US2021328A - Method of rolling metal sheets - Google Patents

Description

Nov. 19, 1935. N, C. REN'DLEMAN 7 2,021,328

METHOD OF ROLLING METAL SHEETS Filed Feb. 25, 1955 L O O 3 I" l O O I: 9 f) O :l

1 5 m-Ef INVEINVITOR NOAMAM c.R -a9-w\w Wm MRMM Patented Nov. 19, 1935 UNITED STATES PATENT OFFICE METHOD OF ROLLING METAL SHEETS Application February 25, 1933, Serial No. 658,569

8 Claims.

This invention relates to the rolling of metal sheets and provides a method whereby the same may be produced over a wide range of sizes at a very low labor cost and with a low capital investment.

In the Welsh system of sheet rolling, sheet bars are first rolled and these are cut to lengths corresponding to the desired pack width. The sheet bar lengths are then rolled down in single thicklO ness on a hand mill and are then paired and reheated. The pair is rolled out and is then reheated and doubled preparatory to further rolling. The operations of reheating, doubling and rolling are continued until the desired gauge is reached. The number of thicknesses in a pack,

it will be seen, will be 2, 4, 8 or 16.

The Welsh system is open to a large number of defects. The labor cost is high and a large amount of the metal is lost because of the numher of shearings resulting from the practice of doubling again and again. Sheet mill operators usually figure on losing between four and five percent of the metal as scrap on this account.

For rolling different gauges according to the Welsh system, the practice is to vary the thickness of the sheet bar so as to give the requisite amount of metal for the finished sheets. A great deal of difliculty is encountered here because of I the necessity of finishing the pack at a length which will adapt itself to shearing into sheets of commercial size. Severe limitations on the rolling practice are imposed because of this requirement, particularly when we consider it in connection with the first requirement of the Welsh system, namely, that the packs comprise 2, 4, 8, etc, thicknesses. By reason of these limitations it is necessary to vary the sheet bar thickness by a large number of relatively small increments in order to give the desired range of products.

The defects of the Welsh system have long been recognized and numerous plans have been proposed to overcome them. For example, in the patent to Garrett No. 419,008, dated January '7, 1890, it is proposed to have available as many mills at each stage of the operation as may be necessary to simultaneously accommodate all of the pieces from a billet. If, for example, a billet after being rolled to sheet bar is to be cut into eight pieces, there will be four mills to simultaneously accommodate the four pairs in the 5 billet. Then after reheating, additional rolls are available according to this system for further rolling the several packs substantially simultaneously. This process, however, is based upon the use of sheet bar and is open to substantially all of the 10 objections which have been set forth with respect to the Welsh system.

With the development of the wide strip mill it was thought that metal having the width and gauge of sheets might be rolled down by a con- 5 tinuous process. Experience, however, has shown that this is not economical and the practice has been to roll to a given thickness in the strip mill and thencomplete the rolling in the old hand mill. According to such practice, the strip which 20 is rolled in the strip mill is subsequently rolled in the same direction through the hand mill, the width of the strip corresponding to the width of the metal as it is rolled by hand.

This system is also open to a large number of 25 defects. The demands of the trade are such that the width of the finished sheet metal may vary from 14 inches to 36 inches by very small increments. With the system just described, it is necessary to change the width of the strip for 30 every change in width of the finished material.

A continuous strip mill usually comprises a number of stands of two-high or four-high mills and a number of edgers which engage, during the earlier stages of the operation, the slab fed to the 35 strip mill. It is possible by adjusting the edgers to effect minor variations in the width of the strip. Any variations greater than an inch or two must be taken care of by varying the width of the slab which is fed to the strip mill. 40

It is estimated that to meet commercial requirements in the range of sheets from 20 to 36 gauge it is necessary with the system just described to roll some several hundred strips of different width and thickness. This requires a 45 large amount of inventory in partly finished materials and also seriously impairs the efiiciency of the hot strip mill. In practice it is customary to put new rolls into a strip mill at the beginning of the run and to roll the wider gauges first. The width of the strips being rolled is gradually reduced so that at the end of the run the narrowest material is produced. This method of operation, coupled with the large number of changes necessary to roll the wide range of strips required, materially reduces the capacity of the hot strip mill.

