A water-soluble core for investment precision casting and its preparation method

Abstract

The present invention provides a water-soluble core for investment precision casting and a preparation method thereof, belonging to the technical field of core materials. The present invention abandons the addition of inert materials such as talcum powder and quartz powder, and uses urea particles with a low particle size (≤0.5 mm) instead of the addition of inert materials, which can improve the water solubility and dissolution rate of the core while ensuring the surface quality of the core. The present invention uses urea particles, sodium bicarbonate and molten polyethylene glycol as raw materials for preparing the core. After dissolution, there is almost no residual material, and there is no need to spend a lot of time cleaning the inner cavity of the casting, which can improve the production efficiency of the product. During the dissolution process of the core, hydrochloric acid does not need to be added, and high-efficiency dissolution can also be achieved, simplifying the production process. At the same time, the present invention prepares the core by hot die casting. The obtained core has a high forming success rate, high bending strength, high surface quality, small shrinkage rate, good water solubility and fast disintegration speed.

Description

Technical Field

[0001] The present invention relates to the technical field of core materials, and particularly relates to a water-soluble core for investment precision casting and a preparation method thereof. Background Art

[0002] Water-soluble cores are applied to some precision castings such as automotive and aero-engine castings. There are many complex holes or cavities in precision castings that cannot be formed by mechanical machining methods. Among them, there are inner cavities with particularly complex shapes or without draft angles, and the inner cavities cannot be directly formed by mechanical core-pulling methods. Therefore, the water-soluble core process is used to form such inner cavities.

[0003] Currently, most water-soluble cores use urea as the main raw material. However, the surface roughness of the cores prepared by the urea water-soluble core formula is large, resulting in poor quality of the inner cavity of the casting, and it cannot be used for precision castings with complex inner cavity structures and high quality requirements.

[0004] To meet the usage requirements of precision castings, the current methods are as follows: ① Wu Jinzhang et al. used polyethylene glycol as a binder, added sodium bicarbonate and talcum powder and mixed them to make a core and put it into a hydrochloric acid solution of about 10%; ② Du Zhilong et al. used polyethylene glycol and materials such as urea and quartz powder with a size of 0.63 - 0.80 mm to prepare a new type of composite water-soluble core by hot pressing and casting.

[0005] However, in the formula of method ①, there is more talcum powder. Talcum powder is an inert material and is insoluble in water and hydrochloric acid solution. During the dissolution process of the core, talcum powder will cover the surface of the core, hindering the dissolution of polyethylene glycol, resulting in poor water solubility of the core. In method ②, quartz powder is an inert material and is insoluble in water, which will hinder the dissolution rate of the core. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a water-soluble core for investment precision casting and a preparation method thereof. The water-soluble core for investment precision casting provided by the present invention has good water solubility and high surface quality.

[0007] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0008] The present invention provides a preparation method of a water-soluble core for investment precision casting, including the following steps:

[0009] Mix urea particles, sodium bicarbonate and molten polyethylene glycol to obtain a water-soluble core slurry; the particle size of the urea particles ≤ 0.5 mm;

[0010] Perform hot pressing and casting on the water-soluble core slurry to obtain a water-soluble core for investment precision casting.

[0011] Preferably, based on mass percentage, the water-soluble core paste comprises:

[0012] Polyethylene glycol 30 - 40%;

[0013] Urea particles 30 - 40%;

[0014] Sodium bicarbonate 20 - 40%.

[0015] Preferably, the number-average molecular weight of the polyethylene glycol is 4000 - 8000.

[0016] Preferably, the particle size of the sodium bicarbonate is 10 - 100 μm.

[0017] Preferably, the melting temperature of the polyethylene glycol is 80 - 90 °C.

[0018] Preferably, during hot pressing injection molding, the temperature of the water-soluble core paste is 75 - 85 °C, and the temperature of the injection mold is 10 - 20 °C.

[0019] Preferably, during hot pressing injection molding, the injection flow rate is 20 - 100 cc / s, the injection pressure is 1 - 5 MPa, the injection time is 10 - 60 s, and the pressure holding time is 0.5 - 5 min.

[0020] Preferably, the mixing is as follows:

[0021] First, add sodium bicarbonate to the molten polyethylene glycol, and then add urea particles.

