Title of Invention

""AN IMPROVED COILING SYSTEM FOR USE IN THE PRODUCTION OF THIN STEEL STRIP

Abstract

A coiling system for thin metallic strip which avoids problems of the strip head flying and deviating from the center of the rolling line, and thus provides an easy and cost-effective method to avoid cobbling of said strips during coiling process thereby decreasing operational delays and increasing productivity of a thin gauge hot rolling metallic strip mill, particularly steel strip mill. The improved coiling system comprises of a plurality of wedges, made up of an abrasion resistant frictionless material, welded equidistant from each other along the whole length of the strip switch (31) to minimize the troughs (51) below the pinch rolls (41 & 42) of coilers thereby minimizing simultaneously flying of the head of the strip and the subsequent formation of cobbles.

Full Text

Field of invention: The invention relates to hot strip mills and, more particularly, to a method to minimize the troughs below the pinch rolls of coilers thereby minimizing simultaneously flying of the head of the strip and the subsequent formation of cobbles. Background: The general arrangement of a modern hot strip mill includes a runout table of substantial length located between the last finishing stand of the finishing line and the coilers. The runout table, which often reaches lengths in excess of 300 m, is provided with water sprays above and below the table rolls for rapid cooling of the rolled strip to the desired temperature for coiling. The strip, which is carried along the runout table on a driven roller conveyor, is coiled in one of a plurality of coilers located at the end of the runout table. On the rolling line each coiler has got an arrangement of a set of side guides and top and bottom pinch rolls and a strip switch. The function of pinch rolls is to drive the strip at the desired velocity and tension before it is engaged by and wound up on a coiler mandrel. A strip going to the coiler which is sequentially placed last among all the coilers has to pass through the pinch roll, side guide and strip switch of all previous coilers. The strip normally leaves the finishing mill at speeds of the order of 10 m/s. The strip after moving out of the finishing mill accelerates to the down coiler for coiling. During thinner gauge coiling in down coilers, head of the strip shows a tendency to hit the side guide and pinch roll of coilers in the rolling line, and in the process gets folded resulting in a cobble. Since the strip is at its thinnest and since the speed is at its maximum, the area of the runout table is where the greatest number of cobbles occur. Each cobble causes a substantial delay of rolling time and thus reduces the profitability of the mill. The problem of cobbling is more prominent in coilers, which are situated further away from the finishing line. For a hot strip mill that rolls a lot of thinner gauge only in the selective coilers where the problem of 2 cobbling is not manifest decreases the effective percentage utilization of coilers thereby decreasing the rolling rate. Generally the side guides of the first coiler are always kept in set gap (strip width + short stroke) position, but subsequent guides are kept fully open i.e. 2000 mm in case of a 2000 mm hot strip mill. The guides of the predetermined coiler are in set gap position other than the first coiler. Similarly, the pinch rolls of the predetermined coiler are in set gap (strip thickness + correction) position and all other pinch rolls are fully open. There is a gap of 300 mm between the two pinch rolls, when fully opened. When the thickness of the strip is more than 2.5 mm, generally no problems are found in handling the strip, but when the thickness is less than about 2.5 mm, or less than about 2 mm, or still more preferably, less than about 2 mm the strip head has a tendency to jump while crossing the pinch rolls of previous coilers. When the head again lands on the runout roller table it often gets deviated from the center of the rolling line. There also exists a high probability of the head hitting the side guides and/or the projections i.e. strip switch cylinder and fishplate mounting clamps below the pinch rolls. The head by hitting any of the above obstructions gets folded which results in cobbles. This phenomenon aggravates at higher speeds, greater than 10.5 m/s and particularly with thinner gauges. The compulsion of maintaining the rolling speed as high as 12 m/s and more for desired mechanical and metallurgical properties, grain size etc. further compounds the problem. This cobbling problem gets further enhanced when there is a long separation between the finishing mill and the coilers because of space constraints. This greater distance between the finishing mill to the coiler requires a longer runout roller table. In hot strip mills, generally there are more than two coilers, and using them alternately for coiling needs a strip switch arrangement below the top pinch roll and just after the bottom pinch roll of a coiler and no rolls can be put in that place. It leaves a gap of around 1.8-m without any rolls. The distance between two runout roller tables is 8 inches. The strip switch is situated below, a foot below the rolling line and is placed at an angle of 45°. This creates a trough below the pinch rolls of coilers. 