Tech Talk
What is “Concentration”?
When a superabrasive grinding wheel is made there is an additional factor called concentration, which appears in no other abrasive system. It refers to the amount of abrasive per unit volume of usable wheel. Concentration numbers are typically in the range 30 to 175, 30 have only 1.32 carats/cm3 (22carats/in3) and 175 having 7.7 carats/cm3 (126 carats/in3). The grain size will affect the achievable concentration level, as it is easier to completely fill a space with many smaller particles as opposed to very large randomly shaped blocks.
The concentration of the selected grinding wheel is based upon the area of contact between the wheel and workpiece. A large area dictates a low concentration and a small area a high concentration. A rule of thumb to establish a concentration number is as follows: If the contact area between the grinding wheel and the workpiece is less than 15 mm2 (0.025 to 0.075 in2), then use a 75 concentration; and for larger areas use 50 and maybe as low as 30 concentration, particularly for materials like glass which are prone to chipping.
Unfortunately, the industry sees concentration as more of an economic factor than a technical one. Confusion also arises with respect to the meaning of 100 concentration which is often misinterpreted as 100 percent and the maximum concentration. This is not so. A concentration of 100 means that there are 4.4 carats of abrasive per cm3 (72 carats per in3).
