US2344996A - Method of making deep-drawing stock - Google Patents

Description

March 28, 1944. wl M, MCCONNELL METHOD QF MAKING DEEP-DRAWING sTocK original Filed June 14.1939

2 Sheets-Sheet 1 mw, mw

INVENTOR.

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56 AIJIURNEY' March 28, 1944. W` M. MCCQNNELL 2,344,996

METHOD 0F MAKING DEEP-DRAWING STOCK 2 sheets-sheet' 2 Original Filed June 14, 1939 ATTORNEY Patented Mar. 28, 1944 William M. McConnell, McKeesport, Pa., assignor to Mackintosh-Hemphill `Company, a corporation of Delaware Original application June 14, 1939, Serial No. 279,045. Divided and this application July 19, 1941, Serial No. 403,150

3 Claims. (Cl. 80-60) This invention relates to the rolling of steel strips and sheets, and the application herein is a division of my application Serial No. 279,045,

led June 14, 1939, now Patent No, 2,271,459, for y an improvement in a Rolling mill.

It is the object of my invention by rolling steel strip and sheet to produce deep-drawing stock in which the deadening eli'ect has been carried to such stage that there is little or no tendency toward structural rearrangement in the stock, and no substantial loss of its deep-drawing properties during relatively long periods of time intervening between the deadening treatment and the deepdrawing operation.

In cold-rolling strip and sheet steel to the condition of a deep-drawing stock, it has been customary to effect the iinal reduction, after an annealing operation, in what is known au a temper pass under relatively severepressure and tension. This nal rolling results in such structural change in the stock as to adapt it for` use as deepdrawing stock. That is, its ultimate yield point is raised and its elastic limit is lowered, permitting the stock to endure without loss 'of cohesion severe deformation into shapes which it permanently retains. There has been the di-fllculty that the deep-drawing property of the stock has not been persistent, but that in a relatively short time following a deadening operation there will occur such structural rearrangement in the stock that it is not suitable for its intended ube, without having more workdone on it. A

It is, however, a fact that if the stock in temper working be worked with great violence, there is a very great increase in the persistence of deepdrawing properties in the stock. Such persistence in deep-drawing properties may be created by hammering, which is, however, a commercially.

impractical operation for the purpose. I have appreciated that if strip and sheet steel be rolled at abnormally high speed, and under abnormally high pressure, that is, at a speed and under a pressure not previously attempted in the art, persistent deep-drawing qualities might be obtained. That is, the order'of violence in working which is obtainable by heavy hammer blows kmust be approached in rolling in order commercially to obtain a persistence in deep-drawing properties analogous to that attainable under a hammer.

It is to be understood that the word vio1ence" as I above use the term, is descriptive of timeponent. I have found in rolling, and the analogy to hammer action is here yet pertinent, that the greater the violence with which the reduction is effected, the more persistent; will be the deepdrawiig qualities off the stock. When the working (i. e., the violence of reduction) is increased well beyond that eected in normal practice, the

results are striking. For example, by subjecting the stock to a temper-rolling at a rolling pressure of 200,000 pounds per linear inch of Work roll face and at a speed of 2500 ft. of the stock per minute through the work rolls, the deep-drawing proper- .ties of the stock persist for many times the persistence period of stock rolled under the condi# tions previously employed commercially. Albo the proportional permanent retention of deep-drawing properties is far greater than has been obtained in previous commercial practice.

In obtaining this violence in working the stock, I utilize a rolling instrumentality capable of/with'- standing abnormally high pressures, of operating at "abnormally" high speeds, and of working the stock at "abnormal" speed and under abnormal pressure. In speaking of "abnormal loads, and abnormal speed, it may be stated that loads of as much as 150,000 pounds per linear inch have been considered to he higher than normal in temper mills, and it has not been previlously attempted to operate temper mills under so high a. load. Also travel of the strip or sheet steel through temper mills has not previously .been attempted at a speed as high as 1500 feet per minute.

A; illustrative of instrumentalities capable of performing the method of my invention, I may use a rolling mill whichincludes' the novel roll organization disclosed and claimed in my copending application Serial No. 279,045, led June 14, 1939, to which reference has been above made. The accompanying drawings show an embodiment of such exemplary apparatus, as follows:

Fig. I is a diagrammatic elevation of a set, or

' stand, of rolls together with backing structures organized with the rolls.

Fig. II is a view of a rolling mill assembly, partly in front elevation and partly in vertical section, showing a mounted arrangement ofthe rolls and backing structures shown in Fig. I together with means for ultimately receiving and reacting to the pressures of rolling.

Fig. III is a side elevational view of the rollingr mill shown in Fig. II.

Fig. IV is a front elevational view of a set, or l but showing modification in the arrangement of the rolls and backing structures.

