US2075273A - Method of rolling metals - Google Patents

Description

March so, 1937. L s DAHL hwenior.

- March 30, 1937. L. s. DAHL 2,075,273

- METHOD OF ROLLING METALS Filed Feb. 27, 1936 2 Sheets-Sheet 2 CENT E E LINEx,

NJ hwenior:

lflmef/vcf 5. QHHL atented ar. 3, i937 am'rnon or non means wrence S. Dahl, Gary, ind, assignor to e can Sheet and Tin Plate. Company, a corporation of New Jersey Application February 2'7, 1936, Serial No. 66,118

4 Claims.

This invention relates to a method of rollin metals, and more particularly to the cold reduction of thin and relatively wide continuous strip.

Heretofore, in the cold rollingof continuous 5 metallic strip the reduction was largely efiected by enormous screw-pressures on the rolling bodies. This reducing action was sometimes augmented by tensioning the material being worked. That is to say, a substantial pulling tension was uti- 10 lized to move the strip between the rolls which were held thereagainst under extremely high pressure. Sometimes a substantial back, or drag, tension was imposed on the strip with the result that lower rolling pressures could be used. However, resort to substantial back tension, and consequent lowering of rolling pressure, resulted in a lowered percentage of reduction, for the reason that there is a low efiective pulling tension on the strip. This efiective pulling tension is the difference between high-pull and low-back tensions plus resistance established by the rolling bodies.

In the cold rolling of continuous metallic strip it is extremely important that the total reduction is effected in the least possible number of passes;

otherwise work-hardening results with the consequent necessity ofintermediate annealing, which is a costly process.

In Patent No. 2,025,002, to Howard G. Mclflvried, 3Q entitled Method of rolling sheet metal, there is I disclosed a method of efiecting a high percentage of reduction at high speed, whereby the number of necessary passes is greatly minimized. The method of this patent utilizes extremely high 35 compressive forces by applying high screw-pressure to the mill rolls. It is obvious to those skilled in the art that a mill constructed to practice such a method must possess great strength and durability. The rolls of such a mill are sub- 40 jected to terrific strainand require frequent dressing and replacement, which is very costly. The method of the present invention seeks to obtain the advantages and results of the method of the Mcllvried patent referred to while at the 45 same time reducing initial cost and maintenance. It is among the objects of the present invention to provide a novel method of cold-rolling metals, and particularly thin and relatively wide continuous strip by the utilization of lowered rolling 50 pressure together with extremely high back, or

drag, tension. I

The strip metal may optionally be subjected to a slight take-up reel tension, but of such magnitude as to be solely sufllcient to flatten and tightly 5a coil it..

Still another object of the present invention is to provide a novel method of cold-rolling thin and relatively wide continuous strip-metal by the practice of which cross-sectional inequalities are substantially eliminated prior to roll-contact, whereby a. fiat work-piece is presented tothe rolls for further reduction.

A further object is the provision of means for obtaining an efi'ective arc of roll contact with the strip-metal which is substantially less than that of the same rolls as used in prior art methods, whereby crowding and consequent tearing of the metal of the strip is avoided, as well as the overheating of the rolls.

A still further object is to obtain strip-metal having a surface condition which readily lends I itself to subsequent annealing while in coiled form.

The foregoing and still further objects will be apparent after referring to the drawings, in

which:

Figure l is a schematic representation of a modern d-high cold rolling mill on which the method of the invention may be practiced.

Figure -2 is a diagrammatic representation of the effect of the method of the invention as compared with those of the prior art.

Referring more particularly to the drawings, the numeral 2 designates a pair of suitably driven metal-working rolls, each of which is maintained in position by a backing-up roll 3 of greater diameter. The rolls 2 and 3 are suitably supported in the usual housing t and provided with any of the conventional adjusting devices (not shown).

Referring to Figure 1, it will be noted that the diameter of the backing-up rolls 3 is several times that of the metal-working rolls 2. However, I have found from experiment that the method of the invention is best performed on driven metalworking rolls of a diameter considerably in excess of what has heretofore been considered good practice (for example, 15 to 30 inches as compared to 4 to 10 inches).

A pair of reeling devices are provided for handling the strip-metal S being rolled by he driven metal-working rolls 2, one being disposed on each side of the housing 4. Assuming the strip to be moving from left to right, the pay-ofi reel is indicated at 6 and the take-up reel at 1. Upon reversal of the direction of rolling, the function of the reels 6 and I is converse. A pair ofguide rolls 8 and 9 are provided for guiding the strip to and from the reels 6 and 1 and the work rolls 2.

