US2005315A - Method for rolling sheet metal - Google Patents

Description

June 18, 1935. w GQQDHUE 2,005,315

METHOD FOR ROLLING SHEET METAL Filed D90. 22, 1933 Fig.4.

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v HA5 ATTORNE Patented June 18, 1935- UNITED STATES PATEN OFFICE METHOD FOR ROLLING SHEET DIETAL Application December 22, 1933, Serial No. 703,617

15 Claims.

This inventionrela'tes' to an improved method of rolling sheet metal, and more particularly to a method of rolling wide sheet metal from sheet bar to final desired gage and sizes such as is used in the production of deep drawn automobile bodies.

One object of this invention is to produce an extremely wide sheet with a gage from edgeto-center within decidedly closer tolerances than have heretofore ben commercially produced from sheet bar.

Another object is to reduce sheet metal (1 ing the rolling process, both transversely and longitudinally, so as to produce a slight side flow of metal during the rolling operation, thereby not only improving uniformity of gage but also surface finish, including theelimination of stretcher strains; p

The above and other objects will be apparent with those skilled in the art to which this invention belongs from the following specification and claims.

- mill of Figure 4.

In the drawing:

Figure 1 shows a pair of two-high roughing mill rolls as designed for use in carrying out this method with their contour exaggerated for the sake of cleamess. a Figure 2 shows a cross-section of a. pair of,

breakdown sheets as producedby rolling between the breakdown rolls of Figure 1, the contour of the breakdown sheets being exaggerated also for clearness.

Figure 3 is a view similar to Figure 2 with the exception thatthe breakdown sheets have been reversed so that their crowned contours are abutting each other, which is necessary in carrying out one of the steps in this invention.

Figure 4 shows the three rolls of a three-high mill as'designed for carrying out the method of this invention with the contour of the center roll exaggerated for the purpose of clearness.

Figure 5 shows a cross-section of a pair of sheets which have been rolled through the threehigh mill until reduced to approximately 80 percent of their finished gage and size.

Figure 6 shows a cross-section through a finished pack of sheets produced byrolling in the As a result of the mass production of deep drawn automobile bodies it has become necessary to provide automobile sheets not only having uniform deep drawing characteristics, but also of uniform gage from edge-to center. The rolling of continuous strip, which was subsequently cut into relatively short lengths for stamping into body parts, provided suitable material within certain size limits; however, auto body manufacturers have recently demanded widths of metal beyond expectations in an effort 1 tostamp two or more body parts as an integral unit from one sheet. In order that the sheets of metal could stand the punishment to which they were subjected in these extreme stamping and drawing operations, it was necessary for them to have extreme uniformity of surface finish, 1o

ductility, and gage, as well asbeing of extreme size.

The uniformity of gage of these extremely large sheets presented in .itself a major problem which could not be overcome with standard rolling 15 equipment and methods heretoforein use. The method of this invention was developed to provide the sheets required by the automobile body manufacturers. The method of this invention is in many instances contrary to all prior sheet or strip mill practice inthe production of'extremely wide auto body sheets. By wide auto body sheets is meant sheets of 40 inches or more in width, although such sheets are generally over 60 inches in width. Auto body sheets such as this invention relates to are generally composed of metal of low carbon content; that is, steel having carbon under .10 per cent and manganese under .40 per cent, which metal after proper thermal treatment ismost susceptible and commonly-used-for deep drawing purposes. h

In carrying out my invention sheet bars of the proper size are first heated in accordance with the well known practice of heating sheet bars for breakdown rolling. The sheet bars are withdrawn from the heating furnace in pairs, and given several? single passes in a two-higlroonventional, non-reversing roughing or breakdown mill, such as shown in Figure 1. The rolls R of the mill of Figure 1 are ground extremely hollow for the purpose of providing a decided crown on the breakdown sheets. After the sheet bars are passed singly through the mill of Figure 1 several times to partially elongate the bars, the

pair of bars is matched and rolled as a pair, as is usual in forming breakdown sheets, until the breakdown sheets have been elongated to from 45 to 55 per cent of the specified length The breakdown sheets produced by rolling between the rolls R, of Figure 1 are shown in Figure 2 and indicated by the numeral 10. The extreme crown of the breakdown sheets H! is indicated by the reference letter C, and is clearly seen in exaggeration in Figure 2.

