US3913368A

US3913368A - Tandem rolling mill

Info

Publication number: US3913368A
Application number: US503056A
Authority: US
Inventors: Werner W Eibe
Original assignee: Blaw Knox Foundry and Mill Machinery Inc
Current assignee: Blaw Knox Co; Italimpianti of America Inc
Priority date: 1974-09-04
Filing date: 1974-09-04
Publication date: 1975-10-21
Anticipated expiration: 1992-10-21
Also published as: GB1519857A; JPS546023B2; IT1041255B; CA1047286A; JPS5152351A; DE2539215A1

Abstract

A tandem rolling mill in which the utilization time of the mill is increased by having one mill stand more than is required for rolling the pass schedules for which the mill is designed. Each mill stand is designed to cover most of the speed range of a preceding mill stand in the rolling line. In operation, the mill stands downstream of a mill stand whose rolls are to be changed or whose rolls were previously changed are set to provide the necessary strip reduction and maintain the normal rolling action of the mill by having their speeds shifted to that of the mill stand upstream thereof. The roll change can then take place without interruption of the rolling.

Description

United States Patent [191 Eibe Oct. 21, 1975 TANDEM ROLLING MILL Primary ExaminerMilt0n S. Mehr [75] Inventor: Werner W. Eibe, Pittsburgh, Pa. g i Agent or Firmsmith Harding Earley &

0 mer [73] Assignee: Blaw-Knox Foundry & Mill Machinery, Inc., Pittsburgh, Pa. [57] ABSTRACT [22] Fil d; S t 4, 1974 A tandem rolling mill in which the utilization time of the mill is increased by having one mill stand more [21] Appl 503056 than is required for rolling the pass schedules for which the mill is designed. Each mill stand is designed [52] US. Cl. 72/234; 72/238; 72/249 to cover most of the speed range of a Preceding mill 51 Int. c1. B21B 1/24; B21B 35/04 stand in the rolling line- I operation, the mill stands [58] Field of Search 72/238, 239, 234, 249, downstream of a mill stand whose rolls are to be 72/226 365 changed or whose rolls were previously changed are set to provide the necessary strip reduction and main- [56] References Cit d tain the normal rolling action of the mill by having UNITED STATES PATENTS their speeds shifted to that of the mill stand upstream 3,331,232 7/1967 King 72/250 x .thereof' roll change can take place wlthout 3,754,426 8/1973 Adair 72/238 lmerruptlo of the 01mg 11 Claims, 3 Drawing Figures FIG.2.

U.S.'Patent Oct.2I, 1975 Sheet2of2 I I 3,913,368

ENTRY DELIV TOTAL SPD.INTO DELIV. THEOR. COIL GAuGE GAUGE ELONG- IsnsTAND SPEED PRODUC.

IN. IN. ATION ERM. Ema. T/HR.

A .oeo ae .OO74X36 10.81 555 6000 I63 9 .IOOX36 .DII2 use 6.95 572 G000 246 C .09o:4a-.o23 4e 3.9I IoaI 4250 476 D .I 87 48 .059 4a 2.?! I200 3250 I097 RPM I I I I I I l STAND o I 5 G GEAR RATIO man 15:: o.G:I 0.523 MOTOR HP 4000 G000 G000 G000 G000 G000 (zoo/Goo F? m STD 5 CHANGED 2 Fl (5 3 STD 4 CHANGED I 2 STD G CHANGED l 2 STD 5 CHANGED I 2 sTD'5 CH NGED I 2 .STD 2 CHANGED l (:9

STD G CHANGED I STD l CHA GED ()9 m ()l m CH G) u u u 01 4 a CD a Q 0: b u b u a Q) TANDEM ROLLING MILL BACKGROUND OF THE INVENTION The invention relates to tandem rolling mills and a method of operating the same whereby the utilization time of the mill is increased.

