Water Glass Investment Casting Carbon Steel Valves

1. 介绍

水玻璃投资铸造 (also known as sodium silicate investment casting) is a precision casting technology that uses water glass as the binder for the shell, combined with refractory materials to form a high-strength mold, and then casts molten carbon steel to obtain complex-shaped valves.

Carbon steel valves, as core components in fluid conveying systems, are widely used in petroleum, 化学, 力量, municipal and other fields, and their manufacturing precision, structural integrity and corrosion resistance directly determine the safety and stability of industrial systems.

Compared with traditional sand casting and silica sol investment casting, water glass investment casting has the advantages of low cost, short production cycle, and strong adaptability to complex structures, making it the mainstream process for mass production of medium and low-precision carbon steel valves.

2. 什么是水玻璃投资铸造?

水玻璃投资铸造, 也称为 sodium silicate shell casting, 是一个 precision casting method widely used for manufacturing carbon steel valves.

The process is a multi-step, systematic operation designed to produce high-quality valve blanks with complex geometries and reliable mechanical properties.

Its core principle is to replicate the valve geometry using a fusible wax pattern, form a high-temperature resistant shell through successive coating and refractory layers, remove the wax to create a cavity, and finally cast molten carbon steel into the mold.

This technique integrates 尺寸精度, 表面质量, and adaptability to complex internal structures, making it suitable for medium- to high-performance valves in industrial and petrochemical applications.

Process Characteristics and Adaptability

Water glass investment casting has obvious technical advantages and application boundaries in the production of 碳钢 阀:

• Cost Advantage: The price of water glass is only 1/20-1/30 of that of silica sol, and the requirements for production environment (temperature and humidity) are not strict,
  which can reduce the production cost by 30-40% compared with silica sol investment casting.
  It is suitable for mass production of medium and low-end carbon steel valves.
• Adaptability to Complex Structures: Through the use of soluble cores, it can accurately form complex internal structures of valves such as curved flow channels, multi-stage cavities, and narrow sealing surfaces, which is difficult to achieve with traditional sand casting.
• 生产效率: The chemical hardening method of the back layer of the shell enables rapid hardening and establishes wet strength,
  with a shorter process cycle and higher production efficiency than silica sol investment casting, and the daily output of a single production line can reach thousands of valve blanks.
• 限制: The dimensional accuracy (IT11-IT13) 和表面饰面 (Ra6.3-12.5μm) of the castings are lower than those of silica sol investment casting,
  and the shell has poor air permeability, which is prone to defects such as porosity and sand sticking, requiring strict process control.

3. 材料选择: Carbon Steel Grades for Valves and Casting Suitability

The selection of carbon steel for water glass investment-cast valves must balance service requirements—such as pressure, 温度, and medium compatibility—with the 铸造性能 needed for the water glass process.

Different steel grades offer varying mechanical properties, 化学成分, and casting behaviors, making grade selection critical for both performance and manufacturability.

Core Carbon Steel Grades and Standards

The primary carbon steel grades used for valves conform to ASTM A216 和 GB/t 12229 标准, 和 WCB being the most widely applied.

Key characteristics of common grades are summarized below:

Casting Suitability for Water Glass Investment Casting

The water glass investment casting process imposes specific requirements on carbon steel grades to ensure successful filling, 凝固, and defect-free components.

The main considerations include 流动性, 收缩, and hot cracking susceptibility:

• 流动性: 等级喜欢 WCB 和 ZG280-520 exhibit good fluidity due to balanced carbon and manganese levels, allowing molten steel to fill narrow valve channels and sealing surfaces.
  WCA, with lower manganese content, shows slightly reduced fluidity, making it more suitable for simpler valve geometries. Proper control of pouring temperature is essential to avoid cold shuts or incomplete fills.
• 收缩: Carbon steel typically shrinks 4.5–5.5% 在凝固过程中. Since the water glass shell has low elasticity, risers must be carefully designed—typically 15–25% of the casting volume—to compensate for shrinkage and prevent cavities in critical areas like valve bodies and bonnets.
• Hot Cracking Tendency:WCC contains higher manganese content, which increases its susceptibility to hot cracking.
  Mitigation strategies include controlling cooling rates during solidification and designing smooth transition fillets in the valve geometry to reduce stress concentration.

