RU2626114C1 - Production method of castings in induction furnace - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: in the method provide the preparation, charge and melting of the stock in the melting pot with the bottom drain, the melting of the plug and the metal discharge into the mould, after charging the stock into the melting pot the oxygen-free flux is added, wt %: alumina 10÷12, fluorspar 7÷10, cryolite is the rest in the amount of 10÷15% from the mass of the stock. The plug is made of the material with the melting point at 100-200°C is higher than the metallic part of the stock, in the content of which it is taken into account, and its melting is carried out together with the stock. The melting pot and the mould is placed in the single female inductor, and the stock has the following composition, wt %: metal part 95÷97 and ferrosilicon 3÷5.

EFFECT: invention makes possible to improve the quality of the iron based castings by performing the melting in the flux protective medium during induction heating and introduction of the active alloying elements.

5 cl, 6 ex, 1 tbl, 5 dwg

Description

The invention relates to the field of metallurgy and foundry, in particular, to technologies and equipment for melting metals and alloys in induction furnaces equipped with crucibles with bottom discharge, and the production of castings, mainly from alloys based on iron with a high content of active alloying elements, and to get new materials.

In foundry, the main methods for producing castings are: - casting: in sand and shell molds, - investment casting and gasified casting, - chill casting, - injection molding and centrifugal casting [Foundry: textbook for metallurgical specialties of universities / Ed. . A.M. Mikhailova. - M.: Mechanical Engineering, 1987. - 256 p.]. All of the above methods for producing castings provide the following typical sequence of operations: 1) melting of the metallurgical charge (in cupolas, arc, induction, and other furnaces); 2) discharge of slag and pouring metal into the bucket; 3) the movement of metal to the molds; 4) metal casting in molds.

A common disadvantage of the known methods is that the above operations require an increase in overheating of the molten metal, while the likelihood of oxidation of the molten metal by oxygen from atmospheric air increases and the process of producing castings from alloys having a narrow temperature interval between liquidus and solidus is complicated. In addition, the duration of standard operations and metal contacting with air limit the production of high-quality castings from alloys with a high content of active alloying elements (Cr, Ni, Mn, Mo, V) and modifiers (Ti, Al, B, N, etc.). Therefore, it is desirable to eliminate or minimize in time the operation of pouring liquid metal into the ladle and casting in molds.

To minimize the time from the stage of melting the metal to its casting in molds, from a known level of development of foundry, there is a method of steelmaking in an induction furnace equipped with a removable portable metal crucible (analog). The removable crucible is made of cast iron or heat-resistant steel in the form of a body in which a bath for a charge or a melt is made, and is equipped with loop-shaped handles for its transfer [Farbman SA, Kolobnev I.F. Induction furnaces for melting metals and alloys. - M .: State scientific and technical publishing house of literature on ferrous and non-ferrous metallurgy, 1958. - 705 p. - S. 356.].

However, the disadvantage of this method is the limited scope of use of the removable crucible, due to the impossibility of melting alloys with a melting point of more than 1100 ° C, for example, steels, since the molten metal is heated from the crucible body, which, in turn, is heated by eddy currents, and heat resistance material of the crucible itself does not exceed 1100 ° C. In addition, servicing a removable crucible is characterized by increased laboriousness of gripping the loop-shaped handles of the crucible, its transfer and, especially, turning when casting metal in molds.

The disadvantages of this method are eliminated when receiving castings using another analogue - the crucible induction melting furnace according to [Auth. testimonial. No. 645012 SU. IPC ² F27B 14/10. Declared: 12.04.76. Publ. 01/30/79. Bull. No. 4.]. The crucible according to this analogue is made non-removable, in the form of a container surrounded by an induction coil and having a sealed ceramic drain cup in the bottom part, concentric with which a sleeve of refractory electrically conductive material is located in the zone of action of the electromagnetic field of the inductor. The use of a ceramic crucible with bottom discharge expands the scope of its use, as it allows it to melt various alloys, including cast irons and steels with a melting point of 1300-1550 ° C, and to cast the metal into molds without additional movement operations.

However, obtaining high-quality castings from alloys with a high content of active alloying elements using an induction furnace and the crucible described above is still limited. In addition, the manufacture of a crucible with a built-in (lined) inductor, a ceramic cup and a sleeve in the bottom is laborious and uneconomical, since the number of thermal shifts of the crucible is limited.

