CA1095751A - Plate mill method and apparatus - Google Patents

Abstract

ABSTRACT
The plate mill line includes a heating means such as a slab reheating furnace for obtaining the slab rolling tempera-ture. A hot reversing plate mill is positioned downstream of the furnace and is preferably of the four high type. A coiling furnace is positioned on each side of the hot reversing plate mill. Shearing means and finishing means are positioned downstream of the re-versing plate mill and the coiler furnaces. A slab to be rolled leaves the furnace and is passed directly to and back and forth though the hot reversing plate mill. At a given reduction, the plate is re-ceived by one of the coiler furnaces and thereafter rolling of the plate continues with the workpiece passing back and forth through the hot reversing plate mill between the coiler furnaces. After a final pass the plate is fed from the coiler to a shearing means and finishing means for final processing of the plate to the desired width and lengths.

Description

~5~751 FIELD OF THE INVENTION
This invention relates specifically to the rolling of plate and, more particularly, to plate mill lines employing hot reversing mills and coilers in heat conserving chambers to achieve the reduction of a slab to a plate of a desired thickness.
DESCRIPTION OF THE PRIOR ART
Heretofore hot rolled steel plate has generally been produced in one of two ways. ~idths of plate 72 inches and less and 3/16 to 3/4 inch thick are generally produced on continuous or semi-continuous hot strip mills rather than plate mills per se.
The product is reduced from a slab in the flat by passing it through a standard hot strip mill roughing and finishing train after which it is coiled on a hot strip coiler after being cooled on the run-out table. Subsequently the coiled material is uncoiled, leveled, side trimmed and cut to plate lengths.
; On carbon steel plate wider than 72 inches or thicker than 3/4 of an inch and on stainless and other specialty steel items as well as for nonferrous metals, it is the usual practice to produce plate on a single stand or a two-stand plate mill. Each combination of thickness, width, and length of plate rolled from the ~nill requires a properly proportioned "pattern" slab with the appropriate volume of metal. The slabs are reduced to plates by passing back and forth through a hot reversing plate mill. It is often necessary to cross roll a slab to achieve the desired plate width. Thereafter the rolled plates are flattened hot on a leveling machine, transferred to a cooling bed for cooling and subsequently ~ .

~g~53l side sheared and end sheared to finished plate dimensions. This reduction normally takes place on a four high hot reversing mill although it is also common to utilize a two high hot reversing mill upstream of the four high to increase productivity by having two slabs on line at a time.
There are a number of existing limitations on plate mills utilized in rolling carbon steel, stainless or specialty --steel and nonferrous plates. Thexe is a definite limitation of the lengths that can be rolled which is usually dictated by the cooling rate and the time of rolling. For example, when rolling a 100 inch wide carbon steel plate to 3/16 inch thickness, the usual ma~imum length that can be rolled is 55 to ~5 feet. A typical slab pattern would have a volume of 15, 440 cubic inches and would weigh about 4, 375 pounds. The same size plate in stainless steel can be rolled to only 40 to 45 feet due to the higher resistance of stainless steel to deformation. If the slab is oversize in weight or size, it may be impossible to finish the plate to the desired thickness and width as the material will become too cold for hot plastic deformation by the rolling mill.
The drastic limitation of conventional plate rolling ~-methods and apparatus are shown more fully in Table 1 (left side) which is set forth hereinafter and which will be discussed later and contrasted with the results achieved by this invention.
A common problem associated with the rolling of plate on a plate mill is camber. Camber is normally defined as the nonlinearity of the longitudinal edges of the plate. Because of

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camber, excess rolled width must be provided and then subse-quently side trimmed to meet the desired width. This rnaterially reduces the yield obtained. A ty,oical product yield for a plate mill of 112 inches wide for carbon steel plate is about 86 per cent.
In addition, since each plate size has a corre-sponding pattern slab, the reheat furnace must accommodate a wide range of slab sizes to produce the product mix, thereby making heating efficiency and uniformity more difficult. Further, the slab producing facility, whether it be a continuous caster or a blooming or slabbing mill must turn out a large number of small size slabs for subsequent processing into the plates.
All of these factors are further compounded by the typical market demand for carbon steel plate wherein the great-est demand is for 1/2 inch thick plate or less, see Fig. 3. To meet this market the mill must roll many srnall slabs at a resultant low production rate and with a low product yield.
Greater productive capacity is obtained by installing (or expanding to) a two-stand mill facility. Such an installation consists of a roughing mill (usually two high) and a four high finishing mill. Capacity cf the facility is increased by the fact that both stands are used to accomplish the rolling on each slab, thus reducing the time required for each slab Gn each mill stand, and thus increasing the overall rate of number of slabs rolled per hour. However, the slab sizes utilized are the same as for the single stand mill and the ultimate productive capability approaches twice the capacity of the single stand mill provided arnple slab ~s~