In the past, tandem rolling mills had downtimes due to porter bar type roll changing of 15 to 20 percent. The use of rapid roll changers reduces this downtime of the mill up to about one-half or more. However, rapid roll changers still require a downtime of about five minutes.

The utilization time (i.e., the time the mill is actually used) could be increased another 5 to 6 percent by saving the downtime it takes to perform a rapid roll changing operation. This could bring the utilization time of a tandem cold roll mill to above the 90 percent level.

SUMMARY OF THE INVENTION It is the general object of this invention to provide a tandem rolling mill and a method of operating the same which increases the utilization time of the mill by saving the downtime resulting from a roll changing operaton. This objective is particularly advantageous in a fully continuous rolling mill.

Briefly, the general object of this invention is achieved by adding to a tandem rolling mill one more mill stand than is required by the mill to achieve the rolling of strip in the pass schedules for which the mill is designed. Thus, if a rolling mill requires 5 mill stands to perform the rolling of the design pass schedules, the tandem rolling mill of the invention is provided with 6 mill stands, a prior art four stand cold rolling mill is provided with 5 mill stands, and so on. By reason of the provision of an additional mill stand, there is always a mill stand which can be substituted for that mill stand which is to have its rolls changed. More specifically, the mill stands are designed so that each mill stand can achieve the rolling action of a preceding upstream mill stand. To this end, the mill stands are designed such that each can operate throughout most of the speed range of the adjacent mill stand. Accordingly, a mill stand can be taken out of the rolling line for roll changing without interrupting the rolling action to any appreciable extent by adjusting the remaining operative mill stands and the substitute mill stand to achieve the necessary rolling conditions.

The obvious objection to the concept of adding to a rolling mill a mill stand which is unnecessary to rolling the pass schedules for which the mill. isdesigned is that it involves a substantial initial investment and substantially increases the cost of the mill. The additional investment for the extra mill-stand is about 12 to 15% of the total mechanical and electrical cost of the mill. However, the economies that are poduced by saving the roll changing time more than offset this increased initial cost. With modern high speed rolling mills it is frequently necessary to change the work rolls several times each shift because of the changing nature of orders available, because of steel analysis or for any variety of reasons all recognized in the trade. Moreover, the savings are even greater in the case of fully continuous rolling mills because of the higher production involved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a continuous rolling mill in accordance with the invention in diagrammatic form;

FIG. 2 is a graph showing a speed cone which illus trates the principles of the invention; and

FIG. 3 is a chart showing a programmed roll changing procedure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown a fully continuous tandem cold roll mill illustrating the invention. The mill comprises six mill stands I, 2, 3, 4, 5 and 6 of the conventional four-high type. A three roll bridle unit 18 is located adjacent the entry end of mill stand 1 and serves to control the tension of the strip delivered thereto. Adjacent the bridle unit 18 is a mill entry section 20 comprising a pair of

payoff reels

22 and 24 and a pair of flatteners 26 and 28. Adjacent the mill entry section 20 is a strip cutting and joining section 30 which comprises a conventional cutting shear and welder for joining the ends of successive coils to be rolled. From the section 30 the strip is fed to a looper section 32 comprising the usual loop cars driven back and forth along tracks to accumulate a predetermined length of strip to deliver strip to the mill stands continuously while a strip joining operation is performed in the strip cutting and joining section 30 as is conventional in the art. From the looper section 32 the strip is fed around a roller 34 to the bridle unit 18 from which it enters the mill stands.

At the exit end of the mill, the strip is delivered from the mill stand 6 to a dividing, shear and tension reel section 40 which comprises a pinch roll 42, a shear 44 and a pair of tension reels 46 and 48. Adjacent section 40 is a coil delivery, inspection and strapping section 50 which comprises a coil transfer car 52, a circumferential and eye bander 54 and a delivery conveyor 56.

The drive means for each of the mill stands 1, 2, 3, 4, 5 and 6 are indicated at 61, 62, 63, 64, 65 and 66, respectively, and comprise motor driven speed reducers with speed ranges as will be described hereafter.

