US2038917A - Method of cold rolling sheets - Google Patents

Description

April 28, 1936. P. F. WILSON El AL METHOD OF GOLD ROLLING SHEETS Filed April 1, 1931 5 Sheets-Sheet 1 I Q) INVENTOR PM I .L,

Fan/MILK K [3. @Jzq (3W) H mm ruby/J April 28, 1936. P. WILSON El AL 2,038,917

METHOD OF GOLD ROLLING SHEETS Filed April 1, 1931 5 Sheets-Sheet 2 April 28, 1936. P. F. WILSON ET AL 2,033,917

METHOD 0F COLD ROLLING SHEETS I Filed April 1, 1931 5 Sheets-Sheet 3 INVENTOR APE'EH 28, 1936- RF. WILSON ET AL METHOD OF COLD ROLLING SHEETS Fild April 1, 1951 5 Sheets-Sheet 4 April 28, 1936. P. F. WILSON El AL METHOD OF COLD RQLLING SHEETS Filed April 1, 1931 5 sheets-sheet 5 Patented Apr. 28, 1936 UNITED STATES PATENT OFFICE METHOD OF GOLD ROLLING SHEETS Parker F. Wilson, Wheeling, W. Va, and Lorenz Iversen, Pittsburgh, Pa..

Application April 1, 1931, Serial No. 526,810

1 Claim.

limited with respect to the particular material being rolled, and is useful in theproduction of various materials, we have found that it is particularly advantageous in the production of sheets, tin plate and flat materials generally of the nature requiring great ductility andhigh drawing properties. Tin plate being a representative material, is hereinafter more specifically referred to, by way of example only.

In the past, it has been customary in the art of producing tin plate and sheet, to roll the same in individual lengths from bars or breakdown sheets of suitable sizes. These bars or breakdowns, after having been heated in a furnace to the desired temperature, were withdrawn in pairs and passed, one following the other, between chilled iron rolls until they were sufliciently reduced in thickness to permit matching of the sheets. After the matching operation had been accomplished by placing one sheet directly on top of the other, the pack was passed and re-passedthrough the rolls until loss of heat hindered further rolling.

After the original bars or-breakdowns had been rolled separately, matched and re-rolled, until cooled below rolling temperature, the pack was then conveyed to a doubling apparatus effective for overlapping the sheets on a line through the center of the pack. The doubled packs were then again heated and subjected to further rolling" operations.

While such practice enabled the production of commercial tin plate and sheet, it was open t6"'- certain objections. In the first place the repeated heating operations not only required considerable time, but due to the fact that each heating necessitated a re-handling of the material, there was a considerable expense representednot only by the handling but by the heating itself. Also, the repeated handling of the material in short lengths was both difficult and expensive, not only with respect to the heating operations, but with respect to the rolling operations.

Quite apart from the questions of expense, time and labor involved, the heating as heretofore practised was objectionable for the reason that it injured the quality of the material. Experience has demonstrated that the size of the grains grows with repeated heating operations, and therefore any practice requiring repeated heatsentative only; they varying proportionately in gorse-s) ing prevents the obtaining of a product having the proper grain size. In accordance with the present invention, we not only eliminate all of the re-heating operations and 're-handling operations and effect a substantial saving thereby, but likewise produce a material having an improved grain structure, and consequently improved characteristics.

Sheets and tin plate as produced by the ordi-g nary process before described were also charac 1o terized by a variation in thickness in different portions transversely thereof. Thus, in prior commercial tin plate and sheet it was not unusual to find a thickness variation at different points in the width of a given sheet amounting to as much 15 as .0018 inch, with an average variation of .0010 inch and higher. As an actual matter of fact, ex perience shows that less than 50% of the sheets produced commercially in the past in accordance with the process described have a total variation in thickness of less than .001 inch. In accordance with the present invention it is entirely practicable to consistently produce wide thin sheet material in which the maximum variation in thickness does not exceed .001 inch and may be as low as .0006 inch. The above figures are applicable to material having a specified or contemplated thickness of approximately .010 inch. The figures above given are thus seen to be reprethe rolling of other gauges.

As to the variation of .0018 inch above referred to, it is to be noted that this variation, which is not uncommon with ordinary so-called coke tin plate, is greater than the usual tolerances for cold rolled strip of this gauge, having a width of 5 inches or over, such tolerances being plus and minus .0015 inch.

To overcome this dimculty, attempts have heretofore been made to produce materials of the character herein contemplated, by means of a socalled continuous cold rolling process in four high mills. Such mills have always been operated on the basis that relatively wide thin materials could be produced only by theuse of small diameter working rolls, and they have not been successful in the production of such materials. In accordance with the present invention we employ a different principle involving the use of large diameter working rolls efiective for producing the desired grain structure by an extremely heavy reduction or reduction by means of a simultaneous rolling and pressing operation. To make such an operation commercially successful, it must be effective for completing the reducing operation by 5 one pass through a plurality of roll stands consingle thickness only.

With small diameter working rolls it has been necessary to use two or more passes with intermediate annealing in order to obtain light gauges. Heavier gauges have been produced in one pass, but they have not had the desired grain structure, thus requiring normalizing and box annealing to obtain a useful product. Our invention overcomes these diiiiculties, and enables the direct production in one pass and at single thickness of light gauge material of the desired width and having the required grain structure.

