Sodium silicate casting process

Abstract

The invention discloses a water glass casting process, which belongs to the technical field of precision casting, and comprises the following steps: (1) wax material preparation; (2) manufacturing a wax mold; (3) preparing a coating; (4) shell making; (5) dewaxing with hot water; and (6) roasting the mold shell. Through a layered composite hardening process (the first 2-3 layers of ammonium chloride are hardened, and the subsequent layer of crystallized aluminum chloride or magnesium chloride is hardened) and differentiated sanding (the surface layer of 70-mesh quartz sand and the reinforcing layer of 20-mesh bauxite sand), the high-temperature strength of the shell is improved by more than 40%, and the deformation resistance is superior to that of a traditional single hardening agent process. The overall thickness of the shell is larger than or equal to 8 mm, the cracking risk of the shell in the pouring process is effectively reduced, and the mold is especially suitable for large-size complex castings.

Description

Technical Field

[0001] The invention belongs to the technical field of precision casting, and in particular relates to a water glass casting process. Background Art

[0002] Precision casting technology, as the core process for forming complex metal components, is irreplaceable in the fields of aero-engines, gas turbines, and high-end equipment manufacturing. Although the traditional silica sol-water glass composite shell process is widely used, it still has significant technical bottlenecks in actual production: the shell's room temperature strength and high temperature strength are unbalanced, and creep deformation is prone to occur when pouring large-sized castings. Especially for castings with larger sizes or complex structures, the shell has a higher risk of cracking; the wax mold preparation process is not completely purified due to the recycled wax, resulting in a low wax reuse rate, and the fixed proportion of stearic acid addition is prone to seasonal shrinkage defects; the coating system mostly uses a single hardener, and the liquid-to-powder ratio is roughly controlled, resulting in insufficient coating density and weak moisture absorption resistance, which is prone to metal liquid penetration defects during pouring; the dewaxing process is generally time-consuming, and residual wax easily blocks the shell pores, resulting in increased porosity of the casting; the roasting process and the pouring sequence lack coordinated control, and the shell is exposed for too long after leaving the furnace, which can easily lead to strength decay, seriously affecting the dimensional accuracy of the casting. The existing process system can no longer meet the precision casting needs of complex thin-walled components and large-size structural parts in aerospace, and it is urgently necessary to achieve technological breakthroughs through material modification, process parameter optimization and coordinated process control. Summary of the Invention

[0003] The present invention aims to provide an optimized water glass casting process to address existing problems such as insufficient shell strength, low wax pattern precision, and high production costs. This process significantly improves shell performance and casting quality by dynamically adjusting the wax-to-wax ratio, optimizing the coating and hardener combination in layers, and precisely controlling dewaxing and firing conditions.

[0004] The present invention is achieved through the following technical solutions: A water glass casting process, characterized by comprising the following steps: (1) Wax preparation Mix 50% to 95% recycled wax, 5% to 50% paraffin wax, and 5% to 50% stearic acid by mass percentage, heat to 70-90°C to melt to form wax liquid, stir to a wax paste, control the wax paste temperature at 45-48°C, and filter impurities through a 100-mesh sieve; Dynamic ratio adjustment: Stearic acid content is adjusted according to the season (the lower limit is taken in winter and the upper limit is taken in summer); Recovered wax treatment: The recovered wax is treated with 3% to 6% sulfuric acid or hydrochloric acid boiling for 45 to 90 minutes, allowed to stand for 2 hours and then filtered, and the pH value of the acid water is adjusted to 6-7.

[0005] (2) Wax model manufacturing At room temperature of 16-28°C, die-cast the wax paste into the die at a pressure of 0.3-0.5 MPa, hold the pressure for 3-10 seconds, and demould after cooling; Wax mold quality requirements: smooth surface without shrinkage or cracks, tight welding between the sprue and the wax rod, minimum pressure head of the mold ≥90mm, and wax mold spacing ≥10mm.

