US2116126A - Method of cold reducing ferrous material - Google Patents

Description

y 1938. J. M. SMITH METHOD OF GOLD REDUCING FERROUS MATERIAL A Filed June 12, 1934 INVENTOR MW WWW MH w IHH Patented May 3, 1938 UNITED STATES PATENT OFFICE ,METHOD OF GOLD REDUCING FERROUS MATERIAL Application June 12, 1934, Serial No. 730,201

' 4 Claims.

This invention relates to the cold rolling of relatively wide strip or sheet material and more particularly to the cold rolling of ferrous material in widths of and over and to tin plate and lighter gauges.

Cold rolling of sheets and strip material to such gauges is not new, even in connection with relatively wide material, but in all such operations, a relatively narrow range of cold reduction is employed. For example, it is old to produce cold rolled strip in widths of 20 and over, and in gauges as light as .0075" from stock ap proximately .060 thick, and it is also old to produce such cold rolled material in gauges from- .03" to .05" from stock approximating .080" to .109" thick, but materially larger ranges of cold reduction have not been practiced commercially. The necessity for employing hotrolled stock of the lighter gauges above noted, requires a heavy investment in hot rolling equipment and a 'material increase in the cost of hot rolling such stock over the cost of hot rolling substantially heavier gauge stock. With this in mind, it is apparent that a material advantage is gained 'in the manufacture of sheets and sheet-like material by subjecting the material to greater total cold reduction than has heretofore been employed in commercial operations, and I have therefore devised a method or procedure whereby I produce strip and plate in widths of 20" or over and in gauges of .01" or less from hot rolled stock approximating in thickness.

In this connection it should be noted that the present equipment of universal plate mills, now installed in the plants of many steel producers, can, with slight additions, produce this heavier gauge hot rolled material, whereas the production of the lighter gauges of hot rolled stock involves theuse of elaborate and expensive continuous mill equipment.

An object of my invention is, therefore, to produce amethod of rolling relatively wide sheets or sheet-like material which is less expensive from an investment standpoint.

In all rolling operations and particularly in strip rolling operations, various expedients have been employed for the purpose of accomplishing the desired reduction in each pass and also for the purpose of causing the material processed, to

properly track through the pass, but nevertheless, diiliculties encountered in connection with; the

cold rolling of ferrous material in the form of relatively wide strip and to gauges such as are here contemplated, have, as above stated, minimized thedegree of coin rolling reductions employed in commercial operations.

A further object of my-invention is the production of a cold rolling procedure wherein a large cold reduction such as here contemplated, is accomplished in a single stand of rolls, and by relatively few passes through that stand.

The improved procedure, constituting my invention, not only results in a greater cold reduction than has heretofore been commercially accomplished in connection with relatively Wide material, but it also makes it possible to take substantial reductions per pass andthus minimize the amount of labor and the time necessary to complete the product. i

I have discovered .that such cold reductions, as are here contemplated, can be obtained if it is borne in mind. thatevery portion of the cross section of each piece cold rolled must be reduced or elongated in substantially the same proportion. There is some indication that this has been recognized in a vague .way,as is evidenced by the fact that the necessity for pass control has been commented on both in patents and in trade literature. I have, however, found that in order 25 to obtain the results here contemplated, something more than the so called pass control must be accomplished and while my procedure involves the use of at least some of the old and well known expedients,'it i'nvolves an accurate pass adjustment and such as will insure substantially equal reduction or elongation of all transverse portions of the piece or strip traversing the pass. My invention also contemplates a novel procedure in the manner of employing these old expedients and as a result! ain able to accomplish what has not heretofore been accomplished in commercial operations, namely, the cold rolling of .wide ferrou's material, 20" or more in width, to gauges such as .01 and lighter from hot' rolled stock of approximately 4" in thickness and all in a single stand of rolls without the necessity of intermediate anneals and without changing or redressing the rolls during the cold rolling opera tion. 1

In carrying out the procedure here contemplated, I preferably employ a four-high mill, because of its rigid and rugged construction .and I preferably employ an old expedient to insure proper tracking to wit, I preferablydeliver the material to and discharge it from the mill while maintaining it under tension. I necessarily employ the screw-downs of the mill for subjecting the material tothe desired pressure for each pass and I necessarily carefully adjust 'the screwdowns on each end of the mill so as to insure, as far as is possible with such adjustments, that each edge of the material or strip traversing the,

pass is subjected to the same rolling pressure.

