Information About Grinding Wheels

In this article, under the grinding-operations and grinding category, we’ll share information about grinding wheels. We’ll cover topics like the types of grinding wheels, their hardness grades, and the meanings of the letters and numbers on grinding wheel labels.

Information About Grinding Wheels

In the grinding process, the method is to abrade the work surface with very small cutting grains to achieve a high degree of dimensional accuracy.  The cutting tools used to do this are called “grinding wheels.”  Grinding wheels are cutting tools made by bonding abrasive grains together with organic or inorganic bonding agents.

Grinding was done with natural stones even long before industrialization, for purposes such as sharpening cutting tools. However, since these hand- or foot-powered setups didn’t operate at very high speeds, the properties sought in a grinding stone didn’t need to vary much.

After industrialization, operating at high speeds, along with factors like the hardness of the material being ground and its ability to be cut, created the need to produce artificial grinding wheels with different properties.

Today, these artificial grinding wheels are used, produced by homogeneously combining abrasive grains with a bonding agent, then pressing them into a mold and firing them.

Types of Grinding Wheels

Natural Grinding Wheels:

Natural Corundum
Natural Diamond
Quartz

Artificial Grinding Wheels:

Aluminum oxide (Used for hardened materials and materials with high tensile strength. White in color)

Silicon carbide (Harder than aluminum oxide. Dark green – black color. Used for sintered carbide, cast iron, and low-tensile-strength materials.)

CBN – Cubic Boron Nitride (The second-hardest abrasive.
Uses special bonding materials. • Used for hardened steel and materials with high tensile strength.

Diamond Grinding Wheels (The hardest abrasive.
Same bonding material as CBN. Used for sintered carbide.

Beryllium oxide

What the Letters on Grinding Wheel Labels Mean

Grinding wheels are made up of 54% abrasive grains, 26% bonding material, and 20% pore space.

Grinding wheel labels carry a series of letters and numbers that describe the wheel’s properties. These convey information such as the wheel’s hardness, structure, the type of abrasive used, and the grain size.

In grinding, not every grinding wheel is suitable for grinding every material. We see that some wheels used in grinding are gray, some pink, some white, and some green. These vary in terms of grain size. (table above)

Hardness Grades of Grinding Wheels

Grade is not a measure of the hardness of the abrasive material itself, but a measure of the wheel’s overall durability. Hardness varies with how firmly the bond holds the abrasive grains together. It’s designated alphabetically, ranging from “E” to “Z.”

E = very soft grinding wheel Z = very hard grinding wheel

For example, the darker-colored wheel shown in the image above is harder than the white one. It can hold its shape for longer. However, its disadvantage is that it grinds hotter than a soft white wheel. Too much heat will weaken the steel. A soft wheel needs to be dressed more often with a dressing tool, but you’re less likely to burn the workpiece you’re grinding.

Grinding wheels carry information such as the wheel’s dimensions, maximum peripheral speed, and hardness, and these labels must not be removed.

Recommended peripheral speeds for different grinding operations (above)

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