A method for preparing a water-soluble salt core by semi-solid die casting and a method for using the water-soluble salt core

Abstract

The present invention discloses a method for preparing a water-soluble salt core by semi-solid die casting and a method for using the water-soluble salt core, and belongs to the field of casting technology. The present invention first performs pretreatments such as drying, mixing, and ball milling on inorganic salts and additives, and then melts the inorganic salts, and prepares a semi-solid molten salt slurry by adding nano-scale inorganic salt powder and temperature-controlled cooling, and then performs high-pressure die casting. The semi-finished product obtained by high-pressure die casting is slowly cooled and processed to remove the pouring system, so as to obtain a molten salt core that can be used as a standby or directly. The molding process of the present invention can effectively improve the molding efficiency of the core and the solidification shrinkage of the molten salt, and enhance the strength and toughness of the core.

Description

Technical Field

[0001] The invention belongs to the technical field of casting, and in particular relates to a process for preparing a water-soluble core by utilizing a high-pressure casting process and a method for using the water-soluble salt core. Background Art

[0002] Complex inner cavity and curved channel castings have very wide applications in modern industry. When preparing complex inner cavity castings, the organic resin will be cracked under the action of high temperature molten metal to produce a large amount of gas, which will lead to pores on the inner wall of the casting and toxic and harmful gases polluting the environment. In addition, in the context of energy saving and consumption reduction, low temperature casting of castings makes the core collapse performance poor, and it is very difficult to remove the core of complex inner cavity and curved channel castings. Therefore, water-soluble cores with excellent water-soluble collapse performance and environmentally friendly characteristics have broad application prospects in the molding of such castings.

[0003] There are many types of water-soluble cores, but most of them have low strength and are generally only suitable for gravity casting. There are relatively few reports on water-soluble cores for pressure casting, especially high-pressure casting. According to the patent literature published in recent years, the water-soluble salt core molding processes used for pressure casting mainly include several typical process forms such as pressing sintering, melt casting and pressure casting. For example: Patent CN200710113017.8 discloses a process for preparing salt cores for oil-cooled pistons using sodium chloride powder, rutile titanium oxide powder, aluminum oxide powder, etc. as raw materials; Patent CN201710117447.0 also discloses a high-pressure resistant salt core for aluminum alloy piston casting. The above-mentioned methods for preparing water-soluble salt cores are all pressing and sintering processes, which require special high-pressure equipment and are only suitable for cores with simple molding structures, and their molding process is long.

[0004] Patents CN202010703060.5 and CN202010703905.0 disclose a process and method for preparing a water-soluble salt core using NaCl and Na2SO4 as raw materials, and the bending strength of the obtained water-soluble salt core can reach more than 20MPa. Fan Zitian et al. also introduced a process for preparing die-casting cores using magnesium sulfate and other raw materials in "Research on the Performance of Composite Sulfate Water-Soluble Sand Cores for Aluminum-Magnesium Alloy Castings". The molding of these cores all adopts a melt casting process, which casts molten inorganic salts into the core mold, and the desired core can be obtained after it cools. However, due to the moisture absorption problem of the salt core, the pressed core must be put into use quickly or stored in a drying oven, which leads to the disadvantage that the process has low efficiency and cannot meet the requirements of modern industrial process production. Patents CN201810877770.2 and CN202011125362.5 respectively disclose a method for preparing a core by melt die casting using NaCl as the main raw material. However, since die casting is suitable for forming thin-walled castings and the solidification shrinkage of molten salt is large, when preparing larger-sized salt cores, there are problems such as large shrinkage pores in the salt core and insufficient density, which seriously affect the strength and service performance of the core. Summary of the invention

[0005] 1. Problem to be solved

[0006] The purpose of the present invention is to solve the above problems existing in the existing water-soluble salt core preparation process, and provide a method for preparing water-soluble salt core by semi-solid die casting, which can not only realize the efficient molding of water-soluble salt core, but also obtain high-strength and tough water-soluble and dispersible water-soluble salt core suitable for pressure casting.

