SU996064A1 - Method of producing castings in non-detachable ceramic moulds with use of investment patterns - Google Patents

Description

one

The invention relates to foundry and can be used for the manufacture of castings, mainly from non-hardening low-carbon and stainless steels, in one-piece casting ceramic molds on removable models.

A known method of making shell molds includes obtaining a cast model from a low-melting material (composition), applying layers of the shell to the model, drying or chemically hardening the Shells, removing the melted model from the ceramic shell, calcining the shell 1.

There is also known a method of making ceramic molds and rods based on a refractory filler, ethyl silicate binder, solvent and hardener by applying the prepared mixture to the model, removing the latter from the mold after curing, followed by ignition, the mold and rods being heated to 50-200 ° C. for 5- 60 min 2.

The closest to the invention in its technical essence and the achieved result is a method for producing castings in permanent ceramic molds on removable models, mainly from non-hardening low-carbon and stainless steels, including

5 application to the model of a curable ceramic mass based on oxychloride hardening magnesia-based substances, removing the model by melting it, subsequent calcination of the mold and pouring molten metal 3.

The disadvantages of this method are limited technological capabilities; limited raw material base of expensive molding material; high labor intensity of cleaning works; not being able to reuse the material of the destroyed shell due to complex regeneration; slow cooling of castings, in addition, does not use the heat of molten metal poured into the mold. It is known. use of caustic

20 magnesite as a binder, and metallurgical as a basis for the manufacture of shell forms. The composition of the suspension: caustic magnesite, sifted through a sieve M. 005-36%, an aqueous solution of magnesium chloride with a density of 1.32 46%, metallurgical magnesite, sifted through a sieve No. 005-18%. Magnesian cement is an airborne substance based on caustic magnesite mixed with a solution of magnesium chloride. Ingredients: 62-67% MgO; 33-38% MgC, 6. The salt concentration in the thinner corresponds to 12–30 ° Baume, density 1.091–1.262 g / cm. The disadvantage of magnesia cement products is hygroscopicity, greatly increased with an excess of magnesium chloride. In this connection, the optimum composition of magnesian cement was established with regard to mobility sufficient for free pouring: 71.4% MgO; 28.6% MgCs. 6Н О, at a salt concentration in the condenser 24 ° Baume (density 1.2 g / cm) Starting materials: magnesite caustic powder of the grade PMK-75 GOST 1216-75, sifted through a sieve No. 0315 and a solution of cholesterol magnesium chloride GOST 4209-77 were mixed vigorously in 1 × dish until a homogeneous suspension was obtained, and the mass ratio of the powdered part and the mixing liquid was 2.5: 1, which corresponded to the accepted formula of optimal composition. The purpose of the invention is to reduce the labor intensity of the cleaning work and simplify the regeneration of the molding material. The goal is achieved in that according to the method of making castings in one-piece casting ceramic molds according to removable models, including Application of a curable ceramic mass based on magnesian oxychloride hardening substances on the model, removing the model by its melting, subsequent calcination of the mold and pouring molten metal , the casting at a temperature of its outer surface 700-720 ° C together with the form is placed in a vessel with water at an initial temperature of 5-25 ° C and the ratio of the masses of water and matter la form 3.7: 1 - 5: 1. The temperature range of 700-720 ° C of the outer surface of the casting, placed together with the mold in water, ensures optimal conditions for the proposed method. Lowering the temperature of the outer surface of the casting below 700 ° C leads to an increase in the time of destruction of the mold. For example, lowering the specified temperature by 100 ° C leads to an increase in the time of destruction of the mold by a factor of 6 or is 30 minutes instead of 5 minutes at 700 ° C (Table 1). Dried samples of the used ceramic-shaped material were heated to various temperatures and placed in tap water. Increasing the temperature above the upper limit, i.e., higher than 720 ° C, intensifies the water vapor formation, requires the introduction of additional economically unjustified cooling of water, which complicates the regeneration of the molding material. In addition, temperature is limited by safety conditions. Water in the range of 5-25 ° C in this case provides optimal conditions for cooling the casting; water, in the specified temperature range, has the largest specific gravity: at 5 ° 0.99975 V10 ° 0.9970 y20 ° 0.99820 V25 ° 0.99691 UZO ° 0.99562 y40 ° 0.99216 50 ° 0.98804 If60 ° 0.98328 70 ° 0.97790 Y80 ° 0.97191 G90 ° 0.96534 Lowering the water temperature below 5 ° C almost does not reflect on the specific gravity of the water, but adversely affects the quality of the castings, leading to the appearance of small cracks as a result of rapid cooling. Increasing the water temperature above 25 ° C leads to a significant decrease in specific gravity. Water in the specified temperature range has the highest heat capacity Cf kcal / kg ° C with the lowest vaporization.

Although in the temperature range 60-90 ° C an increase in the heat capacity is observed, but the use of water at temperatures close to the boiling point, in this case, jj is impractical.

In addition, the use of water at temperatures close to the boiling point.

unsafe in terms of safety.

