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Edge Diamond – The Facts

The Diamond

The most important factor associated with the diamond product industry is the diamond. Diamond technology has been in existence since the 1950’s. Key performance criteria in diamond products is the quality, shape, size, concentration, crystal purity, strength and thermal stability of the diamonds.

There are two types of diamond in existence, naturally mined and synthetic industrial diamonds. Synthetic industrial diamonds are generally stronger and their characteristics are more consistent than natural diamonds making them more suited to sawing, cutting and grinding although for certain applications we do use naturally mined diamonds with specific morphology.

During cutting the diamonds are exposed to tremendous stresses. Diamond crystals with blocky shapes and smooth faces (cubo-octahedon) with good cutting edges that have a low breakdown rate or wear rate are required to ensure proper cutting speed and life. This morphology gives the crystal additional strength and allows it to cope with the colossal stresses during its
working life.

Working applications range from the hardest granites, refractories and heavily reinforced concrete to soft marbles, limestones and other general building materials. This broad spectrum facilitates the use of a large variety of diamond grits. Diamond grit is graded in a controlled process for its different characteristics. During the cutting action the diamond needs to perform in a sharp free-cutting way.

If a wrong type of grit or grade of diamond has been chosen then the product will not perform to its full potential. Diamond grit needs to crack and break off from the cutting edge in a controlled manner after it has become blunt, to allow a new piece of sharp diamond grit to begin cutting. If this does not happen, the blade will become blunt. If this process happens too soon then the blade will wear too quickly.

On severe applications we can also coat the diamond with special compounds such as tungsten nitride to help it adhere to the bond.

The Matrix or Bond

To be able to hold the diamond in place is the fundamental factor that contributes to the performance of the product. The bond is a result of creating a strong holding matrix designed with a varying degree of hardness and abrasion resistance.

Various metals with different hardness and characteristics are used, such as, Copper, Cobalt, Aluminium, Tungsten, Iron, Manganese, Bronze and many other rare earth metals. Varying micron sizes and grades of these rare earth metals in a powder form are bonded together with the diamond to form the segment, depending on the application, (this is called Powder Technology).

The varying strength of the bond depends upon the chosen application, holds each diamond in place within the cutting segment, and this provides the cutting or grinding section of the product. As the cutting commences, calculated erosion of the bond takes place exposing the diamond. This is critical to the overall performance of the cutting or grinding action. As the bond wears in a controlled manner, the support for each diamond crystal is removed and the worn or blunt diamond breaks out, which in turn exposes a new diamond crystal to continue the cutting action. This should happen in conjunction with the original diamond becoming blunt. This wear characteristic of the bond should determine the speed of cut and product life.

The abrasive nature of the product being cut determines the hardness of the bond. For instance a product intended to cut hard engineering brick will have more Bronze in the bond, since the application is not abrasive and the bond will need to be soft enough to wear and expose the diamonds. On the other hand a segment cutting asphalt would have more Tungsten within its bond because it will have to withstand premature wear rates attributable to the abrasive nature of the aggregates and petrological substances within the asphalt.

If a blade is used on the wrong application, either the product will wear too quickly or “glaze over” which means there is no diamond exposure, so the product will not cut. (In general terms, hard but less abrasive aggregates and sand require softer bonds. Softer but more abrasive aggregates and sand require harder bonds).

The Segments

Segments are a mixture of different diamond grits and specially formulated metal powders. This mixture is then loaded into a mould and pressed under varying pressures dependent on its intended application.

The segment is then heated to a temperature of around 800°c to form the desired product that comes in a variety of sizes and shapes dependent upon their purpose and application. The segment is made wider than the steel core to which it is to be attached. This difference in dimension allows the blade to cut freely without binding the core against the application when it is in the cut. Clearance helps to remove the residue and debris from the cut and thus stops the core blank from wearing prematurely which would result in blade failure.

Deep draft protection segments are attached to blades that may encounter abrasive applications to also help in the removal of the abrasive slurry from the cut. This also eliminates any undercutting of the core. The part of the segment that is to be attached to the core is manufactured without diamonds and this is usually called “freeback”.

This transitional area is to be adhered to the core, usually by laser welding. Any impurities or foreign bodies within this weld area would jeopardise the stability of this area and could finally result in segment loss.

The Core

Edge diamond cores are made from high alloy, heat treated steel. A bore hole is milled out of the centre to the required size. Radial slots or gullets are machined out of the outer diameter to facilitate the attachment of the segments bonding process. These can be machined in a variety of forms, wide gullet, narrow gullet, recessed or many others.

The various types of gullet are needed for different cutting applications. They enhance the performance of the product and its cutting characteristics. The different shaped gullets improve water and air flow around the periphery of the blade and help dissipate the heat and slurry and are critical to the cutting process.

The segments are laser welded or brazed onto the core to complete the finished product. The core itself must be balanced and true. This is checked throughout our manufacturing process both before and after segment attachment. It is also checked again after dressing.

The term “dressing the segment” refers to grinding away the metal matrix or bond by use of a specially designed grinding wheel. This exposes the primary layer of diamond crystals ready for use.

Core bit barrels are made with seamless tubing or from rolled or welded steel. Due to the high RPM’s the core is subjected to, it is critical that the tube is true, straight and round. Out of round tubes will result in core drill failure or premature uneven wear of the barrel.