RU2516210C2 - Method to control process of crystallisation and device for its realisation - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy. The device comprises a vacuum induction furnace, a cylindrical container and a hydraulic press. The press comprises two hydraulic cylinders arranged coaxially with the container and each developing a force of 0.3 MN, a closing hydrauloc cylinder with a force of 3 MN, a multiplier and a high-pressure valve. Press-plungers of cylinders are installed as capable of opposite movement. Liquid metal at temperature above liquidus by 150-200°C, poured into a vacuumised container - a crystalliser from a vacuum chamber. The vacuum value in the container makes 0.2-0.3·10^-5 mm of mercury column. The crystallising metal is exposed to pressure by press-plungers, which is increased with speed of more than 40 MPa/s to the value of 300-400 MPa. After compression of the metal by 10% they increase pressure with the same speed to value of more than 500 MPa, and metal is additionally compressed by 2.4-2.8%. Isostatic compression of metal is carried out until the metal cools down to 100-150°C.

EFFECT: thermodynamic parameters of the method provide for formation of fragments of a nanostructure of separate atoms and associations, which determines production of bars with mechanical properties not inferior to and superior to properties of rolled metal, forged and stamped billets.

2 cl, 6 dwg, 2 tbl, 2 ex

Description

The invention relates to metallurgy, and can be used to control the crystallization process in order to increase the mechanical properties of ingots / products by forming fragments of a nanostructure from individual atoms and associations.

A known method of controlling the crystallization process in a liquid-solid system by applying mechanical vibrations to it with a fixed frequency in the range from 10 to 100 kHz (Swiss patent SN No. 682402, C22F 3/02, s 22 with 21/08, B22D 11/10 , 1993)

However, the scope of this method is limited to obtaining a liquid-solid phase of a metal alloy having thixotropic properties. According to the results of electron microscopy, this method allows to obtain a more ordered and significantly finer structure of the alloys, however, it cannot be attributed to the ultra finely dispersed structure, not to mention the nano structure. In this case, the vibrational - mechanical effect requires a large expenditure of electricity per unit mass of crystallized substance. In addition, vibration exposure is a type of industrial hazard.

Also known is a method of injection molding with crystallization under pressure on a machine with a horizontal pressing chamber, comprising filling the mold with metal by pouring it into the pressing chamber and squeezing the metal with a pressing piston. The metal form is filled through a relatively large feeder with a pressing piston speed of 0.3-0.5 m / s (patent RU 2033892, B22D 17/00, B22D 18/02, 1992).

The disadvantages of the second analogue are the coarse-crystalline structure of the obtained ingots, and additional heat treatment is required to obtain higher values of the mechanical properties of the alloys.

A close analogue to the claimed technical solution is a method of manufacturing metal billets by injection molding, according to which a metered volume of molten metal is poured into a pressing cylinder, the mold cavity is filled with a melt, then pressure is applied to it and soaking is carried out. Before pouring, the melt is overheated at 40-70K above its liquidus temperature. In this case, the melt is poured into the intermediate vessel, and at this time the mold cavity is evacuated, after which the mold cavity and the associated pressing chambers are filled with the melt from the intermediate vessel. Simultaneously with filling the pressing chambers in communication with the mold cavity, evacuation continues. The filling speed is regulated by changing the speed of pumping air and gases from the mold cavity and the pressing chambers until the end of their filling. At the same time, the speed of evacuation of air and gases is controlled by changing the area of the hole connecting the mold cavity through the compression chamber with the vacuum system, by moving the counter plunger. Then, bilateral pressure is applied to the melt along the axis of the workpiece, while the pressure is 200-500 MPa. Exposure of the metal under pressure is carried out until the end of crystallization. To implement this method, an injection molding machine is used, which is equipped with a hydraulic system and a control unit, contains a pressing mechanism with a plunger and a chamber placed in the housing and an associated releasable mold with a casting cavity in communication with the holes for filling the melt and removing it air and gases. In this case, the pressing mechanism is equipped with an additional pressing chamber and a counter plunger located in a fixed part of the housing coaxially with the mold in response to the chamber and plunger made in the movable part of the housing. The hole for pouring the melt is made with the possibility of overlapping it with a plunger and communicated with an intermediate tank rigidly fixed to the movable part of the housing, and the hole for removing air (gases) is made with the possibility of overlapping it with a counter plunger and communicated with a vacuum system. (Patent RU No. 2252108 of 05/20/2005 IPC B22D 17/00, filed on 05.08.2002. Published on 02.27.2004).

