US894428A - Process of raising the elastic limit of metals and relieving them of injurious strains. - Google Patents

Description

v To all whom. it may concern:

UNITED STATES PATENT OFFICE.

ALBERT H. EMERY, OF STAMFORD, CONNECTICUT I raocn'ss or RAISING THE ELASTIC 1.1m or METALS AND nnnmvme 'rn'n'm or mnmrous srrmms.

Specification of Letters Patent.

' retentea July as, 1908.

Be it known that I, ALBERT H. EMERY, a citizen of the United States, and resident of Stamford, in the county of Fairfield and State of Connecticut, have invented a certain new and useful Process of Raisin the Elastic Limit of Metals and Relievin hem of Injurious Strains, of which the f0 owing is a specification.

-When metals are loaded with compression, tension or torsion beyond their elastic limit, they take a permanent set and if the strain of compression, tension or torsion is sufiicient to make the ermanent set very considerable, the elastic limit is raised very considerably. Thus, if a compression member of a bridge is loaded sufliciently to give it a large permanent set of compression, its limit of elasticity will be much'raised and the initial strains which werein itbefore this loading, will be changed, usually much reduced. If a member, such as a bridge link is put under heavy load tension suflicient to give it a large permanent set, the limit of elasticity will be greatly raised and the initial strains which existed in it rimarily,-will be modified and greatly re uced. If a gun tube is strained by interior strains, such as by'introducing into it a heavy hydraulic'pressure suflicient to very materially permanently enlar e the tube, the initial strains in this piece will be reatly modified, the limit of elasticity will be greatly raised and when the internal load is removed the metal will take on strains of compression on the interior until these strains balance the remaining strains of tension on the exterior. In like manner, if a coiled s iral spring is loaded with compression su ciently to give it avery considerable permanent set, its elastic limit will be very materially raised. That. is to-say, it will, after this overloading, receive a larger loading Without ermanent set than it would previously and t e same is true with a spiral spring if loaded with tension to give it a ermanent set. Its limit of elastlcity w' be raised. Or the load again carried without vadditional set will be very materially increased. If now very careful tests are made of either the compression column or the tension link or the expanded tube it will be found that the movement caused by added loads giving a curve of pressure, Willbe different from the movements caused-by the removal of those loads. That is to say, if a bar in the gradual removal of these fixed loads. In other words,"suppose a load of five parts would load a bar to its limit of elastl 'ty.

the length with the same'loads which occur f This bar should stretch one-fifth-as muclrfor one part of the load as it does with five; three-fifths as much with three arts as it does with five. It will be. foun however, on removing the load, that the bar will be slightly longer with the three parts of the load on, than it was when the load was being put on. It will also be slightly longer when two parts of the load only remain than it was when two parts were put on in the initial loading. Likewise, when we load the s iral s ring with compression, if a certain oad sliows a movement of one inch, the perfect spring would show two inches with twice the load, three inches with three times the load, four inches with four times the load, &c. up to the limit'of elasticity; that is to say, the limit from which, when allloads are removed,

- the spring regains its full length. If now we remove these loads part by part, we will find the s ring successively'shorter at each point 7 of u oadmg than it was when itreached the same poirit in loading.

he difference between the lengths of the sp n at. loading and the corresponding lengt at unloading is what I term the curve of fatigue, and this in the ordinary springs i of commerce will often reach with full oads,

two, three, four, or even five per cent. of the maximum movement. I desire to get rid of this curve of fatigue, as far as practicable. For this purpose, when the column is com pressed or the bridge link extended or the gun tube expanded, or the spring for compression compressed, or the spring which is to be usedin tension has been extended, in each case by overloading, I anneal such work after it has been overloaded. This-annealing takes out some of the initial strains which are in a iece and enablesit to have the loads tlng twelve inches and receiving a permanent set of two inches in said shutting will then have an elastic movement of ten inches wlth this full load. But if we now carefully measfire the loads whichshut the spring each successive inch for the ten inches, and then grad:

dened. It has been customary to harden or oiltemper andanneal gun tubes. It has been uall unloadand weigh the load on the spring as the spring reaches eachsuccessive inch in opening, it will be found that .the loads will be less at each returning inch than were the loads which'caused the com ression of the spring to the same oints. of loading, as I saidef'ore, I-call the fatigue of the spring. If now I an'neal this spring at a proper temperature, which must not be too high, I find that the difference between the curves of loading and unloading will be very greatly reduced. Proper annealing may reduce this difference to one-fourth or one-fifth w'hat it'was before the annealing. That is to say, the differences of loading on the return movements after annealing should" be not more than one-fourth or one-fifth What they were before the annealing.

