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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D7/00—Casting ingots, e.g. from ferrous metals
  • B22D7/06—Ingot moulds or their manufacture
  • B22D7/10—Hot tops therefor
  • B22D7/102—Hot tops therefor from refractorial material only

Definitions

• metal casting vessels such as tun­dishes and ladles, etc.
• metal casting vessels such as tun­dishes and ladles, etc.
• the metal casting vessels are prevented from contacting with such metals and/or slags by lining the vessels with heat-insulating refractory boards.
• the MnO and FeO formed can further attack the silica in the heat-insulating refractory linings by forming low melting liquid oxide slags at metal casting temperatures.
• the temperature associated with cold tundish linings increases quickly to that of casting such that by the time the carbon bonds are completely disintegrated, the linings are still held together by the formation of ceramic bonds resulting from the sintering of the refractory oxides.
• preheating may sometimes last up to, for example, 12 hours before casting actually begins, the linings utilized in cold tundish practice are unsuited for preheating use.
• the problem basically is due to oxidation of the carbon bonds within the linings at preheat temperatures which are generally too low for ceramic bonds to form resulting in usually soft and weak linings which will collapse due to their own weight or wash away as the molten metal enters the vessels.
• low-melting glass formers are generally thermodynamically unstable to, for instance, ferrous alloys.
• B2O3 it can be reduced resulting in the incorporation of boron into the molten metals, such as ferrous alloys, that can alter the properties of the ferrous alloys as well as product oxide inclusions.
• preheatable linings are those made with the addition of about 5% to about 20% quartz (silica) for the purpose of bonding with MgO.
• quartz or other silica forms utilized by these liners is sufficiently high enough to cause formation of oxide inclusions by reaction of the molten metals with the linings.
• the metal manufacturers specify that the quartz or free silica levels should be as low as possible.
• presence of finely divided quartz or free crystalline silica can become airborne when, for instance, the boards are removed from the vessels after use presenting health hazards to the metal manufacturers and workers.
• Examples of still other types of preheatable linings are those which contain about 85-90% magnesite and about 5% to about 10% calcium fluoride.
• the calcium fluoride is typical of a strong fluxing agent which reacts with oxides to develop a liquid bonding phase at preheat temperatures.
• These linings like those utilizing the low-melting glass formers, develop a liquid bonding phase when the organic binder is burnt out at, for instance, 1900°F. and up (preheat temperatures).
• the linings are also very soft and weak at such temperatures after the organic binder is oxidized. Thus, as with the pre­heatable linings containing low melting glass formers, these preheatable linings fail to develop the suffi­cient hot strength for casting when heated at preheat temperatures for typical preheat periods of time.
• the present invention seeks to alleviate the above-mentioned problems and shortcom­ings of the present state of the art through the discovery of novel preheatable molded refractory insulating liners and methods of use thereof for lining metal casting vessels intended to contain, for instance, ferrous alloys, such as steel and in par­ticular low hydrogen grades of steel.
• a method of making a preheatable molded refractory insulating liner of predetermined shape which assists in the solution of these problems, in accordance with the invention, comprises making a preheatable molded refractory insulating liner structure of predetermined shape having insulating porosity for temporarily lining a casting vessel and for developing sufficient hot strength to maintain the integrity of the structure at vessel preheat and metal casting temperatures which are in the range of about 1900°F. to about 3000°F.
• a liner resulting from this method is a preheatable molded refractory insulating liner for a casting vessel suitable for developing sufficient hot strength at vessel preheat and metal casting tempera­tures which are in the range of about 1900°F. to about 3000°F.
• a liner structure of predetermined shape comprising a liner structure of predetermined shape, the liner structure comprising a molded uniform mixture containing a particulate refractory component comprised of zircon and MgO refractory grain and a binder for the component to maintain the predetermined shape at least prior to the preheat temperatures wherein the zircon and MgO refractory grain are in amounts proportioned in the liner structure to facili­tate the formation of fosterite bonding which results in increased hot strength at vessel preheat and metal casting temperatures when such a liner structure is heated for a sufficient period of time.
