US2043521A

US2043521A - Method of rolling ferrous sheet material

Info

Publication number: US2043521A
Application number: US759566A
Authority: US
Inventors: Sykes Wilfred
Original assignee: Individual
Current assignee: Individual
Priority date: 1934-12-28
Filing date: 1934-12-28
Publication date: 1936-06-09
Anticipated expiration: 1953-06-09

Description

June 9, 1936.

W. SYKES METHOD OF ROLLING FERROUS SHEET MATERIAL Filed Dec. 28, 1934 2 Sheets-Sheet 1 June 9, 1936. w. sYKEs 2,043,521

' METHOD OF ROLLING FERROUS SHEET MATERIAL Filed Dec. 28, 1934 2 Sheets-Sheet 2 J6 19 g g1 22 23 24 71?] 603 O5 ed,

I Patented June9, .1936" UNITED STATES PATENT OFFICE nm'rnon or aommc cannons suns-r m'raamn Wilfred Sykes. chicarmlll. Application December 28, 1934, Serial No. 759,586 16 Claims. (01. 80 60) My inventionrelates to the rolling, more particularly the continuous rolling, of ferrous sheet material but more especially to so-called strip oi! relatively light gauge and relatively great width,

such as for examplejstrips of .035 inch thickness and 36 inches width; .05 inch thickness and 48 inches width and .062 inch thickness and 62 inches width, though the invention may be utilized for the producing of strips'of lesser or greater thickmass and of lesser or greater widths than those specifically mentioned.

One of my objects is .0 provide a novel method of rolling the strip, to the end more especially of reducing to the minimum waste of the strip material from fish tail projections at its ends.

Another object is to provide a novel method whereby variations in thickness of the strip product lromedge to edge shall be reduced to the a strip of relatively thin gauge which when cold will lie flat and be free of buckles in the central part or waves on its edges; and other objectsas will be manifest from the following description. By strip-sheet as used in the claims herein is meant a sheet of great length which in present .30 practice may be stated to be at a maximum about 600 feet;

Referring to the accompanying drawings:

Figures 1 and 2 show, by a plan View, a continuous mill for hot rolling strip and by which 35 my invention may be practiced, Fig. 2 being a continuation of Fig. l. I

Figure i is a diagrammatic sectional elevational view of the roll stands of the portion of the mill shown in Fig. l; and

40 Figure 2. a similar view of the roll stands of the portion of the mill shown in Fig. 2.

In the manufacture of hot rolled strip on socalled continuous mills as illustrated-the heated slab of steel is passed successively through a series 45 of mills operating to successively reduce the thickness and increase the width of the work until reduced to that desired of the finished product.

. In the arrangement illustrated It represents furnaces in which the billets are heated to the desired temperature for rolling and from which they discharge, under the control of the operator, to a table along which the billet is caused to move to a scale breaker l and thence, in succes- 5 sion, to reducing roll-stands l2, it, it, and i5,

shown by way of example, as four in number, with tables l6 interposed between them. From the last stand l5 the'work-piece is moved along a table I! to a scale breaker l8 and then, in succession, through a series of roll-stands, shown 5 as six'in number and represented at l924, inclusive, wherein the work-piece is rolled to successively reduced thickness emerging from stand 14 of the desired thickness of the finished hotrolled product. The hot-rolled strip may, if de- 19 sired, and where it is to be reduced to less thickness than obtainable in the hot mill, be passed through any suitable cold-reducing mill.

rolls 25. and 26 which make contact with the material to be rolled, and two rolls 2! and 28 of larger diameter backing the

rolls

25 and 26. However, the various stands referred to may be of the 20 A two-high type though this is not so desirable from an operating standpoint. k

The rolls of the various stands run continuously in the same direction and in the particular arrangement shown the last six stands is to M, 5 inclusive, are arranged closely together so that it is possible that the same strip of the material is in the first stand I9 of these six while at the same time being delivered from the last stand 24 of this series. Thus in practice the delivering 30 speed of the various stands l9 to 24, inclusive, must be such that each of them is delivering thesame weight of material in, or approximately in,.

a unit of time. However, in the particular layout illustrated the work-piece is/not in engagewent, at any one time, with any more than one of the stands l3 to it, inclusive. V

