US2255572A - Method of making nonferrous articles - Google Patents

Description

Sept. 9, 1941. D, L. v. SCHWARTZ METHOD OF MAKING NONFERROUS ARTICLES 2 She etS-Sheet 1 Filed Aug. 10. 1939 Fig.2

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Sept. 9, 1941. 1:). v. SCHWARTZ METHOD OF MAKING NONFERROUS ARTICLES Filed Aug. 10, 1939 2 Sheets-Sheet 2 Fig/1 INVENIOR. OOIVALDL. 1 SCHWARTZ BY JMu ATTORNE Patented Sept. 9, 1941 METHOD OF MAKING NONFERROUS ARTICLES Donald L. V. Schwartz, Cleveland, Ohio, assignor to The Cleveland Graphite Bronze Company, Cleveland, Ohio, a corporation of Ohio Application August 10, 1939, Serial No. 289,453

4 Claims.

The present invention, relating as indicated, to a method of changing the nature of strains in one surface of a formed metal article, is more particularly directed to amethod of removing the ex-.

cessive tensional strains resulting in the surface layer of a metal article, and particularly a nonferrous article which has been rolled, forged or otherwise plastically deformed. In the manufacture of such products as rolled non-ferrous strip sheets or the like or the manufacture of products drawn or formed therefrom in the cold state, the entire body of metal is plastically deformed by one operation to which it is subjected. Since this is .done in the cold state the result is a hardening of the metal and the production of work hardening strains, either of tension or compression, in various parts of the body of the metal. It is, however, standard practice to carry the plastic deformation of metal in the cold condition to a point at which further deformation would result in breakage and then anneal the metal to remove the work hardening strains and place it again in condition for further cold working. Not only is the annealing operation expensive, but it usually results in the removal of all of the strains and in bringing the metal back to its original soft condition while the nature of the production may require that the metal should retain some of the work hardening resulting from deforming operations.

I have found that a simple operation performed upon one surface of a non-ferrous work hardened article or strip of metal will alter the work hardening strains in some possibly extremely thin surface zone of the metal and thus permit further plastic deformation of the metal without breakage and without excessive work hardening.

To the accomplishment of the foregoing and related ends; said invention, then, consists of the means hereinafter described and particularly pointed out in the claims; the annexed drawings and the following description setting forth in detail certain means of carrying out the invention, such disclosed method however, constituting but one of the various ways in which the principle of the invention may be used.

In said annexed drawings:

Fig. 1 is a diagrammatic view of a side elevation illustrating a rolling operation to which a 'non ferrous strip has been subjected;

. Fig. 2 is a longitudinal sectional view of a strip Fig. 3 is a similar view on an enlarged scale showing greatly exaggerated, the character of the surface resulting from a deforming operation;

Fig. 4 is a similar view showing the incipient breaks resulting from this surface condition;

Fig. 5 is a similar view of a formed article or strip of the same character again showing incipient breaks resulting from the surface which is produced;

Fig. 6 is a view diagrammatic in character illustrating one method of removing the work hardening strains from the surface layer of the article;

Fig. 7 is a similar view showing another method of removing the strains; 5

Fig. 8 is a longitudinal section on a greatly enlarged scale illustrating the nature of the strains in the article after subjection to the operation of Fig. 6 or Fig. '7;

Fig. 9 is a similar view of a curved strip showing the nature of the strains in the radially outer surface after being subjected to an operation of the character shown in Figs. 6 or 7;

Fig. 10 is a view in perspective showing the progressive steps in the manufacture of non-fer rous bushings in which the present method may be applied; and I Fig. 11 is a view of the completed bushing.

In Fig. 1, I have shown a strip 1 which may represent any non-ferrous material, such as brass, bronze or the like, which has been subjected to a deforming rolling operation performed by the rolls 2 and 3. Such an operation, whether performed by rolls or by forging, stamping or otherwise, causes a hardening of the metal and sets up work hardening strains throughout the metal which are roughly proportionate to the amount of reduction in the thickness of the metal. In Fig. 2, I have shown the strip on an enlarged scale which illustrates what I believe to be the strains resulting in the metal from a rolling operation. Following such an operation I believe the interior 4 of the strip or article to be in a state of compression, which I have indicated by transverse parallel lines. The two surface areas of the strip 5 and 6 which I believe to be in a state of tension'I have indicated by parallel lines which are parallel to the upper and lower surface of the article.

