RU2359777C1 - Manufacturing method of shell moulds by dispensable pattern - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to foundry field. Method includes layerwise application of suspension on pattern, dusting of each layer by particulate material, drying, consolidation and melting of patterns. Layers dusting by particulate material and drying are overlapped and implemented in the layer of particulate material under the action of external excess pressure gradient into controlled - directed flow of drying agent. For patterns with ethyl silicate binding agent drying is implemented at external excess pressure gradient of air up to 0.1 MPa, herewith excess pressure at out into the work chamber is up to 0.3 MPa.

EFFECT: it is achieved improvement of finished casting moulds by strength and density.

2 cl, 1 tbl

Description

The invention relates to investment casting and can be effectively used in operations of layer-by-layer deposition and drying of coatings in the process of manufacturing shell molds.

A known method in which the external pressure on the coating material is carried out throughout the drying and curing of each of the coatings. (USSR author's certificate No. 944746, class B22C 9/12, 07.23.1982.)

However, the magnitude of the external pressure used in the known method is very small and insufficient to increase the strength and crack resistance of shell forms.

It is known to manufacture shell molds by investment casting, including the operations of layer-by-layer application of a suspension onto a model, sprinkling of each layer with granular material, drying and processing of the mold, and melting of models. (UK patent No. 1124828, CL B5A, 1968.)

Closest to the claimed one is the method, which consists in the fact that in the manufacture of shell molds by investment casting, including the operations of layer-by-layer application of a suspension on a model, sprinkling of each layer with granular material, drying and curing of each layer is carried out under an external overpressure of not more than 1.5 MPa . In this case, drying and curing of the last layer is carried out simultaneously with the smelting of models at a temperature of 10-15 ° C above the melting temperature of the model. (RF patent No. 2033292, class B22C 9/04, 1995.)

The disadvantages of this method include the low intensification of the drying process. The concentration of binder vapors in the volume of the drying agent above the surface of the formed layer increases with drying, reducing the speed of the evaporation process.

The technical result of the invention is to increase and implement the ability to control the quality of produced shell molds.

The technical result is achieved by the fact that in the inventive method for manufacturing shell molds by investment casting, including the operations of layer-by-layer application of a suspension onto a model, sprinkling of each layer with granular material, drying and processing of the mold, smelting of models, operations of sprinkling layers with granular material and drying are combined. The drying operation is carried out in a layer of supporting, granular material of the base of the mold under the action of a gradient of external excess pressure in a controlled flow of a drying agent. For drying molds with an ethyl silicate binder, a gradient of external excess pressure is created in a controlled directional air flow up to 0.1 MPa with an excess air pressure at the inlet of the working chamber up to 0.3 MPa.

The essence of the proposed technical solution lies in the fact that after applying a layer of refractory base material, the model block remains immersed in the off "fluidized bed". After sealing the working chamber, through special fittings, supply to the chamber (with overpressure p _in ) and removal of the drying agent (with overpressure p _out ) at a given pressure gradient are provided:

p _in- p _out ≤0.6 MPa.

Setting a predefined optimal gradient of the excess pressure of the drying agent in the working chamber makes it possible to widely control the formation processes and obtain cast ceramic shell molds with increased strength, density and lower roughness of the working surface.

Pressure gradients with absolute values of external excess pressures up to 0.2 MPa at the inlet to the working chamber and from 0.0 MPa at the outlet do not provide:

1) the necessary pressure on the grains of the base material involved in the formation of the shell mold layer to increase the strength and density of the molds;

2) the required speed of movement of the drying agent over the surface of the deposited layer to intensify the drying processes by creating conditions of forced convection.

Pressure gradients from 0.3 MPa with absolute values of external overpressure from p _i = 0.3 MPa at the inlet to the working chamber and p _o = 0 MPa at the outlet from the chamber negatively affect the quality of the shell molds, since under these conditions the destruction of the binder film in the formed shell layer is observed.

To assess the influence of the conditions of the volume-stress state on the formation of the properties of cast ceramic shell molds, an experiment was performed on a laboratory setup with a working cylinder capacity of 1.6 dm ³ , which had separate fittings for supplying and discharging the flow of the drying agent.

For the manufacture of prototypes were used: electrocorundum of various grades (from 012 to 50), a binder - hydrolyzed ethyl silicate ETS - 40, a drying agent - compressed air from a factory pneumatic network. Drying operation time - 40 min.

The strength of ceramic shell forms was determined by the formula

where σ _and is the strength of the ceramic shell forms in bending, kgf / cm ² ;

P is the force bending a ceramic sample in the form of a plate, kg;

l = 5 cm - the distance between the supports on which the bent sample of the shell shape is laid with a length of L = 6.5 cm,

b = 2 cm is the width of the shell-shaped sample;

h = 4 cm is the thickness of the shell-shaped sample.

The quality of shell-type ceramics was evaluated on the same samples by the parameters of gas permeability, density, and roughness of the working surface.

Table 1 - Technological parameters of prototypes and serial samples

Sample Overpressure at the inlet to the working chamber, MPa Overpressure at the outlet of the working chamber, MPa Pressure gradient, MPa Strength σ _and , kgf / cm ² Density,
g / cm ³ Gas permeable
bridge, units Experienced 0.5 0.4 0.1 18,235 2,155 2.96 Experienced 0.4 0.3 18,620 2,326 2.99 Experienced 0.3 0.2 20,185 2,447 3,028 Serial - - - 19.33 2,3160 3,514 Note: errors in determining pressure up to 0.02 MPa, strength up to 0.1 kgf / cm ² , density up to 0.01 g / cm ³ , gas permeability up to 0.1 units.

The use of the invention will improve the manufacturing quality of cast ceramic shell molds by investment casting in terms of strength and density.

Claims (2)

1. A method of manufacturing shell molds according to investment patterns, including layer-by-layer deposition of a suspension on a model, sprinkling of each layer with granular material, drying and curing, melting of models, characterized in that the layers are sprinkled with granular material and drying are combined, while drying is carried out in a granular support layer base material under the action of a gradient of external excess pressure in a controlled directional flow of a drying agent. 2. The method according to claim 1, characterized in that the drying of the molds with an ethyl silicate binder is carried out with a gradient of external excess pressure in a controlled directional air flow of up to 0.1 MPa, while the excess air pressure at the outlet to the working chamber is up to 0.3 MPa