Sand core coating for aluminum alloy castings and its preparation method

Abstract

The present invention belongs to the technical field of core coating preparation, and particularly relates to a core coating for aluminum alloy castings and a preparation method thereof. The core coating for aluminum alloy castings consists of the following raw materials: pyrophyllite, fayalite, zircon powder, magnesia, calcium titanate, cryolite, phosphorus pentoxide, sodium pyrophosphate, rectorite, octylphenol polyoxyethylene ether, n-octanol, and water. The core coating for aluminum alloy castings of the present invention uses a mixture of pyrophyllite, fayalite, zircon powder, calcium titanate, magnesia, cryolite, and phosphorus pentoxide as refractory materials, water as a carrier liquid, a mixture of sodium pyrophosphate and rectorite as a suspending agent, and simultaneously adds an n-octanol defoamer and an octylphenol polyoxyethylene ether surfactant. The synergistic effect between the raw materials ensures that the prepared core coating has good resistance to metal liquid erosion, anti-adhesion to sand, and thermal stability during application, thereby enabling the core coating to have excellent stripping strength and refractoriness.

Description

Technical Field

[0001] The present invention belongs to the technical field of core coating preparation, and particularly relates to a core coating for aluminum alloy castings and a preparation method thereof. Background Art

[0002] Casting coatings generally consist of refractory materials, carrier liquids, binders, suspending agents, and other additives, and are widely used in various molds and cores in casting production. They have the functions of preventing casting sand sticking, reducing the surface roughness of castings, increasing the service life of sand molds, and improving the surface material of castings.

[0003] Casting coatings can be classified by various methods. According to the refractory degree, they can be divided into high-refractory coatings, medium-refractory coatings, and low-refractory coatings; according to the carrier liquid used, they can be divided into water-based coatings and alcohol-based coatings; according to the mold materials, they can be divided into coatings for clay sand molds, resin sand coatings, water glass sand coatings, and metal mold coatings; according to the casting alloy materials, they can be divided into steel casting coatings, cast iron coatings, and non-ferrous alloy coatings, etc.

[0004] When casting castings with complex internal cavity structures such as water-cooled motor casings with integrated curved and special-shaped water channels that require airtightness tests, due to the complex curved and special-shaped cavities, subsequent processing such as sandblasting and shot peening cannot be carried out, and the internal cavity cleanliness is poor. Although abrasive flow and other polishing technologies are applied, the original pitted surface of the product water channels cannot be retained, resulting in the failure to achieve the cooling effect. Complex-structured aluminum alloy castings often require cores to form internal cavities or complex shapes. At this time, the selection of core coatings is particularly important. Core coatings can ensure the stability of cores at high temperatures and prevent deformation or damage during the pouring process of molten metal. If a core coating with good performance cannot be selected well, it will not only cause serious defects such as sand sticking and sand inclusion, but also cause difficulties in sand cleaning, increase the workload of cleaning and grinding, seriously affect the quality of castings, and even scrap the castings. Moreover, it will also affect the internal quality of castings, resulting in defects such as pores and porosity inside the castings, causing the airtightness test of the castings to be unqualified after processing, that is, penetration occurs during the pressure test.

[0005] Therefore, exploring a new type of core coating for aluminum alloy castings has become an urgent technical problem to be solved. Summary of the Invention

[0006] The object of the present invention is to provide a core coating for aluminum alloy castings. The core coating has the properties of resistance to molten metal erosion, anti-sand sticking, and thermal stability. The present invention also provides a preparation method thereof at the same time.

[0007] The core coating for aluminum alloy castings according to the present invention is composed of the following raw materials in parts by weight: 22-24 parts of pyrophyllite, 11-13 parts of fayalite, 7.2-7.6 parts of zircon powder, 3.1-3.4 parts of magnesia, 5.1-5.5 parts of calcium titanate, 4.3-5.2 parts of cryolite, 1.5-1.7 parts of phosphorus pentoxide, 2.6-2.8 parts of sodium pyrophosphate, 3.2-3.5 parts of rectorite, 0.18-0.21 parts of octylphenol polyoxyethylene ether, 0.35-0.37 parts of n-octanol, and 24-26 parts of water.