As previously pointed out, the method of the invention includes 4 driving the metal-working 70 Q imately 158% of its elastic limit) and that the Pay-ofl Take-up Mill (rolls) m1 mi (3086 .075 Gage out- 1a)" Volts 570 680 570 Amps 2, 200 810 175 Actual H. P.- 1, 626 094 100. 6 Total (utilized) kilowatts"--- 1, 139. 0 517 81. 7 Strip travel ltJmin. an 104 262 Total l)bs. thrust (tangential 192,111! lb orce Thrust per inch oi width.-. 5,130 lb all 130,700 lb. 13,800 lb. 31,000 lb. 4,010 lb. 10, 000 21, 600 158% 22. 8% Total screw pressure 850,000 lb. Screw pressure per inch oi width 22,700 lb Second reduction Take-up Mill (rolls) Pay-oi! real ml 060 m5" 670 685 570 2000 745 210 Actual H. 1397. 0 642 127. 8 Total (utilized) kilowatts 1040 478 00. 3 Strip travel it./min $7 178 I 207 Total lbs. thrust (tangential ior 172, 700 Thrust per inch of widt To p 119, 000 lb. 15, 800 lb. Total pull r sq. in. 42, 250 lb. 8, 430 lb. Elastic lim t of metal 21, 500 lb. 34, 000 lb. Tenslon+elastic limi 197% 24. 8% Total screw pressure 900, 000 lb Screw pressure per inch oi width 24, 000 lb Third reduction Pay-oi! Take-up Mill (rolls) M1 M1 Gage in; 038" 6 out .000" V0 ts 580 578 5M Am 1060 020 2330 Actual H. P 762 525 152. 3 Total (utiliud) kilowatts-...- 50L 3 301. 3 113. 6 Strip travel ltJmiiL 216 110 275 otal lbs. thrust (tangential 6o iorcs) 90. 110

Thrust per inch 0! width-- M00 7 Total pull. 82, N0 18, $0 Total pull per sq. in 44, 200 12, 840 Elastic lilnJ 34, 000 50, ill) Tension+elastic limit 130% 25. 7% g t alscrew pressura n uu 750,000lb w pressure per no 0 width. no, 000 lb rolls 2 under relatively light screw-pressure, utilizing a very substantial back, or drag, tension, and removing the strip S from the delivery side of the mill with little or no tension. In other words, the tension, if any, is of such magnitude as to be solely suilicient to flatten and tightly coil the reduced strip.

As an example of the method of the invention the i'ollowingv data respresent conditions actually encountered in a three-step cold-reduction of a coil of low-carbon (approximately .07%) steel strip, 37.5 inches in width, which had previously been hot-rolled and pickled:

First reduction From the foregoing data it is apparent that during the first reduction (or in the first -pass") the back, or drag, tension imposed on the strip 8 as it entered the mill was very high (approxtotal screw-pressure on the metal-working rolls 2 was of a low magnitude (approximately 22,700 lb. per inch of width of metal being reduced). The take-up reel tension imposed on the-strip S on this first pass was oi an extremely low magnitude (approximately 23% of its elastic limit) being solely sufficient to flatten and tightly coil it, The power required to establish a tension of this order is only a small portion of the power applied to the metal-working rolls 2 of the mill. In the above instances it was only approximately 7% of the power on the mill.

The percentage of reduction of the section of the strip S on the first pass was approximately 37.5%, and it will be readily understood by those skilled in the art that this percentage could have been substantially increased by corresponding increases in the power utilized to drive the metalworking rolls 2 and the degree of back, or drag, tension established by the pay-of! reel 6. For example, the percentage of reduction of the sec tion of the strip S could have been increased to approximately 60% with the back, or drag, ten- I sion increased to approximately 200% of its elastic limit.

After the strip S has completed its first pass (left to right in Figure 1) throughthe metalworking rolls 2, the entire operation is reversed. That is to say, the reel I is operated to act as the pay-0i! reel under substantial back, or drag, tension, while the reel 6 acts asrthe take-up reel under tension of such magnitude that it is solely sufilcient to flatten and tightly coil the reduced strip S. As the strip 5 moves from right to left (Figure 1) on its second pass, the metalworking rolls 2 will, of course, be driven in a direction opposite to their movement during the first pass.