In cold reducing the thicker stock, such as here contemplated, the first passes will naturally be run at less screw pressures than later passes, since the thick material permits the rolls to bite in so readily that practical reductions will not result from the heavier screw pressures such as I employ in later passes. As the cold rolling operation progresses, the screw pressures are increased, consequently in order to maintain a constant ratio of reduction in all transverse parts of the piece, under the changing condition of screw pressures encountered, the changed deflection of the rolls must be compensated for in such a way as to maintain the required pass adjustment. In other words, Where all the passes are accomplished in a single stand, rolls of a predetermined contour to suit the conditions encountered in the earlier passes where the lighter screw pressures are employed, must have their convexity increased for the later or heavier screw pressure passes, and this increase in convexity must conform to the increasing screw pressures of the successive passes.

I have discovered that even where an extremely rigid and rugged four-high mill is employed,

.the rolls distort under the working pressures encountered, and particularly under pressures encountered in the later passes of the procedure here contemplated. The friction between the rolls and the material operated upon, the molecular displacement or the distortion of the piece acted upon, and the active and reactive forces in general, generate heat both in the rolls and in the material traversing the rolls, with the result that the rolls tend to rise in temperature as the rolling operation progresses. This mechanically generated heat has heretofore been considered a disadvantage and a source of difficulty and it is an old expedient to employ a coolant, such as water or oil and to flood either the working rolls or both the working rolls and the backing rolls with the coolant in order to dissipate this heat. The temperature to which the rolls are raised necessarily depends upon the rate of heat generation and the rate of heat dissipation, or the rate at which heat is transferred from the rolls to the coolant employed. While it has been recognized that the heating of. the rolls results in a change in roll contour, and while elaborate and complicated devices and systems have been suggested for obviating the difficulties arising from this variation in contour or from roll heating, no attempt has heretofore been made to take advantage of the mechanically generated heat and to control and employ it in such a way that the contour of the rolls of a single stand is changed in successive passes so as to compensate for the varying conditions encountered during such passes.

One of the features of my present invention is the utilization of the mechanically generated heat as an aid to pass adjustment or, as above set forth, as a means for changing the contour of the rolls in successive passes so as to compensate for the varying conditions encountered by rea son of the successively increasing screw pressures employed in the successive passes. For

this purpose I provide the roll stand with a controllable supply of coolant so arranged that the effect of the mechanically generated heat, in accomplishing changes in roll contour, can be controlled. The preferred way of accomplishing this is to provide means for delivering two separate flows of liquid to the rolls so that a hot liquid may be employed on the central portions of the rolls when necessity requires it, and while the ends of the rolls are subjected to a flow of a cold liquid. It will, of course, be apparent that to increase the convexity of the rolls to, compensate for the increased screw pressure or increased rolling pressure encountered in the later passes, it is necessary to conserve at least a portion of the mechanically generated heat in the central portion of the rolls. This may be done by decreasing the rate of heat transfer from the central or intermediate portion of the rolls below that at the ends oftl'ie rolls and can be accomplished by diminishing or checking the flow of coolant to the central portions of the rolls, or by applying hot liquid to the central portions of the face of the rolls or to the face of the upper backing roll, but in any case, the effect is broadly the same, i. e., the rate of heat transfer or heat dissipation is reduced at the central portion below that at the ends, with the result that the central portion of at least one roll responds to the increased heat retained in that portion of the roll, and consequently takes on a convex contour, the degree of which will correspond to the difference in temperature between the central portion and the ends of the roll. It will, of course, be apparent that the rate of heat transfer is greatly diminished by subjecting the particular portion of the roll to a flow of hot liquid and that therefore a nice control may be ob tained by providing roll flooding means so ar ranged that the entire roll may be flooded from end to end by a cold liquid, or the ends only of the roll be flooded by such liquid, or the ends be flooded by a cold liquid while the central portion of the roll is flooded by a heated liquid. It is of course apparent that a further control of the degree of convexity obtained may be had by providing means for varying the temperature of the heated liquid supplied to the central portion of the roll.