[0008] Among them:

[0009] The pyrophyllite described above has the following chemical composition in mass percentage: MgO 0.76%, CaO 2.13%, Al2O3 15.89%, SiO2 76.37%, Fe2O3 0.41%, P2O5 0.67%, K2O 0.36%, Na2O 0.05%, and the loss on ignition is 3.36%.

[0010] The fayalite described above has the following chemical composition in mass percentage: FeO 67.59%, SiO2 24.52%, MgO 2.54%, Al2O3 0.21%, TiO2 0.03%, CaO 0.32%, K2O 0.03%, Na2O 0.02%, P2O5 0.01%, and the loss on ignition is 4.73%.

[0011] The magnesia described above has the following chemical composition in mass percentage: SiO2 9.32%, Al2O3 1.45%, MgO 72.65%, Fe2O3 0.58%, CaO 5.32%, SO3 0.12%, and the loss on ignition is 10.56%.

[0012] Preferably, the core coating for aluminum alloy castings according to the present invention is composed of the following raw materials in parts by weight: 23 parts of pyrophyllite, 12 parts of fayalite, 7.4 parts of zircon powder, 3.3 parts of magnesia, 5.3 parts of calcium titanate, 4.8 parts of cryolite, 1.6 parts of phosphorus pentoxide, 2.7 parts of sodium pyrophosphate, 3.3 parts of rectorite, 0.20 parts of octylphenol polyoxyethylene ether, 0.36 parts of n-octanol, and 25 parts of water.

[0013] The core coating for aluminum alloy castings described in the present invention uses a mixture of pyrophyllite, fayalite, zircon powder, calcium titanate, magnesite, cryolite powder, and phosphorus pentoxide as refractory materials, enabling the core coating to have resistance to metal liquid erosion, anti-adhesion to sand, and thermal stability. Among them, pyrophyllite and fayalite are used in combination to ensure that the prepared core coating has resistance to metal liquid erosion. The main component of pyrophyllite is aluminosilicate, and pyrophyllite can form a silicate melt after contacting with metal liquid at high temperature, thereby enhancing the resistance of the core coating to metal liquid; while the main component of fayalite is iron silicate, and its crystal structure is relatively dense, showing high inertness in both high-temperature and chemical corrosion environments. Therefore, its addition can further improve the resistance of the core coating to metal liquid erosion. Zircon powder, magnesite, and calcium titanate are used in combination to ensure the anti-adhesion to sand, thermal stability, and chemical stability of the prepared core coating. Among them, the high refractoriness and low thermal expansion of zircon powder enable it to remain stable at high temperature, and its high thermal conductivity can quickly conduct heat to the casting, thereby reducing the contact time between the metal liquid and the core, and further enabling the core coating to have anti-adhesion to sand. The crystal structure of calcium titanate helps to form a dense coating, enhancing the mechanical strength and thermal stability of the coating. In addition, its stable chemical properties enable it to resist the erosion of metal liquid in high-temperature environments, thereby reducing chemical sand adhesion. The chemical inertness of magnesite makes it not easy to react with metal liquid at high temperature, thereby reducing mechanical and chemical sand adhesion. At the same time, its high wear resistance enables it to resist the erosion of metal liquid and reduce the wear of the core surface. Thus, the combined use of pyrophyllite, fayalite, zircon powder, calcium titanate, and magnesite ensures the resistance of the prepared core coating to metal liquid erosion, anti-adhesion to sand, and stability. In addition, cryolite and phosphorus pentoxide are added to the refractory materials described in this application. The addition of cryolite and phosphorus pentoxide can, firstly, improve the fluidity of the core coating, and secondly, through the filling effect, enable the core coating to form a denser structure at high temperature, thereby further improving the comprehensive performance of the core coating.