As will be noted, each roll stand is represented as separately driven as by a motor 29 in accordance with common practice and which is particularly desirable as to the stands IE to 24, inclusive. Any suitable provision may be made for separately controlling the speed'at which the rolls of the various stands are driven, thus permitting the speed of the'stands i9 to 24, inclusive, to be individually adjusted to any desired value within the range or the equipment, and thechanging of the draft, or reduction in the thickness of the work piece, at each stand, provided the corresponding speed change is within the range of the 5Q the rolls without the aid of guides especially in the case of relatively thin strip inasmuch as guides for such strip cannot be effective as they turn up the edges of the strip if there is an appreciable force tending to cause the strip to move against the guides. Naturally any roll under a separating pressure such as is involved in rolling such material will have some deflection which will be greatest in the middle and as this should be the center of pressure and as the rolls when idle may be perfectly flat, the shape of the piece being delivered will be slightly convex, this convexity of the piece, or the concavity of the space between the rolls, depending upon many factors as hereinafter mentioned. It is common practice to turn or grind the rolls so that they are somewhat convex which may partially compensate for their bending, so that the finished product will be more nearly of the same thickness across its entire width. The use of four-high mills as shown reduces this bending of the rolls to a very small amount so that the final product varies onlyfslightly in thickness from edge to edge.

It has been thought that it would be necessary toroll material on mills of this type in such a way that the convexity of the material being rolled would be progressively reduced by the various roll stands, such as disclosed in U. S. Reissue Patent No. 16,884 of February 21, 1928, issued to J. B. Tytus, and which method is generally in accordance with that used in the production of sheets rolled in packs, rather than as individual pieces, and which are generally not produced on continuous mills. Such method, however, presents among certain of its disadvantages that of producing so-called elongated fish-tails at the ends of the strip required to be cut therefrom and useless. from a commercial standpoint. It is desirable that the ends of the strip at the finish of the rolling operation be as square as possible to minimize waste, viz., that in the rolling from the slab to the finished strip the disposition of the end surface of the piece relative to its sides as exists in the slab, be maintained substantially the.

same through the mill"operation.

I have found that the practicing of this successive reduction convexity method with its disadvantages is not necessary to ensure the proper straight travel of the piece through the rolls but that a variation of only a few thousandths of an inch in any pass is all that is necessary for this purpose. In other words, if it is possible to finish any particular strip with a variation of three or four thousandths of an inch in the last pass of the mill, the same amount of variation or even a lesser amount, will be sufiicient to cause the strip to pass through the previousmill without any tendency of the strip to deflect laterally out of a straight line path.

There is another factor, in addition to that 0 providing for the guidance of the strip through the rolls as above stated, which controls the desirable method of rolling where the strip materialis relatively thin and wide. In addition to evenness of gage from edge to edge, it is also necessary that the strip, when cold, shall lie fiat and be free from buckles at itscentral portion, or waves on its edges. This is accomplished by delivering the material from the hot mill in such condition that its opposite lateral edges are slightly wavy, while the central portion is fiat, the edges being thus slightly longer than the central portion. Thus during cooling the edges of the strip contract first at a greater rate than the central part of as to lie flat when finally cooled. To so roll the 10 strip material 'the rolls in the stand are ground convex so that with a relatively light pressure more work will be done on the center of the strip material than on its edges. By increasing the pressure on the rolls, bending becomes a 15 greater factor and work may be done on the edges of the strip material, as well as on its central portion which occurs when the reduction of thickness in the finishing stand is increased. By properly adjusting this draft in relation to the quality of material being rolled, its temperature, thickness and width, the desired final shape can be obtained to insure the strip being in the desired fiat condition, when cold.

It is desirable that the end edges of the finished strip be as square as possible to the lateral edges thereof to minimize waste, and thus overcome the above noted objection of the production of elongated fish tails in the practicing of the progressively reduced convexity method above referred to, and this ondition will app y if the rolls and drafts are p operly proportioned under the method which I have found to be more desirable. The end of the slab when it first enters the mill, is as near as possible at right angles to the edges of the slab and such condition should be maintained throughout the mill operation which will be the case if the final convexity or crown is approximately the same throughout the passes.

