Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/16—Controlling or regulating processes or operations
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
  • B22D11/0637—Accessories therefor
  • B22D11/0648—Casting surfaces
  • B22D11/066—Side dams
  • B22D11/0662—Side dams having electromagnetic confining means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/10—Supplying or treating molten metal
  • B22D11/11—Treating the molten metal
  • B22D11/114—Treating the molten metal by using agitating or vibrating means
  • B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields

Definitions

• Steel sheet thickness reduction is accomplished by a rolling mill which is very capital intensive and consumes large amounts of energy.
• the rolling process is very capital intensive and consumes large amounts of energy.
• SUBSTITUTE SHEET therefore contributes substantially to the cost of the steel sheet.
• a 10 inch thick steel slab must be manipulated by at least ten rolling machines to reduce its thickness.
• the rolling mill may extend as much as one-half mile and cost as much as $500 million.
• the rollers are made from a metal with high thermal conductivity, such as copper or copper alloys, and water-cooled in order to solidify the skin of the molten metal before it leaves the gap between the rollers.
• the metal leaves the rollers in the form of a strip or sheet.
• This sheet can be further cooled by water or other suitable means via jets.
• This method has the drawback that the mechanical seals used to con ⁇ tain the molten metal at the roller edges are in physical contact with both the rotating rollers and molten metal and therefore subject to water, leaking, clogging, freezing and large thermal gradients. Furthermore, contact between the mechanical seals and the solidifying metal can cause irregularities along the edges of sheets cast in this manner thereby offsetting the advantages of the roller method. Accordingly, it is an object of the present inven ⁇ tion to provide an improved method and arrangement for casting thin metal sheets.
• a still further object of the present invention is to produce thin metal sheets using less energy.
• Still another object of the present invention is to produce a metal product having good metallurgical properties and surface characteristics as it leaves the caster. Another object of this invention is to provide for continuous roller casting of metal sheets.
• An additional object of the present invention is to electromagnetically cast metal sheets with a minimum of electromagnetic heating of the molten and solid metal.
• Another object of the present invention is to provide a system and method which is particularly adapted for the continuous casting of thin sheets of steel.
• the present invention provides for confinement of molten metal with a horizontal alternating magnetic field.
• this invention employs a magnet that can produce a horizontal alternating magnetic field to confine a molten metal at the edges of parallel horizontal rollers as a solid metal sheet is cast by counter-rotation of the rollers.
• Figure 3 is a view along section line 3-3' of Figure la.
• Figure 4 is a cross sectional view of the core as depicted along section line 4-4' of Figure 2.
• Figure 5 is a perspective view of the magnet and coil of one embodiment of this invention.
• Figure 6 is a perspective view of another embodiment of the magnet and coil of this invention.
• Figure 7 is a cross section of the yoke as depicted in Figure 6.
• Figure 8 is a perspective view of another embodiment of the magnet core of this invention.
• Figure 9 is a front sectional vertical front view of another embodiment of this invention.
• Figure 12a is a front view of a portion of another embodiment of the roller rim of this invention.
• Figure 12b is a top view of the embodiment of the roller rim of this invention as depicted in Figure 12a.
• Figure 13a is a view of a portion of a roller showing another embodiment of the roller rim of this invention.
• Figure 13b is a sectional view along line 13b-13b' of Figure 10.
• Figure 14 is a side view of another embodiment of this invention.
• SUBSTITUTE SHEET Figure 15a is a side view of still another embodi ⁇ ment of this invention.
• Figure 15b is a horizontal view along line 15b- 15b' of Figure 15a.
• the present invention overcomes the problems of roller casting with a novel design which features electromagnetic containment of the liquid metal at the roller edges in place of mechanical seals thereby overcoming the problems associated with mechanical seals.
• the present invention provides a shaped hori ⁇ zontal alternating magnetic field to confine a pool of molten metal between the cylindrical surfaces of a pair of rollers as the molten metal is cast into a thin vertical sheet by counter rotation of the rollers which force the molten metal between them.
• the horizontal alternating magnetic field of the present invention can also be used to prevent or regulate the flow of molten metal from weirs or orifices of other geometries.
• the pressure, p, exerted by the molten pool of metal consists essentially of ferrostatic pressure p n and pressure p r induced by the rollers via the solidifying metal to be cast
• the magnetic pressure, p m exerted by the horizontal alternating magnetic field, B, must balance the pressure from the top of the metal pool to the region where the shell of the metal has solidified sufficiently thick to withstand the pressure.