[0014] In addition, the core coating for aluminum alloy castings described in this application uses a mixture of sodium pyrophosphate and rectorite as a suspending agent. Sodium pyrophosphate keeps the particles suspended in the carrier liquid by increasing the electrostatic repulsion between the particles, and the layered structure of rectorite can evenly distribute the solid particles in the core coating while improving the adhesion of the core coating. Octylphenol polyoxyethylene ether is used as a surfactant to reduce the surface tension of the core coating, and n-octanol defoamer is added at the same time.

[0015] The preparation method of the core coating for aluminum alloy castings described in the present invention consists of the following steps:

[0016] (1) Grind pyrophyllite, fayalite, zircon powder, calcium titanate, magnesite, cryolite, phosphorus pentoxide, sodium pyrophosphate, and rectorite, and pass through a 1500-mesh sieve to prepare a first mixture;

[0017] (2) Mix octylphenol polyoxyethylene ether and water evenly, and then add the first mixture prepared in step (1), and continuously stir and mix for 65 - 70 min to prepare a second mixture;

[0018] (3) Add n - octanol to the second mixture prepared in step (2), and continuously stir and mix for 40 - 45 min to prepare a core coating for aluminum alloy castings.

[0019] Wherein:

[0020] In step (2), the stirring speed is 500 - 550 r / min.

[0021] In step (3), the stirring speed is 1000 - 1100 r / min.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The core coating for aluminum alloy castings of the present invention uses a mixture of pyrophyllite, fayalite, zircon powder, calcium titanate, magnesite, cryolite and phosphorus pentoxide as refractory materials, water as a carrier liquid, a mixture of sodium pyrophosphate and rectorite as a suspending agent, and at the same time adds n - octanol defoamer and octylphenol polyoxyethylene ether surfactant. The synergistic effect between the raw materials ensures that the prepared core coating has good resistance to metal liquid erosion, anti - sintering property and thermal stability during application, so that the core coating has excellent stripping strength and refractoriness.

[0024] (2) The preparation method of the core coating for aluminum alloy castings of the present invention has a simple production process, is easy to operate, has high production efficiency, high finished product quality and stable comprehensive performance. Specific Embodiments

[0025] The following further describes the present invention in conjunction with embodiments.

[0026] Example 1

[0027] The core coating for aluminum alloy castings described in Example 1 of the present invention is composed of the following raw materials in parts by weight: 23 parts of pyrophyllite, 12 parts of fayalite, 7.4 parts of zircon powder, 3.3 parts of magnesite, 5.3 parts of calcium titanate, 4.8 parts of cryolite, 1.6 parts of phosphorus pentoxide, 2.7 parts of sodium pyrophosphate, 3.3 parts of rectorite, 0.20 parts of octylphenol polyoxyethylene ether, 0.36 parts of n - octanol, and 25 parts of water.

[0028] Wherein:

[0029] The pyrophyllite described above, in terms of mass percentage, has the following chemical composition: MgO 0.76%, CaO 2.13%, Al2O3 15.89%, SiO2 76.37%, Fe2O3 0.41%, P2O5 0.67%, K2O 0.36%, Na2O 0.05%, and the loss on ignition is 3.36%.

[0030] The fayalite described above, in terms of mass percentage, has the following chemical composition: FeO 67.59%, SiO2 24.52%, MgO 2.54%, Al2O3 0.21%, TiO2 0.03%, CaO 0.32%, K2O 0.03%, Na2O 0.02%, P2O5 0.01%, and the loss on ignition is 4.73%.

[0031] The magnesia described above, in terms of mass percentage, has the following chemical composition: SiO2 9.32%, Al2O3 1.45%, MgO 72.65%, Fe2O3 0.58%, CaO 5.32%, SO3 0.12%, and the loss on ignition is 10.56%.

