Abrasive material: characteristics, application

Mankind has known about abrasives for many 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 role of the active substance played the smallest quartz grains. Up to the discovery of methods of metal processing, this abrasive material caused the possibility of the development of all mankind, since people then simply had no other ways to make tools for work and weapons.

What is this from a physical point of view?

Usually abrasives are very hard minerals that are located in the upper edge of the Mohs hardness scale - from quartz to diamond. But even soft materials can perform this function. Sponges, baking soda and fruit bones can, with good reason, be called abrasives. We face them daily, and their significance in everyday life is great.

In what processes can they be used?

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 greatest 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-chopper.

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 organic materials to the smallest pieces of steel, slag, glass or even baking soda.

Main Components

Quartz sand is the most popular abrasive for sandblasting of bridges and other steel structures. At the same time, very effective cleaning of rust occurs, which significantly increases the durability of engineering structures. This process requires abrasives with high density. As a rule, cleaning of metal structures involves the use of compressed air. It acts as a particle accelerator and does not have an additional corrosive effect.

However, in some cases, water can also be used. In particular, when cleaning concrete structures. Virtually all the structures built in the coastal zone, periodically need it. The fact is that on their surface over time a thick layer of salt and other aggressive compounds builds up. Fresh water, which was previously added to the appropriate material (abrasive), not only removes them from concrete, but also produces "desalting". Again, this event significantly increases the service life of buildings.

Polishing of 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 some details to perfection. Even a simple abrasive sponge is in demand. Cerium oxide, diamond, quartz, iron oxide and chromium oxide - compounds, which are used today 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 glass polishing. This connection does not scratch it, but gives a special smoothness and shine. In recent years, however, silicon carbide and artificial diamonds have been used for this purpose more often. On their basis, a particularly expensive and effective abrasive tape is produced. It is very suitable for processing especially "capricious" materials.

Use of magnetic fields

In recent years, the process of abrasive grinding has been increasingly practiced in industry. For this, not water under pressure and not compressed air is used: the tiniest particles of abrasives float in a powerful magnetic field, which forms the grinding wheel. This method is used in precision engineering, since with its help it is possible to polish or sharpen those parts that under normal conditions are too expensive and / or long to process. As an abrasive, aluminum compounds are most often used with those metals that possess this property.

Magnetorheological methods of polishing

With a rheological polishing method, a "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 largely similar to the one described above, it is also used to process certain details in precision engineering and similar industries.

In general, in recent years, abrasives, previously mixed with liquids or synthetic resins, are increasingly being used in production. A good example is wetted abrasive paste GOI based on chromium oxide. She has been known for a long time, but only in recent years she has been paid 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 material being processed without scratching or damaging it.

Abrasive wheels for the USM ("Bulgarians")

They are used not only for polishing. Abrasives can still cut very strong 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 mining marble in quarries. The fact is that this mineral is very dense, it is difficult to saw with conventional saws.

As we have already said, aluminum oxide, silicon carbide, artificial diamonds and boron carbide are used for sawing. Of these, an abrasive disc can be made, of which special saws are made for particularly strong materials.

The main tools used for industry

Thus, these compounds are necessary for grinding, 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 aluminum oxide mentioned repeatedly, as well as silicon carbide, zirconium dioxide and so-called superabrasives (diamond or boron nitride).

Exceptions are rare and are mainly represented by corundum. It is very expensive, and its use in production is rather limited. In even more rare cases, natural diamonds are used which are unsuitable for cutting because of extremely small dimensions or structural defects.

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 and was called "emery". It was the first abrasive bar. The abandonment of natural minerals began in the first half of the twentieth century and was almost completely completed to its end. And it was not just about the high cost of natural materials. The fact is that they all have strictly defined properties, which can not be changed anyway. Synthetic abrasives, created under certain conditions, can be completely different and are better suited for solving some atypical tasks.