heating and plate cooling and shearing facilities are installed. In addition, a two-stand plate mill requires a high investment cost in equipment, buildings, labor and services.
SUMMARY OF THE INVENTION
My plate rolling method and apparatus provides increased production and lower manufacturing costs over a con-ventional single stand plate mill. With the higher producti~ity capability, the new plate mill which utilizes a single stand can approximate the productien capabilities of a standard two-stand plate mill facility. The new plate mill requires less building, equipment, manpower and services than the equivalent two-stand facility which means an appreciably lower capital expenditure. The new plate mill provides a substantial increase in product yield which lowers unit manufacturing costs and conserves raw material, energy and other resources. 33y handling larger slabs my plate mill results in more uniform heating practices and increased utilization of the reheat furnace and increases the productivity of the processing units which transform the metal product to a slab.
Further, my method and apparatus can be applied to e~isting plate mills through a simple conversion or can form a part of new installations .
My plate rnill line includes a heating means such as a slab reheat furnace, a hot reversing plate mill down-stream of the heating furnace and coiler furnaces which are preferably heated, positioned on either side of the hot reversing plate mill. Shearing means and finishing means are positioned 5~

downstream of the reversing mill and the coiler furnaces for final processing of the plate product.
The slab, after being heated to a desired rolling temperature, is passed back and forth through the hot reversing plate mill to obtain a vworkpiece of a desired intermediate thickness and length. When the desired intermediate workpiece is achieved, one of the coiler furnaces is activated and the workpiece is there-after coiled within the furnace. The workpiece is thereafter passed back and forth through the hot reversîng plate mill between the two coiler furnaces until the desired final plate reduction has been achieved. The coil is then further processed into the desired plate length or multiples thereof and the finishing operations on the plate are completed. The coiler furnaces can be positioned either below or above the pass line and means such as deflector plates are employed to direct the workpiece into the coiler furnaces. Pinch rolls are used for feeding and to assist in maintaining tension on the strip as it i3 being rolled and means such as a mechanized feed roll is provided to maintain the workpiece out of engagement with the rolls during payoff to the shear.
BRIEF DESCRIPTION OF THE DRA~INGS
Fig. 1 is a schematic of the layout of one possible configuration of a plate n~ill embodying my invention;
Fig. 2 is a schernatic, partly in section, show-ing the hot reversing mill and the two coiler furnaces; and Fig~ 3 is a bar graph showing a typical product ~nix and productivity of existing plate mills.

DESC~IPTION OF THE PREFERRE~D EMBODIMENTS
. . .
The general arrangement of my plate mill, designated 10, is illustrated in Flg. 1. Large slabs are brought up to rolling temperature in a conventional reheat slab furnace lZ.
The slabs are normally pushed out of furnace 12 onto a conveyor line 24, also termed a mill table. A four high hot reversing plate mill 14 is positioned downstream of the furnace 12. Pinch roll pairs 32 and 34 are located on each side of hot reversing plate mill 14 and assist in decoiling as will be described hereinafter.
Coiler furnaces 16 and 18 are also positioned on either side of the four high hot reversing plate mill 14. A conventional shear 20 is positioned between coiler furnace 16 and the slab reheat furnace 12 and a conventional shear 22 which may be an upcut, downcut or flying shear is positioned downstream of the coiler furnace 18.
Conveyor line 24 terminates in a transfer table 26 for moving the plates onto a paralllel processing conveyor line 40. Processing line 40 includes a conventional roller leveler 28 for leveling the plate. A third conveyor line 42 parallels lines 24 and 40 and is connected to line 40 through a transfer cooling bed 30 located along the terminal portion of conveyor line 40. Conveyor line 42 includes a side shear 38 and a final end shear 36 for cutting the plate into the final desired length.
The details of the hot reversing plate mill 14 and the coiler furnaces 16 and 18 are shovwn in Fig. 2. The hot reversing plate mill 14 is conventional having a pair of work rolls 50 journaled in work roll chucks 5Z and a pair of backup rolls 54 ~s~