3 When rolling is done and strip is coming out of the finishing mill, the mill is in accelerating mode. In case of shorter rolling lines, the strip head is at a lower speed whereas in case of longer rolling mills, the head end of the strip acquires a very high speed. If the strip is to be rolled on the last coiler, it has to pass through all the troughs of the previous coilers. Thinner gauges have little head weight and greater flexibility. When it passes through the strip switch it enters the trough and while coming out, it flies and lands at maximum possible distance. The same problem is repeated, though of a diminutive stature. If the strip already has even a slightest of camber, the flying of the strip will increase chances of its getting hit somewhere resulting in a cobble. Further, with the advent of longer slabs from slab casters and always-increasing demand for larger coils, the rolling lines have to be continuously lengthened to achieve the necessary cooling and the associated handling. Since the strip is at its thinnest gauge on the runout table and is travelling at its fastest speed, the likelihood of cobbling is greatest in the area of runout table. Hot mil! designs that attempt to achieve greater speeds require even larger runout tables in order to achieve the proper cooling. OBJECTS: It is therefore an object of the present invention to provide an improved coiling system for use in the production of thin steel strip, for example coiling systems associated with hot strip mills in continuous casting plants. It is another object of the invention to provide an improved apparatus in a coiling system for guiding a thin steel strip to the mandrel of a coiler without interfering with the normal operation and high velocity movement of pinch rollers in said coiler. Yet another object of the present invention is to provide a coiling system to provide reliability and to lower operation costs of steel making plants reducing off times and yield loss. It is yet another object of the present invention to provide an improved coiling system for use in the production of thin steel strip in which the troughs below the pinch rolls of coilers is minimized, thereby minimizing simultaneously flying of the head of the strip and the subsequent formation of cobbles particularly in hot strip mills. 4 Summary: An improved system for coiling a metallic strip in a hot strip mill, said system comprising: (a) at least a runout roller table; (b) at least pinch roll unit comprising at least a pair of pinch rollers; (c) at least one coiler mandrel; (d) at least a side guide; (e) at least a strip switch characterized in that the said strip switch comprises a number of wedges, welded equidistant from each other along the whole length of the strip switch to minimize the trough created below the pinch rolls of coilers. DETAILED DESCRIPTION OF THE INVENTION: In order to effectively devise a solution to this problem,, the present inventors made the following observations: (a) for strips having dimensions 2.8 by 1200 mm, there was no problem of flying head irrespective of rolling speed, (b) when the gauge dimensions went below 2.5 by 1000 mm at a speed of over 11 m/s it started showing a tendency of flying of head, though not in alarming proportions, (c) when the gauge dimensions went below 2 by 1000 mm, the flying tendency of the head became dangerously high even at a rolling speed of 11 m/s. Faster speeds caused a cobble, (d) if the strip is even slightly cambered and it touches the side guides, the flying of head is even more dangerous, and (e) the flying starts at the first coiler, it increases in the next coiler and further keeps on increasing. On the basis of the above observations, it was found that the main reason for cobble was flying of the head of the strip, which was in turn caused by the trough created by the strip switch. Thus, minimizing the trough would also minimize the flying of the strip head as well as the formation of cobbles. 5 To minimize the said troughs, the present inventors have ingeniously designed a C 45 material having the shape as shown in Figure 3. Plurality of such wedges was welded, equidistant from each other, along the whole length of the strip switch of all the coilers. It was observed that the tendency of the strip to fly away reduced considerably. The problem of cobbling was especially severe in the coiler situated furthest away from the finishing line. Hence, if the situation could be controlled in the last coiler among all the coilers, it was known that the other coilers could be tackled simultaneously. Once the last coiler was made ready for coiling the strip, the side guides of the previous two coilers were set at fully open positions. The side guide of the first coiler was set at a value of strip width + 80 mm (short stroke) all the time. It was believed that if the side guides of the previous few coilers were kept closed when the strip was going through the last coiler, it would invariably guide the strip head towards the center of the rolling line. Inspired by this logic, when the last coiler was made ready for coiling, the previous coilers' side guides were set at a value of strip width + 80 (short stroke) + 60 mm. Once coiling started in the last coiler, the side guides of the previous few coilers were opened fully. It was observed that this new setting of guides helped in keeping cambered bars onto the center of the rolling line. For the coilers that are not in operation, the position of the side guide is fully opened. In the instant invention, the position of the side guide of the previous few and preferably two coilers was adjusted, when