RU2718038C1 - Device for production of casts by directed crystallization - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to foundry production and can be used for production of large-size castings by directed crystallization from nickel alloys and steels. Proposed device comprises sealed chamber accommodating rotary induction melting furnace and mold heating furnace arranged below melting furnace and rod to lift mold into heating furnace. Mold in heating furnace is located on splined support. Water-cooled tray is arranged on the stock. Container for liquid metal cooler is arranged on tray. Container with liquid metal cooler is able to rise into mold heating furnace to contact with mold, wherein liquid metal cooler completely covers the lower part of mold surface in liquid state. At the same time container for liquid metal cooler and tray are made as integral and monolithic, and liquid metal cooler can be in both solid and liquid state prior to lifting into mold heating furnace. Thickness of layer of molten metal liquid cooler is within 1–5 mm. Container for liquid metal cooler can be coated with a layer of aluminum oxide or zirconium oxide with thickness of 0.03–0.25 mm.EFFECT: higher efficiency of heat removal from casting.5 cl, 3 dwg, 1 tbl

Description

FIELD OF TECHNOLOGY

The technical solution relates to the field of foundry and can be used to obtain large-sized castings by directional crystallization from nickel alloys and steels.

BACKGROUND

A device is known for producing directional crystallization castings, containing a vacuum chamber, where an induction furnace for melting and pouring metal is located, a mold heating furnace, a mold suspension system with a moving mechanism, a container with a low-melting liquid metal cooler (LMO) is placed in the cooling zone of the furnace chamber for cooling mold mounted on a pallet and a water-cooled table [RF patent No. 2267380, IPC B22D 27/04, publ. 01/10/2006].

The advantage of the device is the full contact of the bottom of the uneven ceramic mold with LMOs over the entire surface with effective heat removal and the provision of a sufficiently high temperature field gradient between the molten metal and the bottom of the mold to form a directional structure and minimize the microporosity of the casting.

The disadvantages of the analogue are the small size in height (up to 200 mm) and the small weight (up to 10 kg) of the molded parts. This is due to the fact that when fastened to the suspension in the upper part, fragile and brittle ceramic forms often come off and fall into the LMO with a corresponding loss of casting, failure of the LMO or even damage to the equipment, which limits the dimensions of the obtained castings.

In development of this analogue, a device is proposed in which the suspension system for securing the mold with the mechanism for moving it further comprises a device for placing the mold, and the LMO tank is made in the form of a coil of a copper water-cooled tube or a water-cooled annular tank including an autonomous heater [RF patent No. 22292026, IPC B22D 27/04, publ. 09/10/2013].

This design allows for efficient heat removal from the lower part of the mold to the LMO and to obtain castings with increased dimensions.

The disadvantages of the device:

- the fragility of the suspension system of molybdenum, immersed in the LMO and chemically interacting with them and the need for an individual suspension system for each form;

- inefficient use of the working space of the heating furnace due to the substantial dimensions of the suspension system of the mold.

A device is known for producing directional crystallization castings, comprising a vacuum furnace with a mold heating chamber, melt and pouring melt, and a mold cooling chamber with an LMO bath, a mechanism for moving the mold from the heating chamber to the cooling chamber, a vacuum system and a cooling inert gas supply system, a jet distribution device gas flow along the perimeter of the form through gas pipelines located in the LMO bath to a depth of 15 cm [RF patent No. 2226449, IPC B22D 27/04, publ. 04/10/2004].

In this device, the effectiveness of creating a high gradient of the temperature field during crystallization of large castings and reduce the volume of microporosity in it is achieved by:

- an increase in the intensity of cooling by jet supply of inert gas to the surface of the mold immersed in the LMO;

- increase the residual pressure in the chamber and suppress the possibility of boiling LMOs with the formation of vapors of monatomic metals, the thermal conductivity of which is extremely low, and the coefficient of heat transfer through the film does not exceed 10 W / m ^{2 *} deg.

The disadvantages of the device are:

- excessive increase in the wall thickness of the ceramic mold fixed in the upper part on the suspension to harden it and to prevent destruction when pouring metal, which, due to the low thermal conductivity of the material of the ceramic mold, reduces the heat flux from casting and the temperature field gradient;

- the complex design of the device for supplying cooling gas to the mold in the LMO;

- the need for a large amount of LMOs.