[0032] The preparation method of the sand core coating for aluminum alloy castings described in Example 1 consists of the following steps:

[0033] (1) Grind pyrophyllite, fayalite, zircon powder, calcium titanate, magnesia, cryolite, phosphorus pentoxide, sodium pyrophosphate, and rectorite, and pass through a 1500-mesh sieve to prepare a first mixture;

[0034] (2) Mix octylphenol polyoxyethylene ether and water evenly, then add the first mixture prepared in step (1), and continuously stir and mix for 65 min to prepare a second mixture;

[0035] (3) Add n-octanol to the second mixture prepared in step (2), and continuously stir and mix for 43 min to prepare the sand core coating for aluminum alloy castings.

[0036] Wherein:

[0037] The stirring speed in step (2) is 525 r / min.

[0038] The stirring speed in step (3) is 1050 r / min.

[0039] Example 2

[0040] The sand core coating for aluminum alloy castings described in Example 2 is composed of the following raw materials in parts by weight: 24 parts of pyrophyllite, 11 parts of fayalite, 7.2 parts of zircon powder, 3.4 parts of magnesite, 5.1 parts of calcium titanate, 5.2 parts of cryolite, 1.5 parts of phosphorus pentoxide, 2.6 parts of sodium pyrophosphate, 3.5 parts of rectorite, 0.18 part of octylphenol polyoxyethylene ether, 0.37 part of n-octanol, and 26 parts of water.

[0041] Among them:

[0042] The pyrophyllite described above, in terms of mass percentage, has the following chemical composition: MgO 0.76%, CaO 2.13%, Al2O3 15.89%, SiO2 76.37%, Fe2O3 0.41%, P2O5 0.67%, K2O 0.36%, Na2O 0.05%, and the loss on ignition is 3.36%.

[0043] The fayalite described above, in terms of mass percentage, has the following chemical composition: FeO 67.59%, SiO2 24.52%, MgO 2.54%, Al2O3 0.21%, TiO2 0.03%, CaO 0.32%, K2O 0.03%, Na2O 0.02%, P2O5 0.01%, and the loss on ignition is 4.73%.

[0044] The magnesite described above, in terms of mass percentage, has the following chemical composition: SiO2 9.32%, Al2O3 1.45%, MgO 72.65%, Fe2O3 0.58%, CaO 5.32%, SO3 0.12%, and the loss on ignition is 10.56%.

[0045] The preparation method of the sand core coating for aluminum alloy castings described in Example 2 consists of the following steps:

[0046] (1) Grind pyrophyllite, fayalite, zircon powder, calcium titanate, magnesite, cryolite, phosphorus pentoxide, sodium pyrophosphate, and rectorite, and pass through a 1500-mesh sieve to prepare a first mixture.

[0047] (2) Mix octylphenol polyoxyethylene ether and water evenly, then add the first mixture prepared in step (1), and continuously stir and mix for 70 min to prepare a second mixture.

[0048] (3) Add n-octanol to the second mixture prepared in step (2), and continuously stir and mix for 40 min to prepare the sand core coating for aluminum alloy castings.

[0049] Among them:

[0050] The stirring speed in step (2) is 500 r / min.

[0051] In step (3), the stirring speed is 1100 r / min.

[0052] Example 3

[0053] The core coating for aluminum alloy castings described in this Example 3 is composed of the following raw materials in parts by weight: 22 parts of pyrophyllite, 13 parts of fayalite, 7.6 parts of zircon powder, 3.1 parts of magnesia, 5.5 parts of calcium titanate, 4.3 parts of cryolite, 1.7 parts of phosphorus pentoxide, 2.8 parts of sodium pyrophosphate, 3.2 parts of rectorite, 0.21 part of octylphenol polyoxyethylene ether, 0.35 part of n-octanol, and 24 parts of water.

[0054] Among them:

[0055] The pyrophyllite described has the following chemical composition in mass percentage: MgO 0.76%, CaO 2.13%, Al2O3 15.89%, SiO2 76.37%, Fe2O3 0.41%, P2O5 0.67%, K2O 0.36%, Na2O 0.05%, and the loss on ignition is 3.36%.

