Abrasive grain based on melted spherical corundum

1. An abrasive grain consisting of:

a core of fused spherical corundum, wherein the fused spherical corundum is a porous spherical Al 2 O 3 body provided by back-filling a liquid melt with an air/water mixture;

fine-grained abrasive solid particles; and

at least one binder used to bind said fine-grained abrasive solid particles to said spherical corundum,

wherein the abrasive grain is characterized in that a thickness of a layer of said fine-grained abrasive solid particles ranges from 50 to 500 μm,

wherein the abrasive grain is characterized in that the contents of fine-grained abrasive solid particles amount to 20 to 40 wt.-percent, as relating to the overall solids content of the abrasive grain,

wherein the abrasive grain is characterized in that the abrasive grain has an open porosity of 10 to 30%, as well as a closed porosity of 60 to 90%, and a ratio of R of the overall porosity to the open porosity of 3 to 10, based on the following formula:

R

=

Porosity

open

+

Porosity

closed

Porosity

open

,

and

wherein the abrasive grain is characterized in that the abrasive grain has a bulk density of 0.5 to 1.0 kg/l.

2. The abrasive grain according to claim 1 , wherein the spherical corundum having has a medium diameter ranging from 0.05 to 5 mm.

3. The abrasive grain according to claim 1 , wherein the fine-grained abrasive solid particles have a medium diameter ranging between 0.1 and 100 μm.

4. The abrasive grain according to claim 1 , wherein the thickness of the layer ranges from 1/20 to ⅕ of the sphere's diameter.

5. The abrasive grain according to claim 4 , wherein the layer is 5 times to 100 times a medium particle-size of the fine-grained abrasive solid particles.

6. The abrasive grain according to claim 1 , wherein the abrasive grain shows a specific surface BET of 0.1 to 0.3 m 2 /g.

7. The abrasive grain according to claim 1 , wherein the binder is an inorganic siliceous or phosphatic binder.

8. The abrasive grain according to claim 1 , wherein the binder is an organic binder.

9. The abrasive grain according to claim 8 , wherein the quantity of binders, as related to the overall solids content, amounts from 0.05 to 5 wt.-percent.

10. The abrasive grain according to claim 9 , wherein the choice of fine-grained abrasive solid particles is selected from a group consisting of special fused aluminum oxide, standard corundum, semi-friable aluminum oxide, zirconic corundum, zirconic mullite, silicon carbide, diamond, and cubic boron nitride.

11. An abrasive grain consisting of:

a core of fused spherical corundum, wherein the fused spherical corundum is a porous spherical Al 2 O 3 body provided by back-filling a liquid melt with an air/water mixture;

a coating layer consisting of:

fine-grained abrasive solid particles;

at least one binder used to bind said fine-grained abrasive solid particles to said spherical corundum, and

additives from a group consisting of sinter additives, cement molders and active grinding substances, such as sulfides, carbonates, halogenides, and phosphates from the group of elements that consist of N, K, Li, Mg, Ca, Al, Mn, Cu, Sn, Fe, Ti, Sb, and Zn,

wherein the abrasive grain is characterized in that a thickness of the coating layer of said fine-grained abrasive solid particles ranges from 50 to 500 μm,

wherein the abrasive grain is characterized in that the contents of fine-grained abrasive solid particles amount to 20 to 40 wt.-percent, as relating to the overall solids content of the abrasive grain,

wherein the abrasive grain is characterized in that the abrasive grain has an open porosity of 10 to 30%, as well as a closed porosity of 60 to 90%, and a ratio of R of the overall porosity to the open porosity of 3 to 10, based on the following formula:

R

=

Porosity

open

+

Porosity

closed

Porosity

open

,

and

wherein the abrasive grain is characterized in that the abrasive grain has a bulk density of 0.5 to 1.0 kg/l.

12. The abrasive grain according to claim 11 , wherein the core consists of a hollow-sphere corundum from melted spherical corundum.

13. The abrasive grain according to claim 11 , wherein the core consists of porous spherical corundum from melted spherical corundum.

14. An abrasive grain according to claim 2 , wherein the fine-grained abrasive solid particles have a medium diameter ranging between 0.1 and 100 μm.

15. The abrasive grain according to claim 11 , wherein the thickness of the coating layer ranges from 1/20 to ⅕ of the sphere's diameter.

16. The abrasive grain according to claim 15 , wherein the coating layer is 5 times to 100 times the medium particle-size of the fine-grained abrasive solid particles.