The present invention is not only characterized by fewer wasters or seconds, and by a product having a greater uniformity of thickness, but also by the following attributes:

1. Substantial absence of usual steel defects such as seams, blisters and scale. a

2. .A superior surface finish, the tin plate being appreciable smoother and having a much closer texture.

3. A superior surface for the application of coatings.

4. A distinctly different grain structure from ordinary wide thin sheet material, and more closely approaching a normalized grain structure instead of an elongated and distorted grain structure as usually found in ordinary sheet or tin mill product.

5. Increased ductility, adapting the sheets to deep drawing operations.

6. An increased yield and a decreased cost.

The invention further lends itself to the use of a wide range of steel analyses for producing tin plates and similar light gauges that it is not possible to use in the ordinary process. It further enables the material to be furnished with any desired temper or stiffness.

The foregoing attributes and characteristics are obtained by subjecting a given piece of material, preferably a plate of 18 gauge material or heavier and of single thickness, to a continuous cold rolling operation without annealing or heating and effective for reducing the material to base plate of commercial gauges and dimensions effective for tin plate, roofing sheets or the like, sheets for galvanizing, or other similar light gauge material. The term base plate is hereinafter used in this generic sense.

In accordance with known practices as applied to continuous mill operation, it has heretofore been possible in some instances, with exceedingly narrow material, not exceeding 12 to 20 inches, to

reduce hot rolled material to a thickness of approximately .025 inch without annealing or heating. In accordance with the present invention, however, we are able to reduce hot rolled material having a width of 30 or more inches and a thickness of about .062 inch to a thickness of .009 inch or less by a continuous operation without reheating or annealing, and even greater reductions are practical, using a single thickness of strip material. r

In view of the difliculties inherent in the heating of packs, and particularly uniformly heating the same, it is'apparent that any pack process for producing tin plate and sheets necessarily results in a product of more or less non-uniform characteristics at diiferent portions throughout a operation of a single sheet, however, the difliculties incident to a pack operation are obviated,

and greater uniformity as to thickness and characteristics are easily obtainable.

Reference has hereinabove been made to the fact that the present invention lends itself to the use of different steel analyses. In rolling operations in which reheating, annealing, or the like is required, and particularly where repeated reheating or annealing operations are necessary in order to obtain the desired reduction, it has been customary to effect a compromise in the analyses of the steel utilized. It is well recognized that heat treating operations of the character referred to tend to produce grain growth. In order to minimize, to as large an extent as possible, such a tendency ,toward grain growth, it has heretofore been customary to use special analyses which will partially offset such a tendency. It has also been customary in the usual processes to add phosphorus to prevent sticking of the sheets. Not only does the addition of phosphorus represent an increase in cost, but it oftentimes imparts objectionable characteristics to the product.

The present invention, however, is characterized by taking a hot-mill product, such as a strip, cleaning the surface or treating the same in such manner as to prevent or remove oxidation, scale and the like, and then passing the same directly through a continuous mill of the four-high type. Such an operation is characterized by a complete absence of any heat treating of the character referred to, and therefore enables the material to have any desired composition. We have found, for example, that it is possible in accordance with the present invention to produce a cold-rolled sheet having a carbon content of from .07 to .11%, a manganese content of from 35% to 50%,

a phosphorus content from .02% to .03%, and a sulphur content of from .03% to .05%. To those skilled in the art, it will be apparent that it has not heretofore been possible to produce satisfactorily a light gauge rolled product having such an analysis. This possibility of rolling material without the necessity of effecting a special compromise in its composition constitutes one feature of the present invention. Hereinafter it will be understood that expressions such as "usual steel analyses" have reference to compositions of usual characteristics and are not specially prepared to offset grain growth. a

Not only is the invention characterized by the reduction of a hot-mill product directly into a product having gauges as light as tin-plate gauges and corresponding widths without any reheating or heat treating, thus enabling an increased production at a minimum cost, but it is further characterized by the utilization of rolls of such characteristics that a press action is obtained on the material of such nature as to be effective for controlling the metal flow during the reduction in thickness. Four-high mills, as ordinarily utilized, have been designed for the purpose of obtaining a maximum pressure concentrated in as small a zone as can be mechanically produced. To this end it has been customary to make the working rolls of a four-high mill of relatively small diameter to thereby give a condition of approximately a line contact. Such a line contact, afforded in.the bite of small diameter rolls, produces a maximum amount of work in a minimum amount of time with respect to any given portion of the material being rolled. The contact zone, however, is of such small area as to produce a maximum amount of work substantially instantaneously, this necessarily resulting in a condition of comparatively easy metal flow. The present diagrammatically,

.ing rolls of such large diameter as to simulate in their action the operation produced by a press. As a matter of fact, it is one of the objects of the present invention to provide and continuously maintain what may be designated as a rollerpress action, such action being characterized by a substantial increase in the area of material within the bite of the rolls at any one time. This area may be referred to as the pressure area, and is suihcient to effect a substantial holding action or restraining action on the metal to such an extent that the original grain characteristics of the metal may be controlled and improved. It necessarily follows that material having desirable grain characteristics before cold rolling may be cold rolled in accordance with the present invention and retaining or actually improving such characteristics. In this respect, the present invention differs radically as to both its principle and the manner of operation from four-high mills as usually provided. In one case the construction is such as to produce a maximum amount of work in a minimum amount of time, while in the other case the object is to effect a maximum holding or restraining influence concomitantly with the performance of work.

