Grit Size And Its Impact On The Grinding Process
Shop for sandpaper in the hardware store and you'll see a numbering system indicating roughness. A coarse 80 grit grade removes material quickly but leaves the surface rough while a fine 400 grit won't take much off but leaves a smooth finish.
Superabrasive grinding wheels are no different. The size or coarseness, of the grit is indicated numerically in the wheel identification code, and guides the user in how that particular wheel should be used. Diamond is available in grit sizes from 40 to 8,000 mesh while CBN comes in the range of 50 to 8,000 mesh. As with sandpaper, a smaller number signifies the abrasive particles are larger.
RELATING GRIT TO SIZE
Grit numbers are derived from mesh sizes, mesh being the standard way of grading powder. The general principle is that of sieving: the finer the mesh the smaller a particle must be to pass through the gaps between the wires. Mesh size is indicated in gaps per inch, so a mesh of 16 has 16 gaps per inch.
When referring to powders mesh size is actually shown by two numbers, such as 50/60. The first number is the sieve through which most of the powder grains would pass, and the second is the mesh size that traps most of the grains. For simplicity, in the superabrasives industry the grit number refers to the larger size mesh, the one through which most particles would pass, so powder with a mesh size of 50/60 is referred to as 50 grit.
On average, in a 50 grit powder the particles are around 300 microns or 0.011 inches in diameter. That's roughly the size of grains of beach sand, although it's important to note that sieving result s in a distribution of sizes and shapes.
IMPACT ON GRINDING PERFORMANCE
As with sandpaper, larger abrasive particles, (a smaller grit number,) remove material faster but leave a coarser finish. With a finer grit, (larger number,) each particle removes less material. The removal rate will be lower but the surface finish will be smoother.
Grit size only approximately correlates to surface finish: machine condition and the type of workpiece make a big difference. Grit size, concentration, bond type plus hardness, and the grinding process (machine, wheel speed, coolant, work-piece) all greatly impact the surface finish achieved. Our engineers take all of these factors into consideration when optimizing custom grinding tools for our clients. Contact CDT for engineered superabrasive grinding solutions.