US2177971A

US2177971A - Mill for hot rolling strip

Info

Publication number: US2177971A
Application number: US143987A
Authority: US
Inventors: Worthington Warren
Original assignee: Individual
Current assignee: Individual
Priority date: 1937-05-21
Filing date: 1937-05-21
Publication date: 1939-10-31
Anticipated expiration: 1956-10-31
Also published as: GB509951A

Description

Oct. 31, 1939` w.woR1H|NGToN v MILL FOR HOT ROLLING STRIP S'Sheets-Sheet l Filled lay 21. 1937 w. woRrl-"NGTON Mm..v Fon HOT RoLLING snmD Filed may 21. 19,57

3 Sheets-Sheet 2 C/VENTOR. gif/ @ME 4Z-,f ATTORNEYS.

Oct. 31, 1939. w WORTHlNG-roN 2,177,971'

MILL FOB HOT ROLLING STRIP gli INVENTOR www d Bym 649.4 TToRNEYs.v

Patented Oct. 3l, 1939Y UNITED is'rnrl-:s

2,177,971 MILL ron 11ery ROLLING s'rmr Warren Worthington, Pittsburgh, Pa. yApplication May 21, '1937. serial No.14a9s7 I 6 Claims.

This invention relates to metal rolling and more particularly to the hot rolling of metal strip.

An object of this invention is to provide an improved method andmill whereby metal strip of sheet widths and gauges can be hot rolled rapidly and economically.

Another object is to provide a method and mill for hot rolling metal strip whereby completecontrol of the temperature of the strip can be obtained in all passes. I e

Another object is toprovide a methodl and mill for hot rolling metal strip in which the temperature of the strip being rolled is controlled throughout the rolling operation and in whichV scale is removed by exing and inverting the strip between passes.

A further object is to provide a method and mill for hot rolling strip metal in which the reducing rolls can be run at a uniform and high cheap and improved mill adapted to the hot rolling of strip steel in sheet widths and gauges.

These and. other objects which will be apparent to those skilled in this particular art I obtain by the method and apparatus disclosed herein.

In the drawings accompanying and forming part of this application:

Figure l is a diagrammatic View in plan 'of a hot strip mill embodying this invention and Such as may be utilized in carrying out the method disclosed herein;

Fig. 2` is a view in side elevation of the mill of Fig. l; v

Fig. 3 isa view similar to Fig. 2 but with certain modifications incorporated therein;

Fig. 4 is a plan view of a roughing mill such as may be used for reducing an ingot or slab to -a starting piece of strip form so as to be capable of being handled by the mill of Figs. 1, 2 and 3 in accordance with'the method of this invention;

Fig. 5 is a view in side elevation of the roughing mill of Fig. 4;

Fig. 6 isa view generally in side elevation with parts in section of aY portion of the mill disclosed in Figs. 1 and 2;

Fig. 7 is a transverse section of one of the heating furnaces of the mill shown in Fig. 2 g

Fig. 8 is a fragmentary View in sectional elevation of the conveyors and furnaces of Fig. 7 and is taken on line 8 8 of that figure;

Fig. 9 is a transverse section of one of the heat- (c1. ca -2) ing furnaces shown' at the left side of the mill of Fig. 3; I Y

Fig. 10 is afragmentary view in longitudinal. section of the furnace. structure of Fig. 9 and is taken on line Ill- I0 of such ligure; and

Fig. 11 is a transverse section of one of the heating furnaces shown at the right side of Fig. ,3. In practicing -the method of this invention, a slab or slab ingot after being reduced in a suitable roughing mill to strip form of such thinness that it is capable of being passed'tlirough a repeater, has its ends squared and is then fed to a roll pass in which it is further reduced in thickness and elongated. It is then exed by being progressively bent upon itself until it is turned over. It is then fed through a second roll pass which reduces its gauge and increases its length. It is again exed by being bent upon `itself until it is completely turned over and then again fed through the first pass. This procedure of passing alternately through said passes with the exing and .turning over between passes' is continued until the strip is reduced to. the proper gauge at which time it is either sheared intosuitable lengths or coiled. The temperature of the strip is controlled throughout the entire rolling procedure by applying sumcient heat thereto to obtain just the temperature desired for each pass. 'Y

