Humanity has known about abrasives for millennia. People used stones and sand to shape and sharpen knives, spears and arrowheads and fishhooks. The first abrasive was sandstone, in which the role of the active substance was played by the smallest grains of quartz. Until the discovery of metal processing methods, this abrasive material made it possible for the development of all mankind, since then people simply had no other ways to make tools for work and weapons.
What is it from a physical point of view
Usually abrasives are very hard minerals that are located at the upper end of the Mohs hardness scale - from quartz to diamond. But even soft materials can perform this function. Sponges, baking soda, and fruit pits can rightfully be called abrasives. We encounter them daily, and their importance in the daily life of a person 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 a 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 at great speed. In some cases, an abrasive mesh is used, which plays the role of a chopper filter.
Sandblasting machines are used to polish and finish parts and finished products. In this case, virtually any abrasive material can be taken: from the shells of nuts and seeds of fruit crops, shells of mollusks and other organic matter 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 of metal structures involves the use of compressed air. It acts as a particle accelerator and has no additional corrosive effect.
However, in some cases, water can also be used. Particularly when cleaning concretestructures. Almost all structures built in the coastal zone periodically need it. The fact is that a thick layer of s alt and other aggressive compounds grows on their surface over time. Fresh water, to which the appropriate material (abrasive) was previously added, not only removes them from the concrete, but also produces a “desalination”. Again, this action significantly increases the 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 perfect finished products or some parts. Even a simple abrasive sponge is in demand. Cerium oxide, diamond, quartz, iron oxide and chromium oxides are the most commonly used compounds today.
Novaculite (dense siliceous rock) is also a good raw material for the production of polishing materials. Cerium oxide is the most common mineral used to polish glass. This compound does not scratch it, but gives it a special smoothness and shine. In recent years, however, silicon carbide and synthetic diamonds have been used more frequently for this purpose. Based on them, a particularly expensive and effective abrasive belt is produced. It is very well suited for processing particularly "capricious" materials.
Using magnetic fields
In recent years, the abrasive sharpening process has become more and more widespread in the industry. This does not use water.under pressure and not compressed air: the smallest particles of abrasives hover in a powerful magnetic field, which forms the "grinding wheel". This method is used in precision engineering, as it can be used to polish or sharpen those parts that are normally too expensive and/or time-consuming to process. As an abrasive, aluminum compounds with those metals that have this property are most often used.
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 very similar to the one described above, and is also used on some 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 GOI wetted abrasive paste based on chromium oxide. It has been known for a long time, but only in recent years has it received special attention. The reason is simple - the low cost of this compound and its high efficiency in 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 also cut particularly hard materials. To do this, use thin grinding wheels made on the basis of aluminum oxide and phenolicpitches. In rare cases, a metal abrasive disc is used. Such tools are indispensable, in particular, in the extraction of marble in quarries. The fact is that this mineral is very dense, it is difficult to cut with ordinary saws.
As we have already said, aluminum oxide, silicon carbide, artificial diamonds and boron carbide are used for sawing. They can be used to make an abrasive disc, they are also used to form special saws for especially durable materials.
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 aluminum oxide, which we have repeatedly mentioned, as well as silicon carbide, zirconium dioxide, and 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 rarer cases, natural diamonds are used that are unsuitable for cutting due to their extremely small size 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 received the name "emery". It was the first barabrasive. The rejection of natural minerals began in the first half of the twentieth century and was almost completely completed by its end. And it was not only the high cost of natural materials. The fact is that they all have strictly defined properties that cannot be changed in any way. Synthetic abrasives, created under certain conditions, can be completely different and better suited for solving some atypical tasks.
For example, a compound with a particle shape resembling a chip can be created through new technologies. This material is ideal for applying polishing wheels to the surface. In addition, completely new materials can be created by combining, for example, titanium oxide with aluminum compounds. These abrasives are ideal for particularly hard surfaces.
When did the "abrasive breakthrough" in the industry happen?
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, you can register a new trademark. But what is the basis for synthetic abrasives, and when did the industry get the opportunity to use them on a mass scale?
A truly significant event was the discovery of silicon carbide, a mineral not found in nature. The creation of synthetic alumina in the 1890s only stimulated the beginning of research in this area. By the end of the 1920ssynthetic alumina, silicon carbide, garnet and corundum were the main industrial abrasives.
But the real breakthrough came in 1938. It was then that it became possible to obtain chemically pure aluminum oxide, which immediately found the widest application in mechanical engineering. It soon became clear that a mixture of zirconia and alumina was ideal for demanding cutting jobs in particularly hard metals. This is a truly unique abrasive powder: it retains high performance, but is relatively cheap. Today, the palm is still held by synthetic aluminum oxide, which has retained the original microcrystalline structure of bauxite raw materials. In particular, the unique Cubitron™ was created in this way, as well as ceramic-based abrasives under the SolGel™ brand.
About "girls' best friends"
Natural diamond is the oldest abrasive stone. It became popular in 1930. There were two reasons for this. First, until that year, the volume of diamond mining was simply negligible and physically could not cover the growing needs of the industry. Secondly, due to the acute sense of impending war, many countries began to urgently look for ways to process tungsten carbide using machines. This substance is still used in the production of cores for armor-piercing projectiles.
The problem was the unrealistic hardness of this material, which abrasive processing simply did not take. A study conducted in the 1960s by the General Electric Companyled to the development of synthetic diamonds. Ultimately, research in this area leads to the discovery of cubic boron nitride, CBN. This diamond-hard compound is widely used in the manufacture of other abrasives, as it can literally grind hard steels to dust.
Of course, all these abrasive substances, in addition to all their wonderful properties, have one huge drawback - the cost. A recent exception is the Abral abrasive, synthesized by the European concern Pechiney. This company has developed a kind of "substitute for diamonds", which, while not inferior to them in hardness, significantly wins in price.
But it wasn't just the abrasives themselves that drove 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 yet more durable grinding wheels. They grinded more evenly, and abrasives were better distributed in their internal volume. This resulted in significantly better material handling.
Sandpaper
Emery skins use artificial and natural fabrics, films and even plain paper reinforced with woven fibers as a base. In some cases, "sandpaper" is obtained by impregnating a fabric with a solution based on phenolic resins or water (with the addition of abrasives, of course). An abrasive sponge can also be obtained. Such tools are widely known to almost everyone, we encounter them constantly anddaily.
We have described many applications of these materials. But the fact is that the average average person does not encounter most of them in their life at all. So, many people know about grindstones, whetstones or the same sandpaper, someone used an abrasive mesh. But few people know the specific types of substances that are used, for example, by manufacturers of bearings or high-quality knives made of super-hard steels. The latter, by the way, are almost impossible to sharpen at home. "Sharpeners" for them need very special.
Which applications are suitable for this or that abrasive?
For specific needs, superabrasives are needed, which we have already briefly mentioned above. They are also presented in the form of emery skins, abrasive brushes, discs and circles. So, in the production of knives from standard grades of steel, manufacturers use aluminum oxide and silicon carbide. Mass production, on the other hand, usually requires more extensive use of sandblasting machines: stainless steel, ball bearings and mass processing of especially hard woods. However, in most cases, industrialists remain true to the "good old" aluminum oxide. This abrasive powder is cheap yet highly effective.
Finally
Abrasives, directly or indirectly, play a role in the production of almost everything that people deal with on a daily basis. In particular, without them, it is impossible to create cases made of anodized aluminum, whichso popular with fans of "apple" products. Do not forget that a simple abrasive stone "grinder" or even ordinary sandpaper is the fruit of the activity of many generations of scientists and artisans who have collected and systematized 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 during 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.