In Fig. 3 I have shown on a still larger scale the same strip shown in Fig. 2 but have indicated at the surface 1 the type of irregularities which exist therein. Even though a strip is rolled through smooth heavy rolls, the surface is still not uniform'nor level and consists of a series of crests 8 and valleys or depressions 9. If the article is now subjected to further work hardening on the surface I which would, of course, be done I if this article be bent in the form shown in Fig. 5,

then the transverse crack I would start from I thebottorn of the depression 9 and would result in either asevere cracking or complete breakage of the article. At the present the only method of preventing such cracking orv breakage is in either a complete or a partial anneal of the article to're'lieve the strains and to soften the metal, but in many cases this is not desirable as the temper and resiliency imparted to the metal by the work hardening were desired in the final product. e I

The method which I have found capable of preventing the cracking orbreakage of the ar-'- ticle upon further workingcis illustratedin two forms in Figs. 6 and '7. It is based upon the tion which produces the blank I! the metal is stressed on its outer surface and particularly at v the points 20 and 2| to a degree which often results in breakage. I have found-that it is extremely difficult to give the metal any particular annealing action and still maintain the degree of work hardening in the metal which meets the required specifications, but that ,by applying a assumption'that since the surface of the'article has been placed under high, tension strains ,by

the working to which it hasbeen subjected, it

- may be further worked without causing cracks to form with resultant breakage if the surface strains can be changed. I have accomplished this by the method shown in Fig. .6 in which the strip I is subjected to a burnishing operation effected on the strip by means of a number of burnishing wheels, depending upon whether or not one or both sides of the strip are to be treated. If the article is in the form of a strip as shown in this diagrammatic view, it may be passed longitudinally between the-two burnishing wheels II which press against one (or both) of the surfaces of the strip producing asmoothing of the surface and possibly a surface anness in which layer the tension strains are relieved, placing this surface layer l3 (see Figs. 8

and 9) in a neutral, that is an unworked condition, or possibly in a state of compression. In either case further working of the metal either in forming or bending the metal into the condition shown in Fig. 9 will produce its strains in the surface layer,- but since the surface layeris either in a state of compression or in a neutral 1 "state, an ordinary amount of working will not produce the initial cracking or breaking that is produced if the surface is in a state of high tension when the further working is applied theretol In the manufacture of bushings from a nonferrous strip, such for example as copper lead,

a strip I4 is passed through successive forming operations to produce first, oil grooves I5 and I6, then a blank of the proper length [1, next a partially formed blank l8 and in the next step a more completely formed blank I9 which is of roughly cylindrical or horseshoe shape, depend- In the manufacture of such bushings, the specification sometimes requires a certain degree of work hardening in the finished article, and the burnishing operation of the character already 'd/described to the outer surface'of the strip u,

that is to the surface of the strip which produces the outer surface of the final., bushi:ng, it

is possible to use a strip which, has been work hardened to a' high degree without any cracks or breakage during the final forming operations. In the manufacture of a great number of bushings of the type shown in Fig. 11 by the method indicated-in Fig. 10 in which a burnishing operation has not been applied to one side of the strip, no breakage has occurred to the surface which forms the face or inside surface ofthe final bushing, but breakage occurred in agreat number of cases to the outer surface. This seems to support the theory which I have suggested herein as the explanation of the action secured in a strip of work hardened non-ferrous material by the burnishing operation which I have described. v

. It will be obvious that the present method of burnishing strips can be applied not only to nonferrous material in strips or other form but also to many articles formed therefrom during a series of forming operations in order to relieve thestrains on a tensioned surface of such article and permit further plastic deformation within I certain limits without breakage. Apparently the operation to which I suggest that the metal be subjected does not affect the internal characteristics of the metal nor the degree of hardness or temper in the article proper. Examination of surfaces of an article subjected to the burnishing operation herein described, discloses no differences in the surface or in the characteristics of .the metal, but it is possible after such an operation to subject'the article to further work hardening operations'without breakage.

As a modification of the invention, a partial anneal could be used to remove afew points of hardness, leaving the material in a statewhich cannot be formed properly without cracking. To

avoid cracking, the material can then be burnishedin the manner which has been described.

I ing, of course, upon the construction of the dies.

strip M from which the bushings are'manufactured, is therefore rolled to produce a very con siderable degree of work hardening when the articleis further formed and during the opera- Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the means and steps herein disclosed, provided those stated by anyof the following claims or their equivalent be employed. I therefore particularly point out and dis tinctly claim as my invention:

"1.. In a method of making bushings from nonferrous rolled strip, the step which consists in applying frictional pressure to one surface of said strip to remove the tension strains therein, then forming bushings from said strip and forming the same with such surface on the exterior thereof,

2. In a method of forming bushings from work hardened non-ferrous metal strip which has been worked to substantially its ,limit of ultimate f strength, the steps which consist in changing the .character of the strains on the surface of said strip from tensile to compression without appreciablychanging the hardness of the strip, and

then forming said strip into bushings, saidj 'flrstnamed step preventing cracking in the formed bushings.

3. In a method of making 'articlesfrom plastically deformed metal strip, the step which consists in applying frictional pressure to one surface of said strip to remove the tension strains therein, then forming articles from said strip and forming the same with such surface on the exterior' thereof.

4. In 'a method of forming articles from work 10 hardened metal strip which has been worked to substantially its limit of ultimate strength, the steps which consist in changing the character of the strains on the surface of said strip from tensile to compression without appreciably changing the hardness of the strip and then forming said strip into articles, said first named step preventing cracking in the formed articles.

DONALD L. V. SCHWARTZ.

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