journaled in backup chucks 56. A hydraulic automatic gauge control system 58 can be used to control the rolling thickness in the conventional manner or a rQotor driven screw-down mechanism can be utilized.
Pinch roll pairs 32 and 34 are operable on each side of and adjacent to the mill 14. Immediately adjacent to and on each side of the pinch roll pairs 32 and 34 are the coiler furnaces 16 and 18, respectively. The coiler furnaces 16 and 18 are illustrated as mounted below the front and back mill tables 60 and 62, respective-ly, which make up a part of conveyor line 24. This positioning is preferable since the coiler furnaces are located in a position to not interfere with the conventional flat rolling conducted in the early passes. When converting an existing mill it may be necessary to locate the coiler furnaces above the mill tables.
Each furnace, 16 and 18, is lined with a light-weight fiber type refractory lining 64, which because of its low heat sink value, is responsive to modulating heat input. Of course, other conventional linings can be employed. The furnaces are preferably heated by gas, oil or electricity and can be equipped with controls (not shown) to modulate the heat input to the furnace as the plate is wound and unwound on the coilers in order to main-tain a more uniform temperature throughout the plate length for metallurgical control.
Each coiler furnace 16 and 18 includes coilers 66 and 68, respectively~ The coilers 66 and 68 can be any one of several conventional types including motor driven coiling reels, ~5'7~i1 or even mandrelless coilers.
Located at the entrance of each coiler fur-nace 16 and 18 and adjacent to the pinch roll pairs 32 and 34 are deflector plates 70 and 72, respectively. These deflector plates lie in a plane below the mill tables 62 and 64 and when activated by the operator or automatic controls pivot into the open position so as to deflect the plate being rolled into the coiler furnaces.
The first table feed rolls 74 and 76 on each side of the mill are vertically operable by conventional means to lift the running plate out of contact with the bottom ~,vork roll 50.
A slab is initially rolled straight away through the hot reversing plate mill 14. The slab is then reduced by rolling it back and forth through the mill in a conventional manner until a thickness of approximately 1-1/4 inches to 1/2 inch is obtained, at which time the deflector plates 70 and 72 are activated and the reduced slab will enter into one of the coiler furnaces 16 or 18 for winding onto the mandrel or other coiling mechanism. The shears 20 and 22 on either side of the coiler furnaces permit the cropping of the ends of the elongated slab before it is reduced to the thick-ness at which it enters the coiler furnaces. ThereafterJ the coiled plate is passed back and forth between the coiler furnaces and through the hot reversing plate mill 14 until such time as the plate is reduced to the desired finished plate thickness. As the plate is wound on the mandrel in the coiler furnace, the exposed surface area of plate is greatly reduced as each wrap covers the preced-ing wrap. The end of each plate is retained by the pinch rolls for feeding into the roll bite for the next pass through the mill.

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The last rolling pass through the mill is usually in the reverse direction so that the entire plate is coiled on the front furnace mandrel 16 except for the front end of the plate which is retained between the front pinch rolls 32. The plate is then uncoiled from the coiling furnace 16 with the aid of the pinch rolls and is cut into the desired length by the shear 22. The shear 22 can be a flying shear or a stationary shear. If a flying shear is used, the plate runout table has to be long enough so that a running gap can be opened up between the back end and the front end of the cut lengths of the plate to provide sufficient time for a plate takeoff mechanism (not shown) to remove the plate from the runout table.
Other coiler furnace designæ can be employed to modify the plate rolling procedures after the final reduction in thickness has been achieved. For example, the downstream coiler furnace 18 can be of the type which coils in one direction from the mill 14 and pays off in the other direction to the crop shear 22. In this embodiment the mill 14 can be used for the early passes while the coiler furnace 18 pays off the previously rolled plate in coil form to the crop shear Z2.
Where a stationary shear is employed, the runout table need not be much longer than the cut length. In this case the rolling mill rolls are open so that the finished plate can pass freely through the roll bite when the plate is unwound from the front coiler by the pinch rolls. The liftable first table feed roll 34 prevents the plate from rubbing on the bottom mill roll.
As the plate is unloaded from the furnace mandrel, it is cut to cooling bed length by the stationary shear in 7~i~