The automatic roll changing and setting means for each of the mill stands 1, 2, 3, 4, 5 and 6 are indicated schematically at 71, 72, 73, 74, and 76, respectively, and may take various forms which are well known in the art. Such means operate by computer signal to set the roll gap or bite (gauge) and/or effect a roll changing operation.

There is provided a conventional in-line computer of a type presently in use today for controlling operation of fully continuous rolling mills. The computer 80 controls the entire automatic operation of the rolling mill and controls, for example, the whole mass flow of the rolling mill, the speed, the amount of reduction, and dynamic gauge changes. The computer 80 is arranged to set up each stand for rolling a desired pass schedule as is conventional in operational computers for continuous rolling mills in use today. For the purposes of this invention, the computer 80 is arranged to control the drive means 61-66 and the automatic roll changing and setting means 71-76 for the mill stands l-6, respectively, for programmed roll changing, as will be more fully described hereafter.

In the operation of the mill shown in FIG. 1 as a fully continuous rolling mill, the strip is fed from the coil on payoff reel 22 through the strip cutting and joining section 30 and the looper 32 and around the roller 34 to the bridle unit 18 from which it enters the mill stand 1.

The strip is rolled by five of the six mill stands 1 to 6 which are set by the computer 80 to the proper rolling condition for the pass schedule being rolled.

When all of the coil has passed off the reel 22, the trailing end is joined with the beginning end of a coil on the payoff reel 24. The coil on the payoff reel 24 is passed through the flattener 26 to the strip cutting and joining section 30 where it is joined with the trailing end of the coil just paid off from reel 22. During this end joining procedure, which requires that the strip within the strip cutting and joining section 30 be stopped for a short while, strip is continued to be fed to the mill stands from the looper section 32 to thereby maintain a continuous supply of strip for rolling. A fully continuous rolling operation is maintained by alternately supplying coils from the

payoff reels

22 and 24 and by joining in the strip cutting and joining section 30 the trailing end of the coil being rolled to the beginning end of the new coil.

Conventional rolling may be performed by delivering strip from a coil on payoff reel 24 through the flattener 28 and the bridle unit 18 directly to the mill stand. This alternate is shown by the dashed arrow line in FIG. 1.

At the exit end of the mill, the strip is passed alternately to one of the tension reels 46 and 48 whereat the strip is coiled. The rolled coil is then transferred to the circumferential and eye bander 54 by the conveyor 56. From the bander 54, the rolled coil continues to move along the delivery conveyor 56 for removal as is conventional in the art. Some coils are taken at random off conveyor 26 by the coil car 52 for inspection.

In accordance with the invention, the utilization time of the mill is increased by the addition of one mill stand more than is required for rolling the pass schedules for which the mill is designed. This is illustrated in FIG. 2 which shows a speed cone type of graph as is conventionally used in the art in designing a mill 'for rolling a group of random pass schedules. On the left vertical side of the graph there is shown the speed at which the rolls are to be driven in feet per minute. The bottom horizontal line of the graph indicates the entry speed and the speed at each of the six mill stands at equally spaced locations. At the bottom of the graph there is also listed the gear ratio and the motor horsepower for each of the six mill stands. At the top of FIG. 2 there is a chart showing the essential conditions of four random pass schedules A, B, C and D. These conditions include the entry gauge, the delivery gauge, the total elongation, the entry speed into the first mill stand, the delivery speed and the theoretical production.

The pass schedules A to D are shown graphically by indicating the speed at which each of the five mill stands in the rolling line must operate to perform the strip reduction required for that mill stand. The designer of the mill also adds to the graph what is known in the art as a speed cone which comprises the two lines [-1, so as to be certain that each of the mill stands in the rolling line can be operated at the speeds required for each of the pass schedules. The lower line I of the speed cone passes through the minimum or base speeds of the mill stands 1 through 6. The upper line I of the speed cone passes through the maximum speeds of the mill stands 1 through 6.