In practicing my invention I prefer to provide a crown'or heavy center on sheets 60 inches wide or less of .003 greater than the edge of the sheets. Such a crown or extra thickness is usually pro-.- duced on 60 inches or less sheet width in a breakdown mill, such as indicated in Figure 1, both rolls of which are ground so as to produce a concavity at the center of about .025". In other words, the diameter of the center of these break down rolls is .050" less than the diameter at both ends thereof. In 60 inch to 72 inch wide rolls for producing sheets of corresponding width, I prefer to provide about a .015" concavity, which results in producing the crown on the sheets of .005". A sheet of from 72 inches to 84 inches, or wider, is usually rolled in the mill to provide a crown of .007".

The crowned breakdown sheets of Figure 2 are preferably reversed so that their crowned portion 0" are facing or contacting each other," as illustrated in Figure 3. The reversing of the breakdown-sheets has a dual purpose in that it multiplies the'crowned action and also prevents sticking of the matched or double breakdown sheets during their subsequent processing, due to the fact that the outer surfaces which have been somewhat oxidized have been reversed so as to be next to each other.

The matched and reversed breakdown sheets shown in Figure 3 are re-heated in any suitable pair furnace and are then rolled in a three-high mill F indicated in Figure 4. The three-high mill of Figure 4 may be of any conventional type having the usual large top and bottom rolls l4 and I 5, which are preferably ground straight, and

a small center working roll l2. The roll l2, in order to carryout the method of this invention, is ground or turned with a crown or center ap proximating .015".

The crowning of the center roll l2, as set forth above, together with the crown formed in the breakdown sheets II, has a decided effect on the gage and the surface of the material rolled in the three-high mill. This crowning of the roll I! and of the breakdown sheets Ill causes a decided and distinct side movement or flow of the metal from the heavy center of the sheets toward the sides thereof. This side flow of metal does not necessarily manifest itself in any over-'- all elongation of the width of the sheets, but on the contrary, it produces a more uniform edge to center gage in the finally finished product. This improved uniform gage of the finished sheets is of decided importance when producing the extremely wide sheets (for example, 60 inches to 84 inches wide) for automobile body use. In ordinary mill rolling of either sheet or strip the edge'to center gage variation is considerable and increases more or less in proportion to the width of the sheets being produced.

Not only does the side flow of metal produced by crowning decrease the edge to center gage variation, but it materially improves the surface of the sheets over the surface heretofore possible to obtain in standard methods of producing wide sheets. The movement of the metal flowing from the center to the edge of the sheets is maxichanical processing the grains of the metal are caused to become fairly equal in size and so disposed to each other that their longitudinal and transverse axes are equal and opposite within each grain and to adjacent grains. The cross or side flow of metal is, insofar as I am aware, a radical innovation in the rolling of metallic sheets. Furthermore, this side flow enables the production of extremely wide sheets having decidedly close edge-to-center" thickness tolerances, a smoother surface condition and the elimination of stretcher strains.

Experience has shown that the small center roll l2 of the three-high mill must have its crown of .015" maintained closely if the results as to gage, finish and grain structure are to be had. If the crown of the center roll I2 becomes less than .010" the results set forth above are not obtained and, therefore, this roll must be removed and re-ground in order to secure the benefits of this method of processing.