The disadvantages of the above method is that it does not improve the mechanical properties of castings by forming fragments of nanostructures from individual atoms and their associations, since the superheat temperature of a liquid metal at 40-70 K is insufficient to provide a degree of supercooling, which is determined by the difference between the equilibrium crystallization temperature and the actual solid phase formation temperature. The decrease in the degree of subcooling is also connected with the fact that the metal is poured from an unevacuated intermediate tank, which requires degassing of the liquid metal. At the first stage of applying pressure to the metal, which fills the mold cavity with free filling, it increases the rate of gas removal and compression of interplanar surfaces with the formation of voids. The temperature of the melt decreases to the temperature of formation of solid crystalline phases. At this moment, the second stage of pressure application begins, which consists in applying pressure from the inside from under the crust of the crystallized metal. At the same time, the structure is formed as a result of pressing in additional volumes of metal to compensate for shrinkage, as well as plastic molding of molten crystals formed before pressure was applied. This method does not provide the formation in the metal of nanostructure fragments from individual atoms and their associations, since solid phases of crystals have already formed, for which nanostructures need plastic deformation of the solid metal due to the application of pressure of several gigapascals. The structure obtained by this method has no shrinkage defects, is characterized by high tightness, but it consists of separate zones-fragments that differ in the type and nature of the structure. Thus, the method solves the problem of compaction of crystallized metal by applying pressure, i.e. the effect of pressure on the quality and properties of castings is manifested only in the elimination of ordinary defects of shrinkage origin.

The closest analogue to the claimed technical solution is the injection molding method, which is selected as a prototype. The method consists in pouring a metered volume of molten metal into a pressing cylinder, filling the mold cavity with a melt, then applying pressure on it and holding it. Before pouring, the melt is overheated at 40-70K above its liquidus temperature. In this case, the melt is poured into the intermediate vessel, and at this time the mold cavity is evacuated, after which the mold cavity and the associated pressing chambers are filled with the melt from the intermediate vessel. Simultaneously with filling the pressing chambers in communication with the mold cavity, evacuation continues. The filling speed is regulated by changing the speed of pumping air and gases from the mold cavity and the pressing chambers until the end of their filling. At the same time, the speed of evacuation of air and gases is controlled by changing the area of the hole connecting the mold cavity through the compression chamber with the vacuum system, by moving the counter plunger. Then, bilateral pressure is applied to the melt along the axis of the workpiece, while the pressure is 200-500 MPa. Exposure of the metal under pressure is carried out until the end of crystallization. To implement this method, an injection molding machine is used, which is equipped with a hydraulic system and a control unit, contains a pressing mechanism with a plunger and a chamber placed in the housing and an associated releasable mold with a casting cavity in communication with the holes for filling the melt and removing it air and gases. In this case, the pressing mechanism is equipped with an additional pressing chamber and a counter plunger located in a fixed part of the housing coaxially with the mold in response to the chamber and plunger made in the movable part of the housing. The hole for pouring the melt is made with the possibility of overlapping it with a plunger and communicated with an intermediate tank rigidly fixed to the movable part of the housing, and the hole for removing air (gases) is made with the possibility of overlapping it with a control plunger and communicated with a vacuum system (Patent RU No. 2193945, C2 , IPC B22D 18/02, claimed May 30, 2000. Published December 10, 2002).

The disadvantage of the above method is that it does not improve the mechanical properties of castings by forming fragments of nanostructures from individual atoms and their associations, since the superheat temperature of a liquid metal at 40-70K is insufficient to provide a degree of supercooling, which is determined by the difference between the equilibrium crystallization temperature and the actual solid phase formation temperature. The decrease in the degree of subcooling is also connected with the fact that the metal is poured from an unevacuated intermediate tank, which requires degassing of the liquid metal. At the first stage of applying pressure to the metal, which fills the mold cavity with free filling, it increases the rate of gas removal and compression of interplanar surfaces with the formation of voids. The temperature of the melt decreases to the temperature of formation of solid crystalline phases. At this moment, the second stage of pressure application begins, which consists in applying pressure from the inside from under the crust of the crystallized metal. At the same time, the structure is formed as a result of pressing in additional volumes of metal to compensate for shrinkage, as well as plastic molding of molten crystals formed before pressure was applied. This method does not provide the formation in the metal of nanostructure fragments from individual atoms and their associations, since solid phases of crystals have already formed, for which nanostructures need plastic deformation of the solid metal due to the application of pressure of several gigapascals. The structure obtained by this method has no shrinkage defects, is characterized by high tightness, but it consists of separate zones-fragments that differ in the type and nature of the structure. Thus, the method solves the problem of compaction of crystallized metal by applying pressure, i.e. the effect of pressure on the quality and properties of castings is manifested only in the elimination of ordinary defects of shrinkage origin.

The closest analogue of the claimed device adopted for the prototype is a device for the manufacture of metal billets by injection molding, containing a pressing mechanism with a pressing chamber and a plunger, a housing consisting of two parts mounted on a fixed and movable plate of a casting machine, a hydraulic system, a control system, and split mold with a casting cavity. The mold communicates with a hole for pouring the melt and with a hole for removing air and gases associated with a vacuum system. Moreover, the intermediate container is rigidly fixed on the movable part of the housing and communicates with the hole for pouring the melt, and the pressing mechanism is equipped with an additional pressing chamber with a counter plunger located in the stationary part of the housing coaxially with the mold and opposite to the main pressing chamber with the plunger located in the movable part corps. The hole for pouring the melt is positioned so that it is possible to overlap it with a plunger, and the hole for removing air and gases is placed with the possibility of overlapping it with a counter plunger (Patent RU No. 2193945, C2, IPC B22D 18/02, filed 05/30/2000. Published 10.12. 2002).