[0022] Preferably, before mixing, the urea particles and sodium bicarbonate are also dried; the drying temperature is 80 - 100 °C, and the time is ≥ 2 h.

[0023] The present invention provides a water-soluble core for investment casting prepared by the above preparation method, and the components are polyethylene glycol, urea particles and sodium bicarbonate.

[0024] The present invention provides a method for preparing a water-soluble core for investment casting, comprising the following steps: mixing urea particles, sodium bicarbonate and molten polyethylene glycol to obtain a water-soluble core slurry; the particle size of the urea particles is ≤0.5 mm; performing hot injection molding on the water-soluble core slurry to obtain a water-soluble core for investment casting. The present invention omits the addition of inert materials such as talcum powder and quartz powder, and uses urea particles with a low particle size (≤0.5 mm) instead of the addition of inert materials, which can improve the water solubility and dissolution rate of the core while ensuring the surface quality of the core. The present invention uses urea particles, sodium bicarbonate and molten polyethylene glycol as raw materials for core preparation, and there is almost no residual material after dissolution, so there is no need to spend a lot of time cleaning the inner cavity of the casting, which can speed up the production efficiency of the product. During the dissolution process of the core, hydrochloric acid does not need to be added, and high-efficiency dissolution can also be achieved, simplifying the production process. At the same time, the present invention prepares the core by hot die casting, and the obtained core has a high forming success rate, high bending strength, high surface quality, small shrinkage rate, good water solubility and fast collapsibility. The results of the examples show that the water dissolution rate of the water-soluble core for investment casting of the present invention is 0.484-0.682 g / min; the bending strength is 5.872-6.219 MPa, and the shrinkage rate is 0.103-0.147%. Description of the Drawings

[0025] Figure 1 It is a flow chart for the preparation of a water-soluble core for investment casting;

[0026] Figure 2 It is a physical diagram of the water-soluble core obtained in Example 1. Detailed Embodiments

[0027] The present invention provides a method for preparing a water-soluble core for investment casting, comprising the following steps:

[0028] Mix urea particles, sodium bicarbonate and molten polyethylene glycol to obtain a water-soluble core slurry; the particle size of the urea particles is ≤0.5 mm;

[0029] Perform hot injection molding on the water-soluble core slurry to obtain a water-soluble core for investment casting.

[0030] The present invention mixes urea particles, sodium bicarbonate and molten polyethylene glycol to obtain a water-soluble core slurry. In the present invention, in terms of mass percentage, the water-soluble core slurry preferably comprises 30-40% of molten polyethylene glycol, more preferably 35%. In the present invention, the number-average molecular weight of the polyethylene glycol is preferably 4000-8000, more preferably 5000-7000.

[0031] In the present invention, the melting temperature of the polyethylene glycol is preferably 80-90°C, more preferably 85°C.

[0032] In the present invention, by mass percentage, the water-soluble core paste preferably comprises 30-40% of urea particles, more preferably 35%. In the present invention, the particle size of the urea particles is ≤0.5 mm, preferably 0.1-0.5 mm, and further preferably 0.2-0.4 mm.

[0033] In the present invention, the preparation method of the urea particles preferably comprises the following steps:

[0034] Grind and sieve the urea raw material to obtain urea particles.

[0035] The present invention preferably uses a pulverizer for the grinding; in the present invention, the grinding time is preferably 3-10 s, more preferably 5-8 s. In the present invention, the sieving is preferably through a 32-mesh sieve, and the undersize is taken. The present invention uses a pulverizer to crush and selects particles below 0.5 mm, with a simpler process, no waste of urea, and can be applied to more complex water-soluble cores.

[0036] The present invention preferably dries the urea particles. In the present invention, the drying is preferably drying by baking; the drying temperature is preferably 80-100 °C, more preferably 90 °C; the time is preferably ≥2 h, more preferably 2-4 h.

[0037] In the present invention, by mass percentage, the water-soluble core paste preferably comprises 20-40% of sodium bicarbonate, more preferably 30%. In the present invention, the particle size of the sodium bicarbonate is preferably 10-100 μm, more preferably 30-60 μm. In the present invention, the function of the sodium bicarbonate is to reduce the use of polyethylene glycol, accelerate the solidification speed of the production of the water-soluble core, improve the toughness of the core, reduce shrinkage, and accelerate the dissolution speed of the core.

