GB2030491A - Process for rolling plates, and plate mill therefor - Google Patents

Abstract

A plate mill comprises a slab heater (12); a hot reversing mill (14) positioned downstream of said heating means (12); a first coiler furnace (16) positioned in line with and adjacent to the hot reversing mill on the upstream side thereof; a second coiler furnace (18) positioned in line with and adjacent the hot reversing mill (14) on the downstream side thereof; shearing means (22) positioned downstream of the second coiler furnace (18) for shearing plate into desired lengths; and finishing means for receiving the sheared plate and finishing it into a final plate. <IMAGE>

Description

SPECIFICATION Process for rolling plates, and plate mill therefor This invention relates to the rolling of plate and, more particularly, to plate mill lines employing hot reversing mills and coilers to achieve the reduction of a slab to a plate of a desired thickness.

Heretofore hot rolled steel plate has generally been produced in one of two ways. Widths of plate 72 inches (182.88 cm) and less and 3/16 to 3/4 inch (0.476 to 1.905 cm) 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 (182.88 cm) or thicker than 3/4 of an inch (1,905 cm) and on stainless and other specialty steel items as well as for non-ferrous 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 mill 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 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 non-ferrous plates. There 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 (254 cm) wide carbon steel plate to 3/16 inch (0.476 cm) thickness, the usual maximum length that can be rolled is 55 to 65 feet (16.764 to 19.812 m). A typical slab pattern would have a volume of 15,440 cubic inches (253015.28 cm3) and would weigh about 4,375 pounds (1984.5 Kg.). The same size plate in stainless steel can be rolled to only 40 to 45 feet (12.192 to 13.716 m) 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 fulling in Table 1 (left side) which is set forth hereinafter and which will be discussed later and contrasted with the results achieved by the present invention.

A common problem associated with the rolling of plate on a plate mill is camber. Camber is normally defined as the non-linearity of the longitudinal edges of the plate. Becaused of camber, excess rolled width must be provided and then subsequently side trimmed to meet the desired width. This materially reduces the yield obtained. Atypical product yield for a plate mill of 112 inches (284.48 cms) wide for carbon steel plate is about 86 per cent.

In addition, since each plate size has a corresponding 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 greatest demand is for 1/2 inch (1.27cm) thick plate or less, see Figure 3. To meet this market the mill must roll many small 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 of the facility is increased by the fact that both stands are used to accomplish the rolling on each slab, 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 ample slab heating and plate cooling and shearing facilities are installed. In addition, a two-stand plate mill requires a high investment cost in equipment, buildings, labour and services.

According to the present invention there is provided a process for rolling plates on a plate mill comprising the steps of heating a slab to a desired rolling temperature; passing the slab back and forth through a hot reversing mill to obtain a workpiece of a desired intermediate thickness; coiling the workpiece in a first coiler furnace positioned on the upstream or downstream side of the hot reversing mill; 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 reversing mill until the workpiece has been reduced to a desired plate thickness; and processing the coil of desired plate thickness into a desired plate length.

Broadly, the invention comprises a plate mill line having at least one hot reversing mill for passing a workpiece back and forth therethrough in a reduction cycle to reduce the workpiece to a desired thickness, and a coiler furnace placed on opposite sides of the hot reversing mill in the plate mill line for receiving and paying out the workpiece in coil form during a portion of the reduction cycle.

The invention also comprises a plate mill for reducing a slab to a plate of a desired thickness comprising heating means for establishing a predetermined slab rolling temperature; a hot reversing mill positioned downstream of said heating means; a first coiler furnace positioned in line with and adjacent to the hot reversing mill on the upstream side thereof; a second coilerfurnace positioned in line with and adjacent the hot reversing mill on the downstream side thereof; shearing means positioned downstream of the second coiler furnace for shearing plate into desired lengths; and finishing means for receiving the sheared plate and finishing it into a final plate.In its preferred form,the invention comprises a plate mill line for reducing a slab to plates of a desired thickness comprising a series of mill tables positioned end to end to form a conveyor line; a reheat slab furnace positioned adjacent one end of the conveyor line; a first shear positioned downstream of the reheat slab furnace along the conveyor line; a four high hot reversing mill positioned downstream of the first shear; a set of pinch rolls positioned adjacent to and on opposite sides of said mill along said conveyor line; a first and second coilerfurnace, each including a coiling mandrel, an insulating lining and an external heating source, said coiler furnaces being positioned on opposite sides of said pinch rolls; a deflector plate positioned at an entranced to each coilerfurnace and movable between a first position out of a pass line to a second position in the pass line to deflect a workpiece into the coiler furnaces; and a second shear along the conveyor line and downstream of the coiler furnaces and the hot reversing mill.