• preheat times can be from about one half-hour and extend to about twelve hours or more.
• the MgO refractory grain may be derived from, for instance, natural, seawater or brine magnesite, periclase grain, or other suitable sources, or mixtures thereof plus, if any, incidental impuri­ties.
• the MgO refractory grain and the zircon are the main essential constituents responsible for the development of the hot strength at the vessel preheat and metal casting temperatures.
• the MgO refractory grain and zircon react as follows to form the fosterite bonds and zirconia needed for hot strength and refrac­toriness: 2MgO + ZrO2 SiO4 Mg2SiO4 + ZrO2 It is thought that the formation of zirconia and fosterite enhances the desirable hot strength and corrosion resistance to the molten metals, such as ferrous alloys, and slag. It should be appreciated, however, that the formation of fosterite and zirconia is believed to occur over the entire range of vessel preheat and metal casting temperatures which are on the order of about 1900°F. to about 3000°F. More particularly, the vessel preheat temperatures, for instance, can range from, for example, about 1900°F. to about 2400°F. whereas, in the case of ferrous alloys, the metal casting temperatures are generally at about 2800°F. or above.
• the particulate refractory component may contain in addition to the zircon and MgO refractory grain a suitable refractory filler in acceptable amounts, such as olivine or zirconia.
• the new and vastly improved preheatable liner structures provide means for developing effectively the increased hot strength needed for casting molten metals at both vessel preheat and metal casting temperatures.
• the unique preheatable liners possess the necessary hot strength during the range of casting temperatures that are experienced in the metal making industry and especially the ferrous alloy making industries.
• a feature of the present invention is to provide preheatable molded refractory insulating liners that possess corrosion-erosion resistance to metal making environments which is greatly superior to that of the common commercial preheatable refractories used heretofore.
• the present invention provides a solution to the art that has long sought suitable liners for preheating and makes it now possible to make preheatable casting vessels lined with the preheatable refractory insulating liners of this invention for extended periods of time prior to the start of cast­ing. Further, it is found that extended preheating advantageously enhances the development of the desired increased hot strength in the liners of the present invention.
• zircon and MgO refractory compositions have been well known in the glass and metal making industries, it has been heretofore unknown to utilize zircon and MgO refractory compositions to form fosterite at low vessel preheat temperatures. Further, it has been heretofore unknown to utilize such compositions to fabricate preheatable molded refractory insulating liner structures for casting vessels. Moreover, it has been surprisingly discovered that such composi­tions in the liners react to facilitate development of effective hot strength at low vessel preheat tempera­tures.
• the heat-insulating refractories employed to line the casting vessels which come into contact with the molten metals should be composed of the most stable oxides possible (i.e., the stronger the chemical bonding of the oxides, the higher the melting point).
• temperatures greater than preheatable tempera­tures which are generally from about 1900°F. to about 2400°F. are required to sinter the refractory grain of the stable oxides present in the linings.
• a balance or compromise has to be struck between the refractory stable oxides and impurities utilized in the present heat-insulating refractory boards.
• the refractory stable oxides must have enough impurities, but without sacrificing quality of the casting metals, to develop a dense sinter surface at temperatures of about 2800°F. or higher.
• the types and amounts of unstable impurities which act to lower temperatures needed for sintering and solidus must be controlled to maintain the needed heat-insulating refractory lining requirements and to minimize the contamination of the casting metals by the unstable oxides.
• the present invention has remark strictlyably overcome this arduous dilemma by providing a unique blend of stable and unstable oxides which is suitable for developing the necessary refractoriness and hot strength at vessel preheat and casting temperatures while developing a dense sinter at about 2800°F. without significantly contaminating the molten metals, such as ferrous alloys, with impurities during casting.
• the binder component may be derived from organic and/or inorganic binders or mixtures thereof in the range from about 1.5% to about 15% by weight.