In Fig. I there is shown a stand of two work rolls I and 2 against the faces of which bear respectively the faces of the back-up rolls 3 and 4. Upon the back-up rolls 3 and 4, and laterally beyond the contact faces of these rolls, are pairs of wheels 5 and 6. The wheels 5 contact back-up roll 3 on both sides of the median portion in which it is'in contact with the face of work roll I, and the wheels 6 similarly contact the back-up roll 4. The pairs of wheels 5 and 6 are carried respectively on relatively heavy shafts 1 and 8,

so that the backing structures have a general spool shape. For reasons which will appear, the wheels should preferably be made' integral with, or otherwise be fixed to, their carrying shafts.

By consideration of Fig. I, it will be seen that the spool-form backing members relieve the necks of the back-up rolls, and their associated bearings, from the rolling pressure sustained by the back-up rolls. These backing members have in the assembly the specialized function of receiving and enduring the high stresses incidental to the rolling pressure, and they are, therefore, specically adapted to that purpose. Thus the shafts 1 and 8 may be designed for great strength, and a high factor of safety may be provided both in the shafts and in their associated bearings.

The structural arrangement of the spoolshaped backing members tends to distribute reaction to the rolling pressure symmetrically along the beam formed by the shafts and wheels, and

provides both end and intermediate bearing spaces of relatively great length, both outwardly of, and between, the wheels. In the assembly shown in which the bearings and screwdowns are symmetrically located, and equidistant with respect to the pressure transmitting wheels on shafts 1 and 8, the arrangement will tend to balance the rolling pressures on the mill, by tending strongly to centralize reaction to those pressures.

'In Fig. I of the drawings there is indicated the relative loads on the wheels and shafts forming the ultimate backing structures, when the rolling pressure is uniform throughout the entire width of the stock being rolled. An inherent characteristic of the backing structure is that it tends, in accordance with the principle of a continuous beam, to centralize reaction to the rolling pressure of the mill. It thus functions also to decrease inequality in reaction to non-uniformly distributed rolling pressure, by its tendency to resolve the reaction toward a central line- The value oi' thus centralizing reaction to rolling pressures is most striking when considered in connection with the conditions which exist in the use of a conventional 4-high mill. In such practice there are usually changing and highly unbalanced loads on the opposite necks of each of the back-up rolls, resulting from the reaction of those rolls to the rolling pressures in the mill.

As shown in Fig. I of thedrawings, the backup rolls 3 and 4 are shouldered to provide respectively ln the two back-up rolls peripheral surfaces 9 and I0, against which the pairs of `wheels 5 and 6 respectively bear. There is substantial advantage in such a structure of the back-up rolls, in that it provides a progressive decrease in angular velocity from the work rolls upwardly and downwardly of the roll stand to the shafts 'l and 8. Thus, the work rolls, being of lesser diameter than the back-up rolls, the back-up rolls will be driven less rapidly than the work rolls, and the back-up rolls being formed, as shown, with a diameter less than that of the Wheels which they. contact, there is a further drop in angular velocity from the back-up rolls to the shafts 1 vand 8. This decreased angular velocity simplifies the bearing problems for the pressure-receiving spools.

.Whereas it is desirable that the wheels of each backing structure be fixed on a rotatable shaft; the wheels may be rotatably mountedon a fixed shaft, Without sacrificing the principle of pressure centralization, and the relief given the roll necks.

In Figs. II and III of the drawings there is illustrated mounting structure for the roll assembly of Fig. I. `The mounting structure shown lis preponderantly conventional in its form and arrangement, and comprises roll housings Il supported by shoes I2 and having therein windows I3. The work rolls I and 2 have their necks extended respectively into chocks I4 and I5, and the back-up rolls 3 and 4 have their necks extended respectively into chocks I6 and I1. The necks of the upper spool are carried by chocks I8, each of which is shown as provided with sleeve bearings I9 surrounding the necks of the spools, and the necks of the lower spool are carried by blocks 20 equipped with sleeve bearings 2l. Balancing springs 22, 23 and 24, arranged in sets, serve to maintain the rolls in operative contact with each other and with the adjusting means of the assembly. Desirably in large installations, these springs are replaced, in accordance with common practice, by fluid pressure cylinders or counterweights.

The mounting assembly, thus described, is of conventional form and arrangement. There are. however, a chock 25 and a block 26 having respectively sleeve bearings 21 and 28, which are adapted intermediately to support the shaft 1 of the upperA spool and the shaft 8 of the lower spool. The bearing block 26 is held against horizontal displacement by a beam structure 33, which is supported on the mill shoes I2, and the chock 25 for the upper spool is held against horizontal displacement by means of webs 29 extended from the lroll housings II at the edges of the windows therein. screwdowns 30 and 3| bear against the chocks I8, and a third screwdown 32 bears against the chock 25. It is to be understood that power to drive the mill may be directly applied to the work rolls, to the back-up rolls, or to the spools, in the conventional manner, by a suitable pinion stand and drive operating through driving spindles.