Lowering the water temperature below 5 ° C leads to a slight increase in heat capacity, but negatively affects the quality of the castings.

Thus, the use of water for this method of manufacturing castings, taking into account the largest specific gravity and the highest heat capacity C in the temperature range of 5-25 ° C, ensures the most optimal process conditions and simplifies the regeneration of the molding material, since it does not require the introduction of economically unjustified additional water cooling. The best achievement of the goal of the proposed sposbb casting production is provided with a mass ratio of water and material of the form of 3.7: 1-5: 1. Reducing the mass ratio of water and the mold material below 3.7: 1 leads to a strong overheating of water, intensive evaporation, which requires the introduction of an economically unjustified additional cooling of water. An increase in the mass ratio of water and material of the form over 5: 1 leads to an increase in the time of destruction of the form, an increase in the labor intensity of the cleaning works, and a decrease in productivity. FIG. 1 shows a model block of a fusible composition (PS50-50); FIG. 2 — tooling for making a ceramic mold; in fig. 3 - removing the model block from the equipment after applying a curable ceramic mass on it; in fig. 4 — removing the model from the ceramic mold by melting it; in fig. 5 - calcination of a ceramic mold furnace; on. FIG. 6 - casting molten metal; in fig. 7 - ceramic form after pouring molten metal; in fig. 8 - a vessel with tap water, ceramic mold and casting; in fig. 9 - removing the cooled casting from a vessel with tap water and settling the material of the destroyed ceramic form. . The operations are carried out in the following sequence. Preparation of magnesia cement, installation of a model block in a tooling, pouring magnesia cement and hardening it in a tooling; removing the model block from the equipment after applying a curable ceramic mass on it, removing the model block from the ceramic mold by melting it and drying the mold in a drying cabinet, calcining the ceramic mold in a calcining furnace (t 850–900 ° C); die casting molten metal. The mold temperature before pouring is 700–750 ° C, solidification from Casting, cooling the casting to its outer surface temperature of 700–720 ° C and lowering the mold together with the casting into a vessel with water at an initial temperature of 5–25 ° C, destruction of the mold, cleaning the casting in a vessel with water using the heat of molten metal (accompanied by boiling in the casting zone), removing the casting after equalizing the temperatures of the casting and water, settling the material of the destroyed form in the vessel with water, draining the aqueous solution of magnesium chloride (density less than 1.2 g / cm), drying the supernatant of the mold material by heat treatment at 400-450 ° C, after which it was milled and sieved; reuse of the regenerate by adding it in an amount of 40-50 May. / o in basic composition for making ceramic forms according to. removed models according to the proposed method. Model block 1 (Fig. 1) of a low-melting composition includes a model of casting 2, associated with stand 3 using a model of a gating system 4. A tool for making a ceramic mold (Fig. 2) contains a cup 5, an ejector 6 with a needle 7 the cup 5 is designed to be filled with a curable ceramic mass 8 after the installation of the model block 1. To remove the model from the mold by melting it, a drying cabinet 9 (Fig. 4) is used, in which there is a tray 10 for the flowing low-melting composition II, stand 12. To ignite the odds s is an oven 13 (FIG. 5). For casting the mold with molten metal, there is a casting ladle 14 with molten metal 15 (Fig. 6). FIG. Figure 7 shows the ceramic mold and the casting 16 with an outer surface 17, over which temperature is controlled. For cooling castings from non-hardening low carbon or stainless steels, there is a vessel 18 with tap water 19 (Fig. 8). FIG. 9 shows a vessel 18 with tap water 19, in which material 20, of the destroyed form, is defended. The method is implemented as follows. A model block 1 of a fusible composition is installed for a stick 7 of the ejector 6 in cup 5, after which a cured ceramic mass based on magnesian oxychloride hardening material is poured into the glass. Then the model block 1 with the cured ceramic mass 8 is removed from the equipment (Fig. 3) and placed in a drying cabinet 9 on a pallet 10 with a stand 12, while the cabinet is maintained at 90 ° C, resulting in the molten model composition 11 flowing into the pallet 10. The resulting mold is set in a calcining furnace 13 in which is subjected to calcination at 850-900 ° C. After extraction from the furnace 13, the mold.ff at 700-750 ° C is fed to the pot (Fig. 6). After pouring the casting mold 8 with molten metal 15 from the casting ladle 14 and solidifying the casting 16, the casting 16 at 700-720 ° C of its outer surface 17 (control with a probe) is placed in a vessel 18 with tap water 19 having an initial temperature of 5-25 ° C (Fig. 8), wherein the mass ratio of water and mold material is 3.7: 1 - 5: 1. As a result of intensive heat exchange, the mold 8 is destroyed, the casting is cleaned from the ceramic mold material, the casting is cooled intensively, and the destroyed mold material 20 settles to the bottom of the vessel 18. The cooled casting 16 is removed from the vessel 18. After settling the destroyed material in the vessel 18 separated from the remaining aqueous solution (the density of which is 1.008-1.012 g / cm) by draining the aqueous solution, the mold material is dried by heat treatment at 400-450 ° C and reused for detecting shapes, it is added in an amount of 40-50 wt.% in fresh molding material. As a result of the experiments, it was established that the calcined casting molds during storage On the air for 24 hours, they increased their weight by 5%, became friable and quickly collapsed in water. Because when magnesia cement loses its mechanical properties and becomes friable during water absorption, the model is smelted from a mold not in hot water, but in an oven, after which the mold was calcined at 850–900 ° C in a tempering furnace, and after being removed from the furnace, the casting was performed. Example. After annealing, the casting mold with a holding time at 880 ° С for 1 h was removed from the calcining furnace and at 730 ° C was poured with 20L steel weighing 1.29 kg at 1600 ° C. After cooling the outer surface of the casting to 700 ° C (control with a probe in the area of the pouring funnel), the casting together with the mold was placed in a vessel with water at an initial temperature of 5 ° C. The mass of the form is 2.13 kg, the mass of water is 7.90 kg, that is, the mass ratio is 3.7: 1. After termination of the water in the casting area, the ceramic mold material was almost completely separated from the casting and settled on the bottom of the vessel. The remains of the ceramic mold material on the casting were easily washed by hand with water. The surface of the casting horoshka at the level mainly). The density of the remaining aqueous solution of magnesium chloride was 1.012 g / cm. After draining the aqueous solution, the remaining mass was dried, milled, sieved. A solution of magnesium chloride and regenerate was reused after enrichment to produce casting molds using the proposed method. The proposed method for the production of castings expands the technological capabilities of manufacturing castings in permanent forms, because instead of expensive electrocorundum magnesia cement can be used, to expand the raw material base of foundry production using magnesia cements as a molding material, to reduce the labor intensity of refining works by using the heat of the molten metal cast into the mold, simplify the regeneration of the molding material and reuse the material p broken mold, speed up the process of cooling the casting by lowering the casting together with the mold into a vessel with water; to intensify the process as a whole due to the heat of the molten metal poured into the mold, to destroy the mold, to clean the casting, to regenerate the molding material, to reduce the casting cost due to the casting mold. The calculation of the expected economic efficiency of the mass of the form 2.13 kg and specially made shell of ethyl silicate coating weighing 0.415 kg, while using the model block. A comparative analysis of the known and proposed methods is given in table. 2 and 3. As a result of a comparative analysis, it was established that the reduction of time costs only in the manufacture of one casting mold for a steel casting weighing 1.29 kg is 7.5 hours, a reduction in the cost of manufacturing a casting mold by replacing expensive material with ethyl silicate refractory suspension. cheaper, based on magnesian oxychloride hardening substances, amounts to 0.14 rubles, for steel castings weighing 1.29 kg (according to an example). In this case, the laboriousness of applying a multilayer ethyl silicate coating, as well as the economic effect of using the heat of molten metal poured into the mold, is not taken into account.

