Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/20—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/18—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents
  • B22C1/185—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents containing phosphates, phosphoric acids or its derivatives
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/18—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents
  • B22C1/186—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents contaming ammonium or metal silicates, silica sols
  • B22C1/188—Alkali metal silicates
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
  • C04B28/34—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing cold phosphate binders

Definitions

• This invention relates to improvements in W silicate-containing mo s a apte ened by impregnation with carbon dioxide or other gaseous curing agent to molds formed therefrom and to methods for their preparation and use.
• molds and cores from sand-silicate mixtures which are cured or hardened in the desired casting-defining shapes by exposure to carbon dioxide or other gaseous curing materials.
• the curing of molds embodying binders of this type involves a chemical reaction between carbon dioxide or other gaseous material and the alkali metal silicate dispersed throughout the sand or other refractory material substantially completely to convert the alkali metal silicate into a uniformly-dispersed silicon dioxide gel binder and an alkali metal carbonate.
• prior silicate-containing moldforming compositions generally have been characterized by excessive evolution of steam and/ or other gases during casting, if sufficient organic additive was present to provide satisfactory collapsibility.
• the present invention comprises an improvement over the prior inventions described and claimed in the above-identified applications especially with respect to improvements in the collapsibility or so-called fired strength of alkali metal silicate-containing mold-forming compositions.
• a further object of the invention is to provide new and improved compositions for forming alkali metal silicate- 5 containing molds adapted to be cured by exposure to carbon dioxide or other substances.
• a still further object of the invention is to provide new and improved methods of metal casting.
• a still further object of the invention is to provide an improved shell mold and methods of shell molding.
• mold is intended in a generic sense to mean casting forms which include both molds and cores, this invention in no manner being limited to the former. Moreover, mold is intended to include various patterns for use in the casting art, as well as shell molds including shell mold-forming elements in addition'to a completed shell mold structure prepared by assembling two or more complementary thin-walled shell mold elements. Hence, it will be appreciated that the term mold is used to include a casting-defining surface broadly.
• the present invention contemplates as a mold-forming composition a mix tgrepimammfii rnptq ortionof .afinelyrL refractory ater al.amino:. pr.oponion-n.an alkali metafl filieafe'and a min r proportion lnfhatl least 'ofiephbsphateiieif'a"salt'or e ster of anoxygen acid of fifimfiis'ifgiiding 5Ttidffbf orthophosphoric v E).
• This invention also contemplates as a novl'c'dmposition of matter a mixture of a major proportion of a finely-divided refractory material,
• composition which can be cured readily by carbon dioxide or other curing agent to form a rigid mold having an excellent unfired or green strength and yet which after firing and solidification of a casting therein, is characterized by such a low fired strength as to permit its ready removal from the casting surfaces.
• the phosphate employed generally should be an alkali phosphate, the term alkali phosphate being intended to include both alkali metal phosphates and alkaline earth metal phosphates as well as ammonium phosphates.
• phosphates of the alkaline earth metals generally are contemplated such as calcium phosphates, magnesium phosphates, beryllium fi plelsss rmimr osph t a.bfi ifiiil i fidium phosphates, although calcium phosphates'cornprise the preferred type of alkaline, .earth metal phosphates.
• alkali metal phosphates include, in addition to sodium phosphates, phosphates of lithium, potassium, rubidium and cesium. It will be further understood, of course, that of these materials, sodium phosphates and potassium phosphates represent the most readily available and practicable materials, it being specifically preferred that sodium phosphates be employed from the alkali metal phosphate group.
• organic phosphates are advantageous and are intended to be encompassed by the term phosphate.
• triaryl phosphates e.g., tricresyl phosphate and triphenyl phosphate, trialkyl phosphates, and the like, as well as diand mono-organic phosphates, may be used.
• alkali phosphates of the foregoing types are calcium phosphates, such as CaHPO CaH (PO and Ca(PO tricalcium phosphate being preferred.
• Specific phosphates include metaphosphates, e.g., NaPO (NaPO KPO; and their hydrates; polyphosphates, e.g., Na P O and its hydrates; pyrophosphates, e.g., Na P O and its hydrates; orthophosphates, e.g., NaH POI, and its hydrates including NaH- PO -H O, Na' 'HPUZWI-I O, and Na PO,,-12H O; and alkali metal phosphates such as monoand di-alkali metal phosphates, e.g., monosodium phosphate and disodium phosphate, monopo assium p e and dipotassium phosphate, and ammonium phosphates, e.g., NH
