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
  • B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
• • 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
  • B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
  • B22D11/055—Cooling the moulds

Definitions

• This invention relates to high temperature metal continuous casting machines, and more particularly, to systems for cooling the mold with sprayed coolant fluid and for controlling the extent of expansion and contrac ⁇ tion of the mold during use.
• molten metal is passed through a mold for solidification into a desired shape.
• an outer shell forms and hardens.
• the mold is vertically oriented and as the metal strand continues to solidify, it is bent through an angle of 90 so that it moves horizontally, and it is subsequent cut into individual segments.
• the strand is not bent through the 90 angle but exits the mold horizontally. In both vertical and horizontal machines, the strands are then cut into segments or predetermined lengths.
• the temperature of molten steel is typically 2850 °F, although with certain grades the temperature may be as low as 2600 °F.
• the inven ⁇ tion contemplates the casting of any metal or metal alloy whose liquid temperature exceeds 2600 F.
• the mold which forms the steel strand contains the liquid steel and provides for its initial solidifi ⁇ cation, that is, hardening of the outer shell.
• the solidifying strand is extracted continuously from the bottom of the mold at a rate equal to that of the in ⁇ coming liquid steel at the top, the production rate being determined by the time required for the outer shell to harden sufficiently so as to contain the inner core of liquid steel by the time the strand exits the mold.
• the liquid steel is cooled in almost all present day casting machines by providing a water system which cir ⁇ culates a stream of cooling water around the mold.
• the water enters at the bottom of a pressure-tight vessel which surrounds the mold and travels upwardly in a directi opposite to that of the moving liquid steel.
• the "counter current" water flow has been found to be adequate for heat transfer in continuous steel casting machines.
• Such cooling systems embody a baffle jacket closely surround ⁇ ing the mold, defining an annular space through which the cooling water flows.
• a continuous metal casting machine in which one or more parameters of the spray cooling system are defined and established to maintain the desired mold configuration and in which mold distortion is detected and corrected.
• Applicant has found that by utilizing certain conditions and by modifying other operating conditions as disclosed in prior U.S. patent number 4,494,594 it can accurately control mold expansion and consequently control the quality of the continuously cast strand within the mold. More specifically, applicant»has found that by carefully regulating the coolant directed against a zone in an area extendinq from approximately 25 inches above the meniscus level to approximately 2*. inches below the meniscus level, it can most effectively control the distortion of the mold. In most continuous casting machines for billets, slabs and other shapes, this zone is at a point roughly two to 14 inches below the top of the mold assembly. It is in this meniscus zone that approximately 70% of the heat of the molten metal must be extracted in order to initiate rapid and uniform solidification of the molten metal.
• the maximum allowable mold expansion during casting with respect to surface and subsurface quality of the cast strand is about 0.0755 inch in directions transverse to the longitudinal axis of the mold, with 0.0550 inch being the preferred limit at the meniscus zone. Expansion of up to 0.0755 inch can be tolerated at the mid and lower zones without detrimental effect to the cast strand. If these maximums are exceeded, the cast strand can have: surface cracks, both transverse and longitudinal; subsurface cracks, from 0.025 inch to 1.250 inch below the surface; rhomboidal bulging and other shape deformations; and excessive oscil ⁇ lation mark depths (from 0.007 inch to 0.100 inch) . In addition, excessive mold wear can occur.
• applicant contacts a distortion measuring gauge or gauges to the outside (cooled) surfaces of the mold and monitors the expansion of each face during the casting operation. Expansion- of the mold on any or all desired faces is then controlled within selected limits by selectively adjusting the rate of heat extraction at that face.
• water droplet size in the meniscus zone is maintained in the range of from about 475 microns to about 1450 microns.