a start-stop cut manner. The speed of withdrawal of the coiled plate depends on the type of cutting shear~ the length of cut, the speed of the plate pushoff transfer mechanism and the production rate required. The length of the plate cut by the shear 22 is nor-mally in accurate multiples of ordered shipping lengths. The plate then travels down the runout table 22 and is transferred laterally as quickly as possible onto transfer bed 26 to make room for the following length. The operation of the shear 22 can be actuated from controls receiving information from a digital counter on the discharge pinch roll 18. The plate then travels through the plate leveler 28 across the cooling bed 30 and through the side trimmer 38 and end shear 36 on conveyor line 42 to shear the length and width to the desired size.
In order to compare the productivity and product yield of my invention with existing plate mill facilities, it is necessary to fircit review the total tonnage produced for the marketplace and the time required to roll the various thickness plate produced. This is shown graphically in Fig. 3. It can be seen that although 3/16 inch plate represents on the order of 13%
of the market, almos+ 30% of the total rolling time of the mill is spent to achieve that 13%. Likewise 5/16 inch thick and thinner plates represent 30.1% of the product tonnage but require 55. 8%
of the rolling time. This is true because the thinner plate requires smaller pattern slabs, hence, most of the rolling time available is required for such rolling.
Table 1 compares the data for producing 96 inch wide carbon steel plate on a single stand 112 inch plate mill i7~

in accordance with the product mix of Fig. 3, with and without my invention. The data for the Table 1 conventional mill is based on average actual production figures for several different operating mills, whereas the data for my ;nvention has been calculated rom slab sizes and the resultant anticipated yields. The production rate (tons/hr. ) is based on rolling rate only with product yield as shown and 80% mill utilization without any consideration of slab heating furnace or cooling bed capacities.

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As shown in Table 1, $he average tons per hour which is the product tonnage and hours required based on 100, 000 tons of total product divided by product mix (Fig. 3) is 180. 8 tons/hr. for my invention and 85. 9 tons/hr. for the conven-tional mill.
It is readily apparent that by rolling large slabs into long plate lengths in accordance with my invention, the productivity of the plate mill facility is tremendously increased over existing processes which re~uire the rolling of individual pieces .
- ~ The single stand rnill of my invention achieves . . , results which can only be realized with a two-stand mill facility at a much reduced capital cost.
~-~ Of equal importance is the increased overall product yield from about 86% on a conventional mill to about 96% with my new plate mill design. This increase in product yield is even more significant when rolling stainless steels where the increase in yield can be from 78% to about 95%.
Since the plate is rolled under tension while it is wound in the coiler furnace, there is very little camber from end to end of the plate which can be as long as 1000 feet long. This means the scrap allowance for side trimming can be reduced to a minimum value and there are only two ends of the plate to be crop-ped as compared to many ends when rolling !'pattern" slabs.
All these benefits of the plate mill facility back up all the way through the primary mills and steelmaking facilities where the manufacture of large ingots and slabs, be they 1~57S~

cast or rolled, lower the overall manufacturing cost per ton of product produced. And the plate produced is a high quality product having been rolled in long lengths under tension and accurate tem-perature control for precise physical properties.
Although a 112 inch wide mill was used as an example, this new concept is applicable for plate mills of any width. Further, the coiling furnace mandrels do not necesaarily have to be as wide as the maximum product rolled on a rnill, but their application can be limited to medium wide products. For example, although a 160 inch wide plate mill can roll plate up to 155 inches wide, only a small percentage of the production is rolled that wide. Normally such a mill is rolling in the range of 72 inch to 120 inch wide plate and, as explained heretofore, it is in thin products in this width range that the small "plate pattern"
slabs limit the production capability of the mill.
Therefore, if coiling furnaces for a 126 inch wide product are installed on a 160 inch wide mill, the overall production will increase as larger slabs can be rolled to the thin, med;um width products. In such cases the conversion of the mill to the use of my invention avoids the necessity of installing an additional plate mill facility.

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the continuous and uninterrupted converting of a large slab into a number of plates, said plates having a minimum thickness of at least 3/16 of an inch, on a plate mill comprising:
A. heating said slab to a desired rolling temperature;
B. passing the slab back and forth through a hot reversing mill to obtain a workpiece of a desired intermediate thickness;
C. coiling the workpiece in a coiler furnace positioned on one of the upstream or downstream sides of the hot reducing mill;
D. immediately passing the workpiece back and forth from said coiler furnace through the hot reversing mill to and from a second coiler furnace positioned on the other side of the hot reducing mill without delaying in either furnace and until the workpiece has been reduced to a desired plate thickness;
E. maintaining tension on the workpiece during process step D so as to minimize camber;
F. decoiling the workpiece of desired plate thickness from one of said coiler furnaces;
G. feeding the decoiled workpiece to an in-line shear; and H. shearing the workpiece into a number of plates of desired length.

2. The process of Claim 1 including deflecting said intermediate workpiece from a pass line into the coiler furnaces.

3. The process of Claim 1 wherein said intermediate thickness if from 1/2 inch to 1-1/4 inches.

4. The process of Claim 1, said slab being generally 36 tons or more in weight.

5. The process of Claim 1, said plates having a width on the order of 72 inches to 155 inches wide.