• a phosphate in the form of a relatively inexpensive material such as one of the naturally occurring phosphatecontaining minerals such as are used as fertilizers and in other applications.
• a relatively inexpensive material such as one of the naturally occurring phosphatecontaining minerals such as are used as fertilizers and in other applications.
• Such materials provide the desired phosphate largely as a calcium phosphate and do not contain as non-phosphate ingredients substances which interfere with the formation of molds and casting of metals therein when this type of phosphate is employed in combination with an alkali metal silicate in accordance with the practice of this invention.
• ground phosphate rock substances such as that which contains about 68%-78% tricalcium phosphate and minor amounts of calcium fluoride, silica and oxides of iron and aluminum.
• a typical analysis of such a material is the following wherein the quantities are expressed in terms of percent by weight:
• Other finely-divided phosphate rock materials variously termed in the trade but generally characterized by containing a substantial proportion of available P also may be used.
• those products containing apatite, (CaF)Ca (PO or CaF -3(Ca P O and the so-called bone phosphates may be used.
• silicates of the various alkali metals including potassium, sodium, cesium, rubidium and lithium may be employed, although sodium silicates and potassium silicates represent the more readily available silicates while sodium silicates clearly constitute the preferred and most practicable silicates. For that reason, special reference will be made herein to sodium silicates although it will be understood that the present invention is not limited thereto.
• alkali metal silicate preferably a odium silicate
• alkali metal silicate may include silicates having varying silic em oxide ratios, e.g., those having a silica to alkali metal oxide ratio greater than l.0:1.0 and desirably within the range from about 1.5 to 3.8 generally being suitable, those silicates having a silica to alkali metal oxide ratio within the range from about 2.4 to 2.84 being preferred at present.
• both liquid and dry silicates may be employed using, where necessary, sufficient water or other liquid to provide the desired silicate solution, slurry, plastic mixture or the like, depending upon the application intended.
• the present invention contemplates the use in the preparation of gas-curable molds of a binder containing an alkali metal silicate having an alkali metal oxide to silica ratio of from about 1.0:1.5 to 1.03.8, such as an Na O:SiO, ratio of 1.0:1.5 to 1.0:3.8.
• the practice of the present invention contemplates as a. finely-divided refractory material refractory substances such as sand, e.g., Ottawa sand, finely-divided a l 14nina, zirconia, ground silica, silica flour, ground firebrick, ground magnesia firebrick, fused r n a gnesia, titanium oxide, beryllium oxide, mullite, sillimanite, as well as various mixtures thereof as well as other materials useful as refractory substances.
• sand e.g., Ottawa sand, finely-divided a l 14nina, zirconia, ground silica, silica flour, ground firebrick, ground magnesia firebrick, fused r n a gnesia, titanium oxide, beryllium oxide, mullite, sillimanite, as well as various mixtures thereof as well as other materials useful as refractory
• phosphate and finely-divided refractory material can be varied, depending upon the metal being cast, the application intended, temperatures employed, and various other factors related to foundry practice, it generally is desirable to employ a major proportion of the finely-divided refractory material and only a minor proportion of the phosphate, this both on the grounds of economy and because only a minor proportion of the phosphate of this invention provides entirely adequate mold collapsibility.
• a mold-forming mixture comprising a phosphate in an amount up to about 5% by weight of the refractory material is desirable, generally amounts ranging from 0.5% to 2.5% by weight being preferred at present, 2% by weight being the specifically preferred amount.
• Optimum results are obtained when at least enough phosphate is added to react with the alkali metal carbonate formed on curing of the mold, e.g., with carbon dioxide, to form a tri-alkali metal phosphate instead of an alkali metal silicate.
• finely-divided refractory and silicate it is preferable, of course, to employ a major proportion of the refractory material and a minor proportion of the silicate as a binder.
• a silicate in an amount up to about 15% by weight, smaller amounts within the range from about 3% to 6% by weight being preferred at present, the specifically preferred amount being 5% by weight.
• the formation of a cured structure in accordance with the present invention comprises subjecting a mixture of a finely-divided, e.g., 60 to l00 mesh, refractory material containing a phosphate and a silicate binder to the action of carbon dioxide, carbon dioxidecontaining gases or other reactive substances capable of converting the mixture into a rigid, high strength material.
• a finely-divided e.g., 60 to l00 mesh
• refractory material containing a phosphate and a silicate binder e.g., a finely-divided, e.g., 60 to l00 mesh, refractory material containing a phosphate and a silicate binder
