US2945273A - Casting mold and method of preparation - Google Patents

Casting mold and method of preparation Download PDF

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Publication number
US2945273A
US2945273A US730481A US73048158A US2945273A US 2945273 A US2945273 A US 2945273A US 730481 A US730481 A US 730481A US 73048158 A US73048158 A US 73048158A US 2945273 A US2945273 A US 2945273A
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Prior art keywords
mold
layer
layers
binder
molds
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US730481A
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English (en)
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Herzmark Nicolas
Clarens-Montreux
Leschot Auguste
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    • 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
    • B22C1/165—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 in the manufacture of multilayered shell moulds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C9/00—Moulds or cores; Moulding processes
    • B22C9/02—Sand moulds or like moulds for shaped castings
    • B22C9/04—Use of lost patterns

Definitions

  • the invention relates to improved refractory jointless shell molds for investment casting, and to a method of preparing such molds.
  • Such molds are generally made by applying to the surface of a destructible or fusible pattern a slurry of a finely divided refractory material with a binder, which consists mostly of organic silicates, aquaor organosols of silica, or acidified inorganic silicates.
  • a binder which consists mostly of organic silicates, aquaor organosols of silica, or acidified inorganic silicates.
  • Such molds should combine sufficient strength for withstanding mechanical stresses, particularly the pressures produced by pouring the metal to be cast, with a certain porosity allowing escape of water vapor and gases so as to avoid cracking of the mold during manufacture and use.
  • the conventional procedures for the preparation of investment molds have not yet solved satisfactorily the problem of imparting to molds simultaneously optimum strength and porosity, because said two properties appeared to a certain extent to be mutually exclusive.
  • the shell mold is built up from several layers,'whereby the inner layers provide the required porosity and elasticity and the outer layers impart the necessary strength and rigidity.
  • the inner layers provide the required porosity and elasticity and the outer layers impart the necessary strength and rigidity.
  • We obtain such differentiation by converting a major portion of the used potassium or sodium silicate binder in the inner layer to a silica gel while the binder in the outer layers is essentially silicate which has been insolubilized by heating.
  • Fig. 1 is a diagrammatic View, partly in section of a mold according to the invention built up around a cluster of patterns attached to a main sprue;
  • Figs. 2 to 6 illustrate diagrammatically on an enlarged scale the gradual build-up of the mold by applying tothe patterns successive alternate layers of refractory coatings and sandings, whereby the four outer refractory coatings are treated differently from the preceding inner coatings.
  • the reference numeral 1 designates a preformed refractory or metallic block, carrying a main sprue 2 attached to the patterns 3.
  • said patterns are shown as simple cylindrical bodies with a cylindrical stem.
  • a first layer d of a refractory slurry (Fig. 2) is formed.
  • a refractory slurry (Fig. 2) is prepared by combining two diiferent refractories with an alkali metal silicate binder.
  • thermal shock treatment has the efiiect of removing 2345273 Patented July 19, 1960 Said slurry is applied by spraying or. dipping in such an amount that the thickness of the layer is about 0.2 to 0.4 mm.
  • coated patterns are then sanded with a coat e of a dry refractory such as silica sand of to mesh whereby the thickness of the layer is increased to about 0.7 to 0.9 mm.
  • a dry refractory such as silica sand of to mesh
  • the entire cluster is then contacted with an acid atmosphere for a short period of time, for instance one minute or less, whereby the gaseous acid reacts with the silicate to, form the corresponding sodium salt and free SiO
  • This treatment hardens the coating and renders it suitable for the subsequent application of a second slurry layer d and sand layer e which are treated with a gaseous acid in the same manner as described for the first layers.
  • This procedure is repeated until a mold of a desired thickness, for instance, 4.5 to 6 mm, has been built up; in the mold shown in the drawing, seven layers (slurry+sanding) were used (Fig. 6).
  • the rapid insolubilization of the successive layers provides for 'a firm anchoring of each layer in the preceding layer.
  • the silica gel binder is formed by the reaction
  • such an amount of acid should be reacted with the alkali metal silicate that the mol ratio of silica gel formed to remaining alkali metal silicate in the treated layers is about 2 to 5:1.
  • the acid treatment is not applied to the last layer or layers where-. by the number of untreated outer layers will depend on the strength and hardness of the mold required for the particular casting process used. Generally, it will be adequate to omit the acidfying treatment of the outermost or the last two to four layers and to replace said treatmentby drying instead each of said layers in a current of air at a temperature of about 40 to 45 C.
  • Said air drying operation converts the layer within 30 to 40 minutes to a very hard rigid structure of reduced porosity, whereby the sodium silicate is insolubilized.
  • the mold may be dipped into an inflammable organic solvent for water, such as alcohol, acetone, or dioxane.
  • an inflammable organic solvent for water such as alcohol, acetone, or dioxane.
