« ZurückWeiter »
WILLIAM SELLERS, Philadelphia.—The very interesting paper upon the wear of steel rails that has just been read presents the record of a series of investigations that are extremely valuable, and the deduction that has been drawn from the results noted seems to be unavoidable; the tests, however, to which it is proposed steel rails shall be subjected hereafter, with a view to determine their quality, should have our careful attention, and with reference to these I desire to make a few suggestions.
While the manufacture of soft steel was yet in its infancy it was believed that the presence of phosphorus in any notable quantity was very deleterious, in fact fatal, to the good quality of this product, and the greatest care was exercised to procure materials in which this element could not be more than traced. With the development of this art it has been found that larger and larger proportions of this hurtful ingredient may be used, providing always corresponding changes in the chemical composition shall be made to accord therewith.
It is, perhaps, besides the point to inquire whether the earlier beliet was correct or not, the fact remains that steel is now produced which contains much larger proportions of phosphorus than would have been permitted a very few years ago, and that this steel is now considered to possess qualities which fit it admirably for use in rails; moreover, it is well known that the degree of heat, and the manipulation to which the ingot is subjected in transforming it into the finished product has an important influence in determining the characteristics that product will exhibit.
These facts have an important bearing upon the question, What shall be the tests which are to determine the quality we desire to attain? If the engineer is to specify the chemical composition, and the mode or process of manufacture by which the manufacturer must work, it would seem that improvement in the art must, to a certain extent, be limited, and a vicious system would be introduced, injurious alike to the engineer and the manufacturer. The chemical composition has no value to the engineer, for no matter what the chemical composition, it is upon the physical qualities at last that he must rely to determine whether or not it will answer his purpose. It should be his business, therefore, to devise such physical tests as will determine absolutely whether or not the quality that he desires has been produced, while the manufacturer should be left free to make such chemical combinations or adopt such processes of manufacture as will fulfill the requirements of
the engineer. It may, however, be questioned whether the physical data we now possess will enable us to agree upon the physical tests requisite to demonstrate the quality; but if this is admitted it only proves that further physical data are wanting, for the quality is finally determined by use, the result of which our physical data should enable us to predict. Of these data the one most abundant is the ultimate strength, and next to this ductility, bending, shearing, punching, torsion, impact and fatigue, in all of which, except the last, abundant facts are at hand. As most specifications prescribe a high and a low limit for ultimate strength, it would seem to be the prevalent opinion among engineers that high or low steel, as it is technically termed, is to be determined by its ultimate strength; and it becomes important at this stage to define what quality it is that most accurately defines this term, that is to say, does it consist in high or low ultimate strength, or in high or low ductility relatively to its ultimate strength. It is essential for all structural uses that the engineer should know upon what ultimate strength he can rely, for upon this all his calculations must be based; but it is upon ductility that he must depend for safety, the measure of which he must determine, after which the higher the ultimate strength he can obtain the better his material will be for any structural purpose; that is to say, with a given ductility the higher the ultimate strength of his material the safer it is, and conversely, with a given ultimate strength, the higher the ductility the safer it is. High ductility and high ultimate strength cannot be produced except with the most favorable conditions, both as to chemical composition and as to the mode of manufacture; the quality is, therefore, to be ascertained with most certainty by determining the relation of the one to the other, and for the same reason this relation would seem to be the factor which should most accurately define the term high or low, as applied to steel, and the requirements simply of an ultimate strength not less than pounds per square inch, with a ductility not less than
per cent., would at once determine the character of steel required and the quality of it. It must not be understood, however that the determination of this relation is the sole requisite in determining quality for every purpose, for the capacity to bear fatigue and shock is scarcely less important, as, for example, the question now under consideration. And although it is probable that the material which exhibits high ultimate strength coupled with high ductility will prove to be capable of enduring the most fatigue and shock,
we cannot affirm that there is any definite relation between the two, in fact we have many data tending to show that such a relation does not exist.
An examination of the data which Dr. Dudley has tabulated indicates that to establish the relation between ultimate strength and ductility alone would be insufficient to determine the wearing quality of rails, so that these data must be supplemented by some other. This other, I suggest, should be that of fatigue from shock, not that of simply bending, which last Dr. Dudley “has found to bear a closer relation to the loss of metal per million tons than any of the other tests.” I take exception to the classification of this test as one of the four ways in which a bending test could be applied. A rail bent under the drop test, and one bent in the testing machine by pressure slowly applied, would not be subjected to the same character of strains. While a drop test is a bending test, it is also much more; the same number of degrees of deflection in the one case as in the other would, I think, represent very different powers of resistance in the material operated upon. With the same weight falling from the same height in properly constructed guides, the same effect must be produced with every blow. In fact, it is difficult to conceive how any other form of test can produce more uniform effects or which can be more accurately measured; the results may be more diverse with such a test than with others, because they are produced by pressure and shock, whereas nearly all other forms of testing produce their results by pressure alone. It is this difference, however, which commends the drop as the test above all others for rails as being more analogous to that by which the rail is tested in use, and we should be well satisfied that the objections urged against it are well founded before we abandon it for others which may appear to offer more uniform results. It may well be that uniform results obtained by a system of testing widely different from that we require our material to sustain in use may have small value for determining in advance the effect of that use. I am thus driven to the conclusion that to obtain the relation of ductility to ultimate strength, together with the capacity to sustain fatigue from shock, would be to attain to absolute certainty as to the quality in an engineering sense.