The breakdown sheets ID are preferably processed or rolled after once re-heating in the three-high mill F so as to produce sheets having approximately 80 per cent of their final length, although in some cases they may be rolled to finished length without re-heating. When the sheets are rolled so as to be approximately 80 per cent of their finished length, they are generally pickled and given a charcoal dip. The charcoal dip is composed of a water and charcoal solution maintained at approximately 190 degrees Fahrenheit. The heat of the mixture is such as to cause the water to readily evaporate from the sheets when they are withdrawn from the solution and leave the sheets with a charcoal film which prevents the sheets from sticking during subsequent re-heating and rolling. After the sheets which have been reduced to approximately 80 per cent of their final length have been pickled and subjected to the charcoal dip, they are matched in packs of two, three, or more sheets, depending on the final gage desired. The thinner the gage of the final sheet the greater number of sheets are assembled in a pack as is usual in rolling sheets.

It will be noted that the usual pickling step is omitted for the breakdown, and this is generally the practice followed, although the breakdowns may be pickled before heating and rolling on the three-high mill if desired. In following the general practice of not pickling until the sheets have been rolled on the three-high mill to approximately 80 per cent of their final length, I have been able to impart a surface to the finished for automobile body material which is to be subsequently subjected to painting or sprayed coating.

After the sheets have been rolled on the threehigh mill F to approximately 80 per cent of their final length and have been pickled and charcoal dipped as described above, and assembled in packs, the packs are re-heated to a rolling temperature and the packs of sheets which still carry a slight crown, as indicated at IS in the sheets of Figure 5, of approximately .002", are re-rolled in the three-high mill F until the crown is entirely eliminated and the sheets are elongated to final length and gage. The sheets thus produced have a uniform gage from the edge to the center Y, as indicated in Figure 6, and have a smooth surface and gloss heretofore unobtain- While I have shown and described certain specific embodiments of my invention, it will be understood that I do not wish to be limited thereto since modifications may, be made without departing from the scope thereoi, as defined in the appended claims.

I claim: i

1. The method 'of rolling wide sheet metal for deep drawing purposes comprisings'rolling and matching pre-heated sheet bars in -a roll pass having gradually reduced dimensions from its center toward each end to form crowned breakdowns, reheating said crowned-breakdowns to rolling temperature, and rolling said re-heated breakdowns in a roll pass having gradually increasing dimensions from its center toward each end to finished gage and size.

2. The method of rolling wide sheet metal for deep drawing purposes comprising rolling and matching pre-heated sheet bars in a roll pass having gradually reduced dimensions from its center toward each end to form crowned break-' matching pre-heated sheet bars in a roll pass having gradually reduced dimensions from its center toward each end to form crowned breakdowns, reversing and matching the so-formed breakdowns so that their crowned surfaces are abutting, re-heating said crowned breakdowns to rolling temperature, and rolling said re-heated breakdowns in a roll pass: having gradually increasing dimensions from its center, toward each end to finished gage and size.

4. The method of rolling wide sheet metal for deep drawing purposes comprising rolling and matching pre-heated sheet bars in a roll pass having gradually reduced dimensions from its center toward each end to form crowned breakdowns having a crown of at least '.003", reversing and matching the so-formed breakdowns so that their crowned surfaces are abutting, re-heating said crowned breakdowns to rolling temperature, and rolling said re-heated breakdowns in a'roll pass having gradually increasing dimensions from its center toward each end to finished gage and size.

5. A method of rollingwide sheet metal for deep drawing purposes comprising rolling and matchingfpre-heated sheet bars in a roll pass having gradually reduced dimensions from its center toward each end to form crowned breakdowns, matching and re-heating said crowned breakdowns to rolling temperature, rolling said matched and re-heated breakdowns in a roll pass having gradually increasing dimensions from its center toward each end to approximately 80 per cent of their finished length and gage, again reheating said sheets and'rolling said re-heated sheets in said last named pass'to finished size and gage- 6. A method of rolling wide sheet metal for deep drawing purposes comprising rolling and matching pre-heated sheet bars in a roll pass having gradually reduced dimensions from its center toward each end to form crowned breakdowns, matching and re-heating said crowned breakdowns to rolling temperature, rolling said matched and re-heated breakdowns in a roll pass having toward each end to approximately 80 per cent of their finished length and gage, re-heating and re-matching said sheets to form multiple packs and rolling said re-heated multiple packs in said last named pass to finished size and gage.