• the magnetic pressure is given by
• the ferrostati ⁇ pressure Ph exerted by the molten pool of metal increases linearly with increasing down ⁇ ward distance h from the surface of the pool
• the roller induced pressure p r depends on the pro ⁇ perties of the metal being cast, the roller diameter and speed and the thickness of the metal strip or sheet being cast. In case of steel sheets, it is estimated that p r can be many times larger than the hydrostatic pressure pj--,.
• Figure la depicts a cross sectional view of the roller casting arrangement of the present invention.
• a pair of rollers 10a and 10b (referred to collectively as rollers 10) are parallel and adjacent to each other and lie in a horizontal plane so that a molten metal 12 can be contained between them above the point where the rollers are closest together.
• Rollers 10 are separated by a gap, d (shown in Figure 2).
• Counter rotation of rollers 10a and 10b (in the direction shown by the arrows 11a and lib) , operating with gravity, forces the molten metal 12 to flow through the gap d between the rollers 10 and out the bottom.
• Magnetic poles 16a and 16b located on both sides of the gap d between rollers 10a and 10b generate an alternating magnetic field which exerts an electromagnetic inward force that prevents the molten liquid 12 from flowing out the sides at the edges of the rollers 10a and 10b.
• references will be made to confinement at one end of a pair of rollers. It should be understood that confinement of molten metal between a pair of counter rotating rollers as provided by the present invention will be used at both ends of the pair of rollers.
• Coils 28a and 28b wind around the magnet.
• Coils 28a and 28b carry an electric current supplied by an alternating current source thereby magnetizing the magnet 24 and inducing a magnetic field between poles 16a and 16b.
• the major portions of magnetic poles 16a and 16b are located inside the outer edges 30a and 30b of the rollers.
• the magnetic poles 16a and 16b are stationary and radially separated from the rollers 10a and 10b by a space clearance large enough to allow free rotation of the rollers 10.
• the poles 16 extend axially into the ends of the rollers 10 a short distance.
• the rollers 10 also have outer rims 34a and 34b which form extensions of middle portions 32 of rollers 10.
• Rims 34 are located in the area between the mag ⁇ netic poles 16. Poles 16 generate a magnetic field that penetrates through the rims 34 of rollers 10 in this embodiment. Therefore, for this embodiment rims 34 must be made of a material suitable for the transmis- sion of a magnetic field. In this embodiment of the present invention, the rims are made of stainless steel.
• Figure 3 there is depicted a hori ⁇ zontal cross section of the present invention as viewed along section line 3-3' of Figure la.
• Figure 3 depicts a section between the rollers at a point displaced vertically from the horizontal axes of the rollers 10.
• Figure 3 shows containment of the molten metal 12 by the rollers 10 and the interaction of magnetic field, B, and eddy currents i.
• Figure 3 depicts rollers 10 having middle portion 32 and rims 34.
• the magnet 24 having a yoke 26, poles 16 coil 28 and shield 33.
• the magnet 42 has a square shaped core 44 connecting poles 46a and 46b. Poles 46a and 46b in this embodiment have shaped pole faces 48a and 48b but squared off backs 50 to con ⁇ form to the square shape of the core 44. As illustrated by the cutaway view of pole 46b, an insulated copper shield 51 encloses the core to reduce leakage flux. A gap 52 in the shield 51 prevents the shield from being a shorted turn around the magnet core.
• Coil 60 encircles core 44 and shield 51. In this embodiment, the coil 60 is a single layer coil instead of a coil pair as in the previous embodiment.
• FIG. 9 A further modification to the magnet is depicted in Figure 9.
• a molten liquid 12 is being cast into a sheet 18 between rollers 10.
• magnet poles 59a and 59b confine the molten metal at the edges of the rollers 10.
• the magnetic poles 59 are adjustable in position.
• the poles 59a and 59b can be slanted and moved to be closer to or further away from the roller rims. This feature enables adjustment of the magnetic field.
• the upper parts of the poles 59 have been moved further away from the roller rims as compared to the bottom part of the poles.
• the magnetic field can be made relatively stronger near the lower end and weaker at the higher end as compared to the pole configuration shown in Figure la. This adjustability can be utilized for casting metal sheets of different thickness where different forces of confinement may be necessary.
• FIG. 10 shows still another variation of the magnet in the present invention. This variation offers the most flexibility of any of the designs shown so far. (Figure 10 depicts just one magnet pole; it should be understood that an identical pole would be positioned opposite this pole in the other roller.)
• each magnet pole is divided into three discreet separate magnetic elements 61a, 61b, and 61c.
• Each of these elements is an independent magnet comprising cores 62, excitation coils 63, and eddy-current- shields 33, which enclose their respective coils and cores, except for an air gap which prevents the shields from becoming a shorted turn such as depicted in Figures 4 or 7.
• Magnetic element 61a contains the upper portion of the sidewall of the molten metal pool 12
• element 61b contains the center of the pool sidewall
• element 61c contains the lower portion of the pool sidewall.
