US1842220A - Sheet metal rolling process - Google Patents

Description

J. B. TYTUS 1,842,220

SHEET METAL ROLLING PROCESS Jan. 19, "1932.

Filed Jan. 8,. 1929 Mam; [11m WZZMY w D D 0 0v 0 0. ii \mi t i& Q 3 -m RQ g 623 5 QMQ x WZQQQQ L01 E Patented Jan. 19, 1932 UNITED STATES PATENT OFFICE JOHN B. TYTUS, OF MIDDLETOWN, OHIO, ASSIGINOR TO THE AMERICAN ROLLING MILL COMPANY, OF MIDDLETOWN, OHIO, A CORPORATION OF OHIO SHEET iami. ROLLING rnoorzss Application filed January 8, 1929. Serial No. 330,989.

My invention is of importance in sheet metal rolling processes in which a hot rolling is followed by a cold rolling, and it is of.

particular importance in connection with the so called continuous methods of rolling sheet metal. It will be described and may be understood to have a special application to processes involving the rolling of sheets from wide strip; but my application is not restricted thereto and it is equally as adaptable to the other processes in which hot and cold working join in the production of a finished article. i

In such sheet rolling processes and particularly in continuous wide strip mills, there hasbeen a tendency toward the production of thinner gauges on the hot mill as a starting point for a. further cold rolling reduction. This tendency has greatly increased the importance of a serious problem in connection with these processes. This problem is concerned primarily with non-uniformityin the product of the hot mills; and this non-uniformity may be due to a number of concurring causes.

In the first place, 1t is not possible to carry on the hot rolling step at a uniformity of temperature in the piece and as between pieces. This results in inequalities of strain in various parts of a sheet or strip and in inequalities of strain as between separate sheets and strips. There is no way of avoiding this, short of conducting the entire hot rolling operation with the metal heated at or above the critical range and this is impractical. Secondly, concurrent with these variations in resident strain in the product of the hot mill, there will be variations in gauge. It is not practicable in rapid reduction processes in the hot mill rolling of single thickness pieces to comparatively thin gauges, to deliver a uniform product. There are no rolls available which will long withstand the excessive wear resulting from rapid reduction processes. The result is that the piece develops roughness, the rolls cut out in the active portions and do not give a piece which accurate as to gauge. In my copending application. Serial No. 227,600, I have described a process for obtaining, in a procedure involving rapid hot rolling reduc tion to thin gauge, a. product suitable for pack forming. This process involves a certain cold rolling step with attention to the transverse contour of the sheet, following the preliminary hot rollin and coming before hot rolling in packs. fily present invention has to do with the production of a product for a cold rolling step which product is in such a condition that it may be reduced to the required gauge by cold rolling and will be substantially uniform.

WVe have as a product of the hot mill a sheet or strip which varies not only in gauge but also in strain. As is well known, the existence of these irregularities is responsible for a number of defects in a finished sheet sufficient to justify rejections in a deep drawmg product. My present invention is concerned with the ultimate elimination of these defects; but it is primarily concerned with the production of an ultimate product which shall be uniform in gauge.

It is a fact in cold rolling that a product which shows both variations in gauge and 1n strain as it comes from the hot mill will also show proportionate variations in these particulars at the exit end of the cold rolls. The exact reasons why this is so may not be entirely clear; but if the resident strain inequality in the material is removed, the cold rolls will, in a substantial reduction, bring about substantial uniformity of gauge,- that is to say, that whereas gauge variations persist practically proportionately in a cold rolled product where the strains accompanying initial gauge variations are present, they do not persist in proportion at all where the initial product was not badly strained nor strained with great irregularity, or where the strains have been removed.

An object of my invention therefore is to provide as the starting product of a cold rolling operation, a sheet or strip which, While characterized possibi'y by gauge inequalities, is characterized by substantial. absence of strain and substantial equality of such resident strains as have not been removed.

It is a further object of my invention to produce this preliminary product less expensively than has been possible hitherto.

