RU2402405C2 - Electromagnetic form-investment-pattern casting - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy. Proposed method comprises producing mould from loose fire resistant material, removing the pattern, pouring metal melt into mould and removing casting by breaking the mould. Mould is fabricated from magnetic loose fire resistant material by evacuating mould cavity with single pattern and using electromagnetic field to compact said magnetic material. Single pattern is cast and remove by vacuum. Water-cooled mould is used. Molten metal is poured into produced mould by evacuation mould cavity and feeding pressure to melt. After crystallisation, casting is removed by removing magnetic field and destructing fire resistant magnetic material.

EFFECT: higher quality.

9 cl, 2 dwg

Description

The invention relates to techniques and technology for foundry. Complex cast billets or finished parts are produced in mass production by investment casting in shell forms, mainly from steel. High precision castings is achieved by the fact that the mold has no connector, no rods, and the thermal expansion of the mold is minimal.

The essence of the process for producing castings according to investment casting consists in manufacturing the model from fusible material, coating it with refractory coating, and then melting it from the formed shell. The shell is calcined to give it strength, fire resistance, gas permeability and removal of model residues, and then filled with metal. The investment casting method in industry has received the highest technical development.

The main components of the model compositions are paraffin, stearin, rosin, wax and other materials with a melting point of 50-80 ° C. The model composition is heated in closed containers and contained in a paste-like state. Models are made in molds having internal cavities corresponding to the configuration of the future casting. Its dimensions take into account the shrinkage of the model composition and the shrinkage of the casting alloy of the casting. Inside the working cavity of the mold using syringes through the sprue channels, the model composition is pressed. After crystallization of the composition, the mold is opened and the model is removed. Individual models are assembled in blocks with a common gate system by soldering. In one block there can be several tens and even hundreds of models.

Refractory coating includes binders (ethyl silicate, water glass, boric acid), solvents (ethyl alcohol, acetone; sulfuric and hydrochloric acids, water) and a refractory base (quartz sand, pulverized quartz, ground chamotte, electrocorundum). Refractory coating (coating) consists of ~ 25% liquid phase and 75% solid. It is stored in tanks with a temperature of 10-15 ° C with constant stirring.

The process of applying a refractory coating consists of a series of repetitive operations: coating with a coating, sprinkling with refractory material and drying the layer. The model is applied 4-6 refractory layers. The block of models with a refractory coating is supplied to the smelting of the model composition.

Model composition is smelted with hot air, steam or in bathtubs with hot water. As a result, a molten model composition flows out of the ceramic shell, leaving voids. Then the shell is calcined at a temperature of 850 ± 20 ° C in electric gas furnaces with their preliminary placement in flask with sand filling. The calcined forms are poured with metal immediately after calcination or after cooling.

Annealed molds are poured with metal in the following ways: by free pouring from a pouring ladle or from a furnace toe. After crystallization of the alloy, the refractory shell is separated from the casting and casting from the riser. To do this, use a vibration setting. Separating the casting from the riser, it is sent to a treatment drum to remove the remnants of the refractory ceramic shell in an alkaline solution.

See Kuzmin B.A. - M.: Mechanical Engineering, 1981 "Technology of metals and structural materials", pp. 169-172. Lost wax castings.

Barnaultransmash OJSC, hazardous precision casting workshop 320 is mainly located on three floors: A - foundry first floor, B - model second and C - molding (molding) third floors. The weight of steel castings is 5-30 kg or less. Materials and products are transported by elevator, to it - by carts. The company is 65 years old, since 1942. The workshop has been working without any technical updates.

Significant disadvantages in all areas of the process are as follows.

I. Category A - casting compartments and a site for casting extraction from flasks and removal of refractory shells.

The finished melt in the melting furnace with mold acceleration is poured from a ladle on a stretcher, the superheated metal absorbs air into itself, while porosity, shells are formed in the castings, as well as underfill due to the fact that in this casting method there is no possibility of using means of compaction of the cast metal in form and other reasons.

In the disassembling section, the casting is separated from the refractory shell in a vibrating installation, which creates a lot of noise from the shot, the requirements for working with headphones, which creates inconvenience: dust and debris, the waste stream underfoot makes the production time-consuming (heavy), harmful and poor culture in comparison with model department.