The disadvantages of the prototype include the fact that it does not increase the mechanical properties of castings by forming fragments of nanostructures from individual atoms and their associations, since the pressure on the metal, which fills the mold cavity with a free fill, is transmitted using a pressing plunger on one side, namely: from the side of the pouring bowl, which leads to the formation of asymmetric temperature fields, and, consequently, unequal thermodynamic conditions in different parts of the casting volume; the pressure application rate is not consistent with the state of the metal, therefore, the effect of pressure on the quality and properties of castings is manifested only in the elimination of ordinary defects of shrinkage origin.

The objective of the claimed invention is to obtain a higher level of mechanical properties of ingots / products, by forming fragments of a nanostructure from individual atoms and associations. At the same time, crystallization control is aimed at ensuring that the all-round pressure applied to the liquid metal is aimed at forming a predetermined structure during crystallization that determines properties that are not inferior or superior to the properties of rolled, forged and stamped blanks.

The problem is solved due to the fact that in the method of the invention, the control of the metal crystallization process includes heating the metal to a temperature above liquidus, pouring the liquid metal into the evacuated mold from the vacuum chamber, applying pressure to the liquid crystallizing metal, sealing the metal and holding it under pressure (according to the invention), the mold is evacuated to a value of 0.2-0.3 · 10-5 mm Hg, the metal is heated to a temperature of 150-200 Celsius above liquidus, the pressure is applied with increasing it at a speed > 40 MPa / s to a value of 300-400 MPa, after compressing the metal by 10%, increase the pressure at the same speed to a value> 500 MPa and additionally perform isostatic compression of the metal by 2.4-2.8%, while the metal is held under pressure is carried out until the metal cools to 100-150 Celsius.

The problem is also solved by the fact that the device for controlling the process of metal crystallization contains a vacuum induction furnace with a vacuum of 1 · 10 ^-5 mm Hg, a cylindrical container with a horizontal axis (hereinafter referred to as the mold), evacuated to 0.2-0 3 · 10 ^-5 mm Hg, a hydraulic press consisting of two hydraulic cylinders coaxially with the mold and developing individually 0.3 MN force, designed to move the press plungers by 125 mm, a closing hydraulic cylinder, which develops the force 3 WE at a stroke of 250 mm, a pressure multiplier and a high pressure valve, while the press plungers are installed with the possibility of counter movement along the axis of the container to apply pressure to the crystallizing metal and comprehensively compress the metal, programmed under the law, taking into account the specific characteristics of the alloy and the shape of the product, and providing melt compaction of the metal by 12.4-12.8% at a pressure of more than 500 MPa.

The proposed method of crystallization control is based on the laws of pressure, which were previously unknown for the first time and have been established by the authors on a liquid metal (i.e., on a metal that is in a state where interatomic interactions are more likely probabilistic - statistical in nature), which leads to an increase in the compressibility coefficient associated with the formation of liquid phase clusters due to the relatively easy approach of atoms to a distance commensurate with the amplitude of atomic vibrations relative to the initial Proposition. The proximity of atoms in a liquid metal to distances at which their interactions, diffusion, separation, and mutual sliding substantially change (by analogy with thermal quenching for martensite) and the formation of a structure under pressure occurs from a highly nonequilibrium state. An increase in pressure and a decrease in the volume of the metal are associated with an improvement in the crystallization process in that the clusters remaining in the liquid phase occupy a position and orientation in space that contribute to the crystallization process at the time of crystallization and during crystallization. Moreover, accompanied by the release of latent heat of crystallization, it is aimed at the formation of additional interatomic bonds, leading to the formation of nanostructures.

The use of a vacuum induction furnace, airlock, evacuated to 1 · 10 ^-2 mm RT.article and a crystallizer evacuated to an experimentally established value of 0.2-0.3 10 ^-5 mm RT.article allows you to create a single vacuum space through which the metal moves from a melting vacuum induction furnace into the mold. In the process of this casting method, firstly, the metal is not saturated with gas, and, secondly, a single vacuum space allows you to uniformly and quickly fill liquid metal without cooling during the casting process. A feature of the process is that during filling of the mold with liquid metal, as a result of connecting it to an additional vacuum system, a vacuum of 0.2-0.3 · 10 ^-5 mm Hg is created. against 1 · 10 ^-2 mm RT.article in the lock chamber, which favors an increase in the rate of pouring of liquid metal, and that is not achieved either by casting ingots into the molds, or by liquid stamping, or by injection molding. The consequence of this filling method is that the pressure feed rate increases and, as established experimentally, can reach a value of more than 40 MPa / s, since pressure is not required to remove the residual gas content and the pressure begins even before the formation of the first crystallized particles. Thus, it becomes possible to change the pressure feed rate, and experimentally tested the possibility of applying pressure according to parabolic, exponential or other law, taking into account the specific characteristics of the alloy and the shape of the products.