  • the outer non-acidified layers may be dried by subjecting the mold for a short time of about 30 to 60 seconds to a temperature of about 250 to 850 0, whereby the higher temperatures correspond to shorter heating times.
  • a short time of about 30 to 60 seconds to a temperature of about 250 to 850 0, whereby the higher temperatures correspond to shorter heating times.
  • the wax patterns areprotected by several acidified layers containing .a certain amount of moisture, the short heat shock will not produce premature melting of the pattern.
  • the heating time and temperature will depend on the surface of the mold; the larger the surface, the shorter will be the heating time to avoid the penetration of the heat beyond the thickness of the treated layer.
  • the completed mold consists of an inner and an outer shellportion whereby the major part of the silica binder in the inner shell portion is present in the form of'silica gel and in the outer portion in the form of insolubilized alkali metal silicate; the thicknessof the inner shell portion should be about 4 to 4 times that of the outer shell portion.
  • the mold is then subjected to a drying operation, Where slowly increasing temperatures are applied. We have found it of great advantage to carry out the first drying step at a temperature of 35 to 45 C. because at said temperature the viscosityof the water decreases by 50 percent, which increases considerably the rate of diffusion of the water contained in the mold layers to the outside.
  • the temperature may be increased rapidly until the patterns of fusible material have been molten and withdrawn through the sprue.
  • the drying cycle may be as follows: 3 hours at 40 C., 2 hours at 50 C., Zhours at 60 C., and then heating at 100 C. until the wax patterns have been melted out.
  • a total amount of .about 40 .to 50 percent of the total water contained in the coatings should be removed at temperatures not exceeding about 60 C.
  • the gradual pro-heating of the molds maybe omitted and the molds may be heated directly to atemperature of 80 to 90 C. to melt the patterns. The remaining moisture is quickly removed at said temperature-whereupon the molds are ready for the final heat treatment described hereinafter.
  • the shell moldsstill adhering to the refractory block are placed in a dryingoven for complete drying and removal of any organic substances.
  • the conventional preparation of shell molds it is generally necessary to increase the temperaturegradually from about 200 to 1000 C.'over a period of 12m 22 hours to prevent cracks and deterioration of the molds,- molds prepared according to the invention may be heated directly without injury at about 800 to 900, and are. ready to receive the casting metal after a heating time of only about 1 hour.
  • a wax pattern was dipped in aslurry of the following composition:
  • the coated pattern was dusted with silica. passing a 1.00 mesh sieve, thereby increasing the thickness of the layer to 0.7 mm., and then exposed for-50 seconds to the action of. carbon dioxide.
  • the dipping, sanding, and carbon dioxide treatment were repeated 3 times; subsequently a fourthlayer was applied by dipping andsanding, .butthistimethe mold was not exposedto carbon dioxide but heated for 30 minutes in air of about 42 C., whereby about 25 g. of water were evaporated.
  • a fifth and sixth layer were applied in the same manner, and the mold was once more dipped and sanded to apply a seventh layer as the last layen The heating insolubilizes'thesodium silicate and prevents its dissolution on application of the next layer.
  • the mold was then heated to about 100 C. to melt the wax, and after removal of the wax it was fired, withoutany external support, for only 50 minutes at 900 C., whereupon it was ready for casting, which was also carried out in the unsupported shell.
  • the molds according to the invention comprise an elastic and porous inner gel portion and ahard rigid outer portion .of insolubilized silicates, -the invention allows of adjusting the properties to the desired requirements by adjusting the relative thicknesses of said inner and outer portions.
  • the very short manufacturing cycle considerably'simplifies the manufacture of the shell molds and renders our process suitable for automatic mold production.
  • a shell mold for investment casting consisting essentially of a comminuted refractory material and a silica binder for said refractory material, said mold comprising at least one inner layer in which the major portion of said binder is present in the form of silica gel, the balance being alkali metal silicate, and at least one outer layer containing the binder essentially in the form of alkalimetal silicate, said inner layer imparting to the mold porosity and elasticity and said outer layer imparting strength and rigidity.
  • a 'method of preparing a jointless'shell suitable for investment casting comprising repeatedly coating a fusible pattern with an aqueous slurry containing comminuted refractory material and an alkali metal silicate binder, treating each coat with an inorganic gaseous acid for a time sufiicient to convert at least half the amount-of said alkali metal silicate binder into a silica gel and the alkali metal salt of said acid, applying to the thus coated pattern additional outer coatings of said the the aqueous slurry while discontinuing said treatment withan inorganic gaseous acid, partially dehydrating and thereby insolubilizing the alkali metal silicate binder individually by a heat shock treatment of each of said additional coatings, and removing the fusible pattern, said first applied silica gel containing coatings providing a porous inner shell portion of the mold and said insolubilized alkali metal silicate containing coatings providing a hard rigid outer shell portion of the mold.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Mold Materials And Core Materials (AREA)
  • Molds, Cores, And Manufacturing Methods Thereof (AREA)
US730481A 1957-04-25 1958-04-23 Casting mold and method of preparation Expired - Lifetime US2945273A (en)