In carrying out my invention I prefer to so form or dress the rolls that they are slightly convex. During the first pass and possibly the first few passes, I flood the rolls with a cold liquid and in such quantities as to insure a rate of heat transfer from the rolls to the liquid as will maintain the rolls cold and thus insure maintaining the predetermined contour during the rolling operation. In the later passes, I flow cold liquid in adequate quantities over the ends of the rolls to keep the ends cool and to dissipate the mechanically generated heat from those portions of the rolls, but at the same time proceed so as to build up the temperature of the central portion of at least one of the rolls. That is, I'may reduce or check the quantity of cold liquid delivered to the central portions of the rolls, and I may flood the central portions of the rolls with a hot liquid while maintaining the flow of cold liquid over the ends of the rolls. This last mentioned procedure is resorted to in the last few passes, or when the metal being processed is of-light gauge and the rolling pressures are high, but in all cases I obtain the pass adjustment here contemplated by maintaining a temperature differential between the ends and the center of at least one of the backing rolls and in progressively increasing this differential to effect a progressive increase in the convexity of such roll to compensate for the rolling pressures encountered.

ile I have generally outlined the preferred procedure for taking advantage of, and efiectively utilizing the mechanically generated heat, it will be apparent that a substantial reversal of the procedure here outlined may be resorted to. That is to say, the mechanically generated heat .may be utilized to increase the temperature of the roll or rolls during the earlier passes and the pass adjustment, essential in the later passes, may then be obtained by flooding the ends of one or more of the rolls in such a way as to control the rate of heat transfer from those portions of the roll or rolls, while maintaining the temperature of the central portion of the roll or rolls.

The entire pass adjustment is for the purpose of issuing substantially equal reduction or elongation of each transverse portion of the piece or strip simultaneously traversing the rolls, since it y will be apparent that if the contour of the rolls is not adjusted to compensate for the deflection occasioned in the rolls by the various screw pressures encountered, the edge of the piece or strip will be over-rolled, resulting in a pinching or tearing of the strip, or the central portion of the piece or strip will be over-rolled, resulting at the best in an objectionable product.

My invention may be summed up as a coldrolling procedure employed in connection with a single stand of rolls, wherein that stand is employed in reducing strip material by successive passes and wherein a pass adjustment is resorted to which compensates for varying pressures encountered in the different passes and insures substantiallyequal reduction or elongation of every transverse portion of the piece or strip simultaneously acted upon by the rolls. This enables me to increase the total cold rolling reduction above such as has been heretofore employed in commercial operation, and it therefore enables me to employ a cheaper andmoreeasily obtained hot rolled stock, as compared to the lighter gauge material. This heavy stock may be obtained, in many cases, from existing rolling mill equipment, whereas the light gauge material must be produced on an expensive continuous mill or its equivalent.

In the accompanying drawing, Figure l is a diagrammatic side elevation of apparatus, such as may be employed in carrying out my invention; and

Fig. 2 is an end elevation of a four-high stand of rolls such as is illustrated in Fig. l.

In order to more'fully disclose the procedure involved by my invention, I refer particularly to the apparatus disclosed by the drawing, but only for illustration purposes. The apparatus consists essentially of a four-high mill 3, reels of coilers l, 4', and idler or guide rollers 5, 5. The mill 3 includes working rolls 6, 6' and large diameter backing rolls 1, i.

All these rolls are mounted in the usual way in a housing 8 and the housing is provided with the usual screw-downs 9, one of which is located at the top of each housing and which are employed for varying the setting of the rolls 6, 6' or for the purpose of varying the rolling pressure to which the piece is subjected during the cold rolling operation here contemplated. Any suitable means may be employed for delivering flooding liquid to the rolls, provided such means is capable of controlling the flow of such liquid in the manner heretofore described.