The closest in technical essence to the proposed method, the prototype, is the production of castings (billets) in induction vacuum electric furnaces (IVEP), equipped with a crucible with bottom discharge, cork and mold [Leykand MS Designs of induction vacuum furnaces and their components. - M.-L.: Gosenergoizdat, Ser .: library of an electrothermist; Vol. 4, 1960 .-- 95 s. - S. 34-37]. The preparation of castings (billets) in IVEP according to the prototype consists in the sequential preparation and melting of the metallurgical charge in the crucible, removal (melting) of the cork, and the discharge of the finished metal into the mold (mold) through the bottom opening of the crucible to obtain the finished ingot. The location of the crucible and the mold in a single vacuum space of the furnace allows to obtain castings from alloys with a high content of active alloying elements without a significant change in their chemical composition, with low labor intensity and high efficiency.

The disadvantage of the prototype is the complex hardware design of the method, the need to use a vacuum furnace and additional devices to create and maintain a vacuum, the inability to transfer the crucible to load the mixture and pour the melt outside the furnace, special design requirements for fixing the melting plug, as well as the design of the crucible and furnace (presence of an elongated drain sock in the bottom of the crucible for installation of a melting plug, presence of a ring from an electrically conductive refractory in the drain hole of the crucible material, the presence in the furnace of a special inductor melting the cork), etc. In addition, there is the possibility of solid parts of the molten cork getting into the hardened metal and changing its chemical composition, which leads to a decrease in the quality of casting.

The objective of the present invention is to simplify the hardware design of the method and improve the quality of the obtained castings.

The present problem is solved in that in a method for producing castings in an induction furnace, which includes preparing, loading and melting a mixture in a crucible with bottom discharge, melting the cork, draining the metal into a mold located under the crucible and obtaining an ingot, the mixture consists of a metal part, ferrosilicon and oxygen-free flux; the cork is made of a material with a melting point 100-200 ° C higher than the metal part of the charge; melting the cork is carried out together with the melting of the charge, the crucible and the mold are placed in a single covering inductor, and the charge has the following composition, wt. %:

metal part (filling) 95 ÷ 97 ferrosilicon (filling) 3 ÷ 5,

and after loading the mixture into the crucible, oxygen-free flux is additionally added in an amount of 10-15% by weight.

The metal part is set from 3 components in the proportion necessary to obtain a casting of a given composition: alloys containing alloying elements; an alloy containing a metal base; material containing modifiers.

Oxygen-free flux contains the following ingredients, wt. %:

alumina 10 ÷ 12 fluorspar 7 ÷ 10 cryolite rest

The mass and composition of the cork material is taken into account in the metal part of the charge. The volume of the mold is set smaller than the volume of the metal part of the mixture by the volume of the cork.

The technical result of the implementation of the invention is to simplify the hardware design of the method, since the manufacture of castings is carried out not in IWEP, but in special equipment - assembling a crucible with bottom discharge / casting mold installed in a covering inductor connected to an inverter or a high-frequency generator. The process of melting the cork and draining the metal occurs simultaneously under a layer of a special oxygen-free flux, that is, without contact with air. The quality of castings is improved by a set of measures: composing the metal part of the charge from several components, deoxidizing the metal with ferrosilicon with a high silicon content, taking into account the composition and amount of cork material in the charge, and also making the mold smaller in volume than the volume of the molten metal.

The invention is illustrated by the following examples.

Example 1. Preparation of oxygen-free flux

To prepare the flux, they take alumina from the metallurgical grade G-0 (GOST 30558-98), concentrate fluor-spar metallurgical grade FK-95A (GOST 29220-91) and cryolite artificial technical grade KA, first grade (GOST 10561-80). All flux components are dried at a temperature of 95-110 ° C for 1.0-2.0 hours, ground in a ball mill and sieved through a 0.5 mm sieve. Finished components are loaded into a ball mill without grinding media in the following proportion, wt. %: alumina 10 ÷ 12, fluorspar 7 ÷ 10, cryolite - the rest, so that its volume is filled n.b. than 1/3 and stirred for 0.5-1.0 hours. The finished powder of oxygen-free flux is stored in a hermetically sealed container.

Example 2. The manufacture of the crucible, mold and tooling for implementing the method

First prepare the lining mixture, consisting, wt. %: silica sand 90-92; washed clay 2-4, calcined borax 1.5-2.5, water - the rest. Then the mixture is well mixed, the walls of a special steel mold are moistened, the mixture is placed in it and compacted by pressing with a punch that gives the crucible the desired shape and size, the excess mixture is removed, the crude crucible billet is removed from the mold and a hole with a diameter of 6 is made in the center of its bottom mm

The mold is made from the same mixture as the crucible in the same mold, reducing its volume by 10-15%, by reducing the height of the walls.