It is noted that the mill stand 1 can operate in a speed range of between 686 and 2058 feet per minute (FPM) which is sufficient to cover each of the speeds required by the pass schedules A through D at the entry end.

This is confirmed by reference to FIG. 2 since these speeds lie between the speed cone I-I. Also, mill stand 5 can operate in a speed range of 2050 to 6150 FPM which is sufficient to cover the speeds required by the pass schedules A through D at the delivery end. This is also confirmed by viewing FIG. 2. The speed ranges for each of the mill stands 2, 3 and 4 is also sufficient to cover the speeds for each of the pass schedules A through D as is apparent from FIG. 2.

For example, in pass schedule A the entry speed to mill stand 1 is 555 FPM. In accordance with the gauge setting to achieve the desired strip reduction, mill stand 1 is operated at a delivery speed of about 900 FPM. Correspondingly, mill stand 2 is operated at a delivery speed of about 1600 FPM, mill stand 3 is operated at about 2700 FPM, mill stand 4 is operated at about 4175 FPM and mill stand 5 is operated at 6000 FPM. The computer is programmed to perform the gauge settings for each mill stand 1 to 6 and control the appropriate drive means 61 to 66 to drive the mill stands 1 to 6 at the speed corresponding to the gauge setting in accordance with pass schedule A.

It is noted that in accordance with the invention each of the mill stands is designed to be driven in a speed range covering most of the speed range of a preceding mill stand. This is apparent from a consideration of the graph shown in FIG. 2.

A second speed cone comprising lines II and II is shown in FIG. 2. This speed cone represents the condition when the mill stand 1 is out of the rolling line for a roll change and each of the mill stands 2, 3, 4, 5 and 6 is shifted to cover the speed of a preceding mill upstream thereof. This shifting is illustrated in FIG. 2 by the horizontal arrow lines extending from lines II to lines IIII. It will be noted that the speed cone II--II embraces the pass schedules A through D wherefore the design is such that all of these pass schedules can be rolled by any appropriate combination of the mill stands, i.e., when anyone of the mill stands 1 to 6 is taken out of the rolling line for a roll change.

It is noted that the motor speed ranges employed to achieve the above-described flexibility of rolling is achieved by utilizing a 3 to 1 speed range ratio. Equipment of this type is readily available in the art.

FIG. 3 illustrates a typical computer programmed roll change schedule in accordance with the invention. This schedule takes into account that the mill stands near the end of the rolling line are changed more often than the front ones, although any variation in the program is possible. The sequence of roll changing progresses downwardly as viewed in FIG. 3. Thus, in the upper row there is illustrated what occurs when the mill stand 6 has its rolls changed. In this case mill stands 1 through 5 are active while the rolls for mill stand 6 are changed. The mill stands 1 through 5 are, of course, set for the speed indicated by the pass schedule such as those shown at A through D in FIG. 2.

The next row illustrates what occurs when the rolls for mill stand 5 are changed. In this case, mill stands 1 through 4 remain active at their previous setting while stand 6 is reset to take over the rolling action of the stand 5. This mode of operation is illustrated in FIG. 1.

The next row illustrates what occurs when mill stand 4 is changed. In this case, stands 1, 2, 3 and 5 remain active at their previous setting and mill stand 5 is set to take over the rolling action of mill stand 4.

The next row illustrates the changing of mill stand 6 again in which case mill stands I through 5 perform the rolling operation in accordance with the pass schedule.

The next row illustrates what occurs when mill stand 3 is changed. In this case, stands I and 2 remain active at their previous setting and mill stands 4, 5 and 6 are reset to take over the rolling action of mill stands 3, 4 and 5, respectively.

The next line illustrates what occurs when mill stand 5 is changed and this is described above.

The next line illustrates what occurs when mill stand 2 is changed. In this case, stands 1 and 6 remain active at their previous setting and mill stands 3, 4 and 5 are set to take over the rolling action of mill stands 2, 3 and 4, respectively.