In the drawing I have illustrated three sets of sion as the rolling operation progresses.

nozzles it, ill and if, so located and arranged that the outermost nozzles Ilil are adapted .to

deliver a flooding flow of liquid to the ends of the working face of the upper backing roll i, whereas the nozzles ii. are adapted to deliver such a flow to the intermediate portion of the working face of that backing roll. A liquid delivery pipe We is shown communicating with one set of nozzles. Wipers it may be employed for the purpose of,

to some extent, confining the flow of liquid dem livered by the various nozzles and the arrangement of the wipers may besuch as to in effect provide three compartments, each opening onto the face of the associated backing roll and each provided with a drain pipe it. For example, the w arrangement may be such as to provide compartments it, M, in which the nozzles [It-it are located, and a central compartment it in which the nozzles ii function.

Such an arrangement of compartments insures the roll. It will, however, be apparent that details of constructionof the mechanisms employed for delivering the flooding liquid to the roll or rolls is not essential so long as the arrangement is such that the flooding mechanisms are capable of delivering sufficient liquid to insure a high 0 rate of heat transfer, and thus maintain all portions of the rolls cold when it is desirable so to do. In carrying out my invention, I place a coil of hot rolled stock W in a decoiling box H, which is associated with a series of pinch'and flattening g5 rolls ill and H8. The forward end of the stock is passed through the rolls Ill and it, over a guide roller IS, a conveyor 20 and the guide rollers 5 and into and through the pass deflned by the reducing rolls 6i5. This forward end is 40 then passed over the guide roller 5 and secured to the coller 4', on which it is wound under ten- The stock on .the entering side of the stand is not under tension during this, its first pass, through 5 the mill. This stock is approximately A" thick and of the desired width and. length.

When the rear end of the stock approaches the rolls 6-6 of the stand, the mill is reversed and this rear end is fed into and attached to the coller d, which is then so driven that the piece being rolled is under tension during the second pass of the material through the mill. It will be understood that the caller 4 is so operated,.dur

ing this pass, as to impose tension on the strip 5 as it enters the mill, and I prefer to so gauge the tensions on the entering and exit side of the mill that the stress in the material occasioned thereby is substantially equal on both sides of the mill.

It should be understood that this tension does not so exceed the elastic limit ofthe material, either on the entering or leaving side of the mill, and that the pull exerted by the coller 4"is preferably such that the drag of the strip on the entering side is greater than the pull of the strip on the exit 05 side. After the second pass is completed, the direction of rolling is again reversed and the piece is then subjected to the desired number of back and forth passes through the mill, with both ends continuously secured to their respective coilers and maintained under approximately equal tension, as above described, and until the predetermined gauge is reached. A

It will, of course, be understood thatif the coil or hot rolled stock is on a spool, the spool Cal may be mounted in the position indicated by either coiler 4 or 4. The end of the hot rolled stock is then guided over the associated roller 5 or 5' and into and through the pass defined by the working rolls 66, whence the process as above described is followed, except that the rear end of the stock is already secured to one of the coilers 4-4 and consequently the first pass may be accomplished while both the entering and exit portions of the material are maintained under tension.

Thus the strip stock passes first in one direction and then in the other through the mill and each pass accomplishes a material reduction on the strip. I contemplate reducing the hot rolled stock to final gauge by a minimum number of passes and, for this reason, I contemplate a substantial reduction per pass. The following table discloses examples of actual commercial practice and sets forth the procedure here contemplated in terms of number of passes, the gauge of material as it enters and leaves each pass, and the percentage of reduction per pass and the pressure, in thousands of pounds on the neck of each backing up roll.

A reference to the table discloses that the pressures are gradually increased from 900,000 pounds to 1,300,000 pounds. In this example of the rolling procedure, nine passes were employed for reducing hot rolled stock having a thickness of .265 inch to the finished product having a thickness of .0088 inch, and one of the features of the invention is to accomplish the cold rolling reduction in a minimum number of passes, i. e., from 7 to 9, or even fewer passes. It will be apparent that the table is merely illustrative of the procedure here disclosed and that the rolling pressures will naturally vary with the varying Width and thickness of the material rolled and as the reductions and number of passes are modified.

