Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D41/00—Casting melt-holding vessels, e.g. ladles, tundishes, cups or the like
  • B22D41/02—Linings

Definitions

• the present invention relates to a method for coating a metallurgical container, such as a tundish or ladle, with a purifying coating.
• purifying coating is meant a coating capable of reducing pollution of the liquid metal by impurities such as oxides.
• means are currently used such as pouring tubes interposed between the ladle and the tundish and covering powders. arranged on the surface of the liquid metal.
• Coatings are known for metallurgical vessels, in particular flow distributors, obtained by spraying a composition in the form of an aqueous slurry containing refractory particles, such as SiO 2, Al 2 O 3, gO or a mixture thereof, and a binder. organic or inorganic. These particles sinter under the effect of the heat of the liquid metal poured into the container, which ensures the cohesion of the coating.
• refractory particles such as SiO 2, Al 2 O 3, gO or a mixture thereof
• a binder organic or inorganic.
• Coatings obtained by applying raw dolomite or calcium carbonate are also known.
• Such coatings have purifying properties with respect to liquid metal. These properties are mainly based on the greed of CaO for oxides which pollute the metal such as AI2O3, FeO, ⁇ 2O3, giving compounds which are more fusible than the constituents and which migrate towards the slag.
• aqueous mixture comprising approximately 98% of raw dolomite and 2% of sodium silicate as a binder.
• the coating was fully baked to around 900 ° C, in order to release the CO2 from the dolomite.
• the coating thus cooked had a porous structure whose mechanical strength was insufficient to resist the abrasion caused by the liquid metal.
• REPLACEMENT SHEET forming a mold so that this procedure is of no industrial interest.
• the Applicant has continued its research in order to discover an industrially acceptable solution making it possible to produce a purifying coating from raw dolomite or calcite.
• the object of the present invention is precisely to provide a method and a composition for producing such a purifying coating, and a coating obtained by the implementation of this method.
• the invention thus relates to a method and a composition for coating the interior wall of a metallurgical container, so as to produce a purifying coating based on at least one oxide of an alkaline earth metal.
• this process is characterized by the following stages:
• composition is applied to the inner wall of the container containing at least one simple or multiple carbonate of alkaline earth metal added with a certain proportion of refractory material in grains, and
• This composition is heated to remove the CO2 and possibly the water of constitution and / or hydration and obtain a layer of the alkaline earth metal oxide (s) of porous structure, the proportion of refractory material being sufficient to impart to the coating sufficient resistance to erosion of the liquid metal poured into the container.
• the composition may also contain a certain proportion of either alkaline earth hydroxides or alkaline earth oxides capable of hydrating during wetting of the composition and of activating lime or magnesia sufficiently "in situ" during the preheating of said composition, ro days in order to impart sufficient resistance to the coating.
• the method according to the invention thus makes it possible to obtain an economical purifying coating since it uses as starting material one or more alkaline earth carbonates such as dolomite or calcite.
• the coating obtained has good resistance to erosion caused by the metal poured into the metallurgical vessel.
• the coating according to the invention has a double function, namely the purifying function and the function of wear coating, so that it can advantageously replace all the wear and protective coatings applied so far which do not have no purifying function.
• the merit of the present invention lies in the fact that it has surprisingly discovered that the addition of a certain proportion of refractory material to one or more simple or multiple alkaline earth carbonates made it possible to obtain, after baking, that is to say after the elimination of the CO 2, a structure having an erosion resistance markedly greater than that obtained in the absence of this refractory material.
• the coating obtained in addition to its purifying properties due to the alkaline earth oxide which is obtained after baking, has a structure which is sufficiently porous to give it thermal insulation properties making it possible to limit the cooling of the liquid metal contained in the pouring container. Furthermore, the coating obtained according to the process according to the invention does not adhere strongly to the permanent refractory coating on which it is applied so that at the end of casting, it can be easily detached in order to 'coii ⁇ uer a new coating.
• the aforementioned composition can be advantageously sprayed in the form of aqueous mud, with. About 15 to 20% by weight of water.
• the composition can also be poured between the interior surface of the metallurgical container and a mold wall.
• the coating is heated to the core around 900 ° C, to release the CO2 from the alkaline earth carbonate and optionally the water of constitution and / or hydration.
• This heating can be carried out by any means such as a burner, electric heating elements by Joule effect or with emission of infrared radiation.