II. Category B. Models are made in metal forms by pressing the model composition by force using a syringe, depending on the size of the volume or weight, the complexity of the external and internal configurations of the model. For example, in operations such as final crystallization inside models in chilled water, assembly of models on a riser in a block, etc. Due to the fragility of the models, the blocks are carried carefully in the hands, which eliminates the possibility of making the model on machines or with a mechanical hand.

III. Category B. The model block is coated with constantly mixing in the container, then the coating is sprayed with boiling refractory material, while the moulders work in respirators. Covered blocks for drying are hung on cords in a ventilated room at room temperature, the process is repeated several times. Smelting of the model is carried out by immersion in a container with hot water.

After smelting the models, the block with shells is placed in dryers, after the final drying is transferred to category A, where the block (blocks) are placed in flasks, covered with quartz sand, calcined at a temperature of 850 ± 20 ° С. For the piece production of the shell mold, not including the cost of materials and the following operations of category A, the average labor costs are 75-80 n / hours. In this production it is advantageous to replace the skillful actions of the hands of masters with universal automation is impossible.

It is known that castings for burned-out models are produced in single and small-scale production in the form of large blanks (beds, stamp plates, etc.). The essence of the method lies in the fact that the model is made of expandable polymers and is not removed from the mold before filling it with metal. Before molding, models are coated with a layer of non-stick paint with a thickness of at least 0.2 mm. A model with a sprue system is installed in a flask, filled to the top with a mixture with simultaneous vibration to seal it.

As the molding mixture, dispersed ferromagnetic powder, cast iron or steel shot is used, which is compacted by means of an electromagnetic field for the period of filling the mold with metal and crystallization of the casting. After crystallization of the casting, the magnetic field is removed, the mold loses strength and the molding material falls out of the container flask, freeing the casting. Before filling the mold with metal, it is covered with a metal sheet with perforation for the release of gases and pressed with a load.

The gating system structures are partially made of ceramic tubes, the metal is supplied by the siphon method from the bottom, as this provides sequential gasification of the models from the bottom up.

A significant disadvantage of this method is that during the hardening of the dry molding sand by means of an electromagnetic field, deformation and distortion of the polystyrene foam model (block models) occur, and there is a need for hardening, i.e. increasing the thickness of the refractory coating of the paint by 2-3 times or more, which firmly closes the outlet of the combustion gases of the model and the air in the pores, which prevents filling the mold with metal, which creates casting marriage. With this casting method, a large emission of toxic gas-smoke combustion models, which requires powerful ventilation. The high cost of material processing and manufacturing models of only one-time use is not widely used in technology.

The casting of low-melting alloys under low pressure of inert gas or air is not high 0.1-0.8 kgf / cm ² for the reason that the mirror area of the molten metal in the crucible is many times larger than the area of the metal wire. A slight movement of the metal in the crucible causes the liquid metal to rise inside the metal wire and in the mold.

Casting is carried out by vacuum absorption. Inside the mold, a vacuum pump creates a vacuum, and the molten metal is drawn into the cold mold, where it crystallizes.

Castings from fusible alloys in the lost-wax form according to the lost-wax model.

The essence of the process lies in the fact that a mold is cast in an automated case according to the lost wax model, the model is melted, the cast metal is poured into the cavity formed by the model, and the mold is melted during its crystallization.

The installation for the manufacture of castings contains a housing, in it there is a container at the bottom containing the mold material, and on top there is a molding and casting zone. The molding and casting zone is equipped with a high-frequency current inductor cooled by water, which, when the electric current is turned on, serves as a heater, when the current is turned off, it is a refrigerator and other elements.

Accepted for the prototype, see on the website of Rospatent www.fpr.ru No. 2007118032 (019629) or Figs. 1 and 2 in order to improve the manufacturing technology of investment casting. The essence of the process is to make a model of fusible material. To obtain, for example, a steel or cast iron casting in the form of bulk refractory materials, such as bulk dispersed ferromagnetic powder, cast iron or steel shot, which is compacted using an electromagnetic field in the molding and casting body, are used. Then the model is smelted from the mold. The casting metal is poured into the prepared form.

