Besides conventional abrasive discs based aluminum oxide or Silicium carbide Commonly used in grinders, grinders, grinders, miter saws and other electrical machines, technology has advanced in the manufacture of stronger discs that broaden the spectrum of applications.
This has made possible the commercialization of the so-called super-abrasive discs, whose cutting element is two of the hardest and most durable materials that exist today: the polycrystalline diamond (PCD) and the cubic boron nitride (CBN).
Manufacture and operation of PCD or CBN discs
In the manufacture of this type of disc, the abrasive grains (PCD or CBN) adhere to the periphery of a metallic disc (made of aluminum, bronze, steel, ceramic or composite materials, depending on the requirements for strength, stiffness and dimensional stability) at depths of 6mm or less using powder metallurgy techniques. Metallic adhesion can be of three types, resulting in three different types of super-abrasive discs:
- Sintered: it is carried out at elevated pressure and temperature.
- Silver solder: It is welded by depression, silver wire is added to the weld that joins the abrasive grains to the metal disc, so that they remain firmly glued.
- Laser welding: it is the safest and most accurate. It is made with the most advanced technology and requires a higher quality of materials, both of the abrasive grains and of the metal disc.
When the super-abrasive disc is in use, the cutting material has a much longer useful life than that of the conventional discs and requires less force from the operator. When the diamond or CBN parts finally wear out, they expose other new parts that will continue with the cutting or roughing operation, so it is also a tool of self-sharpening.
Despite its exceptional toughness characteristics, however, the Diamond It has the disadvantage of becoming brittle above 600ºC. On the other hand, as it is basically a carbon compound, it has an affinity with ferrous materials and nickel alloys. This feature makes diamond blades are not suitable for use in steels and their alloys, so their use mainly encompasses the cutting and roughing of materials such as tungsten, quartz, ferrite, graphite, gemstones, carbides, ceramic oxides, glass, granite, concrete, fiberglass reinforced materials, semiconductor materials and hard facing alloys.
The gap left by the diamond in the cut of ferrous materials was covered by CBN discs, which have no affinity for carbon, and are therefore ideal for machining treated steels with a hardness greater than 50 HRC, difficult-to-cut steels, tempered high-alloy, high-speed, tool, chrome, alloy steels based on nickel, powder metal steels and steely cast irons.
In a similar way to conventional abrasive discs, the PCD or CBN discs They also have a universal classification based on the same parameters that conventional discs classify. The figure below shows the typical nomenclature of the super-abrasive discs.
In addition, many manufacturers offer diamond blades They are differentiated by their type of band (or “rim”), by their diameter and by the type of cut. Let’s briefly look at these classifications.
a) Band type
Generally, the market offers three types of band: keep going, segmented or Turbo, which respond to different technologies used to adhere the diamond particles to the discs. Cutting speed and finish depend on belt type.
The depth of cut is directly related to the diameter of the disc (the larger the diameter, the greater the depth) and this, in turn, with the maximum speed of use, so the choice of diameter depends on the machine in which it is to be used. use the disc.
Diameters generally range from 10 cm to 35 cm, with the smallest diameters being used in portable tools, and the largest in bench machines or concrete and asphalt cutters.
c) Type of cut
The diamond blades offered in the market can effect wet cuts Y dry.
The wet cutting It is the most recommended and, to prolong the life of the blade and maintain a constant temperature during cutting, it uses water as a lubricant.
The dry cut it is recommended only in cases where the use of water is not suitable, for example, near electrical installations or with materials susceptible to humidity. Therefore, since the process does not use lubricant, it is necessary to regularly stop the operation of the machine to allow the disc to cool.
In general, diamond blades for dry cutting can be used for wet cutting, but the wet cutting discs they cannot be used for dry cutting.
In the following video we see a summary of these characteristics that we have just detailed.
The super-abrasive discs they are also marketed in their forms flat, from depressed center and of Cup, and we can summarize its applications and features in the table below.
The PCD or CBN discs They must be mounted on robust and well-maintained machines, so that vibrations do not occur during work, which reduce the quality of the ground surface and shorten the service life of the disc.
If the operating regime is incorrect, the disc is clogged with chips and becomes dull. In this case it is necessary to remove the adhering chips and this can be done with discs Silicium carbide or from corundum pure white, grades I – L (soft-medium) and with a grain size somewhat coarser than that of the super-abrasive disc.
In a future article we will detail a guide that will help us choose the super-abrasive disc more suitable for the operation we wish to carry out and the type of material of interest.