Application and Selection of Refractory Adhesive

1、 The core role of refractory adhesive
In precision casting, refractory adhesive is the key to shell forming and stability. Its functions include:
1. Bonding performance: Firmly bond refractory aggregates (such as zircon sand and corundum) to ensure that the shell does not collapse during high-temperature casting. For example, the ambient temperature bonding strength of silica sol adhesive can reach 1.8-2.2 MPa (data source: "Casting Technology" 2023), meeting the needs of most alloy casting.
2. Fire resistance matching: The adhesive needs to be compatible with the temperature of the metal melt. When casting high-temperature alloys (≥ 1500 ℃), the refractoriness of phosphate binders must be above 1650 ℃.
3. Process adaptability: It is necessary to consider demolding, breathability, and collapsibility. Water glass adhesive is widely used in aluminum alloy casting due to its low cost and good collapsibility, but its low fire resistance (about 1300 ℃) makes it unsuitable for high-temperature scenarios.
2、 Mainstream adhesive types and selection criteria
According to the requirements of precision casting, adhesives can be divided into three categories:
1. Inorganic adhesive
-Silica sol: a dispersion of nano-sized SiO ₂ particles with high bonding strength (2.0 MPa ± 0.2) and shell accuracy of CT6-CT7 levels (referring to ISO 8062), but with a long drying time (24-48 hours).
-Phosphate: Excellent high temperature resistance (1700 ℃), suitable for nickel based alloys, but requires the addition of curing agents (such as MgO), and the process is complex.
2. Organic adhesives
-Polyvinyl alcohol (PVA): environmentally friendly, but prone to decomposition at high temperatures (decomposition temperature of 200 ℃), only used for low-temperature casting.
3. Composite adhesive
-Silica sol aluminum sol hybrid system: Combining the high strength of silica sol and the fast drying characteristics of aluminum sol, the drying time is shortened to 8-12 hours (data source: "Precision Casting Engineering" 2022).
The selection criteria need to consider:
-Metal melt temperature (such as titanium alloy requiring ≥ 1600 ℃ adhesive);
-Surface quality requirements for castings (silica sol suitable for high smoothness parts with Ra ≤ 3.2 μ m);
-The production cost of water glass is 40% -50% lower than that of silica sol.