It is further to be found that a concentrated pressure zone of the line contact type involves.

ing with consequent greater uniformity in thickness.

The present invention is further characteri by a materially greater reduction in the first stand of rolls than in any of the stands subse-' quent thereto. We have found that inthis manner superior results are obtainable, the heavy draft having a marked effect on quality as well as thickness. While we are not definitely advised of the reasons entering into such a superior product by reason of a maximum initial reduction,- it is our belief that in this manner the maximum heating, by reason of maximum work, is obtained in one pass at the commencement of the rolling operation, this heat being availed of to some extent in the subsequent passes. It is to be understood, however, that the heat generated due to rolling is not such as to effect an actual annealing of the material.

In the accompanying drawings we have shown for purposes of illustration only, and more or less certain preferred embodiments of the present invention. In the drawings:

Figure 1 is a sectional diagrammatic view illustrating one form or layout in accordance with the present invention;

Figure 2 is a partial top'plan view of the layout shown in Figure 1, taken along the line II--II;

Figure 3 is an electric circuit diagram showing how the mill is controlled:

Figure 4 is an end elevation of one of the fourhigh stands in detail;

Figure 5 is a diagrammatic view illustrating the different stages through which the materialpasses both before and after our cold rolling process; and

Figure 6' is a view similar to Figure 5, illustrating another embodiment of the invention.

In carrying out the present invention, we preferably provide a plurality of mills -of the fourhigh type so arranged as to act successively on the material. In Figure 1, four such mills A, B,

C and D are illustrated. Each of these mills comprises backing-up rolls 2 and working rolls 3, all of the rolls being supported in anti-friction roller bearings for the purpose of improving the product of the mill by obviating misalignment I of the rolls and the resulting injury'to the material.

So far as we are aware it has not heretofore been proposed to utilize roller bearings both for the working rolls and for the backing-up rolls. We have found, however, that the use of such roller bearings on all of the rolls materially assists in the quality of the product and the accuracy of rolling. Roller bearings of the character used are not only effective for minimizing friction, and consequently heat generated in the necks of the rolls, but are also effective for maintaining the rolls in absolute alignment whereby any crossing tendency of the rolls is precluded under the tremendous pressures to which they are subjected. This in turn makes it possible to maintain at all times a pressure zone which is exactly at right angles to the direction of rolling and which obviates any tendency toward end thrust on the rolls.

Each of the mills possesses the novel characteristicof employing working rolls 3 having a diameter materially greater than the diameter ofworking rolls such as have been heretofore considered desirable. In the ordinary practices of rolling with backed up rolls, there has been a tendency to utilize working rolls of relatively small diameter for the purpose of obtaining a greater concentration of the reducing pressure. .In accordance with the present invention it is not only desirable but necessary to utilize working rolls having a diameter greater than the maxi- 'rhum diameter which has heretofore been imour invention, each of the working rolls preferably has a diameter of not less than 16 inches, and the diameter is preferably greater than this amount.

This materially greater diameter is important in a continuous rolling operation of the character herein contemplated for at least four reasons; In the first place, it is possible, by the increased diameter, to obtain more draft on the material. In the second place, it is possible to maintain the material flatter as delivered from the rolls. In the third place, the larger rolls lend themselves to a heat controlling operation of a character impossible with rolls of smaller diameter. In the fourth place, the larger rolls result in giving a superior quality product.

In operating on material of approximately 16 gauge, i. e., having a thickness of approximately .0625 inch; very desirable results are obtained by the use of working rolls having a diameter of 18 sults in practice.

a thickness of approximately .062 inch to a thickness of approximately .011 inch the mill may be so operated that in the first mill the material is reduced approximately 43 in the second mill the material is reduced approximately 38 in the third mill the material is reduced approximately 30%%, and in the last mill the material is reduced approximately 27%. In other words, starting with a material having a thickness of .062 inch it is reduced first to .035 inch, second to .0215 inch, third to .015 inch, and fourth to .011 inch. After this, the material may be rerun to reduce it from .011 inch to .009 inch if desired. We have found that the desired results can be obtained by some departure from these percentages, although it is desirable to maintain the percentage of reduction in the stand A between the range of 40 to 55%, the reduction in the mill B within the range of 30 to the reduction in the mill C within the range of 10 to 45%, and the reduction in the mill D within a range of 5 to 30%.

The above percentages are given by way of illustration only, and not for purposes of limiting the present invention. For purposes of further illustration we will nowgive other concrete examples of the dimensions of material operated upon in accordance with this invention. In the first instance the material having an original average thickness of .063 inch was reduced to an average thickness in the mill A of approximately .027 inch; in the mill B to approximately .017 inch; in the mill C to approximately .015 inch, and in the mill D to approximately .0133 inch.

In the second case, material having an original thickness of .062 inch was reduced in. the first stand A to approximately .032 inch; in the stand B to approximately .020 inch; in the stand C to approximately .014 inch, and in the stand D to approximately .0137 inch. It will be noted that in the second example the amount of reduction in the stand A was considerably less than the amount in the corresponding stand in the first example, while the reduction efiected by the stand C was considerably greater than that effected by the corresponding stand in the first example. These figures illustrate the latitude permissible in carrying out our invention.

In the following tables we give other concrete examples of what we have found to give good re- In each case the material being rolled is hot rolled strip having a thickness of approximately .0625 inch.

