Question

Describe the physical structure of bonded abrasives.

identifying what is grit number, bond strength, and porosity.

Answer 1

Physical structure of a bonded abrasive is important because it determines the grit geometry e.g. rake angle, clearance angle etc. Grits do not have a definite geometry unlike the cutting tool.

Rake angle can be positive, zero or negative ranging from 45° to -60°. Shear angle is generally low.

GRIT NO.-- The grit no. Is a indicator of the size of the grits. The larger the grit no. Smaller will be the grit size or we can say finer will be the grit. Finer grits have small material removal rate but give good surface finish. On the other hand coarse grit size ( small grit no.) give high material removal rate but produces rough surface.

BOND STRENGTH-- please note that a worn out grit must be pulled out from bond and make room for fresh grit (to avoid high force and temperatures). In grinding a wheel with weak bonds is called soft wheel which is used for hard workpieces. Wheel with strong bonds is called hard wheel which is used for soft materials. ( If you want the reason behind this please comment below the solution I will explain).

POROSITY-- Porosity is the space between the two grits. A structure having high porosity is called open structure and with low porosity is called dense structure.

Space between two grit serves as a pocket for holding the lubricant and the chips produced during machining.

In addition to your knowledge I also want to add that coarse grain size+open structure wheel is used for stock removal grinding.