Apparatus for slag removal during metal processing

A skimmer (100) for removing a slag layer (24) from hot metal (6) in a ladle (2) during a process of metal purification such as steelmaking. The improved skimmer (100) is a steel framework covered in reinforced refractory, having a system of internal piping (60) that at one end is attached to a source of gas and at a second end terminating at one or more ports (64). The improved skimmer (100) is attached to a boom for a prior art skimming machine. In use, the improved skimmer (100) is moved along a top surface (6a) of the hot metal, though the slag layer, and predetermined flows of gas are forced into the piping system and expelled through the port or ports to move the slag layer out from the back of ladle so it can be skimmed into a slag pot (4).

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NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

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INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC OR AS A TEXT FILE VIA THE EFS WEB SYSTEM

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BACKGROUND OF THE INVENTION

Field of the Invention

The present invention pertains to the field of steelmaking. More particularly, the present invention pertains to an improved apparatus configured as an improved skimmer paddle for separating slag from a quantity of desired molten metal during the steelmaking process.

Background Art

The present invention relates to removal of slag from the surface of a quantity of molten metal after the metal has been treated in a ladle. Efficient removal of slag reduces production costs, and improves yield and steel quality. Slag is a waste product formed during the steelmaking process that separates and floats to the surface of the molten metal, where it can be removed by skimming the surface of the molten metal, to scrape the slag off into a slag pot or other waste collection container. Under normal circumstances, when skimming, a small portion of the slag will be inaccessible to the skimmer paddle and scattered along the surface of the molten metal. Consequently the remaining slag will be very difficult to remove. The most popular method for moving the slag into a position where it can be skimmed from the ladle is by installing a bubbling system. Typically, the bubbling system consists of a motor driven “bubbler”, a refractory encased pipe “bubbling lance” (i.e. a pipe encased in a heat-resistant material) inserted into the hot metal in the back portion of the ladle. The refractory coating on the bubbler pipe keeps the pipe from melting due to the temperature of the hot metal. Gas is injected through the pipe and into the hot metal causing turbulence, which tends to push the remaining slag away from the back of the ladle and gather into a position where the skimming paddle can reach it. At this point the skimmer paddle, a hoe-type apparatus, can reach the re-positioned slag and skim it off of the surface of the hot metal and into the slag pot.

The prior art describes an apparatus for efficient slag removal using a paddle and a separate bubbling system in U.S. Pat. No. 5,360,204 (Mancuso). While highly effective, the Mancuso bubbling system requires a motorized hoist to raise and lower the pipe as well as the devices required to start and stop gas flow. The hoist arm in particular is expensive and many steelmakers balk at the extra cost of this permanent equipment. Additionally, the system described in Mancuso requires additional space around the skimming area which in many instances may not be readily available, thus limiting the applicability of the Mancuso system.

The bubbler pipe and the skimming paddle are both consumables used during the steelmaking process, requiring regular replacement as they become damaged by repeated exposures to the hot molten metal. Thus having both a bubbler and a paddle increases production costs, further deterring steelmakers from investing in the bubbler system, despite increased yield and efficiency in slag removal. Steelmaking is a highly competitive industry, and unfortunately better systems such as Mancuso's are unattractive due to increased cost and space requirement. Thus many steelmaking mills lack a bubbler system, and rely only on the skimming process despite being less efficient. Skimmers are mainly used in the process of making iron, but can be utilized for other skimming processes involving molten metal.

What is needed is an improved skimmer that removes slag more efficiently and improves yield, all at a lower the cost for steelmakers as well as requiring no additional space.

What is also needed is an improved method of removing slag using the improved skimmer.

BRIEF SUMMARY OF THE INVENTION

In a first aspect, the invention is an improved skimmer for use with a boom of a skimming machine for removing a quantity of slag from a quantity of hot metal contained in a ladle, the improved skimmer comprising a steel framework having a front face, a piping system housed inside the framework comprised of at least one pipe having a gas intake end and a gas output end terminating in a port disposed as a gas-permeable structure formed in at least the front wall, and means for attaching the improved skimmer to the boom of the skimming machine. The steel framework is coated in reinforced refractory.

In a second aspect of the invention, the improved skimmer is further comprised of a first side wall and a second side wall, the side walls affixed to opposed sides of the front wall, and each side wall angled below a horizontal plane of the front wall at a predetermined angle such that the steel framework is convex-shaped.

In yet a third aspect of the invention, the steel framework of the improved skimmer is greater than three quarters of an inch thick.

In yet a fourth aspect of the invention, the at least one port of the improved skimmer is positioned in an uppermost third portion of the front face.