It is still another object of my invention to secure in such a starting product a comparatively thin gauge, and in the production thereof to relieve the hot mills of extra duty.

It is still a further object of my invention to cut down the cost of the annealing and pickling steps which may intervene between the hot rolling and cold rolling 0perations.

These and other objects of my invention which will be pointed out hereinafter or will be apparent to one skilled in the art upon reading these specifications, I accomplish by that certain process of which I shall now describe a preferred embodiment having to do with the production of sheets from wide strip, it being understood that my process is equally applicable to the production of other rolled articles from sheets or other starting forms which are not comprised within the term wide strip. Reference is hereby made to'.

the drawing which accompanies this specification in which is illustrated diagrammatically the steps of my process as set forth in the exemplary embodiment which I shall now describe.

As hitherto pointed out, when, in the prodnot of the hot mill, irregularities of gauge and strain exist, gauge irregularities will persist through the cold rolling step. It is possible to anneal between the hot rolling and the cold rolling, but this is expensive. It involves careful time and temperature control because the strains in the hot rolled product are comparatively slight and as is well known, a much more careful controlled annealing treatment is required to equalize and wipe out comparatively slight strains than is required for comparatively great strains. Annealing also involves a pickling step before subsequent cold rolling. Further it is to be pointed out here that all of the difiiculties so far discussed are increased many fold in the practise of hot rolling to comparatively thin gauges for the purpose of securing a product which may be cold rolled to gauge without intermediate annealings. Each intermediate annealing involves further expense and difiiculty together with further pickling, which is highly undesirable.

My invention broadly comprises hot rolling to a comparatively light gauge followed by red rolling, annealing, pickling and then cold rolling.

The most obvious initial advantage of this process is that it relieves the hot mill of duty by the amount of actual reduction produced in the red rolling.

Secondly, the red rolling increases the residual strain in the metal to such an extent that a very much less carefully controlled and consequently a less expensive annealing process will serve to eliminate the strains. I

Thirdly, there is no annealing or pickling step between the hot rolling and the red rolling, which again saves expense. Thus my process is not analogous to a process involving hot rolling, pickling, cold rolling, intervening annealing, pickling, and further cold rolling.

Thus I secure from the hot mill a product which in general commercial operation will be unequal in gauge and will have resident strain inequalities. By the amount of reduction in the red rolling operation, I relieve the hot mill of duty. \Vithout any intervening annealing or pickling, I red roll the product of the hot mill. This red rolling is a cold rolling carried on while the product is covered with the hot mill oxide, which is the explanation for the name of the step. The resident strain and gauge inequalities in the cold strip from the hot mill will not be eliminated by the red rolling but will persist in substantial proportion in the product of that step. The reasons why this is so have been discussed above. But I have added to the resident hot mill strains, those produced by the red rolling operation; and I now have a product which has been considerably strained and which is suitable for quick annealing. Therefore it is susceptible to and is most advantageously treated by a continuous annealing in a tunnel furnace. the annealing being preferably carried on between the Al and A3 points. These are termed critical points as defined at pages 530 and following of The Making. Shaping and Treating of Steel, Carnegie Steel Co.. second edition. The time duration of the annealing treatment need not be long and the product can be comparatively quickly cooled thereafter without detriment.

As the product of the red rolling step, I now have a sheet or strip possessing, commercially, inequalities of gauge but having the strains substantially removed therefrom. By the combination of the hot rolling and red rolling it will have been brought to a comparatively thin gauge which is suitable for cold rolling to gauge by a continuous operation not involving intermediate annealings. Further. it is in such a condition that this cold rolling operation will reduce it to substantial uniformity of gauge.

