What does the IU of chromite sand products refer to?
The “IU” in chromium ore you mentioned usually refers to the “Index of Uniformity,” which translates to “uniformity index” in Chinese.
This is a very important quality indicator in the foundry industry, especially when using chromium ore as a molding material.
Detailed Explanation:
1. What does it measure? The IU value measures the uniformity of the chromite sand particle size distribution. It is not a simple average particle size, but rather reflects the degree to which the sand particles are concentrated within a certain major particle size range.
2. How is it calculated? The uniformity index is generally calculated as follows: IU = (A + B) / (A + B + C)
· A: The mass percentage of sand retained on the primary sieve. The primary sieve is the sieve with the highest concentration of sand after screening.
· B: The mass percentage of sand retained on the auxiliary sieves (front and back sieves). These are typically the sieves immediately above and below the primary sieve.
· C: The mass percentage of sand retained on the bottom pan and coarser and finer sieves (i.e., particles further away from the primary sieve).
3. The significance of the IU value:
· A higher IU value (closer to 1 or 100%) indicates a more uniform sand particle size and better concentration. This sand has a high bulk density and low porosity, resulting in high-strength sand molds. It also has relatively low but more uniform air permeability, resulting in a denser and smoother surface.
· A lower IU value indicates a more dispersed sand particle size distribution, with both coarse and fine particles. This sand has high porosity and good air permeability, but also low strength and potentially poor surface quality.
4. Application in Casting: Foundries select chromium ore sands with different IU values based on the requirements of different castings.
For large steel castings with extremely high surface quality requirements (such as turbine blades and pump casings), chromium ore sands with high IU values are generally selected to ensure a smooth surface and prevent mechanical sand sticking.
For castings where surface requirements are less stringent but good air permeability is required, sands with slightly lower IU values may be acceptable.