Fig. IV of the drawings illustrates a modified arrangement in which the backing rolls are not shouldered. In this modification the wheels 5a and 6a have contact with the faces of the unshouldered back-up rolls 3a and 4a in zones 3b and 4b which lie outwardly of the working faces of the work rolls I a and 2a, so that the spool has similarly the effect of straddling the ultimate working faces of the rolls.

Since I obtain my desirable effect of imparting persistent deep-drawing properties to'steelstrip and sheets by violent working, it is important that not only the pressure under which the stock is rolled and the speed of its travel be high, but it is also important that the reduction in the gauge of the stock in a single passage through the rolls be relatively great. If the size of the work rolls were to be so increased as greatly to decrease the angle at which the work rolls bite into the stock, the effective rolling pressure would be decreased by slippage, and the utility of exerting great pressure through the screwdowns of the rolling mill assembly would in large measure at least be lost. This necessitates the employment of work rolls providing a relatively great bite angle with the stock. In previous practice in 40" to offset by work rolls so largeas to provide a rela tively low bite angle and thereby to minimize the reduction in the stock caused by a single passage of the stock through the rolls.

I prefer to use rolls the diameter of which is small as compared with the diameter of work rolls in temper mills of like size used in like oper.=

ations. Thus in 40" to 42 temper mills, I pre= fer in conducting my method to use work rolls down to diameter and even less, and in small mills correspondingly to use work rolls of lesser diameter. In temper mills larger than 40" to 42" mills the diameter of the work rolls will be correspondingly greater, but in any case I use work rolls having a diameter no greater than those commonly used in temper mills of like size and on like work, and prefer to use work rolls which are relatively small with respect to the common practice of the art. I have found that if the backing for the work rolls be of very high value, as is the case in the exemplary apparatus described-above, I am able to use work rolls of very small diameter to apply abnormally high pressures.

Utilizing work rolls of adequately limited di ameter I thus retain or increase the effect of violence caused by the high pressure and high speed at which I roll the stock. As exemplary of procedure in accordance with my invention, I may give an operation upon cold coiled strip of about 16 gauge and 34 width of a composition generally accepted as giving full deep-drawing properties, such as 0.06 to 0.10 carbon steel having no substantial content of alloying metals, normalized. Having used the screwdowns to establish a pass,. and to exert a pressure in the neighborhood of 200,000 pounds per linear inch on the stock. I pass the stock through the work rolls at a speed between 2,000 ft. per minute and 2,500 ft. per minute. 'Ihe work rolls are of about 14" diameter and the reduction in the stock is about 30%. No tensioning means tending to pull the stock through the temper mill is used. Such sheets show no substantial decrease in their deep= drawing properties even when relatively long periods of time intervene between the temperrolling and the deep-drawing operation.

I have shown herein as illustrative of .an in.

strumentality usable in effecting my purpose, a rolling mill organization capable of sustaining abnormally high pressure without making the structure of the apparatus of abnormally great size.

method may be performed by using back-up rolls of abnormally great size in the temper mill or by otherwise so organizing the temper mill that it is capable of applying and sustaining abnormally great rolling pressures and operating at abnormally high speeds.

I claim as my invention:

l. The herein-described method of making from steel strip and sheeta cold-rolled product having persistent deep-drawing properties by cold-rolling a normalized steel strip or sheet of deep-drawing composition under a rolling pressure approximately as great as 200,000 pounds per linear inch of roll contact with the stock at a speed approximately as great as 2,000 feet per minute in work rolls of a diameter so small as to give a bit angle at least as great as that conventional in temper mill practice; by the abnormally severe working thus effected so deadem ing the stock as substantially to eliminate tendency toward structural rearrangement therein.

2. The herein-described method of making from steel strip and sheet a cold-rolled product hav ing persistent deep-drawing properties by cold rolling a normalized steel strip or sheet of deepdrawing composition under a rolling pressure .within the approximate range of 150,000 pounds I per linear inch of roll contact with the stock to 200,000 pounds per linear inch of roll contact with the stock at a speed of from about 1,500 feet per minute to about 2,500 reet per minute in work rolls of a diameter so small as to give a bite angle at least as great as that conventional in temper mill practice; by the abnormally severe working thus eected so deadening the stock as substantially to eliminate tendency toward structural rearrangement therein. v

3. The herein-described lmethod of making from steel strip and sheet a cold-rolled product having persistent deep-drawing properties by cold-rolling a normalized steel strip or sheet of deep-drawing composition under a rolling pressure in excess of 150,000 pounds per linear inch of roll contact with the stock at a speed in excess oi 1,500 feet per minute in work rolls of a dlameter so small as to give a bite angle at least as great as that conventional in temper mill practice; by the abnormally severe working thus efiected so deadenlng the stock as substantially to eliminate tendency toward structural rearrangement therein.

M. MecoNNELL.

It is to be understood, however, that lnsofar as concerns my method herein disclosed, such

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