The Structure or Porosity of Vitrified-Bonded Grinding Wheels

These are microscope photographs of a range of structures, all using a grit size of 60 mesh.

Photograph 1:
This type of structure is called "dense" because the grains lie closely side-by-side, held together directly with the bond. The small hollow spaces remaining in between result in a very fine structure or porosity. However, the total content of spaces in relation to the volume of the grinding wheel should not be underestimated, since it can certainly be very large. Grinding wheels with such a structure are not suitable for high material removal rates. The free space needed to accommodate a high material removal (long and/or thick chips) does not exist here. This structure is therefore mainly used for grinding work where accuracy and surface quality are important, and not so much the mateial removal rate.

Photograph 2:
The medium structure shown in photograph 2 has a wide field of use. It can be used for fair removal rates and produces good surface finish at the same time. Furthermore, it has the advantage over the dense structure of being able to accommodate considerably more chips in the hollow spaces available and – with correct feed – can transport significantly more coolant emulsion into the contact zone. It is therefore suitable for creep feed grinding if a good edge consistency (e.g. profiles with very small radii) is required.