RU2741044C1 - Method for production of small-section casting bars and device for implementation thereof - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to metal casting. Device of casting equipment, which is a single assembly unit, contains trays with moulds (7) of equal length installed on them, connecting chutes between moulds and two rings (1, 4), connected by three support posts (3) into rigid frame. Moulds (7) are installed in one row, thermal insert (6) is installed in each ingot mould. Thermal insert is made in the form of a tubular bushing with a trapezoidal neck collar with a centre of metal flow and a longitudinal axial channel. Collar flange ensures the moulds assembly into a monolithic closed circle, and the longitudinal axial channels of the inserts form an adapter flute. Foundry equipment is placed in vacuum induction furnace on casting table of drum type. Casting is carried out in vacuum by successive filling of moulds from ladle through steel-pouring trough. At overflow of heat insert at the mould filling end, metal is poured by gravity into the previous mould, which excludes casting mould return for profit refilling.EFFECT: reduced scrap formation due to reduced metal sputtering in flutes-adapters and increased yield.7 cl, 3 dwg, 2 ex

Description

1. Field of technology

The invention relates to the field of special metallurgy, namely to a method for casting bar billets from heat-resistant nickel-based alloys, and can also be used when casting other steels and alloys in a vacuum induction furnace.

2. Prior art

A known method of producing a charge blank from a casting heat-resistant alloy (Patent RU 2254959 (B22D 7/00), 2003), the method includes melting the alloy, pouring it into a mold, in the upper part of which a heat-insulating ceramic insert with an additionally installed ceramic baffle with holes is pre-installed. The disadvantage is the large loss of metal in the form of scrap.

There is a known method of manufacturing cast bar stocks from heat-resistant nickel-based alloys (Patent RU 2714788 (B22C 9/02, B22D 35/00), 2019), including pouring a liquid self-hardening mixture into a flask with a pre-installed model, drying the liquid self-hardening mixture in a furnace. less than 7 hours according to the mode, including raising the temperature to 200-300 ° C, holding and cooling with the oven, removing the model, covering the entire surface of the hardened mixture with non-stick paint, installing the flask on a steel base, and between the said base and the hardened mixture, a sprue is formed for a siphon filling the obtained casting mold with an alloy, filling the casting mold with an alloy and solidifying the alloy, while filling the casting mold with alloy 30 is carried out through a casting trough in a vacuum by a siphon method. The disadvantage is large losses of metal to the sprues during siphon filling of the casting mold.

It is also known, adopted by the applicant for the closest analogue, a method of casting metal from above and a device for its implementation (Patent RU 2023528 (B22D 7/00), 1991) in which a ladle with a melt is installed above the molds, the melt is fed into the molds, and the filling of the molds and the formation of ingots of a finite length is carried out by sequential overflow of the melt from the molds into the mold and subsequent crystallization of the melt.

The disadvantage is the lack of the possibility of using in the melting and casting of alloys in vacuum induction furnaces.

1. The essence of the invention

1.1. Technical problem statement

Improving the quality of the metal by reducing shrinkage and surface defects, increasing the yield by reducing scrap formation, reducing the casting time and reducing energy consumption.

The result of solving a technical problem

The task is realized by pouring metal in a vacuum through a steel-pouring chute, by sequentially filling molds of the same length, located in one row in a casting equipment installed on a drum-type casting table, and connected into a circle closed without gaps by a trough-adapter formed by thermal inserts.

1.2. Features

In contrast to the known technical solution for the preparation of a device for casting metal, including the installation of a ladle with a melt above molds of the same length, located on pallets and connected by chutes, feeding the melt from the ladle and forming ingots of a finite length, in the proposed technical solution at the stage of preparation of the foundry equipment, preliminary rejection is carried out molds, metal casting is carried out through a steel-pouring chute in a vacuum, by sequentially filling molds of the same length, located in one row in a casting equipment installed on a drum-type casting table, and connected into a circle closed without gaps by a trough-adapter formed by thermal inserts. At the stage of culling the molds, they are annealed in a hydrogen atmosphere, which ensures the removal of chemically bound water, and then the inner surface is machined.

In addition, after casting and final solidification of the metal, the casting tooling is disassembled, and the resulting blanks with a diameter of 50 ÷ 150 mm are subjected to mechanical processing.

3.3. List of drawing figures

FIG. 1 shows the casting equipment for casting a cast bar stock (LPZ) from a heat-resistant alloy on a nickel base, where 1. - The bottom ring, which is the base of the equipment and has a recess with holes for installing steel fungi; 2. - Steel (or ceramic) liner, which acts as a bottom (plug) for each mold; 3. - Stand, cylindrical, made vertically and designed to adjust the height of the upper ring to the required height of the molds used; 4. - Upper ring designed for fixing and fixing the molds and preventing their displacement during loading or unloading of the assembled casting equipment, as well as accurate centering relative to the casting axis; 5.- Holes for installation of molds, coaxial with holes for steel (or ceramic) inserts of the lower ring; 6. - Thermal inserts; 7. - Molds of the same length; 8. - Trunnion, designed to move the equipment with a crane.

