Mankind has known about abrasives for millennia. People used the help of stones and sand to form and sharpen knives, spears and arrowheads and fishing hooks. The first abrasive was sandstone, in which the smallest quartz grains played the role of the active substance. Until the discovery of metal processing methods, this abrasive material made it possible for the whole of humanity to develop, since then people simply did not have other ways to make tools for work and weapons.
What is it from a physical point of view
Usually abrasives are very hard minerals, which are located at the upper edge of the Mohs scale of hardness - from quartz to diamond. But even soft materials can fulfill this function. Sponges, baking soda and fruit pits can rightfully be called abrasives. We encounter them daily, and their importance in everyday life is great.
What processes can they be used in?
Abrasive material is often called so not because of its physical properties, but because of the features of use. There are several classes of such processes. In particular, in the sandblasting machine, the largest number of materials can be used, which under normal conditions do not have pronounced abrasive properties. This equipment uses a powerful stream of air or water, in which small particles of some substances move with great speed. In some cases, an abrasive mesh is used, playing the role of a filter-grinder.
Sandblasting machines are used for polishing and final finishing of parts and finished products. In this case, virtually any abrasive material can be taken: from the shell of nuts and seeds of fruit crops, shells of mollusks and other organics to the smallest pieces of steel, slag, glass or even baking soda.
Main components
Quartz sand is the most popular abrasive for sandblasting bridges and other steel structures. In this case, a very effective cleaning of rust occurs, which significantly increases the durability of engineering structures. This process requires high density abrasives. As a rule, cleaning metal structures involves the use of compressed air. It plays the role of a particle accelerator and does not have an additional corrosive effect.
However, in some cases, water may also be used. In particular, when cleaning concrete structures. Almost all structures built in the coastal zone periodically need this. The fact is that over time a thick layer of salt and other aggressive compounds builds up on their surface. Fresh water, into which the appropriate material was previously added (abrasive), not only removes them from the concrete, but also produces “desalination”. Again, this event significantly increases the service life of buildings.
Polishing finished products
Polishing is the most important process in which abrasives are in great demand. As a rule, special pastes or soft disks, as well as compounds based on synthetic resins, are used to bring finished products or parts to perfection. Even a simple abrasive sponge is in demand. Cerium oxide, diamond, quartz, iron oxide and chromium oxide are the compounds that are currently used most often.
Novakulit (dense siliceous rock) is also a good raw material for the production of polishing materials. Cerium oxide is the most common mineral used for polishing glass. This compound does not scratch it, but gives it a special smoothness and shine. In recent years, however, silicon carbide and artificial diamonds have been used more frequently. On their basis, a particularly expensive and effective abrasive tape is produced . It is very well suited for the processing of particularly "capricious" materials.
The use of magnetic fields
In recent years, the process of abrasive sharpening has begun to practice more and more widely in industry. For this, neither pressurized water nor compressed air is used: the smallest particles of abrasives soar in a powerful magnetic field, which forms the “grinding wheel”. This method is used in precision engineering, since it can be used to polish or sharpen parts that are too expensive and / or long to process under normal conditions. Compounds of aluminum with those metals that possess this property are most often used as an abrasive.
Magnetorheological polishing methods
With the rheological polishing method, the “physical” abrasive tool is not used at all. Materials are mixed with liquids, in the thickness of which they move under the influence of electric fields. This method is in many ways similar to that described above; it is also used to process certain parts in precision engineering and similar industries.
In general, in recent years, abrasives pre-mixed with liquids or synthetic resins are increasingly being used in production. A good example is moistened GOI abrasive paste based on chromium oxide. It has been known for a long time, but only in recent years have special attention been paid to it. The reason is simple - the low cost of this compound and its high efficiency when polishing. In addition, the abrasive paste gently acts on the processed material without scratching or damaging it.
Abrasive wheels for angle grinders ("grinders")
They are used not only for polishing. Abrasives can still be cut especially durable materials. To do this, use thin grinding wheels made on the basis of aluminum oxide and phenolic resins. In rare cases, a metal abrasive disc is used. Such tools are indispensable in particular when quarrying marble. The fact is that this mineral is very dense, it is difficult to saw with ordinary saws.
As we have already said, aluminum oxide, silicon carbide, artificial diamonds and boron carbide are used for sawing. An abrasive disk can be made of them, and special saws for especially durable materials can be formed from them.
The main tools used for industry
Thus, these compounds are necessary for sharpening, polishing, cutting materials. Modern industry most often uses an abrasive tool of artificial origin. The reason for this is the relatively low cost of synthetics. Compounds of natural origin are much more expensive. These include the alumina we have repeatedly mentioned, as well as silicon carbide, zirconia and the so-called superabrasives (diamond or boron nitride).
Exceptions are rare and are represented mainly by corundum. It is very expensive, and its use in production is quite limited. In even more rare cases, natural diamonds are used that are unsuitable for cutting due to extremely small sizes or structural defects.