Then the crucible and the mold are placed in a furnace where they are dried at 110-120 ° C for 0.5-1.5 hours, and then fired at a temperature of 850-870 ° C for 4.5-5.0 hours.

Finally, the equipment is assembled, for which a melting plug is installed in the hole of the bottom of the finished crucible using refractory clay, the volume of which is taken equal to or greater than the difference in the volumes of the metal part of the charge and the shape (resulting casting).

The cork is made of material with a melting point of 100-200 ° C higher than the metal part of the proposed charge, with a diameter of 6 mm

The surface of the mold is dusted with foundry graphite or soot.

Then set the crucible on the mold, covering the resulting cracks with refractory clay or a lining mixture. After that, the equipment is dried in an oven at 110-120 ° C for 0.2-0.5 hours

Example 3. Obtaining castings from steel 50G

The metal part of the charge is calculated from carbon and the alloying system, which in the example is specified by scrap steel 65G (alloy containing alloying elements — Mn) and scrap steel 20 (alloy containing iron base), taken in a ratio of 0.7: 0.3 wt. share.

The hole in the crucible is closed with a stopper made of St2KP steel (steel close in chemical composition to steel 20 and having a melting temperature 100-200 ° C higher than the steel we need 50G), which is weighed and considered to be part of the mass of scrap of steel 20 included in selected ratio. The volume of the cork is selected equal to or greater than the difference in the volumes of the metal part of the charge and the resulting casting.

The filling, consisting of the metal part of the charge and deoxidizer - ferrosilicon grade FS65 is placed in a crucible, and oxygen-free flux prepared according to Example 1 is placed there (over filling), and the following composition of the charge for melting, wt. %:

metal part (filling) 95 ferrosilicon (filling) 5 oxygen-free flux (over filling) 10

A mold with a crucible mounted on it is placed in an ELSIT-100 / 20-70 inverter enclosing a water-cooled copper inverter, and the entire equipment is heated with a high-frequency current, a frequency of 60-70 kHz, and a power of 75-85 kW.

After melting the mixture in the crucible (1-1.5 min), continue melting for another 1-2 minutes, after which the power is raised to 95-100 kW. After 0.5-1 min, the plug melts, the metal is drained into the mold, and the flux melt remains in the crucible. After that, the power is again reduced to 75-85 kW, continuing melting for another 1-2 minutes. Upon reaching the total melting time of 3.5-6.5 min, the current is turned off, the metal is allowed to crystallize and the equipment is cooled, after which the entire assembly is removed from the inductor and disassembled. The riser formed by the metal frozen in the crucible drain hole and connecting the casting with the metal residues and slag is removed by a grinder.

The chemical composition of the casting material is established by a non-destructive method on a Foundry-Master UVR atomic emission spectrometer (OXFORD Instruments, UK).

Example 4. Preparation of casting from steel 50XGA

The metal part of the charge is calculated from carbon and the alloying system, which in the example is specified by 65G steel scrap, 30X5 steel scrap (alloys containing alloying elements - Mn, Cr) and 35 steel scrap (iron base), which are taken in a ratio of 0.6: 0 2: 0.2 wt. share. In addition, in addition to the resulting mixture in wt. a fraction of 0.05 take SK20 grade silicocalcium (a material containing modifiers — Ca). Ferrosilicon in the filling take the FS90 brand.

Then proceed analogously to example 3, with the difference that the hole in the crucible is closed with a stopper made of St3PS steel, and the composition of the charge for melting is set as follows, wt. %:

metal part (filling) 96 ferrosilicon (filling) four oxygen-free flux (over filling) 10

Melting is also carried out analogously to example 3, the total melting time is 4-7 minutes The chemical composition of the casting material is also determined by a non-destructive method.

Example 5. Preparation of steel casting 38XC.

The metal part of the charge is calculated, which in the example is specified by scrap steel 30X5, scrap steel 2311 or 2312 (alloys containing alloying elements — Cr, Si) and scrap steel U10 or U12 (iron base), which are taken in a ratio of 0.5: 0. 2: 0.3 wt. share. In addition, in addition to the resulting mixture in wt. a fraction of 0.05 is taken from titanium aluminide TiAl obtained by the interaction of a pressed equimolar mixture of powders of aluminum grade PA-1 and titanium grade PTM-1 in the mode of self-propagating high-temperature synthesis (material containing modifiers - Al, Ti). Ferrosilicon grade FS75 is used.

