Mold core for investment casting and preparation method thereof

Abstract

The invention discloses a mold core for investment casting and a preparation method thereof, the mold core comprises sand A and sand B, and the mass ratio of the sand A to the sand B is 2: 1; the sand A is prepared from the following components in percentage by mass: 84 to 86 percent of 60 to 80-mesh mullite sand I, 1.5 to 2.0 percent of aluminum phosphate powder, 3.5 to 4.0 percent of surface layer silica sol and 9 to 11 percent of furan resin; the sand B comprises the following components in percentage by mass: 92-94% of 60-80-mesh mullite sand II and 6-8% of a curing agent; the mold core is prepared through the links of sand making, sand filling and tamping, baking and curing, liquid immersion, drying and the like, the mold core combines the advantages of sand mold casting and investment casting core making, and compared with a sand mold casting core making process, the prepared mold core has the high high-temperature strength, the low expansion coefficient and the good metal permeability resistance; compared with a ceramic core, the cost of the ceramic core is 30-60% of that of the ceramic core, and the ceramic core has good air permeability.

Description

Technical Field

[0001] The present invention relates to the technical field of investment casting, in particular to a core for investment casting and a preparation method thereof. Background Art

[0002] Investment casting typically achieves complex cavity structures through the use of cores. During the wax pattern creation process, the core is placed in the mold, and after the shell is fabricated and fired, the core is removed after smelting and pouring, forming the cavity. Because the core and shell must be fired at 1050±50°C for 45-180 minutes, and because they are subject to the impact of molten metal during pouring, the core must possess a certain level of high-temperature strength and impact resistance.

[0003] Currently, cores made of scrubbed sand from sand casting have low high-temperature strength. After firing, these cores can break apart during pouring, causing mold leakage and resulting in rejects. Another approach is to use ceramic cores. While these cores meet the requirements, they are expensive and difficult to break apart after pouring. Removing the cores often requires alkali blasting, which increases overall production costs. Summary of the Invention

[0004] The object of the present invention is to provide a core for investment casting and a preparation method thereof.

[0005] The innovation of the present invention lies in: this application combines the advantages of sand casting and investment casting core making. Compared with the sand casting core making process, the prepared core has higher high-temperature strength, lower expansion coefficient, and good resistance to metal permeability; compared with ceramic cores, the cost is 30%-60% of that of ceramic cores, and it has better air permeability.

[0006] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is: A core for investment casting comprises sand A and sand B, wherein the mass ratio of the sand A to the sand B is 2:1; the sand A comprises 84-86% by mass of 60-80 mesh mullite sand, 1.5-2.0% by mass of aluminum phosphate powder, 3.5-4.0% by mass of a surface layer of silica sol, and 9-11% by mass of a furan resin; and the sand B comprises 92-94% by mass of 60-80 mesh mullite sand and 6-8% by mass of a curing agent.

[0007] A method for preparing a core for investment casting comprises the following steps: Step S1: preparing sand A, adding the aluminum phosphate powder to the mullite sand, stirring evenly, then sequentially adding the surface layer silica sol and furan resin and stirring evenly to prepare sand A; Step S2: preparing sand B, adding the curing agent to the mullite sand 2, and mixing them evenly to prepare sand B; Step S3: Mix sand A and sand B in a mass ratio of 2:1, stir evenly, and put them into the core mold, while tamping them; Step S4: baking and curing the core mold made in step S3 at a temperature of 100±10°C; Step S5: taking the core out of the core mold in step S4 and placing it at room temperature until it is completely cured; Step S6: Immerse the fully cured core obtained in step S5 in the hydrolyzed solution for 1-2 minutes, remove it and allow it to stand for 2-3 minutes until no more hydrolyzed solution drips out, and then repeatedly immerse it in the zircon powder coating until the surface color matches the color of the zircon powder coating and no sand core is exposed; Step S7: placing the core in step S6 in an environment with a temperature of 22-26° C. and a humidity of 40-80% until completely dry; Step S8: The core that has been completely dried in step S7 is repaired with sandpaper until the surface is smooth.

[0008] Furthermore, the hydrolysis solution in step S6 includes 55-56% by mass of ethyl silicate, 0.5-1.0% by mass of 36% hydrochloric acid, 9-10% by mass of distilled water, and 34-35% by mass of alcohol.

[0009] Furthermore, the zircon powder coating in step S6 includes 23-24% by mass of surface silica sol, 76-77% by mass of 325-mesh zircon powder, 0.04-0.06% by mass of a wetting agent, and 0.03-0.05% by mass of a defoaming agent.