There are two ways to make molds in a machine in an automated molding and casting casing: the method of drawing a refractory powder mixture into the mold cavity from the bottom up or a mixture of solid (heavy) materials is filled from top to bottom. In the manufacture of molds for small and small castings of non-ferrous and ferrous metals inside the molding cavity formed by the model, a vacuum pump is created in the casting casing by a vacuum pump, which in an electromagnetic field draws the mixture from below into the molding cavity from its container in the molding cavity, where compacted by an electromagnetic field.

The form, depending on the mass or volume, is made of loose dense (heavy) materials by turning (tipping) the case. As a result, the mixture is poured from its capacity in the rarefaction of the molding cavity, where it is compacted by an electromagnetic field. Then the case with the form returns to its original position.

Both after the first and second molding methods, the body is placed on the smelting capacity of the model material. The model is smelted by an electric heater, the melt of the model is removed by vacuum depression, which ensures the removal of the melt without residue. A housing with a prepared mold is placed with molten metal on a low pressure casting furnace. The rarefaction metal is drawn into the water-cooled form, where it crystallizes. At the same time, metal is poured under low pressure with a vacuum in the mold. The furnace maintains an adjustable pressure, thereby compacting the casting, eliminating shrinkage. Moreover, thermal expansion of the mold also exerts pressure on the casting everywhere. After crystallization of the casting, the electromagnetic field is removed, the mold loses strength and the molding material is poured from the molding cavity into its location capacity.

Figure 1 illustrates a laboratory installation that allows testing the parameters of the main types of casting.

1 - housing; A is the capacity of finding the molding sand; B - zone of molding and casting; 2 - melting furnace metal casting; 3 - housing rearrangement mechanism; 4 - heated capacity of the material of the model; 5 - mold manufacturing model; 6 is a block of devices and a drive containing a compressor, a vacuum pump, an electric actuator by cranes of vacuum, air compression, pressure, cooling, solenoid, electromagnetic field, heating, moving the housing; 7 is a cabinet containing a voltage transformer with a high frequency current converter; 8 - a lagometer for monitoring the temperature of the melt in the tank 4 of the material of the model; 9 - potentiometer for monitoring the temperature of the melt in the furnace 2; 10 - a process control unit by both an operator and an automatic molding and casting process program.

In figure 1, the capacity 4 of the material of the model is included in the complex installation of molding in the form of a granular mixture, sealed by an electromagnetic field. Capacity 4 is equipped with means for evacuating the model melt from the mold into the casing 1 and low pressure of compressed air for the manufacture of the model (parts of the model), vacuum and compressed air are produced by pumps. Capacity 4 by diameter inside is divided into lower and upper parts by a rotary shutter from a vertical to a horizontal position, connected by a crane to the positions: closed, vacuum, air. When closing the lower part, the upper part becomes a vacuum tank, the lower part with the melt is a crucible casting the model under low pressure. The amount of compressed air pressure and vacuum in the form is controlled by pressure gauges and limited by the actions of the crane. The damper, valve, etc. are not shown. In this method, for the manufacture of models using known materials: stearin, paraffin, etc. with a melting point of 50-80 ° C and above.

The manufacturing process of the model is carried out in interchangeable molds, put on the lid of the tank 4, the channels of the mold (s) should coincide with the channels made in the tank 4 almost to the bottom of the molten model composition. Under the action of low pressure of 0.1 atm compressed air, the cavity of the water-cooled form is filled through the channel through the channel, where it crystallizes. After crystallization of the model, it is removed from the mold, a layer of non-stick (anti-corrosion) paint is applied. If it is necessary to alloy the surface layer of the casting, alloying elements (tellurium, chromium, etc.) are applied to the surface of the model.

Figure 2 shows the installation for casting casting in the form of bulk refractory materials, which are sealed using an electromagnetic field.