[0056] The fayalite described has the following chemical composition in mass percentage: FeO 67.59%, SiO2 24.52%, MgO 2.54%, Al2O3 0.21%, TiO2 0.03%, CaO 0.32%, K2O 0.03%, Na2O 0.02%, P2O5 0.01%, and the loss on ignition is 4.73%.

[0057] The magnesia described has the following chemical composition in mass percentage: SiO2 9.32%, Al2O3 1.45%, MgO 72.65%, Fe2O3 0.58%, CaO 5.32%, SO3 0.12%, and the loss on ignition is 10.56%.

[0058] The preparation method of the core coating for aluminum alloy castings described in this Example 3 consists of the following steps:

[0059] (1) Grind pyrophyllite, fayalite, zircon powder, calcium titanate, magnesia, cryolite, phosphorus pentoxide, sodium pyrophosphate, and rectorite, and pass through a 1500-mesh sieve to prepare a first mixture.

[0060] (2) Mix octylphenol polyoxyethylene ether and water evenly, then add the first mixture prepared in step (1), and continuously stir and mix for 65 min to prepare a second mixture.

[0061] (3) Add n-octanol to the second mixture prepared in step (2), and continuously stir and mix for 45 min to prepare the core coating for aluminum alloy castings.

[0062] Wherein:

[0063] The stirring speed in step (2) is 550 r / min.

[0064] The stirring speed in step (3) is 1000 r / min.

[0065] Comparative Example 1

[0066] The preparation method of the sand core coating for aluminum alloy castings described in this Comparative Example 1 is the same as that of Example 1, and the only difference lies in the raw material composition. The sand core coating for aluminum alloy castings described in this Comparative Example 1 is composed of the following raw materials in parts by weight: 12 parts of fayalite, 7.4 parts of zircon powder, 3.3 parts of magnesia, 5.3 parts of calcium titanate, 4.8 parts of cryolite, 1.6 parts of phosphorus pentoxide, 2.7 parts of sodium pyrophosphate, 3.3 parts of rectorite, 0.20 part of octylphenol polyoxyethylene ether, 0.36 part of n-octanol, and 25 parts of water.

[0067] Comparative Example 2

[0068] The preparation method of the sand core coating for aluminum alloy castings described in this Comparative Example 2 is the same as that of Example 1, and the only difference lies in the raw material composition. The sand core coating for aluminum alloy castings described in this Comparative Example 2 is composed of the following raw materials in parts by weight: 23 parts of pyrophyllite, 7.4 parts of zircon powder, 3.3 parts of magnesia, 5.3 parts of calcium titanate, 4.8 parts of cryolite, 1.6 parts of phosphorus pentoxide, 2.7 parts of sodium pyrophosphate, 3.3 parts of rectorite, 0.20 part of octylphenol polyoxyethylene ether, 0.36 part of n-octanol, and 25 parts of water.

[0069] Comparative Example 3

[0070] The preparation method of the sand core coating for aluminum alloy castings described in this Comparative Example 3 is the same as that of Example 1, and the only difference lies in the raw material composition. The sand core coating for aluminum alloy castings described in this Comparative Example 3 is composed of the following raw materials in parts by weight: 23 parts of pyrophyllite, 12 parts of fayalite, 4.8 parts of cryolite, 1.6 parts of phosphorus pentoxide, 2.7 parts of sodium pyrophosphate, 3.3 parts of rectorite, 0.20 part of octylphenol polyoxyethylene ether, 0.36 part of n-octanol, and 25 parts of water.

