RU2323802C1 - Method of making moulding - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: before filling up of moulds by the modified melt it should be cooled in the stove to the temperature T_lw +10÷50°C for pure metals and eutectic alloys, where T_lw - the temperature of zero fluidity; T_cr - the temperature of crystallization. For more full removing remised in the alloy gas, before filling up of moulds the stove is cooled to the temperature T_sol of alloy and to the temperature T_lw of pure metals and eutectic alloys, and then rapidly heated till temperature T_lw +10÷50°C for alloys or T_lw +10÷50°C for pure metals and eutectic alloys, where T_sol - final temperature of alloy consolidation. The filling up of the mould is done with the speed of melt with gate speed up to 10 m/s. The consolidation of the alloy filled the mould is done with supply of gas pressure to it. EFFECT: it is increased the mechanical qualities of derivable mouldings.

3 cl, 5 dwg, 6 ex.

Description

The invention relates to mechanical engineering and can be used in foundry for the manufacture of castings from ferrous and non-ferrous metals and alloys.

A known method of manufacturing low-pressure castings using ceramic casting molds for investment casting (Application 59-54458, Japan. Application. September 20, 82 No. 57-164438, published on March 29, 1984 MKI B22D 18/04, B22D 18 / 06).

The closest analogue to the claimed technical solution adopted for the prototype is the "Method of producing castings in the shell mold and the casting mold for its implementation." (SU 1197767, B22C 9/04, B22D 18/06. Application No. 3696250 / 22-02 of January 31, 84 Bull. No. 46.)

According to a method for producing castings in a shell mold, comprising immersing the open end of the central gate of the mold in a crucible with molten metal, forcing mold cavities to be filled with metal by vacuum or low pressure, and pouring the liquid metal from the central gate in the crucible, filling the shell mold with liquid metal produced through an additional metal-conducting riser, forming an annular cavity with a central gate, with the supply of metal first in the upper part part of the central gate, then immediately after filling the mold with metal, the vacuum or pressure is turned off, and after the liquid metal is drained from the additional riser, the molds are subsequently fed with molten metal from the annular cavity.

A disadvantage of the known casting method is the low mechanical properties of metal castings, inferior to the mechanical properties of the deformed metal (forgings and rolled products) due to microporosity, chemical inhomogeneity and large primary grain of the casting metal, especially when casting in single low-conductivity, for example, ceramic, investment casting molds .

The objective of the invention is to eliminate the noted drawback, namely, increasing the mechanical properties of the metal castings to the level of the deformed (forgings and rolled).

The problem is achieved in that in a method of manufacturing castings, including the preparation of a molten metal, immersing the open end of the central gate in a crucible with molten metal, forcing mold cavities to be filled with metal by vacuum absorption or under low pressure, feeding solidified castings before filling molds with metal modified melt is cooled in the furnace to a temperature T _nJ + 10 ÷ 50 ° C (alloys) or T _cr + 10 ÷ 50 ° C (pure metals and eutectic alloys) are filled of the mold produced from the melt in the riser during speed up to 10 m / s, and solidifying the melt poured into the form produced at feed gas pressure therein in the range 0.4-0.6 MPa.

Under the accepted conditions, the molten metal entering the working cavity of the mold in a liquid-solid state hardens immediately after filling. In this case, the crystallization process occurs throughout the entire volume of the molten melt and this ensures chemical homogeneity and a small primary grain of the casting metal, while crystallization under gas pressure suppresses the release of gases dissolved in the metal, microplastic deformation and micropores are eliminated in the cast metal. Those. cast metal in its structure is equivalent (with the exception of anisotropy) to deformed metal (forgings and rolled products). This makes it possible to reduce the weight of castings by 10-30% while maintaining their structural strength, transfer parts from deformed metal with a low CMM to precision cast billets, and replace individual welded structures with cast ones.

The lower limit of gas pressure of 4 atm is adopted on the basis of practical data, and the upper limit of 6 atm is assigned from the conditions of sufficiency and safety. The melt filling speed of the mold is taken from the need to quickly fill the mold and maintain the laminar regime (the laminar regime in the liquid-solid phase is maintained up to a speed of 10 m / s).

The next difference of the proposed method lies in the fact that the melt before filling the mold is first cooled to a temperature of T _salt (for alloys) and to a temperature of T _cr (for pure metals and eutectic alloys), and then quickly heated to a temperature of T _nzh + 10 ÷ 50 ° C (for alloys) or T _cr + 10 ÷ 50 ° C (for pure metals and eutectic alloys), where:

T _NJ - temperature zero fluidity,

T _salt - the temperature of the end of solidification of the alloy,

T _cr - crystallization temperature.