FIG. 2 shows a top view of the foundry equipment for casting the LPZ.

FIG. 3 is a schematic representation of the assembled foundry tooling.

4. Description of the invention

In the claimed technical solution, at the stage of preparation of the casting equipment, the selection of low-quality molds (7) with corroded areas (rust) and other defects on the inner surface is carried out, then the molds are annealed in a hydrogen environment, which ensures the removal of chemically bound water (hydrated moisture) from their inner surface and corroded areas.

Heat treatment of molds in hydrogen atmosphere is carried out in a bell-type furnace according to the following regime:

- purging the muffle with nitrogen at a pressure of 80 ÷ 200 mm Hg. Art. within 40 ÷ 120 minutes, for air displacement;

- warming up the bell-type furnace up to 700 ÷ 850 ° С;

- supply of hydrogen under the muffle with a pressure of 30 ÷ 90 mm Hg. Art .;

- holding the molds in a hydrogen atmosphere for 1.5 ÷ 2.5 hours;

- purging with nitrogen under a pressure of 80 ÷ 200 mm Hg. Art. within 40 ÷ 60 minutes;

- cooling of molds under a muffle to a temperature of 100 ÷ 150 ° C, in a nitrogen atmosphere.

After heat treatment, the inner surface of the molds is cleaned to remove scale and other secondary neoplasms obtained as a result of heat treatment, and blown with compressed air. This ensures the best quality of the surface of the LPZ, since there is no boiling of liquid metal, its oxidation and the formation of cavities, films and other surface defects. Then the casting equipment is assembled for casting the cast bar blanks.

Steel (or ceramic) inserts (2) are installed in the lower ring (1), which is the base of the equipment and has a recess with holes, which act as a bottom (plug) for each mold. This excludes:

- metal leakage under the bottom of the mold;

- the wear of the lower part of the mold is reduced;

- the defect of the cast bar stock of the "elephant foot" type is excluded.

To prevent erosion and welding of the liner to the cast workpiece, a layer of 0.5 ÷ 1.0 mm of liquid ceramic refractory is applied to it.

Next, the required height of the upper ring (4) relative to the lower one (1) is set, which is provided by three cylindrical construction sites (3) spaced 120 ° apart. The upper ring is designed for fixing and fixing the molds and preventing their displacement when loading or unloading the assembled casting equipment, as well as accurate centering relative to the casting axis. Then, molds of the same length are installed through the existing holes (5) in the upper ring, coaxial with the holes for steel (or ceramic) inserts in the lower ring. At the same time, the upper ring ensures a strictly vertical position of the pipes throughout the entire production cycle: assembly → metal casting → holding.

The distances between the holes in the upper ring are designed in such a way as to ensure satisfactory cooling of each mold, which does not lead to warping of either the molds or the entire casting tooling due to thermal loads.

Then, thermal inserts (6) made of mullite-silica fiber in the form of a tubular sleeve with a collar flange, trapezoidal, with a funnel centering the metal stream and a longitudinal axial channel are installed in each mold (7). The trapezoidal shape of the collar flange makes it possible to assemble the upper part of the casting equipment into a monolithic closed circle without gaps, and the longitudinal axial channel serves as a trough-adapter during the transition from one mold to another during casting.

The assembled foundry equipment is placed in electric or gas heating furnaces, with a temperature range of 500 ÷ 800 ° C, to ensure the heating of the equipment before casting the metal.

The heated casting tooling is placed in a vacuum induction furnace on a drum-type casting table, which allows filling each mold with metal placed in the tooling sequentially. The filling of the casting equipment takes place from above through a steel pouring chute in a vacuum.

After casting and final solidification of the metal, the casting tooling is disassembled, and the resulting blanks with a diameter of 50 ÷ 150 mm are subjected to machining.

Thus, the use of the proposed technical solution allows:

- to reduce scraping due to less metal spattering in - grooves-adapters, and as a consequence to increase the yield of suitable metal.

- eliminate the need to return to the previous mold for refilling - metal into profit, since when the thermal insert is overfilled at the end of filling

- molds, the metal is poured by gravity into the previous mold.

The application of the claimed technical solution ensures the production of a casting bar stock with a diameter of 50 ÷ 150 mm of the required quality and a measured length of 700 ÷ 500 mm.

5. An example of a specific implementation

Example 1. Production of LPZ ∅90 mm.

In order to obtain a casting bar stock with a diameter of 90 mm and a measured length of 1200 mm from a heat-resistant alloy ZhS32-VI, melting and casting was carried out in a vacuum induction furnace using specially prepared casting equipment.