The evolution of industrial abrasives
The history of industrial abrasives for grinding wheels began with natural minerals - quartz and silicon, as well as corundum. It was the latter, by the way, for the first time that he received the name "emery". This was the first abrasive block. The abandonment of natural minerals began in the first half of the twentieth century and was almost completely completed by its end. And the point here was not only the high cost of natural materials. The fact is that they all have strictly defined properties, which cannot be changed in any way. Synthetic abrasives, created under certain conditions, can be completely different and better suited to solve some atypical tasks.
For example, through new technologies, a compound with a particle shape resembling sliver can be created. This material is ideal for applying to the surface of polishing wheels. In addition, completely new materials can be created by combining, for example, titanium oxide with aluminum compounds. These abrasives are ideal for working on extremely hard surfaces.
When did the “abrasive breakthrough” take place in industry?
The modern production of abrasives, including the production of grinding wheels and emery skins, is difficult to describe due to the mass of trademarks and patents, which in many cases describe the same product. The solution to such collisions is simple - because of the smallest differences in the chemical composition, a new trademark can be registered. But what is the basis for synthetic abrasives, and when did industry get the opportunity to use them massively?
A truly significant event was the discovery of silicon carbide, a mineral not found in nature. The creation of synthetic aluminum oxide in the 1890s only stimulated the beginning of research in this area. By the late 1920s, synthetic alumina, silicon carbide, garnet, and corundum were the main industrial abrasives.
But a real breakthrough occurred in 1938. It was then that it became possible to obtain chemically pure alumina, which immediately found the widest application in mechanical engineering. It soon became clear that the mixture of zirconium dioxide and alumina is ideally suited for complex work in the field of cutting particularly hard metal grades. This is a truly unique abrasive powder: it retains high efficiency, but is relatively cheap. Today, synthetic alumina, which retained the original microcrystalline structure of bauxite starting materials, still holds the palm. In particular, unique Cubitron ™ was created as well as ceramic abrasives under the SolGel ™ brand.
About the "best friends of girls"
Natural diamond is the oldest abrasive stone. He became popular in 1930. There were two reasons for this at once. Firstly, until that year, diamond production was simply insignificant and could not physically cover the growing needs of industry. Secondly, in connection with the acute sensation of the impending war, many countries began to urgently look for ways to process tungsten carbide using machines. This substance is still used in the manufacture of cores of armor-piercing subcaliber shells.
The problem was the unreal hardness of the material, which abrasive processing simply did not take. A study conducted in the 1960s by General Electric led to the emergence of synthetic diamonds. Ultimately, research in this area leads to the discovery of cubic boron nitride, CBN. This compound, which has a hardness of diamond, is widely used in the production of other abrasives, since it can literally grind hard grades of steel into dust.
Of course, all these abrasive substances, in addition to all their wonderful properties, have one huge drawback - the cost. A recent exception is Abral, synthesized by the European concern Pechiney. This company has developed a kind of "substitute for diamonds", which, not inferior to them in hardness, significantly wins in price.
But not only the abrasives themselves moved the industry forward. Of great importance were the materials used as the basis for their application. In particular, when bakelite was created, it became possible to produce lighter and more durable grinding wheels. They grind more evenly, and abrasives are better distributed in their internal volume. This provided a significantly better quality of material processing.
Emery skins
Emery skins use artificial and natural fabrics, films and even plain paper reinforced with woven fibers as a basis. In some cases, “sandpaper” is obtained by impregnating with a solution based on phenolic resins or water (with the addition of abrasives, of course) fabric. An abrasive sponge can also be obtained. Such tools are widely known to almost everyone, we encounter them constantly and daily.
We have described many areas of application of these materials. But the fact is that the majority of average people in their lives do not encounter most of them at all. So, many people know about whetstones, whetstones or the same sandpaper, someone used an abrasive mesh. But few people know the specific varieties of substances that are used, for example, by manufacturers of bearings or high-quality knives from superhard grades of steel. The latter, by the way, can hardly be imprisoned at home. Sharpeners need completely special ones for them.
For what tasks is this or that abrasive suitable?
For specific needs, superabrasives are needed, which we briefly mentioned above. They are also presented in the form of emery skins, abrasive brushes, discs and circles. So, in the manufacture of knives from standard grades of steel, manufacturers use aluminum oxide and silicon carbide. Mass production usually requires more widespread use of sandblasting machines: stainless steel, the production of ball bearings and mass processing of especially hard wood. However, in most cases, industrialists remain faithful to the "good old" alumina. This abrasive powder is cheap, but it is very effective.
In conclusion
Abrasives directly or indirectly play a role in the production of almost all the things that people face daily. In particular, without them it is impossible to create cases of anodized aluminum, which are so popular among fans of "apple" products. Do not forget that a simple abrasive stone of the “grinder” or even ordinary sandpaper is the result of the activities of many generations of scientists and craftsmen who have been collecting and systematizing their knowledge over the years.
Companies that produce various types of abrasives, grinding wheels and emery skins use the theoretical knowledge that is present in many related industries. They are guided by the data obtained in the study of ceramics, widely practice applied chemistry, physics and metallurgy. Abrasives will always be useful, they are a key feature of the modern production cycle of many enterprises.