• the inorganic binder may, for instance, constitute low melting fluxing compounds, such as boric acid.
• the preheatable liners may contain a fibrous material component which may also be derived from organic and/or inorganic materials in the range from 0% to about 10% by weight.
• the preheatable liner may further contain a thioxotropic substance, such as bentonite, in amounts ranging from 0% to about 5% by weight.
• a further feature of the present invention resides in providing preheatable molded refractory insulating liner structures suitable for lining casting vessels like hot tops, ladles, tundishes, troughs, or pipes, etc. for conveying molten ferrous alloys.
• the preheatable liners if desired, can be molded into the form of a plurality of predetermined shaped inserts, such as tundish boards.
• An especially desirable corrosion-erosion resistant preheatable molded refractory insulating liner comprises by weight about 80% to about 95% a particulate refractory component containing MgO refractory grain and zircon wherein the MgO refractory grain and zircon are in a ratio of about 5:1 to about 18:1, respectively, about 1% to about 8% fibrous material, about 1.5% to about 10% binder, and about 0.5% to about 5% a thixotropic substance.
• the MgO refractory grain may be derived from, for instance, natural, seawater or brine magnesite, periclase grain, or other suitable sources, or mixtures thereof.
• the lower silica and hydrogen content of the preheatable structures provide a further feature for reasons recited above; that is, the cast molten metals and particularly the ferrous alloys are distinctly purer as a result of less contamination presently experienced from high silica and hydrogen content associated with the common preheatable refractories available hitherto.
• a preferred form of liner resulting from the present invention and possessing the high degree of hot strength developed at vessel preheat and metal casting temperatures comprising by weight about 10% zircon and about 80% MgO refractory grain plus incidental impuri­ties, wherein the MgO is preferably derived from dead burned natural, seawater or brine magnesite, periclase grain or mixtures thereof which may range from about 80% to about 98% MgO purity, the balance being binder, and if desired fibrous material or bentonite or mixtures thereof. Keeping the silica and bydrogen contents low in this preferred form, the same as aforesaid, will also provide distinctly purer cast molten metals.
• incidental impurities are merely those of extremely minor contaminants which result from the ordinary impurity contents normally associated with different grades of raw material sources for MgO, zircon, etc.
• the total amount of impurities should be kept to a minimum, if possible, to reduce or avoid possible detrimental effects to the above-noted properties and structural characteristics.
• in still another feature of the present invention is directed to a method of casting using a casting vessel comprising the steps of providing within the vessel a preheatable molded refractory insulating liner of this invention, heating the vessel to at least a vessel preheat temperature to initiate the development of hot strength in the preheatable liner for casting at metal casting temperatures, and introducing a molten metal, such as a ferrous alloy, into the vessel.
• a preheatable molded refractory insulating liner for lining a casting vessel made by the process of the invention is suitable for developing sufficient hot strength at vessel preheat and metal casting temperatures which are on the order of about 1900°F. to about 3000°F. when such a liner is heated for a sufficient period of time.
• a preheatable molded refractory insulating liner may comprise a liner structure of predetermined shape, the liner structure comprising a uniform molded mixture containing a particulate refractory component comprised of zircon and MgO refractory grain, and a binder therefore.
• the preheatable liner preferably contains a fibrous material and, if desired, minor amounts of bentonite or other suitable thioxtropic substances.
• the term "hot strength" refers to a liner having sufficient hot strength to support itself during extended preheating and to withstand erosion resulting from a molten metal entering a vessel during casting.
• the preheatable liners made and used in accordance with the teachings of this invention unexpectedly and advantageously generally do not soften or weaken, collapse or wash away after being preheated by a molten metal entering the vessel, as currently ex­perienced with other prior art preheatable liners. Additionally, the preheatable liners of the present invention are less prone to contaminate the molten metals because of their low free silica and low hydrogen contents.
• the preheatable molded refractory insulating liners are formed of by weight of about 75% to about 98.5% a particulate refractory component comprised of zircon and MgO refractory grain being in a ratio from about 1:1.5 to about 1:24, respectively, about 1.5% to about 15% binder, 0% to about 10% fibrous material and 0% to about 5% a thixotropic substance.