With reference now to the drawing illustrating the production of sheet from wide stri by my process, I may start with a slab 1, which is heated to hot rolling temperature in a slab furnace generally of the pusher type indicated at 2. Preferably I next roll the slab into a strip plate by a succession of passes through a universal mill 3. The still heated strip plate may then be rolled into a wide strip of considerable length in hot mills which are preferably tandem mills of fourhigh construction. 'I have indicated at 4, 40, etc. a tandem of four four-high hot mills, at the end of which the strip designated as 14 may be coiled in a coil 5 on a coiler 6. These coils will be cooled and held pending the next step in the process. T heyare characterized, as explained, by inequalities of gauge and of strain which cannot be avoided in commercial practice. In the next step the coil 5 is straightened in an uncoiler 7, and is passed one or more times through a red rolling mill 8, 8a. etc. which I have shown as consisting of four stands of four-high cold rolls but which'may in practice consist of one roll, or any expedient number. The product from the hot mill may, as an example but without limitation, be twelve gauge material and in the red rolling operation, it may be reduced to sixteen gauge; and-it may then be coiled into a coil 5a on a coiler 9 of standard construction.

The red-rolled coils 5a are next uncoiled and straightened by the uncoile'r 10 and are preferably fastened together for continuous 'irocessing by any of the well known methods. I have indicated at 11 a traveling spot welder for the purpose. The continuous band of metal thus formed is next passed through a continuous annealing furnace 12 equipped with a cooling duct 13. In this furnace the metal is heated to preferably between the A1 and A3 points and held for a length of time depending upon the gauge and strain and is thereupon cooled with some time lag by passage through the cooling duct. The combination of the resident strains of hot and cold work will produce in the coils 5a a condition suitable'for annealing without too long soaking. and without the necessity for very slow cooling, so that the continuous apparatus indicated ,diagrammatically in the drawing will be found adequate for the purpose. Continuous annealing furnaces are well known and require no description by me.

From the annealing furnace, the band of metal which I have indicated at 14a is passed through a continuous pickling tank 15 which may be equipped with scrubbers and drying furnace 16 to a shear 17 which will shear it apart again into individual strips which are usually coiled-upon the coiler 18 into coils 5?) ready for the cold rolling operation.

The cold rolling operation may be carried on in a tandem or four four-high cold rolls 19, 19a, etc. to which the metal is led'after the coil 5?) is uncoilecl by the mechanism 20. At the end of the cold rolling operation, the metal may be recoiled by the mechanismQl into the coils 50. It will be found that the metal has been reduced to substantial uniformity of gauge; and a further description of subsequent steps in the production of finished sheets is not necessary by me. Various subsequent finishing processes may be used as for example, the process which is described in my copending application Serial No. 333,263, filed Jan. 18, 1929 and which comprises, after such a substantial cold rolling to gauge as is carried on in the cold rolls 19, etc., a continuous normalizing followed by pickling, shearing, box annealing and skin passing or the like. Such processes have the advantage among others of eliminating coiler break difiiculties and open surface difficulties. As pointed out, the intermediate product as prepared for cold rolling in my present process is characterized by practical absence of strains, but by the presence of gauge inequalities which are afterwards eliminated by the cold rolling. The high portions of the product however, receive more cold work than the lower ones and thus become harder, and ordinary annealing processes are commercially unsatisfactory for bringing the sheet to a condition of uniformityt= The process described in my copending application referred to will do this.

It will be understood that my process, while it has been described with reference to'the instrumentalities and practices of making wide strip of considerable length, is equally applicable to other sheet processes. Thus sheet bars may be broken down and then reduced to heavy gauge in the hot mills either by hand or continuously. The heavy-gauge hot mill sheets may then be cooled and redrolled cold. After this they will be annealed and pickled, which may be done by stitching the sheets together or otherwise fastening them, and proceeding continuously. Then they will be sheared apart and cold rolled, being subsequently finished as desired.

Skin passing as referred to in my specifications means finishing passes through the cold rolls. It is a term commonly used in the rolling art to indicate a finishing cold rolling whether merely for surfacing or for a slight hardening after annealing. It should be distinguished from cold rolling to gauge.