'2. A method of rolling wide sheet metal for deep drawing purposes comprising rolling and matching pre-heated sheetbars in a roll pass having gradually reduced dimensions from its center toward each end to form crowned breakdowns, matching and re-heating said crowned breakdownsto rolling temperature, rolling said matched and re-heated breakdowns in a roll pass having gradually increasing dimensions from its center toward each end to approximately 80 per cent of their finished length and gage, pickling the sheets which have been rolled to 80 per cent of their finished length and gage, re-heating the matched said sheets to form multiple packs and rolling said re-heated multiple packs in said last named pass to finished size and gage.

8. A method of rolling wide sheet metal for deep drawing purposes comprising rolling and matching pre-heated sheet bars in a roll pass having gradually reduced dimensions from its center toward each end to form crowned breakdowns, matching and re-heating said crowned breakdowns to rolling temperature, rolling said matched and re-heated breakdowns in a roll pass having gradually increasing dimensions from its center toward each end to approximately 80 per cent of their finished length and gage, pickling the sheets which have been rolled to approximately 80 per cent of their finished length and gage, applying a charcoal film to said pickled sheets, re-matching said sheets to form multiple packs, re-heating said multiple packs and rolling said re-heated packs in said last named pass to finished size and gage.

9. The method of rolling wide sheet metal which comprises forming crowned breakdowns in a roll pass having gradually decreasing dimensions from its center toward each end and rolling said breakdowns in a roll pass having gradually increasing dimensions from its center toward each end.

10. The method of rolling wide sheet metal which comprises forming crowned breakdowns in a roll pass having gradually decreasing dimensions from its center toward each end, said breakdowns having a crown of at least .003" and rolling said breakdowns in a roll pass having gradually increasing dimensions from its center toward each end.

11. The method of rolling wide sheet metal which comprises forming crowned breakdowns, matching said breakdowns so that their crowned surfaces are abutting and rolling the matched breakdowns in a roll pass havin gradually increasing dimensions frdm its center toward each end.

12. The method of rolling wide sheet metal which comprises forming crowned breakdowns in a roll pass having gradually decreasing dimensions from its center toward each end, reheating them, rolling them in a roll pass having gradually increasing dimensions i'rom its center toward each end to approximately 80 per cent of their finished length and again reheating and rolling to finished size and gage in a rolling pass having gradually increasing dimensions from its center toward each end.

13. The method of rolling wide sheet metal which comprises .forming crowned breakdowns in a roll pass having gradually decreasing dimensions -from its center toward each end and rolling them in a roll pass having gradually increasing dimensions from its center toward each end, the

which comprises forming crowned breakdowns in a roll pass having gradually decreasing dimensions from its center toward'each end and rolling them in a roll pass having gradually increasing dimensions from its center towards each end, the extent of the crown of the second named pass being sufllcient to cause \a distinct side flow of metal from the crowned center toward the sidesof the'sheets so as to eifect a substantially uniform gage from edge to center of the sheet and to avoid longitudinal striations of the surface, the said roll pass for sheets of a width 0! about 60" or more having a central crown of more than about 0.10". v

15. The method of rolling wide sheet metal which comprises forming breakdowns .in a roll pass having gradually decreasing. dimensions from its center toward each end to obtain a crown of at least .003", and rolling said crowned breakdowns'in a roll pass having gradually increasing dimensions from its center toward each end, whereby a side flow of metal from the crowned center toward the sides of the sheet is effected.

WlILIAM L. GOODHUE.

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