A device (prototype 1) is known for producing castings directed by crystallization, containing a sealed heating chamber, in which a rotary induction melting furnace and a mold heating furnace are installed, located below the melting furnace, a cooling chamber, an isolation valve located between the heating chamber and the chamber are located below the heating chamber cooling mechanism for vertical movement and rotation of the mold relative to the vertical axis, containing a rod passing through a sealed movable seal in the bottom part and cooling chambers, a tray with a cooled cavity mounted on the upper end of the rod on which the mold is placed, a form fixing mechanism in the heating furnace, consisting of coaxially arranged spline disc and spline support, a spline support is fixed in the lower part of the heating furnace, a spline and spline the support has slots and protrusions with dimensions that enable them to slide relative to each other when lifting the mold into a mold heating furnace [RF patent 2545979, IPC B22D 27/04, publ. 04/10/2015].

The disadvantage of this device is the insufficiently high efficiency of the heat sink from the bottom uneven surface of the mold due to its contact with the cooled tray only at individual points due to the very low thermal conductivity of the vacuum layer.

A device (prototype 2) is known for producing directional crystallization products, including a crucible furnace for melting and pouring metal, a mold heating furnace having a hole in the bottom part in which a seed crystal is located, the mold is located on an intermediate heat-conducting block placed on a water-cooled tray [EP 0496978, IPC B22D 27/04, publ. 08/05/1992]. The mold and the heat-conducting block are hermetically connected through heat-resistant elements. After vacuum cleaning, the heat conduction block rises and the seed crystal enters the bottom hole of the mold. After pouring the metal, heat is removed through the seed crystal to obtain a casting with a directional structure.

This design allows you to get a fairly dense castings with increased dimensions.

However, in this design, the heat conduction block, due to the non-planar nature of the mating surfaces and deformations at high temperatures, contacts the water-cooled tray not over the entire surface, but over individual contact spots with a vacuum layer between them of at least 0.5 mm, which cannot provide a sufficiently intense heat removal from the bottom surface of the mold and high quality castings. In addition, the seals between the mold and the thermal conductivity block are not reliable enough, and the need to accurately combine the seed crystal with the hole in the mold at high temperatures complicates and increases the cost of the device.

SUMMARY OF THE INVENTION

An object of the invention is a device for producing large-sized castings with directional crystallization, which increases the heat sink from the casting by creating a heat-transfer liquid metal cooler of full contact between the lower part of the mold surface and a water-cooled tray.

To solve the technical problem, a device is proposed for producing directional crystallization castings, which contains a sealed heating chamber, in which a rotary induction melting furnace and a mold heating furnace located below the melting furnace are installed, a cooling chamber, an isolation valve located between the heating chamber and cooling chamber, a mechanism for vertical movement and rotation of the form relative to the vertical axis, containing a rod passing through a sealed movable a seal in the bottom of the cooling chamber, a tray with a cooled cavity mounted on the upper end of the rod on which the mold is placed, a mold fixing mechanism in the heating furnace, consisting of coaxially spline disc and spline support, the spline support is fixed in the bottom of the heating furnace, spline the disk and the spline bearing have slots and protrusions with dimensions that enable them to slide relative to each other when lifting the mold into the mold heating furnace, characterized in that a liquid meter container is installed on the pallet of a refrigerant cooler that contacts the pan across the entire surface, the pallet is hermetically and detachably connected to the stem, while the container with a liquid metal cooler can rise into the mold heating furnace until it contacts the lower surface of the mold, and the liquid metal cooler completely covers the lower part the surface of the mold, and the capacity for the liquid metal cooler and the pallet are made as a whole and in one piece.

The liquid metal cooler is in the solid state before being lifted into the mold heating furnace.

The liquid metal cooler is in a molten state before being raised into the mold heating furnace.

The thickness of the layer of molten liquid metal cooler is in the range of 1-5 mm.

The capacity for the liquid metal cooler is coated with a ceramic layer 0.03-0.25 mm thick of aluminum oxide or zirconium oxide.

BRIEF DESCRIPTION OF THE DRAWINGS

The essence of the proposed technical solution is illustrated by the figures:

FIG. 1 - Scheme of the device.

FIG. 2 - Mold with molten metal located on solid LMO (aluminum) - view A in FIG. 1 (increased).

FIG. 3 - Form with hardened metal located on the molten LMO - view B in FIG. 1 (increased).