There is, however, another factor which enters 4o somewhat into this question. The edges of the wide strip tend to be slightly thinner, for a distance of an inch or two, than the central portion of the strip. This is due to the well known fact that while the metal tends to flow mainly in the 45 direction of rolling, the unsupported edges of the strip will spread laterally a small amount and this spreading is liable to be more with colder material than with hot material. Consequently with a given pressure on the rolls the unsupported 50 edges of the strip may be squeezed out. laterally and become a little thinner than the bulk of the metal across the strip. The convexity of the strip, therefore, does not partake of the true nature of an arc of a circle, or some other arc. The 55 relation between the amount of lateral spread and the reduction of the central part of the strip enters somewhat into the problem of finishing flat strip and it has been found desirable in practice that the shape of the strip as it enters the 60 finishing stand be such that the body of the strip is slightly thicker than its lateral edges and that by suitable adjustment of the draft and shape of the rolls in the finishing stand this convexity can be either increased or decreased to give the final desired results. The method of rolling which Ihave foundtobe most desirable limits the amount of convexity in any pass to a minimum, although, due to wear of the rolls, it may be desirable to insure flatness, that the. convexity shall increase toward the finishing stands so that the final finishing stand can be adjusted to so shape the strip that it will cool flat.

To secure this result it is necessary that the various factors affectingthe shape 'of the metal mill stands shownin Figure 1 and the six mill It will be realized that although rolling mills are built very massive, the elastic distortion of the roll housings and other elements is appreciable, and must be considered in arriving at the desired shape of the piece being rolled. As the forces causing the rolls to separate will naturally cause a bending of the rolls, this may be partially or wholly compensated for by initially turning or grinding the rolls with a convexity, so that under the bending forces the surface presented to the material will be fiat, or of such shape as may be desired. The distortion of the mill housings can be also compensated for in this matter to some extent. However, it is necessary to properly correlate the forces which tend to cause a separation of the rolls, with the shape that has been given to the rolls to insure the proper shape of the piece when rolled. Some of the elements which enter into the consideratiomof the forces tending to separate the rolls are as follows:

1. Draft or reduction in thickness of the piece in the rolls.

2. Temperature at which the material is rolled.

3. The composition of the material being rolled.

4. The speed at which the material is being rolled.

All other things being equal, the separating forces will vary directly with the draft until the material becomes relatively thin when there is an increase in the separating force for a given draft. If other conditions are maintained constant, the effect of the temperature is to increase the separating force as the temperature is reduced. The effect of the composition of the material being rolled will vary with the compressive strength of the material, which in turn will vary for difierent metals, and in the case of steel, for different compositions. If the draft, temperature and composition of the material being rolled are fixed, the separating force will increase as the speed of rolling is increased. In other words, to displace a certain volume of metal requires a greater force when it is done quickly than when .done slowly. Thisbecomes a factor of some importance when considering the relations to be maintained when rolling a particular product. As the rate of compression varies with the different mills in a tandem train this factor must be taken into consideration when determining the draft in relation to the shape of the rolls used. By properly correlating these factors it is possible in the case of any particular mill, to produce strip,which may be held in closer tolerance in thickness from edge to edge than has been customary in the past, and to reduce the amount of scrap by avoidance of long fish tails. As an example, the following measurements of the crown of strips nominally inch thick and approximately 37 inches wide show how this sysstands shown in Fig. 2; and they show that in general the crown is substantially constant, except that it is'sharply reduced in the last pass for the reasons previously given:

Average amount center exceeds edge in thickness in thousandths of an inch v l Pass4 Passt Passe Pass? Pass! Pass!) Passlo l l (Passes 5-10 comprise the stands 19-24, inclusive) 7 ll 9. 5 8.5 v 9 6 In practice, of course, all rolls wear with use,

but if the factors enumerated above are properly' coordinated so that the material has approximately the same crown in all the passes except the last, the rolls will wear in such a manner that this relation will be substantially maintained, although there may be, with use, an increase in the crowndue to wear, etc., the general relation between the first and last passes will be maintained, and in general the total crown will be small and consequently the rolls may be run longer for a given tolerance.

The gist of my invention, as regards the matter of the convex rolling of strip material to ensure straight line travel thereof, th'us consists in so rolling it as to avoid the production of elongated fish-tails as result from progressive reduction convexity-rolling as above referred to.

Accordingly by way of examples, the convexity of the strip material may remain substantially constant throughout all passes; or throughout all passes except the last pass; or the convexity of the strip material may be less during the earlier v 1. The process for reducing metal in hot condition to wide and thin fiat sheet form which comprises controlling the active pass of the rolls in the finishing stand so as to cause the longitudinal edge portions of the piece of metal in hot condition to be elongated relative to the central portion thereof, and thus assume wave form, to such degree that the rolled sheet assumes flat condition upon cooling.