The mill illustrated in the drawings comprises a three-high mill stand throughA the upper and PATENT-,orner f l.

lower passes of which the strip is caused to travel alternately in opposite directions. A` seriesof roller tables (one or more) extend in opposite directions from both the entrance and exit sides of each of said passes; those for the top pass being superimposed upon those for the bottom pass. That is to "say, the roller tables are arranged in pairs with the tables of each` pair arranged in a multiple deck relationship. Specifically, the tables of each pair are arranged in a double deck relationship and so located with reference to the three-high stand that the lower deck tables serve the lower pass and the upper deck tables serve the upper pass of the stand. Each such unit of tables, i. e., double decl;` pairs 01E-tables, is provided with a repeater arranged to receive a strip from one table of the pair. ex it as above described, and deliver it to the other table of the pair. In this way each repeater, when operating as such, delivers strip to a table either above or below the table from which the strip is received. The roller tables extend outwardly from the roll stand and each table is aligned with one passof the roll stand. The tables on one side of the roll stand 'are slightly longer than one-half the length of the longest strip to be rolled. In other words, the overall length of the mill including the stand, the tables and repeaters is about equal to the length of the longest strip toA be rolled.

The outer ends of the roller tables of each pair are connected by a repeater and each of the intermediate repeaters is provided with a by pass. I'he outer repeater on the exit side of that pass which functions as the nal pass is also provided with a by pass to permit the finished strip to travel past the repeater to a suitable lcoiler or a shear as desired.

Heating furnaces surround certain of the roller tables so that the desired strip temperature may be maintained throughout the entire rolling procedure.

An 'ingot or slab after being reduced in the roughing mill stand to strip form of such thinness as will permit it to pass through a repeater after the ilrst reduction in the main mill stand, enters the main mill below one of the repeaters and is conveyed to the bottom pass of the three-high mill. In this pass it is given a predetermined reduction. The leading end of the strip (this remains the leading end throughoutthe entire rolling process) travels along the roller tables at the exit side of said pass and through the intermediate repeater to the upper roll table at the entrance side of the upper pass. That is to say, the strip on ilrst leaving the three-high stand exits from the lower pass of that stand and enters the lower table of the double deck pair of tables located on the exit side of the lower pass. The strip is then served by the repeater at the delivery. end oi that table and is thereby delivered to the upper deck table of the pair, viz., the table which serves the entering side of the upper pass of the three-high roll stand. The strip then travels through the upper pass where it is reduced in thickness and elongated, then along the roller table at the exit side of the upper pass to the intermediate repeater on that side, through this repeater and back along the lower roller table to the lower pass where a further reduction is made. That is to say, the strip on ilrst leaving the upper pass of the roll stand is delivered to the vupper deck table of the double deck pair of tables located on the exit side ot the upper pass of the stand. After traversing this table the strip is received by the associated intermediate repeater which ilexes it and delivers it to the lowerl table of the pair, i. e., the tables serving the entrance side of the lower pass of the stand. The by pass around the intermediate repeater on the exit side ot the lower pass is then opened and the strip passes said repeater, travels along the roller tables to the outer repeater through said repeater and back along the upper roller tables to the upper pass where it is given a further reduction. That is to say, the strip on leaving the lower pass of the three-high stand a second time is delivered to the lower table of the double deck pair immediately adjacent the stand on the exit side of the lower pass and is delivered by this table to the lower table of the double deck pair of tables remote from the stand, the associated intermediate repeater being by-passed. 'I'he outer or remote repeater on the exit side of the lower deck of the stand now acts to ex the strip delivered to it by the associated lower table and to deliver that strip to the upper table of the double deck pair remote from the stand and on the exit side ot the lower deck of the stand. The strip then passes along the upper tables of both pairs and is delivered to the entrance side of tle upper pass ci the stand. The intermediate repeater on the exit side oi the upper pass is then bypassed by the strip and the strip is conveyed to the tables for the lower pass by the outer repeater. Here the upper tables of each double deck pair on the exit side of the upper pass of the stand cooperate to deliver the strip to the remote or outer repeater on that side of the stand. The lower tables then cooperate to receive the strip from the repeater and to deliver it to the entrance side of the lower pass of the j stand and in each case the associated intermediate repeater is by-passed or rendered ineffective as a repeater. After a further reduction in the lower pass, the strip bypasses both repeaters and travels to the coiler or shear as the case may be.