[0007] 2. Technical solution

[0008] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0009] The present invention discloses a method for preparing a water-soluble salt core by semi-solid die casting, which comprises adding corresponding micron-sized inorganic salt powder into molten inorganic salt to prepare a semi-solid molten salt slurry; and then using a die casting process to fill the salt core die casting mold with the semi-solid slurry to form a water-soluble salt core.

[0010] The liquid shrinkage of molten salt during solidification is very large, and it tends to produce large shrinkage cavities during solidification, thus affecting the performance of the obtained water-soluble salt core. The present invention adopts semi-solid die-casting technology. Since the cast molten salt enters the solid-liquid two-phase temperature range and solidifies under a certain pressure, the liquid shrinkage accounts for a large proportion of the shrinkage in the entire solidification process, the possibility of shrinkage cavities is reduced, and the density of the die-cast salt core is improved, thereby greatly improving the performance of the prepared water-soluble salt core.

[0011] Furthermore, before mixing with the micron-sized inorganic salt powder, an additional 5% to 15% additive is added to the molten inorganic salt. The additive includes refractory aggregates such as quartz sand, mullite sand, and magnesia sand, and refractory powders such as kaolin, diatomaceous earth, silica powder, and alumina powder. The composite addition of additives is beneficial to further reduce solidification shrinkage and avoid shrinkage cavities and shrinkage porosity on the one hand, and can also serve as a nucleation core, which is beneficial to grain refinement on the other hand.

[0012] Furthermore, the mixing ratio of the refractory aggregate and the refractory powder is 0.2-5, the particle size of the refractory aggregate is 100-200 meshes, and the particle size of the refractory powder is 400-800 meshes.

[0013] Furthermore, the inorganic salt is composed of alkali metal chloride and alkali metal carbonate, the particle size of the micron-grade inorganic salt powder is 10 to 50 microns, and the addition amount thereof is 5% to 10% of the mass of the molten inorganic salt.

[0014] Furthermore, the specific steps include:

[0015] (1) Melting: Place the prepared inorganic salt in a melting furnace, control the temperature in the furnace to 30°C to 100°C above the liquidus temperature of the composite salt, then add the additive, keep warm for 10min to 50min and stir evenly, and then remove the scum on the surface of the solution;

[0016] (2) Slurrying: adding micron-sized inorganic salt powder to the molten salt, and transferring the slurry through a water-cooled mold to a temperature-controlled slurrying container for preparing a semi-solid slurry, stirring it with an ultrasonic agitator, and controlling the temperature of the molten salt slurry to a liquid-solid two-phase temperature range to prepare a semi-solid molten salt slurry;

[0017] The present invention adopts the method of adding micron-sized inorganic salt powder and supplemented by ultrasonic stirring to prepare semi-solid slurry. The purpose is to add inorganic salt powder with lower temperature, which is conducive to the molten salt to quickly enter the liquid-solid two-phase temperature range. At the same time, the added inorganic salt powder can also become the core of the molten salt crystal nucleation. Under the action of ultrasonic stirring, it is conducive to the formation of equiaxed fine grains, thereby obtaining a semi-solid slurry with excellent performance.

[0018] (3) Die casting: pour the semi-solid molten salt slurry into the pouring cup of the die casting machine, use the die casting machine punch to fill the semi-solid slurry into the salt core die casting mold, and form the water-soluble salt core. After the core temperature is cooled to 50°C to 100°C above the solid phase transition temperature of the composite salt core, open the die casting mold and eject the die casting salt core. The purpose of requiring the mold to be opened after the core temperature is cooled to above the solid phase transition temperature of the composite salt core during the die casting process is to avoid poor yield of the die casting mold, which may cause cracks in the composite salt core during solid shrinkage and phase transition, thereby affecting its performance.

[0019] (4) Cooling and processing: The die-cast salt core is cooled, and then its casting system and riser are removed to obtain the desired water-soluble salt core.

