Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/04—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the coating material
  • C23C4/06—Metallic material
• • 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
  • B22D11/059—Mould materials or platings
• • 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
  • B22D11/12—Accessories for subsequent treating or working cast stock in situ
  • B22D11/124—Accessories for subsequent treating or working cast stock in situ for cooling
  • B22D11/1243—Accessories for subsequent treating or working cast stock in situ for cooling by using cooling grids or cooling plates
• • 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
  • B22D11/12—Accessories for subsequent treating or working cast stock in situ
  • B22D11/128—Accessories for subsequent treating or working cast stock in situ for removing
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/18—After-treatment

Definitions

• This invention relates to the coating of components used in the continuous casting of ferrous and non-ferrous materials.
• the topmost stage of a continuous casting machine is composed of a hollow box made up of side plates and end plates (and sometimes a central divider), usually of copper, which are water cooled.
• a plug or dummy bar is positioned at the bottom of the mould and molten metal is poured into the mould from a ladle via a tundish.
• the water-cooled copper walls of the mould and the cold surface of the plug create a thin solidified skin which contains the molten material.
• the plug is slowly withdrawn downwards from the mould zone whilst the level of molten material at the top of the mould is maintained by continuously adding further molten material.
• a mould powder may be added simultaneously, to form a layer on the surface of the molten metal.
• the grid plates are usually made of cast iron or steel.
• Each grid plate comprises several raised "fingers" with surfaces which are in contact with the chilled skin of the slab and which continue to constrain the solidifying slab to the requisite cross-sectional shape whilst cooling water is continuously sprayed onto the surface of the slab in between the fingers.
• the thickness of the chilled skin is increasing.
• the slab then passes further on down through the machine through a series of guides and rolls, which continue to constrain the slab to the designed shape. Whilst passing down the casting machine the plane of the slab is gradually changed from a vertical direction to a horizontal direction until the fully solidified but still hot slab emerges on a conveyor table at the bottom of the machine, where it is cut to the requisite length
• the present invention provides a method of coating the surfaces of such components, comprising the following step
• the coatings are applied to an internal surface of a continuous casting mould, i e a surface which confines the metal being cast. In another aspect, the coatings are applied to strand-constraining surfaces of a grid plate
• Step (e) preferably comprises impregnating the composite surface with a solution of at least one chromia or phosphate forming compound
• the final ceramic coating is preferably a so-called Monitox coating, which is achieved by applying to a substrate a slurry containing a chromium compound capable of being converted into a chromium oxide and/or a chromium phosphate at temperatures of at least 250°C, heating the slurry (e g at about 260°C) to produce a porous ceramic coating, and then densifying and bonding the coating by one or more process cycles comprising impregnating the porous coating with at least one chromia or phosphate forming solution, removing excess impregnant, and heating
• a technique is described in GB-A-1 466 074, for example
• the first coating may be any cermet (ceramo-metallic) coating but is preferably a tungsten carbide cobalt coating and is preferably applied in several successive layers
• the flame spraying process is preferably a high velocity oxygen-liquid fuel process which is often referred to as an HVOF process This process is a commercially available flame spraying process in which fuel and oxygen are combusted in a specially designed chamber which is connected to a water-cooled tube or nozzle at the combustion chamber exit The combustion products are accelerated down the nozzle, constituting a gun or torch.
• Powdered materials of closely controlled sizes are metered into the gun and are thus accelerated and heated as they pass along the hot high-velocity gas stream Upon impacting with the substrate at a specific distance from the gun the particles splat and build up upon each other and the substrate to form a highly bonded and dense coating
• Various coatings can be produced in this manner but a tungsten carbide 17% cobalt coating is the preferred coating for applying to the casting machine components
• All flame sprayed coatings to a greater or lesser degree contain micro-cracks or fissures which are the result of the quench stresses generated as the hot high velocity particles impact upon the substrate. Sometimes these micro-cracks can be extremely small, to such an extent that they are very difficult to discern using normal metallographic techniques.
• the Monitox coating is applied in an aqueous slurry form containing various oxides and chemicals. This layer is then dried and heated (250 to 500°C). At this stage is 'soft' in that it is a collection of hard particles which are not very well bonded to each other or to the substrate. Thus, at this stage, excess coating can easily be removed by scraping or sanding operations so as to reveal the peaks of the underlying tungsten carbide coating which, in the 'as sprayed' condition, exhibits a coarse surface somewhat like a coarse sandpaper. Thus, a relatively smooth composite surface can be produced which comprises areas of ceramic and carbide material. This composite surface is then further densified and hardened by a cyclic process of impregnation and further heat treatment; for example from 3 to 10 cycles of impregnation and heat treatment can be required.
• the composite coating When applying the composite coating to the mould components it has been found to be surprisingly beneficial to deposit the first coating to a tapered thickness profile from the top of each component to the bottom. The hottest region of the end and side plates is at the top at the meniscus zone. The inventor believes that making the coating thin in this area accommodates and withstands the high thermal stresses imposed in this area.
• a suitable variable coating thickness profile has been found to be a substantially linear increase from 0 08 mm (0 003 inch) at the top to 0 46 mm (0 018 inch) at the bottom, although other thickness variations may be preferred depending upon the temperature and pressure characteristics of the casting process
• the coating may extend over the whole height of each mould component However, the coating may terminate below the upper edge of the mould wall, provided it extends above the highest level of the molten metal
• the coating may have a substantially constant thickness in an upper region adjacent the upper edge of the mould wall component, it may have a substantially constant thickness in a lower region adherent the lower edge of the mould wall component, and the thickness may increase progressively in a linear manner, an exponential manner, or any other suitable manner between the upper and lower regions
• the minimum thickness is chosen primarily having regard to heat transfer, preferably in the range from 0 05 to 0 1 mm
• the maximum thickness is chosen having regard to mechanical strength as well as heat transfer, preferably in the range from 0 4 to 1 0 mm
• each island is approx 5 mm square or 5 mm in diameter, each island is defined at its perimeter by an uncoated band approx 2 mm wide
• a suitable thickness range may be from 0 3 to 0 5 mm
• the transverse dimensions of the islands may conveniently be in the range from 4 to 8 mm, the islands being spaced apart by 1 to 3 mm, for example
• the drawing shows a cast iron grid plate 1 with gaps 2, through which cooling water is sprayed, and raised fingers 3 provided with the composite coating 4 made up of a pattern of rectangular islands 5 (approx 5 mm square, separated by at least 1 mm)