4. Fundamental Principles and Process System of Water Glass Investment Casting

The water glass investment casting process for carbon steel valves is a multi-step systematic project, which mainly includes mold making, shell making, 脱瓦, 浇注, cleaning and heat treatment.

Its core principle is to use the fusible wax mold to replicate the valve structure, form a high-temperature resistant shell through multiple layers of coating and sanding, remove the wax mold by heating to form a cavity, and finally cast molten carbon steel to obtain the valve blank.

Core Process Flow and Key Parameters

The process flow of water glass investment casting carbon steel valves is highly standardized, and each link has strict parameter control to ensure the quality of the blank.

The key steps and technical parameters are as follows:

1. Wax Mold Preparation:

The wax mold is the basis for ensuring the dimensional accuracy of the valve. The commonly used mold material is a mixture of paraffin and low-molecular polyethylene wax, with a melting point of 52-56℃.

The injection parameters are strictly controlled: injection temperature 55-58℃, injection pressure 1-2MPa, holding time 3-5s, and standing time after injection 2-4h to eliminate internal stress of the wax mold.

For valves with complex internal flow channels, soluble cores (urea-sugar mixture, 比率 95:5) 使用, which can be dissolved and removed with water after shell making, avoiding the difficulty of core removal for complex structures.

2. Wax Mold Assembly (Tree Grouping):

The qualified wax molds are welded to the sprue cup in a reasonable arrangement, considering the convenience of coating, ventilation and drying, and sequential solidification during pouring.

The distance between wax molds is controlled to avoid mutual influence during shell making and pouring, and the welding temperature is based on the dark red color of the welding knife to prevent scalding the wax mold.

3. Shell Making:

This is the core link to ensure the strength and surface quality of the mold. The shell is composed of a surface layer, a transition layer and a back layer.

The surface layer and transition layer adopt a silica sol-water glass composite process to balance surface quality and cost: the surface layer uses silica sol and 300-mesh zircon powder (比率 1:3.65) to improve surface finish, and the back layer uses water glass and 200-mesh gangue powder to enhance shell strength.

The key parameters of shell making are: room temperature 25±2℃, surface layer humidity 50-60%, 浆液粘度 (surface layer 38±3s, transition layer 35±3s, measured by Jane’s No. 4 viscosity cup), and each layer of sanding is dried until the shell is hard before the next layer is applied.

4. 脱瓦:

The wax mold is removed by steam dewaxing, with steam pressure 0.6-0.8MPa and dewaxing time 15-20min.

The wax removal rate should be ≥98% to avoid residual wax in the cavity, which will cause carbon defects in the valve blank.

5. Roasting and Pouring:

The shell is roasted at 850-950℃ for 2-3h to remove moisture and residual carbon, and improve the high-temperature stability of the shell.

The pouring temperature of carbon steel (taking WCB as an example) is 1520-1560℃, and the pouring speed is controlled according to the wall thickness of the valve: 0.5-1.0m/s for thin-walled parts and 0.3-0.5m/s for thick-walled parts to avoid splashing and porosity.

6. 清洁和整理:

After the casting is cooled to room temperature, the shell is removed by sandblasting (aluminum oxide sand, 粒度 100-120 网), and then the sprue, riser and burrs are removed.

For the sealing surface and flow channel of the valve, further grinding and polishing are required to meet the dimensional accuracy requirements.

5. Post-Casting Treatment of Water Glass Investment Casting Carbon Steel Valves

After water glass investment casting, carbon steel valves require systematic post-casting treatments to ensure 维稳定性, optimized mechanical performance, 表面质量, and long-term service reliability.