The present invention may be utilized for the rolling of any piece of hot rolled fiat material but in actual practice, we preferably take the material'M in reel form as delivered by an ordinary hot rolling mill, such as a strip mill, and place the leading end thereof in the pass of the mill A, the mill having an independent or individual speed control 56 for this entering operation. After the material has passed through this mill, the leading end is inserted into the pass of the mill B which is also individually controlled. Thereafter the leading end is inserted into the pass of the mill C having its individual control.

and then into the pass of the mill D having a similar individual control.

As shown in Figure 5 of the drawings, the material is wound on reels R as it comes from a hot-strip mill H. It is then passed through a cleaning and/or deoxidizing process Z. At this stage, the material may be also annealed if desired, although it is to be understood that this annealing is unnecessary in practising the present invention. Instead of the above, the strips may be cut oif at their ends so as to be square and connected together in series as, for example, by means of electric welding or stitching and then, if desired, the material may be annealed or cleaned, pickled, dried, and covered on both sides with a lubricant such as palm or vegetable oil. The connected series of strips may be disconnected either before or after the above-mentioned oiling step. After being lubricated, the material is wound into coils S which are successively placed in a reel box U conveniently located in front of the stands A, B, C, and D. The material M is then passed through the stands, as described above, and run through a tension stand W or, if desired, it may be wound on a rewinding reel driven by a motor in a manner that will be described presently. After leaving the tension stand W, the material passes under mspring-mounted idler I, thence through a fiat press K for fiattenning and tempering, through a cleaner N, past a scrubber M, through a tension stand W, and finally to one or the other of a plurality of rewinding reels L. Two stands are conveniently provided for holding the rewinding reels L so that the operation of the mill may be continuous and the reels removed, as soon as they have been wound, alternately. After the material has gone through these processes, it may be annealed, slit, leveled and sheared into convenient sizes, which are then handled in any desired manner. If for tin plate, they may be pickled and tinned in the usual manner.

Referring to our rolling 'mill again, as the leading end of the material A is engaged by successive mills, the individual controls are so opx erated as to take up any slack in the material,

the individual mills being speeded up within their allowable range of operating speeds for this purpose. After the material has been entered into all of the mills, a master control 2| is operated which places all of the mills under a common control, eifective for maintaining a predetermined relationship between their speeds of operation. Preferably the individual controls are such as to initiate the feeding operation at a relatively slow speed in the neighborhood of 60-75 feet a minute, while the master control may be used to produce a substantial increase in the speed of operation of all of the mills. The desired control in this respect is obtained by utilizing direct current compound wound motors l2 with individual controls 56 effective for increasing or decreasing the magnitude of the shunt field current.

Referring to the elementary diagrammatic representation illustrated by Figure 3 of the drawings, the stands A, B, C and D are each driven by a compound wound motor l2 having a series winding I3 and a shunt winding Id. The series winding l3 of each motor is connected in series circuit relation with a resistor l0 which is, in turn connected to a main conductor I5. other side of the motor is connected to the other main conductor l6 through a switch I 8. An individual switch i9 is connected between the se- The ries winding of the motor I2 and the main conductors I5 and I6 for switching this circuit into or out of connection with the main conductors I5 and I6. The main conductors I5 and I6 are energized by any suitable source of supply, such as a direct current generator 20.

A variable resistor 2| is inserted in series circuit relation with the main conductors I5 and I8 for controlling the current supplied by the generator 26 to the system through the conductors I5and I6.

The shunt field winding I4 of each of the motors I2 is energized through conductors 22 and 23 by a generator 24. A switch 25 is inserted between each of the shunt field windings and the conductor 23 for automatically switching the shunt field into or out of circuit relation with the source of supply 24. The switch 25 is mechanically coupled to the switch I8 and both of these switches are operated by a relay winding 26. The relay 26 is' energized by a control circuit comprising conductors 21 and 28.

The conductors 21 and." are connected to the main conductors I5 and I6 by means of a startgized. A stop switch 33 is connected in series circuit relation with the relay 30 so that when the former is opened, the relay is de-energized, thereby opening the switches 3| and 32 and deenergizing the control circuit conductors 21 and 28. The relays 26 are then de-energized and the switches 25 and I8 opened, causing the motors 12 to stop running.

The motors I2 are provided with means for automatically maintaining a proper-tension in .the material between passes which preferably comprises a vibrating regulator 34 associated with each of the field circuits of the motors I2. The vibrator 34 consists of magnetically coupled coils 35 and 36 that are energized respectively by a generator 31 through conductors 38 and 39 and by the current short clrcuited around the resistor I0, which is in series with the series field winding I3. The coils 35 and 36 vibrate an armature 40. The armature 40 is biased away from the coils 35' and 36 by a spring 4|. The armature 40 is provided with a contactor 42 for intermittently short-circuiting a resistor 43 that is in series circuit relation with the shunt field I4. The armature 40 is provided with a second set of contacts 44 in series circuit relation with the energizing coil 35 for maintaining the vibrating motion of the armature 46. For example,

when the contacts 44 are closed, the magnetic force of the coils 35 and 36 raise the armatu e 46 against the spring 4| and open the contacts 44. The coil 35 is de-energized thereby, and the spring 4| snaps the armature 40 downwardly. This cycle of operation continues and the armature is vibrated in this manner. But, at the same time, the contacts 42 are opened and closed intermittently, short-circuiting the resistor 43 out of and into circuit relation with the shunt field winding I4. The amount of current traversing the shunt field winding I4 is, therefore, a function of the speed of operation of the vibrating regulator e4. The vibrating regulators are provided with individual adjustments for changing the speed of vibration which may conveniently consist of changing the tension of the spring 4|, the magnitude oi. the resistors 43, or in any other suitable way.