[0038] Before the mixing, the present invention preferably dries the sodium bicarbonate. In the present invention, the drying is preferably drying by baking; the drying temperature is preferably 80-100 °C, more preferably 90 °C; the time is preferably ≥2 h, more preferably 2-4 h.

[0039] In the present invention, the mixing is preferably: first add sodium bicarbonate to the molten polyethylene glycol, and then add urea particles. In the present invention, the sodium bicarbonate is preferably added in 3-5 batches, and after all the sodium bicarbonate is added, then add the urea particles. In the present invention, the urea particles are preferably added in 2-4 batches.

[0040] In the present invention, the mixing method is preferably stirring and mixing. In the present invention, the mixing time is preferably 1-2 h, more preferably 1.5 h.

[0041] After obtaining the water-soluble core paste, the present invention performs hot injection molding on the water-soluble core paste to obtain a water-soluble core for investment casting. The present invention preferably uses an injection molding machine for the hot injection molding. In the present invention, the water-soluble core paste is preferably loaded into the slurry barrel of the injection molding machine and then injected into a water-soluble core mold to form a water-soluble core.

[0042] In the present invention, the temperature of the water-soluble core paste during the hot injection molding is preferably 75 to 85 °C, more preferably 80 °C; the temperature of the injection mold is preferably 10 to 20 °C, more preferably 15 °C.

[0043] In the present invention, the injection flow rate during the hot injection molding is preferably 20 to 100 cc / s, more preferably 40 to 80 cc / s; the injection pressure is preferably 1 to 5 MPa, more preferably 2 to 4 MPa; the injection time is preferably 10 to 60 s, more preferably 20 to 40 s; the holding pressure time is preferably 0.5 to 5 min, more preferably 2 to 4 min.

[0044] After obtaining the water-soluble core for investment casting, the present invention preferably corrects the surface of the core. In the invention, the correction method is preferably trimming the burrs.

[0045] The preparation flow chart of the water-soluble core for investment casting of the present invention is as Figure 1 shown.

[0046] The present invention provides a water-soluble core for investment casting prepared by the above preparation method, which is composed of polyethylene glycol, urea particles and sodium bicarbonate. In the present invention, the water-soluble core for investment casting has good water solubility and good surface quality, and can be applied to the field of precision castings such as automobiles and aeroengines.

[0047] The following combines examples to detail the water-soluble core for investment casting and its preparation method provided by the present invention, but they cannot be understood as limiting the protection scope of the present invention.

[0048] Examples 1 to 4

[0049] The composition ratios of four different water-soluble core formulations are shown in Table 1.

[0050] Table 1 Composition ratios of four different water-soluble core formulations

[0051]

[0052] The preparation method of the water-soluble core is as follows:

[0053] The urea material is processed by grinding in a powder mill for 5 s to obtain urea particles with a particle size of ≤0.5 mm. The processed urea particles and sodium bicarbonate are put into a dryer, and the temperature is controlled at 80°C for 2 h of drying. Then polyethylene glycol is put into a stirring device, the temperature is controlled at 85°C, sodium bicarbonate and urea are added respectively, and stirred for 2 h. The water-soluble core is transferred to an injection molding machine, the temperature is controlled at 80°C, the mold temperature is controlled at 15°C, the injection flow rate is set at 60 cc / s, the injection pressure is 4 MPa, the injection time is 20 s, and the holding pressure time is 60 s.

[0054] The shrinkage rate, flexural strength and water solubility rate of the water-soluble cores obtained in Examples 1 to 4 are shown in Table 2. Among them, the specimen size for measuring the shrinkage rate is Φ5×100 mm, the specimen size for flexural strength is 4×10×60 mm, and the specimen size for water solubility rate is 10×10×50 mm, and it is dissolved at room temperature.

[0055] Among them, the test method for the core shrinkage rate: The cavity size D of the mold is Φ5×100 mm, the actual size D1 of the core after actual injection is measured, and the shrinkage rate &=(D - D1) / D is calculated. There are no less than 5 specimens, and then the average value is calculated.

