What you should know about abrasive wheels’ structure and markings
The term „structure” refers to the ratio between the grit and the bonding material, and between the bonding material and the amount of air between all grits. When it comes to the structure, we can divide abrasive wheels into two main groups: open wheel and dense wheel. Open wheel consists of many open spaces what allows particles to be removed very quickly from the wheel. This helps in prevention of loading of the wheel and causing burning on the workplace. By contrast, a dense wheel includes less air space and can be chosen for fine surface finishes. The amount of removed material is very small what would probably require the wheel to be redressed more often than the open wheel. The structure of abrasive wheels is presented by the numbers. Number 1 relates to the most dense structure, while 15 refers to the more open wheels. However, there should be added that this scale is not closed as in the future production requirements may dictate the increase in those numbers. Describing abrasive wheels, we should also mention some required certain markings that should be affixed to wheels. Based on such markings, the user is informed about the wheel format standards, and how it was constructed. Either letter “A” or “C” represents the type of abrasive used in the construction material of the wheel. “A” refers to Aluminum Oxide, and “C” represents Silicon Carbide. The number next to marks A and C represents the Grain size. The scale of sizes is as follows: numbers from 8 to 24 refer to coarse wheel, numbers from 30 to 60 refer to medium size wheel, numbers from 70 to 180 refer to fine size, and finally, the numbers from 220 to 600 are related to very fine size. There is another symbol you need to pay your attention to – one letter which represents the grade of wheel is ranged from A to Z when “A” refers to the softest wheels, and “Z” refers to the hardest ones.
Under those three symbols, you will find 2 other marks. The first one from the left refers to the density of the wheel. It will be number, which ranges from 1 to 10. The letter on the right side indicates the type of bond used to put all abrasive particles together. There are 5 possible letters which will represent types of bonds: V means vitrified, B means resinoid, R means rubber, E means shellac, S means silicate. In the other type of wheel all symbols might be presented in only one line. Some manufacturers add an extra letter “W” at the beginning. This is an optional item which is used to identify the type of abrasive wheel. Although it is not relevant, you may see it on some wheels. All aforementioned symbols usually appear on all wheels, but keep in mind that sometimes the symbol representing the density of wheel can be also not included. Before you decide on type of wheel, you should know what specific symbol placed on the wheel represents. Otherwise, you may damage your equipment and material that you cut or grind.