The precoated sand process is one of the mainstream technologies for manufacturing stainless steel precision castings. Featuring uniform grain size, excellent moldability and superior thermal stability, precoated sand delivers stainless steel castings with high dimensional accuracy, smooth surface, dense internal structure, as well as outstanding mechanical properties and corrosion resistance. It has been widely applied in automotive, machinery, chemical engineering, hardware, art casting and other fields. This article elaborates on its product characteristics, application scenarios and core production control points.

1. Core Characteristics

• High Precision and Superior Surface Quality

Precoated sand features fine and uniform grains, creating smooth mold cavities. The surface roughness of finished castings reaches Ra 6.3~Ra 12.5 μm with tight dimensional tolerances, which greatly reduces subsequent machining work and improves production efficiency.

• Dense Structure and Excellent Mechanical Properties

With good thermal stability, precoated sand provides a stable solidification environment for molten stainless steel. The castings gain uniform and dense internal structure, along with reliable strength, toughness and other mechanical properties.

• Strong Forming Capacity for Complex Structures

It is capable of producing parts with intricate inner cavities, multi-curved surfaces and irregular shapes. Rational combination of sand cores enables precise forming of highly complex designs.

• High Production Flexibility

The process allows easy parameter adjustment, suitable for both small-batch customized production and large-scale mass production. Molds and process parameters can be modified quickly to meet diverse order requirements and shorten production lead time.

2. Main Application Fields

• Automotive Industry

It is used to manufacture engine blocks, cylinder heads, intake manifolds, exhaust pipes, brake calipers and other key components. These parts demand high precision, structural strength, temperature resistance and corrosion resistance, all of which can be fully satisfied by stainless steel castings made via precoated sand process.

• General Machinery Manufacturing

The process is widely adopted for gears, pump bodies, impellers and other mechanical parts. For 304 stainless steel castings, accurate tooth profiles and inner cavity dimensions are guaranteed. Thanks to the excellent corrosion resistance of stainless steel, pump bodies and impellers can serve longer when exposed to corrosive fluids.

• Architectural & Furniture Hardware

It can produce door handles, hinges and other hardware products. The castings boast smooth surfaces and attractive appearance, combining corrosion resistance and wear resistance to meet both decorative and functional demands for construction and furniture.

• Pipe Fittings for Chemical & Water Treatment Systems

304 stainless steel elbows, tees and other pipe fittings for chemical and water supply & drainage systems are commonly produced by this process. The castings feature smooth inner walls and precise dimensions, which lower fluid resistance and ensure tight sealing and stable operation of pipeline systems.

• Art Castings

Stainless steel presents unique metallic luster. Combined with the outstanding detail reproduction capability of the precoated sand process, the technology is ideal for creating various art sculptures and decorative pieces, perfectly restoring sophisticated designs and surface details.

3. Key Production Control Points

• Chemical Composition Control of Stainless Steel

Taking commonly used 304 stainless steel as an example, the content of each alloy element shall be strictly controlled. Chromium is the core element for corrosion resistance; nickel improves toughness and corrosion resistance; excessive carbon content will impair corrosion resistance; molybdenum enhances resistance to reducing media; silicon and manganese help increase the strength, hardness and wear resistance of steel.

• Melting and Pouring Temperature Control

Melting stage: Initial melting temperature: 1550~1580℃; Refining temperature: 1600~1650℃; Tapping temperature: 1580~1620℃.

Pouring stage: The general pouring temperature ranges from 1520℃ to 1560℃. For thin-walled and intricately structured castings, the temperature is controlled at 1540~1560℃. For heavy-section castings, it is set between 1520℃ and 1540℃. Adjustments shall also be made according to the ambient temperature.

• Requirements for Precoated Sand Preparation

Raw materials: Refined natural silica sand is adopted as the main refractory material. Phenolic resin acts as the binder, hexamine as the curing agent, and calcium stearate as the lubricant. Special functional additives are added according to working conditions.

Preparation processes: There are three production methods for precoated sand: cold coating, warm coating and hot coating. Hot coating is currently the mainstream in the industry for superior sand quality and operational stability.

Xinda specializes in the R&D and production of high-quality phenolic resin for precoated sand, with products tailor-made for stainless steel precision casting:

✅ High strength & low addition rate: Excellent strength at both room and elevated temperatures; resin addition rate can be as low as 3% to cut production costs effectively.

✅ Low gas evolution & fewer defects: Stable and low gas emission greatly reduces blowholes and slag inclusions in stainless steel castings.

✅ Low thermal expansion & high precision: Low thermal expansion coefficient adapts to the high pouring temperature of molten stainless steel, ensuring precise dimensions and smooth surface of castings.

✅ Eco-friendly & low odor: Low free phenol content reduces irritant gas emission by 50%-60% during curing and improves the workshop environment.

✅ Fast curing & easy shakeout: Fast curing speed and good flowability facilitate efficient shakeout, perfectly suited for castings with complex inner cavities and thin walls.

Compatible with the hot coating process, Xinda precoated sand resin helps produce premium precoated sand, enabling large-scale production of stainless steel precision castings with high accuracy, fewer defects and lower costs.