US2433627A - Treatment of metals - Google Patents

Description

Dec. 30, 1947. w. M. ROBERDS TREATMENT OF METALS Filed May 21, 1945 GINA-E0703 (Ittorneg Patented Dec. 30, 1947 TREATMENT OF METALS Wesley M. Roberds, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application May 21, 1943, Serial No. 487,942

3 Claims.

This invention relates to the heat treatment of metals, and more particularly to a method of and means for rendering the metal suitable for a hardening treatment with the aid of heat induced by high frequency currents.

The use of ferrous metal parts in many industrial applications and other fields of use is very well known. Where such parts involve surfaces which rub against each other, as in the case of the bearing surfaces of connecting rods which are in engagement with crank shafts of internal combustion engines, for example, these surfaces are subject to considerable wear. In order to prolong the lifeof the parts involved, it has been necessary to harden the surfaces.

In the copending application of George H. Brown, Serial No. 421,746, now Patent 2,424,794, assigned to Radio Corporation of America, there is disclosed a method of hardening various metals by the use of high frequency electrical energy at sufficiently high power to obtain extremely rapid heating of the work along only a relatively thin layer under the surface to be hardened, and thereafter permitting the heat to be dissipated through the metal which backs up the heated layer at a rate which is of the order of the rate at which the heat is applied. The heated work thus undergoes self-quenching, so to speak.

Where the work is of substantial thickness, the portion thereof in back of the thin, heated layer is ordinarily adequate to conduct away the heat with sufficient rapidity. In some instances, however, the work is very thin, and it becomes necessary to back up the work with a relatively thick material of high conductivity in order to provide the requisite backing to permit selfquenching. For this purpose, Brown has proposed backing up the work with a relatively low melting point metal, such as Woods metal or solder. This is, of course, feasible only where the surface to be hardened is surrounded by a hollow enclosure as, for example, in the case of hollow engine block u ed in airplanes. Here, the cylinder bores are surrounded by hollow enclosures into which the low melting point metal can be poured and from which it can be permitted to run out when it melts while the heat developed in the block by the radio frequency energy treatment is dissipated therethrough. In a great many instances, however, there is no such hollow enclosure which can be filled with the low melting point backing metal, and therefore the proposal made by Brown is inapplicable.

The primary object of my present invention is to provide a method of and means for backing up the work to be treated in cases where the method proposed by Brown is not feasible.

More particularly, it is an object of my present invention to provide an improved method of and means for backing up thin-walled metals one surface of which is to be hardened, which method and means are applicable in cases where the thin-walled metal is not surrounded by a hollow enclosure or the like in which a low melting point backing metal may be placed.

Another object of my present invention is to provide a method of and means for backing up metal as aforesaid which can be practiced and utilized even by one not skilled in the art, which are inexpensive in cost, and which are highly efiicient in use.

In accordance with my present invention, I apply to that surface of the metal which is not to be hardened a solid backing material of requisite thickness and of a character such that it can be forced into intimate contact with such surface. The backing material should, of course, be one which is highly heat conductive, and for this purpose a metallic backing member is preferably employed. Thus, for example, if the outer surface of a cylindrical, metallic member is to be hardened, there may be employed an expansible bolt or core which is placed within the cylindrical. member, and the core or bolt expanded to make intimate contact with the inner wall of the cylindrical member. The outer wall thereof may then be scanned by a suitable applicator to which radio frequency energy is supplied and which will induce in the work a current for heating the outer surface thereof. If the work is heated rapidly in the manner taught by Brown, only a very thin layer under the outer surface of the work will be heated to the hardening temperature, and the backing bolt, which is made thicker than the thickness of the wall of the cylinder-member, will conduct away the heat at substantially the same rate as it is applied. Shouldit be desired to harden the inner surf-ace of the cylindrical member, then the outer surface thereof may be backed up by a contractible sleeve which may be contracted into intimate contact with the outer surface of the work. In such case, the inner surface of the cylindrical member is suitably scanned as above described, and the heat developed in the work is rapidly dissipated through the outer and relatively thick, backing member.

