What is Chromite Flour?
Chromite flour is a fine powder made by grinding chromite sand (which itself is made from the mineral chromite, or iron chromite). Its properties are derived from the source material:
Very high refractoriness (melting point >1900°C)
High thermal conductivity
Chemical inertness (resists reaction with molten metal, especially steel)
Neutral pH
These properties make it invaluable in several industrial applications, with its primary use being in foundries.
| PHYSICAL PROPERTIES(TYPICAL) | AVERAGE CHEMICAL COMPOSITION(TYPICAL) | ||
| PH | 7-9 | Cr2O3 | ≥46.0% |
| Color | Black | SiO2 | ≤1.0% |
| Acid Amount | ≤2m | Fe2O3 | ≤26.5% |
| Soil% | ≤0.1 | CaO | ≤0.30% |
| Bulk Density | 2.5-3.0g/cm3 | MgO | ≤10.0% |
| Specific Gravity | 4.0-4.8g/cm3 | Al2O3 | ≤15.5% |
| Moisture | ≤0.1% | P | ≤0.003% |
| Sintered temperature | ≥1800℃ | S | ≤0.003% |
| Free Acid | 0 | Cr/Fe | 1.55:1 |
| Filling density | 2.6g/cm3 | ||
| Melting temperature | ≥2180℃ | ||
| Size | Sieve | Passing%（GURANTEE ） | Passing%（test result） |
| 325# | 325#（45um） | ≥95% | ≥98.5% |
Primary Application: Foundry (Metal Casting) Coatings
This is the most significant and common use of chromite flour. It is used as the refractory aggregate in coatings (or paints) applied to sand molds and cores.
Why it’s used in coatings:
Prevents Metal Penetration & Burning-On: The fine particles create an extremely dense, impermeable barrier between the molten metal (especially steel) and the sand mold. This prevents the metal from seeping into the sand gaps, a defect known as “metal penetration” or “burning-on,” which makes castings difficult to clean.
Excellent Surface Finish: By creating a smooth, refractory barrier, it ensures the final casting has a very smooth surface finish, reducing costly and time-consuming post-casting cleaning and machining.
Chemical Inertness: Unlike silica sand, chromite flour does not react with the oxides in molten steel, preventing a severe casting defect called “chemical sand burn-on” or “silicate glaze,” which can ruin a casting surface.
High Refractoriness: It is ideal for casting high-temperature alloys, such as steel, manganese steel, and high-alloy steels, where other coating materials might break down.
How it’s used: The flour is mixed with a liquid carrier (water or alcohol), a binder (like bentonite, resin), and other suspending agents to create a slurry. This slurry is then sprayed or brushed onto the surface of sand molds and cores before casting.
Other Key Applications
Besides being the star ingredient in foundry coatings, chromite flour has other important uses:
1. Additive in Molding Sand:
It can be added in small percentages (2-5%) to silica sand mixes used with furan or phenolic urethane binders.
Purpose: This addition helps to control expansion defects (like veining and rat-tails) in iron and steel castings by improving the overall thermal properties of the mold.
2. Raw Material for Refractory Bricks:
Chromite flour is a key ingredient in the manufacture of basic refractory bricks (e.g., chromite bricks, chromite-magnesia bricks).
Purpose: These bricks line industrial furnaces, like cement kilns and ladles used in steelmaking, where their high refractoriness and resistance to corrosive slags are critical.
3. High-Temperature Ceramics:
While a more niche application, its properties make it suitable for certain specialized ceramic compositions that require thermal stability and inertness.