Stress Relief and Heat Treatment

Heat treatment is essential to relieve 残余应力 caused by uneven cooling and solidification and to refine the 微观结构 for improved toughness, 延性, 和硬度.

Key treatments include:

Thermal Stress Relief

• 客观的: Reduce internal stresses from solidification and uneven cooling.
• 参数: 典型温度: 550–650°C for medium-carbon steels (例如。, WCB), 期间: 1-2小时, 然后冷却缓慢.
• 影响: Residual stresses are reduced by 30–50%, minimizing 翘曲, 失真, and dimensional deviation during machining or assembly.

标准化

• Procedure: Heating the casting above AC3 (~850–900°C) 其次是空气冷却.
• 目的: 完善谷物结构, homogenizes the microstructure, 改善韧性, and reduces brittleness.
• 应用: Especially important for high-carbon WCC valves, which are used in high-pressure or low-temperature applications where brittleness could lead to catastrophic failure.

淬火和回火

• Applicable Grades: High-carbon or specialized steels (例如。, WCC) requiring higher strength and hardness.
• 过程: Quenching followed by tempering to achieve a balance of high yield strength and ductility.
• Critical Considerations: Cooling rates must be carefully controlled, 特别是 complex valve geometries, 预防 cracking or distortion.

概括: Heat treatment ensures uniform mechanical properties, 压力缓解, and preparation for subsequent machining and surface finishing.

Surface Cleaning and Defect Removal

热处理后, 表面准备 ensures that the valve meets 尺寸, 密封, 和表面质量要求:

射击 / 砂砾爆破

• Removes residual sand, 氧化物, 和比例 from the casting surface.
• 提供 controlled surface roughness that enhances adhesion for coatings or paint.

Machining and Trimming

• Critical surfaces, 密封面, threaded holes, and flanges are machined to 严格的公差 using CNC or conventional milling.
• 确保 维度的准确性 and proper assembly fit.

Welding Repairs (如果需要)

• 大的 收缩腔, 吹孔, 或裂缝 may be repaired using TIG or MIG welding with compatible filler metals.
• Post-weld stress relief is mandatory to prevent localized distortion or stress concentrations.

This stage guarantees that valves are structurally sound and dimensionally ready for final finishing and coating.

Surface Protection and Coating

Carbon steel is susceptible to 腐蚀, especially in water, 蒸汽, 油, or mild chemical environments. Surface treatment protects the valve and extends service life.

Typical methods include:

Additional Notes:

• Surface treatments also enhance hydraulic performance, 减少湍流, and prevent 材料退化 in long-term service.
• Proper 表面准备 (打扫, blasting, 脱脂) is crucial for coating adhesion and corrosion resistance.

非破坏性测试 (NDT) and Functional Verification

Before final assembly, valves undergo comprehensive inspection 确保完整性和遵守设计规范:

• 超声测试 (UT): 检测内部裂纹, 空隙, 和夹杂物.
• 影像学测试 (X射线): Reveals porosity, 收缩腔, and hidden internal defects.
• 染料渗透剂测试 (pt): Detects surface cracks, particularly on sealing faces.
• Hydrostatic and pressure testing: Confirms leak-tightness and operational integrity under design pressure.

These inspections are critical for 高压, low-temperature, or corrosive-service valves, where failure can have serious safety and economic consequences.

6. Application Scenarios and Market Positioning

Water glass investment casting carbon steel valves, with their cost-effectiveness and process adaptability, occupy an important position in the industrial valve market, and their application scenarios are closely related to their performance and precision levels.

