PROCESS FOR

ANNEALING CAST IRON BY A. P. GREAVES, ESQ.

MR. PRESIDENT AND GENTLEMEN, I have' the privilege of bringing under your notice to-night

the Process for Annealing Cast Iron, lately discovered in our midst at the works of Messrs. Jenkins and Law.

Though there are few members of this Association, I am sure, who have not read or heard something of this new invention, and while there are others to whose very courteous assistance I am much indebted, I still think that for greater clearness it will be as well to recapitulate and trace the Process up to its present development, from its source in the observations and experiments of the inventors.

Such being the case, then, it will be necessary to explain the-necessity which became the mother of this particular invention. A great portion of their work—that of making bedsteads—is, like all bedstead manufacturers, accomplished by using iron or chilled moulds, instead of the ordinary ones of sand and loam. The castings produced, however, by this means, though perfectly satisfactory where little or no fettling is required, turn out, as most of us are aware, quite intractable if it is attempted to submit them to the ordinary workshop tools, and, indeed, so hard is the skin produced, that a file glances over it without making the slightest impression.

The inventors, like many others before them, found, however, that it would be much more satisfactory could this skin be reduced, and made amenable to the action of machinery or other tools. After a series of experiments—lasting, I am told, for some 18 months—a step in the right direction was made some 15 months ago, and some bars, tin. x lin. x lin. were very satin.

Process for Annealing Cast Iron. 63

factorily annealed in the presence of Mr. Newbery, at the Tech-nological Museum, and afterwards broken in the testing machine at the University by Professor Kernot.

These tests showed that the metal had undergone a distinct change, and that while its texture was closer and finer, its strength had been increased nearly 100 per cent.

Feeling, then, that they had discovered something more than common, the inventors placed their property in the hands of a syndicate of Melbourne gentlemen, who instructed me to make a series of experiments, carried out as nearly as possible on the lines of those in older countries, with a view of finding out the real increase of strength which the process added to the ordinary pig, and any collateral advantages appertaining thereto.

Mr. Newbery was also asked to make such experiments as he deemed fit—to discover, if possible, the change, chemically speaking, under which the iron goes during treatment, and, if possible, the reason why.

Such, then, Mr. President, are in brief the circumstances which surround the discovery of this process, so far as it is at present developed, and I will now proceed to explain the modus operandi of the process—the appliances required—and the behaviour of the annealed metal in the testing machines, and while being submitted to the tools used in an engineer's work-shop.

I will then refer to the analytical experiments just success-fully completed by Mr. Newbery and his assistant, Mr. Dunn,. after a great deal of laborious and very often disheartening work and, lastly, we will discuss the question as to the various uses to which this process could be applied, and the best means of apply-ing it.

First, then, the process is a very simple one, as can be seen by the Patent Specifications. The articles to be annealed are first heated to a yellow-red heat, or about 1000° Cent., or 1800° Fahrenheit ; they are then allowed to cool slowly and regularly to a heat of 450° Fahrenheit, and while at this temperature they are plunged into a bath of treacle and water, the specific gravity of which has been raised to •005.

From this description it will be seen that the appliances re-quired are neither numerous nor expensive, and, as experience directs, we shall, no doubt, in time be able to turn out unusually clean, good castings with very great rapidity and precision. At present, the only difficulties worth the word have been in con-structing a well-formed chill, and next, in immersing the casting in the bath at a uniform temperature.

On some future evening, when it is proposed to discuss this subject, I will take care that the Association is supplied with

64 Process for Annealing Cast Iron.

some samples of chills, as well as the castings turned out of them, and, indeed, I would have done so to-night hard it been in the power of the Secretary to have given me a longer notice.

The few samples I have brought, however, will serve to show what can be done by this process, while the two sheaves or pulleys, both cast in the same chill, and from the same iron, but only one of which is annealed, will serve to show the great difference of texture in the one and the other. The bar lying on the table is one that was broken at the University after carrying a load of 18501bs., or, in other words, giving a modulus of rup-ture (according to Rankin's formula) of nearly 100,0001bs. ; and as from the same formula the average modulus of cast-iron is about 40,000, and the minimum for steel 80,000, we may be tempted, with every show of reason, to believe that this process really and truly produces a form of mild steel. This theory, too, is still further backed up by two facts which were evolved during the experiments. The first is that the form of cleavage at the point of rupture was almost always of a curvilinear character, and totally different to the plain transverse sections shown by the broken sand-cast bars.