The process and plate mill of the present invention provide increased production and lower manufacturing costs over a conventional single stand plate mill. With the higher productivity capability, the plate mill of the present invention which utilizes a single stand has the production capability of roughly a standard two-stand plate mill facility. The plate mill of the present invention requires less building, equipment, manpower and services than the equivalent two-stand facility and thus requires appreciably lower capital expenditure. The plate mill of the present invention provides a substantial increase in product yield which lowers unit manufacturing costs and conserves raw material, energy and other resources.By handling larger slabs, the plate mill of the present invention 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, the process and plate mill of the present invention can be applied to existing plate mills through a simple conversion or can form a part of new installations.

The coiler furnaces can be positioned either below or above the pass line and means such as deflector plates can be employed to direct the workpiece into the coilerfurnaces. Pinch rolls may be used for feeding and to assist in maintaining tension on the strip as it is being rolled, and means such as a mechanized feed roll can be provided to maintain the workpiece out of engagement with the rolls during payoff to the shear.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which: Figure lisa schematic view of the layout of one possible configuration of a plate mill according to the present invention, Figure 2 is a schematic view, partly in section, showing an hot reversing mill and two coiler furnaces forming part of the said plate mill, and Figure 3 is a bar graph showing a typical product mix and productivity of existing plate mills.

The general arrangement of the plate mill of the present invention, designated 10, is illustrated in Figure 1.

Large slabs are brought up to rolling temperature in a conventional slab reheat furnace 12. The slabs are normally pushed out of the furnace 12 onto a conveyor line 24, also termed a mill table. Afour high hot reversing plate mill 14 is positioned downstream of the furnace 12. Pinch roll pairs 32 and 34 are located on opposite sides of the hot reversing plate mill 14 and assist in decoiling as will be described hereinafter. Coiler furnaces 16 and 18 are also positioned on opposite sides 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 ,ay 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 parallel processing conveyor line 40.Processing line 40 includes a conventional roller leveler 28 for leveling the plate. Athird conveyor line 42 is disposed parallel to the lines 24 and 40 and is connected to the line 40 through a transfer cooling bed 30 located along the terminal portion of conveyor line 40. The 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 ofthe hot reversing plate mill 14 and the coilerfurnaces 16 and 18 are shown in Figure 2. The hot reversing plate mill 14 is conventional having a pair of work rolls 50 journaled in work roll chucks 52 and a pair of backup rolls 54 journaled in backup chucks 56. An hydraulic automatic gauge control system 58 can be used to control the rolling thickness in the conventional manner, or a motor 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 coilerfurnaces 16 and 18, respectively. The coiler furnaces 16 and 18 are illustrated as mounted below front and back mill tables 60 and 62, respectively, which make up a part of conveyor line 24. This positioning is preferable since the coilerfurnaces are located in a position such as not to 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 lightweight fibre 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 maintain a more uniform temperature throughput 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, or even mandrel less coilers.

Located at the entrance of each coilerfurnace 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.

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 work 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 (3.175 to 1.27 cm) is obtained, at which time the deflector plates 70 and 72 are activated and the reduced slab will enter into one of the coilerfurnaces 16 or 18 for winding onto the mandrel or other coiling mechanism. The shears 20 and 22 on opposite sides of the coiler furnaces permit the cropping of the ends of the elongated slab before it is reduced to the thickness at which it enters the coiler furnaces.

Thereafter, 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 preceding 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.

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. lf 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 take-off mechanism (not shown) to remove the plate from the runout table.

Other coiler furnace designs can be employed to modify the plate rolling procedures after the final reduction in thickness has been achieved. For example, the downstream coilerfurnace 18 can be of the type which coils in one direction from the mill 14 and pays off in the opposite 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 22.

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 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 push-off transfer mechanism and the production rate redquired. The length of the plate cut by the shear 22 is normally in accurate multiples of ordered shipping lengths. The plate then travels down the run-out table 24 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 58 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 the present invention with existing plate mill facilities, it is necessary to first review the total tonnage produced for the marketplace and the time required to roll the various thickness plate produced. This is shown graphically in Figure 3. It can be seen that although 3/16 inch (0.476 cm) plate represents something of the order of 13% of the market, almost 30% of the total rolling time of the mill is spent to achieve that 13%. Likewise 5/16 inch (0.794cm) 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 is required for such rolling.

