Why Different Materials Need Different Grinding Wheels
With all of the grinding wheel options available, figuring out which one is going to be the most efficient and cost effective for your working material can feel overwhelming, to say the least.
This article will help cover the basics as to why different materials will need different grinding wheels - and how to select the appropriate abrasive type for your grinding wheel.
So why exactly do different materials require different types of grinding wheels?
It comes down to the material properties (i.e. material hardness and chemistry) and the proposed grinding process: factors like machine, coolant, dressing, stock removal, etc.
First, consider which type of abrasive will be best for your material: conventional or superabrasive?
Conventional Abrasives
Aluminum Oxide
Silicon Carbide
Aluminum oxide has a hardness of 1800 HrV and is commonly used in grinding of ferrous or other materials that are known to chemically react with carbon.
Silicon carbide has a hardness of 2800 HrV and is used on "hard" materials such as glass, ceramics and non-ferrous metals such as aluminum and copper.
Superabrasives:
Diamond
Cubic Boron Nitride (CBN)
Superabrasives are both harder (longer lasting) and have much higher thermal conductivity (remove heat of grinding more efficiently) compared to conventional abrasives.
Diamond is the hardest known substance with a hardness of 9000 HrV and is the most effective abrasive in grinding of materials that don't react with carbon such as glass, ceramics, and non-ferrous metals. It can increase wheel life by several orders of magnitude when compared with conventional wheels. Advancements in production of synthetic or man-made diamonds have brought their cost down and led to expanded use. We commonly see diamonds used for grinding tough materials such as very hard steels, cemented carbide, and aluminum oxide cutting tools.
CBN is the second hardest known material at 4500 HrV and is ideal for grinding ferrous metals and other materials that are known to react with carbon. It is commonly utilized in the grinding of high-speed steel, hardened cast iron, tool and die steel, and stainless steels. When appropriately specified and optimized, CBN can outlast conventional Aluminum Oxide wheels by a factor of up to 300:1.
NOTE: With so many benefits, you may be wondering “What type of materials cannot be ground on a grinding wheel?” Superabrasives (Diamond & CBN) are focused on hard materials. We turn to CBN for hardened ferrous alloys, stainless steel, and nickel alloys. Diamond is ideal for even harder materials such as glass, carbides, and ceramics. The harder the material, the better it is for grinding with superabrasives, which is what we customize for our clients at Continental Diamond Tool.
You often cannot justify the cost of a superabrasive grinding wheel for soft nonferrous metals (<30 HrC) like aluminum, brass, and copper. Materials with such soft properties tend to “clog'' and coat the wheel and would require continuous dressing.
Some have asked, “Can you use a superabrasive grinding wheel on wood?" Wood is a very soft, inexpensive substance and would not be well suited for superabrasive grinding. For similar reasons, we do not recommend superabrasive grinding wheels for other soft nonmetallic materials like fabric, leather, certain plastics and rubber, etc.
Now that you know the differences between Conventional and Superabrasive grinding wheels, you can see how each caters better to different materials and uses. Once you’ve narrowed down the proper abrasive type, a grinding wheel expert can help you narrow your selection further with a selection of different bond types, such as Resin Bond, Metal Bond, Vitrified Bond, and Electroplated.
The bond is what holds the wheel’s abrasive grains together. The strength of bonding of a grinding wheel is often referred to as its hardness. Generally speaking, grinding wheels with a higher grade or hardness are recommended for softer materials and vice versa. It is also now possible to combine bonds to form custom hybrid variations that have unique properties.
NOTE: You may be thinking “Why do we use hard wheels for soft materials in grinding?” This is a complicated subject with the actual grinding mechanism (chip formation) being different between ductile or soft metals and hard materials like ceramics. Grinding wheels for metals act like micro-cutting tools where metal chips are cut or torn away. The chip size and shape is dependent on the material properties.
With harder materials such as carbides and ceramics, there are brittle fractures where small chips are actually fractured away in the grinding process. The material itself is very abrasive. Because the chips in carbide and ceramics are so abrasive, softer wheels are often more efficient at removing the small abrasive chips (a.k.a. swarf).
When shopping for a grinding wheel manufacturer, it’s helpful to have some basic parameters handy to get the most accurate quote and best product for your application. For a whole list of considerations to bring with you for selecting the best grinding wheel, check out our article on How To Order Custom Grinding Wheels.
Then contact us to collaborate with our engineers, product managers, and technical sales people to go over all of these considerations with you. If you’d like, we can even come to your facility to review your process first hand and make recommendations.
When you have the optimal grinding wheel for your material, you will see the difference in speed, durability, and performance.