For example, by means of new technologies a connection with the shape of particles resembling a piece of wood can be created. This material is ideal for applying polishing wheels to the surface. In addition, you can create completely new materials, combining, for example, titanium oxide with aluminum compounds. These abrasives are ideal for processing particularly hard surfaces.

When there was an "abrasive breakthrough" in the industry?

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 of such collisions is simple - because of the smallest differences in the chemical composition, a new brand can be registered. But what is the basis for synthetic abrasives, and when did the industry get the opportunity of their mass application?

A truly remarkable 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 field. By the end of the 1920s, synthetic alumina, silicon carbide, garnet and corundum were the main industrial abrasives.

But a real breakthrough occurred in 1938. It was then possible to get chemically pure aluminum oxide, which immediately found the widest application in engineering. Soon it turned out that the mixture of zirconium dioxide and aluminum oxide is ideal for complex work in the field of cutting particularly hard sorts of metals. This is really a unique abrasive powder: it retains high efficiency, but it is comparatively cheap. Today the palm tree still holds synthetic aluminum oxide, which preserved the original microcrystalline structure of bauxite raw materials. In particular, the unique Cubitron ™, as well as abrasives based on ceramics under the brand SolGel ™, were created in this way.

About "best friends of girls"

Natural diamond is the oldest abrasive stone. It became popular in 1930. There were two reasons for this at once. First, before that year, the volume of diamond mining was simply negligible and physically could not cover the growing needs of the industry. Secondly, in connection with the acute sensation of the impending war, many countries began to urgently seek ways to process tungsten carbide by means of machines. This substance is still used in the manufacture of cores of armor - piercing sub - caliber projectiles.

The problem was in the unreal hardness of this material, which simply did not take abrasive treatment. 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 the hardness of a diamond, is widely used in the manufacture of other abrasives, since with its help it is possible to literally grind hard grades of steel into dust.

Of course, all these abrasive substances, in addition to all their remarkable properties, have one huge drawback - cost. The recent exception is the abrasive Abral, synthesized by the European concern Pechiney. This company has developed a kind of "substitute for diamonds", which, yielding little 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 at the same time durable grinding wheels. They were more evenly grinded, and abrasives were better distributed in their internal volume. This provided a much better quality of material processing.

Sandpaper

Sandpaper as a basis use artificial and natural fabrics, films and even ordinary paper reinforced with woven fibers. In some cases, "nazhdachku" is obtained by impregnating a cloth 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 and daily.

We described many areas of application of these materials. But the fact is that with the majority of them the average people in their lives do not collide at all. So, many know about grindstone, bar or the same sandpaper, someone used a mesh abrasive. But few people know the specific types of substances that are used, for example, by bearing manufacturers or high-quality knives made of superhard grades of steel. The latter, by the way, at home, it is almost impossible to imprison. "Sharpeners" for them are very special.

For what tasks does this or that abrasive work?

For specific needs, superabrasives are needed, of which we have already briefly mentioned above. They are also presented in the form of emery skins, abrasive brushes, discs and circles. Thus, in the production of knives from standard grades, steel producers use aluminum oxide and silicon carbide. Mass production, however, usually requires more extensive use of sandblasting machines: stainless steel, the production of ball bearings and mass processing of particularly hardwood varieties. However, in most cases, industrialists remain faithful to the "old-good" aluminum oxide. This abrasive powder is cheap, but very effective.

In conclusion

Abrasives directly or indirectly play a role in the production of almost all things that people face every day. In particular, without them it is impossible to create cases of anodized aluminum, which are so popular with fans of "apple" products. Do not forget that a simple abrasive stone "Bulgarians" or even ordinary sandpaper is the fruit of the activities of many generations of scientists and artisans who have collected and systematized their knowledge for many years.

Companies that produce various types of abrasives, grinding wheels and sandpaper, use theoretical knowledge that is present in many related industries. They are guided by the data obtained during the study of ceramics, widely practiced applied chemistry, physics and metallurgy. Abrasives will always be useful, they are a key feature of the modern production cycle of many enterprises.