I provide a system which eliminates the defects of both methods above described, and which gives numerous advantages not. attained by either. I employ a strip mill producing strip of substantially the same width for all gauges. The strip is cut into lengths corresponding to a desired pack width, and a plurality of such lengths are assembled into a pack, heated, and rolled in a direction crosswise of the original direction of rolling. Preferably the rolling is carried out in a continuous mill. After this rolling, the packs are preferably opened and repiled to form packs containing more sheets than the original packs. The packs thus formed are heated and subjected to further rolling to reduce them to the final gauge. I eliminate all doubling, and instead of forming a thickened pack in this fashion, I take one or more sheets from another pack formed in the first pack-rolling operation and add such sheet or sheets to one of the original packs.

I diiferentiate a strip as that term is used herein from a sheet bar by reason of the fact that a strip is very wide relative to its thickness and this is not true of a sheet bar. In ordinary sheet mill practice the ratio of width to thickness of the sheet bar never exceeds about 20 to 1. In my improved system, employing strip, the ratio of strip width to thickness is to 1 or more. Because of the fact that this much higher ratio is obtained in the strip mill, a very large amount of the reduction is done at much lower cost and the problem of reducing the strip to sheet dimensions is materially simplified. The amount of hand labor is greatly reduced. This is best shown by a specific example. In the rolling of tin plate of, say, 31 gauge (0.0109 inch) there will ordinarily be used a sheet bar whose thickness is .5 inch. The ratio of original thickness in the sheet mills to final thickness is therefore 45.87 to 1. In my method the ratio of original thickness in the sheet mills to final thickness does not exceed 20 to l and preferably is not more than about 10 to 1. To state it in another way, the thickness of the sheets in my system is not less than 5% and preferably not less than 10% of the original strip thickness.

The strips which are formed in the strip mill will be of varying thicknesses, there being a specified thickness for each gauge over the range that it is desired to produce. Furthermore, the thicknesses are preferably such as to give in all gauges sheets of substantially the same length. For commercial purposes it is desirable, although by no means essential, to produce by my system packs which will cut to a length of 144 inches, since this length best lends itself to shearing into smaller lengths required in commerce. According to the old practices, the final pack length may vary widely for different gauges, thus occasioning scrap loss and, as above stated, limiting the operation generally.

In the accompanying drawing illustrating a present preferred embodiment of the invention,

Figure l is a diagrammatic view of a strip mill for producing the strip which I employ,

Figure 2 is a diagrammatic view illustrating the mills and the furnaces employed for rolling the packs, and

Figure 3 is a view corresponding to Figure 2 but showing cold rolling stands for the finishing passes.

The strip mill shown in Figure 1 is of a conventional type comprising a furnace 2 and a series of roll stands 3 and edgers 4. The stands 3 may be of two-high or four-high type, as desired. Slabs are fed from the furnace 2 through the strip mill and the issuing strip is coiled on a coiler 5.

The strips thus formed are cut into lengths corresponding to a desired pack width and are piled in packs and fed through a furnace 6. They issue from the furnace 6 onto a roll table 1 and pass through successive roll stands 8, 9 and I0 driven by a motor H. The stands 8, 9 and I0 constitute a tandem mill wherein the roughing operation is performed and the pack is rolled out to, preferably, approximately 40 percent of its final length. The packs are opened and are repiled. A pack for the roughing operation, for example, may comprise two thicknesses of strip metal, whereas the pack for the finishing operation may contain three thicknesses. In this case three of the packs of the roughing operation will be made into two packs for the finishing operation.