My process is directed to a solution of spe-- cialized problems, namely: those problems which have to do with the continuous rolling of sheet metal. This is comparatively a new art. The problems manifested themselves in the fact that when it was desired to cold roll strip metal of sheet width to uniform gauge, the roller did not find himself able to do this in commercial practice. The reason was found to reside in the fact that the hot mills or whatever combination of process steps preceded the cold rolling to gauge, delivered a piece of'metal for such cold rolling which was characterized by considerable gauge and strain inequality; and while a cold rolling to gauge, if it effected a very considerable reduction, could bring metal to uniform gauge, it could only do to strain and gauge; but this is not possible in continuous rolling, because continuous rolling methods imply an absence of continuous skillful attention to the rolls to adjust them to the particular conditions surrounding the rolling of each piece. The gauge and strain inequality trouble is characteristic of continuous rolling methods.

Persons have tried to anneal continuousl the hot mill strip sheet or sheets as the case may be, but this has not been altogether sue-- cessful, partly because the strains in the hot mill product, while unequal, are not large enough in the aggregate to permit of a quick continuous annealing. Other remedies for the situation have been proposed with which my present invention is not concerned. My remedy as set forth herein, is to cold roll the hdt mill strip or other pieces, with the hot mill oxide still on them, thereby (.1) etfecting a further reduction and relieving the hot mills of duty to some extent, and (2) so increasing the inherent strain in the metal pieces that they can be removed by a quick annealing. It is well known that the more heavily the metal is strained, the quicker will be the erasing of these strains in a heat treatment.

Various modifications can of course, be nade in my invention without departing from that specific series of steps which will be set forth in the appended claims. The apparatus may be modified as desired.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is

1. That process of producing sheet metal which comprises hot rolling a piece to materially reduce its thickness. cold rolling said piece without removal of the hot mill oxide therefrom, afterward heat treating and pickling said piece to prepare it for cold rolling and cold rolling it to gauge with substantial reduction and without intervening annealings.

2. That process of producing sheet metal which comprises effecting a preliminary reduction of metal in a hot mill, cold rolling the reduced piece without removal of the hot mill oxide therefrom to an extent suflicient to produce a further reduction and increase the strains therein, relieving said strains by a brief heat treatment, and further reducing the thickness of said ,piece to uniform gauge by cold rolling,

3. That process of producing sheet metal which comprises rolling metal to sheet width and a thickness greater than desired for cold rolling to gauge. cooling said metal. red rolling said metal to the desired gauge for cold rolling, annealing said metal and cot-d rolling itto gauge.

4:. That process of producing sheet metal which comprises hot rolling with a substanneeaaao rolling said metal without removal of the hot mill oxide, annealing and thereafter cold rolling it to gauge without intervening annealings.

7. That process of producing sheet metal which comprises hot rolling said metal, and without removal of the hot mill oxide, cold rolling said metal to increase the strains therein, to such an extent that they may be removed by quick continuous annealing, annealing and pickling said metal and cold rolling it to gauge with a substantial reduction and without intervening annealings.

8. That process of producing sheet metal which comprises hot rolling said metal to heavy gauge thereby producing a product characterized by gauge and strain inequalities, cold rolling said metal thereby producing a product also characterized by gauge and strain inequalities but in which the strains have been increased to such an extent that they may be substantially removed by briefly heating said metal to between its A1 and A3 points followed by a quick cooling thereof, removing said strain substantially from said metal by a quick heating thereof, to between the A1 and A3 points followed by a quick cooling, whereby a product is produced characterized by gauge inequalities but substantial absence of strains, and cold rolling said product to gauge with a substantial reduction and without intervening anneallngs.

9. That process of producing sheet metal which comprises interposing between the hot rolling and cold rolling steps in each of which a substantial reduction is effected, a red rolling whereby the gauge of the hot mill product is further reduced and the material straightsued by cold work, and annealing said metal between the red rolling and cold rolling steps. 1

10. That process of producing sheet metal 7 which comprises hot rolling and cold rolling said metal before any annealing, thereafter annealing said metal and cold rolling it to gauge with a substantial reduction and with out intervening anncalings.

JOHN B. TYTUS.

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