This allows you to more fully remove the gases dissolved in the metal. To obtain additional crystallization centers, the melt is modified with refractory nanoparticles of Al ₂ O ₃ , TiCN, CrN, etc., or, for example, pure copper is modified with zirconium.

The features of the proposed method are that the best option for its implementation is the use of all the metal melted in the furnace for one casting, without dosed casting, as is usually accepted, in casting molds. It is advisable to obtain castings of medium and large weight, as well as small castings in large quantities in multi-unit form, which cannot be carried out by known casting methods, except gravity casting with crystallization under atmospheric pressure, by which castings are obtained with metal chemically inhomogeneous and large primary grains, with micropores.

Figure 1 shows a container with a casting mold for casting a railway cross of the railroad switch (before pouring), figure 2 - a container with a casting mold for receiving this casting with a melting furnace (after pouring), figure 3 - a container with a casting a mold for producing railway wheels according to gasified polystyrene foam models, Fig. 4 shows a container with ceramic molds for producing steel castings, and Fig. 5 shows a container with a dry stacked mold for producing bimetallic plain bearings.

Examples of the method.

Example 1

Railway crosspiece turnout of steel 110G13L weighing 1 ton is obtained as follows.

Expanded polystyrene gasified models of railway crosspieces 1 are covered with quartz sand in a container 2 having a sealing seal 3. From the bottom, a metal wire 4 is connected to the container 2 through a sealing gasket 5. The metal wire 4 is attached to the bottom of the container with an arm 6. The container 2 is equipped with a gas pipeline 7 for evacuation, a gas pipeline 8 - for supplying gas pressure, gas pipeline 9 - for communication with the atmosphere. The filling hole in the container 2 is formed by a sand insert 10, for sealing the container 2 there is an annular groove 11 below. For horizontal movement of the metal wire 4 there is a hydraulic cylinder 12 with a rod 13.

Steel smelting is carried out according to known modes. Steel deoxidation is performed by compacted shavings made of aluminum or its alloys, which has a surface layer of refractory oxides of Al ₂ O ₃ with a thickness of 0.01 μm.

The prepared steel is cooled in a furnace to a solidus temperature (approximately 1300 ° C), while the gases dissolved in the steel are removed and then quickly heated to a temperature of 1340 ° C (t _nzh ≈1325 ° C). Thus, in liquid-solid steel there is a certain percentage of its solid phase and nanoparticles of Al ₂ O ₃ , which together are ready crystallization centers, at this temperature, the preheated metal wire 4 is immersed in the molten metal (figure 2) and the container 2 is connected with a vacuum system through a gas pipeline 7 (a vacuum system is not shown in the drawing). The molten steel through metal wire 4 enters the container 2 at a speed of 5 m / s (in the gate run of the sleeve 10), burning out the polystyrene foam model, the first portions of the metal are poured into the groove 11 and seal the container, the gasification products of the model are sucked out of the container 2 by a vacuum system. After filling the working cavity of the mold, the hydraulic cylinder 12 is turned on and the metal wire 4 is displaced to the right by the rod 13, cutting off the metal melt in the metal wire from the metal melt in the mold, after which compressed air is supplied to the container through the gas line 8 under a pressure of 0.5 MPa and holding until the casting solidifies. Liquid-solid pouring provides chemical uniformity and fine primary grain of the casting, and crystallization under gas pressure - a non-porous metal (due to microplastic deformation). After the solidification of the metal, the container 2 is connected to the atmosphere, the casting is cooled in the container 2 with sand to a temperature of 1150-1110 ° C, then it is removed from the sand and quenched by cooling in water.

The resulting casting is chemically homogeneous, with a fine primary grain, does not have micropores and, as a result, increased mechanical properties compared with the requirements of GOST for casting: up to 30% higher strength than conventional casting, and higher ductility.

Example 2

A slab of steel Kh18N9T with a size of 1200 × 100 × 2500 (weight ≈ 2.5 t) is obtained as follows.

Steel is melted in an induction furnace according to known modes. Titanium is introduced into steel in the form of shavings that have previously undergone nitrocarburizing to form titanium carbonitrides on its surface with a thickness of not more than 0.1 μm.

The molten steel with a given chemical composition is cooled in a furnace with a temperature of 1560 ° С to 1470 ° С (t _нж ≈1450 ° C) and a preheated metal wire connected to a sealed container in which the mold is placed is immersed in the melt. When the metal wire is immersed in the melt, the container is connected to a vacuum system and the mold is filled with the melt. After filling the mold, the metal wire is shifted, blocking the filling hole, and compressed gas is supplied to the container under a pressure of 0.5 MPa.