During the second pass the pay-oil reel 1 tensions the strip S to the extent of 197% of its elastic limit, while the tension imposed by the take-up reel 0 is only approximately 25% of the elastic limit. The power required to establish -a tension of this order is again only a small portion of the power required to deliver the strip from the metal-working rolls 2 of the mill. In the above instance it was'only approximately 7% of\ the power on the mill. The screw-pressure on this pass is approximately that of' the first pass (22,700 lb. per inch of width 01' strip).

The percentage of reduction of the section of the strip 8 on the second pass was approximately 34%, and here again it will be readily understood by those skilled in the art that this percentage could have been substantially increased by corresponding increases in the power utilized to drive the metal-working rolls 2 and the degree of back, or drag, tension established by the payofif reel "I. For example, the percentage of reduction oi the section of the strip S could have been increased very substantiallyby increasing the back, or drag, tension to approximately 300% of its elastic limit.

The third and final pass is very similar to the second pass as to the magnitude of back tension, take-up reel tension and screw-pressm'e. On this pass the strip 8 moves from left to right v(Figure 1) withthe metal-working rolls 2 driven in a direction corresponding to the first pass. Thus, the reel 0 acts as the pay-ofl reel, while the reel 1 is operated to act as the take-up reel. The percentage of reduction of the section of the strip 8 on this third pass'was approximately 24%; the back, or drag. tension approximately 130% of its elastic limit; the take-up reel tension approximately 25.7%; and the total screwpressure on the metal-working rolls 2 was 20,000 lb. per inch of width of metal being reduced. The power required to establish a take-up reel tension of such 'low magnitude is again only a small portion of the power required to deliver the strip from the metal-working rolls 2 of the In this instance it was only approximately 5 17% of the power on the mill.

From the foregoing it will be seen that, briefly stated, the method of the invention contemplates extremely high back, or drag, tension (100% to 300% of the elastic limit to the metal of the strip); low screw-pressure (averaging only approm'mately 22,000 lb. per inch of width of metal being reduced); and extremely low take-up reel tension (averaging only approximately 25% of the elastic limit of the metal of the strip) whereby it is solely sufilcient to flatten and tightly coil it.

The advantages of such a method are graphically represented in Figure 2 of the drawings, which compositely represents the effect of the methods of the prior art above the center line of the strip S; while the effect of the method of the present invention is represented below the center line. The apparatus is substantially the same in both cases, the portions illustrated being the metal-working rolls 2 and a suitable spray device 12 which dispenses a liquid spray l3 into the'initial areas of reduction of the former. The liquid utilized is preferably a combined lubricant and coolant.

Referring to that portion of Figure 2 which is above the center line of the strip S, the efiect of rolling without back, or drag, and take-up reel tensions is graphically illustrated. The arc of contact of one of the metal-working rolls 2 with 35 the strip S is indicated at AB. The area bounded by the .letters ABCD illustrates the approximate size and distribution of the radial pressure between a metal-working roll 2 and the strip S.-

I 50 As pointed out, that portion of Figure 2 which is below the center line of the strip S represents the effect of the method of the invention. By utilization of extremely high back, or drag, tension. a greatly reduced arc of contact of a metalworking roll 2 with the strip S results, as illustrated at FG. The area bounded by. the letters FGH illustrates the approximate size and dis;

tribution of the radial pressure between a metalworking roll 2 and the strip S. This area, as before stated, represents a measurement of the total screw-pressure per inch of width of strip being rolled. According to this representation, there is a gradual building-up 01' unit radial pressure from the point F to the point H and a marked decrease in total screw-pressure.

The efiect of the greatly increased high back, or drag, tension disclosed is to draw out, or neck, the metal of the strip S immediately adiacent the "nip, or initial point of contact, of the metal-working rolls 2. This necked portion establishes a space K between each of the metal-working rolls 2 and the tensioned strip S into which a liquid having lubricating and a So far as I am aware, no prior art method of cold rolling establishes a necked portion on the work-piece which is similar to the area indicated at K in Figure 2 of the drawings. This condition at the nip or *inital point of contact of the driven metal-working rolls 2, permitting the application of lubricant, together with lowered rolling pressure, is responsible for the results heretofore mentioned. This necked" portion, or area K, reduces the arc of contact of the large metal-working rolls with the work-piece.

' The arc ofcontact is less than it would be in and imposing an extremely heavy drag on the pay-oil? reel, I can utilize screw-pressures comparable to those of the prior art mills employing much smaller metal-working rolls; and this is particularly true of those mills whose rolls are not driven. As a matter of fact, I have operated a mill according to the method of the invention at screw-pressures and rolling speeds comparable to those of prior art methods and effected an increase thereover in percentage of reduction per passwhich is in excess of 150%.