[0020] Furthermore, in step (4), the die-cast salt core ejected from the die-casting machine is quickly transferred to a furnace 20°C to 80°C above the solid phase change temperature for slow cooling, and the cooling rate is 1°C 1min to 10°C 1min. The slow cooling treatment can reduce the solid phase change rate of the salt core, prevent the salt core from generating microcracks due to rapid phase change, and reduce the strength of the salt core.

[0021] Furthermore, the die-cast salt core is taken out from the furnace after being slowly cooled to 50°C to 100°C below the solid phase transition temperature.

[0022] Furthermore, the inorganic salt and additive are dried at 120°C to 200°C before use.

[0023] The method for using the water-soluble salt core prepared by the present invention comprises placing the water-soluble salt core in a temperature-controlled box at 200°C to 300°C for standby use or directly installing the water-soluble salt core on a die-casting mold when the core temperature is 200°C to 300°C for use, thereby effectively preventing the salt core from being directly subjected to the heat stimulation of molten metal during use and causing cracks or brittle fractures. Moreover, direct use thereof greatly reduces energy consumption during heat preservation storage and improves the molding and use efficiency of the salt core. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a process flow chart of the method for preparing a water-soluble salt core by semi-solid die casting. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with specific embodiments.

[0026] Example 1

[0027] Combination Figure 1 A method for preparing a water-soluble salt core by semi-solid die casting in this embodiment comprises the following steps:

[0028] (1) Raw material pretreatment: Place sodium chloride, sodium carbonate, 200 mesh quartz sand, and 400 mesh kaolin in an oven for drying, and control the oven temperature at 120°C. Mix the sodium chloride and sodium carbonate used to prepare the salt core in a mass ratio of 1:2 and wait for melting. Mix the dried sodium chloride and sodium carbonate in a mass ratio of 1:2 and ball mill to obtain 10-50 micron inorganic salt powder, which will be used to prepare semi-solid slurry. Mix the dried 200 mesh quartz sand and 400 mesh kaolin in a mass ratio of 1:1 and prepare them when melting.

[0029] (2) Melting: Place the mixed inorganic salt in a melting furnace, control the furnace temperature to 800°C-850°C, add the quartz sand and kaolin mixed in the pretreatment process (the total amount added is 10% of the mass of the molten inorganic salt), keep warm for 10 minutes and stir evenly, and then remove the scum on the surface of the solution.

[0030] (3) Slurry preparation: Add the ball-milled micron-sized inorganic salt powder prepared in the raw material pretreatment stage (the added amount is 8% of the mass of the molten inorganic salt) into the molten salt, and transfer the slurry through a water-cooled mold to a temperature-controlled slurry preparation container for preparing a semi-solid slurry. Use an ultrasonic agitator to stir it and control the temperature of the molten salt slurry to 660-620°C to prepare a semi-solid molten salt slurry.

[0031] (4) Die casting: Pour the semi-solid molten salt slurry into the pouring cup of the die casting machine, use the die casting machine punch to fill the semi-solid slurry into the salt core die casting mold to form a water-soluble salt core. When the core temperature cools to between 530610℃, open the die casting mold and eject the die-cast salt core.

[0032] (5) Slow cooling: The die-cast salt core ejected from the die-casting machine is quickly transferred to a furnace with an initial temperature of 500°C-610°C for slow cooling. After it is cooled to below 350°C at a cooling rate of 1°C per minute, the salt core is taken out of the furnace.

[0033] (6) Processing: The salt core is taken out from the furnace, and its casting system and riser are removed to obtain the required water-soluble salt core.

[0034] (7) Usage: Place the water-soluble salt core in a temperature-controlled box at 250℃-610℃ for standby use or directly install it on the die-casting mold when the core temperature is 250℃-610℃ for use.