In carrying out the procedure as exemplified by the table, the working rolls 66' are preliminarily dressed so that each has a convexity of approximately ,006" in diameter. During the first passes a sufiicient fiow of coolant is de livered to all portions of the rolls to maintain all portions of the rolls cold. The strip traversing the pass is also flooded with sufficient cooling liquid to keep it cool. Throughout the entire procedure, as defined, I flood at least the end portions of the rolls with sufficient cooling liquid to maintain them reasonably cold. As the rolling pressures increase throughout the successive passes, I manipulate the flow of liquid to the rolls and the temperature of the liquid in sucha way as to establish what may be termed a thermal crown on at least one of the rolls. That is to say, I so manipulate the flooding liquid as to maintain the pass adjustment heretofore referred to, and'this may be accomplished by building up a thermal crown, of the right degree of convexity to maintain the pass adjustment, on one backing roll only.

There is some advantage gained by limiting the thermal crown to one backing roll, since in so doing, I accomplish the pass adjustment, from pass to pass, by larger variations in the thermal crown than would bepossible if a thermal crown were built up on both backing rolls 1-1 or on both reducing rolls 66 and in this way, I halve such error as the operator may make in building up the crown and therefore minimize the effect of the error, with the result that the commercial operations are speeded up by reason of the fact that the pass adjustment is rendered less sensitive.

It will be apparent, from what has been said, that this pass adjustment may be accomplished. throughout the successive passes, by reducing the flow of cooling liquid to the central portion of the face of one backing roll, by checking the flow of this liquid altogether, and by delivering a heated liquid to that portion of the face of the backing roll, and in the drawing, I have diagrammatically illustrated apparatus for thus controlling the flow of flooding liquid to the upper backing roll. It will be apparent that the preferred procedure contemplates an adequate flow of cooling liquid over the end portions of the face of the upper backing roll at all times for the purpose of dissipating the mechanically generated heat in those portions of that roll.

In carrying out the defined procedure it is desirable to keep the ends of the rolls as cool as possible, in order to accentuate the effect of the mechanically generated heat and to obtain a greater variation in the degree of roll convexity in accomplishing the pass adjustment here contemplated, and that therefore provision should be made for an adequate and copious flow of coolant.

By following the procedure above outlined, each pass can be so adjusted as to compensate for the effect of roll deflection encountered during the pass. It will also be apparent that some advantage and some flexibility of control may be gained by employing heated liquids of different temperatures, although satisfactory results have been obtained by employing hot oil at a temperature approximating 190 F., since considerable flexibility is obtained by varying the rate of flow of the hot oil to the central portion of the face of the uppermost backing roll.

While I have set forth what I now consider to be the preferred procedure in cold rolling hot rolled stock from approximately A" in thickness to the lighter gauges of commercial sheets, and black plate, it will be apparent that various changes in the procedure may be resorted to without departing from the spirit and scope of the invention, which resides primarily in maintaining a'pass adjustment, during the successive passes of the material through the mill, such that all transverse portions of the strip, simultaneously acted on by the rolls, are reduced or elongated substantially equal amounts.

What I claim is:

1. A method of cold rolling hot rolled ferrous stock in the form of relatively wide strip approximately one fourth inch in thickness to the gauges of commercial strip, which consists in passing such stock back and-forth through a single fourhigh stand of rolls, in increasing the rolling pressure exerted on such material in its passage through the rolls and as its thickness is reduced,

in maintaining a temperature differential between the ends and center of at least one of the backing' rolls of such stand and in increasing such differential to compensate for the increased deflection in the rolls of the stand occasioned by such increased rolling pressure.

2. Amethod of cold rolling strip material which includes subjecting a hot rolled work piece of fer- -rous metal having, a thickness of at least three .sixteenths of an inch to successive cold reduc- 3, A method of cold reducing ferrous stock in the form of relatively wide strip of approximately one fourth inch in thickness to the lighter gauges of commercial sheets, whichconsists in passing such material back and forth through a single four-high roll stand, in increasing the rolling pressure exerted on such material in at least the later passes, in maintaining a temperature differential between the ends and center of at least one of the backing rolls and in varying such differential to substantially compensate for the increased deflection in the rolls occasioned by the increase in roll pressure.

4. A method of cold rolling strip material, which includes subjecting a work piece to successive reductions in a single four-high stand of rolls, in increasing the rolling pressure in at least the later passes, in maintaining a temperature differential between different portions of at least one of the backing rolls and in increasing such temperature differential to substantially compensate for the increased deflection in the rolls oc-' casioned by such increase in rolling pressure.

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