• the zircon is about 5% to about 15%, and most preferably about 10% by weight of the liner.
• zircon also known as zirconium silicate (ZrSiO4 or ZrO2 SiO2), and sometimes known as hyacinth, jargon, etc.
• ZrSiO4 or ZrO2 SiO2 zirconium silicate
• hyacinth, jargon, etc. can be derived from natural or synthetic products, or any other suitable sources not inconsistent with the teachings of this invention. It has been surprisingly discovered that when zircon, and especially finely comminuted zircon, or zirconium silicate, is intimate­ly mixed with MgO refractory grain in sufficient amounts and made into a molded refractory insulating liner for a casting vessel, the zircon and MgO refrac­tory grain unexpectedly react at vessel preheat temperatures which are in the range of about 1900°F. to about 2400°F.
• zircon, or zirconium silicate, used be very finely comminuted.
• the zircon particles should pass through a 325 mesh screen, and more preferably substantially all should pass through a 400 mesh screen.
• the zircon should have an average particle size of about 10 microns.
• ground zircon sand and especially zircon flour, for instance are suitable sources of highly comminuted zircon to be employed pursuant to the invention.
• zircon employed herein is to be understood in each instance as referring to a chemical combination of zirconium, silicon and oxygen designat­able by the formula ZrSiO4 and irrespective of its origin be it synthetic or natural.
• the MgO refractory grain also known as magnesium oxide or magnesia
• the magnesite or periclase grain preferably is of the type commonly referred to as dead burned magnesite or dead burned periclase.
• magnesite or periclase By “dead burned” magnesite or periclase is meant magnesite or periclase fired to high temperatures to produce a hydration resistant grain consisting essentially of well-sintered low porosity periclase crystals and this grain structure distinguishes it from the more reactive lower tempera­ture calcined caustic magnesites. Nevertheless, it should be understood that it is preferred that the MgO refractory grain content, whether derived from natu­ral, seawater or brine magnesite, periclase grain, or other suitable sources, should be substantially pure. By “substantially pure”, it means containing at least about 80% MgO by weight on the basis of an oxide analysis, with the remainder, if any, being only minor amounts of incidental impurities.
• the best results are achieved when the particle size distri­bution of the MgO refractory grain is not too coarse or too fine.
• such particles should be sized so that no more than about 40% are retained on a 50 mesh screen and no more than about 40% can pass through a 325 mesh screen. More preferably, no more than about 15% of the MgO refractory grain particles should be retained on a 50 mesh screen and no more than about 30% should pass through a 325 mesh screen.
• the use of a blend of different magnesite sources for MgO refrac­tory grain achieve the best results.
• the blend should be of sources for MgO refractory grain having an MgO content of at least about 80%.
• sources for MgO refractory grain should be selected to minimize silica and hydrogen content.
• sources of MgO refractory grain should be selected on the basis of their low tendency to hydrate due to their high dead burning temperatures and as a result of their composition.
• the preheatable molded refractory insulating liners comprise by weight about 10% zircon, about 40% of an about 88% MgO magnesite and about 40% of an about 95% MgO magnesite wherein the zircon and MgO refractory grain are in a ratio of about 1:8, respectively, about 1.5% to about 15% binder, 0% to about 10% fibrous material, and 0% to about 5% a thixotropic substance.
• a suitable refractory filler may be added in acceptable amounts to the particulate refractory component which comprises zircon and MgO refractory grain.
• Exemplary of such fillers are olivine and zirconia wherein the olivine may be by weight of the liner from 0% up to about 70% and the zirconia may be by weight of the liner from 0% up to about 80%.
• a refrac­tory filler is added to the particulate refractory component, however, it should be understood that such a mixture will still be by weight of the preheatable liner from about 75% up to about 98.5% as afore­mentioned.
• the zircon and MgO refractory grain are in the stated ratios not inconsistent with the teachings of this invention so that sufficient hot strength is developed in the preheatable liners at vessel preheat tempera­tures and metal casting temperatures.
• the refractory fillers preferably should have a particle size approximating the size distribution of the MgO refractory grain.