• carbon dioxide, carbon dioxidecontaining gases or other reactive substances capable of converting the mixture into a rigid, high strength material.
• Mixtures of these or other gaseous materials such as sulfur dioxide, nitrous oxide, hydrogen chloride, as well as various stack gases or other combustion gases, containing substantial amounts of carbon
• the refractory material is blended with the hosphate, which pre era y 15 o t e same or er f mummy term binder being intended to refer to the various alkali metal silicates and alkali metal silicate-containing binder compositions.
• the blending may be done in any suitable manner, as by mulling, or other mixing operation.
• the thus-prepared mixture is then placed in contact with a mold-defining surface such as a pattern.
• a mold-defining surface such as a pattern.
• This can, if desired, be coated with a suitable parting or separating agent.
• carbon dioxide may be injected into a sandphosphate-sodium silicate binder mixture for a period of a few seconds up to one minute or more, depending on the size of the mold being prepared, the fineness of the sand, the proportions of the reactants and the like. After the gas-curing treatment, the mold is ready for immediate use without aging, heating or other curing treatments or processing.
• the unfired or green strength is sulficiently high to permit handling of the mold during mold assembly and other foundry operations without injury thereto.
• the data indexed comparatively in the following examples is obtained by preparing 2" cubes from a mixture of Ottawa 60 grain sand, containing less than .25% water, and a phosphate compound in the indicating percent by weight of said sand, and as a binder a sodium silicate having a ratio of sodium oxide to silicon dioxide within the range from 1:2.2-2.6l which constitutes the especially preferred type of sodium silicate.
• the mold-forming composition is prepared by adding the phosphate compound to the sand and intimately mixing it therewith and then introducing the silicate to complete the mixture.
• the resultant cubes are then cured by impregnation with carbon dioxide for seconds at 20 p.s.i.g. at room temperature.
• the cubes are then sintered at the temperatures indicated for a period of five minutes, and subjected to compression loading using a Tinius Olsen compression testing machine.
• shell molding art which employs thin-walled dispensable molds and cores generally formed of sand and a suitable binder.
• shell molding processes generally have utilized a thermosetting resinous binder and have required a heat curing step prior to casting.
• shell molding operations may be conducted using rigid, thinwalled molds having high gas permeability, good surface smoothness and dimensional stability formed in accordance with this invention by applying a layer of a mixture embodying the invention against a pattern. The thus-formed layer in contact with the pattern can then readily be subjected to the action of carbon dioxide or other gases as described hereinbefore.
• the method of forming a metal casting mold which comprises placing in contact with a casting-defining surface an intimate mixture of a major proportion of a finely-divided refractory material, a minor amount of a phosphate compound selected from the group consisting of alkali metal phosphates, alkaline earth metal phosphates,
• ammonium phosphates and triaryl phosphates the amount of said phosphate compound being at least sufficient to provide mold collapsibility after casting and not greater than about 5% by weight of said refractory,
• silicate is sodium silicate.
• a composition of matter which consists essentially of a major proportion of a finely-divided refractory material, about 3 to 15% by weight of said material of a sodium silicate binder, and a phosphate selected from the group consisting of alkali metal phosphates, alkaline earth metal phosphates, ammonium phosphates and triaryl phosphates in an amount sufficient to provide mold eo'llapsibility and not in excess of about 5% by weight of said refractory.
• composition according to claim 6 wherein the phosphate is an alkali metal phosphate.
• composition according to claim 6 wherein the phosphate is an ammonium phosphate.
• composition according to claim 6 wherein the phosphate is an alkaline earth metal phosphate.
• composition according to claim 6 wherein the phosphate is a triaryl phosphate.
• a metal casting mold comprising a casting-defining structure formed of an intimate mixture of a composition according to claim 7.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Ceramic Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Inorganic Chemistry (AREA)
• Structural Engineering (AREA)
• Organic Chemistry (AREA)
• Mold Materials And Core Materials (AREA)
• Compositions Of Oxide Ceramics (AREA)

Priority Applications (5)

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Cited By (27)

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Citations (8)

• 0
  • BE BE560558D patent/BE560558A/xx unknown
  • LU LU35432D patent/LU35432A1/xx unknown
• 1956
  • 1956-09-05 US US608000A patent/US2895838A/en not_active Expired - Lifetime
• 1957
  • 1957-09-03 GB GB27806/57A patent/GB870805A/en not_active Expired
  • 1957-09-04 FR FR1187827D patent/FR1187827A/fr not_active Expired

Patent Citations (8)

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