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CH841873X 1957-04-25

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US (1) US2945273A (sl)
AT (1) AT208006B (sl)
BE (1) BE566932A (sl)
CH (1) CH344526A (sl)
FR (1) FR1204586A (sl)
GB (1) GB841873A (sl)
IT (1) IT588302A (sl)
NL (1) NL227109A (sl)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3070861A (en) * 1960-03-10 1963-01-01 Philadelphia Quartz Co Molds utilizing acid hydrolysed isopropyl silicates as binders
US3209421A (en) * 1961-03-30 1965-10-05 Monsanto Chemicals Production of refractory molds
US3241200A (en) * 1963-09-20 1966-03-22 Howe Sound Co Precision mold and method of fabrication
US3262792A (en) * 1962-09-14 1966-07-26 Harbison Walker Refractories Investment molding method and composition
US3451831A (en) * 1964-07-24 1969-06-24 Glaverbel Process for agglomerating vitrifiable masses and the products thereof
US3692086A (en) * 1968-12-27 1972-09-19 U C P I Sa R L Pour L Utilisat Method of making a precision casting layered mold
US3854961A (en) * 1970-12-30 1974-12-17 Stauffer Chemical Co Preparation of high temperature shell molds
US4059453A (en) * 1973-10-03 1977-11-22 Dynamit Nobel Ag Method of making molds for the casting of metals
US4226277A (en) * 1978-06-29 1980-10-07 Ralph Matalon Novel method of making foundry molds and adhesively bonded composites
US4244551A (en) * 1978-06-30 1981-01-13 United Technologies Corporation Composite shell molds for the production of superalloy castings
US4541474A (en) * 1979-12-21 1985-09-17 Castolin S.A. Process for manufacturing a moulding plunger for hollow glass objects

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1216492B (de) * 1961-10-31 1966-05-12 Prec Metalsmiths Inc Verfahren zur Herstellung von Praezisionsgiessformen mit verlorenen Modellen

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB712276A (en) * 1951-09-05 1954-07-21 Renault Preparation of moulds for precision casting
GB716394A (en) * 1952-04-03 1954-10-06 Shaw Processes Ltd Improvements in or relating to moulds for metal casting
GB742361A (en) * 1951-08-30 1955-12-21 Renault Improved process for making moulds for "cire-perdue" precision casting
GB774184A (en) * 1954-03-31 1957-05-08 Shaw Processes Ltd Improvements in or relating to moulds for metal casting
US2806270A (en) * 1953-07-17 1957-09-17 Rolls Royce Method of making moulds for precision casting
GB787052A (en) * 1954-10-25 1957-11-27 Rolls Royce Moulds for casting metals and alloys

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB742361A (en) * 1951-08-30 1955-12-21 Renault Improved process for making moulds for "cire-perdue" precision casting
GB712276A (en) * 1951-09-05 1954-07-21 Renault Preparation of moulds for precision casting
GB716394A (en) * 1952-04-03 1954-10-06 Shaw Processes Ltd Improvements in or relating to moulds for metal casting
US2806270A (en) * 1953-07-17 1957-09-17 Rolls Royce Method of making moulds for precision casting
GB774184A (en) * 1954-03-31 1957-05-08 Shaw Processes Ltd Improvements in or relating to moulds for metal casting
GB787052A (en) * 1954-10-25 1957-11-27 Rolls Royce Moulds for casting metals and alloys

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3070861A (en) * 1960-03-10 1963-01-01 Philadelphia Quartz Co Molds utilizing acid hydrolysed isopropyl silicates as binders
US3209421A (en) * 1961-03-30 1965-10-05 Monsanto Chemicals Production of refractory molds
US3262792A (en) * 1962-09-14 1966-07-26 Harbison Walker Refractories Investment molding method and composition
US3241200A (en) * 1963-09-20 1966-03-22 Howe Sound Co Precision mold and method of fabrication
US3451831A (en) * 1964-07-24 1969-06-24 Glaverbel Process for agglomerating vitrifiable masses and the products thereof
US3692086A (en) * 1968-12-27 1972-09-19 U C P I Sa R L Pour L Utilisat Method of making a precision casting layered mold
US3854961A (en) * 1970-12-30 1974-12-17 Stauffer Chemical Co Preparation of high temperature shell molds
US4059453A (en) * 1973-10-03 1977-11-22 Dynamit Nobel Ag Method of making molds for the casting of metals
US4226277A (en) * 1978-06-29 1980-10-07 Ralph Matalon Novel method of making foundry molds and adhesively bonded composites
US4244551A (en) * 1978-06-30 1981-01-13 United Technologies Corporation Composite shell molds for the production of superalloy castings
US4541474A (en) * 1979-12-21 1985-09-17 Castolin S.A. Process for manufacturing a moulding plunger for hollow glass objects

Also Published As

Publication number Publication date
FR1204586A (fr) 1960-01-27
AT208006B (de) 1960-03-10
GB841873A (en) 1960-07-20
CH344526A (fr) 1960-02-15
BE566932A (sl)
IT588302A (sl)
NL227109A (sl)

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