JPS63248775A - Manufacture of ceramic core - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to ceramic cores used in investment casting processes, and more particularly to the production of ceramic cores using a single cycle of core firing in refractory sand. It relates to a method of manufacturing cores.

Conventional technology Investment casting methods are widely used in the manufacture of nickel-based and cobalt-based superalloy blades and vanes for gas turbine engines, especially those requiring internal cooling passages. Investment casting methods provide relatively tight dimensional tolerances and excellent surface finishes. In investment casting,
A ceramic mold is formed around the wax mold, and the ceramic core is precisely placed within the wax mold to approximate the desired holes and passageways. The wax pattern is removed during the firing process, leaving the mold and core in place, thereby forming the mold cavity. Molten metal is poured into the mold cavity, where it solidifies and the ceramic core is chemically removed by a method such as leaching with a hot alkaline solution. The use of a removable ceramic core eliminates the need for machining and drilling steps that cannot be performed on superalloy materials.

Ceramic cores are generally manufactured by mixing a core molding composition that includes a ceramic material, such as an amorphous silicon, and a binder. These materials and other ingredients added to adjust various properties are mixed, fluidized, injected into a mold, formed into a core shape, and the molded core is removed from the mold. , placed in a furnace and heated to remove the binder. U.S. Pat. No. 3,234,308 describes a core that is impregnated with a thermosetting resin, such as shellac, before the binder removal process so that the core maintains its shape even after the binder is removed. has been done. The core is then fired to sinter the ceramic material, form a solid core, and decompose the resin.

Many core manufacturers support the core accurately to prevent it from warping during the firing process! It uses a closed ceramic soxé vine that deforms according to the shape of the core.
The removal of the binder and the firing of the core are performed in two independent steps.

For compositions containing binders of different types, two steps are required between the binder removal step and the sintering step.
Weeks may also be required. Over such a long period of time, the fragile core is susceptible to breakage or cracking, and processing time is substantially increased.

Therefore, what is needed in the art is a method of manufacturing ceramic cores that reduces cracking and reduces processing time.

DISCLOSURE OF THE INVENTION One object of the present invention is to provide a method for manufacturing cores for investment casting in which binder removal and sintering are performed in one firing cycle.

Another object of the present invention is to provide a one-cycle method for manufacturing cores that greatly reduces the time required to manufacture cores.

These and other objects of the present invention provide for preparing a core molding composition (7) mixing the composition with a low viscosity evaporable binder, molding the mixture into a desired shape, embedding the core in non-reactive refractory sand and firing the sand and the shaped core disposed therein at a controlled temperature, the binder being drawn into the sand pile by capillary action; This is accomplished by using a method of manufacturing cores that evaporates or decomposes in the sand pile.The core, with the binder removed and well supported in the sand pile, is then exposed to relatively high temperatures to cause sintering. Ru.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will be explained in detail below by way of example embodiments with reference to the accompanying figures.

DETAILED DESCRIPTION OF THE INVENTION A process for manufacturing a ceramic core includes preparing a core molding composition, molding the core, removing the binder, and sintering. Powder mixing, ceramic powder surface treatment,
Preparing the binder, mixing the treated powder mixture with the binder, molding the core molding composition, and pelletizing the composition so that the core molding composition is uniformly fed into the injection molding machine. Other processing steps may be included, such as.

For purposes of illustration, the core molding composition may contain up to 35 wt% zircon, up to 5 wt% fumed silica, and 6.5 wt% zircon.
t% of alumina fibers and the balance amorphous silica, added in an amount sufficient to ensure that the binder maintains the molded shape until firing, and to ensure optimum wetting of the binder to the surface of the powder. It is assumed that a sufficient amount of silane binder is added. These components are described in Japanese Patent Application No. 1983 filed on the same date as the present application and by the same applicant. This composition is an exemplary composition;
It will be appreciated that the components of the composition and their concentrations may be varied to produce cores with varying strength and shrinkage properties. For example, the method of the invention may be applied to core components of silica, alumina, and zircon and mixtures thereof.

The selection of binder components generally depends on the particular application1 and includes mixtures of paraffin waxes, lubricants, and mold release agents. However, the actual relaxation of the method of the present invention requires a low viscosity, vaporizable binder. In this specification,
"Low viscosity" means that the binder has fluidity even at the binder removal temperature, and "evaporable" means that the binder substantially evaporates or decomposes at the binder removal temperature. It means to get. It should be noted that a small amount of the binder composition may not be vaporizable without departing from the above definition. For example 20
% of the binder mixture may remain in the core without detracting from the advantages of the invention. Additionally, the binder selected must exhibit a low viscosity under injection molding conditions to increase moldability, with viscosities of about 10,000 centipoise being typical.

One such low viscosity evaporable binder is 131~
Contains 3363% paraffin wax with a melting point of 136°C, 33.3% paraffin wax with a melting point of 144-149°C, and 33.3% mineral wax with a melting point of 163-1.72°C. Contains aluminum stearate, phosphoric acid, and beeswax, which are used as internal lubricants, mold release agents, and peptizers.

Once the core molding composition is mixed with a low viscosity evaporable binder, the core molding composition is molded into the desired shape using a plunger or screw molding machine and conventional molds. Any molding machine may be used, but
Best results are obtained when using a molding machine in which injection temperature, injection speed, and injection pressure are electronically feedback controlled. It is not possible to find universal molding conditions, and the optimal molding conditions must be determined through trial and error, but the molding temperature is 180~230°C (82~110°C) and about 4000~jo000 ps! (281-70
A pressure of 3 kg/cd) is common.