In their passage through the roughing mill the sheets are rolled in a direction crosswise of the original direction of rolling in the strip mill. This is important because it eliminates the necessity of rolling different strip widths for each pack width required. It also has the advantage that it does away with any difficulties which might arise by reason of the strip having a center crown. In practically all hot strip mill operations the strip has a center crown. According to my system this has no effect on the pack rolling step since the crown in the strips simply means a little additional thickness in the middle of the pack considering it in the direction of pack rolling. Considering it crosswise of the direction of pack rolling there is no crown.

The packs which are formed for the finishing operation are passed through a furnace I2 and after reheating are supplied to a mill comprising roll stands l3, l4 and i5 driven by a motor l6. These stands constitute a tandem mill wherein the material is rolled to final gauge. It is desirable to employ three roll stands in both the roughing and the finishing mills. Two stands are not sufiicient to give the desired reductions, and any number of stands greater than three will introduce undue complications. With three stands in each mill the desired reductions can be obtained with a minimum of equipment.

The apparatus shown in Figure 3 comprises a furnace 6a, a table 1a and hot mills 8a, 9a and Illa driven by a motor I la. After the packs have passed through these several stands constituting a tandem mill, the packs are opened and repiled. Instead of being reheated as in the embodiment of the invention shown in Figure 2, the packs are fed cold through cold mills I311, Ma and l5a. With cold rolling somewhat greater reductions may be employed than in the case of the hot finishing mill shown in Figure 2. As illustrating the advantages of my system, I here insert a tabulation showing the strip width and thickness employed for the rolling of sheets of different gauges, the ratio of strip thickness to final thickness, the ratio of strip width to strip thickness, the number of pieces in the packs, and the reductions in the several stands.

from the standpoint of labor and equipment. My system permits of maintaining the original thickness of the packs at a thickness which has been found by experience to be best suited to Gage Roughing operation N0 Ratio; Ratio Original Pass No. 1 Pass N0. 2 Pass No. 3

Deci- Strip Strip 5MP Strip N111? pack ma] Width thlcktltnctkness twlrith ber g1 thick "4 ness 0 na 0 S 11 pac thickness thickness 11655 Gage Length Gage Length Gage Length Finishing operation No. Original Pass N0. 1 Pass N0. 2 Pass N 0. 3

Number pac in pack thickness Gage Length Gage Length Gage Length It will be understood, of course, that the above present-day sheet-rolling operations. I may, for figures are given by way of example only. They example, employ an original pack thickness apshow, however, the marked advantages obtainable proximating inch. With such thickness and by my method. Only one width of strip is emwith a sheared final pack length of 144 inches, I ployed over the entire range given. There is find it desirable to make the strip approximately only one thickness employed for each gauge. All seven times the final thickness of the sheet. For of the sheets are of the same final length. The example, the strip width may be 22 inches, which, elongation in each pass is the same. The pack elongated seven times on crossrolling, gives a thicknesses remain relatively constant and all doubling and intermediate shearing are eliminated. By reason of the uniformity of the packs as to dimensions after each stand, they adapt themselves readily to automatic guiding and handling. The highly skilled crews now required are dispensed with and only a small amount of relatively unskilled labor is required. The duties of the men required for supervising the heating and the rolling are materially reduced and the conditions under which they work are greatly improved.

The length of 144 inches plus allowance for trimming is not too great to permit of ready handling. There is no limitation on the number of thicknesses which may be used in the packs either for the roughing or for the finishing operation. This constitutes a marked advantage of my system. Instead of being limited to pack thicknesses of 2, 4, 3, etc., sheets as in the Welsh method, or alternatively being forced to employ a large number of stands, as in the Garrett system, I may employ an odd number of sheets in one or both of the packs and feed them through tandem mills one after the other with a minimum of cost both sheet length of 154 inches. This allows ample metal for trimming and squaring the packs. At the same time, the scrap loss is materially reduced as compared with the old processes.

I have illustrated and described a present pre- :3;

ferred embodiment of the invention and have given an example showing the range of strip thicknesses employed in the mill illustrated. It will be understood, however, that the invention is not limited to the form shown but may be otherwise embodied or practiced within the scope of the following claims.