What I have said applies to columns, links, gun tubes, or springs hardened or unharcustomary to harden springs. It would be better for the bridges if the compression and tension members were also hardened and annealed. Whether the members mentioned for compression, tension or torsion are hardened or not, they should be treated by the process I have described by overloading in the direction in which the load is applied in the use of such parts and then annealed asdescribed. Such overloading will increase the elastic limit and this annealing after the overloadin will remove some injurious strains an will greatly' reduce the curve of fati ue. This is also true of'parts which are har ened very much and then annealed to temper them when theymay .be much overloaded in thedirection-of'use, receiving a large permanent set and a great increase of elasticity and then again annealed. This annealing after the straining-will in general be at-a lower heat than should be the annealing to temper them after they are hardened. Thisover-straining the parts to raise the limit of elasticity. and then annealing to remove injurious 'strains'may be done once or twice and sometimes thrice with profit, each time the limit of elasticity being raised higher and the art being enabled to carry a higher load with ing may be repeated, followed by a single annealing. a I

In the case of'a springthat has not been made very hard when hardenin it may receive its overload without annea 'ng for temper, and permanent set given it before anfib nealing at all, and then, after annealin it may, if desired, again be overloaded an re- ,annealed at a somewhat lower temperature.

But the best springs would be made over hard at the outset, then annealed for temper before loading, then overloaded to give a large permanentjset by a load once or twice his difference out injury', or the overload-- seeaas repeated and then annealed at a somewhat lower temperature than the first annealing, and this process of overloading and again annealing may be repeated one or more times if desired;

I have mentioned this process as being applied to separate pieces, but it may beuscd with several arts in combination in the same way in princlple and plan as shown applied to single pieces and when properly applied to structures, the different members of the structure will be better able to perform their functions properly.

In all cases, the annealing of strained parts which have not been hardened before straining, should be at a temperature notsufiicicnt to reduce the ap arent limit of elasticity below what it was before'straining, nor should it be sufficient to much reduce the limit of elasticity from that point to which it has been raised by the overloading. And in case of those parts which have been hardened previously to straining, the annealing after heavy final straining should be at a temperature not suflicient to reduce the limit of elasticity much if any below that which the part had before overloading or straining. And in general, this final annealing after straining, should be at a temperature lower than that at which the piece should be annealed when it re uires softening before straining.

Having t us described my invention, what I claim and desire to secure by Letters Patent is 1. The rocess of treating metals, for the purpose of raising their elastic limit and reieving them from injurious strains, which consists in loading a part made from the metal, in the direction of the load which it is to bear when in use, sufiiciently to give it a permanent set and increase its limit of elasticity and then annealing it at a low temperature not sufiicient to much reduce the imit ofelasticity, but sufficient to reduce the curve of fatigue.

2. The process of treating metals, for the urpose of raising their elastic limit and relieving them from injurious strains, which consists in repeatedly loading the metal in the direction of the load which it is to bear when in use, sufiiciently to give it a permanent set and increase its limit of elasticity and then annealing it at a low temperature not sufficient to much reduce the limit of elasticity, but suflicient to reduce the curve of fati ue.

3. T e rocess of treating/metals, for the purpose 0 raising their elastic limit and reieving them from injurious strains, which consists in repeatedly loading the metal in the direction of the load which it is to bear when in use sufliciently to give it a permanent set and increase its limit of elasticity and then annealing it at a low 'tem erature not sufficient to reduce the limit of e asticity,

' 5 urpose 0 but sufficient to much reduce thecurve of consists in first hardening the metal, thenis fatigue',.then repeating said steps of loading tempering it by annealing, then loading it in and annealing in the order named; I i the direction of the load which it is to'bear '4."-The Frocess of treating metals for the when in use, sufliciently to give it a permaraising their elastic limit and renent set, andthen annealing it substantially 'evmg them from injurious strains, which as set forth. 20 consists in first hardening the metal, then, Theforegoing specificationsigned atWashloading it in the direction of -the' load which ington, D. 0., this 12th day of November, I it is to bear when in use sufiiciently. to give it 1907. v 1

A BERT H. EMERY.

10 a permanent set and then anneahng it, substantially as st forth. 4 1', I

5. The process of treating metals-for the. In presence of urpose 0 'raising their elastic limit and 're- HERVEY S. KNIGHT,

ieving them from injurious strains which EDWIN S. CLA'RKsoN.