[0035] Example 2

[0036] A method for preparing a water-soluble salt core by semi-solid die casting in this embodiment comprises the following steps:

[0037] (1) Raw material pretreatment: Put potassium chloride, potassium carbonate, 100 mesh mullite sand, and 600 mesh diatomaceous earth into an oven for drying, and control the oven temperature at 200°C. Mix the potassium chloride and potassium carbonate used to prepare the salt core in a mass ratio of 2:1 and wait for melting. Mix the dried potassium chloride and potassium carbonate in a mass ratio of 2:1 and ball mill to obtain 10-50 micron inorganic salt powder, which will be used to prepare semi-solid slurry. Mix the dried mullite sand and diatomaceous earth in a mass ratio of 0.2:1 and prepare them when melting.

[0038] (2) Melting: Place the mixed inorganic salt in a melting furnace, control the furnace temperature to 900°C-950°C, add the mullite sand and diatomaceous earth mixed in the pretreatment process, keep warm for 50 minutes and stir evenly, then remove the scum on the surface of the solution. The amount of additives added is 15% of the mass of the molten inorganic salt.

[0039] (3) Slurry preparation: Add the ball-milled micron-sized inorganic salt powder prepared in the raw material pretreatment stage into the molten salt (the added amount is 10% of the mass of the molten inorganic salt), and transfer the slurry through a water-cooled mold to a temperature-controlled slurry preparation container for preparing a semi-solid slurry. Use an ultrasonic agitator to stir it and control the temperature of the molten salt slurry to 680-620°C to prepare a semi-solid molten salt slurry.

[0040] (4) Die casting: Pour the semi-solid molten salt slurry into the pouring cup of the die casting machine, use the die casting machine punch to fill the semi-solid slurry into the salt core die casting mold to form a water-soluble salt core. When the core temperature cools to 500℃610℃, open the die casting mold and eject the die-cast salt core.

[0041] (5) Slow cooling: The die-cast salt core ejected from the die-casting machine is quickly transferred to a furnace with an initial temperature of 430°C-610°C for slow cooling. After it is cooled to below 350°C at a cooling rate of 10°C per minute, the salt core is taken out of the furnace.

[0042] (6) Processing: The salt core is taken out from the furnace, and its casting system and riser are removed to obtain the required water-soluble salt core.

[0043] (7) Usage: Place the water-soluble salt core in a temperature-controlled box at 290℃-610℃ for standby use or directly install it on the die-casting mold when the core temperature is 290℃-610℃ for use.

[0044] Example 3

[0045] A method for preparing a water-soluble salt core by semi-solid die casting in this embodiment comprises the following steps:

[0046] (1) Raw material pretreatment: Put potassium chloride, potassium carbonate, 200 mesh magnesia, 800 mesh alumina powder, etc. into an oven for drying, and control the oven temperature at 170°C. Mix potassium chloride and potassium carbonate used to prepare salt cores in a mass ratio of 1:1 and wait for melting. Mix the dried potassium chloride and potassium carbonate in a mass ratio of 1:1 and ball mill to obtain 10-50 micron inorganic salt powder, which will be used to prepare semi-solid slurry. Mix the dried magnesia and alumina powder in a mass ratio of 5:1 and prepare them when melting.

[0047] (2) Melting: Place the mixed inorganic salt in a melting furnace, control the furnace temperature to 920°C-970°C, add the quartz sand and kaolin mixed in the pretreatment process (the amount of additives added accounts for 13% of the mass of the molten inorganic salt), keep warm for 25 minutes and stir evenly, and then remove the scum on the surface of the solution.

[0048] (3) Slurry preparation: Add the ball-milled micron-sized inorganic salt powder prepared in the raw material pretreatment stage into the molten salt (the added amount is 5% of the mass of the molten inorganic salt), and transfer the slurry through a water-cooled mold to a temperature-controlled slurry preparation container for preparing a semi-solid slurry. Use an ultrasonic agitator to stir it and control the temperature of the molten salt slurry to 690-620°C to prepare a semi-solid molten salt slurry.

[0049] (4) Die casting: Pour the semi-solid molten salt slurry into the pouring cup of the die casting machine, and use the die casting machine punch to fill the semi-solid slurry into the salt core die casting mold to form a water-soluble salt core. When the core temperature cools to 510℃610℃, open the die casting mold and eject the die-cast salt core.