The overheating of the metal before pouring 150-200 Celsius above the liquidus temperature allows, firstly, to bring the metal to a more unbalanced state and secondly to the ability to control the cooling rate. It was experimentally established that by increasing the cooling rate at the beginning, it is possible to achieve the formation of a higher hardness of the surface layer and lower hardness inside the casting. This allows you to exclude from the process the operation of surface hardening in the manufacture of this method of products. At the same time, it was experimentally established that the delay in the control of the method of action leads to significant deviations from the desired result. The delay in the effect on the liquid metal is felt for the first time 3-5 s after the metal is fed into the mold. To exclude the possibility of uncontrollability of the crystallization process for the first 3-5 s, it turned out to be sufficient to overheat the metal by 150-200 Celsius. Pouring metal through the lock chamber does not require any intermediate containers and proceeds without contact with the walls of the lock chamber, which does not require additional protection that increases the durability of the equipment. By controlling the effect of pressure and varying the cooling rate in the first seconds on the liquid metal entering the mold cavity, the method allows to achieve the solution of the problem, both on massive castings and in the production of thin-walled products.

The initial pressure in the range of 300-400 MPa was experimentally determined for alloys of various compositions, while it was experimentally established that 10% compression of the metal is necessary, which is much higher than volume shrinkage and this allows creating conditions for the formation of clusters in a liquid metal melt.

Thus, it was experimentally established that the method of applying pressure to obtain the requirements of a given result must be carried out in two stages:

Stage 1 - compression of a liquid metal by 10% with a pressure of 300-400 MPa, which determines the approximation of atoms and obtaining a nonequilibrium state of a liquid metal;

Stage 2 - isostatic compression of a liquid melt in a nonequilibrium state, contributing to the release of nanostructures of quasicrystalline and amorphous phases.

At the first stage, the pressure on the liquid on the metal is not high, after which an increase to> 500 MPa is necessary, and only at this pressure, as experimentally established, is the isostatic compression of the crystallizing metal occurs, leading to the creation of long-range order in the liquid metal. In this case, the isostatic compression of the crystallizing metal is 2.4 ... 2.8%.

The application of pressure> 500 MPa to the liquid metal creates conditions for overcoming the resistance and the approach of atoms, the amplitude of atomic vibrations decreases, or the mutual spatial arrangement of atoms changes, and the coordination number increases.

The proposed method allows you to control the crystallization of the melt, the application of an isostatic pressure of more than 500 MPa to the entire volume of the crystallizing metal and keep it up to a cooling temperature of 150-200 Celsius. The method, due to the isostatic compression of the liquid metal, allows the manipulation of atoms in the molten state, when the crystal lattice is destroyed, and there is no pattern in the mutual arrangement of atoms. The main features of such an interaction are formed already in the melt, which leads to the appearance of a certain type of chemical short-range order in the melt, which controls the possibility of precipitation of nanoscale amorphous and quasicrystalline phases. The causal relationship of the increased level of physical and mechanical properties is that the obtained state of the liquid metal is inherited by the solid state and the metal becomes a nanostructured material strengthened by amorphous and quasicrystalline phases. The properties of such materials significantly exceed the values obtained on alloys using traditional metallurgical technology, and, consequently, the technological and operational properties of the products change.

In the proposed method, pressure is used as a factor of a thermodynamic parameter, which, like temperature, determines the composition of phases under nonequilibrium conditions and affects phase transformations and structure in the solid state with a change in the pressure application rate. That is, the application of isostatic pressure is an influence factor that determines many options for technological parameters leading to the formation of nanostructured materials.

The formation of nanostructure fragments can be achieved, in accordance with this application, under conditions of comprehensive compression at a temperature above the onset temperature of crystallization, when the atoms lose their characteristic diffusion mobility and the ability to form equilibrium phases that differ in the composition and structure of the crystal lattice. Such a state can be achieved if process parameters such as overheating of the liquid metal above the liquidus temperature, the rate of pressure rise, the pressure applied to the liquid metal, the degree of isostatic compression of the liquid metal prior to crystallization are selected previously experimentally and provide the necessary approximation of the atoms before crystallization; during crystallization, additional isostatic compression of the metal is required to compensate for shrinkage, the pressure must be increased and not removed from the pressing plungers until the casting temperature drops to 100-150 degrees. Celsius.

Unlike injection molding machines, where the sequence of operation of the mechanisms is strictly regulated, when carrying out the process using a device that is an automated reprogrammable complex based on a hydraulic press, it is possible to change the order of activation of the mechanisms and the time of their functioning and thus control the change or another parameter, in particular, the pressure applied to the metal, taking into account the influence of other parameters and external disturbances. In this case, the hydraulic press is a power unit of two additional hydraulic cylinders located coaxially with the axis of rotation of the mold in the horizontal plane of the press, and each developing individually a force of 0.3 MN and designed to move the press plungers by 125 mm, to directly apply pressure to crystallizing metal; as well as a form-closing hydraulic cylinder with a pressure multiplier and a high pressure valve, and the force developed by the hydraulic cylinder is 3 MN, with a stroke of 250 mm. Thanks to the aforementioned arrangement, it is possible to realize a two-sided approach of the plungers, which ensured the effective isostatic compression of the liquid metal in the mold, which has a rather complex internal shape. In addition, this design of the press made it possible to compose all the elements of the automatic reprogrammable complex in such a way that the convenience of operation, maintenance and repair is provided. In this case, the horizontal axis of the press does not depend on the level of the casting pad, which allows pouring liquid metal into the mold directly from the vacuum melting - induction furnace through the lock chamber.