the last coiler was made ready for the strip coiling. The side guides of the previous coilers were set at a position of strip width + 80mm + 60mm when the last coiler was the pre-determined coiler. As soon as the coiling begins in the last coiler, the side guides of the previous coilers were opened fully. After observing rolling of the thinner gauge strips, it was observed that the two problems: (a) flying of the head of the strip, and (b) deviation of the head of the strip from the center of the rolling line; 6 could be effectively eliminated. Thus, the furthest situated coiler could be used for rolling of thinner gauges having thickness of less than 2.5 mm, or more preferably less than 2 mm, or still more preferably less than about 1.5 mm at all mill speeds. This leads to an increase in the yield of the mill in terms of the number of coils and tonnage. Thus, according to the present invention, the improved system for coiling a metallic strip comprises: (a) at least a run out roller table for carrying the strip from the finishing mill to the coiler; (b) at least a pinch roll unit comprising at least a pair of pinch rollers provided to serve for guiding the strip head when it enters the coiler and for generating the strip tension required for the coiling operation wherein the said top roll and the bottom roll may optionally be driven separately and the said rolls being raised and lowered separately by two hydraulic cylinders; (c) at least one coiler provided to hold the coiled strip; (d) at least a side guide provided to serve for precentering as well as lateral guiding of the strip in order to ensure that the coil is wound with flush edges; and (e) at least an improved strip switch for guiding the strip to the mandrel at the corresponding down coiler or to a down coiler arranged behind the related coiler, the said strip switch being closed until the coiler is selected and made ready for the incoming strip. The improved switch comprises a plurality of wedges, made of an abrasion resistant durable material, which are welded equidistant from each other along the whole length of the strip switch. Thus, using the coiling system of the present invention, aluminium or steel strips having thickness below 1.5 mm can be coiled at speeds of over 10 m/s, preferably over 10.5 m/s, more preferably over 11 m/s and most preferably over 12 m/s without causing any cobbles in the said strips. 7 Reference is now drawn to Figure 1, which shows the relative position of the finishing mill and coilers. 11 and 12 refer to the last two finishing stands, which comprise the finishing line. c 21, 22, 23 and 24 refer to the coilers, wherein 21 is the first coiler and 24 is the last coiler. 3 refers to the runout roller tables or the rolling line. Reference is specifically drawn to the strip switch arrangement 31 which has been provided in every coiler and which is inclined at an angle of 45° with the rolling line. The metallic strip leaves the finishing mills 11 and 12, travels through the run out roller table 3 to get wound up on any of the down coilers 21 to 24. Reference is now drawn to Figure 2 which shows the pinch rolls and the strip switch arrangement 31.41 and 42 refer to the top and bottom pinch rolls respectively and 51 refers to the area, which is known as the trough. The presence of this trough causes the strip head to fly resulting into cobbles. Reference is now drawn to Figure 3, which shows the detailed plan and shape of the wedge. In the most preferred embodiment of the invention, the top view has a cross-section of 20 by 260 mm. B shows the side view of the wedge and C shows the AA view or the front view having a cross-section of 20 by 63 mm. Reference is now drawn to Figure 4, which shows the top view of the strip switch and mounting of the wedges on it. 31 refers to the strip switch and 2 refers to the five number of wedges mounted on it. Reference is now drawn to Figure 5, which shows the side view of the strip switch and the wedge mounted over it. 41 and 42 refer to the top and bottom pinch rolls respectively. 31 refers to the strip switch and 2 refers to the wedge. This figure illustrates how the trough has been effectively eliminated by mounting a plurality of wedges on the strip switch. The various terms used within this specification shall be construed to include the meanings as follows: "Run Out Roller Tables" consists of table rollers arranges after the last finishing stand until the coiler. It serves the purpose of carrying the strip from the finishing mill to the coiler. 8 "Side Guide" are arranged in front of the pinch roll unit, which can be shifted crosswise to the direction of rolling. The guides serve for precentering as well as lateral guiding of the strip in order to ensure that the coil is wound with flush edges. "Pinch Roll Unit" is arranged in front of down coiler. The pinch roll unit is provided to serve for guiding the strip head when it enters the coiler and for generating the strip tension required for the coiling operation. The top roll and the bottom roll are driven separately. The roll can be raised and lowered separately by two hydraulic cylinders. "Strip Switch" is arranged behind the pinch roll unit and is used for guiding the strip to the mandrel at the corresponding down coiler or to a down coiler arranged behind the related coiler. After the coiling of a strip is finished, the strip switch is closed until the coiler is selected and made ready for the next strip. "Set Gap" means the strip width plus the extra opening of the side guides. This extra opening is also referred to as the short stroke of the guides. The set gap depends on the width of the strip and may vary from strip to strip. Although the invention has been described as applied to the production and coiling of hot rolled steel strip, as one of the immediate applications of the invention, it will be evident to those skilled in the art that in its broader aspects, it can be utilized and provide advantages in other similar applications of industrial processes, for example in the production of aluminum strip. All such modifications and variations are intended to be within the scope and ambit of the present invention. 