The above description assumes that the rolling operation consists of but iive reductions from the thickness of the roughed down strip to the strip of nal gauge. If more reductions are to be made, three or more repeaters may be utilized on each 1 side oi' the mill stand. I nd, however, that for most purposes, four repeaters are suilicient and that by starting with a strip 1%; inch thick, I can reduce the same in ve passes through the threehigh mill to a thickness of .076 inch or 14 gauge.

The strip passes alternately under and over the middle roll 'of the three-high mill stand and is ilexed by being bent back upon itself by the repeaters after each pass except the last. The strip is thus incrementally inverted or turned upside down after each but the last pass. The ilexing of the strip loosens the scale and this drops oi! when the strip is inverted. 'Ihe mill is provided with motor operated screwdowns.

The roller tables are driven by motors. The l repeaters are provided with pinch rolls and each repeater is driven by an independent motor. The mechanisms for operating lche bypass gates of the repeaters are electrically operated.

A control lever located in the path of travel of the strip at the entrance side of both the upper and lower passes is held in off position by the strip and when the trailing end of the strip passes by these control levers they move to on or operative p omtion. The control levers are adapted to be connected to operate cam type limit switches which will control the sequence of operation of the several elements entering into the make-up of the mill. In other words, they may control the motors which operate the screwdowns, the raising and l lowering mechanism for the middle roll of the mill stand, the roller tables; the pinch rolls of the repeaters and the bypasses for the repeaters. so that the rolling procedure from the time a starting piece enters the mill until it leaves the same in nished form may be automatic.

-Where extremely wide strip is to be rolled, instead of utilizing a three-high mill, I prefer a live-high mill. In such a mill, the upper and lower rolls will be backing rolls of relatively large 0 diameter and will be idler rolls. The middle roll as in the three-high mill will be an idler floating roll and will be raised and lowered to position by means of mechanism under the control of the limit switch. The work or reducing rolls above a and below the middle roll in a tive-high mill as well as in a three-high mill are driven rolls.

AIn one mill embodying this invention in which 14 gauge strip is rolled in 300 foot lengths. the ingot is reduced in the roughing mill to a strip 71 having a thickness of three-eighths of an inch and this strip in ilve passes-in the three high mill stand is reduced to 14 gauge. A 40% reduction is made in the first pass, a 33% reduction in the second pass, a 30% reduction in the third pass, an 7| 18% reduction in the fourth pass, and a 12% reduction in the fifth and final pass.

In this mill, the intermediate repeater on the entrance side of the .mill is located 88 feet from the mill stand and the outside or remote repeater is located 56 feet from trie inside repeater making a distance of 144 feet from the mill stand to the outside repeater on the entrance side of the. mill. The intermediate repeater on the exit side of the mill is 64 feet from the mill stand and the outside repeater is 40 feet from the intermediate repeater, making 104 feet from the outside repeater to the mill stand on the exit side.

The location of the repeaters is determined by the drafts to be made in the different passes and the length desired in the finished strip.