Filling the mold with liquid-solid melt ensures the chemical uniformity of the workpiece metal and small primary grains, and crystallization under gas pressure - microplastic deformation.

The mechanical properties of the metal of the cast slab already meet the requirements of the rental, which is guaranteed to ensure the quality of the rolled products obtained from it.

The presence of gas pressure in the mold eliminates the mechanical burn, and the chemical burn is eliminated due to the low casting temperature.

Example 3

The copper tips of the oxygen-converter tuyeres to a 350-ton converter in a multi-seater form (6 nests) are obtained as follows.

The smelted copper is deoxidized with zirconium to remove oxygen and provide volumetric solidification of the castings, it is cooled in a furnace to a temperature T _cr (1083 ° C), as a result of which dissolved gases are removed from the metal, including hydrogen. Then the metal is quickly heated to a temperature of 1130 ° C and the open ends of the mold are immersed in the melt while evacuating them. After filling the working cavities of the molds with the melt, the melt is cut off from the melt in the furnace and compressed gas is fed into the molds under a pressure of 0.5 MPa. The melt in the mold is held under gas pressure until solidification is completed, after which the castings are removed from the molds and the process is repeated.

The obtained cast tips have several times greater resistance than welded from rolled products due to the lack of welds.

Example 4

Railway wheels made of steel EI293 (chemical composition: C 1.5-1.65%; Si 0.75-0.90%; Mn 0.20-0.40%; S and P not more than 0.003%) receive 20 castings per casting ( the total weight of the melt poured per casting ≈3 tons) as follows.

Expanded polystyrene models 14 of the wheels (Fig. 3) connected to the riser model 15 are placed in a sealed container 16 provided with gas pipelines 17, 18, 19, respectively, for evacuation, supplying compressed gas to it and connecting to the atmosphere. The metal wire 20 is connected to the bottom of the container 16 through a sealing seal 21. The gate is located in the sand insert 22. To seal the container, there is an annular groove 23. The metal wire 20 can be moved horizontally in the bracket 24 by the hydraulic cylinder 25 using the rod 26.

Steel is smelted according to known conditions; during smelting, it is modified with cementite nanoparticles at a temperature below its melting point (the melting temperature of cementite is 1500 ° C).

From a temperature of 1500 ° С, the steel is cooled to 1400 ° С (t _нж ≈1350 ° C) and the metal wire 20 is immersed in the molten metal, while simultaneously connecting the container 16 to the vacuum system. Steel fills the working cavities of the molds, burning polystyrene foam models 14. After filling the mold with the melt, the metal wire 20 is moved horizontally by the hydraulic cylinder 25 and the rod 26 to the right, cutting off the melt in the container 16 from the melt in the metal wire 20. The vacuum is also disconnected into the container 16 supply compressed air through the gas pipe 18 under a pressure of 0.5 MPa.

Liquid-solid steel with cementite nanoparticles solidifies in bulk and has a chemically uniform structure with a fine primary grain, and crystallization under gas pressure leads to microplastic deformation of the solidified casting metal and the elimination of microporosity in the cast metal.

The structure of the obtained casting is granular perlite + graphite.

Mechanical properties: σ _in > 590 MPa, δ> 14-17%, HB> 220-230.

Example 5

Castings of bicycle carriages made of steel St45 are obtained in investment casting molds (12 castings in 1 mold) as follows.

Cold ceramic molds 27 (FIG. 4) are installed in the container 31 on sand inserts 28 and 29, interconnected by tubular molds 30 forming the central gate, and the free space is covered with quartz sand. A total of 24 ceramic molds 27 are installed in the container 31.

In the lower part of the container 31 there is a sand insert 32 for forming the gate, and for sealing the container - an annular groove 33.

On the lid of the container 31 are located gas pipelines 34, 35, 36, respectively, for evacuating the forms, supplying them with compressed gas and for communication with the atmosphere.

Steel is smelted in an induction furnace using known technology. When steel is deoxidized, aluminum pressed shavings are used having Al ₂ O ₃ oxides on the surface with a layer thickness of 0.01 μm (nanolayers).

