US3236086A - Production of flat metal sheets - Google Patents

Description

1966 R. 0. STEIGERWALT 3,233,085

PRODUCTION OF FLAT METAL SHEETS Filed April 9, 1964 INVENTOR. ROBE]? T 0. STE/GERWALT @MM M Attorney United States Patent ()fiice 3,236,086 Patented Feb. 22, 1966 3,236,086 PRODUCTION GF FLAT METAL SHEETS Robert D. Steigerwalt, Pittsburgh, Pa, assignor to United States Steel Corporation, a corporation of Delaware Filed Apr. 9, 1964, Ser. No. 358,587 1 Claim. (Cl. 72-296) This application relates to the production of large metal sheets and more particularly to stretcher levelling large steel sheets.

Metal sheet material formed of steel and the like is conventionally flattened or levelled by roller levelling or stretcher levelling. In the former, the sheet or strip material is run through a series of rollers disposed to bend the material in alternate directions and achieve a flattened condition. This is generally applied to strip material but due to the necessity of using rather small diameter rolls is limited to the width of material that can be handled. Stretcher levelling is the method most generally used for flattening plates and is applicable to the heavier sheet gauges. However, large, lighter sheet gauges, i.e. those having a length/ thickness ratio in excess of 3000 cannot be stretcher levelled because stretching produces a wavy out-of-flat condition.

Accordingly, it is an object of this invention to provide a method of flattening large, light gauge sheets.

The foregoing and further objects will be apparent from the following specification when read in conjunction with the attached drawing, wherein:

FIGURE 1 is an isometric view of an assembly of sheets to be straightened and cover plates therefor, partially broken away to show the interior of the pack;

FIGURE 2 is a side view showing the combined flattening and stretching operation of my invention; and

FIGURE 3 is a view similar to FIGURE 1 of a modification.

Referring more particularly to the drawing, the letter P denotes a sandwich or pack composed of outer or cover plates 2 and inner sheets 4 to be stretcher levelled. Preferably the cover plates have a thickness greater than that of the sheets and preferably at least 5 times that of the sheets. Generally the inner sheets are composed of high yield strength steel and are of large size such as 12 feet or more in length and less than .04" gauge thereby having a length/ thickness ratio in excess of 3000.

In FIGURE 2, the pack P is shown disposed between platens 12 with the ends of the pack extending outwardly therebeyond a sufiicient distance to be gripped by grips 20 of a conventional hydraulically operated stretcher levelling machine.

Due to heat treatment, the sheets of the pack are considerably distorted so that preliminary to the stretching operation, pressure may be applied to the platens by a suitable press to partially straighten the sheets and substantially remove warpage therefrom. The warpage results in the sheets being longer on one side than the other and such distortion is removed by the preliminary pressing to prevent one side being stretched more than the other in subsequent stretcher levelling. Such pressing may be applied to the sheets individually or to the pack.

After pressing, the grips 20 are operated to grip the sheets and the cover plates, and tension applied to the assembly to stretch the sheets and cover plates beyond the yield point of the material. The pressure of the cover plates, which may be augmented by the platens, prevents rippling or furrowing of the sheets during stretching so that a completely flattened condition is obtained. The tension may be applied while the pack or assembly is below, at or above room temperature but below the critical temperature.

In one application of the invention, the pack P may be assembled prior to rolling to final gauge. In this form the pack will have side bars B surrounding the inner sheets 4 of difiicult to roll material. The side bars are welded to the cover plates 2 to form a unitary assembly. The cover plates have a lower yield strength than the inner sheets 4. Following rolling to produce large size sheets and thereafter heating to develop the required physical properties, the assembly is quite distorted and warped and should be stretched as described in connection with the foregoing assembly of sheets and cover plates to flatten the inner sheets. The grips 20 of the stretcher leveller exert force on the top and bottom cover plates of the pack. The inner sheets between the cover plates are gripped by frictional forces exerted through the cover plates. During stretching, horizontal forces are applied stretching the pack past the yield point of the members until a permanent set and flatness is obtained. Due to the lower yield strength thereof, the cover plates stretch first. Also transverse forces are set up during the stretching operation along with the frictional forces resulting from the cover plates stretching before the inner sheets. These forces combine to prevent the formation of the wavy out-of-flat condition normally resulting from stretching sheets having a length/thickness ratio in excess of 3000.

This is a continuation-in-part of my copending application Ser. No. 39,542, filed June 29, 1960 and now Patent No. 3,152,383, issued on Oct. 13, 1964.

While I have shown and described certain specific embodiments of my invention, it will be understood that these embodiments are merely for the purpose of illustration and description and that various other forms may be devised within the scope of my invention as defined in the appended claim.

I claim:

A method of producing large flat heat-treated sheets having length/thickness ratio in excess of 3000 comprising forming a pack of sheets having said length/ thickness ratio, said pack having cover plates on both sides thereof having a lower yield strength than the sheets of said pack, and stretching said pack and cover plates beyond the yield point of the sheets of the pack and of the cover plates whereby large flat sheets are obtained.

References Cited by the Examiner UNITED STATES PATENTS 1,811,599 6/1931 Thomas.

2,693,637 11/1954 Peabody et a1. 15335 XR 2,961,028 11/1960 Bath 15335 3,018,817 1/1962 Wheeler et al. 15335 3,066,384 12/1962 Heger 153-86 XR CHARLES W. LANHAM, Primary Examiner.

JOHN F. CAMPBELL, Examiner.

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