Each of the motors I2 is also provided with a manually adjustable rheostat 58 in circuit relation with the shunt field I4 for manually controlling the speed of the motor.

The generators 24 and 31 are conveniently coupled to and driven by a. compound wound direct current motor 46 that is energized by the main source of supply generator 20. The motor 46 is provided with a series field winding 41 and a shunt field winding 48. The speed of the motor 46 is controlled by changing the current flowing through its shunt field winding 48. by means of a variable resistor 49. The variable resistor 49 may be manually controlled, but it is preferably controlled by means of a control motor 50.

The control motor drives the arm 5| oi the variable resistor 49 and also drives an armature 52 for opening contactors 53 and 54 for cutting itself out of circuit. The limit switches 53 and 54 are adjustable in position relative to each other and relative tothe armature 52.

The control motor 56 is energized by the main source of supply generator 20, which preferably has an output of about 230 volts.

If it is desired to speed up or slow down all of the motors I2 at the same time, one of the switches 53 or 54 is closed and the motor 50 turns the armatures 5| and 52 until the armature 52 reaches one of the limit switches 53 or 54, depending upon which one is closed, and opens it, stopping the motor 50. In the meantimeythe arm 5| has moved over the contacts of the resistor 49 and changed the amount of current flowing through the shunt field winding 48 of ,the motor 46, causing it to correspondingly change its speed. Since the generators 24 and 31 are coupled to the motor 46, their speed is also changed and their output voltage is correspondingly changed. If the speed of the generators 24 and 31 is increased, their voltage is increased and the vibrators tend to vibrate more rapidly because of the increased strength of the coils 36 of the vibrators. The efiect of this is to hold the contacts 42 open longer, which, in turn, tends to place the resistors 43 in the shunt field circuit longer, tending to decrease the current flowing through the shunt field circuit. But, since the generator 24 is also speeded up, its voltage is correspondingly increased, tending to cause more current to flow through the shunt field winding I4.

The speeding up of the generators 24 and 31, therefore, has the efiect of causing them to counteract each other, but, since the shunt field is connected directly across the conductors 22 and 23 of the generator 24, the efiect of its increased voltage overbalances the efiect of the. vibrator 34 and causes more current to flow through the shunt field. This, in turn, strengthens its field and causes the motor I2 to slow down. The vibrating regulator 34 has, however, been compensated for by the increase in speed of the motor, and it automatically functions inits intended manner to control the speed of the motor I2 so as to maintain the tension constant in the ma,- terial being rolled. Y

The motor 50 is provided with the usual shunt winding 55 having a variable resistor 56 in series circuit relation therewith for adjusting the speed of the motor 56. The limit switches 53 and 54 of the motor 50 are connected, respectively, in series circuit relation with series field windings 51 and'58, one of which causes the motor to operate in one direction, and the other one of which causesthe motor to operate in a reverse direction when it is energized. The vibrating regulators 34 operate in the following manner to maintain constant tension in the material being rolled. Let us suppose material is being rolled by the stand A, but momentarily there is an excess of material inserted in front of it tending to decrease the tension of the material being rolled. In that case, the load on the motor i2 is decreased, which causes less current to flow through the resistor III. This increases the effective opening of the contacts 40, causing the resistor 43 to impose more resistance in series with the shunt field, weak ening it, and causing the motor I 2 to speed up, thereby re-establishing the proper tension on the material being rolled.

The re-winding reel 1 is driven by a motor 59 that is, in turn, energized by a generator 60 having its shaft coupled to the motor I2 driving the last stand D. The motor 59 is of the compound type having the usual shunt winding 6i and series winding 62. For starting purposes, the motor 59 is connected across the main conductors l5 and I6 through a resistor 63 and a starting switch 64. To start the motor 59, the starting switch 64 is closed, and, as it comes up to speed, it operates a relay 65 which opens a switch 66 and closes a switch 61. Operation of relay may be delayed for a'suitable time by any convenient, known means. The switch 66 is in series circuit relation with the conductors leading to w the main conductors l5 and I6, and the switch 61 is in series circuit relation with the conductors connecting the motor 59 to the generator 60. The operation of the relay 65, therefore,-takes the motor 59 out of circuit with the main conductors l5 and I6 and places it in circuit with the generator 90.

above in connection with the motors I! for controlling the tension between the last stand D and the re-winding reel 1.

In actual operation, finishing speeds as high as 300 to 400 feet a minute have been obtained. As with the case of reduction, however, the rolling j speeds are subject to variation at the will of the operator by a proper control of the individual mills.