[0006] (3) Coating configuration Mix water glass with a modulus of 3.1-3.6 and refractory powder (quartz powder, high alumina powder or bauxite powder) according to the liquid-to-powder ratio: Surface layer: liquid-to-powder ratio 1:1.10-1.30, using crystalline aluminum chloride hardener (modulus 3.2-3.6, density 1.26-1.28g / cm³); Reinforcement layer: liquid-to-powder ratio 1:1.20-1.50, using ammonium chloride hardener (modulus 3.1-3.4, density 1.30-1.32g / cm³); Additives: Add 0.05% by weight of JFC to adjust the coating viscosity to 20-65 seconds (cup flow method), and adjust it dynamically according to the room temperature (viscosity increases by 2-3 seconds when the room temperature is less than 8°C, and decreases by 2-3 seconds when the room temperature is greater than 30°C).

[0007] (4) Shell making Apply the paint in layers and sand: Surface layer: Sprinkle 70 mesh quartz sand, hardening time 12 to 15 minutes (hardening with aluminum chloride at room temperature); Reinforcement layer: Sprinkle 20 mesh bauxite sand or kaolin sand, hardening time 6 to 8 minutes (ammonium chloride hardening); Composite hardening: The first 2-3 layers are hardened with ammonium chloride, and the subsequent layers are switched to crystallized aluminum chloride or magnesium chloride hardening; Layer number rule: For castings weighing ≤0.4kg, four and a half layers are applied; for castings weighing 0.4-1.0kg, five and a half layers are applied; for castings weighing >1.0kg, six and a half layers are applied; the total shell thickness is ≥8mm.

[0008] (5) Hot water dewaxing Immerse the module in a 90-98°C dewaxing solution containing 1.0% HCl or 5%-10% NHCl with a pH of 1.0-1.5 for 15-25 minutes. Module storage: Storage time before dewaxing ≥ 24 hours, ammonium chloride hardened module storage time ≤ 3 days.

[0009] (6) Shell firing Firing at 890-900℃ for 60-90 minutes, the shell becomes white and transparent before being taken out of the furnace, and metal pouring is completed within 0.5 hours; Mold shell quality requirements: effective pressure head ≥80mm, pouring cup intact without breakage, mold shell with missing parts >1 / 3 will be scrapped.

[0010] Compared with the prior art, the present invention has the following advantages: Significantly Improved Mold Shell Strength: Through a layered composite hardening process (with 2-3 layers of ammonium chloride hardening followed by crystallized aluminum chloride or magnesium chloride hardening) and differentiated sanding (70-mesh quartz sand for the surface layer and 20-mesh bauxite sand for the reinforcement layer), the mold shell's high-temperature strength is increased by over 40%, and its deformation resistance is superior to that of traditional single-hardener processes. The total mold shell thickness is ≥8mm, effectively reducing the risk of mold shell cracking during casting, making it particularly suitable for large, complex castings.

[0011] 2. Improved wax model precision and recovery rate: Dynamic adjustment of the wax material ratio (recycled wax accounts for 50% to 95%, with stearic acid adjusted seasonally) ensures stable wax paste fluidity, a smooth wax model surface free of shrinkage and cracks, and dimensional accuracy reaching CT6. The recycled wax undergoes acid treatment (boiling purification with 3% to 6% sulfuric acid or hydrochloric acid), resulting in a recovery rate of ≥90%, a 20% to 30% improvement over traditional processes, significantly reducing raw material costs.

[0012] 3. Optimizing Coating Performance: High-modulus crystalline aluminum chloride (3.2-3.6) is used for the surface layer, and ammonium chloride (3.1-3.4) is used for the reinforcement layer. Combined with dynamic adjustment of the liquid-to-powder ratio (1:1.10-1.30 for the surface layer and 1:1.20-1.50 for the reinforcement layer), the coating density is improved and the shell's resistance to moisture absorption is enhanced. The coating viscosity is dynamically adjusted based on room temperature (increasing by 2-3 seconds when the room temperature is <8°C and decreasing by 2-3 seconds when the room temperature is >30°C), minimizing the impact of ambient temperature and humidity on coating quality and addressing the flaking problem associated with traditional coating processes.

[0013] 4. Dewaxing Efficiency and Mold Integrity: Using an acidic dewaxing solution (1.0% HCl or 5%-10% NHCl, pH 1.0-1.5) at 90-98°C, dewaxing time is shortened to 15-25 minutes, achieving a wax removal rate of ≥99%, preventing residual wax in the mold and casting defects. Molds should be stored for ≥24 hours before dewaxing (≤3 days for ammonium chloride-cured molds) to ensure full mold curing and minimize mold breakage during the dewaxing process.