• the advantages to adding a refractory filler to the particulate refractory component include, for instance, a reduction in manufacturing cost or to improve the corrosion resistance of the liner.
• An example of a preheatable refractory liner containing olivine as a refractory filler has a composition comprising by weight olivine about 62%, zircon about 4%, MgO refractory grain about 25%, binder about 1.5% to about 15%, fibrous material 0% to about 10% and a thixotropic substance 0% to about 5%. It can be noted that in this exemplary composition the MgO refractory grain and zircon ratio by weight is about 6:1, respectively.
• the binder component may be derived from any suitable binder or mixtures of binders of those known in the refractory making and allied industries including organic and/or inorganic binders.
• vessel preheating is conducted at about 1900° F. to about 2400° F. and more typically between about 2000°F. and 2300°F.
• These preheat conditions cause the organic binders incorpo­rated within the liners to burn out, for instance, starting at the hot face and sometimes throughout the entire board thickness, of course, depending upon preheat time, temperature and board thickness. Nonetheless, up until the point of burnout, the organic binders serve to hold or bind the other materials together and comprises by weight of the liner from about 1.0% to about 10%.
• Samples of organic binders suitable to be employed in the liners include, starches, cereals, natural or synthetic resins, such as amino resins, phenolic resins or mixtures thereof. More particularly, the phenol-formaldehyde and urea-­formaldehyde resins are best suited for use and most preferably is the phenol-formaldehyde resin.
• a catalyst such as hexamethyl­enetetraamine, also known as HMTA, Hexa, methenamine, hexamine, aminoform, etc., should be added in suf­ficient amounts to polymerize the phenolformaldehyde resin to bond the refractory grains for making a rigid structure suitable for use as a liner.
• the inorganic binder In addition to providing binding support prior to the burnout of organic binder, the inorganic binder generally serves to stick or hold the particu­late refractory component together during preheat conditions particularly after the organic binder has been consumed or burnt out. To this end, it is believed that the inorganic binder forms a glassy or viscous phase under preheat conditions developing characteristics suitable for sticking or binding the particulate refractory component together.
• an inorganic binder can act as a temporary binder characterized as a low melting fluxing material which aids in maintaining the particulate refractory component together subsequent to organic burnout under preheat conditions and until the fosterite refractory bonding develops.
• inorganic binders suitable for use are boric acid, borax, colemanite, etc., and preferably boric acid.
• boric acid comprises by weight from about 0.5% to about 5% of the structure.
• B2O3 upon heating boric acid is converted to B2O3 which advantageously pro­motes sintering of the MgO refractory grain for improving the hot strength of the preheatable liner.
• the fibrous materials may comprise inorganic fibrous materials such as rockwool, slag wool, glass wool, refractory alumi­num silicate fibers, and especially slag wool; and organic fibrous materials such as cellulosic materials derived from paper, paper wood, sawdust, wood meal, synthetic organic fibers or the like, and particularly paper.
• inorganic fibrous materials such as rockwool, slag wool, glass wool, refractory alumi­num silicate fibers, and especially slag wool
• organic fibrous materials such as cellulosic materials derived from paper, paper wood, sawdust, wood meal, synthetic organic fibers or the like, and particularly paper.
• These fibrous materials generally serve to reinforce the preheatable liners so that the liners are not damaged by any impact during the manu­facturing, shipment and installation. Additionally, the fibrous materials serve to prevent the particulate refractory component from settling out of the slurry and to control porosity and permeability of the liner.
• the resulting preheatable liners can become a porous board which has low bulk density, whereby the heat-­insulating effect thereof is improved.
• the fibrous materials represents by weight of the liner from 0% to about 10% and preferably about 5%.
• thixotropic substance As to the incorporation of a thixotropic substance, it generally acts as a thickening agent or forming aid during preparation of the desired shape and generally comprises by weight of the liner from 0% to about 5%.
• exemplary of thixotropic substances are bentonite, methylcellulose, alginates, etc., and especially bentonite.
• bentonite it is preferred that the calcium bentonite is employed as opposed to the sodium bentonite.
• the preheatable molded refractory insulating liner structures resulting from the method of the invention are suitable for the forming linings for casting vessels, such as hot tops, ladles, tundishes, troughs and pipes etc., which are intended to contain molten ferrous alloy metals.
