Brown corundum （Brown Fused Alumina） is made of high-quality bauxite, anthracite, and iron filings. It is smelted at a high temperature of more than 2000 degrees in an electric arc. It is crushed and shaped by mechanical processing, and iron is removed by magnetic separation. It is sieved into various particle sizes. Brown fused alumina is of high density and hardness up to Mohs 9.0. The grains form a spherical shape. It is suitable for manufacturing vitrified abrasives, refined resin-boned abrasive tools, as well as grinding, polishing, sandblasting, precision casting, etc. It can also be used for manufacturing advanced refractory materials as a very important industrial raw material.
It is often divided to two type hardness when we talk about hardness of BFA. One is the bulk density (LPD) of brown corundum, and the other is the true density (specific gravity) of brown corundum. The two concepts are showing as below：
| BULK DENSITY |
| 1.53-1.99g/cm3, the bulk density of the abrasive is related to the abrasive particle size, particle size composition, variety, particle shape and other factors. Generally speaking, the bulk density of coarse-grained abrasives is higher than that of fine-grained abrasives, and the bulk density of mixed-grained abrasives is greater than that of single-grained abrasives. |
| TRUE DENSITY |
| 3.95-4.0/cm3, the particle density of the abrasive refers to the mass of the abrasive contained in the unit volume (excluding the volume of open pores). |
At present, there are several applications of brown fused alumina ：
l First-grade brown fused alumina grain for sandblasting
l Brown fused alumina for polishing
l Brown fused alumina sand for metal polishing and rust removal,
l Brown corundum for blasting on jeans,
l Brown corundum sand for hot drilling and rhinestones
l 100#-180# Brown corundum for manufacturing resin grinding wheel,
l Brown corundum abrasive for wear-resistant floor,
l Brown corundum for making coated abrasive tools such as strong abrasive belt,
l Micro powder brown corundum used as coating sand for foundry.
The bulk density of each type of sand is definitely different. The bulk density of brown corundum is closely related to the processing technology of abrasives, specifically:
l Brown fused alumina made with ball milling process is of low bulk density.
l The brown corundum produced by the ball milling process has a moderate bulk density,
l The brown corundum produced by Barmac machines has a higher bulk density,
l The particle shaped brown fused alumina produced by a special process has the highest packing density.
For different applications, customers need to choose brown corundum with appropriate technology according to their own product requirements. For the brown corundum abrasives used in the manufacture of coated abrasives and fixed abrasives, the quality of abrasives is mainly reflected in the two indicators of bulk density and toughness. These two indicators are related. The high bulk density results in high abrasive toughness, the particle size composition is easy to concentrate, and the produced abrasive products have better durability.