[0014] 5. Synchronous management of firing and pouring: The mold shell is fired at 890-900°C for 60-90 minutes, and pouring is completed within 0.5 hours after exiting the furnace. This effectively prevents the mold shell from absorbing moisture and softening, avoiding the mold shell cracking caused by delayed pouring in traditional processes. The pouring cup is intact and unbroken, with an effective pressure head of ≥80mm, ensuring smooth metal filling and free of internal pores and shrinkage defects in the casting.

[0015] 6. Process Adaptability and Economy: The number of shell layers can be flexibly adjusted based on the unit weight of the casting (from four and a half to six and a half layers), covering a wide range of complex castings weighing 0.4-2.5 kg (such as turbocharger housings and aerospace components), with a yield rate of ≥97%. This reduces overall production costs by 25%-35%, making it particularly suitable for mass production of precision castings and possessing significant industrial application value. DETAILED DESCRIPTION

[0016] The following is a complete and organized investment casting process technology solution, including three optimized embodiments and their performance comparison data with existing technologies: Example 1: Small precision aluminum alloy casting (unit weight ≤ 0.4kg) (1) Wax preparation Formula: Paraffin 10% ± 0.2%, stearic acid 10% ± 0.1%, recycled wax 80% ± 0.5% (optimized ratio for winter) Melting process: Step heating: 60°C → 75°C (heating rate 3°C / min), magnetic stirring (300 rpm, 30 minutes) Wax paste state: needle penetration 45±3 (25℃), shrinkage 0.8% Recycled wax processing: Boil in 5% sulfuric acid for 60 minutes → Centrifugal removal (1500 rpm × 10 min) → Activated carbon adsorption → Ash content ≤ 0.1% (2) Wax model manufacturing Die casting parameters: Injection pressure 0.4MPa, injection speed 15cm³ / s, mold preheating 40±2℃ Cooling system: dual-channel water cooling (main channel 18℃±1℃, auxiliary channel 10℃±2℃) Quality inspection: Dimensional error ≤ 0.05mm, surface roughness Ra0.8μm, no sink marks (3) Coating configuration Surface layer: Water glass modulus 3.4, density 1.27g / cm³ Liquid-to-powder ratio 1:1.20 (quartz powder, 270 mesh), JFC wetting agent 0.05% Viscosity 50 seconds (cup flow method), coating method: rotary dip coating (15rpm, 8s) Reinforcement layer: Add nano-alumina (50nm, 0.1%), thermal expansion coefficient matching agent (silicon powder 2%) (4) Shell making process Layering parameters: 1st-2nd layer: ammonium chloride hardening (25℃, 8 minutes), quartz sand 70 mesh From the third layer onwards: Crystallized aluminum chloride hardening (room temperature, 12 minutes), bauxite sand 20 mesh Total number of layers: four and a half layers, shell thickness 6mm, bending strength 4.2MPa (5) Hot water dewaxing Dewaxing solution: 1.0% HCl (pH 1.2, 95°C), pulse pressure ±0.02 MPa Effect: Dewaxing time 20 minutes, wax recovery rate 98.7%, residual amount ≤ 0.08g / dm³ (6) Firing and pouring Calcination curve: Room temperature → 300°C (5°C / min, hold for 30 minutes) → 900°C (8°C / min, hold for 70 minutes) Pouring management: ZL102 aluminum alloy (720℃±10℃), vacuum assisted (-0.08MPa), pouring time ≤0.5 hours

[0017] Through nano-alumina reinforced coating and gradient filtration technology, the mold shell strength is increased to 4.2MPa, solving the casting deformation problem caused by the brittleness of the mold shell in traditional processes.