The roughing mill for reducing the ingot preferably a slab ingct to a starting piece of strip form is diagrammatically shown in Figs. 4 and 5. While any mill suitable for this purpose may be used, I prefer the three-high universal mill and in these figures such a mill is indicated at 2U. The mill motor is indicated at 2| and its pinion stand at 22. 23 represents a roller table for conveying the ingots from a soaking pit to the mill.

Shears

24 and 25 are shown for cropping the ends of the starting piece.

The preliminary or roughing mill for preparing the starting piece forms no part of this invention and, as before said, any other type of mill which is suitable may be utilized.

The mill utilized for carrying out the method of this inventionds ,diagrammatically illustrated in Figs. 1, 2 and 3 of the drawings and the threehigh mill stand utilized in said mill is indicated at 26. In Fig. 1 the housings have been omitted. The lower roller tables are numbered 21, 23, 29 and -39 and the upper roller tables 3 32, 33 and 34, the

upper roller tables being superposed upon the lower roller tables. Intermediate repeater 35 connects the outer ends of roller tables 28 and 32, while intermediate repeater 36 connects the outer ends of roller tables 29 and 33. Outer repeater 31 connects the outer ends of roller tables 21 and 3| while outer repeater 38 connects the outer ends of roller tables 30 and 34. Thus it is apparent that roller tables 29 and 33 constitute one double deck pair and are associated with and served by the intermediate repeater 36. Roller tables 28 and 32 constitute another double deck pair and are associated with and served by the intermediate repeater 35. The roll tables 30 and 34 constitute a double deck pair which is associated with and served by the repeater 38 and tables 21 and 3| constitute a double deck pair which is served by the remote repeater 31. The

repeaters

35 and 36 may be termed the intermediate repeaters since they intervene between adjacent tables and when by-passed, function to some extent as a roller in the delivery of strip from one table to an adjacent table of the same deck or level. The

repeaters

31 and 38 are properly termed remote repeaters because they are located at the greatest distance from the stand 26.

Roll stand 25 is driven by a D. C. motor 39 through a pinion stand 4D and a motor generator set 4I supplies current to motor 39. The roller tables are preferably driven by individual D. C. motors supplied by current from suitable motor generator sets, not shown. Each of the repeaters is driven by its own D. C. motor and pinion stand. The motor and pinion stand for repeater 35 is numbered 42; that for

repeater

36, 43, for

repeater

31, 44 and that for

repeater

38, 45. A coiler 46 is diagrammatically illustrated in Figs. 1, 2 and 3.

Where it is desired to shear the strip into sheet lengths a shear may be substituted for the coiler.

A form of repeater suitable for use in this mill is more or less diagrammatically shown in Fig. 6 and comprises a main roll 41 and

supplementary rolls

48 and 49. One of the bypasses before referred to is shown at 59 and is used for bypassing repeater 36. Portion of the repeater housing is pivotally mounted at 52 in order that the repeater may be opened in case a cobble occurs or if for any other reason access to the interior of the repeater is desired.

The temperature of the strip being rolled is under control throughout the entire rolling procedure and my invention contemplates heating furnaces for enclosing all or only a portion of the roller tables. In rolling certain types of alloy steels, especially when reducing the same to thin gauges, it may be found desirable to enclose all of the roller tables with heating furnaces. When rolling certain grades of steel and particularly where certain types of scale are desired on the finished strip it is preferable to have certain of the roller tables enclosed by heating furnaces and certain others of the roller tables open to the air. In Figs. l and 2 all of the roller tables are shown enclosed by heating furnaces but in Fig. 3 roller tables 29, 30, 3| and 32 are open to the atmosphere while tables 21, 28, 33 and 34 are enclosed in heating furnaces.