The novel feature that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing, in which Figure 1 is a central, sectional view of a thinwalled, cylindrical member the outer surface of which is to be hardened and in connection with which my present invention is employed for backing up the wall thereof at the inner surface,

Figure 2 is a sectional view taken along, the plane of the line 11-11 of Figure 1,

Figure 3 is a view similar to Figure 1 but showing the backing member applied to the outer surface of the cylindrical member in the case where the inner surface of the work is to be hardened,

Figure 4 is a side elevation of a connecting rod bearing in connection with which my present invention may be employed, and

Figure 5 is a plan view of the connecting rod bearing along the plane of the line VV of Figure 4.

Referring more particularly to the drawing, wherein similar reference characters designate corresponding parts throughout, there is shown,in Figs. 1 and 2, a cylindrical member I of ferrous metal or the like and the outer surface of which is to be hardened. For this purpose, there may be utilized a suitable applicator 3 in the form of an inductor which is connected through a pair of leads 5 and a transformer 'I to a source of high frequency energy 9, such as a vacuum tube oscillation generator. The applicator 3 surrounds the work I in closely spaced relation thereto. Relative movement between the work I and the applicator 3 in a direction longitudinally of the member I may be effected in any suitable manner whereby the work will be scanned by the applicator to effect heating of only a very thin, skin layer under the outer surface of the member I.

Within the hollow cylinder I, there is placed a radially eXpansible bolt I I having a plurality of longitudinally spaced, circumferentially distributed slots I3 and a tapered bore I5. Within the tapered bore I5 is a correspondingly tapered member I? which can be forced into the bore I5 by a nut lea threaded on the smaller, threaded end Ha thereof. A nut ISb on the larger, threaded end Ilb of the tapered member I! may be later utilized for withdrawing the tapered member from the bolt I I. Forcing the tapered member Il into the bore I5 causes the bolt II to expand radially outwardly into very intimate or snug engagement with the inner surface of the cylindrical member I. Thus, there is afforded a thick, backing member I I, I! behind the unhardened, inner surface of the member I for rapidly conducting away from the member I the heat deveioped in the thin, heated layer thereof under its outer surface, so that the Work can be quickly self-quenched.

The expansible bolt I I and the wedge II should, of course, be made of highly heat conductive material and are preferably made of metal. The slots I 3 may be milled or formed in any other suitable manner in the bolt II and preferably terminate at points short of each end of the bolt, as clearly shown in Figure 1. The number of slots I3 which are necessary will vary with the type of work involved, and may vary from two upwardly in number. In any case, the slots I3 should be narrow compared to the thickness of the material between them, and the fewer in number, the better, as this affords more area of contact between the bolt I I and the inner surface of the work I.

In Fig. 3, I have shown an arrangement for heating the inner surface of the cylindrical member I. For this purpose, there may be fitted onto the outer surface of the member I a contractible sleeve 2I provided with longitudinally extending, circumferentially distributed slots 23 similar to the slots I3 of the expansible bolt II except that, in this case, the slots 23 extend clear to one end of the sleeve 23, as shown in Figure 3. After placing the sleeve 2| on the thin-walled cylinder I, one or more clamping rings 25 of suitable internal diameter are force-fitted over the sleeve 2I to contract it into intimate engagement with the outer surface of the cylindrical member I. The inner surface of the member I may then be scanned by the applicator 3 as above described, and the heat developed in the work I will be rapid'y dissipated through the relatively thick, backing member 2I to effect self quenching of the work.

In Fig. 4, I have shown my invention applied specifically to a connecting rod 3I of the type used to connect a piston to the crank shaft of an internal combustion engine, and the bearing surface 3Ia of which is to be hardened. The connecting rod 3| is provided with bolt holes 33 which are so located that they are surrounded by Very thin Wall portions 35 adjacent the surface 3Ia of the connecting rod. To prevent the thin wall portions 35 from becoming overheated and warped or otherwise distorted, it is necessary to have the heat developed therein conducted away rapidly. For this purpose, there may be inserted into each of the bolt holes 33 an expansible bolt arrangement such as described above in connection with Figs. 1 and 2.