It was experimentally established that in order to realize the task for a given volume (2000 cm3), the press should have the following parameters, which are shown in table 1.

Table 1. Options Value Diameter of casting, mm 90 Casting Height, mm 200 Diameter of pressing plungers, mm thirty Stroke of the right pressing plunger, mm 150 Stroke of the left pressing plunger, mm 125 Multiplier hydraulic stroke, mm 250 The working force of the hydraulic cylinder, for applying pressure, MN 0.3 Locking force, MN 3 Plate travel required to open the mold, mm 250 Number of hydraulic cylinders four Location of hydraulic cylinders Towards each other coaxially to the axis of rotation of the mold.

It was experimentally established that the presence of two additional hydraulic cylinders, pressed one into a fixed plate and through a pressing hydraulic cylinder connected to a movable press plate, allows a force of 3 MN to be developed on any segment within 250 mm. With this effort, a comprehensive isostatic compression of the molten metal up to 10 mm is performed, which corresponds to a stroke of the multiplier of 250 mm. This creates the conditions for a sufficiently wide range of variation of kinematic and force parameters. At the same time, hydraulic cylinders are unified by an inner diameter of 200 mm. Thus, the piston stroke of the multiplier and the stroke of the power rod of the hydraulic cylinder are 250 mm, with the ratio of the areas of the piston and the rod of the multiplier 1:10, so that the pressure on the piston of the hydraulic cylinder with a pressure in the hydraulic system equal to 10 ... 50 MPa is 100 ... 500 MPa, respectively. To maintain this pressure, an additional hydraulic cylinder is pressed into a fixed plate.

The press plate is equipped with a reinforced guide in the form of a block, which, in addition to the existing plate, includes an additional plate and sleeve. Such a system of the power press allows the supply of pressure simultaneously to both cavities of the hydraulic cylinders of the power circuit with subsequent pulse bleeding of the working fluid into the drain.

The alignment of the plungers of the axis of the mold allows you to configure the desired product relative to the surface of the mold, which is considered as a technological base for further machining. This allows, in addition to obtaining good surface quality, to carry out surface treatment with removal of an allowance of 0.3 ... 0.5 mm with a uniform distribution of masses in the entire volume, both in the axial and in the radial direction.

To provide 0.2-0.3 · 10-5 mm in the mold. Hg in the process of pouring liquid metal in an automatic reprogrammable complex, an autonomous vacuum system is provided, which is a vacuum pump, a vacuum receiver, a nozzle, etc., providing a specified value of the discharge during the entire process. The difference in vacuum in the mold is 0.2-0.3 · 10-5 mm. Hg against 1 · 10-2 mm. Hg in the vacuum housing - induction furnace and airlock, it allows not only to increase and control the rate of filling of the mold with liquid metal, but also creates the conditions under which the mold is filled with liquid metal at a given speed in a smooth, continuous front, without spraying. The use of this method of pouring liquid metal into the mold allows you to obtain the desired desired properties not only in ingots, but also in products of complex shape, including hollow billets such as bushings, rings, etc., without the use of rods, the installation of which requires additional equipment . Pouring molten metal into the mold with a solid front provides the surface of the ingots / products, on which there was no waviness, burrs and other surface defects. In addition, the use of this method of pouring allows you to abandon the installation of pilots and profits, which significantly reduces the cost of their manufacture and installation and reduces the time of the process. Under these conditions, when the mold cavity is filled with liquid metal, then (with such a scheme and process parameters), the temperature distribution throughout the entire volume of the ingot / product occurs uniformly. Thus, favorable conditions are created for applying pressure on the liquid, and not on the crystallizing, and especially not on the already crystallized (solid) metal. The crystallized metal has an order of magnitude higher resistance to deformation and eliminates the spread of pressure on the liquid metal that is not yet in the cavity of the crystallizer.

The hydraulic system is controlled from the control panel in automatic mode from the control system. Using the application program, the crystallization control mode is fixed, and the values and parameter changes from the process time are reflected in the oscillogram. To apply pressure to the molten metal according to some law, the control program provides the ability to control the parameters of wide-pulse modulation of the electrical signal to a discrete electromagnetic valve of the press. This control principle provides wide control limits, both in pressure and in the time it is maintained, and allows you to effectively use programming capabilities without including commonly used additional elements in the hydraulic system: volumetric or discrete regulators.

An essential feature of the system is the presence of feedbacks in the form of correction blocks that provide the generation of new knowledge about the complex processes of mutual arrangement, interaction, packing of atoms, energy dissipation on vibrations of the crystal lattice, etc.

Automatic control of the pressure and, accordingly, the movement of the hydraulic actuator's executive body by the plunger takes place in such a way that its stroke meets the tasks that solve the process, which ensures obtaining a higher level of mechanical properties of the ingots / products by forming fragments of the nanostructure from individual atoms and associations.

