CS215590A3 - Method of shaped casting in unbound sand mixtures - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method for casting castings into moldable compositions, in particular a casting process, wherein the molding composition comprises a high-thermal gas in the grain boundaries. Quartz sand has traditionally been used as a molding mixture in molding various metals and their alloys. A number of casting processes include casting in a sand mold, in which molten metal is poured into a mold made of sand and binder, casting in CO 2, in which the binder (waterglass) is reacted with CO 2 gas. in order to activate it, a castable model in which the casting mold is formed by casting a refractory model with a refractory slurry, and a shell casting into a casting mold, wherein the mold is formed of particles contours of sand bound so as to form a shell occupying (embedding) Another interesting casting process is an evaporative foam casting process in which a foam model, usually made of polystyrene foam, is made in a cast part, which is typically provided with a refractory after-casting, embedded in a molding mold. frame and drenched with quartz sand as a molding compound In order to achieve the necessary density and density of the molding composition, the molding frame is brought into 2 vibrations when filled into the molding frame. The molten casting metal is then fed into the molding frame by the inflow channel, whereby both the foam casting channel and the model are evaporated and the resulting gases are expelled. The result is a casting that reproduces perfectly the stiff foam pattern. The vaporization of the molystyrene gas formed penetrates the coating of the model and the molding sand and escapes from the molding frame by the exhaust gas produced therein.

Various metal materials have been tested as molding mixtures to obtain a higher thermal conductivity of the molding composition. For example, in the USSR, studies have been carried out on the use of crude iron or cast or chopped steel shot as a ferromagnetic molding composition used in the evaporative foam treatment process. These studies were reported in 1979 in the professional literature of the USSR. While these metallic materials provide the desired increased thermal conductivity of the molding composition, they are heavy materials that cause deformation of the foam models used in the vaporizing foam casting process, resulting in inaccurate castings. In addition, such heavy molding compositions cannot be handled in conventional molding equipment used in quartz sand molding.

Also described is the use of zirconium sand as a molding composition in an evaporative foam casting process. Since the zirconium new sand has a higher bulk density than the quartz sand, the approximate mass of the molten metal cast, it is judged that the casting force acting on the hydrostatic force is reduced, thereby substantially improving the casting mold resistance and thus the final accuracy of the casting thus obtained. Otherwise, however, at 600 ° C, the zirconium thermal conductivity of 0.83 W / m 2 K is only about twice as high as the thermal conductivity of quartz (silica-to-silica), which is 0.5 µm · W / m ° K. Since the heat removal intensity is roughly proportional to the square root of the thermal conductivity mixture, zircon sand provides an increase in cooling intensity of about 24 $.

A method for increasing the solidification rate of the casting was also described. According to this proposal, a metal mold, acting as a potential heat sink, is attached to the evaporative foam model. When pouring the liquid metal into the casting mold, the coolant accelerates the cooling and solidification of the casting. However, the attachment of a mold to each model is a costly process and provides a very limited increase in casting rate.

It has also been proposed to improve the thermal conductivity of the molding composition by coating the grain with a refractory coating. This process has been described in the United States in 1987, and according to it, such refractory coatings are provided with grains of quartz sand, alumina, zirconia or a store. The coating also modifies the grain shapes of the molding material so that they obtain a more spherical shape so that they are deposited more evenly around the choked model, thereby increasing the accuracy of the obtained casting. However, these materials do not again have the high thermal resistance required to increase the solidification rate of the casting.

Another molding composition that improves the evaporative foam casting process is aluminum grain. It has been found that the tatoforming composition is highly effective in its ability to increase heat removal, avoiding the problems of using heavier metals as molding compositions. However, all of the above proposals and investigations have focused on the properties of the solid phase of the molding composition and have not taken into account the gaseous phase contained in the gaps between the solid grains of the molding composition to influence the heat transfer properties of the molding composition. However, the use of helium gas has been suggested earlier in order to adjust the intensity of the transfer mixture through the molding composition.

