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
  • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
• • 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
  • B22D11/0651—Casting wheels

Definitions

• the present invention relates to an ingot mould roll for continuous casting machines and, more specifically, to the superficial conformation of the counterotating rolls of the ingot mold for the metal strip production.
• strips are obtained by a conventional process that provides for the continuous casting of the flat bloom, followed by an eventual beveling, flat bloom heating and hot-rolling.
• the continuous casting process of strips is a technique that enables to produce slim strips, directly as a cast product, thus eliminating the beveling and hot-rolling processes and maintaining the cold-rolling for the slimmer thicknesses only.
• the present invention aims at solving the aforementioned drawbacks and at providing an ingot mold wherein the heat extraction and the metal solidification are functions of the ingot mold design, rather than of the inherent features of the material.
• the invention provides a cooling roll possessing surface wrinkles, for continuous casting machines with a pair of counterotating rolls in contact with the molten metal, characterized in that the surface wrinkles thereof consist in a multiplicity of cavities of a first and a second dimensional order, unevenly spaced on its surface, and optionally, being at least partially in contact among them.
• the first order of cavities serves to the purpose of reducing the thermal flux between the solidifying metal and the roll.
• the depth of these cavities may vary between 2 and 10 ⁇ m, and their equivalent diameter is comprised between 10 and 50 ⁇ m.
• the second order of cavities serves to the purpose of creating local gaps.
• the solidification is piloted by making it discrete rather than continuous, thereby breaking up and reducing the stresss caused by the shrinking that cause the strip flawing.
• this second order is constituted of cavities of different shapes and of dimensions contained in an equivalent diameter comprised between 0.2 and 1 mm, while the depth of each cavity thereof is comprised between 40 and 200 ⁇ m, with a consequent advantage for the surface aspect of the strip.
• the distance between each of the first order cavities is comprised from 0 to 60 ⁇ m, while the distance between each of the second order cavities is comprised from 0 to 1.5 mm.
• the strickle impressed on the roll surface of each cavity of at least one of said first and second orders of cavities has a shape selected from the group comprising the polygonal and the circular shape and, more preferably, rhomboidal.
• the surface of each roll that comes in contact with the cast metal is constituted of a material having a thermal conductivity comprised between 15 and 380 /m-K. and is embodied in a material selected from the following group: steel, copper, nickel and chrome, and/or their alloys, selected in order to provide the constancy of cavities for the entire rolls life
• the system is capable of producing flawless strips possessing a controlled wrinkledness such that it can be restored in the subsequent processes.
• the webbing is obtained with a peening process of the surface of the rolls, in order to produce cavities on the same roll surface.
• cavities are closely distributed, randomly spaced, of shape that may vary according to the kind of shots employed and anyhow characterized in that it comprises the presence of two different orders of cavity.
• the solidification is piloted by making it happen in a discrete rather than continuous way, thereby breaking up and reducing the stresses due to the shrinking that cause the strip flawing.
• Figure 1 is a schematic sectional view showing the surface of a roll modified according to the present invention
• Figures 2a, 2b and 2c are schematic views showing the behaviour of a cast metal when it is solidified on a smooth surface
• Figures 3a and 3b are schematic views representing the behaviour of a cast metal when it is solidified on a surface according to the present invention
• Figure 4 is a diagram reporting the values of the probability index of crack formation on steel strips depending on the strip temperature and on the smooth surface typology of a roll and for a surface modified according to the present invention.
• the cast metal is austenitic inox steel AISI 304 as metal to be solidified with the shape of a strip with a 3 mm thickness.
• the sequence shown in figs. 2a, 2b and 2c reports the behaviour of that material when it is solidified on a smooth cooled copper chaplet .
• fig.2a in it the surface of a roll 1 as an element of an ingot mold is schematically represented. The surface is smooth and is in contact with a cast metal. It can be evidenced how the steel begins to solidify at the meniscus 3 of the ingot mold, forming a thin layer 2 of an all but uniform thickness of the order of 70-100 ⁇ m.
• the thin layer 2 detaches itself off the roll, and as it is a very thin and not very resistant structure, it is subject to great instability, therefore creating random waving with a variable pitch of around 30-80 mm.
• the existence of waves causes the formation of an air space 4 of variable thickness between strip and roll, with maximum detachment values of the order of 20 ⁇ m.
• heat extraction from the strip becomes remarkably uneven and temperature differences of over 120 °C are generated on the strip surface, as the strip zones more detached from the roll remain very hot.
• the solidified thickness 2 increases in an uneven way, with the forming of relevant thinnings 5 correspondingly to the zones that are more detached from the roll.
• the ferrostatic pressure reaches a predetermined value equal to about 10 cm of depth off the meniscus, the same pressure brings again the strip in contact with the roll and the wavings gradually disappear. Nevertheless, even if temperature differences lessen, they persist until the exiting of the strip from under the rolls.
• the intense initial thermal exchange is significantly curbed by the presence of a multiplicity of small cavities 6, and, moreover, as the steel 2 does not seep completely into a second multiplicity 7 of larger cavities , there is a slight delay in the solidification of the same correspondingly to the latter.
• FIG 4 in it a diagram is shown, reporting the values of the probability index of crack forming on steel AISI 304 strips, depending on the latter temperature, and on the typology of a smooth roll surface and for a surface modified according to the present invention.
• the crackability index is significantly better for a roll with a surface peened according to the present invention, in an interval comprised between 1370 and 1390 °C, i.e. in the low ductility zone of the AISI 304 steel, in which the forming of cracks mainly occurs.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Continuous Casting (AREA)
• Heating, Cooling, Or Curing Plastics Or The Like In General (AREA)
• Heat Treatments In General, Especially Conveying And Cooling (AREA)

Priority Applications (7)

Applications Claiming Priority (2)

Publications (1)

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ID=11405348

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Cited By (2)

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Citations (3)

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• 1997
  • 1997-11-12 IT IT97RM000694A patent/IT1295859B1/it active IP Right Grant
• 1998
  • 1998-11-12 AU AU12587/99A patent/AU743949B2/en not_active Ceased
  • 1998-11-12 AT AT98955902T patent/ATE291978T1/de active
  • 1998-11-12 US US09/554,248 patent/US6431256B1/en not_active Expired - Lifetime
  • 1998-11-12 DE DE69829578T patent/DE69829578T2/de not_active Expired - Lifetime
  • 1998-11-12 EP EP98955902A patent/EP1028821B1/en not_active Expired - Lifetime
  • 1998-11-12 WO PCT/IT1998/000319 patent/WO1999024193A1/en active IP Right Grant
  • 1998-11-12 JP JP2000520254A patent/JP2001522723A/ja active Pending
  • 1998-11-12 MX MXPA00004608A patent/MXPA00004608A/es not_active IP Right Cessation
  • 1998-11-12 ZA ZA9810353A patent/ZA9810353B/xx unknown
  • 1998-11-12 KR KR1020007005113A patent/KR100613032B1/ko not_active Expired - Lifetime
  • 1998-11-12 MY MYPI98005129A patent/MY132918A/en unknown
  • 1998-11-19 IN IN2004CA1998 patent/IN192000B/en unknown

Patent Citations (3)

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