2. The process for reducing metal in hot con- I dition to wide and thin flat sheet form which comprises passing a sheet of metal in hot condition from one stand to another successively and controlling the active passes of the rolls in the various stands so as to cause the piece to be reduced in each pass and run straight through the rolls of the'stands and the longitudinal edge portions of the, piece to be elongated, in the finishing pass, relative to the central portion of the piece and thus assume wave form. to such degree that the rolled sheet assumes fiat condition upon cooling.

3. The process for reducing metal in hot condition to sheet-like form in successive stands of rolls which comprises passing a piece of metal in hot condition from one stand to another succeesively and controlling the active passes of the rolls in the various stands so as to cause the piece to be of general convex form in the several passes, and of practically constant convexity from the beginning to the end of the series of passes, with the maximum variations of convexity within a few thousandths of an inch only, and the longitudinal edge portions of the piece to be elongated, in the finishing pass, relative to the central portion of the piece and thus assume wave form, to such degree, that the rolled sheet assumes fiat condition upon cooling.

4'. The process of reducing metal to strip-sheet form consisting in rolling the metal in successive stands of rolls with slight convexity, but suflicient to insure the straight line travel of the metal through the roll stands without lateral guidance as the metal leaves the rolls, and maintaining said slight convexity practically constant throughout at least all except the last operable stand.

5. The process of reducing metal having a slight convexity, but sufficient to insure the straight line travel of the metal through the roll stands without lateral guidance as the metal leaves the rolls, to strip-sheet form consisting in rolling the metal while maintaining said slight convexity substantially constant in successive stands of rolls.

6. The process of reducing metal to strip-sheet form consisting in rolling the metal initially with a slight convexity, but sufiicient to insure the straight line travel of the metal through the roll stands without lateral guidance as the metal leaves the rolls, and in thereafter continuing the rolling of the metal while maintaining said slight ,convexity substantially constant.

7. The process of reducing metal to strip-sheet form consisting in rolling the metal in successive stands of rolls with slight convexity, and maintaining said slight convexity practically constant throughout all stands, and in varying the aforesaid rolling of the metal at the last operable stand of rolls.

8. The process of reducing metal to strip-sheet form consisting in rolling the metal in successive stands of rolls with slight convexity, and maintaining said slight convexity practically constant throughout all stands, with a reduction of convexity of the metal at the last operable stand.

9. The process of reducing metal to strip-sheet form consisting in rolling'the metal in successive stands of rolls with slight convexity, but sumcient to insure the straight line travel of the metal through the roll stands without lateral, guidance as the metal leaves the rolls, and maintaining said slight convexity practically constant throughout .all stands in advance of the last stand. I

10. The process of reducing metal to stripsheet form consisting in rolling the metal in suc- 'cessive stands of rolls with slight convexity, and

constantly maintaining said slight convexity throughout a plurality of the first engaged passes and, increasing gradually up to the last operable pass and reducing its convexity in the last operable pass. 1'

12. The process of reducing metal to strip sheet form consisting in rolling the metal in successive stands of rolls with slight convexity, and

constantly maintaining said slight convexity throughout a plurality of the first engaged passes and increasing gradually up to the penultimate pass and in reducing the metal in the last pass to control the shape of the finished sheet. 7

l3. The process of-reducing metal to sheetlike form but (i great length consisting of rolling the metal in successive stands of rolls and maintaining an initial slight convexity, but suificient to insure the straight line travel of the metal through the roll stands without lateral guidance as the metal leaves the rolls, practically constant in all stands of rolls which operate simultaneously on the metal to reduce it to the final desired thickness.

14. The process of reducing metal to sheet-like form of great length consisting of rolling the metal in successive stands of rolls and maintaining an initial slight convexity practically constant in all stands of rolls which operate simultaneous 1y on the metal to reduce it to the final desired thickness, except in the last of said stands and reducing its convexity in this last stand.

15. The process of hot rolling metal to stripsheet form which comprises passing hot metal successively through a plurality of stands of rolls so formed and adjusted for draft as to maintain a slight convexity, but suflicient to insure the straight line travel of the metal through the roll stands without lateral guidance as the metal leaves the rolls, and keeping said convexity within commercial tolerance for saleable. strip throughout all stands.

16. The process of hot rolling metal to stripsheet form which comprises passing hot metal successively through a plurality of stands of rolls so formed and adjusted for draft as to maintain a slight convexity, keeping said convexity within commercial tolerance for saleable strip throughout all stands, and varying said convexity in the last operable stand as required to produce a strip which when cooled shall be flat with properly aligned edges.

WILFRED SYKES.

cessive stands of rolls with slight convexity, and