[0010] The beneficial effects of the present invention are: 60-80 mesh mullite sand has a high melting point, a low expansion coefficient, and good resistance to metal penetration; aluminum phosphate powder has high refractory properties, which can prevent molten metal from corroding the core surface; silica sol forms an inorganic network structure mainly composed of SiO2 after roasting, which gives the core high strength and air permeability; furan resin and curing agent, the curing agent promotes polymerization reaction between furan resin molecules, forming an infusible body network polymer with a three-dimensional spatial structure, forming a hard skeleton structure; the zircon powder used in zircon powder coating is 325 mesh, with fine particles, which can achieve better surface roughness, low reactivity with molten metal, avoid sand adhesion and burr defects, and low thermal expansion coefficient, reducing the risk of core cracking.

[0011] Therefore, the core and its preparation method of the present application utilize a sand casting core making method (mixing sand A and sand B and then placing them into a mold to form them), using raw materials for investment casting (silica sol, hydrolyzed liquid, zircon powder coating), and combining the advantages of sand casting and investment casting core making; First: Compared with the sand casting core making process, it has higher high temperature strength (1700℃) and can withstand the impact of molten metal during the pouring process; Second: Compared with the sand casting core making process, the lower expansion coefficient ensures the dimensional stability of the cast parts; Third: Compared with the sand casting core making process, it is resistant to metal penetration and ensures that the casting surface has a better finish; Fourth: Compared with the existing ceramic core process, it has good air permeability and prevents the formation of pores in the casting; Fifth: Compared with the existing ceramic core process, the price is lower and it is easier to clean. DETAILED DESCRIPTION

[0012] The technical solutions in the embodiments of the present invention will be described clearly and completely below.

[0013] A core for investment casting comprises sand A and sand B, wherein the mass ratio of the sand A to the sand B is 2:1; the sand A comprises 84-86% by mass of 60-80 mesh mullite sand, 1.5-2.0% by mass of aluminum phosphate powder, 3.5-4.0% by mass of a surface layer of silica sol, and 9-11% by mass of a furan resin; and the sand B comprises 92-94% by mass of 60-80 mesh mullite sand and 6-8% by mass of a curing agent.

[0014] Furthermore, the mullite sand 1 and mullite sand 2 mentioned in sand A and sand B are just for distinction, and both are mullite sand.

[0015] A method for preparing a core for investment casting comprises the following steps: Step S1: Prepare sand A by adding the aluminum phosphate powder to mullite sand 1, stirring evenly, then sequentially adding the surface layer silica sol and furan resin and stirring evenly to prepare sand A. Visually inspect the sand to see if there are no lumps or dry sand, and if the sand can be held in a clumping state and can be dispersed by light touch, the sand is prepared. Step S2: preparing sand B, adding the curing agent to the mullite sand 2, and mixing them evenly to form sand B. Visually inspecting the sand, if there is no agglomeration or dry sand, and the sand can be held in a ball and dispersed by light touch, the sand is ready. Step S3: Mix sand A and sand B in a mass ratio of 2:1, stir evenly, and put them into the core mold. Tamp the sand while adding it. After tamping, the surface of the core can leave a slight fingerprint when pressed by hand without collapsing. Step S4: baking and curing the core mold made in step S3 at a temperature of 100±10°C for a time determined by the size and thickness of the core; this process can accelerate curing and improve production efficiency; Step S5: taking the core out of the core mold in step S4 and placing it at room temperature until it is completely cured; Step S6: soaking the completely cured core in step S5 in the hydrolyzed solution, taking it out and leaving it aside until no more hydrolyzed solution drips out, and then repeatedly immersing it in the zircon powder coating until the surface color matches the color of the zircon powder coating and no sand core is exposed; Step S7: placing the core in step S6 in an environment with a temperature of 22-26° C. and a humidity of 40-80% until completely dry; Step S8: The core that has been completely dried in step S7 is repaired with sandpaper until the surface is smooth.

[0016] Furthermore, the hydrolysis solution in step S6 includes 55-56% by mass of ethyl silicate, 0.5-1.0% by mass of 36% hydrochloric acid, 9-10% by mass of distilled water, and 34-35% by mass of alcohol.

[0017] Furthermore, the zircon powder coating in step S6 includes 23-24% by mass of surface silica sol, 76-77% by mass of 325-mesh zircon powder, 0.04-0.06% by mass of a wetting agent, and 0.03-0.05% by mass of a defoaming agent. Example 1

[0018] Add 200g of aluminum phosphate powder to 10kg of mullite sand (60-80 mesh), repeatedly sieve out the agglomerated aluminum phosphate powder with a sieve, crush it, and stir it evenly. Then add 450g of surface silica sol and stir it evenly. Finally, add 1150g of furan resin and stir it evenly to make sand A. Visually inspect the sand and find that there is no agglomeration or dry sand. It can be clumped when held by hand and can be dispersed by light touch.