Referring again to the representation of the prior art which appears in Figure 2 above the center line of the strip S, it will be readily understood that .the formation of the shoulder (or Welling-up of metal) E is responsible not only for excessive generation of heat at the arc of roll contact, but also a flow of metal which is not uniform. If this shoulder were not present, and the surface of the strip S plane, it would be possible to inject a' liquid lubricant into the nip or initial point of contact of the metalworking rolls. With the shoulder E present it is impossible to provide liquid lubricant where it is most needed (i. e., betweenthe letters A and L). Therefore, the method of the invention not only seeks to remove a shoulder (and thus provide a plane surface) but actually to neck in the work-piece at this point, whereby the numerous benefits are obtained.

The method of the invention makes possible the use of at least one metal-working roll 2 whose surface has been deliberately roughened to secure advantages which will be later described. The roughening may be accomplished in any suitable manner as, for instance, grinding, etching, blasting with sand or shot, etc. The roughened roll, or rolls, provides a surface condition of the strip S which is conducive to the retention of a liquid having lubricating and cooling qualities. These factors enhance the possibilities of employing even higher degrees of back, or drag, tension, resulting in an increased rate of reduction.

In addition to the foregoing, -a strip S which has been cold reduced in a mill employing at least one roughened metal-working roll is characterized by having one roughened side which will retain a separating coating. The reduced strip S may be provided on its roughened surface, or surfaces, with such a separating coating, and subsequently coiled and annealed. Ordinarily, highly finished strip cannot be annealed in coiled form. for the reason that the convolutions thereof will adhere. It has therefore been proposed to roughen the strip by the use of a roughened roll, or rolls. In the past, such roughened rolls have not met with material success,v

due to the fact that when used in desirably large sizes they resulted ina Welling-up ofthe metal l cific embodiments of my invention, it will be understood that I do not wish to be limited exactly thereto, since various-modiflcationsmay be made without departing from the scope of my invention, as defined by the following claims. I claim:

1. In a method of cold reducing strip metal, the steps consisting of passing the strip metal under a tension 01' from materially more than 100 per cent of its elastic limit to 300 per cent of its elastic limit toa rolling mill so as to neck down the strip metal over its entire cross-section as it enters the mill, applying a compressive force to said strip metal as it passes through the mill of a magnitude suilicient to separately and permanentlyreduce the cross-sectional area of said strip metal an appreciable amount over its entire width, and applying tension. of a magnitude materially less than the elastic limit of the strip metal to that portion of the strip metal issuing from the mill.

2. In a method of cold reducing strip metal, the steps consisting of passing the strip metal to a rolling mill under a tension of from 125 to 300 per cent of its elastic limit so as to materially reduce its entire cross-section and form a necked-down portion adjacent the mill and materially reduce the arc of contact between the mill rolls and the strip metal, applying a com- 'pressive force to said strip metal as it passes through the mill of a magnitude suflicient to separately and permanently reduce the crosssectional area of said metal an appreciable amount over its entire width, and applying tension of a magnitude materially less than per cent of the elastic limit of the metal strip issuing from the mill.

3. In a method of cold reducing strip metal,

the steps consisting of passing the strip metal to a rolling mill under a tension of from materially more than to 300 per cent of its elastic limit so as to materially reduce its entire crosssection and form a necked-down portion adjacent the mill, forming a wedge-shaped space between the strip metal and a portion of the mill rolls above and below the metal strip, delivering a lubricant into the so formed spaces, applying a compressive force to said strip metal as it passes through the mill of a magnitude suilicient to separately and permanently reduce the crosssectional area of said metal strip an appreciable amount over its entire width, and applyin tension 01' a magnitude materially less than the elastic limit of the metal strip to that portion of the metal strip issuing from the mill.

4. In a method of cold reducing strip metal, the steps consisting of passing the strip metal under a tension of from to 300 per cent of its elastic limit to a rolling mill so as to neck down the mill over its entire cross-section as it enters the mill to form with the rolls of the will a substantially wedge-shaped space above and below the metal strip, delivering a lubricant into the so formed spaces, applying a compressive force to said strip metal as it passes through the mill of a magnitude suillcient to separately and permanently reduce the cross-sectional area of said metal strip an appreciable amount over its entire width, and applying tension 01' a magnitude materially less than 50 per cent of the

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