For example, in a proposal filed in 1973 in the USSR, a process is described for freezing sand casting molds, presumably for bonding the molding grain grains prior to casting, to fill the casting mold with a higher thermal conductivity gas than air. However, this procedure was aimed only at cooling the casting mold below 0 ° C and not casting the molten metal.

Another suggestion, filed in the USSR in 1985, relates to a casting mold with a porous core whose porosity gradually increases the pore pores on the core surface to coarse continuous cavities in the middle of the core. These coarse core cavities can then be filled with various cooling media, including helium, to change the core heat recovery capacity as well as the core cooling cooling intensity. In a proposal filed in 1987 in the United States, the use of a helium layer between the molten metal and the face of a moving selector belt is described in a continuous casting machine for producing metal belts. The purpose of helium, however, is here only to form a gaseous layer between the strip and the web. The influence of argon and other gases present in the atmosphere above the molten gas is also described in the paper "The Effect of Different Gas Atmospheric Gas Attributes on Some Casting Characteristics, for example in AISi 12.8", published in 1977 in Giesserei. metal in the melting furnace, the ladle and pouring the molten metal from the ladle into the mold. The purpose of this gas was to reduce the melting of molten metal during its melting and transport in the ladle. It is noted that by reducing the pressure of any gas and replacing the air with argin, a reduction in the cooling rate, i.e., an increase in setting time, is achieved. It is an object of the invention to provide an improved casting system with higher heat transfer through the molding composition. In studying the conditions for carrying out the present invention, it has been found that by replacing the air normally present in the boundaries between the unbound (free) grains of the molding mixture with a higher thermal conductivity, such as helium, substantially higher rates of cooling and speed can be achieved solidification of castings.

Accordingly, in a general sense, the invention relates to a casting casting casting into a molding composition consisting of a casting model casting mold which is to be cast into a molding composition in a molding frame, i.e., a mold formed from non-binding heat-resistant molding material, and in a casting mold melt into a molding frame to obtain a cast having a rod tucked into the molding composition. According to the new casting process, a displacement phase between the grains of the non-bonded molding mixture of the normally contained air is formed therein, and the gas is thermally conductive higher than the thermal conductivity of the air. A preferred feature of the invention relates to the progressive casting of castings into unbound molding compositions, consisting of the stages of making a model of a gasifiable material substantially free of the action of a casting batch of molten metal and having a shape corresponding to the cast article, stoking the model in a molding frame into a molding composition of unbonded material and pouring a batch of molten metal into the molding frame, thereby evaporating the model and forming the molding in the mold. A new characteristic of the casting process includes incorporating a displacement phase in the interstitial gaps between the non-bound forming mixture of normally contained air by a thermal conductivity gas higher than the air thermal conductivity. The preferred displacement gas is lilium because it is inert, non-toxic, non-corrosive and relatively inexpensive. However, there are also other gases with high thermal inertia, namely hydrogen and neon, but there are practical limitations on their use for reasons of hydrogen safety and relatively high costneon. In certain applications, when specified cooling rates are required faster than those achieved by air, but slower than those achieved by pure. helium, skytají - 8 - the benefits of a mixture of helium with other non-reactive gases with lower thermal conductivity. In these cases, the desired cooling intensity is achieved by using a mixture of helium with air, helium with nitrogen, argon or helium with another gas, not reacting with molten or solidified casting metal, or with the molding composition. accurately define the cooling intensity and solidification rate of the castings. In one embodiment of the casting process according to the invention, before the casting of the casting, the gaps in the granular molding mixture are simply filled with a high thermal conductivity gas. Alternatively, however, the casting mold may be filled with molten metal by pre-introducing a high thermal conductivity gas to completely fill the mold cavity under the conditions of low heat dissipation, and then increase the cooling rate of the high thermal conductivity gas, such as e.g. helium or helium-air mixtures as described herein to obtain moderate heat dissipation intensities.

Various types of granular materials such as quartz sand, zirconia sand, chrome magnesite sand (steel shot, silicon carbide, alumina, granulated aluminum, and the like can also be cast with various materials, such as various types of casting materials, such as various types of casting materials) can be used as molding compositions. aluminum, magnesium, zinc and their alloys.