The roller tables and furnaces of the form shown in Figures 2 and 6 of the drawings are illustrated in Figs. '7 and 8. `Rolls 53 of the upper roller tables 3|, 32, 33 and 34 are preferably formed from a heat resisting alloy and are cooled by circulating water therethrough. These roller tables are located within heating chambers 54 formed by suitable refractory walls as shown, and are supplied with the requisite number of burners 55, for maintaining the heating chambers at the desired temperature. Refractory aprons 56 having heat resisting metal tops 51 are supported between the rollers and, as shown in Fig. 8 have their upper surfaces tilted upwardly in the direction of travel of the strip.

Rollers 58 for the lower roller tables 21, 28, 29 and 30 are located within heating chambers 59 which are similar to heating chambers 54 and which are also supplied with suitable burners 6D.

The metal topped aprons 6| which are supported between the rollers 56 have their tops tilted in the opposite direction from rollers 53 to accommodate the strip moving along the roller table in the direction of the arrow as indicated.

In Figure 3 the upper roller tables 3| and 32 are open to the atmosphere and the lower tables 21 and 28 are located within heating furnaces. The construction of these superposed roller tables with the heating furnaces for the lower tables is disclosed in Figures 9 and 10. The rollers for the upper roller table are numbered 62 and flat metal aprons 63 are supported between the rollers. The upper roller tables 3| and 32 are provided with side guides 64. The lower roller tables 21 and 28 are enclosed within heating furnaces. The rollers of these roller tables are numbered 65 and the heating chambers surrounding the roller tables are numbered 66. These furnaces are also Yprovided with suitable burners 61 and aprons as shown in Fig. are supported between the rollers.

The upper roller tables 33 and 34 (Fig. 3) are enclosed in heating furnaces while the lower roller tables 29 and 30 (Fig. 3) are open to the atmosphere. The rollers of roller tables 33 and 34 are numbered 68 while the rollers for roller tables 29 and 30 are numbered 69. Roller tables 33 and 34 are located within heating chambers 10 having suitable burners 1l. Aprons similar to those shown in the upper half of Fig. 8 are interposed between rollers 68, and aprons similar to those shown in the upper half of Fig. 10 are interposed between rollers 69.

All of the roller tables enclosed within heating chambers are water cooled while those open to the atmosphere are not.

The levers before referred to for controlling the operation of the time limit switches are diagrammatically illustrated in Fig. 6; that for the lower pass is numbered 'I2 while that for the upper pass is numbered 13.

If desired, high pressure water jets such as jets 14, 15, 16 and l1 may be utilized to assist in scale removal. These jets are directed against the top and bottom of the stripon the entering side of both the upper and lower passes of the three-high mill.

Each motor generator set is under the control of one of the cam type limit switches. In addition to controlling the speed of the tables and the repeaters, these switches control the screwdowns and the bypasses for the repeaters. The roll tables on the entering side of each pass operate at a slower speed than those on the exit side. For example, assuming that the strip approaches a pass at 750 feet per minute and a 30% reduction is made in the pass, it will leave the pass at 1000 feet per minute. The speed of the tables is regulated to take care of this condition.

The speed of the repeaters is controlled so that as soon as the strip leaves a pass, the repeater on the exit side of that pass is slowed down from 1000 to 750 feet so that the strip is entered in the next pass at 750 feet. The repeater will be run at this speed until the strip leaves the next pass when it will be speeded up to receive the elongated strip from such pass. For this reason, that portion of the strip between the repeaters and the next succeeding roll pass is put under tension or stretched; the pinch rolls of the repeater tending to hold back the strip in opposition to the pull of the reducing rolls of the next succeeding pass.

The screwdowns will be operated to reduce the distance between the top and bottom roll (in the three-high mill stand) each time the strip leaves a pass except `after the last pass when the screwdowns will be backed off allowing the top roll to be moved up to starting position.

Each of the controls for the limit switches will be provided with a dwell so that its switch will not operate until the trailing end of the strip emerges from a pass. As soon -as the trailing end of the strip does emerge from a pass, the roller tables and the repeater on the outlet side of that pass will be slowed down to entrance speed then the tables and the repeater will again be speeded up to exit speed as soon as the trailing end emerges from the next succeeding pass.