Table 1 compares the data for producing 96 inch (243.84 cm) wide carbon steel plate on a single stand 112 inch (284.48 cm) plate mill in accordance with the product mix of Figure 3 with and without this 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 the present invention has been calculated from 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.

The term "tons" used therein has reference to metric tons.

Table 1 Data for Producing a 9B' (243,8cm) Wide Plate on Single Stand Plate Mill Conventional 112" (284.5cm) Plate Mill Plate Slab Wt. % Metric Hrs/ Thickness Size Metric Yield Tons/ 90,700 Tons Hr Metric Tons 3/16" 6"x33"x78" 1.99 86.7 28.9 413.8 (0.48cm) (15.3x83.8x198.1cms) 1/4" 6"x40"x100" 3.08 86.4 44.8 247.0 (0.64cm) (15.3x 101.6x254cms) 5/16" 6"x64"x100" 4.93 86.3 78.0 60.0 (0.79cm) (1 5.3x 1 62.6x254cms) 3/8" 6"x77"x100" 5.93 86.0 97.8 116.0 (0.95cm) (15.3x195.6x254cms) 1/2" 8"x69"100" 7.09 86.6 118.3 158.0 (1.27cm) (20.3x 175.3x254cms) 5/8" 8"x86"x100" 8.84 86.9 148.2 41.0 (1.59cm) (20.3x218.4x254cms) 3/4" 8"x100"x104" 10.69 85.0 175.3 45.0 (1.91cm) (20.3x254x264.2cms) 7/8" 10"x96"x100" 12.33 85.0 199.5 15.0 (2.22cm) (25.4x243.8x254cms) 1" 10"x100"x110" 14.13 85.0 230.2 39.0 (2.54cm) 25.4x254x279.4cms) 1-3" 10"x100"x138" 17.73 85.0 286.1 29.1 (2.54cm- (25.4x254x350.5cm's 7.62) Total Hours 1163.9 Average metric tons/hour = 90.700 = 77.9 1163.9 Plate Slab Wt. % Metric Hrs/ Thickness Size Metric Yield Tons/ 90,700 Tons Hr.Metric Tons 3/16" 10"x98"x288" 36.28 96.6 101.8 117.6 (0.48cm) 25.4x248.9x731.5) 1/4" 10"x98"x288" 36.28 x 98" x 288" 36.28 96.9 128.8 85.9 (0.64cm) (25.4x248.9x731.5) 5/16" 10"x98"x288" 36.28 96.5 139.7 30.5 (0.79cm) (25.4x248.9x731.5) 3/8" 10"x98"x288" 36.28 96.3 151.5 74.9 (0.95cm) (25.4x248.9x731.5) 1/2" 10"x98" > c288" 36.28 96.2 178.7 104.6 (1.27cm) (25.4x248.9x731.5) 5/8" 10x98"x276" 34.47 95.8 213.1 28.5 (1.59cm) (25.4x248.9x701.0) 3/4" 10"x98"x260" 32.65 95.2 239.4 33.0 (1.91cm) (25.4x248.9x660.4) 7/8" 10"x98"x260" 32.65 95.0 239.4 12.5 (2.22cm) (25.4x248.9x660.4) 1" 10"x98"x297" 37.19 95.0 249.4 36.0 (2.54cm) (25.4x248.9x754.4) 1-3" 10"x98"x302" 38.09 93.6 250.3 29.7 (2.54cm- (25.4x248.9x767.08) 7.62) Total Hours 553.2 Average metrictons/hour90,700 = 164.0 553.2 As shown in Table 1, the average tons per hour which is the product tonnage and hours required based on 90,700 tons of total product divided by product mix (Figure 3) is 164.0 tons/hr for this invention and 77.9 tons/hr for the conventional mill.

It is readily apparent that by rolling large slabs into long plate lengths in accordance with the present invention, the productivity of the plate mill facility is tremendously increased over existing processes which require the rolling of individual pieces.

The single stand mill of the present 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 a plate mill design according to the present invention. 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 (304.8m) 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 cropped 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 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 temperature control for precise physical properties.