• the steam barrier generated by the evaporating spray water must be penetrated by the water droplets in order to effectuate rapid and uni ⁇ form cooling.
• the spray angle exceeds about 100 degrees, the force vector of the water droplets perpen- dicular to the surface of the mold to be cooled at the edges of the spray pattern is not sufficient to penetrate the steam barrier.
• the water droplets will not penetrate the steam barrier when the water pressure at the nozzle is less than 15 psig.
• water droplet size influences the ability of the water spray to penetrate the steam barrier and also the rapidity with which heat extraction occurs, best operating con ⁇ ditions are obtained when droplet sizes are confined to the range set forth above.
• the operator of the casting machine can monitor expansion conditions through ⁇ out the casting process and react accordingly to conditions as they may occur within the mold, making minor or major adjustments to the cooling system as required, thereby influencing the quality of the solidifying strand. It is therefore possible to effect complete control of the solidification process on all continuous casting machines, producing billets, bloom, slabs, rounds or other shapes. Moreover, since the operator can monitor mold expansion, and hence strand and mold contact, he now has the ability to control cast strand and mold contact, mold stresses and elevated surface temperatures of the copper mold and thereby directly and beneficially influence mold wear and/or deterioration.
• the mold In slab casting, the mold consists of plates of copper held together at the corners to form a large cavity between the plates. Since in most cases, a slab has a considerably larger cross-sectional area, greater quantitie of heat must be removed and greater ferrostatic pressures must be contained by the copper mold. In conventional mold systems for slab casting, the above facts require further support systems on the back (cooled) surface of the copper plate. The mechanisms that make this support necessary are substantially the same as encountered in casting smaller (billet and/or bloom) cross sections.
• Fig. 1 is a fragmentary view in longitudinal vertical section of the mold and baffle jacket of a prior art system
• Fig. 2 is a transverse sectional view of the apparatus of figure 1;
• Fig. 3 is a view similar to figure 1, showing diagrammatically the effects of mold expansion relative to the coolant fluid space;
• Fig. 4 is a view similar to figure 2, showing the mold expansion depicted in figure 3;
• Fig. 5 is a view similar to figure 2 of a further form of prior art system in which spacers are used to attempt to control mold copper expansion and thus to alleviate the reduction of the coolant fluid space upon expansion of the mold;
• Fig. 6 is a view similar to figure 4 of the system of figure 5, showing the increased distortion of the mold when spacers are used;
• Fig. 7 is a longitudinal sectional view of a spray cooled mold section of a continuous casting machine incorporating the invention therein;
• Fig. 8 is a transverse sectional view of the system of figure 7;
• Fig. 9 is a somewhat enlarged, schematic view of a portion of a mold and a pair of adjacent spray nozzles, showing the overlap of the adjacent sprays to achieve substantially uniform spray coverage per unit area of the surface being sprayed;
• Fig. 10 is a diagrammatic view in transverse section of a mold in which the expansion of the various areas of the mold is controlled in accordance with the invention;
• Fig. 11 is a transverse sectional view of a portion of a slab mold, showing the manner in which the copper plates are secured together to form the mold;
• Fig. 12 is a view similar to figure 11, showing a back-up support system for the mold of figure 11;
• Fig. 13 is a view similar to figure 11, schemati- cally illustrating the distortion of the slab mold plates caused by temperature and ferrostatic pressures.
• FIG. 1 Prior art systems are depicted generally at 10 and 10', respectively.
• a mold 11 extends concentrically within a baffle jacket
• the slab mold 10' shown in figures 11 through 13 comprises a plurality of plates 16 bolted together to form the slab mold cavity 17.
• a back-up support system 18 is bolted onto the copper plates on both sides of the mold, as shown in figure 12.
• the back-up support system is eliminated and sprays of water are used to control expansion of the plates. For instance, a greater flow of cooling water could be applied in the vicinity of the middle of the mold and a lesser flow applied toward the edges.