It will of course be understood that but one reduction is made on the strip at a time. The trailing end of the strip leaves one pass before the leading end enters the next pass. The screwdowns are operated in the interim when the strip is out of both passes.

It will be noted that the middle roll of the mill is in contact with the same side of the strip in all passes, and because of this, the strip which takes ashape to lit this roll in the rst pass maintains this shape throughout the rest of the passes. This adds to the ease with which I obtain flat material and perfect tracking. In the preferred apparatus the multiple pass roll stand is a three-high stand,

each multiple deck roller table unit is a pair of double deck tables and two such pairs of such tables are located on each side of the roll stand but it will be apparent that various changes, additions, omissions, substitutions and modifications may be made in the apparatus illustrated without departing from the spirit and scope of the invention here dened. I have also employed the term pair, when associated with roller table or conveyor, to designate two or more strip conveyors arranged in a multiple deck relationship.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a mill for hot rolling metal strip, a multiple pass roll stand, two pairs of double deck roller tables located on one side of said stand with the lower tables of each pair adapted to serve the lower pass of said stand and the upper tables of each pair adapted to serve the upper pass of said stand, a repeater located between said pairs of tables, a second repeater located at the end of the pair of tables remote from said stand, a third pair of double deck roller tables located on the other side of said stand with the lower table of said pair adapted to serve the lower pass and the upper table adapted to serve the upper pass of said stand, a repeater located at the end of said last mentioned pair of tables remote from said stand and means for bypassing at least two of said repeaters.

2. In a mill for hot rolling metal strip, a threehigh roll stand, two pairs of double deck roller tables located on one side of said stand with the lower tables of each pair adapted to serve the lower pass of the stand and the upper tables of each pair adapted to serve the upper pass of the stand, a repeater between said pairs of tables, a second repeater located at the end of the pair ol tables remote from said stand, a third pair of double deck roller tables located on the other side of the stand, the lower table of said pair adapted to serve the lower pass and the upper table adapted to serve the upper pass of said stand, a repeater located at the end of said last-mentioned pair of tables remote from said stand, means for bypassing at least two of said repeaters and strip heating furnaces enclosing certain of the aforementioned tables.

3. In a. hot strip mill, a three high roll stand, a pair of double deck strip conveyors located on one side of said stand, each conveyor of said pair adapted to serve one pass of said stand, a repeater located at the end of said pair remote from said stand, two pairs of double deck conveyors located on the other side of said stand with a repeater intervening between them, the lower conveyors of said pairs adapted to serve the lower pass of the stand and the upper conveyors adapted to serve the upper pass of said stand, a third repeater located at the end of the last-mentioned pair of conveyors remote from said stand and means for bypassing two such repeaters.

4. In a hot strip mill, a multiple pass roll stand, a pair of double deck strip conveyors located on one side of said stand, each conveyor of said pair adapted to serve one pass of said stand, a repeater located at the end of said pair remote from said stand, two pairs of double deck conveyors located on the other side of said stand with a repeater intervening between them, the lower conveyors of said pairs adapted to serve the lower pass of the stand and the upper conveyors of said pairs adapted to serve the upper pass of said stand, a third repeater located at the end of the last-mentraverse decks of one or more such pairs on issuing tioned pair of conveyors remote from said stand, strip heating furnaces enclosing certain of said conveyors and controllable means for bypassing at least two such repeaters.` l

5. In a mill for hot rolling metal strip, a multiple pass roll stand, a plurality of pairs of multiple deck strip conveyors mounted on each side of said stand, each, deck of each conveyor adapted to serve one pass of said stand, heating furnaces enclosing certain of such decks, and means for selectively causing strip'issuing from said stand to from said stand.

6. In a mill for-hot rolling metal strip, a multiple I pass roll stand, two pairs 'of multiple deck strip