[0019] Add 500g of curing agent to 5kg of mullite sand (60-80 mesh) to make B sand. Visually inspect the sand and see if there is no lumps or dry sand. If it can be lumped together when held by hand and can be dispersed by light touch, it is ready.

[0020] Mix sand A and sand B in a mass ratio of 2:1, stir evenly, put into the core mold, and tamp while adding sand. After tamping, the core can leave slight fingerprints when pressed by hand on the surface but will not collapse.

[0021] Place the core mold with sand next to an electric furnace for baking to accelerate curing. Turn the mold over during the process to evenly heat it. The baking temperature is 100±10℃. After baking for a period of time, take out the core directly. The baking time depends on the size and thickness of the core. This process can accelerate curing and improve production efficiency.

[0022] The core was taken out and placed at room temperature for 8 hours.

[0023] Immerse the core in the hydrolyzate for about 1-2 minutes, take it out and let it sit for 2-3 minutes (no more hydrolyzate drips out), then put it into the zircon powder coating, immerse it repeatedly until the surface is evenly covered with a layer of zircon powder coating, with no sand core exposed, and put it into the transition layer workshop to dry for 12 hours.

[0024] After drying, if any cracks are found, you can use a brush to apply zircon sand paint to repair them, and then repair the raised flow lines on the surface to make the surface smooth, and finally obtain the core.

[0025] Comparison table of the effects of using different core processes on the same product: Core name Surface quality Core strength production costs Production cycle Cleaning efficiency (shot blasting time) in conclusion This application core good whole Low About 24 hours 30min High pass rate, short cycle and low cost Casting process core good whole high About 84 hours 90 minutes High pass rate, long cycle and high cost Sand casting core Difference fracture Low About 8 hours - Low pass rate is not feasible Ceramic core good whole high 5-10 days Alkali explosion + shot blasting 150min High pass rate, long cycle and high cost As can be seen from the above table, the core of the present application has good surface quality, complete strength, low production cost, short production cycle, and is easy to clean, which is very suitable for promotion and use.

[0026] The embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

Claims

1. A core for investment casting, characterized in that: Comprising A sand and B sand, wherein the mass ratio of A sand to B sand is 2:1; The A sand comprises 84-86% by mass of 60-80 mesh mullite sand, 1.5-2.0% by mass of aluminum phosphate powder, 3.5-4.0% by mass of surface silica sol, and 9-11% by mass of furan resin; The B sand comprises 92-94% by mass of 60-80 mesh mullite sand and 6-8% by mass of a curing agent.

2. A method for preparing an investment casting core according to claim 1, characterized in that: The following steps are included: Step S1: preparing sand A, adding the aluminum phosphate powder to the mullite sand, stirring evenly, then sequentially adding the surface layer silica sol and furan resin and stirring evenly to prepare sand A; Step S2: preparing sand B, adding the curing agent to the mullite sand 2, and mixing them evenly to prepare sand B; Step S3: Mix sand A and sand B in a mass ratio of 2:1, stir evenly, and put them into the core mold, while tamping them; Step S4: baking and curing the core mold made in step S3 at a temperature of 100±10°C; Step S5: taking the core out of the core mold in step S4 and placing it at room temperature until it is completely cured; Step S6: Immerse the fully cured core obtained in step S5 in the hydrolyzed solution for 1-2 minutes, remove it and allow it to stand for 2-3 minutes until no more hydrolyzed solution drips out, and then repeatedly immerse it in the zircon powder coating until the surface color matches the color of the zircon powder coating and no sand core is exposed; Step S7: placing the core in step S6 in an environment with a temperature of 22-26° C. and a humidity of 40-80% until completely dry; Step S8: The core that has been completely dried in step S7 is repaired with sandpaper until the surface is smooth.

3. The method for preparing a core for investment casting according to claim 2, wherein: The hydrolysis solution in step S6 includes 55-56% by mass of ethyl silicate, 0.5-1.0% by mass of 36% hydrochloric acid, 9-10% by mass of distilled water, and 34-35% by mass of alcohol.

4. The method for preparing a core for investment casting according to claim 2, wherein: The zircon powder coating in step S6 includes 23-24% by mass of surface silica sol, 76-77% by mass of 325-mesh zircon powder, 0.04-0.06% by mass of a wetting agent, and 0.03-0.05% by mass of a defoaming agent.