As a result, we used a control structure belonging to the class of self-tuning systems with a mathematical model that has feedbacks: the main one in temperature (cooling rate) and the internal corrective relationship in position. Using the control function, the required control action of the hydraulic drive force is determined, which is converted into the necessary amount of movement of the plungers. In this regard, the hydraulic drive used to apply pressure on the molten metal, in addition to the static (developed force, stiffness) and dynamic (stability, accuracy, transient quality) characteristics, must meet the requirements of the law of the developed force and speed of movement. Among the parameters that determine the force and speed of movement of the plungers are the pressure in the working cavity of the cylinders and the drain cavity, the mass of the moving parts, the friction force, the piston area in the pressure and discharge planes.

The invention is illustrated by drawings, in which Fig. 1 schematically shows a diagram of an automatic reprogrammable complex, and Figs. 2 and 3 show a diagram of a pressing unit with various molds.

A device for implementing the proposed method comprises a vacuum induction furnace 1 located in a sealed chamber 2, where the metal is melted in a melting crucible to a predetermined temperature, which is measured by an immersion thermocouple 3. The sealed chamber 2 of the vacuum induction furnace 1 is connected to the cavity 5 of the mold 6 through a lock chamber 4 The airlock has two vacuum gate valves, one 7 at the junction of the airlock with a vacuum induction furnace and a second 8 at the junction of the airlock with crystallization torus. The mold 6 is equipped with an autonomous vacuum system 9. The mold 6 is placed in the hydraulic press 10 and is fixed between the movable 11 and the fixed 12 plates of the press body. After the crystallizer is installed, two counter-mounted integrated hydraulic cylinders 13, 14 are aligned with its rotation axis. To achieve a wide range of kinematic and power parameters variation, the press is additionally equipped with two telescopic hydraulic cylinders 15, 16, which are pressed into the fixed plate 17, and provide movement of the movable plate 11 , which moves over any length of time and creates a constant force of 3MN. All hydraulic cylinders 13, 14, 15, 16 are unified by the inner diameter, which ensures isostatic uniform compression of the liquid metal. The stroke of the piston of the hydraulic cylinder 15 and the stroke of the power rod of the hydraulic cylinder 16 is 250 mm. The press plate 11 is equipped with a reinforced guide in the form of a block, which along with the plate 17 includes an intermediate support plate 18. The required structural rigidity is given by the built-in hydraulic cylinder 13. The force is applied to the movable plate 11, which is located between two fixed plates 12, 17, tightened by columns 19. The main hydraulic cylinder 16 for moving the movable plate 11 and create a comprehensive isostatic pressure on the molten metal, is pressed into the plate 17 and has a right and left working cavity. At the same time, a working piston is installed in the right working cavity, which is connected by a support plate 18, and in the left the piston is mounted with the rod 20 of the multiplier hydraulic cylinder. To enable the multiplier to operate, the hydraulic line is shut off using a special high-pressure valve 21. An auxiliary hydraulic cylinder 14 (pressing cylinder), a piston and a rod 22, which is connected to one of the forming parts of the technological equipment or the ingot / product ejector, are installed in the fixed plate 12. To apply pressure according to the law calculated for each type of alloy, an information-measuring system 23 is used, which is part of the supervisory control system 24 of the technological process.

Figure 2 - Device for producing ingots, characterized in that the inner cavity 5 of the mold 6 is in the form of an ingot. And figure 3 - a device for producing rings characterized in that the inner cavity 5 of the mold 6 has the shape of a ring, for which the rods of the hydraulic cylinders 13, 14 are equipped with conical thrust bearings 25.

Thus, the device allows you to get various products without changing the schematic diagram of the technological process, replacing only the mold, and using thrust bearings of various configurations, which are removable equipment.

The device operates as follows. The metal is melted in a vacuum induction furnace 1 and melted in accordance with the technological instruction corresponding to the composition of the molten alloy. The liquid melt is brought to a temperature that is controlled by immersion thermocouple 3, the value of which is 150-200 Celsius above the liquidus temperature of the alloy. Then open the vacuum shutter plug 6 of the lock chamber 4, which is vacuum-tightly mounted with a hole in the bottom of the chamber 2 of the vacuum induction furnace. Then, the space of the chamber 2 of the vacuum induction furnace and the lock chamber 4 is evacuated to a vacuum of 1 · 10-2 mm Hg At the same time, the cavity 5 of the mold 6 is evacuated, installed in the press between the movable 11 and the stationary 12 plates, to a vacuum of 0.2-0.3 · 10-5 mm Hg, using an autonomous vacuum system 9. When the vacuum in the cavity is reached 5 of the mold 6 of the required size, the vacuum shutter plug 8 of the lock chamber 4 is opened, connected to the cavity 5 of the mold 6. After pouring the dosed amount of liquid metal, the vacuum shutter plug 8 is closed by the movement of the plunger. At the same time, with the inclusion of a plunger that provides sealing of the mold cavity, the control unit 24 of the hydraulic system of the press is automatically turned on, in accordance with a predetermined process program using the information-measuring system 23. At the same time, pressure is simultaneously supplied to both cavity of the hydraulic cylinders 15, 16 s subsequent bleeding fluid to drain. The movement of the plungers of the hydraulic cylinders 13, 14 towards each other provides the ability of liquid metal to reproduce the configuration of the inner surface of the mold. In this case, the pressing plunger accelerates the liquid metal to a speed at which hydraulic resistance is achieved. Next, the plunger of the hydraulic cylinder 15 of the multiplier is turned on and the pressure continues to increase according to a predetermined program, while the pressure supply process is continuous. A typical graph of changes in the compressibility coefficient of a liquid (up to R) metal and a metal having ordered clusters is shown in Fig. 4 from time to time, which confirms that the process is carried out in two stages:

Stage 1 - compression of liquid metal;

Stage 2 - compression of a liquid ordered by metal clusters.