• sensors may take the form of discreet beams (rays) that are transmitted parallel to the sidewall from one side and detected by a receiver on the other side (the beam being interrupted when the sidewall moves closer to the magnet) .
• the sensors may take the form of
• SUBSTITUTE SHEET discreet beams that are transmitted normal to the side- wall and their reflection from the surface of the side- wall being detected by a receiver and used to determine the position of the sidewall.
• the sensors may take the form of variable capacitors where the monitored sidewall portion is one electrode of the capacitor and the other is a suitable electrode mounted a fixed distance and in parallel to the sidewall.
• the sensor may take the form of an impedance measurement of the magnet excitation which changes with the flux linkage between the magnet and the liquid metal of the respective sidewall portion.
• Figure 11 depicts a horizontal sectional view of one end of one roller pair.
• the pole assemblies 66a and 66b are hoop- shaped and contained inside and attached to the rollers 10a and 10b behind rims 34a and 34b, respectively. Accordingly, poles 66 will rotate with rims 34 and rollers 10.
• Portion 68 of shield 69 is located between core sections 72a and 72b and close to the area where the casting takes place.
• Poles 66a and 66b are circular and made of a ferromagnetic material.
• the coil 60 magnetizes yoke 70 and magnet arms 72a and 72b as in the previous embodiments.
• Eddy current shields 69 and 79 confine the magnetic flux to the yoke 70, magnet arms 72 and poles 66 (reducing leakage flux) as described earlier. Shields 69 and 79 may also incorporate heat shielding or cooling means to protect the coil or the magnet. Poles 66a and 66b though separated from magnet arms 72a and 72b and rotating with rollers 10a and 10b, are magnetized by their close proximity to arms 72a and 72b via relatively small gaps 74a and 74b. This embodi ⁇ ment has the advantage that the poles can be located as close together as physically possible, i.e. inside the rims.
• This design simplifies the shape of the magnet yoke and permits the use of different magnet yokes and coils when the assembly of rollers 10 and poles 66 is used to cast different thicknesses of metal sheets. Casting sheets, i.e. 0.4" thick would utilize a more powerful magnet assembly than casting 0.04" thick metal sheets.
• the magnetic field penetrates through the outer rim portion of the rollers to confine the molten metal.
• the present invention can also be practiced without a special rim portion provided a suitable material is used for the rollers, such as a ceramic, which enables penetration by a magnetic field without generating eddy currents in the roller.
• a rim portion on the rollers provides for shaping the magnetic field by establishing a well defined transition from the area of a high magnetic flux near the edge of the roller to an area of low magnetic flux further away from the roller's edge. Shaping the magnetic field in this manner provides the advantages of better control of the magnetic field that contains the sidewall of the molten pool of metal.
• the present invention provides for shaping the magnetic field by using a material with a low resistivity, such as copper or copper alloy, for the main portion of the roller and a material with a higher resistivity for the rim portion.
• a material with a low resistivity such as copper or copper alloy
• the copper or copper alloy used for the main portion will effectively prevent penetration of the magnetic field (except for a small negligible skin layer on the surface) and will, at the same time, cool the molten metal efficiently causing it to solidify.
• the present invention includes several different embodiments of the rim portion designed to allow penetration of the magnetic field. In one embodiment, this is accomplished by connecting a rim made of a material with a much higher resistivity, such as stainless steel, to the edges of the copper rollers.
• TE SHEET Figures 2, 3 and 11 depict stainless steel rims 34 of this type.
• the stainless steel rims may be connected to the copper rollers by brazing, bolting or other suitable methods.
• the stainless steel rims provide a smooth surface for the casting surface in case the molten metal encroaches on the rim.
• the roller 80 is made of a low resistivity material such as copper.
• a plurality of slots 82 all the way through the roller.
• the slots 82 extend a short distance, s, in the axial direction of the roller.
• the slots 82 permit the magnetic flux in the edge portion, or rims of the rollers, defined by the slots.
• the slots can be left empty, it is preferred that the slots be filled with a material of relatively high resistivity such as ceramic or stainless steel, which is insulated from the sides of the slots, or filled with a material of high magnetic permeability.
• Figure 13a is a horizontal cross section along line 13b-13b' of figure 10.
• the water-cooled rollers 10 are made of high thermal conductivity material such as copper.
• At the edges and around the circumference of the rollers are one or more hoop-shaped extensions 91 of rollers 10.
• hoop-shaped extensions 91 Arranged between these hoop-shaped extensions 91 are similar hoop-shaped members 92 made of copper. These hoops, 91 and 92, are insulated from each other and mounted to the rollers 10 with bolts 93.