The finished steel is cooled in a furnace from a temperature of 1560 ° С to a temperature of 1475 ° С (t _нж ≈1460 ° C), a plate 37 with a metal wire 38 and a container 31 located on top is placed on the casing 39 of the melting furnace, gas is supplied to the furnace casing 39 under pressure 2 atm through the gas pipeline 40 and at the same time the container 31 is evacuated. The molten steel through the metal 38 fills the working cavities of the molds 27 with a flow velocity in the runway 5 m / s. After filling the working cavities of the molds 27, the container 31 is shifted to the right along the plate 37, cutting off the melt in the molds from the molten metal in the metal wire 38, after which compressed gas is supplied to the container 31 through the gas pipeline 35 under a pressure of 0.5 MPa and holding under pressure until all are solidified castings. Then the gas pressure in the container 31 through the gas pipe 36 is released to atmospheric, the castings are cooled in the container to 900 ° C, and then cooled in air, performing the normalization operation.

Finished castings are chemically homogeneous, with a fine primary grain, do not have micropores, and the mechanical properties of the metal castings correspond to the mechanical properties of forgings and rolled products. The total number of castings obtained in one casting is 288 pieces.

Example 6

Bimetal plain bearings made of anti-friction Al-Sn alloy (working layer) and AK9 alloy (supporting layer) with dimensions: D _outer = 60 mm, D _inner = 40 mm, N = 60 mm; the total weight of the casting of 0.2 kg is obtained as follows.

The working layer is obtained from a tape with a thickness of 1.5 mm in the form of bushings 41 (Fig. 5), which are mounted on the protrusions 42 of the sand forms 43 with the formation of a gap 44 for filling the base layer with alloy. In each mold 43 there are 30 working nests. The molds 43 assembled with the sleeves 41 are installed in a stack of 15 molds into a container 45 (the total number of castings obtained per filling is 450 pcs.) On the lid of the container 45 there are gas pipelines 46, 47, 48, respectively, for evacuation, supply of gas pressure, connection with the atmosphere, and at the bottom of the container 45 is a sand insert 49 and an annular groove 50 for sealing it. A metal wire 52 is mounted in the plate 51, immersed in the molten metal in a furnace located in a sealed casing 53. There is a gas pipe 54 for supplying gas pressure. The container 45 assembled with the casting molds 43 is mounted on the plate 51 and the hole in the metal wire 52 is aligned with the hole in the sleeve 49 .

The prepared melt is cooled in an oven to a temperature of 600 ° C (the temperature range for crystallization of AK9 alloy is 600-577 ° C). Compressed gas is supplied to the casing 53 of the melting furnace through the gas line 54 at a pressure of 1.0 atm and the working cavities 44 are filled while the container 45 is evacuated through the gas pipe 46.

After filling the working cavities 44, the container 45 is shifted along the plate 51 to the right, cutting off the melt located in the container 45 from the melt in the metal wire 52, after which compressed gas is supplied to the container 45 through the gas pipeline 47 under a pressure of 0.5 MPa. The melt entering the liquid-solid state in the casting molds 43 solidifies in volume, its structure is chemically uniform with small primary grains, and crystallization under gas pressure eliminates micropores in it.

The obtained mechanical properties of the metal of the supporting layer of the bimetallic casting: σ _in ≈200 MPa, HB≈80, which is higher than the requirements of GOST for casting.

Finished castings are removed from the molds and the process is repeated. Using the invention allows to obtain castings from ferrous and non-ferrous metals and alloys with improved mechanical properties at the level of the deformed metal (forgings and rolled products), to reduce the weight of castings with a decrease in their wall thickness and maintaining structural strength, to replace parts made of deformed metal with low CMM by casting with CMM up to 0.95, replace individual welded structures with castings with an increase in their operational characteristics; remove the restrictions on the weight and dimensions of the resulting castings.

Claims (3)

1. A method of manufacturing castings, including the preparation of a molten metal, immersion of the open end of the central gate of the mold in a crucible with molten metal, filling the mold with metal by vacuum absorption or under low pressure, characterized in that the mold is filled with a modified melt at _Tl 10 ÷ 50 ° С for alloys or Т _кр 10 ÷ 50 ° С for pure metals and eutectic alloys, where T _NJ is the temperature of zero fluidity, T _cr - crystallization temperature, in this case, the mold is filled at a melt speed in the central gate up to 10 m / s, and the solidification of the melt poured into the mold is carried out by applying gas pressure to it. 2. The method according to claim 1, characterized in that the pressure of the gas in the mold during the solidification of the casting is maintained within the range of 0.4-0.6 MPa. 3. The method according to claim 1, characterized in that the modified melt is first cooled to T _salt for alloys or to T _cr for pure metals and eutectic alloys before filling the mold, and then heated to T _nzh 10 ÷ 50 ° C for alloys or T _cr 10 ÷ 50 ° C for pure metals and eutectic alloys, where T _sol - the temperature of the end of solidification of the alloy.

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