[0018] Example 2: Large stainless steel structure (unit weight > 1.0kg) (1) Wax preparation Formula: Recycled wax 95% ± 0.8%, paraffin 3% ± 0.2%, stearic acid 2% ± 0.1% (anti-deformation ratio in summer) Melting process: Melting at 82℃ → Magnetic stirring (400rpm, 40 minutes) → Penetration of wax paste 38±2 Recycled wax processing: Boil 6% hydrochloric acid for 90 minutes → Purify by stratification (pH 6.8) → Rinse with deionized water until neutral (2) Wax model manufacturing Die casting parameters: Injection pressure 0.5MPa, hold pressure 10 seconds, mold preheating 45℃ Cooling system: 15℃ circulating water cooling (flow rate 5L / min) Assembly process: Multi-point pouring system, wax mold spacing 15mm, mold head ≥100mm (3) Coating configuration Surface layer: Zircon powder (325 mesh, ZrO2>65%), OP-10 wetting agent 0.03% Viscosity 55 seconds, coating method: vacuum dipping (vacuum degree -0.05MPa) Reinforcement layer: Coal gangue powder (250 mesh), mixed hardening liquid (22% AlCl3·6H2O+9% NH4Cl) (4) Shell making process Layering parameters: 1st-3rd layer: ammonium chloride hardening (30℃, 10 minutes), zircon sand 60 mesh From the 4th layer onwards: Crystallized aluminum chloride hardening (room temperature, 15 minutes), kaolinite sand 16 mesh Total number of layers: six and a half layers, shell thickness 10mm, bending strength 6.8MPa (5) Hot water dewaxing Dewaxing solution: 8% NH4Cl (pH 1.5, 98°C), steam pressure 0.15 MPa Effect: dewaxing time 25 minutes, shell damage rate <0.1% (6) Firing and pouring Calcination curve: Calcination at 890℃ for 90 minutes, oxygen content ≤ 3%, heating rate 5℃ / min Pouring management: 304 stainless steel (1580℃), vacuum casting (CT6 grade precision)

[0019] The mixed hardening liquid (AlCl3+NH4Cl) makes the shell high temperature strength reach 6.8MPa. Combined with vacuum casting, it can solve the thermal cracking and shrinkage defects during the casting of large parts. Example 3: Complex porous aluminum alloy valve body (weight 0.6 kg) (1) Wax preparation Formula: Recycled wax 70% ± 1%, paraffin 20% ± 0.5%, stearic acid 10% ± 0.3% (optimized for low temperature fluidity) Melting process: Melting at 78°C → Ultrasonic dispersion (40kHz, 20 minutes) → Wax shrinkage rate 0.6% Recycled wax processing: 4% sulfuric acid treatment for 75 minutes → activated carbon adsorption → ash content ≤ 0.2% (2) Wax model manufacturing Die casting parameters: 0.45MPa holding pressure for 8 seconds, mold temperature 18℃, ethanol water solution cooling (12℃) Porous structure: The integrity rate of the area with a pore diameter of ≥0.3mm is 100%, and the surface roughness is Ra1.0μm (3) Coating configuration Surface layer: Quartz powder (300 mesh, SiO2>99%), JFC penetrant 0.04% Viscosity 48 seconds, coating method: ultrasonic assisted dip coating (28kHz) Reinforcement layer: Bauxite powder (220 mesh), magnesium chloride curing solution (concentration 18%) (4) Shell making process Layering parameters: 1st-2nd layer: ammonium chloride hardening (28℃, 7 minutes), quartz sand 80 mesh From the third layer onwards: magnesium chloride hardening (25°C, 10 minutes), bauxite sand 30 mesh Total number of layers: five and a half layers, shell thickness 8mm, air permeability ≥120cm³ / (cm²·min) (5) Hot water dewaxing Dewaxing solution: 5% NH4Cl (pH 1.3, 96°C), ultrasonic-assisted (28kHz) Effect: dewaxing time 18 minutes, pore permeability 100% (6) Firing and pouring Calcination curve: Calcination at 895℃ for 80 minutes, nitrogen protection (flow rate 10L / min) Pouring management: ZL101A aluminum alloy (720℃), low pressure casting (0.6MPa)

[0020] Ultrasonic-assisted dewaxing (28kHz) combined with nitrogen-protected calcination can achieve 100% integrity of the microporous structure and reduce the internal defect rate to below 0.7%.

[0021] In summary, through process innovation and parameter optimization, the comprehensive performance of Examples 1-3 is improved by 15% to 40% compared with traditional investment casting technology, and is suitable for high-requirement fields such as aerospace, automotive parts, etc.

[0022] The above description is only a preferred embodiment of the present invention, but the scope of implementation of the present invention is not limited to the embodiment shown. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which do not exceed the spirit covered by the description, should be within the scope of protection of the present invention.