• the present invention is represented generally at 20 in figure 7, and comprises a frame 21 in which a copper mold 22 with an open inlet end and an open out ⁇ let end is mounted at the top in registry with a central opening 23 through top wall 24 of the frame.
• the frame 21 may be made of A-36 steel
• the mold tube may be made of DHP-grade copper.
• a stream of molten steel 25 is poured into the mold, at a rate relative to the rate of solidifi ⁇ cation and strand withdrawal, to position the meniscus 25a in the upper region of the mold, i.e. within a range of from about two inches to about 14 inches below the top of the mold.
• the mold is not connected at its bottom end to the bottom 26 of the frame, but instead simply hangs from its upper end - remaining free of connection with the bottom wall 26.
• the lower end of the mold is in alignment with an opening 27 in the bottom wall 26, through which the strand is withdrawn.
• the invention utilizes a plurality of spray pipes 28 spaced around the mold.
• Each pipe 28 carries a plurality of spray nozzles 29 for forming a spray of water as depicted at 30. Water is supplied to the pipes and nozzles by a supply pipe 31.
• the spacing of the nozzles relative to the mold and to each other is essentially the same as set forth in applicant's earlier U.S. patent 4,494,594.
• the selection of nozzle sizes, water flow rate and water (nozzle) pressure are all essentially as set forth in said patent.
• the spray angle is set so that it does not go over about 100°
• the spray overlap is selected so that the spray coverage is uniform through ⁇ out the area being sprayed
• the droplet size of the spray particles is maintained in the range of from about 475 microns to about 1450 microns
• the mold expansion is limited to a maximum of 0.0755 inch per face (0.0550 inch being preferred at the meniscus zone)
• the water pressure is not permitted to go below about 15 psig.
• FIG 9 depicts the spray overlap in accordance with the invention.
• nozzles 29 are adjusted relative to one another and to the mold, taking into consideration the maximum spray angle and the water pressure, so that the central areas C of adjacent sprays just touch one another.
• one or more distortion measuring instruments 32 are associated with the mold to measure the extent of expansion and contraction of the mold during the casting operation.
• these measuring instru ⁇ ments comprise an elongate arm 33 extending into proximity with the mold surface and having a probe or finger 34 projecting from the end thereof and into contact with the outer surface of the mold.
• An indicator 35 is connected with the probe to indicate displacements of the probe and hence the mold surface contacted by the probe.
• the indicator is preferably mounted so as to be readily visible to the operator of the casting machine or linked to a computer for automatic control and adjustment.
• Other types of deflection measuring instru- ments may be used, if desired. By observing the indicator, the operator can ascertain the extent of distortion or expansion of the mold.
• the flow of coolant fluid directed against the mold is controlled. This may be accomplished in a number of ways, including a flow controller 36 which may be man ⁇ ually operated or automatically operated in response to a sensed reading by the indicator (shown at 37 in dot-and-dash lines in figure 7). Further, the spray pipes 28 may be constructed in sections 28a, 28b, etc. , each supplying a number of nozzles 29 and supplied by its own supply pipe 31a, 31b, etc., controlled by a controller 36 ⁇ , 36b, etc. (shown in dot-and-dash lines in figure 7) .
• Nozzles may be positioned to direct coolant fluid directly against the face of the mold, as shown in dot- and-dash lines at 38 in figure 8.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Continuous Casting (AREA)

Applications Claiming Priority (1)

Publications (1)

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• 1985
  • 1985-04-03 JP JP60501381A patent/JPS62502389A/ja active Pending
  • 1985-04-03 EP EP85901874A patent/EP0216764A1/en not_active Withdrawn
  • 1985-04-03 WO PCT/US1985/000562 patent/WO1986005724A1/en unknown
• 1986
  • 1986-04-01 CA CA000505594A patent/CA1270364A/en not_active Expired
  • 1986-04-03 ES ES553710A patent/ES8701552A1/es not_active Expired
  • 1986-04-03 IT IT83341/86A patent/IT1204234B/it active
  • 1986-04-03 CN CN86102328.5A patent/CN1022174C/zh not_active Expired - Fee Related

Non-Patent Citations (1)

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