We have also found that desirable results are obtained by subjecting the material to a continuous rolling operation such that the tension exerted on the material intermediate successive roll stands is sufficient not only to maintain the same in the desired path of travel through the rolls, but also such as to tend to maintain the material more nearly flat. Successful results are obtainable with an average tension between the rolls A and B of approximately 8,000 to 10,000 lbs. total pull; with a .tension between the mills B and C of from 6,000 to 10,000 lbs., and with a tension between the mills C and D of from 2,000 to 5,000 lbs., when operating on a strip 26 inches wide and.reducing from 16 gauge to 30 gauge. As before pointed out, however, the exact tension, subject to the limitation referred to, is not a critical factor. A suitable tension of the order referred to is also maintained between mill D and the reel I. g

In accordance with present day practice, the

working rolls are preferably initially constructed so as to have a greater diameter at the center than at the end portions to thereby effectively compensate for any tendency toward roll spring. The'construction in this regard is well understood in the art.

We have further found that in order to obtain the results desired it is necessary to maintain the temperature of the working rolls within a certain substantially uniform temperature range for a given material. For this purpose we provide each of the working rolls with independent cooling means 4 capable of adjustment such that the temperature of the working rolls may be held at the temperature desired. This means is herein illustrated as comprising suitable water cooling connections to the respective rolls.

In addition to the cooling means 4, which is effective on the inside of the working rolls, we also preferably provide supplemental cooling means 4' for supplying a cooling fluid directly to the outside of the rolls. We have found in actual practice that much more uniform temperature conditions can be maintained throughout a given rolling operation by temperature controlled means eflective both on the inside and outside of the rolls which actually contact with the material being worked upon.

It is further necessary to maintain the work ing rolls in such a condition that any tendency toward adherence between the rolls and the material is obviated. This is accomplished by pro- .viding lubricating means at least for the mills B, C, and D. For this purpose we have illustrated an oil supply 5 for each of these roll stands, this supply conveniently comprising any suitable number of individually controlled oil delivery nozzles suitably arranged throughout the width of the material. A similar oil supply 6 may be provided for the stand A, but we have found that ordinary strip as delivered from the reel is sufllciently lubricated so as not to require such additional lubrication during the initial rolling operation. This lubrication not only enables the working rolls to act uniformly on the material, but it precludes the possibility of any sticking between the material and the rolls such as would result not only in a non-uniform working of the material but also in a non-uniform product. We have found palm oil to be a highly satisfactory lubricant for this pprpose. Such lubrication also makes possible the heavy drafts which are taken, particularly in the first pass.

The material leaving the last stand of rolls as provided by the mill D, in the embodiment illustrated, is subjected to a reeling operation on a suitable reel 1. Under usual conditions of operation, the material as wound upon the reel 1 may have a thickness, for example, of approximately .012 inch. This reel of material, where particular specifications have to be met, or special orders have to be filled, may be subjected to a further rolling operation in a suitable four-high mill E ,merely for the purpose of insuring 'absolute uniformity of thickness in successive lengths of material, the mill E being set, for example,

to produce a reduction in thickness from .012

inch, in the example given, to approximately .0118 inch and is then wound into a coil 9. This coil having uniform thickness characteristics of the nature referred to, or the coil directly from the reel 1 may then be subjected to a suitable caustic soda bath in the form of a weak caustic soda solution effective for removing all of the oil therefrom. Thereafter the material may be wound into a. coil 9. It may then be annealed as indicated in Figure 1. After annealing it may be given a skin pass in a stand F for re-surfacing and tempering the material. It is then treated in known manner in accordance with the character of the article to be formed. We have found that it is desirable to remove the oil before an:- nealing as otherwise the annealing operation tends to bake the oil into the material and prevents the adherence of any subsequent coating material thereto.

This removal of the oil before annealing is particularly important where a subsequent tinning operation is to be utilized. Where the article is to be zinc coated, we have found that in many cases actual cleaning of this character is either not so important, or may be dispensed with entirely. I

Referring to Figure 4, there is illustrated in end elevation a four-high mill stand constructed in accordance with our invention. The stand illustrated is illustrative of any one of the stands A, B, ,C, or D. The working rolls are preferably of hardened tool steel, and all of the rolls are provided with roller bearings, as previously pointed out. The pressure on the rolls is controlled through screws 0 mounted on either side of the stand. The screws 0 may be controlled in any suitable manner as, for example, by means of motors P that are geared to the screws O.

The motors P are provided with the usual electrical control means. Mounted on a panel near the stand of each mill or on the stand itself are a plurality of switches. Reference numeral 33 indicates the master stop switch below which are mounted the master starting switch 29 and the indivldualmill stop switch l9. On the other .side of the stand illustrated in Figure 4 are mounted a master screw down switch III for controlling the operation of both of the motors P, the master stopping and starting switch H for the motors P, a reel stop switch 12 for the 'rewinding reel 1, a switch 13 for starting and stopping the vibrating regulator 34, switches 53 and 54 for running the mill fast or slow, a switch 14 for energizing one of the motorsP to turn a predetermined amount, and a switch 15 for energizing the other motor P to turn a similar predetermined amount.- Another switch l6 is pro- -vided for energizing both of the motors P to turn at the same time a definite number of predetermined revolutions.

The present invention, which is basically a continuous cold rolling operation, is therefore characterized by several important features, which may be summarized as follows:

1. Relatively large working rolls.

2. Accurate temperature control of and in the working rolls.

3. Lubrication of the material in the working rolls. 4. Sufficient tension on the material intermediate the working rolls to tend to hold the same in the desired path of travel through the rolls and 'assist in maintaining the same substantially flat.