Preferred embodiments of the casting process according to the invention will be illustrated by the following non-limiting examples, with table comparative evaluations thereof. Example 1:

Models of polystyrene foam (32 x 51 x 152 mm) were prepared and molded with Stro-Kote 250.1, available from Thiem Corporation. Tytomodels were clogged into various molding mixtures (granulated aluminum with a particle size of 2.8 - 5.6 mm, silicon carbide granulate with a particle size of 0.6 mm, molding sand). Castings were made by pouring molten Al-4,5 / ° Cu alloys at 750 ° C into models. The central part of the models was; the thermocouple is placed and the continuous casting parts were recorded under the conditions of Table 1. It can be seen from Table 1 that under these conditions, the dusting levels in helium were equivalent to the granulated aluminum cooling rates. with helium and better than in granulated aluminum or in silicon cable with air. By using helium, the cooling intensity was approximately twice that of the castings cast into the sand in an air atmosphere. Example 2:

An extra series of experiments was carried out to evaluate the effect of helium on the heat removal rate under conditions closer to the conventional sand casting process. In the course of these experiments, the molding mixture was thickened around unused, empty box bodies. The Al-4,5% Cu casting metal at 700 ° C was poured directly into the boxes and an insulating cover was placed on the mold. Temperature-time dependencies were recorded in order to compare relative cooling intensities under different casting conditions.

The results obtained are shown in Tables 2 and 3. In the case of these tables, it can be ensured that the presence of helium has an appreciable effect under all conditions tested and that the introduction of helium into the quartz sand is a very effective means of increasing the intensity of the casting cooling. . Example 3:

A further series of tests was performed using the steam-blown foam casting technique into various molding media. An overview of the molding materials used is given in Table 4. Foam polystyrene foam models with a specific gravity of 0.0225

O g / cin, 38 mm and 152 mm in length, were obtained from LOST Foam Technologies. The metal mass required to fill these models was 0.5 kg.

Coated models were prepared by dipping in a Stro-Kote 250.1 slurry so that their specific value was adjusted to 11 L of 56 g / cm after a 0.2 mm thick coating. After soaking, the models were dried in the air overnight or dried in a microwave oven. Before the model was choked into the molding mixture, a depth was inserted into the model in the middle of its length. The model was then inserted into a molding frame, which was then filled with a molding compound to vibrate the entire molding assembly. To prevent heat loss through the bottom of the flask, an insulating layer, either 2.7 mm thick, or two layers of Fiber-Frax, a Carborundum Corporation product, was placed on its bottom. In the gas phase exchange tests, a perforated, non-rusted gas distributor was placed in the bottom of the flask, coupled to the gas inlet and used before casting to displace air from the molding layer.

2.7 l / min of helium was injected for 2-3 minutes to displace air from the molding mixture. Just before the start of draining, the helium flow was reduced to about 0.3 l / min to maintain the helium atmosphere in the cold.

Casting samples were cast from Al-4.5 Cup binary alloy by casting temperature of 700 ° C, while the temperature was monitored by a registration device with a registration trap. This alloy was chosen because it exhibits a well-defined auteectic residence time at 5 ° C-8 ° C, making it easy to determine the solidification time of the casting. When casting at a temperature of 7 ° C, the metal reaching the thermocouple was already at the liquidus temperature. Cooling intensities were calculated by dividing the liquidus temperature in the eutectic yield range (100 ° C) by the time elapsed between casting and the end time of the eutectic delay. a) The results of the solidification rate during air replacement of helium in evaporative foam models without a train were recorded. These results are shown in Table 5, which indicates that the solidification rate was higher in the presence of helium. b) A further experiment was carried out with a vaporized foam-coated model, in the air displacement of helium. The results of this experiment are shown in Table 6 and again show that the presence of helium was a higher solidification rate. c) Another test was performed to determine the velocity of the static air and flowing argon, both of which have lower thermal conductivity than helium. The results of this test are shown in Table 7 and show that both the solidification rates found in air and argon were significantly lower than those of helium. d) Yet another test was carried out by casting an 8 kg cast using an evaporating foam model. The results of this test are shown in Table 8, and it is clear from these that when the air is displaced by helium, the same solidification rate and subsequent cooling to 445 ° C and 395 ° C are achieved. It will be appreciated from the above examples that the solidification rate and the cooling qualities when using evaporative foam models can be considerably increased by using high heat conductivity - thermal capacity molding compositions. The effectiveness of these molding compositions is limited by the thermal resistance between the contact medium of the molding medium. By using a highly conductive gas, such as helium, the solidification rate and cooling intensity can be substantially increased. For example, the use of molded sand helium was even more effective at increasing the solidification rate than in the granulated aluminum tested. Typically, the refractory coatings of the models used in the post-steaming foam casting process create a thermal flux barrier that is marked by the use of helium with a highly conductive molding composition.