A yoke 31 of copper or the like provided with openings 39 adapted to register with the openings 33 for the reception of the protruding end I'Ib and the nut 19b of the respective tapered members I1 is placed against the connecting rod 3| in the manner clearly shown in Fig. 4. The yoke 31 completes the path for the high frequency current induced in the rod 3I when the surface 3 la thereof is scanned by the applicator 3. Since the thin wall portions 35 are suitably backed up by the highly heat conductive bolts II and the Wedges II, the heat developed therein will be rapidly conducted away therefrom to effect selfquenching, and warping thereof will be minimized. In place of the yoke 31, it may be desired to utilize the bearing cap (not shown) which normaliy cooperates with the connecting rod 3I. However, the copper yoke 31 has been found preferable in practice since it makes better electrical contact with the connecting rod 3| and assists in conductin away the heat from the thin wall portion 35, i

From the foregoing description, it will be apparent that I have provided a very simple means for and method of carrying out the teachings of the above identified Brown application in cases where enclosures for reception of the backing metal around the work the surface of which is to be hardened are lacking. Although I have shown and described my invention in connection with two specific applications, it will, no doubt, be obvious to those skilled in the art that many other applications and modifications thereof are possible. Moreover, while I have described my invention primarily with reference to the hardening of metals, it should be apparent that it is equally applicable to the annealing of metals by a heat treatment. I therefore desire that my invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. The method of altering the hardness of one wall surface of a hollow, thin-walled, ferrous metal member hardenable by heating and quenching which comprises placing against the opposite wall surface of said member a relatively thick, second, metallic member of variable diameter, then varying the diameter of said second member to bring it into intimate engagement with said opposite surface whereby said second member will back up said first named member, then subjecting said one surface to the influence of a high frequency magnetic field of such intensity and for such a period of time as to induce in the region of said one surface a current which will rapidly heat only a very thin layer of said member under said one surface to a temperature requisite for hardening thereof while said members are maintained in intimate engagement with each other, and finally permitting the heat developed in said heated layer to be dissipated relatively rapidly substantially solely through said second member.

2. The method set forth in claim 1 wherein said one surface is the outer surface of said thinwalled member, and wherein said second member is an expansible member adapted to be expanded to be brought into intimate engagement with the inner surface of said thin-walled member when said second member is placed therein.

3. The method of altering the hardness of one wall surface of a hollow, thin-walled, ferrous metal member hardenable by heating and quenching which comprises placing against the opposite wall surface of said member a relatively thick, second, metallic member of variable diameter, then varying the diameter of said set:-

ond member to bring it into intimate engagement with said opposite surface whereby said second member will back up said first named member, then continuously subjecting successive 5 portions of said one surface to the influence of a high frequency magnetic field of such intensity and for such a period of time as to induce in the region of said one surface of each of said successive portions a current which will heat only a very thin layer of said member under said one surface to a temperature requisite for hardening thereof while said members are maintained in intimate engagement with each other, and finally permitting the heat developed in the heated layer of said successive portions to be dissipated relatively rapidly substantially solely through said second member.

WESLEY M. ROBERDS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,280,102 Somes Apr. 21, 1942 308,639 Stevens Dec. 2, 1884 1,168,794 Enoch Jan. 18, 1916 1,648,032 Starkin Nov. 8, 1927 1,249,532 Smith et a1 Dec. 11, 1917 455,420 Thomson July 7, 1891 2,316,506 Doelker et a1 Apr. 13, 1943 153,115 Robinson July 14, 1874 539,089 Simonds May 14, 1895 FOREIGN PATENTS Number Country Date 668,820 France July 22, 1929 0 467,308 Great Britain June 5, 1937 OTHER REFERENCES Metals Handbook, 1936 ed., page 94; ibid., 1939 ed., page 329.

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