The next fact was, and this one struck me very forcibly as bearing out strongly my belief in its steely nature, that while the ordinary sand-cast bars commenced to show fatigue or a per-manent set after they had only carried some 100 lbs., the annealed bars cast from the same metal, and quite possibly from the same pot, carried 1230 lbs. before they declined to come back to their original straight form,

As you can well imagine, Mr. President, I watched these particular tests with great interest, and Professor Kernot, who assisted me in many of the experiments, will, I am sure, vouch for the accuracy with which they were carried out. As will be seen by a reference to the pamphlet now before you, the mean tenacity in tons per square inch of the sand-cast iron was 6.15 tons, and that of the same iron annealed 12 tons 7 cwt., and had I had a complete and perfectly designed oven at my disposal, I feel sure that the latter average would have been even higher.

During these experiments, which were conducted at Williams-town, by the aid of the machine there, which was placed at my disposal by Mr. Mirls, I endeavoured to obtain some data from which the modulus of elasticity could be obtained, but unfortu-nately the extension was too small to be measured with any degree of accuracy by the tools at my disposal, and as I had also to give up all hopes of making any experiments for the com-pression stress, that idea was abandoned; and thus, though the figures given for the extension of the annealed bars on page 25

Process for Annealing Cast Iron. 65

of the pamphlet are fairly approximate, I should nevertheless be unwilling to see them used as a basis for any accurate calcula-tion.

The average transverse breaking stress for sand-cast bars, 1 in. x 1 in. and 36 inches between supports was 831.72, and that of the annealed bars 1552.82, showing the moduli of rupture to be 44,911.88 and 83,916.28 respectively. Comparative results will be more clearly appreciated by a glance at the diagrams to be found at the end of the pamphlet, and when an hour can be spared, a perusal of the tables preceding the diagrams will prove very interesting, as presenting a series of apparent anomalies yet to be explained. I must confess, however, that on looking at the very exhaustive tests made at home, in America, and else-where, that after all my experiments look very incomplete beside these, and I must therefore beg you to accept the only excuse I can offer—that the apparatus, though good as far as it went, was not good enough.

To come now to the chemical analysis as prepared by Mr. Newbery and Mr. Dunn. This analysis, which, I may tell you, was only completed after a great deal of disappointment and several failures, was obtained of course from an average of several experiments and divides out thus :---

The percentage of silicon in the chilled but unannealed iron amounted to 3.20 and in the annealed to 3.55.

The percentage of manganese was 0.91 in the former and 0.93 in the latter.

The percentage of phosphorous in the former was 0.78 and in the latter 0.82, while there was found to be a trace only of sulphur in each.

It will be thus seen that the process practically does not alter the proportion of these four constituents, but when the analysis for the carbon, free and combined was made, a most astonishing —and, to use Mr. Newbery's own words---an at present unex-plainable change took place.

There was found to be only 0.74 per cent. of free or graphitic carbon in the unannealed iron, but 3.32 per cent. in the an-nealed iron, while 3.48 per cent. of fixed carbon found in the former had dwindled down to a mere trace in the annealed metal.

This startling, but nevertheless perfectly accurate result, shows us, therefore, that the process causes the iron to throw off the large percentage of fixed carbon, made by using a chill mould, in the form of graphite, or free carbon.

Why this change is brought about by this particular treatment is quite impossible to say ; but, without doubt, it will furnish, until explained, a large amount of food both for careful thòught

66 Process for Annealing Cast Iron.

and scientific research, as well as adding to the already numerous phases in which that most useful metal, iron, sees proper to introduce itself to our notice.

I will not now detain you by endeavouring to point out the numerous avenues of usefulness that are unfolded to this new process, nor will I try to enumerate the various uses to which it might be put by engineering skill. I have no doubt whatever that there is not a member of the Association who would not at once see where its use might be brought in to the particular work in which he was then engaged, and would then find that as its use increased its usefulness would find fresh developments in directions not guessed at before.

In a few months I expect to have erected a plant to carry out this invention, and in that case I hope I shall be permitted to invite the Council and Members of the Association to come and have a look over the works and watch the process from first to last.

I am aware that this short paper does but little justice to the merits of an invention so useful, but at some future time, when we shall know more about it, and when we can speak with more certainty as regards the reason as well as the nature of the operation, I shall be glad to go into the matter more exhaus-tively, and by that time also shall be able to illustrate more freely from the numerous practical uses to which it will no

,doubt be applied.

Library Digitised Collections

Author/s:Greaves, A. P.

Title:Process for annealing cast iron (Paper)

Date:1885

Persistent Link:http://hdl.handle.net/11343/24226