[0050] (5) Slow cooling: The die-cast salt core ejected from the die-casting machine is quickly transferred to a furnace with an initial temperature of 420°C-610°C for slow cooling. After it is cooled to below 350°C at a cooling rate of 6°C per minute, the salt core is taken out of the furnace.

[0051] (6) Processing: The salt core is taken out from the furnace, and its casting system and riser are removed to obtain the required water-soluble salt core.

[0052] (7) Usage: Place the water-soluble salt core in a temperature-controlled box at 210℃-610℃ for standby use or directly install it on the die-casting mold when the core temperature is 210℃-610℃ for use.

Claims

1. A method for preparing a water-soluble salt core by semi-solid die casting, characterized in that: Add corresponding micron-sized inorganic salt powder to the molten inorganic salt, and use ultrasonic stirring to control the temperature of the molten salt slurry to the liquid-solid two-phase temperature range to prepare a semi-solid molten salt slurry; then use a die-casting process to fill the semi-solid slurry into the salt core die-casting mold, that is, to form a water-soluble salt core; specifically, the following steps are included: (1) Melting: Place the prepared inorganic salt in a melting furnace, control the temperature in the furnace to 30°C to 100°C above the liquidus temperature of the composite salt, then add the additive, keep warm for 10min to 50min and stir evenly, and then remove the scum on the surface of the solution; (2) Slurrying: adding micron-sized inorganic salt powder to the molten salt, and transferring the slurry through a water-cooled mold to a temperature-controlled slurrying container for preparing a semi-solid slurry, stirring it with an ultrasonic agitator, and controlling the temperature of the molten salt slurry to a liquid-solid two-phase temperature range to prepare a semi-solid molten salt slurry; (3) Die casting: pour the semi-solid molten salt slurry into the pouring cup of the die casting machine, use the die casting machine punch to fill the semi-solid slurry into the salt core die casting mold to form a water-soluble salt core, wait for the core temperature to cool to between 50°C and 100°C above the solid phase transition temperature of the composite salt core, open the die casting mold, and eject the die casting salt core; (4) Cooling and processing: The die-cast salt core is cooled, and then its casting system and riser are removed to obtain the desired water-soluble salt core; The inorganic salt consists of alkali metal chloride and alkali metal carbonate; the addition amount of the micron-sized inorganic salt powder is 5% to 10% of the mass of the molten inorganic salt, and the particle size of the micron-sized inorganic salt powder is 10 to 50 microns; 10% to 15% of additives are additionally added to the molten inorganic salt, and the additives include refractory aggregate and refractory powder.

2. The method for preparing a water-soluble salt core by semi-solid die casting according to claim 1, characterized in that: The refractory aggregate is at least one of quartz sand, mullite sand, and magnesia sand, and the refractory powder is any one of kaolin, diatomaceous earth, silica powder, and alumina powder. The mixing ratio of the refractory aggregate and the refractory powder is between 0.2 and 5, the particle size of the refractory aggregate is 100 to 200 meshes, and the particle size of the refractory powder is 400 to 800 meshes.

3. A method for preparing a water-soluble salt core by semi-solid die casting according to claim 1 or 2, characterized in that: In step (4), the die-cast salt core ejected from the die-casting machine is quickly transferred to a furnace 20°C to 80°C above the solid phase transition temperature for slow cooling at a cooling rate of 1°C / min to 10°C / min.

4. The method for preparing a water-soluble salt core by semi-solid die casting according to claim 3, characterized in that: The die-cast salt core is slowly cooled to 50°C to 100°C below the solid phase transition temperature and then taken out from the furnace.

5. The method for preparing a water-soluble salt core by semi-solid die casting according to claim 4, characterized in that: The inorganic salt and additive are dried at 120°C to 200°C before use.

6. A method for using the water-soluble salt core prepared by the method according to any one of claims 1 to 5, characterized in that: Place the water-soluble salt core in a temperature-controlled box at 200℃~300℃ for standby use or directly install it on the die-casting mold when the core temperature is at 200℃~300℃ for use.

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