DRAWINGS LIST OF REFERENCE NUMERALS

The following is a list of reference labels used in the drawings to label components of different embodiments of the invention, and the names of the indicated components.2ladle4slag pot6quantity of hot metal or molten metal6atop surface or surface of hot metal8ladle spout11gas bubbles20skimming machine boom or arm22skimming paddle24slag32bubbler or bubbler lance50front wall or front face52first side wall54second side wall56refractory coating58framework or support structure60piping system62internal piping64port66gas fitting68hose reel (connects to gas supply)70high temperature hose100apparatus or improved skimmer paddle110method of removing slag using an improved skimmer120initiate low flow gas122tilt ladle until molten metal appears124position skimmer over ladle126skim slag into slag pot128when heaviest slag has been removed from the ladle130liquid and small chunky slag remains132place skimmer paddle toward back wall of ladle134lower skimmer paddle into the molten metal136initiate high flow gas138slag moves towards spout140skim remaining slag until surface is clean142park skimmer paddle144determine if slag pot is full146replace full slag pot with empty pot

Glossary of Important Terms

High flow of gas: 100-500 SCFM

Hot metal or molten metal: metal heated to a temperature such that the metal is in a liquid state, and includes metals commonly purified in a ladle such as steel and iron

Improved skimmer or skimmer paddle or apparatus: an apparatus having combined bubbler and skimmer paddle features in a single contained unit

Low flow of gas: 10-400 SCFM

Surface of hot metal or hot metal surface: uppermost or top surface of a quantity of metal.

DETAILED DESCRIPTION

An apparatus or improved skimmer100is shown inFIGS. 5a-d, and an improved method110of removing slag using the improved skimmer is shown inFIGS. 6-11. Turning to the Figures, the improved skimmer100is a skimmer paddle comprised of a plate of steel approximately three quarters to one inch in thickness, disposed as a welded steel framework58coated in reinforced refractory56. The steel thickness and refractory coating56are required to keep the improved skimmer100from melting into the hot metal6while the skimming process is underway. A prior art paddle22is typically ¾ inch thick. The weight of the welded framework58and refractory coating56is comparable to the weight of the steel plate originally used for the prior art paddle22, and thus a (prior art) skimming machine can support the weight of the improved skimmer while moving back and forth and side to side while skimming, despite the extra thickness. This is important, as it means existing equipment can be used with the improved skimmer100.

The welded framework58of the improved skimmer100is typically disposed with a flattened front wall or front face50having two ends, a first end having a first side wall52and an opposed end having a second side wall54, the first and second side walls angled at approximately 45 degrees from the vertical away from the front wall50to create a multi-faceted paddle that in a front view (FIG. 5b), the three walls comprised of the front face50and the first and second side walls5254as a whole resemble a portion of a convex octagon. In some other embodiments (not shown) the front wall and the side walls are disposed as a smooth convex paddle when viewed in a front view.

A piping system60having internal piping62is included within the refractory enclosing the welded framework, the piping62having a gas connection fitting66at one end through which a source of gas is introduced via a gas line70and a hose reel68attached to a source of gas (not shown) and at another end, the piping62terminating in a series of ports64formed in the front wall50and the side walls5254.

The ports64are positioned on the front face and on the first and second side walls in a first embodiment, shown inFIGS. 5a-b, and in a second embodiment, shown inFIG. 5c-d, the ports64are positioned on the front face only. Ports64are gas-permeable structures, including porous plugs, nozzles, and pipes formed into the front face and in the first embodiment, side walls of the improved skimmer, and can be as simple as through-bores or more complex such as through-bores fitted with gas permeable plugs such as porous plugs or nozzles to prevent the hot metal from entering the ports and clogging them. In both first and second embodiments, the ports64are positioned so as to be generally in a one third uppermost portion of the welded framework of the improved skimmer100. During a first skimming process (FIGS. 6-8, 11) the port or ports64are located above a surface of the hot metal6a, and are purged with a low flow of gas, to prevent the hot metal from flowing into and plugging the ports64during the skimming process.