5. The removal of lubricant prior to any annealing operation, following by annealing and coating. The employment of a pass, as referred to, for giving uniform characteristics to the material is desirable although not absolutely essential inasmuch as our invention enables material to be produced to sufliciently accurate thickness to comply with commercial specifications. After annealing we may, as before stated, employ a skin pass for flattening, resurfacing and tempering the ma,- terial. v

The invention is further characterized in its commercial aspects bya relatively slow feeding speed at the commencement of the process with individual control of the mills followed by a subsequent simultaneous automatic control with the mills operating at a higher speed.-

From the fact that it is possible to produce material having the desired characteristics by hand control of the individual mills and without tension ofthe character or order referred to, we believe that at no time is the tension condition essential to the production of the desired product: Where an automatic control is utilized, which control is obviously desirable from a commercial standpoint for quantity production, the tension is preferably of the order indicated'not only for the reason that it tends to maintain the mate rial flat, and also tends to maintain it in the desired path of travel through the rolls, but for the further reason that it represents a factor of such nature that it may beeffectively utilized as a basis for automatic control by the proper design of the driving motors for the respective mills.

The continuous operation herein described is not only desirable for the reason that it effects a greater production from a given installation, and also a higher rate of yield, but for the reason that it eliminates any handling of .the material intermediate successive rolling operations and enables each of the mills to function not only as a rolling mill, but as a guiding device for the other mills, whereby the material is held accurately in line therein. The tension exerted by succeeding rolls is also desirable in that it prevents any slippage in the preceding rolls and particularly in the roll stand A and, together with the large diameter working rolls employed therein enables a reduction to be effected in this mill far beyond any .reduction which has heretofore been considered possible in working with material of the 4 general character herein contemplated. It will be apparent to those skilled in the art that slippage between the rolls and material would be objectionable inasmuch as it would mar the surface and thereby prevent the purchaser from making the desired use thereof. Also, it would have a tendency to skew the material in the rolls.

We have also found that material produced by a continuous rolling process of the character herein described possesses desirable characteristics not possessed by black plates or sheets as ordinarily produced. It lends itself to deeper drawing operations, to more pronounced spinningoperations, and to the reception of subsequent coatings, such as enamel and the like,- more effectively than materials as heretofore produced. It is also of such character that it adapts itself to a wide variety of heat treating operations such that the product may either be extremely hard or extremely soft, depending upon the particular uses to which it is to be put.

We further found that material produced in accordance with the present invention possesses greater tensile strength, a higher elastic limit, and a greater percentage or coefllcient of elongation than ordinary black plates or sheets heretoforeproduced. The above characteristics are in part supplemental to those before referred to in detail.

In the specific examples herein given as to the percentage of reduction efiected by the various passes where four mills are utilized, we have described an effective method of producing by continuous cold rolling operation an approximately 30 gauge material in commercial widths for ordinary black sheets and plates. This represents the most difiicult operating condition encountered in the practice of the present invention. Where thicker gauge materials are to be produced, the limits referred to may be widely varied, depending on the quality required, inasmuch as it is obviously not necessary to subject the material to as great a reduction in any of the passes. Regardless, however, of the thickness which it is desired to obtain, the percentage of reduction preferably decreases in successive passes so that the thinner the material, the less the percentage of reduction to which it is subjected.

In Figure 6 we have illustrated a slightly modifled form of the invention, this figure being a diagram illustrating the sequence of steps. The material M is illustrated as being formed into a coil I00 as delivered by the last stand I III of a hot mill, the material thus being in the form of a hot rolled strip. This coil after having been formed, may be passed through a suitable slitter if desired for trimming the edges thereof. Either after the slitting operation, in case such an operation is employed, or directly after having been formed from the hot mill, the coil is placed in a coil box I02 from which it is delivered to a roller leveler I03. From this leveler the material passes through a suitable shear I04 adapted for cutting the ends off square so as to permit such ends to be joined together. This joining is accomplished in a joiner I05 of suitable construction, and the joined material passes from the joiner through a series of pickle tanks I06, and thence into wash tanks I01.

The material having been pickled to remove the scale therefrom, and having been washed, passes to a shear I08 effective for separating the material into individual lengths, which lengths are then formed into suitable coils I09. During the formation of the coils a suitable lubricant is applied to the material by means of a lubricant applicator H0. The coils having thus been formed, with the lubricant substantially covering the surfaces of the material, are delivered to a conveyor III herein illustrated as being of the roller gravity operated type. One section of the conveyor is formed to constitute a scale H2 by means of which the coil in passing over the conveyor may be weighed. The weighed coil at the proper time is transferred to a coil box II4 adjacent the first stand of a continuous mill including three four-high roll stands H5, H6 and Ill adapted to successively and continuously operate on the material. These mills are preferably of the construction heretofore described and need not herein be referred to in detail. The material passes continuously through the mills in a single thickness, and is coiled-adjacent the last stand by means of a reel H8.

During the rolling operation, the previously applied lubricant cooperates in the manner before described and permits the taking of drafts which have heretofore not been considered possible. It also prevents any adherence between the material and the mils. is then transferred to a coil box I I9 and delivered therefrom through a suitable washer I 20 from the exit side of which it is again formed into a rolled material.

The coil of material coil I2I. This washing is preferably performed by means of a bath of caustic soda or the like effective for removing the lubricant from the The coil I2I may thereafter be placed in a coil box I22 for delivery to a roller leveler I23 in turn delivering to a flying shear I24. The flying shear severs the material into individual pieces of the desired size which may be suitably piled or stacked as indicated at I25. These individual pieces are then annealed in a suitable furnace I 26 after which they may be subjected to further treatment. If galvanized sheets are to be formed, they may be delivered from the annealing box into a galvanizing pot I21 and thence through a roller leveler I28 to a pile I29.