9 We claim: 1. In a hot strip mill, an improved system for coiling a metal strip as they are delivered to a coiler from a finishing mill, said improved system comprising: (a) at least a runout roller table for carrying the strip from the finishing mill to the coiler; (b) at least pinch roll unit comprising at least a pair of pinch rollers provided to serve for guiding the strip head when it enters the coiler and for generating the strip tension required for the coiling operation wherein the said top roll and the bottom roll are driven separately and the said rolls being raised and lowered separately by two hydraulic cylinders; (c) at least one coiler mandrel provided to hold the coiled strip; (d) at least two side guides provided to serve for precentering as well as lateral guiding of the strip in order to ensure that the coil is wound with flush edges; (e) at least a strip switch for guiding the strip to the mandrel at the corresponding down coiler or to a down coiler arranged behind the related coiler, the said strip switch being closed until the coiler is selected and made ready for the incoming strip, characterized in that the said strip switch comprises a number of wedges, welded equidistant from each other along the whole length of the strip switch to minimize the trough created below the pinch rolls of coilers. 2. A coiler system as claimed in claim 1, wherein the wedges are made up of an abrasion resistant durable C 45 material. 3. A coiler system as claimed in claim 1, wherein the short stroke is about 80 mm. 4. A coiler system for thin strip, as claimed in any of the preceding claims, wherein said strip has a thickness of less than about 2.5 mm. 10 5. A coiler system for thin strip, as claimed in claim 1, wherein said strip has a thickness of less than about 2 mm. 6. A coiler system for thin strip, as claimed in claim 1, wherein said strip has a thickness of less than about 1.5 mm. 7. A coiler system for thin strip as claimed in any of the preceding claims, wherein said strip is a steel strip. 8. A coiler system for thin strip as claimed in any of the preceding claims, wherein said strip is an aluminium strip. 9. A coiler system for thin strip as claimed in any of the preceding claims, wherein said strip is wound up into a coiler at a speed of over 10 m/s. 10. A coiler system for thin strip as claimed in any of the preceding claims, wherein said strip is wound up into a coiler at a speed of over 10.5 m/s. 11. A coiler system for thin strip as claimed in any of the preceding claims, wherein said strip is wound up into a coiler at a speed of over 11 m/s. 12. A coiler system for thin strip as claimed in any of the preceding claims, wherein said strip is wound up into a coiler at a speed of over 12 m/s. 13. An improved strip switch as claimed in claim 1, wherein between 1 and 9 number of wedges are welded equidistant from each other along the whole length of the strip switch. 11 14.An improved switch as claimed in claim 13, wherein between 3 and 7 number of wedges are welded equidistant from each other along the whole length of the strip switch. 15. An improves switch as claimed in claim 13, wherein five number of wedges are welded equidistant from each other along the whole length of the strip switch. 16. A coiler system as claimed in any of claims 1 to 15, wherein once the last coiler is ready for coiling the strip, the side guides of the penultimate and the coiler before the penultimate are set at fully open position and the side guide of the first coiler is set at a value of strip width + short stroke + 60mm throughout the coiling stage. 17. A coiler system substantially as herein described and illustrated with reference to the accompanying figures. A coiling system for thin metallic strip which avoids problems of the strip head flying and deviating from the center of the rolling line, and thus provides an easy and cost-effective method to avoid cobbling of said strips during coiling process thereby decreasing operational delays and increasing productivity of a thin gauge hot rolling metallic strip mill, particularly steel strip mill. The improved coiling system comprises of a plurality of wedges, made up of an abrasion resistant frictionless material, welded equidistant from each other along the whole length of the strip switch (31) to minimize the troughs (51) below the pinch rolls (41 & 42) of coilers thereby minimizing simultaneously flying of the head of the strip and the subsequent formation of cobbles.

Documents:

00758-kol-2004-abstract.pdf

00758-kol-2004-claims.pdf

00758-kol-2004-correspondence.pdf

00758-kol-2004-description(complete).pdf

00758-kol-2004-drawings.pdf

00758-kol-2004-form-1.pdf

00758-kol-2004-form-18.pdf

00758-kol-2004-form-2.pdf

00758-kol-2004-form-3.pdf

00758-kol-2004-letters patent.pdf

00758-kol-2004-p.a.pdf