At the first stage, the pressure on the liquid metal reaches 300-400 MPa at a speed of more than 40 MPa / s and the liquid metal is compressed by 10%, after the inflection point (R), the pressure increases at the same speed (> 500 MPa) and only at this pressure possibly isostatic comprehensive compression of the liquid metal, leading to the creation of long-range order in the liquid metal. Moreover, at the point R, the coefficient ε≥10%, which is significantly higher than the volumetric shrinkage; beyond the inflection point, the increase is ε = 2.4 ... 2.8%.

Upon reaching an appropriate pressure value> 500 MPa, a predetermined pressure level is maintained for 10-12 s, after which, without removing pressure, the metal in the mold 6 is cooled to a temperature of 100-150 degrees Celsius. Then the pressure is removed, the mold 6 is removed from the press, and the crystallized metal is removed from the mold.

Thus, the quality of products and workpieces is determined by the process of designing, assembling from separate atoms of clusters, crystals, quasicrystals, amorphous and quasamorphic structures based on controlling the behavior of individual atoms and all atoms at the same time under conditions of programmatic methodological application of isostatic pressure on the molten metal, and this improves quality of the target product.

The method is illustrated by the following examples.

Example 1. To control the crystallization process of an alloy of an ingot (size ⌀80 × 160 mm) from an aluminum alloy of grade B95 (Al-Zn-Mg-Cu system) was made in a mold using the proposed method according to the scheme shown in Fig. 1, using a mold presented in figure 2.

The alloy was smelted in an induction furnace with a capacity of 50 kW in an argon atmosphere, followed by evacuation of liquid metal in a crucible of an induction furnace with a resolution of 1 × 10–2 mm Hg. Since the temperature of the metal being poured and the temperature of the mold before casting is of fundamental importance, their measurement was important. During melting, the metal temperature was controlled by a chromel-alumel immersion thermocouple and a KSP-4 device with an accuracy of ± 5K. The alloy was overheated to 850 ° C, thermal treatment of the melt was carried out for 15 minutes, after which the metal was poured through a lock into a crystallizer, vacuumized to a resolution of 0.2-0.3 · 10-5 mm Hg, preheated to 300 ° FROM. The mold was poured with metal through the lock chamber of the bowl for 3 ... 5 s. As a result, the metal fills the mold and, due to the mixing of the jet due to the high pouring speed (within 3 ... 5 s), decreases by no more than 30 K, so that at the moment of filling the mold cavity before applying pressure, the metal overheating is 200 ± 10 K. The specified value of overheating is necessary so that the molten metal before applying pressure is a single-phase system - a solution of homogeneous concentration with clearly expressed properties of a liquid, which, as you know, transfers pressure uniformly in all n directions.

The pressure application rate and the maximum pressure value were selected according to the results of preliminary studies based on the dependence of the relative compressibility coefficient of the alloy on pressure and time.

For alloy B95, it is necessary to apply a pressure p = 450 MPa (t. R), at which the relative decrease in the volume of liquid metal is 12%. In r. R, a qualitatively new state of the metal is recorded, when, on the one hand, overheating over the liquidus line is ~ 200 K, and, on the other hand, the interatomic distances in the solid state, the atoms lose their mobility, as they approach r. melt viscosity.

This state can be called a quasi-solid state. In a quasi-solid state, atoms are fixed in those positions in which they were before pressure was applied, their diffusion is difficult, since interstitial sites, vacancies, dislocations, and other stacking defects of atoms at the achieved degree of compressibility do not have the required throughput.

In order to create a quasisolid state, pressure p = 450 MPa was applied for 5 s, i.e. with a speed of v = 90 MPa / s.

Subsequently, the pressure was increased to p = 500 MPa over time, until the metal temperature drops to a temperature of solidus. In this case, this period of time is 23 s, so the rate of increase in pressure is ~ 2.16 MPa / s.

This stage is associated with a further approach of atoms under conditions of a decrease in temperature, when the resistance to a denser arrangement of atoms increases and to overcome it requires a pressure of ≥500 MPa.

When the temperature in the thermal center of the ingot reached a value below 150-200 ° C, the pressure was removed, the plungers were returned to their original position. The mold was opened, the ingot was removed from the mold and cooled to workshop temperature.

According to the results of the analysis of the structure of the ingot of alloy B 95, performed using scanning electron microscopy, it was found that the structure of the alloy obtained by the proposed method (Fig. 5) is a solid solution hardened with quasicrystals (A16Mn, A181Mn19) with a size of less than 100 nm. Moreover, the alloy has a higher density, and a higher level of mechanical properties (Table 2).