[0071] Add 100 Kg of the core coatings prepared in Examples 1-3 and Comparative Examples 1-3 to a coating mixer, then add 25 kg of pure water, and stir well for 30 minutes. Then, pass the uniformly stirred core coating through an 80-mesh filter screen and pour it into a coating dipping pool. Control the Baume degree at 38. Immerse the core into the core coating dipping pool and stay for 4 seconds. The core coating is uniformly dipped on the surface of the core, and the coating is uniform. Place the core in a drying furnace for drying and then carry out low-pressure casting of aluminum alloy. Perform performance tests on the core coatings prepared in Examples 1-3 and Comparative Examples 1-3, and the results are shown in Table 1 below:

[0072] Table 1 Performance test results of the core coatings prepared in Examples 1-3 and Comparative Examples 1-3

[0073]

[0074] From the data recorded in Table 1, it can be seen that the core coating for aluminum alloy castings prepared by the present invention has excellent stripping strength and refractoriness, and its application can ensure the internal quality of the castings. Thus, it can be reflected from the side that the core coating prepared by the present invention has excellent resistance to metal liquid erosion, anti-adhesion to sand, and stability.

Claims

1. A sand core coating for aluminum alloy castings, characterized in that: The invention is composed of the following raw materials in parts by weight: 22-24 parts of pyrophyllite, 11-13 parts of fayalite, 7.2-7.6 parts of zircon powder, 3.1-3.4 parts of magnesia, 5.1-5.5 parts of calcium titanate, 4.3-5.2 parts of cryolite, 1.5-1.7 parts of phosphorus pentoxide, 2.6-2.8 parts of sodium pyrophosphate, 3.2-3.5 parts of rectorite, 0.18-0.21 parts of octylphenol polyoxyethylene ether, 0.35-0.37 parts of n-octanol, and 24-26 parts of water; in: The chemical composition of the pyrophyllite is as follows, in terms of mass percentage: MgO 0.76%, CaO 2.13%, Al2O315.89%, SiO2 76.37%, Fe2O3 0.41%, P2O5 0.67%, K2O 0.36%, Na2O 0.05%, and the loss on ignition is 3.36%; The chemical composition of the fayalite, in terms of mass percentage, is as follows: FeO 67.59%, SiO2 24.52%, MgO2.54%, Al2O3 0.21%, TiO2 0.03%, CaO 0.32%, K2O 0.03%, Na2O 0.02%, P2O50.01%, and the loss on ignition is 4.73%; The preparation method of the sand core coating for aluminum alloy castings comprises the following steps: (1) grinding pyrophyllite, fayalite, zircon powder, calcium titanate, magnesia, cryolite, phosphorus pentoxide, sodium pyrophosphate and rectorite, and passing the mixture through a 1500-mesh sieve to prepare a first mixture; (2) mixing octylphenol polyoxyethylene ether and water, then adding the first mixture prepared in step (1), and continuously stirring and mixing for 65-70 minutes to prepare a second mixture; (3) Add n-octanol to the second mixture prepared in step (2), and continue stirring and mixing for 40-45 minutes to prepare a sand core coating for aluminum alloy castings.

2. The sand core coating for aluminum alloy castings according to claim 1, characterized in that: The chemical composition of the magnesia is as follows, in terms of mass percentage: SiO2 9.32%, Al2O3 1.45%, MgO 72.65%, Fe2O3 0.58%, CaO 5.32%, SO3 0.12%, and the loss on ignition is 10.56%.

3. The sand core coating for aluminum alloy castings according to claim 1, characterized in that: The invention is composed of the following raw materials in parts by weight: 23 parts of pyrophyllite, 12 parts of fayalite, 7.4 parts of zircon powder, 3.3 parts of magnesia, 5.3 parts of calcium titanate, 4.8 parts of cryolite, 1.6 parts of phosphorus pentoxide, 2.7 parts of sodium pyrophosphate, 3.3 parts of rectorite, 0.20 parts of octylphenol polyoxyethylene ether, 0.36 parts of n-octanol and 25 parts of water.

4. A method for preparing the sand core coating for aluminum alloy castings according to claim 1.

5. The method for preparing a sand core coating for aluminum alloy castings according to claim 4, characterized in that: The stirring speed in step (2) is 500-550 r / min.

6. The method for preparing a sand core coating for aluminum alloy castings according to claim 4, characterized in that: The stirring speed in step (3) is 1000-1100 r / min.

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