• the bolts 93 are insulated from the hoops to prevent electrical contact between the individual hoops and between the hoops and the roller.
• the hoop-shaped extensions 91 serve the same purpose as the slots 82 in the previous embodiment, i.e. to transmit the magnetic field to the confinement region.
• Extensions 91 can be made of similar materials as slots 82. Extensions 91 can be
• SUBSTITUTE SHEET made of an insulating material, such as ceramic, having a high resistivity and relatively low permeability and, therefore, no eddy currents.
• Extensions 91 can be made of a non-magnetic, high resistively metal, such as stainless steel, which also has relatively low perme ⁇ ability, but has higher thermal conductivity than ceramic.
• extensions 91 can be made of a magnetic material, such as silicon steel, which has high magnetic permeability and reasonable thermal conductivity. With a high permeability material the hoop-shaped extensions themselves become magnetized. Thin insulated laminations of a ferromagnetic material could be used.
• each hoop should be insulated from adjacent copper hoops.
• the alternating flux emanating from the magnet pole penetrates the roller through the hoops 91 and through the skin depth of the copper hoops 92. A portion of this flux induces eddy currents in the molten metal 12 between the rollers.
• the interaction between the flux and the eddy currents in the molten metal contains the sidewall of the molten metal pool between the rollers as described before.
• Figure 14 Another embodiment of this invention is shown in Figure 14. This embodiment of the invention may be used where conditions are such that the edge of the cast metal sheet is not fully solidified by the time it exits from between the rollers. This condition may occur for a number of reasons dictated by the casting process, such as the need for high magnetic fields of relatively high frequency resulting in large eddy current heating of the edges of the metal being cast, insufficient cooling effect of the rollers near the edges, thick cast sheet dimensions, or a combination of these or other factors.
• Figure 14 depicts the rollers 10 and molten metal 12 as in previous embodiments.
• Figure 14 also shows poles 95a and 95b which extend below the center line of rollers 10.
• FIG. 15a and 15b Another embodiment of this invention is depicted in Figures 15a and 15b.
• This embodiment presents a combination of a magnetic and mechanical means to contain a molten metal at the edges of a roller casting system.
• the problem of using mechanical seals to contain a molten metal at the edges of counter-rotating casting rollers was that the mixture of the molten and solidifying metal in combination with the rotation of the rollers would clog up around the mechanical seals.
• the present invention shows how a magnetic field can be used to contain the sidewalls of the molten metal. The present
• Magnetic confinement with the poles 16 is used to confine the molten and solidifying metal in the gaps between the mechanical dam 100 and rollers 10.
• Mechanical dam 100 may be made of a ferromagnetic material 101 so that it provides a low reluctance path for the flux between the poles 16.
• the side of the dam facing the molten metal pool may be made of a layer of high temperature ceramic 102 covering a water cooled heat shield 103 in front of the high permeability material which may be made from steel laminations or from high temperature ferrite.
• This embodiment has the advantage of requiring less energy than the previous embodiments because the magnetic field along the molten metal extends only over the gaps between the rollers 16 and mechanical dam 100. Also, because the volume of the molten metal contained by the magnetic field is smaller, there is less heating of the molten metal due to eddy currents.
• Various mechanical dam shapes can be designed for shaping flux density suitable for different casting requirements.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Continuous Casting (AREA)
• Water Treatment By Electricity Or Magnetism (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Treatment Of Steel In Its Molten State (AREA)

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• 1988
  • 1988-11-17 US US07/272,353 patent/US4936374A/en not_active Expired - Lifetime
• 1990
  • 1990-06-07 AU AU58426/90A patent/AU655403B2/en not_active Ceased
  • 1990-06-07 RU RU92016326/02A patent/RU2087248C1/ru not_active IP Right Cessation
  • 1990-06-07 WO PCT/US1990/003243 patent/WO1991018696A1/en active IP Right Grant
  • 1990-06-07 US US07/952,519 patent/US5385201A/en not_active Expired - Fee Related
  • 1990-06-07 JP JP2509097A patent/JPH07115135B2/ja not_active Expired - Fee Related
  • 1990-06-07 DE DE69032562T patent/DE69032562T3/de not_active Expired - Fee Related
  • 1990-06-07 UA UA93002437A patent/UA24014C2/uk unknown
  • 1990-06-07 EP EP90910039A patent/EP0531286B2/en not_active Expired - Lifetime
  • 1990-06-07 BR BR909008029A patent/BR9008029A/pt not_active IP Right Cessation
  • 1990-06-07 KR KR1019920703117A patent/KR960015335B1/ko not_active Expired - Fee Related
• 1992
  • 1992-12-03 NO NO924661A patent/NO304140B1/no unknown

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