The next line illustrates what occurs when mill stand 6 is changed and this was described above.

The last line illustrates what occurs when mill stand 1 is changed. In this case the mill stands 2, 3, 4, 5 and 6 are reset to take over the rolling action of mill stands 1, 2, 3, 4 and 5, respectively. This corresponds with FIG. 2 wherein the entire speed cone appears to be shifted to the left.

The roll changing program then continues back with a roll change for mill stand 6 as illustrated in the top row of the chart shown in FIG. 3 and is continuously repeated under the control of the computer 80 in the progression indicated on this chart.

The entire program is under the control of the computer 80 which sets the drive means 61 through 66 and actuates the roll changing and setting means 71 through 76 to achieve the sequence of operation set in the program. In operation, the computer 80 controls the bite of the stands such that while the mill stand which requires roll changing is having its rolls withdrawn from contact with the strip, the gauge and speed of stands downstream of the stand being changed or the stand previously changed are set to take over the rolling action of the stand upstream thereof. After the computer 80 has completed the changes in roll bite (or gauge), the rolls to be changed can be removed whenever it is convenient without affecting the production. During the time that the computer 80 is directing the changes in roll bite, the strip can be moved slowly or it can be stopped momentarily. However, this involves very little or no loss of strip or reduction in the production of the mill.

It will be apparent that by the above described tandem rolling mill design and method of operating the mill, the utilization time of the mill is increased, since the roll change can take place without interrupting the rolling to any appreciable extent. The design in accordance with the invention saves the downtime it takes to perform the roll changing operation and can thus bring the utilization time of a tandem cold roll mill to above the 90 percent level.

I claim:

1. A tandem rolling mill comprising:

a plurality of mill stands arranged in tandem in a rolling line for successively rolling a strip of material to reduce the thickness thereofa desired amount in a single pass through said mill stands,

said plurality of mill stands being adapted to roll strip in accordance with a predetermined group of pass schedules so designed that all passes of each schedule are required to produce said desired strip reduction,

an additional mill stand added to said plurality of mill stands and arranged in said rolling line,

and independent drive means for each of said mill stands in said rolling line,

the drive means for each mill stand having a speed range covering most of the speed range of the drive means for a mill stand immediately upstream thereof and a maximum speed greater than the maximum speed of the drive means for a mill stand immediately upstream thereof.

2. A rolling mill according to claim 1 including means for controlling said drive means to operate all of said mill stands except one in any combination of mill stands to roll strip in accordance with said group of pass schedules.

3. A rolling mill according to claim 2 including means for changing the rolls of each of said mill stands, and means for controlling said drive means and said roll changing means in a programmed sequence so that the roll changing means for each mill stand and a corresponding drive means is out of operation a predetermined sequence.

4. A rolling mill according to claim 1 wherein the speed cone of said drive means for said first-mentioned plurality of mill stands encloses the group of pass schedules for which the rolling mill is designed and the speed cone for any combination of mill stands minus one also encloses said group of pass schedules.

5. The method of operating a tandem rolling mill having a plurality of mill stands arranged in a rolling line for successively rolling strip to reduce the thickness thereof to a desired thickness in a single pass through said mill stands in accordance with a group of pass schedules for which the mill is designed, and a mill stand added to the first group of mill stands and arranged in the rolling line, each of said mill stands being independently driven and capable of operating in most of the speed range of and at a higher maximum speed than a mill stand immediately upstream in said rolling line, comprising the steps of:

rolling a strip of material by the operation of only said first group of mill stands which are set to operate at successive desired speeds and roll bits in accordance with a pass schedule to achieve the desired strip reduction,

adding said additional mill stand to the rolling line and removing one of said first group of mills from the rolling line,

and operating all of the remaining mill stands in said rolling line at the successive speed and roll bite settings used during said first-mentioned strip rolling operation.

