RU2647074C1 - Method of manufacturing shell molds for consumable patterns - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to foundry. Shell mold is prepared by layer-by-layer application of the slurry onto the model and sprinkling each layer with a granular material. Mold is dried and cured. Model is melted. Sprinkling of the layers with granular material and drying are combined. Drying is carried out in the layer of the back-up granular material of the substrate under the action of the air pressure gradient. Difference in air pressure above and below the layer of the back-up granular material is created by vacuuming the space under a granular material layer.

EFFECT: provides an improvement in the quality of the shell molds produced.

1 cl, 1 dwg, 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 manufacturing process of shell molds.

A known method of drying molds using investment casting, in which the external air 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, dp 23.07.1982).

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 according to investment casting, consisting in the operations of layer-by-layer deposition 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 excess air pressure 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, CL V22C 9/04, 04/20/1995).

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.

Closest to the claimed method is a "Method for manufacturing shell molds using investment casting", in which the manufacture of shell molds using investment casting includes the operations of layer-by-layer application of the suspension on the model, sprinkling each layer with granular material, drying and processing the mold, smelting the models, and operations of sprinkling layers granular material and drying 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 air flow up to 0.1 MPa / m with an excess air pressure at the inlet of the working chamber of up to 0.3 MPa. In this method, it is possible to broadly control the processes of shaping and to obtain cast ceramic shell molds with increased strength, density and lower roughness of the working surface while reducing the drying cycle of each layer of the mold by 2-4 times (RF Patent No. 2359777, IPC B22C 9/04 published on June 27, 2009).

The disadvantages of this method include the need to seal the drying chamber to create above the surface layer of the support granular material of air overpressure. In addition, process vessels with increased air pressure up to 0.5 MPa are related to installations with increased danger, they are subject to stringent requirements for design, protection and use technology.

The technical result is an increase and implementation of the ability to control the quality of the produced shell molds, as well as an increase in the drying speed in comparison with analogues.

The technical result is achieved by the fact that in the method of manufacturing shell molds by investment casting, which includes layer-by-layer application of the suspension on the model, sprinkling of each layer with granular material, drying and curing, smelting of models in which the sprinkling of layers with granular material and drying are combined, drying is carried out in a support layer granular material of the base under the action of a gradient of air pressure, while the difference in air pressure above and below the layer of supporting granular material is created by evacuating the space under OEM particulate material.

The essence of the proposed technical solution lies in the fact that the drying process takes place under atmospheric pressure p _at , and after applying a layer of refractory base material, the model block remains immersed in the off "fluidized bed". The space under the layer with a thickness h of granular refractory material is evacuated (a residual pressure p _{vac is created} ), while a gradient of air pressure in the granular layer is created (p _at -p _vac ) / h = 0.06 ... 0.4 MPa / m with a real possible difference pressure p _at -p _vak = 0.03 ... 0.08 MPa and a granular layer thickness of 0.2 ... 0.5 m. Such a gradient is sufficient to implement the process of intensive drying of the forms.

The method is illustrated in the drawing, which gives a diagram of a vacuum dryer.

The design of the installation includes a housing 1, in which perforated partitions 2 are fixed, a felt pad 3 is clamped between them. A portion of granular refractory 4 is poured into the installation. Pipes 5 and 7, in which valves 6 and 8 are installed, are welded into the lower part of the housing under the partitions 2.

The method is carried out in the next cycle. The valve 6 includes an air supply for boiling a layer of sand. A model (or a model with layers of refractory coating on it) painted with refractory paint is immersed in sand. Switch off the air supply by valve 6 and turn on valve 8 to pump out air from under gasket 3. After the refractory paint has dried (drying time is determined empirically), valve 8 is turned off by vacuum, valve 6 is turned on to boil a layer of sand and a model with a dried paint layer is removed. The next drying cycle can be resumed.

To assess the effect of drying conditions 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 pumping out an air stream.

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 - atmospheric air with a temperature of 20 ° C and a relative humidity of 60%, air was supplied to the boiling layer of sand from a laboratory compressor The air was evacuated from the installation by a VVN-1.5M water ring vacuum pump with an engine power of 5.5 kW. The drying operation time of the prototype molds is 30 minutes. During drying, the residual air pressure under the felt membrane of 0.05 MPa was determined. The pressure gradient with a layer thickness of granular refractory h = 0.15 m was 0.33 MPa / m. Samples were made from 5 layers of refractory coating using serial technology (air drying for 3 hours) and vacuum drying technology in a layer of granular refractory. On the obtained images, density, gas permeability, bending strength, surface roughness are determined.

The use of the invention will improve the quality of cast ceramic shell molds by investment casting in terms of strength, density, and surface roughness. At the same time (in comparison with the prototype) the drying process of the molds is less labor intensive, the drying unit is safe and reliable in operation.

Claims (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 and drying combined with it in a layer of supporting granular material under the influence of an air pressure gradient, curing and melting of the model, characterized in that they create a difference in air pressures over and under the layer of supporting granular material by evacuating the space under the layer of granular material.

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