1 - heating chamber; 2 - cooling chamber; 3 - Melting furnace; 4 - Crucible (Al ₂ O ₃ ); 5 - Metal (nickel alloy or steel); 6 - heating furnace; 7 - Splined annular support; 8 - Slotted disk; 9 - Isolating valve; 10 - Side door; 11 - Mold (Al ₂ O ₃ ); 12 - Stock lifting mold; 13 - Water-cooled pallet; 14 - Capacity for LMO; 15 - LMO (aluminum) solid; 16 - LMO (aluminum) molten; 17 - Metal in the form of molten; 18 - Metal in the form of crystallized; 19 - Foundry funnel; 20 - The protrusion on the form; 21 - The gap between the mold and the pallet.

DETAILED DESCRIPTION OF THE INVENTION

The furnace (Fig. 1) consists of two sealed chambers - a heating chamber (1) and a cooling chamber (2).

In the upper part of the heating chamber is an induction melting furnace (3) with a crucible (4), intended for melting and pouring a metal charge of nickel alloy or steel (5).

In the lower part of the heating chamber there is a heating furnace of the form (6) and a spline annular support (7) having alternating slots in the hole between the protrusions (Fig. 2).

The heating furnace is designed to heat to a temperature of, for example, 1650 ° C and holding the mold therein for a predetermined time. The form rests on the spline disk (8), and the spline disk - with its protrusions on the protrusions of the spline support. The perimeter disk has alternating protrusions between the slots. After rotation about a vertical axis by an angle θ, the spline disk is able to move in a vertical direction relative to the spline support, while the protrusions of the disk slide along the splines of the spline support.

Between the heating chamber and the cooling chamber is an insulating valve (9), designed for their tight shutoff.

The cooling chamber has a side door (10) for loading and unloading the mold (11).

On a lift stem (12) equipped with vertical displacement and rotation drives (not shown), a water-cooled tray (13) with a capacity (14) for a low-melting liquid metal cooler (LMO) in a solid (15) and molten (16) state and a mold are located (Fig. 2 and Fig. 3). The rod has a central hole in which is placed a tube for supplying cooling water to the pan and an annular cavity for its return exit.

The tray is designed to remove heat from the molten metal (17) and molds through the LMO above the tray to provide directional crystallization of the metal (18), poured through a casting funnel (19).

The volumes of the container above the pallet and the LMO placed in it are selected on the basis of ensuring full contact between the lower part of the mold and the LMO.

The furnace operates as follows.

The isolation valve is in the closed position.

The mold heating furnace is turned on, its temperature is brought up to 1650 ° C.

The mold is mounted on a spline disk located on the stem in the cooling chamber. After closing and sealing the side door, the vacuum system is turned on and the residual pressure in the chamber decreases to less than 10 ^-1 Pa.

The isolation valve is set to the “open” position.

The stock lifts the mold into the mold heating furnace. The protrusions of the spline disk slide along the spline of the spline support and the spline disk 3 ... 5 mm rises above the spline support. After that, the rod, respectively, and the spline disk rotate back through the angle θ, the rod moves downward, while the spline disk, falling by 3 ... 5 mm, sits on its protrusions on the protrusions of the spline support, and the rod continues its downward movement into the cooling chamber until extreme lower position.

The isolation valve is in the closed position.

The mold in the heating furnace is maintained for a predetermined time.

The metal charge, until the mold is held in the heating furnace, is loaded into the crucible of the melting furnace, melted and, for example, 1550 ° C, is poured into the mold through a casting funnel (Fig. 2).

After holding the metal in the mold, the isolating valve is put into the “open” position.

A rod with a water-cooled tray and LMO (in solid state) (Fig. 2) located in the tank rises in the heating furnace, abuts against a spline disk with a shape and raises it by 3 ... 5 mm. In this state, the mold is kept in the furnace until the LMO transitions to the molten state. The transition time of the LMO to the molten state is controlled by the temperature of the molten metal in the mold and the volume of the LMO. The transition of the LMO into the molten state is controlled visually and by a pyrometer built into the chamber wall at the mold level (not shown). After that, the cooling of the pallet is started by entering cooling water with the required parameters into its cavity (Fig. 3).

Before rising into the heating furnace, the LMO can be in the molten state, for which the tank (14) can be equipped with an integrated heating element.