The embodiment of the invention herein illustratecl follows in general the sequence of steps disclosed and illustrated in the other figures. Its principal difference therefrom is with respect to the number of passes in the continuous mill, only three roll stands being illustrated in Figure 6, while four such stands are illustrated in Figures 1, 2 and 5 of the drawings. Attention has already been called to the fact that in some cases the commercial requirements are such that the rolling to the desired gauge may be accomplished in a fewer number of passes. In utilizing a three stand tandem mill of this type, it is customary, or desirable, to supply to the mill hot rolled strip having a thickness of approximately .062 inch. Such a hot rolled strip may be continuously rolled to the desired gauge for forming a base material suitable for example for roofing stock, such roofing stock usually being galvanized. For purposes of a better understanding of the invention, we are giving below representative types of rolling operations with this mill:

In the first example it will be noted that there is effected a reduction in thickness of near 47% in the first mill, while in the second example the reduction is slightly less than 47%. In both cases, however, the percentage reduction is within the range heretofore given.

This illustration of the use of a three stand tandem mill will be effective for explaining the flexibility of the present invention and the uses to which it may be put. Thus, in manufacturing certain base materials, one or more of the mills may be utilized as a dummy, the material merely passing therethrough. For all lighter gauges,

however, it is desirable to use at least four mills arranged in tandem for continuous rolling.

We have further referred to working rolls having a diameter of not less than 16 inches. We wish it to be understood, however, that while a 16 inch roll may be utilized where extremely accurate control of all the conditions is possible, its use is not as desirable as a roll of larger diameter, and in actual practice we prefer to utilize working rolls having diameters in excess of 17 inches.

In describing the invention, we have not limited ourselves to the widths of the final material except to indicate that it may be and has been in excess of 30 inches and to further indicate that it has dimensions commensurate'with ordinary tin plate, black plates or sheets. In the actual practice of the invention, however, it is desirable It may be'further pointedout that a rolling operation in accordance with the present inven-' tion is characterized by a gradual increase in hardness as indicated by the Rockwell scale. By

way of further illustration, it may be pointed out that the invention has been utilized for operation on stock having an initial Rockwell hardness of from 37 to 49. This has increased after the first pass to-from to 88; after the second pass from 70.5 to 91; after the third pass there has been substantially the same range as that characterized by the second pass, while after the fourth pass the range has been from .74 to .92. I

After the single pass in the mill E the hardness has varied from to 95. As a typical example,

it may be stated that material having an analysis of approximately .09 carbon, .3'7 manganese, .008 phosphorus, and .035 sulphur with an initial Rockwell hardness of approximately 3'7 to 40 has shown a Rockwell hardness after the first pass of 84 to 86; a hardness after the second pass from 87 to 89; a hardness after the third pass of from 88 to 90, with approximately the same hardnessafter the fourth pass.

As a general proposition, however, it has been observed that the Rockwell hardness is substantially higher after the rolling operation than at the commencement thereof, and that as a general rule it-increases with successive operations.

The present invention is beingsuccessfully utilized for the commercial production of sheet material by a continuous cold rolling operation under conditions of the general character referred to, in contravention to ordinarily accepted rolling mill practice. We are not aware, that it has heretofore been considered possible to produce material having tin plate or sheet widths and gauges or having great width in comparison with the usual tin plate or sheet gauges by any continuous cold rolling operation without annealing or reheating.

The present invention may be used in the direct production of tin plate, sheet, or like materials having a finished surface as contrasted with tin plate or sheet produced by the ordinary process. Due to the fact that the plate or sheet is produced by a cold rolling operation, its surface is not subjected to scaling such as occurs in the usual hot rolling operation. By reason of the better surface characteristics, the material for tin plate leaving the continuous cold rolling mills requires only an annealing operation and a single flattening pass. As' pointed out, the annealing may be preceded by a washing operation to remove the oil from the surface of the material. With ordinary tin plate or sheet, it isnecessary to box anneal the material, pickle the same, cold roll the pickled plates, again anneal the same, and thereafter usually both cold roll and pickle.

For some grades of material, a single flattening pass followed by pickling and coating is required for tin plate. sheets no flattening pass or pickling before coating is essential. Sheets for galvanizing are suitably deoxidized in the box annealing process.

It is thus apparent that with the operations succeeding the cold rolling mill, we are able to replace the two annealing, the two cold rolling and the two pickling operations ordinarily required. When the cost incident to each additional operation is considered, the advantages inherent in the present invention will be further apparent.

While we have herein illustrated and described certain preferred embodiments of the present invention, it is understood that changes in the construction and arrangement of the parts, as well as in the various reductions effected by the different mills, may be made without departing either from the spirit of the invention or the scope of 'our claim.

We claim:

For .black sheets and galvanized The method of cold rolling sheets of metal.

not less than 25 inches wide by .062 inch thick down to sheets-of substantially the same width through-four stands of four-high roller bearing rolls, each having working rolls not less than 16 inches in diameter, cooling said rolls, and lubri-- eating their rolling surfaces.

PARKER F. WILSON. LORENZ IVERSEN.

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