning ; for 

 it was an instance of a piece of crystalline iron being converted into fibrous 

 iron. Iron when it was once heated and allojrcd to cool gradually, acquired 

 a close and fine grain, but became neither crystalline nor fibrous; if cooled 

 suddenly it acquired a crystalline grain, and if rolled while being cooled it 

 became fibrous, but he did not think that it underwent any molecular change 

 from mechanical action after it was cold. 



Mr. Henry Smith observed, that throwing cold water upon hot journals 

 did great injury by crystallising that portion of the axle. 



Mr. Slate did not think that any change from a fibrous to a crystalline 

 texture was produced in iron unless it were strained beyond the hmit of 

 its elasticity. Some of the pump-rods in Staffordshire which had been in 



49 