• the single or multiple alkaline earth carbonate used in the composition is preferably a carbonate chosen from the following compounds: raw dolomite, raw calcite and their mixtures, dolomite being however preferred because of its low cost in the raw state (not calcined).
• the composition used preferably contains a binder chosen from mineral binders such as for example: silicate or alkaline phosphate, organic such as for example phenolic resin, hydraulic such as, for example, cements, and mixtures thereof.
• the refractory material added to the alkaline earth carbonate is preferably chosen from the following compounds:
• REPLACEMENT SHEET The optimal proportions will depend on the desired effect. The higher the proportion of alkaline earth carbonate, the greater the purifying effect. Conversely, the higher the proportion of refractory material, the greater the resistance to erosion of the coating.
• the proportion of refractory material is just sufficient to give the coating the desired resistance to erosion so as to preserve the purifying properties due to the alkaline earth oxide remaining after release of the CO2.
• the elements containing calcium will be favored in the composition.
• the presence of the binder is not compulsory, because a setting effect with water already exists in its absence.
• the alkaline earth carbonate can be pure calcium carbonate or combined with another carbonate, for example magnesium carbonate, in the form of dolomite.
• alkaline earth oxides cited as examples of refractory material can be replaced in whole or in part by hydroxides and / or sulphates, the latter being transformed into oxides during cooking.
• the grains of the refractory material have at least partly a dimension greater than that of the grains of carbonates and / or hydroxides and / or alkaline earth sulfates.
• REPLACEMENT SHEET In fact, the grains of carbonates, hydroxides and sulfates decompose the more easily and quickly the smaller they are.
• the particle size can be adjusted as a function of the desired result, namely the porosity which gives insulating and / or sintering properties which ensures cohesion and resistance to erosion.
• composition according to the invention also preferably contains up to 20% by weight of organic and / or mineral fibers.
• composition according to the invention may also contain a carbonaceous matter in grains.
• the composition additionally contains up to 5% by weight of a surfactant.
• the aforementioned composition can be applied to the bottom and the lateral faces of a tundish, by spraying or molding in one or more layers a few centimeters thick.
• one or more fluxes such as, for example: olivine, colemanite, borocalcite (calcium borate), iron oxide, fluoride, boric acid and its salts (borax) and their mixtures.
• Dolomite and / or calcite and / or hydroxides and / or sulfates 30 to 95%, grain diameter ⁇ 3 mm, preferably ⁇ 1 mm
• Refractory material 70 to 5%, grain diameter ⁇ 5 mm, preferably ⁇ 2 mm
• Binder 0 to 15% Carbon: 0 to 5%
• the composition and the particle size of the grains can vary from one layer to another depending on the desired properties.
• REPLACEMENT PLEASE will contain more refractory material, and will contain fine particles to promote sintering.
• the outer layer adjacent to the permanent refractory lining may be sinter less than the inner layer, so that it can be easily detached from the permanent lining at the end of casting.
• the basicity of the inner layer may be favored by a high calcium content in order to obtain optimal purifying properties.
• a coating in several layers to protect the interior wall of a metallurgical container can thus comprise: - an interior purifying layer of wear coming into contact with liquid steel, based on oxide of an alkaline earth metal (dolomite , hydroxides, sulfates, calcite, carbonates),
• this layer may be either a sinterable layer at the temperatures involved, based on stable refractory oxide grains (for example based on magnesia and / or silica and / or alumina and / or zircon and / or zirconia), or alternatively an outer layer with little or very little sinterability of security based on stable refractory oxides added with carbon (less than 35% carbon).
• This last layer can also play the role of a third layer with little or very little sinterability placed between the aforementioned safety layer and the permanent coating to avoid any clinging of the permanent coating, like any other partially, little or very little sinterable layer.
• first purifying inner layer a second layer with little or very little sinterability or not sinterability, and a third outer sintering layer or at least partially sinterable.

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• 1989
  • 1989-04-12 FR FR8904822A patent/FR2648066B1/fr not_active Expired - Fee Related
• 1990
  • 1990-04-10 CS CS901797A patent/CS179790A3/cs unknown
  • 1990-04-11 ES ES90907138T patent/ES2047930T3/es not_active Expired - Lifetime
  • 1990-04-11 DE DE90907138T patent/DE69005578T2/de not_active Expired - Fee Related
  • 1990-04-11 CA CA002030522A patent/CA2030522A1/en not_active Abandoned
  • 1990-04-11 AU AU55517/90A patent/AU628557B2/en not_active Ceased
  • 1990-04-11 US US07/613,622 patent/US5188794A/en not_active Expired - Fee Related
  • 1990-04-11 WO PCT/FR1990/000263 patent/WO1990011853A1/fr active IP Right Grant
  • 1990-04-11 BR BR909006411A patent/BR9006411A/pt unknown
  • 1990-04-11 HU HU904442A patent/HUT60173A/hu unknown
  • 1990-04-11 EP EP90907138A patent/EP0422192B1/de not_active Expired - Lifetime
  • 1990-04-11 KR KR1019900702594A patent/KR960005886B1/ko active IP Right Grant

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