What is a grinding wheel?
A grinding wheel is a precision tool with thousands of cutting points on its surface - abrasive grains that are held in place by a bond matrix (hence these are known as bonded abrasives) and separated by pores.
These pores are hollow spaces between abrasive grains and the bond, which help with the clearance of discarded metal chips in the grinding process.
When the wheel is in use, the abrasive grains cut into the material that is being ground, removing the unwanted surface material in small chips.
During grinding, the cutting points on the abrasive grains are worn flat, becoming increasingly blunt. At the same time, the increased friction causes a build-up of heat, which fractures the abrasive grain and exposes new cutting edges or begins to disintegrate the bond bridges that hold the abrasive grains in place.
In normal vitrified grinding, the wheel has to be dressed using a dressing tool. By varying the properties of the abrasive, the type of bond, the wheel’s construction, it is possible to produce grinding wheels with a vast range of different grinding characteristics.
What abrasives are available for grinding wheels?
There are 4 main types of abrasive grains available for grinding wheels, these are:
Ceramic Aluminum Oxide
Often referred to as just “Ceramic”, Norton Quantum’s patented ceramic form of aluminum oxide is harder and sharper than conventional abrasive grains.
This ceramic grain has a unique microcrystalline structure that is self-sharpening. This ultimately reduces the regularity that the grinding wheel needs dressing as well and providing a significantly cooler cutting action when in use.
Silicon Carbide
Harder than standard aluminum oxide with a very sharp abrasive grain. It is a versatile material, recommended for grinding relatively soft metals such as aluminum or cast iron but can also be used on extremely hard materials such as cemented carbide.
Zirconia Alumina
For use in rough grinding applications where high stock removal is required. This grain is associated with high tech resin bonds.
Aluminum Oxide
Generally recommended for grinding materials of high tensile strength, such as stainless steel and tool steels but it can also be used on some high tensile aluminum and bronze alloys. Aluminum Oxide is manufactured in varying qualities.
What grit size do I need?
When to select a coarse grit size: where the neatness of the surface finish is not essential to the project, a coarse grit can be used. Also, the coarser the grit, the more rapid the stock removal, which makes it more suitable for large areas of contact than fine gritted abrasives.
They are also the best option for soft, ductile and stringy materials such as soft steel and aluminum. When to select a fine grit size: fine grits are used when the finish is integral to the success of the project.
Also, choose a finer grit when the project requires a closer, more precise operation over a smaller area of contact. Hard and potentially brittle materials such as glass, tool steel, and cemented carbide are most suited to the finer gritted abrasive.
What grinding wheel grade should I choose?
The grade indicates the relative holding power of the bond, which holds abrasive grains in a wheel.
Soft Grades
For hard materials such as hard tool steels & carbides
For large areas of contact
For rapid stock removal
Hard Grades
For soft materials
For small or narrow areas on contact
For longer wheel life
Selecting the right grinding wheel
There are nine main factors to be considered when selecting a grinding wheel for any application:
1. What material will you be grinding and how hard is it?
2. What stock needs to be removed from the material?
3. Work out the shape of the material and the surface finish (or finishes) that are required.
4. What type of machine will you be using? Pay attention to its power and its conditions.
5. What wheel speeds and feeds will be involved? (Norton products are designed and tested for certain applications and operating speeds.
In the interest of safety, please take the time to ensure that the operating speed of the machine does not exceed the maximum operating speed as it is marked on any given product.
6. Determine the size and hardness of the grinding contact area.
7. Will your grinding operation be a wet or dry process?
8. What is the severity of the grinding required?
9. What is the dressing method?
What material will you be grinding?
The type of material affects the selection of abrasive, grit size and grade.
Alumina type abrasives are the most suitable for grinding high tensile materials such as steel and ferritic cast irons. The more friable types of alumina are preferred on harder steels and applications having large arcs of contact.
Low tensile strength materials and non-metallic materials are most efficiently ground or cut with silicon carbide abrasive. The hardness of the material governs the amount of penetration that can be achieved by the abrasive.
For this reason, finer grit sized wheels are required to grind hard materials and soft materials are best ground with medium to coarse grit size wheels. For most efficient operation, the grade must be adjusted to suit the hardness of the material.
As a general guide, the harder the material, the softer the grade of wheel required.
Hopefully this guide has helped you make in making the most informed choice possible.
