Whilst Diamond is available both as a natural or man-made grit, CBN is a purely synthetic product.
In the synthetic production of abrasive grit, characteristics such as grit size, grit shape and structure can be controlled and influenced. This means that the specific demands of different grinding processes can be taken into consideration.
With the aid of "coating" (grit refinement), other grit characteristics can be created in addition to size, form and structure. As a result, the abrasive grit can be even more precisely designed to match the task.
Grit size / surface grades
Next to the abrasive grade, it is the grit size which largely determines the performance of the grinding wheel, the material removal rate, the efficiency of the grinding process and the ultimate quality of the surface. Guaranteeing perfect cutting capacity with predefined roughness ratio requires grit sizes with close calibration. This is achieved by screening or precision elutriation. The table below shows the FEPA standard grit sizes and other common grit designations and rated mesh widths.
Grit sizes - Diamond and CBN
Grinding tools made by DIAMETAL are all marked in compliance with FEPA* standards, with the grit size prefixed with a D (for diamond) and with B (for CBN), (D126 / B151).
For safety guidelines in the grinding process and other information on FEPA, take a look at the internet homepage at www.fepa-abrasives.org
It is the grit size which largely determines the material removal rate of grinding tools and, in particular, the surface quality of the workpiece. Normally, coarser grit sizes will achieve a higher removal rate, but usually at the expense of the surface quality. Conversely, finer grit sizes achieve better surface qualities, at the expense of abrasive performance. This contrast between performance on the one hand and surface quality on the other means that many grinding operations still need rough grinding followed by finish grinding.
The following table shows standard values in connection with grit size and surface quality. The values shown have been determined after cross-grinding (resulting in the best quality) which means that they indicate the best possible results.
Obtainable surface quality according to grinding grit size
Note: When using periphery wheels (flat, external, internal, creep feed grinding, etc.), the grit size selected should be 2 to 3 increments finer to achieve the surface values shown in the table.
Grit shape / structure / finishing (coating)
The quality of the grit has a decisive impact on the properties of the grinding tools. The grit shape, for instance, offers a wide spectrum of options, ranging from rather round and block-like grits (Fig. 1) to oblong, splinter-shaped grits (Fig. 2).
Within the various grit shapes, one also distinguishes between monocrystalline and polycrystalline grits. Whereas monocrystals (Fig. 1) are very tough and impact-resistant, polycrystals (Fig. 3) tend to split up.
During grinding, this splitting tendency keeps on generating new tips and cutting edges which can help to improve the life and the cutting performance of the grinding tool. This is usually referred to as "self-sharpening".
Finishing the grinding grits, also known as coating (Fig. 4), can enhance the anchoring power of the grits in the bond. Also, coated grits generate a thermal barrier between the bond and the grinding grit, which is advisable in some applications. These options gain in importance by the fact that diamond has an excellent thermal conductivity.
Thermal conductivity of diamond versus other materials
Ever since the company was founded, DIAMETAL has always used grit grades of the highest qualities offered by suppliers. Thanks to many years of development and trials involving the performance in use of a wide range of grit grades, we now have unmatched experience with innumerable grit types in the grinding process.
Solving specific customer problems is always a challenge for us which we are always ready to tackle.