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Plasma & Fusion (AREA)
• Metallurgy (AREA)
• Physics & Mathematics (AREA)
• Coating By Spraying Or Casting (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Coating With Molten Metal (AREA)
• Continuous Casting (AREA)
• Mold Materials And Core Materials (AREA)
• Ceramic Products (AREA)
• Moulds For Moulding Plastics Or The Like (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=10802694

Family Applications (1)

Country Status (10)

Families Citing this family (7)

Family Cites Families (18)

• 1996
  • 1996-11-08 GB GB9714452A patent/GB2320034B/en not_active Expired - Lifetime
  • 1996-11-08 GB GB9623344A patent/GB2319042B/en not_active Expired - Lifetime
• 1997
  • 1997-11-07 DE DE69706317T patent/DE69706317T2/de not_active Expired - Lifetime
  • 1997-11-07 DK DK97911364T patent/DK0946778T3/da active
  • 1997-11-07 JP JP52229398A patent/JP2001504162A/ja not_active Ceased
  • 1997-11-07 WO PCT/GB1997/003073 patent/WO1998021379A1/en active IP Right Grant
  • 1997-11-07 PT PT97911364T patent/PT946778E/pt unknown
  • 1997-11-07 EP EP97911364A patent/EP0946778B1/de not_active Expired - Lifetime
  • 1997-11-07 ES ES97911364T patent/ES2163139T3/es not_active Expired - Lifetime
  • 1997-11-07 AU AU48775/97A patent/AU4877597A/en not_active Abandoned
  • 1997-11-07 AT AT97911364T patent/ATE204615T1/de active

Non-Patent Citations (1)

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