6. The method according to claim 5 in which the mill stand removed from rolling line has its rolls changed while the remaining rolls are operated to roll strip.

7. The method according to claim 6 in which all of said mill stands are automatically removed from the rolling line one at a time for a roll change in accordance with a programmed sequence of operation under the control of a computer.

8. The method according to claim 7 wherein there are at least four mill stands in said first group capable of rolling strip in accordance with said design pass schedules for the mill.

9. The method according to claim 7 wherein the computer completes the changes in roll bite and speed for the mill stands downstream of the one being taken out of the rolling line prior to the roll changing operation of the mill stand taken out of the rolling line.

10. The method of operating a rolling mill according to claim in which strip to be rolled is fed continuously to the rolling line and rolled strip is delivered continuously from said rolling line so as to operate the rolling mill as a fully continuous mill.

11. A fully continuous rolling mill comprising:

a plurality of mill stands arranged in tandem in a rolling line for successively rolling a strip of material to reduce the thickness thereof to a desired thick ness in a single pass through said mill stands,

said plurality of mill stands being adapted toroll strip in accordance with a predetermined group of pass schedules so designed that all passes of each schedule are required to produce the desired strip reduction, I

means at the entry end of the rolling line for delivering strip to be rolled continuously to said mill stands, and means at the exit end of the rolling line for continuously receiving rolled strip.

Claims

1. A tandem rolling mill comprising: a plurality of mill stands arranged in tandem in a rolling line for successively rolling a strip of material to reduce the thickness thereof a desired amount in a single pass through said mill stands, said plurality of mill stands being adapted to roll strip in accordance with a predetermined group of pass schedules so designed that all passes of each schedule are required to produce said desired strip reduction, an additional mill stand added to said plurality of mill stands and arranged in said rolling line, and independent drive means for each of said mill stands in said rolling line, the drive means for each mill stand having a speed range covering most of the speed range of the drive means for a mill stand immediately upstream thereof and a maximum speed greater than the maximum speed of the drive means for a mill stand immediately upstream thereof.

5. The method of operating a tandem rolling mill having a plurality of mill stands arranged in a rolling line for successively rolling strip to reduce the thickness thereof to a desired thickness in a single pass through said mill stands in accordance with a group of pass schedules for which the mill is designed, and a mill stand added to the first group of mill stands and arranged in the rolling line, each of said mill stands being independently driven and capable of operating in most of the speed range of and at a higher maximum speed than a mill stand immediately upstream in said rolling line, comprising the steps of: rolling a strip of material by the operation of only said first group of mill stands which are set to operate at successive desired speeds and roll bits in accordance with a pass schedule to achieve the desired strip reduction, adding said additional mill stand to the rolling line and removing one of said first group of mills from the rolling line, and operating all of the remaining mill stands in said rolling line at the successive speed and roll bite settings used during said first-mentioned strip rolling operation.

10. The method of operating a rolling mill according to claim 5 in which strip to be rolled is fed continuously to the rolling line and rolled strip is delivered continuously from said rolling line so as to operate the rolling mill as a fully continuous mill.

11. A fully continuous rolling mill comprising: a plurality of mill stands arranged in tandem in a rolling line for successively rolling a strip of material to reduce the thickness thereof to a desired thickness in a single pass through said mill stands, said plurality of mill stands being adapted to roll strip in accordance with a predetermined group of pass schedules so designed that all passes of each schedule are required to produce the desired strip reduction, an additional mill stand added to said plurality of mill stands and arranged in said rolling line, independent drive means for each of said mill stands in said rolling line, the drive means for each mill stand having a speed range covering most of the speed range of the drive means for a mill stand immediately upstream thereof and a maximum speed greater than the maximum speed of the drive means for a mill stand immediately upstream thereof, means at the entry end of the rolling line for delivering strip to be rolled continuously to said mill stands, and means at the exit end of the rolling line for continuously receiving rolled strip.