How Diamond Blades & Core Bits Work
Diamond blades and core bits don’t cut concrete, granite or other materials, they actually grind away at it. Diamond blades are metal circular saw blades that have an abrasive diamond-embedded metal compound affixed along the outer rim of the saw blade. Core bits are metal right circular hollow cylinders that have an abrasive diamond-embedded metal compound affixed along the circular rim of one open end of the tube and the other end is enclosed and has one of the various types of attachments that allows it to be connected to the drill. The diamonds are suspended in a mixture of various metals that slowly wears away exposing more diamonds as needed. The exposed diamond crystals do the “cutting” work on the marterial like sand on sand paper slowly grinding away material with every pass. The metal matrix, which holds the diamonds in place is called the bond. The “bond” is made up of a special combination of various metals that is designed to expose the diamonds at the optimal speed which is either not too quickly or too slowly depending on the material being “cut”. The optimal bond is dependant on the hardness or softness of the metal matrix. A general rule of thumb is that you want a hard bond for soft abrasive material and a soft bond for hard non abrasive material and every degree in between. If you use a hard bond on hard material (i.e. granite, cured concrete) then it will just glaze up and not “cut”. And if you use a soft bond on soft abrasive material (i.e. asphalt, green concrete) then it will wear away too quickly. Right in the middle between hard and soft bond is a general purpose bond which can be used on everything but will not give the same extended blade life as if you were specing the bond specifically for the material being cut. Because of the different aggrigate used depending on the localtion spectrum and Trailing behind each exposed diamond is a “bond tail” which helps to support the diamond. As the blade or core bit rotates through the material, the exposed surface of the diamonds grinds away at the material being cut into a fine powder.
After several thousand passes through the material being cut, the exposed diamonds begin to crack and fracture. The matrix holding the diamond also begins to wear away.
Eventually, the diamond completely breaks up and its fragments are swept away with the material that it is grinding.
As the diamond wears and fractures, controlled erosion of the metal bond containing the diamond exposes new sharp diamond points. This cycle of erosion and diamond exposure continues until all of the diamond-embedded metal compound is completely worn away. Once the abrasive diamond-embedded metal compound is consumed the blade will no longer grind, letting the operator know it is time for a replacement blade or core bit.
WHY IS THIS IMPORTANT?
When grinding hard concrete you won’t have the same amount of dust, and the dust can be very fine compared to soft concrete; which results in a lot of dust or larger grindings. – Since we know it’s the dust that interacts with the matrix on your diamond tooling in order to expose the diamonds, the hardness of the concrete is an important factor to consider when selecting tooling.
If you choose incorrectly one of two things can happen, and neither are good…
1) The first thing that can happen is you run the machine and nothing happens- the diamonds do not cut, often due to heating up and glazing over. This happens mostly on hard concrete.
2) The other thing that will happen is the diamonds cut like crazy but you can wear them out very quickly- unnecessarily using $350 worth of diamonds in 600sq. ft. is very depressing!
SO WHAT DO YOU DO?
You must find the “sweet spot” that is the balance of diamond use and productivity.
To find this “sweet spot” you need to know the hardness of the concrete and understand how each bond hardness works.
Although there are multiple bond types available, the 4 most commonly used matrix bonds are,
- Hard Bond
- Medium Bond
- Soft bond
- Extra Soft Bond
You must pair the appropriate diamond bond with the hardness of the concrete you’re working with.
You can find examples of varying concrete hardness anywhere, ranging from very soft concrete in places like Florida to the hardest concrete found in places like the Pacific Northwest, especially the Puget Sound area. The variance in hardness is mainly due to the water/cement mix, finishing process (burnishing), how it was cured, and the local aggregate used in the mix. The Northwest uses local aggregate like granite, metamorphic and igneous rock (very hard) and Florida uses mostly sedimentary stone like sandstone, limestone, and ancient marine reefs, shells, and all making for a very soft mix of aggregate and then there is a mix of concrete hardness across the continent.
This is why it is very important to choose the correct matrix for your metal-bond diamonds.
The “Rule of Thumb” is:
Soft concrete requires Hard bond diamonds and hard concrete needs soft bond diamonds– so if you have,
- Soft Concrete = Hard Bond Diamonds
- Medium Concrete = Medium Bond Diamonds
- Hard Concrete = Soft Bond Diamonds
- Very Hard Concrete = Extra Soft Diamonds
Once you understand the concrete hardness, you can easily use the rule of thumb, to find that sweet spot- to balance diamond use and productivity. This will keep more money in your pocket and help you to produce optimum results, efficiently.