The formed core is removed from the mold and placed in a firing sheath or box containing refractory sand therein. It is important that the core is fully embedded in the sand pile to ensure adequate support and maximum heat transfer. For example, about 0. 0017
Alumina sand with a particle size of 1 nch (0,043 mm) is used. Any non-reactive sand that can withstand the firing temperatures may be used.

The firing sheath is then placed in the furnace and the firing cycle begins. The firing shell is heated externally and the heat is transferred through the refractory sand to the core, possibly creating a temperature gradient between them. When the molded core is heated, a low viscosity, vaporizable binder is drawn from the molded core into the sand pile by capillary action. The binder is then evaporated or decomposed, thereby completing the binder removal process. At this point, the core is very fragile. However, since the sand is essentially fluid, it will be displaced as the core shrinks.
The surface of the core remains fully supported throughout the core firing cycle. The temperature is then increased to the sintering temperature, and the sintering temperature is maintained until the ceramic particles are sintered, thereby forming the core.

EXAMPLE A 6-bond (2.7 kg) batch of core molding composition was prepared for injection molding ceramic cores.

The concentrations of each component are shown in Table 1 below.

Table 1 Component Concentration (wt%) Amorphous silica 62.64 Zircon 27.84 Humid silica 4.12 Alumina fiber 4.16 Silane binder 1.24 * Silane binder with fiber diameter 5 lt and fiber length 3.18 mm The substantially polar ceramic surface of the composition is converted to a surface of a non-polar nature that is readily wetted by a non-polar binder material. For example, the silane binder is Union Carbide A1108. After mixing, the wet powder mixture is dried at about 220° C. (104° C.) for 3 hours.

The ceramic core is then mixed with a low viscosity vaporizable binder in a vacuum mixer. The mixture of wax and binder is 33.3% with a melting point of 131-136°C
of paraffin wax, 33.3% paraffin wax having a melting point of 144-149°C, and 163-17% paraffin wax.
3% mineral wax such as ceresin, which has a melting point of 2°C. In order to further optimize the properties of the binder, a mixture of beeswax (4 parts), aluminum stearate (12 parts) and oleic acid (8 parts) is added. Approximately 13.5 wt% binder is added to the core molding composition. The mixing time depends on the batch and in this example is approximately 3 hours at a temperature of 220° C. (104° C.). The core molding composition is then extruded and pelletized, preferably using a die face beretizing process to provide optimum flow properties during the subsequent molding process. The pelletized molding composition is stored in a low humidity room until the need for use arises.

A ceramic core is then molded using a conventional plunger-type injection molding machine and a conventional mold. The core is then removed from the mold and placed in a firing sheath containing approximately 0. It is placed in an alumina sand pile with a grain size of 0.0017 inch (0°043 mm). The glass is then placed in a programmed and electronically controlled furnace and subjected to a firing cycle during which the binder is first removed from the core at a low temperature without disturbing the shape of the core; The ceramic particles are then sintered at relatively high temperatures.

The accompanying figures illustrate an exemplary binder removal and sintering firing program for use with the core molding compositions described above. First, the sand and core are heated to 750 degrees below ambient temperature (399 degrees Celsius).
The temperature is increased at a rate of 135°C (75°C) per hour.

During this temperature rise, the binder is removed from the core by capillary action. As the binder is drawn into the sand pile, it evaporates or decomposes, thereby forming a core supported in alumina sand and free of binder. The remaining binder is combusted during the heating process at a rate of 150°C per hour to a sintering temperature of about 2250'F (1232°C). The core is maintained at the sintering temperature for about 3 hours, during which time complete sintering occurs between the ceramic particles and a solid core is formed. The core is then furnace cooled at a temperature reduction rate of 540° C./hour (300° C.), and the cooled core is removed from the firing sheath and prepared for core finishing and wax molding.

Although preferred embodiments of the present invention have been described in terms of core molding compositions containing specified amounts of ingredients, the composition may be varied to provide other desirable properties within the scope of the present invention. Good things will be understood. Also, although a particular binder removal and sintering program has been described, it will be understood that times and temperatures may be varied within the scope of the invention.

[Brief explanation of drawings]

The accompanying figure is a graph illustrating one typical core firing program. Patent Applicant: UnitedφTenologies Corporation Agent: Patent Attorney: Akashi
Takeshi Shou (self-motivated) 1. Indication of the incident Patent Application No. 41787 of 1988 2.
Name of the invention Method for manufacturing ceramic cores 3, Relationship to the amended case Address of the patent applicant: Financial Brothers, Hartford, Connecticut, U.S.A. 1 Name: United Chiknoroses Corporation 4, Agent's residence: 104 Tokyo, Japan 1-5-19 Shinkawa, Chuo-ku (
1) “Patent Application 1986, page 6, lines 14 to 16 of the specification”
. . .'' is corrected to ``It is described in Japanese Patent Application No. 63-41786. This composition is an exemplary composition.''

Claims (1)

[Claims] A core molding composition is prepared, the composition is mixed with a binder, the mixture is molded at controlled temperature and pressure to form a molded core, and the molded core is formed by molding the mixture at controlled temperature and pressure. a method of manufacturing a ceramic core comprising firing a molded core to remove the binder and sintering the molded core, the method comprising: mixing the composition with a low viscosity evaporable binder; embedding the core in non-reactive refractory sand; the binder is sucked from the core into the sand, the core is fully supported by the sand, and the sand and core are firing the refractory sand and the shaped core within the refractory sand at a controlled temperature to expose it to a sintering temperature, thereby forming a solid core. Method of producing children.