The use of helium in conventional evaporative foam casting was found to be most effective. While the use of alternative mixtures may lead to a further increase in solidification rate, it will be appreciated that highly conductive model coatings or uncoated models are desirable to achieve higher cooling rates than can be utilized with helium and molding sand. While the foregoing detailed description of the invention has been directed mainly to evaporative foam casting, the invention has much broader applicability to other casting processes, such as molding, molding, molding, sand cores, and the like; '.ravll; íKw. v, c. - 15 -

Table 1; Cooling times of Al-4.5% Cu alloy cast at a temperature of 750 ° C. The times are shown in seconds elapsed between the liquidus delay and the temperature. molding mixture granules AI sand SiC atmosphere DEVELOPMENT Ee air Ee air delay liquid-solidus 330 220 420 220 345 liquidus-400 ° C 580 430 760 430 635 liquidus-300 ° C 955 720 1300 740 1105 casting mass (g) 703 800 659 810 659 Table 2: Cooling times (minutes) for Al-4,5 £ Cu, casting temperature = 700 ° C, uncovered mold molding AI sand SiC atmosphere air He air He air He liquidus-solidus 2,9 2,2 8 25 3.6 6.25 3.05 liquidus-500 ° C 3.6 2.6 10.25 4.6 8.0 3.9 liquidus-400 ° C 6.0 4.5 17.75 8.0 13.5 7.0 liquidus-35 ° C 8.0 6.0 23.5 10.75 17.5 9.25 liquidus-300 ° C 10.8 8.25 30.5 15.0 23.25: 12.7 Mass 0 Part (g) 60I 557 684 589 467 713

Table 3 ♦ Cooling times (minutes) for Al-4.5% Cu, casting temperature = 700 ° C, covered mold - ι6 - molding mixture AI sand Sic atmosphere air He air He air Ke 1ikvidus-solidus 6.4 3.3 9.25 3.3 6.5 3.5 Liquid-500 ° C - - - - - Liquid-400 ° C 12.5 6.3 19.0 6.5 13.0 7.3 Liquus-300 ° C 22.0 12.0 33.0 12.0 22.5 13.8 Casting mass (g) 649 630 752 430 683 614

flat Al 2 O 3, the same as the previous one, bound, non-porous, bonded, bound 5% by weight of non-metallic sodium silicate (40-42 Be, stabilizing co), silicon oxide: 0.3 x 0.12 mm 4 part mixture 0 , 0.12 mm, supplied by White Arbrasivesl. unbound, porous, RA 0.7 x 0.5 supplied by Canadian Carborundum

aluminum granules NKE powder AA1100 A1, 1.0x0.6 mm, supplied by NuclearMetal Inc. unbound, porous, metallic

AMPAL AMPAL LO03, supplied by Atomized MetalPowders Inc.

TOYAL

A 5 µM AI JaM powder supplied by AlcanToyo America Inc.