Table 2. Alloy grade Way The properties Hardness, hv σВ, MPa Young's modulus, (E), GPa Density, g / cm2 At 95 famous 140 600 72.00 2.85 proposed 180 710 96.00 2.98

Example 2. In the manufacture of accelerating disks of the separator from BrOFS 13-2-2 alloy (Cu-13% Sn-2% P-2% Pb), a special crystallizer consisting of 4 parts was used.

Schematic diagram of the process of forming a nanocrystalline structure in the production of accelerating disks is shown in figure 1, using the mold shown in figure 3.

Before casting, the molten metal was evacuated in a crucible of an induction furnace with a resolution of 1 × 10–2 mm Hg, which performs modifying and refining functions. The pouring temperature was controlled by an open junction type XA thermocouple. The mold temperature was measured during heating by a gas burner with an integrated thermocouple, a Raynger 3i pyrometer, and a Therma Cam TM S65 thermal imager (manufactured in Sweden).

The prepared melt was poured through the lock chamber into the cavity of the previously evacuated (up to a resolution of 0.2-0.3 · 10-5 mm Hg) mold formed by the forming surfaces of the dies 2 and pressing chambers 3, respectively, to the left and to the right. During pouring into the left bowl, the pressing plunger 1 was diverted to the left, opening the filling hole. As the mold was filled with metal, the right plunger was diverted so as to prevent air from entering, opening the hole and pouring metal into the right bowl. This provided equalization of the temperature of the poured metal. In relation to the BrOFS 13-2-2 alloy, according to the dependence of relative compressibility on pressure and time, the following parameters were used:

- temperature of the poured metal - 1250 ° C;

- pressure on crystallizing metal - 450 MPa;

- pressure application rate of 60 MPa / s;

total pressure application time 35 s;

- the depth of the vacuum in the cavity of the mold before pouring metal 0.2-0.3 · 10-5 mm RT.article

According to the test results of accelerating disks obtained using the proposed method, the alloy hardness increased to 270 units against 125, and the tensile strength reached 610 MPa, against 390 MPa. According to the results of the analysis of the structure of the metal studied by transmission microscopy, it was found that the structure of the alloy obtained by the proposed method (Fig.6) is a solid solution containing amorphous phosphorous copper particles uniformly distributed over the grain and representing polygonal particles of light light with a size of less than 100 nm .

As can be seen from the above examples and confirmed by the results of production tests, the proposed method and device for its implementation in comparison with the known ones, including the prototype allows you to control crystallization in order to obtain a higher level of mechanical properties of the ingots / products by forming fragments of the nanostructure from individual atoms and associations. For its implementation, an isostatic pressure of more than 500 MPa is applied to the entire volume of crystallized metal up to a cooling temperature of 150-200 ° C.

The new method is universal, as it is suitable for controlling the crystallization of liquid metal alloys of various systems. Types of positive effect, derivatives of the achieved technical solution is:

- improving the quality of the target product with respect to the uniformity of the structure of the alloys, increasing the level of mechanical properties of the alloys;

- the formation of fragments of the nanostructure from individual atoms and associations, with a change in the microstructure of the target product;

- a process in which pressure is effectively used to control crystallization;

- principal approaches to the theoretical justification of the modes of applying pressure on the melt directly along the crystallization front

- methods of transferring mechanical energy to crystallizing metal, the principles of designing, manufacturing and using appropriate equipment and accessories have been worked out.

Claims (2)

1. The method of controlling the process of crystallization of metal, including heating the metal to a temperature above liquidus, pouring liquid metal into the evacuated crystallizer from a vacuum chamber, applying pressure to the liquid crystallizing metal, sealing the metal and holding under pressure, characterized in that the mold is evacuated to a value of 0, 2-0.3 · 10 ^-5 mm Hg, the metal is heated to a temperature of 150-200 ° C above liquidus, the pressure is applied with its increase at a speed of> 40 MPa / s to a value of 300-400 MPa, after compression of the metal 10% increase yes Leniye at the same rate to a value of more than 500 MPa, and further compacted metal to 2.4-2.8%, while the metal exposure is carried out under pressure until the metal is cooled to 100-150 ° C. 2. Device for controlling the process of crystallization of metal, containing a vacuum induction furnace with a vacuum of 1 · 10 ^-5 mm Hg, a cylindrical container with a horizontal axis, evacuated up to 0.2-0.3 · 10 ^-5 mm Hg ., a hydraulic press consisting of two hydraulic cylinders coaxially with the container and each developing a force of 0.3 MN individually, designed to move the press plungers by 125 mm, a closing hydraulic cylinder developing a force of 3 MN with a stroke of 250 mm, a pressure multiplier and high pressure valves and this press plungers are installed with the possibility of onward movement along the axis of the container for applying pressure on the crystallizing metal and comprehensive compression of the metal, selected by the program taking into account the specific characteristics of the alloy and the shape of the product and providing a melt seal by 12.4-12.8% at more than 500 MPa.

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