Claims

1. A water glass casting process, characterized in that: The following steps are involved: (1) Preparation of wax material: Mix 50% to 95% recycled wax, 5% to 50% paraffin wax and 5% to 50% stearic acid by mass percentage, heat to 70-90°C to melt to form wax liquid, stir to a wax paste, control the wax paste temperature at 45-48°C, and filter impurities through a 100 mesh sieve; (2) Wax model manufacturing: At room temperature of 16-28°C, the wax paste is die-cast into the model at a pressure of 0.3-0.5 MPa, and the pressure is maintained for 3-10 seconds. After cooling, the wax model is demoulded. The surface of the wax model is smooth and free of shrinkage and cracks. (3) Coating configuration: Mix water glass with a modulus of 3.1-3.6 and refractory powder at a liquid-to-powder ratio of 1:1.10-1.50, add 0.05% by weight of JFC, and adjust the coating viscosity to 20-65 seconds (cup flow method). The surface layer uses crystalline aluminum chloride hardener with a modulus of 3.2-3.6 and a density of 1.26-1.28 g / cm³; the reinforcement layer uses ammonium chloride hardener with a modulus of 3.1-3.4 and a density of 1.30-1.32 g / cm³. (4) Shell making: Apply the coating layer by layer and sprinkle sand, sprinkle 70 mesh quartz sand on the surface layer, sprinkle 20 mesh bauxite sand or kaolin sand on the reinforcement layer, and treat each layer with hardener for 6 to 15 minutes in turn, and dry at 20-35°C; (5) Hot water dewaxing: Immerse the module in a dewaxing solution at 90-98°C. The dewaxing solution is 1.0% HCl or 5%-10% NHCl, with a pH of 1.0-1.

5. The dewaxing time is 15-25 minutes. (6) Mold shell firing: Fire at 890-900℃ for 60-90 minutes. The mold shell becomes white and transparent before being taken out of the furnace. Metal pouring is completed within 0.5 hours.

2. The water glass casting process according to claim 1, wherein: In the step (1), the amount of stearic acid added is dynamically adjusted according to the season: the lower limit of the ratio is taken in winter, and the upper limit is taken in summer.

3. The water glass casting process according to claim 1, wherein: In step (3), the hardener is a mixed solution containing 20% ​​to 24% AlCl3·6H2O and 8% to 10% NH4Cl, with a pH value of 2.0-2.5 and a density of 1.16-1.18 g / cm³.

4. The water glass casting process according to claim 1, wherein: In the step (4), the number of shell layers is selected according to the unit weight of the casting: if the unit weight is ≤ 0.4 kg, four and a half layers are applied; if the unit weight is 0.4-1.0 kg, five and a half layers are applied; if the unit weight is greater than 1.0 kg, six and a half layers are applied.

5. The water glass casting process according to claim 1, wherein: In the preparation of the wax material in step (1), the recovered wax needs to be treated with acid: sulfuric acid or hydrochloric acid is added at 3% to 6% of the mass of the wax material, and the wax is boiled for 45 to 90 minutes. After standing for 2 hours, it is filtered and the pH value of the acid water is adjusted to 6-7.

6. The water glass casting process according to claim 1, wherein: In the step (3), the viscosity of the coating is adjusted according to the room temperature: if the room temperature is less than 8°C, the viscosity of the surface layer increases by 2 to 3 seconds, and the viscosity of the reinforcement layer increases by 1 to 2 seconds; if the room temperature is greater than 30°C, the viscosity of the surface layer decreases by 2 to 3 seconds, and the viscosity of the reinforcement layer decreases by 1 to 2 seconds.

7. The water glass casting process according to claim 1, wherein: In the step (5), the storage time of the module before dewaxing is ≥ 24 hours, and the storage time of the ammonium chloride hardening module is ≤ 3 days.

8. The water glass casting process according to claim 1, wherein: In the step (4), ammonium chloride hardener is used for the first 2-3 layers of the shell, and crystalline aluminum chloride or magnesium chloride hardener is used for the subsequent layers.

9. The water glass casting process according to claim 1, wherein: In the wax mold assembly of step (2), the minimum pressure head of the mold is 90 mm, the wax mold spacing is ≥10 mm, and the inner gate and the wax rod are welded seamlessly.

10. The water glass casting process according to claim 1, characterized in that: After the shell of step (6) is fired, the effective pressure head is ≥80 mm, and the pouring cup is intact without any breakage.

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