THE TREATMENT OF IRON.

South Canterbury Times, Issue 3300, 30 October 1883, Page 2

THE TREATMENT OF IRON.

(“ Melbourne Argus.”) REMARKABLE DISCOVERY. Within the last few months, and after a series of careful experiments, extend, ingover a period of two years, there has been discovered in Melbourne a process of treating cast iron, which bids fair in the future to play a very important part in the iron trade. The ordinary way of (.rodeoing castings in iron, as most people are aware, is somewhat tedious. In the first place the pattern-maker designs in wood an exact model of the object required ; then the moulder takes an impression of the pattern in sand, specially prepared for the purpose, into which the molten metal is run. Left undisturbed until it is cool enough to bear handling, the ca-t iron is then taken from the mould, which, being broken by the action of removal, cannot be used again.

There is however another process by which castings can bo obtained with fur greater rapidity. A mould of the article required is made in iron instead of sand—the common bullet mould being a \ery familiar instance of what is meant —so that when the molten metal is poured in it is almostinstantly solidified. The mould is then opened, the casting thrown out, and the mould is available for the production of other impressions. This is called “casting in a chill,” and though, as is evident, a much more ex peditious method than the former, it carried with it the serious disa Ivantage of making the casting so extremely bird that a diamond, to say nothing of a file, will not scratch it. Now as at least 90 per cent, of the castings produced require afterwards to be sub. mitted to the action of tools of various kinds it will be easily understood that such adamantine hardness as this practically confines the use of the chilling process to the comparatively small number of cases in which the casting requires no further finishing after it leaves the mould.

Bv the new process, however, to which we are referring, and which has been patented by Messrs Jenkins and Law, of this city, not only is this disadv«ntage entirely obviated, hut num rous positive advantages are obtained. One is a saving of tim-i so great that by the new process 10 castings can be procured for one by the old. Increased neatness and accuracy of finish are secured, rendering it in many cases unnecessary to submit the work to that further finishing which is technically known as “fettling.” This is notably the case with regard to cog-wheels, pinions, and simi'ar portions of machinery, while in the case ot ornamental ironwork the increased sharpness and cleanness of outline considerably heightens the artistic effect. The third advantage is an increase of tensile strength so great that a cast-iron bar lin square and Ift long will with stand a strain of over 19001 b, whereas the same bar before being submitted to the new process would not resist a greater pressure than 1200ib. It is scarcely necessary to point out that such a considerable increase of toughness will admit of castings being greatly reduced in weight, and under the altered conditions, cast iron will in many cases be an efficient substitute for malleable. Lastly, the soft, tough, and close grain produced by the new process, not only much increases the facility of working the metal, but proportionately diminishes the wear and tear of tools, and results, moreover, in a great improvement in the appearance of finished article. The now method is very simple, and can be explained in a few words. The castings to be operated on are cast in the chill, allowed to coed, re-heated in a furnace to a certain particular temperature, and then plunged into a liquid containing certain ingredients. Thus treated, the iron develops a close, tough, but comparatively soft grain, so much like that of average steel that experienced ironfounders in the colony have had great difficulty in believing the metal to be cast iron at all. It will be evident from what has been stated above that the new patent is calculated to bring about important developments in every branch of the iron trade, and it may safely be predicted that the locomotive or the marine engineer, no less than the general ironfounder or the tool-maker, will not be long in discovering the advantages which this new and manageable material places in his hands. The discovery was the result of pure accident. A fragment of cast iron, which had been thrown or dropped into a water channel at one of the Melbourne foundries, on being afterwards picked up and broken, was found to bo soft and tenacious instead of brittle. This led to inquiry, and many experiments to ascertain how the change cou>d have been produced. The theory is that the temperature of the fragment and the composition of the water were the two circumstances which produced the transformation, After numerous trials, the right temperature to which the iron should bo reduced before immersion was discovered, and also what foreign elements were required in the water. The metal is dipped, not steeped, in the hath, which contains common and cheap ingredients. 'Hie change wrought in the iron is physical, not chemical. The molecules are apparently affected in their v. ay cf arranging themselves, by the sudden shock caused by precipitating the heated metal into cold water. Some of the experiments were conducted by r members of the University staff, whilst the laboratory of the technological Museum was resorted to on frequent occasions for testa, '