• the versatility of these structures enables them to be shaped, for example, into the form of a plurality of predetermined shaped inserts.
• the preheatable liners are in the form of a plurality of shaped boards employed in tundishes.
• manufacture can be readily done, for instance, by vacuum forming or injection molding methods which, for example, comprise forming an aqueous slurry of solids comprising a mixture con­ taining a particulate refractory component, a binder therefore and, most preferably, a fibrous material component. Bentonite or other suitable thixotropic substances may also be employed as discussed above. Because of the copious amounts of water utilized in making the aqueous slurry, vacuum sources which are well-known in this art for removing substantial amounts of water are preferably employed.
• the raw batch of materials are suitably proportioned to provide the desired final mixture and preferably are intimately premixed in the slurry form prior to vacuum forming.
• the material is usually poured into preformed molds of the desired shape and sub­jected to sufficient sub-atmospheric or vacuum condi­tions to suck away a substantial amount of the liquid in the slurry so that the formed shapes can be removed from the mold and dried.
• the wet vacuum formed shapes are passed through conventional hot air dryers to remove or evaporate virtually all the water and to heat the entire structure thickness to a suitable temperature for curing the organic and/or inorganic binder.
• the thickness of the liner when making a board may range, for instance, from about 3/4 of an inch to about 2 inches.
• the method of casting of the invention using a casting vessel which serves to transfer molten metals, such as ferrous alloys comprises the steps of providing in the casting vessel a preheatable molded refractory insulating liner structure of this invention, heating the casting vessel to at least a vessel preheat temperature to initiate the development of hot strength in the preheatable liner structure for casting at metal casting temperatures and introducing a molten metal, such as a ferrous alloy, into the casting vessel.
• compositions A and B for manufacturing a preheatable molded refractory insulating liner in accordance with this invention: Composition Ingredient % A Phenol-formaldehyde resin 2.30 Hexamethylenetetraamine 0.20 Paper 1.40 Slag wool 3.30 Calcium bentonite 1.60 Magnesite: about 88% MgO 40.60 Magnesite: about 95% MgO 40.60 Zircon Flour 10.00 100.00% Boric Acid 2.5% of dry batch weight.
• Composition Ingredient % B Phenol-formaldehyde resin 2.30 Hexamethylenetetraamine 0.20 Paper 1.40 Slag wool 3.30 Calcium bentonite 1.60 Magnesite: about 88% MgO 24.50 Zircon Flour 4.00 Olivine 62.70 100.00% Boric Acid 1.0% of dry batch weight.
• Preheat increased the porosity by 10% by burning out organic binders sintering and reacting to form fosterite. This effect was also observed by the increase in specific gravity when the low specific gravity organic material was removed.
• Table I shows that after contact with a molten ferrous alloy, the preheatable refractory board formed a dense (approximately 20% porosity), imperme­able 0.5 inch thick layer in contact with the steel.
• the porosity of the cold side of the board remained high at about 55%.
• the dense hot face contained some closed pores and some oxide contamination which lowered the apparent specific gravity compared to the cold face and the preheated specific gravities.
• X-ray diffraction showed that zircon and MgO refractory grain was consumed, and that fosterite and cubic zirconia were formed at tundish preheat condi­tion and both fosterite and cubic zirconia were found present in the hot face and the cold face of the tundish boards after casting ferrous alloys.
• the dense board hot face which developed resisted and reduced erosion and steel contamination.
• the high porosity on the back of the board advantageously gave lower thermal conductivity through the board, thus, lower temperatures at the permanent lining and less heat loss from the vessel resulted.
• Such boards had low erosion with high manganese steels, low hydrogen contribution to the steel and were preheated to about 2300°F for up to about seven hours without adversely affecting their hot strength during casting.
• the gunnable coating referred to in Table I had an intermediate (34%) porosity through its entire thickness. It failed to develop a dense layer at the hot face.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Furnace Housings, Linings, Walls, And Ceilings (AREA)

Priority Applications (2)

Applications Claiming Priority (1)

Publications (1)

Family

ID=8197996

Family Applications (1)

Country Status (1)

Cited By (3)

Citations (2)

• 1987
  • 1987-08-13 EP EP87307164A patent/EP0302975A1/de not_active Withdrawn

Patent Citations (2)

Similar Documents

Legal Events