Aluminum powder1,25x0,3 mm, supplied by Mathey Ltd. 'Cr **** rr ~ r * «f Λ ··? ’18

Table 5 «Solidification rates of castings in air and helium, no coating models solidification rate ° C / s (standard deviation) atmosphere air helium ratio He-air molding sand 0.34 (0.02) 0.74 (0.06) 2 , 2 AI granules: NMI 0.80 (0.06) 1.24 (0.08) 1.6 JaM 0.71 (0.03) 1.10 (0.05) 1.5 AMPAL 0.83 ( 0.04) 1.29 (0.04) 1.6 TOYAL 0.58 (0.07) 0.99 (0.09) 1.7 Flat AI 203 0.42 (0.01) 0.98 ( 0.03) 2.3 Silicon carbide: 0.3x0.12 mm 0.56 (0.01) 0.96 (0.04) 1.7 RA 0.7x0.5 0.43 (0.03) 1 , 02 (0.10) 2.4

Table 6: Casting rates of castings in aircoated and helium models, nutí solidification rate ° C / s (standard deviation) air atmosphere helium He-air ratio molding sand 0.35 (0.02). 0.59 (0.02) 1.7 Al granules: NMI 0.49 (0.02) 0.90 (0.07) 1.8 JaM 0.51 (0.03) 0.84 (0.05 ) 1.6 TOYAL. 0.45 (0.04) 0.72 (0.07) 1.6 Silicon Carbide: 0.3x0.12 mm 0.41 (0.01) 0.64 (0.01) 1.6 RA 0, 7x0.5 0.36 (0.01) 0.71 (0.03) 2.0 Flat AI 203 0.36 (0.01) 0.75 (o, o4) 2.1 19

Table 7 i Influence of helium and argon on solidification rate

focused on the use of TOYAL aluminum granules

solidification rate ° C / s (standard deviation) atmosphere air ^ 'helium * ^ 2 / argon granul AI TOYAL 0.58 (0.07) 0.99 (0.09) 0.50 (0.06) thermal conductivity at temperature: 300 K 1000 K air U £ ixW / m ° K 0.067 W / m ° K helium 0.151W / m ° K 0.35½ W / m ° K argon ©, 0l8W / m ° K 0.0½½ W / m ° K 1 / static 2 / flowing, 0.35 l / min

Table 8; Cooling times as a function of the atmosphere molding mixture for large castings (8 kg) time from casting to: (in minutes) molding gas eutectic dwell time ^ 5 ° C 395 ° C molding sand air l6 38 60 molding sand helium 7 15.5 22 5 granules AI air 9 20,5 32 flat AI 203 helium 7,2-5 13,25 18

Claims (8)

innovation blends consisting of shot molding a casting model to be cast in a molding frame into an unbound molding composition, and pouring a dose of molten metal into the molding frame to obtain a casting having the shape of a model choked into a molding composition, characterized in that a phase of displacement in the gaps between the non-bonded molding mixture of the normally contained air by the thermal conductivity gas higher than the thermal conductivity of the air is incorporated into the process. 2. A casting method according to claim 1, wherein the unbound molding composition comprises refractory particles. 3. A casting method according to claim 1, wherein the displacement gas is helium. 4. A casting method according to claim 1, wherein the displacement gas is a mixture of helium with air, nitrogen, or inert gas. 5. A casting method according to claim 1, wherein the casting material is aluminum or alloys thereof. 6. A method of casting castings from unbound molding compositions, comprising the steps of making a model of a material which is substantially fluid-free, by the casting of a metal flow distribution having a shape corresponding to a cast article, and stitching the mold in the molding frame. a molding composition formed of unbound granular material and pouring a dose of molten metal into the molding frame and thereby vaporizing the model and forming the model mold, characterized in that the casting process comprises incorporating a displacement phase in the gap between the unbound molding media grain normally contained air with a thermal conductivity higher than that of the air. 7. A casting method according to claim 6, wherein the displacement gas is helium. 8. Process according to claim 6, characterized in that helium is used as the high conductivity gas. 9. Process according to claim 7, characterized in that a mixture of hydrogen with air, helium with nitrogen or helium with another inactive gas is used as the higher thermal conductivity gas. Representative: ló. 7. 1990 663 C and DL