US3501935A - Method of flattening metal articles - Google Patents

Description

United States Patent 3,501,935 METHOD OF FLATTENING METAL ARTICLES Don P. Clausing, Wilkins Township, Allegheny County, Pa., assignor to United States Steel Corporation, a corporation of Delaware No Drawing. Filed Feb. 21, 1968, Ser. No. 707,241 Int. Cl. B21d 1/06, 3/00 US. Cl. 72-207 8 Claims ABSTRACT OF THE DISCLOSURE A method of flattening bowed metal articles such as plates, structural shapes, bars, etc. which have a concave and convex surface. The method involves plastically deforming the concave surface without exceeding the yield strength of the convex surface by, for example, rolling the bowed article in contact with a surface having protrusions which cause deformation of the concave surface.

The present invention relates to a method of flattening metal articles such as plates, structural shapes, bars, etc. More particularly, the invention relates to flattening such articles by applying to their concave surface a force sufficient to cause local plastic flow or deformation of the concave surface without substantially exceeding the yield strength of the convex surface.

Metal articles such as structural plates, bars, etc. have a natural tendency to bow as a result of normal production processing. The amount of bow in the article may make it unacceptable for commercial applications. To flatten such bowed metal articles and straighten same, they have been bent to remove the bow, stretched to remove the bow, or restrained in dies during quenching to prevent bowing. Many devices have been employed to perform these methods. However, each of the conventional methods has at least one shortcoming. Firstly, acceptable flatness and straightness cannot always be obtained in some products, particularly those in heat treated form. Secondly, some of these conventional methods have a strong tendency to break certain types of products, again particularly heat treated products. In most cases, processing is difficult to control and the time and cost of these flattening operations are often excessive.

The present invention provides a method of flattening and straightening bowed metal articles by imparting local plastic indentations or deformation into the concave surface of the bowed article while it is in the cold condition. Heated articles are much more easily straightened and flattened but special equipment and processing is necessary. The present invention, however, enables bowed metal articles to be flattened at room temperatures and in the cold condition.

Plates, structural shapes and bars bow or bend generally because the concave surface is smaller in area than the convex surface. Local plastic deformation expands the concave surface to coincide with the area of the convex surface, thereby flattening and straightening the article.

The method of flattening and straightening by cold forming through local, plastic deformation in the concave surface possesses a number of inherent advantages. Thus, for example, with the method in accordance with the invention there is a very small risk of product breakage, good control of the flattening and straightening is achieved and all types of products can be flattened and straightened, including heat treated products which cannot be flattened by conventional means.

In accordance with the invention, flattening and straightening by imparting local plastic deformation into the concave surface through cold forming can be per- "Ice formed in a rolling mill, press or drop hammer forge. One means of flattening and straightening in accordance with a presently preferred embodiment involves the use of a pair of force applying surfaces, one of which has protrusions thereon. The bowed metal article to be flattened is compressed between the force applying surfaces in such a manner that the surface having protrusions induces localized plastic deformation in the concave surface. Sufficient force is applied to accomplish plastic deformation of the concave surface without substantially exceeding the yield strength of the convex surface. :In one presently preferred embodiment, the cold forming is accomplished in a pair of rolls, one of which is smooth and the other of which has protrusions on the roll surface. The bowed article with the concave urface contacting the roll with protrusions is compressed between the rolls causing the concave surface to expand laterally by forming plastic indentations thereon. The lateral expansion of the surface that was originally concave flattens and straightens the metal article. Structural shapes can be flattened and straightened in the same way with the use of rolls contoured to fit the structural shape.

An alternate means of flattening and straightening with the use of a rolling mill involves the use of a die having protrusions as the force applying surface. The bowed metal article is cold rolled with the protrusions in contact with the concave surface of the metal article. Conventional smooth surface rolls may be used in conjunction with one or more dies, preferably one. In this embodiment, the bowed article is sandwiched between a die and a smooth surface roll.

Various patterns of protrusions on the roll or die surface can be usefully employed and any pattern may be used which is capable of providing the plastic deformation of the concave surface necessary for flattening.

In another embodiment of the invention, press or drop hammer forges may be used to flatten bowed metal articles by employing the same principles as described above in connection with the rolling embodiments. The convex surface of the bowed metal article may contact a smooth die or platen while the concave surface is plastically deformed by a die having protrusions on the surface thereof.

In still another embodiment of the invention useful on certain types of products such as bimetallic, dual hardness articles, e.g. plates, which have concave and convex surfaces of differing hardness, and wherein the convex surface is of a greater hardness, such articles may be straightened by rolling same between plates or rolls having smooth surfaces. In this embodiment, a separating force is used such that the relatively soft concave surface of the plate is plastically deformed, i.e. its yield strength exceeded, but the yield strength of the relatively hard convex surface of said article is not substantially exceeded. In this embodiment, a uniform compressive force is applied over the entire concave surface wherein as in the previously described embodiments, plastic indentations, i.e. deformation, of the concave surface is produced. An obvious advantage of this latter embodiment is the avoidance of special dies or rolls. However. greater roll force are necessary.

As discussed above in connection with the earlier described embodiments, flattening and straightening by rolls or dies with protrusions is not limited to any particular array of protrusions. Different patterns may be desirable for various situations and desired results. In some cases, for example, flattening in one direction may be desirable and protrusion patterns for this purpose may comprise a series of linear protrusions parallel or transverse to the rolling direction producing corresponding depressions in the article. Plastic deformation by the use of checkerboard protrusions will produce equal amounts of flattening in both directions.

It is apparent from the above that various changes and modifications may be made without departing from the invention. Accordingly, the scope thereof should be limited only by the appended claims whereby what is claimed is:

1. A method of flattening by cold forming a bowed metal article such as plate, structural shape, bar or the like, having a concave and a convex surface which comprises imparting a force to said bowed metal article to cause localized plastic flow of the concave surface without substantially exceeding the yield strength of the convex surface.

2. A method of flattening a bowed metal article in accordance with claim 1 which comprises compressing said bowed article between two forces applying surfaces, one of said force applying surfaces being smooth and adapted to contact the convex surface of the bowed article and the second of said force applying surfaces having protrusions thereon and being adapted to contact the concave surface of said bowed metal article, applying sufficient compressive force to said bowed metal article with said force applying surface to cause localized plastic deformation of the concave surface of said article by said protrusions without substantially exceeding the yield strength of the convex surface.

3. A method in accordance with claim 2 wherein said compressive force is applied by rolling said bowed metal article between a pair of rolls and said force applying surfaces are the surfaces of the rolls.

4. A method in accordance with claim 2 wherein said force applying surfaces are die surfaces and said com- 4 pressive force is applied by rolling said bowed metal article between said die surfaces.

5. A method in accordance with claim 2 wherein said compressive force is applied by pressing said bowed metal article in contact with a die surface having protrusions thereon.

6. A method in accordance with claim 2 wherein said compressive force is applied by hammering said bowed metal article in contact with a die surface having protrusions thereon.

7. A method in accordance with claim 1 wherein said bowed metal article has a concave and convex surface of different hardnesses with the hardness of the convex surface being greater and said bowed metal article is fiattened by rolling same between smooth rolls to plastically deform the concave surface without substantially exceeding the yield strength of the convex surface.

8. A method in accordance with claim 7 wherein said bowed article is a bimetallic dual hardness plate.

References Cited UNITED STATES PATENTS 681,964 9/1901 Hurst 72192 2,144,783 1/1939 Ungerer 72197 2,771,801 11/ 1956 Wellman 72207 LOWELL A. LARSON, Primary Examiner US. Cl. X.R. 72700, 379, 365