The molding and casting body 1 is an assembly; it can be mounted on different types of transport means: on a bed, frame, rails, etc. Figure 2 shows the installation (vertical section), turning horizontally to the sides of the axis of the telescopic lift 3 with the possibility of tipping over the housing 1 for molding. In cavity 6, a molding loose refractory mixture of form II 12 is used, the pipe 13 is replaced in the bottom by dispersed channels (not shown), 14 is a pipe for casting metal casting, 15 - an electromagnet is made instead of heater-cooler A, 16 - together with a heater-cooler A electromagnetic field solenoid magnet (not shown) is integrated, 17 — housing cover 1.18 — investment casting model, 19 — model block riser, 20 — connection sleeve 14 and 21, sealing lips 22, 23 — housing cover pneumatic cylinder 1, 24 - electric motor, 25 - pouring furnace under low pressure, 26 - a plug coupling 20 is retracted, 27 - fittings molding cavity and forms a compound with a vacuum pump.

Such elements of the device as the pipe 13 for casting metal of the mold, the heater-cooler 15 in the tank A, the plug 26, which closes the outlet of the molten metal and opens under low pressure pouring into the mold of the metal, are needed when receiving castings in the lost wax form.

The manufacturing process of castings is carried out on a comprehensive universal installation, which is an assembly comprising a housing 1 with a capacity And molding refractory bulk material II. At the top of the molding and casting zone with the possibility of its overturning, a container of model material (not shown) is mounted on the bracket of the telescopic elevator 3. The furnace 25 of the molten alloy casting under low pressure inert gas or air is as follows.

In the first method, the housing 1 is placed on the capacity 4 of the model material. A block of models 18, assembled on a riser 19 (sprue), is suspended in the lid 17 using a collet, the force of the pneumatic cylinder 23 is put into the cavity of the form B, the molding mixture is drawn from the container A by the force of the included electromagnetic field with vacuum vacuum into the molding cavity B. As a result of the action electromagnetic field achieved high form strength.

In another way, the molds are made, depending on the mass or volume, of dense (heavy) metals by overturning the housing 1, as a result, the mixture is poured out dispersed along the channels from the vessel A, rarefaction in the molding cavity B, thereby achieving good filling of the mold, and also compaction with an electromagnetic field . The housing 1 is placed on the capacity 4 of the model material, by switching on the heater-refrigerator, the model is melted, the set melting temperature depending on the melting temperature of the model composition, for example, 60-90 ° C, is automatically adjusted by potentiometer 9 of Fig. 1. The melt of the model in a vacuum tank is drawn by vacuum in the tank 4 of the model material, where it merges immediately into the crucible for reuse.

For pouring metal into a water-cooled mold 12, the lifting mechanism of a pneumatic cylinder 3 with an electric actuator 24 puts the housing 1 on the furnace 25, the metal pouring pipe 14 is connected to the pipe 21 by the coupling 20, sealed by the sleeve 22. A vacuum is created inside the mold by the vacuum pump and the molten metal is drawn into the cold mold where crystallizes. At the same time, an inert gas or air pressure is created in the furnace 25, which ensures the lifting force of the metal, under a controlled pressure of 1.5-4 atm, the casting alloy is fed and sealed. Crystallization of the casting occurs sequentially from the cold wall to the center, so there are no shells, porosity and gases are well removed. After crystallization of the casting, the magnetic field is removed. The mold loses its strength and the molding material pours out from the molding cavity B into the container A, freeing the casting. In the best case, at the time of formation of a vacuum in the mold manufacturing cavity, backfilling of the light molding sand is somewhat restrained, and avoidance of a delay in the precipitation of the mixture from the molding zone in the molding material tank is carried out using an electromagnetic field.

For the manufacture of investment castings and increasing their strength, it is possible to use widely used in many branches of technology, in comparison with the model composition, paraffin with wax t _pl 75-80 ° С, P-6 polyamide and others, which have an order of magnitude strength and casting properties higher at a melting point of 90-110 ° C. It is necessary to select reusable materials.

For the manufacture of electromagnetic forms, when choosing metal powders with predetermined stable magnetic properties, fluidity and the bulk volume of bulk powder in grams per cubic centimeter are calculated taking into account their constant use as electromagnetic forms.

For example, the overestimated thickness of the mold walls, in connection with which the volume of bulk powder is increased in the measurement of grams per cubic cm, and therefore, the consumed power of the electromagnetic field, vacuum, for heating the mold during smelting is increased.