The method of using the improved skimmer110is described in flow diagram labelledFIG. 11, as well as in the top and elevation views inFIGS. 6-10. To remove slag from hot metal, the first skimming process begins by an operator initiating the low flow of gas120, ranging between 10-400 SCFM into the piping system. The ladle is tilted122until the hot metal6appears at an edge of the spout. The operator positions124the improved skimmer over the ladle and then using the improved skimmer, skims126slag into the slag pot. When the heaviest slag has been removed128from the ladle, the operator observes the ladle contents. If liquid and small chunky slag remains130, a second skimming process is initiated, where the improved skimmer is placed132towards the back wall of the ladle and then lowered134into the hot metal either less than 3 inches from the top surface6aor more than 3 inches from the top surface6a, as desired by the operator. High flow gas is initiated136for about 10-20 seconds, ranging from 100-500 SCFM. Slag is moved138towards the spout and then skimmed140into the slag pot. If any slag remains, the process132134136138140is repeated until the surface of the hot metal6ais free of slag. The improved skimmer is then parked142and the slag pot inspected144for fullness. If full, the slag pot is replaced146with an empty pot and the skimming cycle ends. If the slag pot is not full, the skimming cycles end and the pot remains waiting for the next skimming cycle.

It should be noted that whether low flow or high flow gas is expelled, gas bubbles11form in the quantity of slag24and help consolidate and move the slag24towards the spout8, where the improved skimmer can then skim the slag layer into the slag pot4. The internal piping system60and gas expelled through the piping replaces the prior art bubbler32and causes a ripple effect on the surface of the hot metal6ato move the quantity of slag24to a position where it can be skimmed off of the surface of the hot metal6a. The prior art bubble system (shown inFIG. 1as the Mancuso patent) is thus not required to move the quantity of slag24. The inventor specifically notes that Mancuso teaches at column 3 lines 21-23 that an end of the bubbler lance32through which gas is expelled is ideally immersed 3 to 20 inches below the surface of the hot metal6a, and in fact into the quantity of hot metal6itself in order to properly move the quantity of slag24.

The improved skimmer100and method110for slag removal as described herein moves the quantity of slag24without using the prior art bubbler32apparatus, in three distinct ways: (1) by forcing gas across a top surface6aof the hot or molten metal (FIG. 7), (2) by forcing gas less than 3 inches below the top surface of the molten metal (FIG. 9) and (3) by forcing gas directly into the quantity of slag itself rather than into the hot metal (FIG. 8). The operator of the improved skimmer, by positioning the ports above the surface of the hot metal, into the slag layer itself, or below the top surface of the hot metal, can thus control how skimming is performed, and therefore choose the most efficient way or ways to remove slag using the improved skimmer. The inventor's method of slag removal using his improved skimmer differs vastly from the method taught by the prior art, which is to introduce gas several inches below the hot metal surface6afor efficient slag movement and removal.

FIG. 11continues to describe a second skimming process, which is an optional process used only when the operator determines that the first skimming process120122124126128is unable to extract a relatively small amount of slag remaining in the ladle, with this second skimming process typically performed at an end of the entire slag removal process. During the second skimming process, the improved skimmer is plunged134below the surface of the hot metal, either less than 3 inches from the surface (FIG. 9) or more than 3 inches from the surface of the hot metal (FIG. 9a) such that the port or ports64are submerged in the hot metal6, and the higher flow gas is expelled through the piping system60, as needed. The second skimming process is also typically used in conjunction with the first skimming process when the quantity of slag24in the ladle is in a liquid state, and the bubbling gas11helps push the slag to the surface of the hot metal6afor removal.

As previously stated, the weight of the welded steel frame and the refractory will be comparable in weight to the prior art skimming paddle22constructed from steel plate. Therefore, no major structural modifications to the operator's existing prior art skimmer machine are necessary. Easy modifications, however, are required in order to use the improved skimmer100. First, a hose reel68with a high temperature hose70must be installed on or through the skimming machine. The hose reel68and the high temperature hose70are necessary to conduct the gas from a gas manifold (not shown) to the piping system60embedded within the refractory material. In addition, a quick disconnect and short section of flexible hose will be required to be installed between the skimming machine and the improved skimmer100. The aforementioned manifold is comprised of regulators and electrically operated valves to control the purge gas as well as the higher velocity gas required to move the quantity of slag24away from the back of the ladle2. Manual and automatic controls will be provided for maintenance purposes as well as for operation by the operator's automation system.

The inventor notes that the improved skimmer and method for using the improved skimmer allow for significant cost reductions and efficiency/quality increases for the mill owner. Steelmaking efficiency is improved without incurring the additional capital equipment cost required by the prior art Mancuso bubbling system, since existing skimming equipment can be used with minor and easy modifications. Since both the bubbler and the skimmer are consumables requiring regular replacement, the improved skimmer and method furnish additional savings to the mill owner, who now neither needs to purchase nor stock an additional consumable item (the bubbler). Additionally, use of the improved skimmer and method for using the improved skimmer increases steel quality, by removing more of the slag impurities, such as sulfur, from the molten metal, and thus reducing reversion of these impurities back into the molten metal.

It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the scope of the present invention.