[0056] The test method for the flexural strength of the core: HB 5353.3-2004.

[0057] The test method for the water solubility rate of the core: For the core specimen of 10×10×50 mm, the mass m of the specimen is weighed, put into water, the water temperature is controlled between 20 and 25°C, and the time t when the specimen is completely dissolved is recorded. The solubility is calculated as m / t. There are no less than 5 specimens, and then the average value is calculated.

[0058] Table 2 Shrinkage rate, flexural strength and water solubility rate of the water-soluble cores obtained in Examples 1 to 4

[0059]

[0060]

[0061] It can be seen that the water-soluble core obtained by the present invention has good water solubility, high surface quality, and has good mechanical properties and low shrinkage rate.

[0062] The physical diagram of the water-soluble core obtained in Example 1 is as Figure 2 shown, and the surface roughness measured by a surface roughness instrument is 1.3 μm. The surface roughness of the water-soluble cores obtained in other examples is similar.

[0063] Comparative Example 1

[0064] The difference from Example 3 is that only the size of urea particles is changed, and the particle size range of urea particles is between 0.85 and 2.80 mm. The preparation method and testing method of the water-soluble core are the same as above. The shrinkage rate of the obtained water-soluble core is measured to be 0.130%, the flexural strength is 4.469 MPa, and the water dissolution rate is 0.487 g / min.

[0065] Comparative Example 2

[0066] The difference from Example 3 is that the mass fraction of polyethylene glycol is 40%, the mass fraction of urea is 50%, and the mass fraction of sodium bicarbonate is 10%. The preparation method and testing method of the water-soluble core are the same as above. The shrinkage rate of the obtained water-soluble core is measured to be 0.118%, the flexural strength is 4.621 MPa, and the water solubility is 0.646 g / min. The injection products of the water-soluble core obtained in Comparative Example 2 are prone to surface defects and are not suitable for use.

[0067] Comparative Example 3

[0068] The difference from Example 3 is that the sodium bicarbonate is replaced with talcum powder of the same particle size. The preparation method and testing method of the water-soluble core are the same as above. The shrinkage rate of the obtained water-soluble core is measured to be 0.117%, the flexural strength is 6.025 MPa, and the water solubility is 0.131 g / min. Since talcum powder is insoluble in water, the dissolution rate efficiency of the obtained water-soluble core drops rapidly.

[0069] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a water-soluble core for investment casting, comprising the following steps: Mix urea particles, sodium bicarbonate and molten polyethylene glycol to obtain a water-soluble core slurry; the particle size of the urea particles is ≤ 0.5 mm; Perform hot injection molding on the water-soluble core slurry to obtain a water-soluble core for investment casting; By mass percentage, the water-soluble core slurry comprises: 30 - 40% of polyethylene glycol; 30 - 40% of urea particles; 20 - 40% of sodium bicarbonate.

2. The preparation method according to claim 1, wherein The number-average molecular weight of the polyethylene glycol is 4000 - 8000.

3. The preparation method according to claim 1, characterized in that, The particle size of the sodium bicarbonate is 10 - 100 μm.

4. The preparation method according to claim 1, wherein The melting temperature of the polyethylene glycol is 80 - 90 °C.

5. The preparation method according to claim 1, characterized in that, During the hot injection molding, the temperature of the water-soluble core slurry is 75 - 85 °C, and the temperature of the injection mold is 10 - 20 °C.

6. The preparation method according to claim 1 or 5, characterized in that, During the hot injection molding, the injection flow rate is 20 - 100 cc / s, the injection pressure is 1 - 5 MPa, the injection time is 10 - 60 s, and the pressure holding time is 0.5 - 5 min.

7. The preparation method according to claim 1, characterized in that, The mixing is as follows: First add sodium bicarbonate to the molten polyethylene glycol, and then add urea particles.

8. The preparation method according to claim 1 or 7, characterized in that, Before the mixing, it also includes drying the urea particles and sodium bicarbonate; the drying temperature is 80 - 100 °C, and the time is ≥ 2 h.

9. A water-soluble core for investment casting prepared by the preparation method according to any one of claims 1 - 8, the components of which are polyethylene glycol, urea particles and sodium bicarbonate.

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