Then proceed analogously to example 3, and the composition of the mixture for melting is set as follows, wt. %:

metal part (filling) 97 ferrosilicon (filling) 3 oxygen-free flux (over filling) fifteen

Melting is also carried out analogously to example 3, the total melting time is 5-6 minutes The chemical composition of the casting material is also determined by the non-destructive atomic emission method.

Example 6. Preparation of castings from hypereutectic cast iron CHH30GS2N2.

According to the alloying system, the metal part of the charge is calculated, which in the example is specified by scrap of wear-resistant cast iron Sormait1 and scrap steel 65G (alloys containing alloying elements - Cr, Ni, Mn and an iron base), which are taken in a ratio of 0.5: 0.5 wt. share and boron carbide (a material containing a modifier - B) which is taken in wt. a fraction of 0.1 in excess of the ratio of steels. Ferrosilicon grade FS75 is used.

Then they proceed analogously to example 3, with the difference that the cork is made of steel 20, and the composition of the charge for melting is set as follows, wt. %:

metal part (filling) 95 ferrosilicon (filling) 5 oxygen-free flux (over filling) fifteen

The casting obtained according to the example has the form of a plate measuring 52.5 × 11.5 × 5.5 mm (taking into account profits), designed after machining for soldering on the drill bit of the Primera DMC-9000 seeder, which operates in conditions of intense abrasive and impact abrasive wear.

Melting is carried out analogously to example 3, the total melting time is 6-7 minutes

The amount of molten metal is set to 5-7% more than is necessary by calculation to obtain a casting in the form of a plate, the excess metal is left in the crucible hole taking into account its diameter and height and, partially, in the bottom of the crucible together with slag, which together allows get a cast without a shrink shell.

The mass of the casting obtained according to the present example was 34-35 g.

The chemical composition of the casting material is also established analogously to example 3, non-destructive atomic emission method.

The invention is also illustrated by the following materials.

In FIG. Figures 1a and 1b show a melting plug made of St2KP steel and a crucible with a bottom in the opening of which a plug is installed.

Figs 2 a and b show a crucible with a loaded charge and a casting mold for producing a casting in the form of a plate intended for soldering onto a drill bit of a Primera DMC-9000 seeder according to Example 6.

In FIG. 3 shows the finished tooling prepared to receive the casting according to example 6, installed in the surrounding inductor.

In FIG. 4 shows the process of melting the mixture in a crucible and draining the metal into a mold.

In FIG. Figure 5 shows the finished casting in the form of a plate intended for soldering onto the chisel of the Primera DMC-9000 seeder, with the riser removed.

In FIG. 6 shows the chemical composition of the metal part of the charge and the obtained castings, showing a high degree of assimilation of carbon and alloying elements in steelmaking by the proposed method.

To clarify the technical nature of the invention, the following data.

It is known that iron-based alloys begin to actively interact with atmospheric oxygen at temperatures above 900–950 ° C. Further, during the melting, overheating and casting of the metal into a mold, the temperature rises even higher, which leads to an increase in oxidation. Therefore, to improve the quality of the ingot (preserving its predetermined chemical composition), the proposed method not only deoxidizes it with high-silicon ferrosilicon (FS 75-90), but also protects the metal from oxygen in the crucible with a special oxygen-free flux, and also takes into account the composition and weight of the material traffic jams. Also, the mirror area of the molten metal is reduced when it is drained and solidified in a mold, which is achieved by using a crucible with a bottom drain and the tightness of the equipment used - assembling a crucible with a bottom drain / mold. The hardware design of the method is simplified by eliminating the use of an induction vacuum furnace, and by using a special inductor that encloses the crucible with the mold placed under it to obtain a casting.

The quality of the casting is improved not only by taking into account the mass and composition of the material of the fusible plug in the charge, but also by changing the nature of metallurgical processes, implementing them in an oxygen-free environment during induction heating, and introducing alloying elements and carbon into the resulting alloy not in the form of ferroalloys, but in the composition of specially selected components (steels, cast irons), where they are already in the form of related, metallogenic forms, in the composition of various eutectics, solutions, metallic, intermetallic and nonmetallic phases . Contributes to improving the quality and low waste of elements in induction furnaces (2-3 wt.%).

The choice of the components of the charge, flux and their concentration limits in the proposed method are optimal, since the components of the metal part (90-95%) and their ratio determine the chemical composition of the obtained ingot and the melting temperature, ferrosilicon (3-5%) provides deoxidation of the bath and compensates fumes of elements during induction melting, and oxygen-free flux taken in excess of 10-15% over filling provides guaranteed protection of the melted metal and casting from oxygen in the air throughout the entire melting process.