Main Application Fields

• Petroleum and Chemical Industry: Used in medium and low-pressure pipelines for oil, gas and chemical light oil conveying,
  such as gate valves, globe valves and check valves of ASTM A216 WCB material, suitable for working temperatures -29℃ to 427℃ and pressure Class 150-300.
• Power Industry: Used in circulating water systems, steam pipelines and auxiliary systems of thermal power plants,
  with WCB and ZG280-520 as the main materials, bearing medium pressure and medium temperature steam.
• Municipal Engineering: Used in water supply and drainage pipelines, heating pipelines and natural gas pipelines,
  with WCA and WCB valves as the main products, requiring low cost and reliable sealing performance.
• 通用机械: Used in hydraulic systems, cooling systems and fuel supply systems of machinery and equipment, suitable for valves with complex structures and small batches.

Market Positioning and Competitive Advantage

Compared with other casting processes, water glass investment casting carbon steel valves have a clear market positioning:

• Compared with Silica Sol Investment Casting: The cost is 30-40% 降低, but the precision is lower.
  It is suitable for medium and low-end valves with no strict requirements on surface finish, and occupies 60-70% of the medium and low-pressure valve market.
• Compared with Sand Casting: It has higher precision and better surface quality, can form complex structures,
  and is suitable for valves with high requirements on internal flow channels and sealing surfaces, gradually replacing sand casting in the medium-precision valve market.

7. Development Trends and Technological Innovations

With the increasing requirements of industrial systems for valve quality, efficiency and environmental protection,

water glass investment casting technology for carbon steel valves is constantly innovating, and the development trends are mainly reflected in the following aspects:

• Environmentally Friendly Binder Development: Develop low-modulus, low-toxicity water glass binders to replace traditional sodium silicate, reduce wastewater discharge and environmental pollution.
  同时, promote the recycling of waste sand and wax to improve resource utilization.
• Process Combination Optimization: Further optimize the silica sol-water glass composite process, improve the surface quality and dimensional accuracy of castings (reach IT10-IT12),
  and narrow the gap with silica sol investment casting, expanding the application in medium and high-end valves.
• Digital and Intelligent Production: Introduce digital simulation technology (such as CASTsoft) to simulate the pouring and solidification process, predict and eliminate defects in advance.
  Adopt automated production lines for wax injection, shell making and sandblasting to improve production efficiency and quality stability.
• Material Upgrade and Performance Improvement: Develop low-temperature and high-strength carbon steel grades to expand the application of water glass investment casting valves in low-temperature (-60℃) and high-pressure (班级 600) working conditions,
  and improve corrosion resistance through surface treatment (such as galvanizing and phosphating).

8. 结论

Water glass investment casting is a 可靠的, 精确的, and environmentally friendly method for producing carbon steel valves with complex geometries.

通过仔细控制 binder chemistry, shell construction, and thermal management, manufacturers can achieve high-quality valves with excellent mechanical performance, 维度的准确性, 和表面饰面.

With the development of environmentally friendly binders, digital simulation and intelligent production,

water glass investment casting carbon steel valves will further expand their application in medium and high-end industrial fields, and play a more important role in the safety and stability of industrial fluid systems.

常见问题解答

What is water glass investment casting?

Water glass investment casting is a precision casting process that uses a fusible wax mold coated with a water glass-based shell to create complex carbon steel valve shapes.

The wax is removed through dewaxing, and molten steel is poured into the cavity.

What are the typical carbon steel grades used for valves?

Common grades include WCB, WCA, WCC (ASTM A216) and ZG280–520 (GB/t 12229). Selection depends on pressure, 温度, and medium.

WCB is widely used for medium- and low-pressure applications, while WCC is suitable for high-pressure or low-temperature service.

How does water glass investment casting compare with silica sol casting?

Water glass casting is more cost-effective, has faster production cycles, and is suitable for medium- and low-end valves, while silica sol casting offers higher surface finish and dimensional accuracy, making it ideal for high-end valves.

What post-casting treatments are required?

Key treatments include: 压力缓解, normalizing or tempering, 加工, defect repair, surface cleaning, 和涂层 (环氧树脂, 粉末涂料, or e-coating) to ensure mechanical integrity, 耐腐蚀性, 和尺寸准确性.