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
  • B22C1/18—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
  • B22C1/183—Sols, colloids or hydroxide gels
• • 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

• ABSTRACT OF THE DISCLOSURE A method of making a mold for the casting of metal articles in which a pattern is first coated with a layer of a fine-grained refractory powder containing a binding agent to which a layer of coarser-grained refractory powder is applied while the first layer is externally wet. The so-coated pattern is then placed in a molding box, the solidified coating layer Wetted with a binder and the socoated pattern surrounded with a binder-free granular refractory powder which serves to support the so-coated pattern such that the majority of the binder-free refractory powder can be removed and reused.
• the invention relates to a method of making molds, particularly molds for casting metal articles.
• the pattern In making molds for use in the lost pattern method, it is known to coat the pattern with a layer (coating layer) by means of a suspension of a fine-grained refractory powder containing a binding agent. The layer, while still moist, is sprinkled with a coarser refractory powder, and the resulting layer allowed to solidify. The pattern provided with the solidified layer is then arranged in a mold and this mold is filled up with a granular refractory powder in order to support the thin first layer by means of a supporting mass.
• the last-mentioned powder may contain a binding agent.
• the use of the supporting mass containing no binder results in molds the inner surface of which is readily damaged.
• the use of a supporting mass containing a binder has a limitation in that when the mold need no longer be used, the solidified mass cannot readily be re-used for making molds, but first has to be broken up and ground.
• the method in accordance with the invention does not suffer from the aforementioned limitations.
• This method readily and directly provides molds having highly smooth inner surfaces which are not likely to be damaged, and enables substantially the entire material of the supporting mass to be readily used repeatedly.
• the invention relates to a method of making a mold, particularly a mold for casting metal articles, in which the pattern to the surface of which a release agent may be; if desired, applied, is coated with a coating layer of a finegrained refractory powder containing a binder.
• a refractory powder of coarser grain is applied to the surface of the said layer when it is still moist externally.
• the coating layer is solidified and the pattern surrounded by the coating layer is arranged in a molding box.
• the coated pattern is surrounded by a granular refractory powder acting as a supporting mass, and is characterized in that the solidified coating layer is wetted by a binding agent.
• the method in accodance with the invention is of particular importance in the method of the releasing pattern, especially for making molds for large-size castings the surfaces of which have to satisfy comparatively stringent requirements.
• a pattern may be made from materials known for this purpose, for example, metal, wood or synthetic material. If desired, the model may be coated with a thin layer of a release agent, for example, Vaseline or silicone grease.
• a release agent for example, Vaseline or silicone grease.
• the refractory powder applied to the coating layer when the latter is still externally moist, for example, by sprinkling may be aluminum silicate (particle size from 250 600,14).
• the coating layer may be caused to solidifygenera1ly by gelation-by a known method.
• an acid silicicacid sol is used as a binder solidification may be effected by the action of ammonia or by spraying the layer with a suitable buffer solution, for example, an aqueous solution containing 700 gms. of ammonium acetate per liter, or by heating.
• the material used for the supporting mass may be normal molding sand.
• the molding box containing the pattern covered by the coatinlg1 layer may be disposed, for example, on a vibrating ta e.
• the binding agent used to wet the solid coating layer may be a substance the use of which as a binder is known in making molds, and especially one of the substances used in making molds for precision castings.
• a silicic-acid sol is preferably used.
• the term silicic-acid sol as used powder of the aforeherein includes a solution of polysilicates in which a greater or lesser amount of alkyl radicals, for example ethyl radicals, are present in the polymeric molecules, and a solution of polysilicic acids.
• An example of another binding agent is a solution of sodium silicate.
• Further suitable binders are albumins, such as gelatine, and synthetic substances, such as methyl cellulose.
• the binding agent is preferably used in the form of an aqueous solution or dispersion.
• the binding agent by which the solid coating layer is Wetted must not solidify before or immediately after the provision of the supporting mass. Before the binder solidifies, material of the supporting mass in contact with the coating layer must be satisfactorily wetted so as to produce, after solidification of the binding agent, satisfactory bonding of the coating layer and the supporting mass.
• the binding agent wets a layer of the supporting mass having a thickness of a few millimeters, for example, from 4 to 5 mm., before solidifying.
• a surface-active substance may be added to the solution of the binding agent or to the binding agent.
• the said surface-active substance may, dodecylnaphthyl sodium sulphonate.
• the solidification of the binding agent must be eifected after a suflicient portion of the supporting mass has been wetted.
• the transition to the solid state will frequently be effected by gelation. Gelation will usually have to be initiated by means of an agent.
• This agent may be present in or added to the material of the supporting mass.
• an acid gellable solution of a binding agent is used in combination with an alkaline powder, for example a naturally alkaline molding sand.
• a highly suitable acid gellable solution of a binding agent is an acid silicic-acid sol which may, for example, be obtained by hydrolysis of organosilicates, for example tetra-ethyl silicate or condensed ethylsilicate, with the aid 'of hydrochloric acid or by acidifying a solution of sodium silicate (water glass).
• organosilicates for example tetra-ethyl silicate or condensed ethylsilicate
• a particularly suitable substance for wetting the solidified coating layer is a silicic-acid sol in which the instant of commencement of gelation is determined by the addition of a buffer solution.
• the commencement of gelation may, for example, be set to 4 minutes after the addition of the buffer solution. This was achieved, for example, by adding 3 cc. of an aqueous buifer solution containing 600 gm. of ammonium acetate and 100 gm. of acetic acid per liter to 100 cc. of a silicic-acid sol produced by stirring a mixture of 100 cc. of polyethyl silicate, 75 cc. of ethanol,
• a mold for casting metal articles comprising the steps of coating a pattern with a layer of fine-grained refractory powder containing a binding agent, applying to said coating layer while externally wet a coarser grained refractory powder, solidifying said coating layer, placing the so-coated pattern in a molding box, wetting the solidified coating layer with a binder, and surrounding the so-coated pattern with a binder-free granular refractory powder serving to support the so-coated pattern such that the majority of said binder-free granular refractory powder may subsequently be removed from said molding box in its original binder-free condition.
• the binder for wetting the coating layer is an acid silicic-acid sol, to which a buffer solution containing ammonium acetate is added.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Dispersion Chemistry (AREA)
• Mold Materials And Core Materials (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=19755036

Family Applications (1)

Country Status (8)

Cited By (1)

Families Citing this family (2)

Citations (5)

Family Cites Families (1)

• 0
  • NL NL297791D patent/NL297791A/xx unknown
• 1964
  • 1964-09-07 DE DEN25474A patent/DE1234939B/de active Pending
  • 1964-09-08 GB GB36738/64A patent/GB1018030A/en not_active Expired
  • 1964-09-08 CH CH1171264A patent/CH425095A/de unknown
  • 1964-09-09 BE BE652877A patent/BE652877A/xx unknown
  • 1964-09-09 ES ES0303898A patent/ES303898A1/es not_active Expired
  • 1964-09-10 SE SE10854/64A patent/SE303016B/xx unknown
• 1966
  • 1966-11-14 US US594256A patent/US3339621A/en not_active Expired - Lifetime

Patent Citations (5)

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