kSQ

100

600

100

700,100

Operations

Making a model Assembling models into a block

Coating them

curing and drying:

applying ethyl silicate refractory slurry and anchoring powder, curing the coating on the model and drying it (7 layers

applying oxychloride hardening magnesia in a binding substance, curing the coating on the model and drying it 1 layer

Deleting a model

Backfilling of ceramic forms with support filler and calcination of forms

Table 1

After 6 days

Not destroyed

30 min

1.008 1.01

5 minutes

table 2

Time of operations, min

Proposed

The known method

30 30

30 30

1050

720 60

Refractory Formula Invention

A method of making castings in one-piece casting ceramic molds on removable models, mainly from non-hardening low-carbon and stainless steels, including applying To a model of curable ceramic mass based on magnesian oxychloride hardening substances, melting the model, then melting the mold and pouring the melt metal, characterized in that, in order to reduce the labor intensity of the cleaning operation and simplify the regeneration of the molding material, the casting peratures

Table 3

its outer surface is 700-720 ° C together

with the form is placed in a vessel with water at the initial temperature of 5-25 ° C and the ratio of the mass of water and the material of the form from 3.7: 1 to 5: 1.

Sources of information taken into account in the examination

1. Dashkarzh I. et al. Production of precision castings. M., “Mashinostroenie, 1979, p. 78

2.Zaretska G.M. Molding into ceramic forms according to permanent models M., Mashinostroenie, 1975, p. 6

3. USSR author's certificate number 287241, cl. B 22 C 9/04, 1969.

Claims (1)

Claim A method of manufacturing castings in one-piece ceramic casting molds according to removable models, mainly from non-quenching mild carbon and stainless steels, including applying a curable ceramic mass based on magnesia binders to oxychloride hardening, removing the model by smelting it, then calcining the mold and pouring it with molten metal, characterized in that, 30 in order to reduce the complexity of the treatment work and simplify the regeneration of the molding material, casting at the temperature of its outer surface 700–720 ° С together with the mold is placed in a vessel with water at an initial temperature of 5–25 ° С and the ratio of mass of water and the mold material is from 3.7: 1 to 5: 1.