Although a 112 inch (284.48 cms) wide mill was used as an example, the invention is applicable for plate mills of any width. Further, the coiling furnace mandrels do not necessarily have to be as wide as the maximum product rolled on a mill, but their application can be limited to medium wide products. For example, although a 160 inch (406.4cm) wide plate mill can roll plate up to 155 inches (393.7cm) wide, only a small percentage of the production is rolled that wide. Normally such a mill is rolling in the range of 72 inch (182.88 cm) to 120 inch (304.8cm) 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 (320.04cm) wide product are installed on a 160 inch (406.4cm) wide mill, the overall production will increase as larger slabs can be rolled to the thin, medium width products. In such cases the conversion of the mill to the use of the present invention avoids the necessity of installing an additional plate mill facility.

Claims (15)

1. A process for rolling plates on a plate mill comprising the steps of heating a slab to a desired rolling temperature; passing the slab back and forth through a hot reversing mill to obtain a workpiece of a desired intermediate thickness; coiling the workpiece in a first coiler furnace positioned on the upstream or downstream side of the hot reversing mill; 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 reversing mill until the workpiece has been reduced to a desired plate thickness; and processing the coil of desired plate thickness into a desired plate length.

2. A process as claimed in claim 1, including de-coiling the workpiece of desired plate thickness from one of said coiler furnaces and feeding it to an in-line shear as part of the said processing step.

3. A process as claimed in claim 1 or 2 including maintaining tension on the workpiece while passing it through the mill between the coiler furnaces.

4. A process as claimed in any preceding claim including deflecting said workpiece of intermediate thickness from a pass line into the coiler furnaces.

5. A process as claimed in any preceding claim wherein said intermediate thickness if from 1/2 inch to 1-1/4 inches (1,27 to 3.18 cms).

6. A plate mill for reducing a slab to a plate of a desired thickness comprising, heating means for establishing a predetermined slab rolling temperature; a hot reversing mill positioned downstream of said heating means; a first coilerfurnace positioned in line with and adjacent to the hot reversing mill on the upstream side thereof; a second coiler furnace positioned in line with and adjacent the hot reversing mill on the downstream side thereof; shearing means positioned downstream of the second coiler furnace for shearing plate into desired lengths; and finishing means for receiving the sheared plate and finishing it into a final plate.

7. A plate mill as claimed in claim 6 in which said hot reversing mill comprises a set of work rolls and a set of back-up rolls.

8. A plate mill as claimed in claim 6 or 7 comprising a set of pinch rolls between each coiler furnace and the hot reversing mill.

9. A plate mill as claimed in claim 7 comprising a mill table on each side of the hot reversing mill, each said mill table including liftable means to disengage a plate passing therethrough from the work rolls.

10. A plate mill as claimed in claim 9 comprising a deflector plate positioned adjacent each coilerfurnace and movable between a first position out of a pass line and a second position in the pass line for diverting plate being rolled into the respective coiler furnace.

11. A plate mill as claimed in any of claims 6-10 in which each of said coiler furnaces includes an insulating lining and an external heat source for supplying heatto the furnace.

12. A plate mill as claimed in claim 9 or 10 in which said coilerfurnaces are positioned below said mill tables.

13. A plate mill line for reducing a slab to plates of a desired thickness comprising a series of mill tables positioned end to end to form a conveyor line; a reheat slab furnace positioned adjacent one end of the conveyor line; a first shear positioned downstream of the reheat slab furnace along the conveyor iine; a four high hot reversing mill positioned downstream of the first shear; a set of pinch rolls positioned adjacent to and on opposite sides of said mill along said conveyor line; a first and second coiler furnace, each including a coiling mandrel, an insulating lining and an external heating source, said coilerfurnaces being positioned on opposite sides of said pinch rolls; a deflector plate positioned at an entrance to each coiler furnace and movable between a first position out of a pass line to a second position in the pass line to deflect a workpiece into the coiler furnaces; and a second shear along the conveyor line and downstream of the coiler furnaces and the hot reversing mill.

14. A plate mill line as claimed in claim 13 wherein a portion of the mill table adjacent the hot reversing mill is vertically movable to lift a plate out of engagement with the mill as it passes therethrough.

15. A plate mill line having at least one hot reversing mill for passing a workpiece back and forth therethrough in a reduction cycle to reduce the workpiece to a desired thickness, and a coiler furnace placed on opposite sides of the hot reversing mill in the plate mill line for receving and paying out the workpiece in coil form during a portion of the reduction cycle.