Before the LMO is melted, the gap between the protrusion of the mold and the spline disk is “G” (Fig. 2). After the LMO is melted, the mold is lowered by this value and with its protrusion (20) sits on the spline disk (8). In this case, the mold squeezes the LMO into the gap (21) between the mold and the container, as a result of which it rises by a predetermined value of "N" relative to the lower surface of the mold (Fig. 3). Thus, full contact of the LMO is ensured not only with the bottom, but also with the lateral surface of the mold and effective heat removal from the casting.

The thickness of the layer δ LMO (16) should be minimal, but sufficient to fully cover the lower part of the mold in the molten state and to raise it by a given value of "N". Preferably, this thickness should be at least 1 mm and not more than 5 mm. Increasing the thickness of more than 5 mm is impractical due to the increase in the dimensions of the device and the unjustified consumption of LMOs.

The rod with the form rotates back through the angle θ and begins to fall at a speed of 1 ... 10 mm / min, while the protrusions of the spline disk slide along the splines of the spline support.

The isolation valve is in the closed position.

The molten metal crystallizes from the lower to the upper part of the mold with the removal of microporosity in the upper part of the casting.

After the mold temperature drops to 400-600 ° C, the cooling chamber is evacuated and the cast mold is removed from the furnace.

The next casting cycle begins.

To confirm the possibility of increasing the efficiency of heat removal and obtaining the claimed result for a significant increase in the temperature field gradient, an estimated calculation of boundary temperatures was performed for three embodiments of the casting process:

Option B1 (prototype 1). The mold is mounted on a copper tray - a vacuum layer between the mold and the tray 2 mm.

Option B2 (prototype 2). The form is installed on the heat conduction block according to the prototype 2, and the heat conduction block on the copper tray is the vacuum layer between the heat conduction block and the pan 0.5 mm.

Option B3 (claimed). The mold is installed in a container with solid LMO from aluminum, which is made on a copper tray; the LMO layer between the mold and the pallet after melting is 2 mm.

Based on the experimental work accepted:

The temperature of the molten metal in the form (Tf1), 1400 ° C;

The temperature of the cooling water in the pan (Tf2), 60 ° C;

The inner diameter of the pipe for supplying cooling water (d), 0,030 m;

Heat transfer surface area (F), 0.008 m ² .

The calculation of boundary temperatures was carried out according to the classical formulas:

Tw1 = Tf1-q⋅ (1 / α1) [° C],

where Tw1 is the temperature at the boundary "molten metal-form", ° C;

q is the surface density of the heat flux, W / m ² : q = (Tf1-Tf2) / (1 / α1 + δ1 / λ1 + δ2 / λ2 + δ3 / λ3) + (1 / α2);

Heat flux Q was determined by the formula:

Q = q ^* F [W].

Calculation of temperatures at the “form-vacuum layer (or LMO)” interface was carried out according to the formula T1 = Tw1-q⋅δ1 / λ1 [° C], and temperatures at the “vacuum layer (or LMO) -pallet interface" according to the formula T2 = Tw1 -q⋅δ2 / λ2 [° C].

In these formulas:

δ1, δ2 and δ3 — thickness of the mold (0.010), vacuum layers (0.002 for B1 and 0.0005 for B2) or LMO (0.002) and pan (0.010), m;

λ1, λ2, λ3 and λ4 are the thermal conductivity coefficients of the form (2.40), the vacuum layer (0.10 for B1 and B2), LMO (100.0), copper pan (373.0) and water (0.65) , W / (m⋅ ° С). The sources of information for these coefficients are taken:

- λ1 for options 1-3 for temperatures of 400-1200 K: Page 359, Physical quantities: Reference book / A.P. Babichev, N.A. Babushkina et al. - M .: Energoatomizdat, 1991 .-- 1232 p.

- λ2 for options 1-2 vacuum with a residual pressure of 0.001 bar, temperature 1500 K: Page 631, Reference to the thermophysical properties of gases and liquids / Vargaftik NB - M .: Nauka, 1972. - 720 p.

- λ2 for option 3, temperature 1000-1200 K: Page 108, Thermophysical properties of metals at high temperatures: Reference book / Zinoviev V.E. - M.: Metallurgy, 1989 .-- 384 p.

- λ3 for options 1 and 2, temperature 293-873 K: Page 180, Thermophysical properties of materials of nuclear engineering: reference book / Chirkin B.C. - M .: Atomizdat, 1968 .-- 468 p.