There are, however, considerations other than that of the tests which must have attention before adopting a system of testing for steel rails, and as to these I would now make a few suggestions. The tests
required to determine quality in the directions indicated are well understood, but, simple as they are, the time that must be consumed in making them would result in serious loss to the manufacturer if his mill is to be held for their determination, and if he proceeds with the execution of his order in advance he incurs a serious responsibility in assuming the risk of rejection for the large product that would be turned out before the requisite tests could be made. While the cost of a test for ultimate strength, ductility and for capacity to bear fatigue would be small, the large number of such tests that would be necessary to establish the quality of an ordinary order for steel rails would be a serious item, and as every item of cost must be eventually borne by the consumer, it is important for the railway companies to adopt a regular system for testing their rails that shall not only be the most expeditious, but the least expensive. For the purpose of inspection, therefore, it would seem to be sufficient to adopt a system that would be simply an indication as to the qualities desired, without subjecting the parties interested to the cost and delay which must result from exhaustive and thorough tests, and upon these indications the rails might be accepted. This would seem to accord with the best foreign practice, as illustrated by the very admirable paper upon “Rail Specifications and Rail Inspection in Europe,” by C. P. Sandberg, C.E., read at the Lake Superior Meeting, August, 1880. There are two tests which would give these indications with great accuracy, both of which could be applied without the expense and delay incident to preparation of specimens, and both of which require comparatively inexpensive machinery. These are the registering punch and the drop test. The former is a special tool which could be applied upon the crop ends, and could be portable; the latter is too well known to require description, but its indications if carefully noted would, I believe, be the most valuable of the two, but in conjunction with the punch they should be conclusive. The punching test would have this advantage: that by its use an inexpensive indication could be had of the quality of every rail. The suggestion that this test should be applied upon the fishplate holes has probably prevented its introduction heretofore; first, because such holes are not now punched, and second, because to make such registration every manufacturer would have to procure a registering punch, and this would be difficult to apply upon existing machines. If this tool should be recognized as a part of the inspector's outfit and
specially adapted to his needs, it might soon come into general use if care was used to maintain the punches and dies in good condition.
In conclusion, I suggest that if the physical tests are to be supplemented by chemical analysis the specification for this analysis should not be complete; that is to say, in place of giving the proportions of carbon, phosphorus, silicon and manganese, a maximum limit should be fixed respectively for phosphorus, silicon and manganese only, leaving the carbon to be varied by the manufacturer, so that he may properly be required to furnish material that will fulfill the physical conditions; for it is evident that if the engineer defines the chemical composition he cannot reasonably ask the manufacturer to gurantee that this composition shall give certain physical results.
W. R. Jones, Pittsburgh, Pa.- The question that naturally occurs to me is this: Has Dr. Dudley in his investigations been aiming to prove a theory, or has he been guided by an earnest desire to discover what are the proper elements in the composition of a good-wearing steel rail:
Unfortunately, for correct chemical information, he has omitted in his analyses two very important elements--sulphur and copper. Now, before we will even begin to admit the correctness of Dr. Dudley's conclusions and the formula he prescribes, we will at the start question the propriety of any chemist or scientist prescribing a formula for making steel when he has ignored such important elements as sulphur and copper. I, for one, will not accept any such formula.
Are we sure, or is Dr. Dudley sure, that the chemical analyses embodied in his paper are correct? This may seem a presumptuous question; yet, with my experience with chemists, I naturally doubt the correctness of the analyses, and, before I will accept them as correct, I will ask that comparative tests of phosphorus and manganese be made by the Pennsylvania Railroad chemists and the chemists of the leading steel-works in the country. Let us first verify the correctness of the analyses before we consider the conclusions. I can enumerate a great number of instances in which chemists have differed very widely in their determinations of phosphorus and manganese. A prominent iron firm made a contract with the Edgar Thomson Steel Company to deliver pig metal guaranteed to be between 0·07 and 0.08 phosphorus. An analysis by our chemist resulted in phosphorus 0:148 and 0:152-a rather startling difference! Again, a sample bar WHOLE No. Vol. CXII.—(THIRD SERIES, Vol. Ixxxii.)