The fluidity of metal powders characterizes the speed of passage of the powder through holes of a certain diameter. The fluidity has a great influence on the uniformity of filling the cavities between the inner surfaces of the casting case and the surfaces of the protrusions of the casting model, forming gaps of ~ 3 mm in narrow places. Under these conditions, it is difficult to transfer the powder from tank A to tank B and vice versa.

The method and technology can be used to produce large castings, for example, a complex aluminum casting a 6-cylinder V-shaped block crankcase obtained by casting in earth form 350 kg, and casting in electromagnetic form without profit with a simplified gate system of 120 kg. When casting AL8 aluminum containing 9.5-11% Mg, the pouring temperature without overheating is 630-650 ° C.

By the combination of vacuum pressure in the furnace and expansion of the mold heated by the cast metal, the wall thickness increases, the possibility of dispersed pores (compressed air) is excluded, which takes place in castings obtained both by high pressure piston casting during casting and by autoclaving under pressure of compressed air 5-6 atm per cast in earthen form without cooling.

Castings in electromagnetic form can be obtained in all branches of technology from ferrous and non-ferrous metals, of simple and complex configuration, of high quality, by increasing the productivity and ecological culture of foundry in the shortest possible way.

Installations and casting machines in electromagnetic form can be manufactured by both the enterprises themselves and enterprises producing foundry machines and equipment.

Claims (9)

1. A method for producing investment castings, including making a mold from bulk refractory material according to a one-time model, removing the model, pouring molten metal into the mold, removing the cast by breaking the mold, characterized in that the mold is made of magnetic bulk refractory material in a casting body with a one-time model by applying a vacuum and an electromagnetic field to seal the refractory magnetic material, a one-time model is melted and removed using a vacuum, the mold is made tons of water-cooled, molten metal castings are poured into the obtained mold by creating a vacuum in the mold and applying pressure to the melt; after crystallization, the casting is removed by removing the magnetic field and pouring out the refractory magnetic material. 2. The method according to claim 1, characterized in that, depending on the mass or volume of the casting, a mold from a dense magnetic bulk refractory material is made by tipping the housing with dense bulk magnetic material, pouring it into a casting housing, sealing with an electromagnetic field and vacuum, installing the housing on the capacity for smelting the model. 3. The method according to claim 1 or 2, characterized in that the molten model composition, melted from a single mold, is pulled by vacuum rarefaction into a container located in the zone of receipt of a single mold in a mold for molding under controlled gas pressure. 4. The method according to claim 1 or 2, characterized in that the one-time model is made from model compositions containing paraffin with wax, as well as from polymeric materials of reusable use, for example polyamide. 5. The method according to claim 1 or 2, characterized in that before molding the model is covered with a non-stick paint layer with a thickness of 0.2 mm, and alloying elements are applied to the surface of a single model to alloy the surface layer of the casting. 6. The method according to claim 1 or 2, characterized in that the casting in the form of aluminum, magnesium, zinc, bronze alloys, brass, as well as cast iron and steel is carried out from the furnace without overheating. 7. Installation for producing castings according to investment castings, comprising a steel detachable foundry body with a container for bulk refractory mold material and a cavity for manufacturing the mold, a water-cooled inductor, a container for melting and casting a one-time model, a melting furnace with molten castings, a drive means block and process control, characterized in that it is equipped with a rotary lifting mechanism mechanically coupled to the casting body with the possibility of tipping over for pouring bulk refractory material from below up and back, and an electric drive for mounting the housing on a container for smelting and casting a one-time model, while the tank for bulk refractory mold material contains a bulk refractory magnetic material and is equipped with an electromagnetic device. 8. A method for producing investment models, including filling a moldable part of a detachable mold, opening the mold and removing the model after crystallization, characterized in that the mold is placed close to or on the container for model material, connected by a pipeline, and filling a molten model composition of a detachable mold is carried out by applying pressure to a container for a model material, while the mold is water-cooled. 9. A device for producing investment castings containing the lower and upper zones, a vacuum tank is located in the upper zone, and a vessel for melt of model material is located in the lower zone, characterized in that the diameter of the container is divided by a rotary damper inside, made with the possibility of installation from a vertical position horizontal, while the tank is equipped with a closed position switching valve, vacuum and air.

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