SU825269A1 - Method of producing casting moulds - Google Patents

Description

This invention relates to foundry, manufacturing, in particular, to vacuum forming technology. A known method of making molds from wet sand, is cured by freezing. Freezing is carried out by circulating air / liquid sal or liquid nitrogen from the cooling device flj. The disadvantage of this method is the complexity and the long duration of the freezing of the mixture over the entire depth of the molds, which leads to a restriction of the weight and dimensions of the castings. Closest to the claimed technical method is a method of making a mold from loose sands, including placing the flask on a submodel slab, forging a facing layer from a molding material containing a binder, filling the flask with a filling material and creating a vacuum in the mold cavity. A mixture of ethyl silicate with a thermoplastic resin is used as a binder. The curing of the binder is accelerated by blowing air to remove the solvent and heating the facing layer of the mold after removing model G21. The disadvantage of this method is the increased consumption of filling and bonding materials and the laboriousness of knocking out castings due to the formation of a durable, non-regenerable casing, as well as poor sanitary and hygienic working conditions due to the release of harmful gaseous substances when it interacts with the metal. The purpose of the invention is to reduce the consumption of molding materials, reducing the labor intensity of casting out castings and improving sanitary and hygienic working conditions. The goal is achieved by the fact that the sealing facing layer is formed of moistened sand, and the submodel slab is cooled to a negative temperature. In addition, the humidity of the sand is kept in the range of 4.0-8.0%, and the submodel slab is cooled to a temperature not higher than -20 ,. In contact with the cooled submodel slab, the moistened facing layer freezes, providing, after the attachment of the submodel slab, sealing and strength of the working surface of the mold for a certain time. Pbd the action of a vacuum occurs mechanical adhesion of the cladding layer with the filling material. In the process of pouring the molten metal, the frozen facing layer retains the necessary strength to form a solid metal rind of the casting, and a layer of water vapor forms between the metal and the mold, which prevents the penetration of the metal into the mold, causing clogging and burnout. Under the influence of casting heat, the cladding layer rises and moisture evaporates, further the strength of the cladding layer is maintained by the air pressure drop. After relieving the vacuum, the sand is lightly poured out and fully returned for reuse. The proposed method is intended for the manufacture of loose sand molds for the production of small and medium weight castings from ferrous and non-ferrous alloys. . Example. Receiving a batch of castings bearing caps from cast iron SCh 12-28 (weight. 1.5 kg, dimensions 145 J 17 mm) in forms of loose dogs Preferred. the way

Options

The temperature of the model plate, with

-15 T -20 G Duration of hardness of the sealing facing layer, min

The condition of the hardening of the ger-

Additive for curing sealing Water-borne

Easy pouring out

2-3

Table 1

Known method 2

35

8-10

Air blowing, heating. layer after removing the tooling

Ethyl silicate 40. Ethyl alcohol. Sol on acid. Polyvinyl acetate. Phenolic resin. Art abili 3 ator

CO COi SpNlP N „

Mechanical force required

12-15 cove with a frozen sealing layer. A sub-model plate is connected to the refrigeration unit and cooled to a temperature. During operation, the set cooling temperature is maintained by the thermostat. After the flask has been installed, a layer of sand (moisture 6%) 16-20 mm thick is applied to the surface of the cooled under-model plate with an organic release coating, filled with casting sand with sand, compressed the sand with vibration and pressurized the hemoform plate. After the flasher for 5 minutes, the semi-mold is connected to the vacuum source and the submodel plate is removed. At the same time, a second mold is made in a similar way. The assembled form is poured with cast iron SCh 12-28 at a temperature of 1340 ° C. Seven minutes after pouring, the mold is disconnected from the vacuum source and the sand is returned to the bunker for reuse. The obtained castings have a clean, non-stick surface, no chilling is observed. The data of the experimental verification of the technological parameters of the proposed and known methods are given in Table. 1 and 2.

The proposed method

Parameters Sand moisture, wt.%

3.5 4.0 G 6.0 G 8.0

table 2

The known method aj

8.5

Data analysis table. Figure 1 shows that the minimum temperature of the sub-model plate, ensuring a satisfactory duration of hardening of the sealing layer, is -20 ° C. With increasing temp. The temperature up to -15 ° C increases the duration of hardening by 1.5-2 times, which is unacceptable under the conditions of the technological process. Lowering the temperature below contributes to shortening the hardening time of the sealing layer and is limited by the energy possibilities of the refrigeration equipment.

The optimum moisture content of the sand to form a sealing layer is 4-8% Stable. 2.) A decrease in moisture content of less than 4.0% leads to an increase in air permeability and a deterioration in the sealing ability of the layer, an increase in moisture content of more than 8% leads to a significant increase in gas creativity and the possibility of gas defects in castings.

Experimental verification of the method was carried out in obtaining castings of bearing caps from cast iron in the experimental area of the IPL of the Academy of Sciences of the Ukrainian SSR.

To prevent the seal layer from being prematurely thawed, the interval between manufacturing and the mold should not exceed 5–8 minutes, and the duration of the fill should not exceed 15–20 s.

The application of the proposed method allows reducing the consumption of molding materials, eliminating the use of expensive organic binders, reducing the laboriousness of knocking out castings and improving the sanitary and hygienic working conditions.

Claims (3)

1. Method of making foundry: molds, including the installation of the mold on the | submodel plate, the formation of the | facing sealant layer, I filling the flask with a bulk filling material and creating a vacuum, 0 characterized in that, in order to reduce the consumption of molding materials, reduce the labor intensity of casting out castings and improve sanitary and hygienic working conditions, the sealing layer is formed from moistened sand, and the submodel plate is cooled to a negative temperature. 2. A method of claim 6, characterized in that the humidity of the sand 0 maintained in the range of 4.0-8.0%. 3. Method according to paragraphs. 1 and 2, that is, that the submodel plate is cooled to a temperature not higher than -20 s. five Sources of information taken into account in the examination 1. Foundry, 1975, No. 5, p. 21. 2. The patent of Switzerland No. 584574, cl. In 22 C 15/28, obpulik. 1977. 0