To ensure the assembly of high-quality foundry equipment for the smelting of the LPZ, the casting molds were preliminarily rejected and heat-treated with their subsequent mechanical cleaning. Further, the assembly of the foundry equipment and the steel-pouring chute was carried out.

In a vacuum induction furnace with a capacity of 1.5 tons, melting and casting of a 90 mm LPZ from a heat-resistant alloy ZhS32-VI was carried out into a prepared casting tooling. The temperature of the metal in the furnace before the start of casting was 1540 ° C. The melt was cast completely with an average mold filling rate of 25 sec / piece. 26 billets were poured, the surface of the billets was satisfactory, there were no transverse cracks, there are no welds of steel fungi to the LPZ.

The obtained casting rod billet of ZhS32-VI alloy was handed over to the customer after machining.

Example 2. Production of LPZ ∅65 mm

In order to obtain a casting bar stock with a diameter of 65 mm and a measured length of 1400 mm from a heat-resistant alloy ZhS6U-VI, melting and casting was carried out in a vacuum induction furnace using specially prepared casting equipment.

The preparation of the foundry equipment for the 065 mm LPZ was carried out in a similarly LPZ ∅90 mm alloy ZhS32-VI. The metal was smelted in a vacuum induction furnace with a capacity of 1.5 tons. The temperature of the metal in the furnace before casting was 1560 ° C. The melt was cast completely with an average mold filling rate of 17 sec / piece. There are no differences from LPZ ∅90 mm alloy ZhS32-VI.

The unloading of the LPZ of the ZhS6U-VI alloy from the molds was satisfactory. Inspection of the surface of the obtained workpieces showed the following: the surface quality is satisfactory, some LBZ had areas with traces of ripples (beads), no transverse cracks. Poured 29 blanks.

To study the macrostructure of the LBP 65 mm alloy ZhS6U-VI, we selected one arbitrary workpiece (weighing 43 kg), from which longitudinal macro templates were cut.

The quality of the casting bar stock ∅65 mm in the longitudinal macro is satisfactory - the peripheral zone is dense, surface defects do not exceed a depth of 1 mm. In the central zone, shrinkage is intermittent with extensive "bridges" of dense metal. Shrinkage diameter no more than 9 mm.

The obtained casting bar stock of ZhS6U-VI alloy was handed over to the customer after machining.

In general, for smelts, the amount of waste during casting (scrap formation) and after machining of the obtained casting bar blanks (surface and trimming of the LFZ) after the application of this method decreased by 5% from the smelting, which accordingly increased the yield of suitable expensive nickel-based alloys.

Claims (7)

1. A method of casting bar billets of small cross-section, including the installation of a ladle with a melt above molds of the same length, located on pallets and connected by troughs with each other and with a ladle, feeding the melt from the ladle and forming ingots of a final length, characterized in that the stage of preparation of the foundry is carried out equipment, on which the preliminary culling of the molds is carried out, the molds are placed in one row in the casting equipment, a thermal insert is installed in each mold, made in the form of a tubular bushing with a collar flange with a longitudinal axial trapezoidal channel that ensures the assembly of the molds into a monolithic closed circle with the formation of a trough - adapter, casting equipment is placed in a vacuum induction furnace on a drum-type casting table and metal is poured in vacuum by successive filling of molds from a ladle through a steel-pouring chute. 2. The method according to claim 1, characterized in that at the stage of rejection, the molds are annealed in a hydrogen atmosphere, and then their inner surface is machined. 3. The method according to claim 1, characterized in that after casting and final solidification of the metal, the casting tooling is disassembled, and the resulting blanks with a diameter of 50-450 mm are subjected to mechanical processing. 4. The device of casting equipment for casting bar billets of small section, containing pallets with groups of molds of the same length installed on them and connecting troughs installed between the molds, characterized in that it is configured to be placed in a vacuum induction furnace and is a single prefabricated unit, containing two rings connected by three support posts in a rigid frame, while the rings are made with the possibility of installing molds of the same length in them, equipped with thermal inserts made in the form of a tubular sleeve with a trapezoidal collar flange, with a funnel centering the metal stream and a longitudinal axial channel, the collar flange of the trapezoidal shape ensures the assembly of the molds into a monolithic closed circle, and the longitudinal axial channels of the inserts form a trough-adapter of the molds. 5. The device according to claim. 4, characterized in that the lower of the two rings contains a recess with holes for mounting steel or ceramic inserts. 6. The device according to claim. 4, characterized in that in the upper of the two rings holes are made for installing the molds, coaxial with the holes for installing steel or ceramic inserts made in the lower of the two rings of the tooling. 7. The device according to claim. 4, characterized in that the three support legs are cylindrical, spaced at an angle of 120 ° and made with the ability to provide the required height of the two rings relative to each other.

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