So, the decrease in the content of the metal part in the charge below 95 wt. % does not provide a predetermined calculated chemical composition of the casting, by reducing the degree of assimilation of alloying elements and carbon, and its increase above 97 wt. % does not allow to enter the minimum amount of ferrosilicon, deoxidizing the bath and compensating for fumes.

The decrease in the content of ferrosilicon in the mixture below 3 wt. % does not provide the necessary deoxidation of the metallurgical bath and compensation of the waste elements. The increase in ferrosilicon content above 5 wt. % causes a difficult to account for the increase in silicon content in the casting.

The decrease in the content of oxygen-free flux taken over filling, below 10 wt. % does not provide guaranteed coverage with a melt of all the initial molten components and protection against metal oxygen and castings from oxygen. The increase in flux content above 15 wt. % leads to its cost overrun, increased melting time and increased energy consumption.

The use of ferrosilicon grades with a silicon content below 63-68% (as, for example, in the FS50 grade) increases its density above 4.5-5.0 g / cm ³ and lowers the upper limit of its melting temperature below 1300 ° C, which causes it uneven distribution in the mass of molten metal, increased fumes of silicon, a decrease in deoxidizing ability and a decrease in the degree of assimilation of alloying elements and carbon in the casting.

The use of oxygen-free flux of this composition is explained by the overlapping by him and his components of the entire temperature range from the onset of oxidation of steels, cast irons and ferroalloys at 900-950 ° C, to their melting temperatures at 1100-1350 ° C.

So, pure cryolite melts at 980-1010 ° C, calcium fluoride (fluorspar) at 1418 ° C, and alumina at 2072 ° C. It is also known that 10-12% of alumina forms a eutectic with cryolite with a melting point of 968-980 ° C, 7-10% of fluorspar forms a eutectic with cryolite with a melting point of about 900 ° C, and in the cryolite-alumina-fluorspar system triple eutectic, the composition of which, wt. %: 75.9 Na ₃ AlF ₆ , 10.5 Al ₂ O ₃ and 13.6 CaF ₂ with a melting point of 923 °.

Thus, setting initially and maintaining during the entire process of melting the mixture the composition of oxygen-free flux by components, taking into account their possible decomposition and evaporation, is close to the following, wt. %: alumina 10-12, fluorspar 10-15, cryolite - the rest, it is possible to protect the molten metal from atmospheric oxygen, which makes it possible to obtain the proposed method of casting from most known cast irons and steels containing active alloying elements (Cr, Mo , V, Ti, Al, B, etc.).

The volume of the mold is taken 5-7% less than the volume of the molten metal, which is necessary to ensure casting without shrinkage, since the excess metal in the form of a riser, repeating the shape and volume of the cork (5-7%), must remain in the hole crucible taking into account its thickness and, partially, in the bottom of the crucible together with slag.

The melting temperature range of the cork is 100-200 ° C lower than the melting temperature of the metal part of the charge is set depending on the composition (grade) of the smelted metal.

So, for example, when smelting high-alloy chromium cast iron of the PG-US25 grade with a melting point of 1280 ° C, the cork is made of steel 20 with a melting point of 1480 ° C, and when melting pro-eutectic cast iron of the SCh30 grade having a melting point of 1360 ° C, the cork is made from steel 1X18H9 with a melting point of 1460 ° C.

FIG. 6.

Claims (8)

1. The method of producing a metal casting in an induction furnace, including the preparation, loading and melting of the charge in a crucible with bottom discharge, melting the cork, draining the metal into a mold located under the crucible and obtaining a metal casting, characterized in that they use a mixture consisting of a metal part and ferrosilicon, and the cork is made of material with a melting point 100-200 ° C higher than the metal part of the charge, while the cork is melted together with the melting of the charge, crucible and cast the new form is placed in a single covering inductor, and the mixture has the following composition, wt.%: metal part 95 ÷ 97 ferrosilicon 3 ÷ 5, and after loading the charge into the crucible, an additional oxygen-free flux is added in an amount of 10-15% by weight of the charge. 2. The method according to p. 1, characterized in that the metal part of the mixture is set from three components in the proportion necessary to obtain a metal casting of a given composition, including alloys containing alloying elements, an alloy containing a metal base, and modifiers. 3. The method according to p. 1, characterized in that the oxygen-free flux contains the following ingredients, wt.%: alumina 10 ÷ 12 fluorspar 7 ÷ 10 cryolite rest 4. The method according to p. 1, characterized in that the mass and composition of the cork material are taken into account in the metal part of the charge. 5. The method according to p. 1, characterized in that the volume of the mold is set smaller than the volume of the metal part of the charge by the volume of the cork.

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