I claim:

1. In the method of rolling sheets over a range of gauges, the steps consisting in rolling strips of substantially uniform width but different strips differing from one another in thickness, the width in each case being at least eighty times the thickness, the thickness being such as to give the desired final gauge, cutting the strips into lengths corresponding to a desired pack width, originally assembling a plurality of such lengths in a pack and rolling the pack in a direction crosswise of the original direction of rolling.

2. In the method of rolling sheets over a range of gauges, the steps consisting in rolling strips of substantially uniform width but different strips differing from one another in thickness, the width in each case being at least eighty times the thickness, the thickness being such as to give in each gauge a sheet of substantially the same length, cutting the strips into lengths corresponding to a desired pack Width, originally assembling a plurality of such lengths in a pack, and rolling the pack in a direction crosswise of the original direction of rolling.

3. In the method of rolling sheets over a range of gauges, the steps consisting in rolling strips of substantially uniform width but different strips differing from one another in thickness, the width in each case being at least eighty times the thickness, the thickness being such as to give the desired final gauge, cutting the strips into lengths corresponding to a desired pack width, originally assembling a plurality of such lengths in a pack, rolling the pack in a direction crosswise of the original direction of rolling, repiling the sheets so as to form new packs, and rolling the same.

4. In the method of rolling sheets over a range of gauges, the steps consisting in rolling strips of substantially uniform width but different strips differing from one another in thickness, the width in each case being at least eighty times the thick ness, the thickness being such as to give the desired final gauge, cutting the strips into lengths corresponding to a desired pack width, originally assembling a plurality of such lengths in a pack, rolling the pack in a direction crosswise of the original direction of rolling, repiling the sheets so as to form new packs, and rolling the same, the strips being substantially seven times the final thickness of the sheets.

5. In the method of rolling sheets over a range of gauges, the steps consisting in rolling strips oi substantially uniform width but different strips diiiering from one another in thickness, the width in each case being at l ast eighty times the thickness, the thickness being such as to give in all gauges a sheet of substantially the same length, cutting the strips to lengths corresponding to a desired pack Width, piling the lengths into packs, and rolling the same, repiling the rolled sheets into packs and rerolling the same, and maintaining a sufiicient number 'of sheets in each pack so that the original pack thickness approximates of an inch.

6. In the method of rolling sheets over a range of gauges, the steps consisting in rolling strips of substantially uniform width but different strips differing from one another in thickness, the width in each case being at least eighty times the thickness, the thickness being such as to give in all gauges a sheet of substantially the same length, cutting the strips to lengths corresponding to a desired pack width, rolling the pieces in a direction cross wise of the direction of strip rolling, piling the rolled pieces into packs and again ro1ling them in a direction crosswise of the direction of rolling in the strip.

'7. In the method of rolling sheets over a range of gauges, the steps consisting in rolling strips of substantially uniform width but diiferent strips difiering from one another in thickness, the width in each case being at least eighty times the thickness, the thickness being such as to give in all gauges a sheet of substantially the same length, cutting the strips to lengths corresponding to a desired pack width, rolling the pieces in a direction crosswise of the direction of strip rolling, piling the rolled pieces into packs and again rolling them in a direction crosswise of the direction of rolling in the strip, there being an odd number of pieces between the rolls in at least one of the crosswise rollings.

8. In the method of rolling a series of metal sheets having a range of gauges from No 20 to No. 34, the steps consisting in rolling a series of strips all of substantially the same width but different strips being of difierent thicknesses according to the final gauge to be rolled from such strips, the different strips each having approximately the same ratio of thickness to the final desired thickness, the width of each strip being at least eighty times the thickness, cutting the strips to lengths corresponding to a desired pack width, rolling the pieces in a direction crosswise of the direction of trip rolling, piling the rolled pieces into packs, and again rolling them in a direction crosswise of the direction of rolling in the strip.

NORMAN C. RENDLEMAN.

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