US2213759A - Method of making sheet metal - Google Patents

Description

Sept. 3, 1940.

J. w. ERB

METHOD OF MAKING SHEET METAL Filed March 9, 1938 J2 SCRUBBER III! 11 711/111,? 1 n r I INVENTOR John W. Erb

I I Patented Sept. 3, 1940 PATENT OFFICE METHOD OF MAKING SHEET METAL John W. Erb, Martins Ferry, Ohio, assignor to Wheeling Steel Corporation, a corporation of Delaware 1 Claim.

This inventionpertains to the manufacture of sheet metal and, in particular, to so-called blued" sheet steel having a tightly adherent skin of oxide extending uniformly over the surface thereof.

Blued sheet steel has customarily been made by admitting an oxidizing agent such as steam to steel sheets or strip while the latter are at an elevated temperature. perform the oxidation step as .one of the later stages of the usual annealing process. In such process, the sheet metal is usually disposed in the form of stacks of sheets or relatively tight coils of strip. Because of the manner in which the sheet material is disposed for annealing it is not always possible to obtain uniform oxidation thereof because the oxidizing agent does not have easy access to the inner portions of the surface of sheets in stacks or strip in coils. As uniformity in appearance of a product is an essential for most uses of blued stock, this problem is a very serious one.

I have invented a method of making blued stock whereby the aforementioned objection to the previous practice is eliminated. In a preferred practice of the invention I provide for easy and uniform access of the oxidizing agent to-all portions of sheets in stacks or strips in coils by so roughening the surface of the material prior to annealing that even when successive layers of stacked or coiled material engage each other with considerable pressure, thereis sufiicient space therebetween. to permit infiltration of an oxidizing agent such as steam. A preferred practice of the invention will be described in detail herebelow with reference to the accompanying drawing illustrating the several steps diagrammatically. In the drawing:

Fig. 1 illustrates the step of rolling pickled hot rolled strip to the desired finished gauge;

Fig. 2 represents. the scrubbing treatment to which the material is then subjected;

Fig. 3 illustrates-the initial annealing operation;

Fig. 4 illustrates the step of toughening the surface of the material by rolling;

Fig. 5 is a plan view with parts omitted showi ing the result produced by this operation;

It is usually preferable to Application March 9, 1938, Serial No. 194,876

stores a smooth surface and bright finish to me material and gives it the temper which is desirable for subsequent fabricating operations.

Referring now in detail to the drawing, I preferably take a coil of pickled hot rolled strip T0 such as low carbon steel strip and subject it to cold reduction to the desired final gauge. This reduction may be effected by passing the material through tandem' rolling mills II which are illustrated as of the 4-high type. It will be understood, however, that the strip may be reduced to gauge by any other suitable form of mill which may be available. The reduction effected by the mills II is usually greater than 50%. Typical starting and finishing gauges are 14 gauge and 30 gauge respectively. These gauges are cited simply by way of illustration as the inventionmay be applied to material varying in thickness.

After the strip has been rolled to the desired final gauge, it is passed through a scrubber II as shown in Fig. 2 for the purpose of cleaning the surfaces thereof. The material is then in condition for'annealing. This operation maybe carried out in a furnace such as that shown at l3 in Fig. 3 or any other suitable form of annealing furnace. In the initial annealing operation, the material is preferably heated to a temperature of between 1200" and 1300 F. A de-oxidizing atmosphere is preferably maintained, bymeans already wellknown, in the annealing box ll in which the material is enclosed as shown at l5; during the cooling stage of the operation;

After the initial anne ng operation, I sub ject the strip to a so'-c lled dullin'g' pass as illustrated in Figures 4 and'5. In this operation.

able degree of roughness't'o the surfacefof-thematerial, as indicated in Fig. 5." ,Littl urns 1. duction in the thickness of by the mill l8.

mill 16 or otherwise, the strip is coiled and again annealed, as illustrated in Fig. 6 in a furnace l'l similar to that shown at l3. Puring this annealing operation, the coils indicated at II disposed in an annealing box ID are heated to a temperature'of between 1000 and 1100' F., and after a suitable soaking period, are withdrawn 'a' material is "eife'c ted '4 After the surface of the material has roughened suitably by pa sing it through'th-e so I from the furnace for slow cooling. When the coils have cooled slightly below the maximum temperature attained during the second annealing, an oxidizing agent such as steam is admitted to the box l9 by means already wellknown. The steam has access to all portions of both surfaces of the strip even though the coils are tightly wrapped, because the roughness imparted to the strip surfaces leaves spaces between adjacent wraps sufiicient' to permit the infiltration of steam therebetween. This condition is illustrated, somewhat exaggerated, in Fig, 7 wherein the successive wraps of a coil are indicated at 20. By reason of the roughness imparted to the surfaces. of the strip, adjacent wraps have close,

contact at spaced points only, leaving sufficient clearance for the entry of an oxidizing agent such as steam. An atmosphere of the oxidizing agent is maintained about the coils for a period sufficient to effect the formation of a uniform coating of tightly adherent blue oxide. The resulting oxidation is substantially uniform throughout the surface of the strip because the oxidizing agent hasready access to all portions as a result of the spaces between adjacent wraps provided by roughening the strip surfaces before the final annealing and oxidizing treatment.

When the oxidizing treatment has been completed, the coils are subjected to a final temper pass in a rolling mill 2| having work rolls with smooth, highly polished surfaces such as that characterizing the work rolls II. This temper pass rolls out the roughness imparted to the strip by the mill I6 and the resulting product is characterized by a smooth surface and a bright, lustrous finish. The temper pass also serves to increase thestifiness of the material sufiiciently to prevent fiuting when formed into cylinders.

It will be apparent from the foregoing description that the method of my invention is characterized by an important advantage over the processes employed heretofore in the manufacture of blued stock in that the oxidizing agent has relatively free access to all parts of the strip surface whereby the degree of oxidation and coloration is substantially uniform throughout the surface of the strip. The resulting increase in uniformity of the final product provides a greater percentage of prime material. The operations involved in the method of my invention are simple and may be carried out at relatively low cost with existing equipment.

As a possible alternative to the specific practice disclosed herein, I contemplate using rou hened work rolls in the last mill H so that a special tially all portions of the surfaces of the material,

when it is disposed in multiple thickness,v heating the material in multiple thickness to a temperature at which it oxidizes rapidly in the presence of an oxidizing agent, admitting such agent in the neighborhood of the heated material while at said temperature, thereby forming a tightly adherent coating of oxide on the material and substantially uniformly bluing all portions thereof, by the infiltration of said agent between ad-.

jacent thicknesses of metal, and finally" rolling the blued steel to produce a smooth surface with out breaking said oxide coating.

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