- λ4 for options 1-3, water at a temperature of 40-80 C: Page 48, Handbook of the thermophysical properties of gases and liquids / Vargaftik NB - M .: Nauka, 1972. - 720 p.

α1 and α2 are the heat transfer coefficients from the molten metal to the mold and from the tray to the cooling water, W / (m ² ⋅ ° С). Sources of information for these ratios:

- α1 (equal to 1050.0): Page 72, Dubrovskaya A.S. Numerical simulation of the manufacturing process for castings of gas turbine engine parts by precision casting. FSBEI HPE Perm National Research. Polytechnics, University. " Thesis for the competition. academic degree Ph.D. - Perm - 2015.

где- α2 (equal to 4902.0): calculated by the classical formula

Where

- безразмерный критерий Нуссельта;

- dimensionless Nusselt criterion;

d is the inner diameter of the pipe (0,030), m

определяется по формуле

гдеAt the same time, the Nusselt criterion

determined by the formula

Where

Re _W - dimensionless Reynolds criterion: Re _W = V _{W I.} ⋅d / ν;

Pr _W ^0.43 - the Prandtl test is 2.97 for heated water at an arithmetic mean temperature of 55-60 ° C;

V _{W I} - the speed of water in the pipe, 1.0 m / s;

ν is the kinematic viscosity coefficient of water, 0.00000055 m ² / s;

Pr _c ¹ - the Prandtl criterion for water is 2.10 at a wall temperature as a first approximation, t _c ¹ = 80-85 ° С;

E _L - correction factor for the initial thermal section of the flow stabilization: at H / d≥50, then E _L = 1,0.

The results of calculating the boundary temperatures are presented in the table.

The data in the table indicate a significant decrease in temperature at the “melt-form” interface (1162 ° C versus 1350 ° C and 1277 ° C) and a multiple decrease in temperature at the “form-LMO” border (123 ° C against 1129 ° C and 737 ° C ) according to the claimed invention regarding prototypes due to efficient heat transfer from the mold to the pallet with an LMO layer, which will create an increased temperature field gradient between the metal melt and the lower mold surface and provide a decrease in microporosity and an increase in the quality of castings.

When the thickness of the LMO is less than 1 mm, full 100% contact between the mold surface is not ensured, and a thickness of more than 5 mm unjustifiably increases the thermal resistance of the heat sink unit and reduces the temperature field gradient, and also leads to an increase in the LMO consumption.

The thickness of the ceramic oxide coating on the inner surface of the container for LMO less than 0.03 mm does not adequately protect the copper tray from interaction with the molten aluminum, and more than 0.25 mm significantly increases the thermal resistance of the heat sink unit.

Claims (5)

1. A device for producing castings by directional crystallization, comprising a sealed heating chamber, in which a rotary induction melting furnace and a casting furnace located below the melting furnace are installed, a cooling chamber, an isolation valve located between the heating chamber and the cooling chamber are located below the heating chamber, a mechanism for vertical movement and rotation of the mold relative to the vertical axis, containing a rod passing through a sealed movable seal in the bottom of the chamber about cooling, a tray with a cooled cavity mounted on the upper end of the rod on which the mold is placed, a mechanism for fixing the mold in the heating furnace, consisting of coaxially arranged spline disk and spline support, the spline support being fixed in the lower part of the heating furnace, and the spline disk and the spline bearing have slots and protrusions with dimensions that allow them to slide relative to each other when the mold is lifted into the mold heating furnace, characterized in that a container for I liquid metal cooler, made with the possibility of contacting with the pallet on the entire surface, while the pallet is connected to the rod hermetically and detachably, and the capacity with the liquid metal cooler is made with the possibility of lifting the heating of the mold into contact with the lower surface of the mold, moreover, the liquid metal cooler in the liquid state completely covers the lower part of the surface of the mold, and the capacity for the liquid metal cooler and the pallet are made integral with one eloe. 2. The device according to claim 1, characterized in that the liquid metal cooler is in the solid state before being raised into the mold heating furnace. 3. The device according to claim 1, characterized in that the liquid metal cooler is in a molten state before being raised into the mold heating furnace. 4. The device according to p. 1, characterized in that the thickness of the layer of molten liquid metal cooler is 1-5 mm 5. The device according to p. 1, characterized in that the tank for liquid metal cooler is coated with a layer of a thickness of 0.03-0.25 mm of aluminum oxide or zirconium oxide.

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