Sandblasting (another name - abrasive) Is one of the highest quality methods of metal cleaning, stone and other surfaces. The cleaning effect is the result of many micro-blows of sand particles on the surface, being cleaned.
During abrasive cleaning, solid particles are fed to the work surface using the kinetic energy of the air flow, supplied under considerable pressure. Sandblasting makes it possible to remove varnish and paint coatings from metal surfaces, rust, scale, etc.. When carrying out repair work on the walls, consisting of bricks and other materials, removes destroyed areas, and is also used before painting various surfaces.
Abrasive material for sandblasting is selected based on many different parameters: the material of the treated surface, her condition, square, faction, particle shape, chemical composition of abrasive material.
Types of abrasive materials
Types of abrasive materials for sandblasting, used in the world, huge amount, and list them all, seems impractical, therefore it is necessary to be limited to the most popular and perspective.
Quartz sand
This is the most common type of material, low cost and ubiquitous availability have made it the most popular for sandblasting.
This is material, obtained by grinding and sifting the so-called milky white natural quartz. After the crushing process, it passes through sieves and the sand is sorted - this method yields fractionated sand. The following fraction size classification is used: powdered quartz - smaller size 0.1 millimeters, sand - within 0.1 to 0.4 millimeters, coarse sand - within 0.5 to 1.0 millimeters, quartz crumb - more 1.0 millimeters.
Compared with sand for sandblasting, of natural origin, white quartz sand has some advantages: homogeneity, monominerality, increased intergranular porosity. Due to its high sorption capacity, it has the ability to extract manganese and iron from water, which are dissolved in it.
But the content of quartz in unbound form severely limits the use of sand for sandblasting, since fine-grained dust, which occurs as a result of particle destruction, causes great damage to health and can cause a deadly and incurable disease - silicosis. In many countries around the world the use of abrasive materials, with a specific quartz content in unbound form more 1%, is prohibited.
It is possible to use quartz sand for sandblasting only when using special dust suppression systems or in specially equipped chambers. But in the second case, the use is not very appropriate, as cleaning filters become clogged very quickly due to excessive dust formation, the visibility of the working operator decreases and due to the high consumption of material there may be additional difficulties with the process of disposal of spent abrasive.
The most reasonable is the use of quartz sand for cleaning concrete surfaces using a dust suppression system.
The consumption of such sand in sandblasting is one of the most significant, the reason lies in its mineralogical characteristics.
Most often calculate in advance, what will be the consumption of sand for sandblasting is impossible, since, when the sand has not been prepared before, washed, dried and fractionated, then in the process of cleaning the inconsistent quality of the material used will lead to a significant variation in the consumption of material and the speed of cleaning surfaces.
Cooper slag and nickel slag
These abrasive materials, which are received after processing of wastes of copper smelting and nickel smelting productions. Unlike sand, contain less 1% quartz in bound form and can be used for open sandblasting. Have higher abrasiveness, level of hardness and dynamic strength of particles and, as a consequence, lower level of dust formation, as well as the possibility of secondary use. The specific gravity of individual particles of Cooper Slag and Nickel Slag is higher, than in the sand, accordingly, the mass of the particles, which further increases the effectiveness of such abrasives.
A higher level of dynamic strength of the particles makes it possible to use (recovered) nickel slag up to three times, while the degree of dust during cleaning is much less, than in Cooper slag. But the specific gravity of nickel slag particles is slightly lower, than in Cooper slag, resulting in energy impact, which is done on the surface of the workpiece, slightly reduced.
Garnett
This material is also called pomegranate sand. This is an abrasive material of mineral origin. The largest producers are countries such as the Czech Republic, India, STEAM, as well as Australia.
As an abrasive material for sandblasting, garnet in its properties far exceeds quartz sand, cooper slag, as well as nickel slag. The high level of hardness and durability of particles allows to use repeatedly pomegranate sand for sandblasting works..
Pomegranate sand in a sandblasting machine is used very widely and the greatest effect is reached at application of devices of dust-free cleaning..
Corundum
Other names - electrocorundum, alumina, aluminum dioxide - obtained by industrial methods, crystalline alumina. It is one of the most effective abrasive materials, electrocorundum. He has a very high abrasive ability, its hardness is second only to diamond 1 paragraph.
Aluminum oxide as an abrasive is often used for decorative work, such as matting steel and other surfaces. Speed of sandblasting, with the use of corundum, one of the highest.
Metal fraction
It can be made of cast iron and steel (chipped fraction). These are some of the most cost-effective abrasives. Their high cost is sufficiently offset by repeated reuse. There is only one restriction for the use of chipped fraction - the ability to collect spent abrasive for future recovery.
The main characteristics in the selection of abrasive material
- Fraction - particle size of abrasive material. Separation of abrasive materials by fractions is carried out by scattering on special sieves, the sieve number indicates the grain size. The following parameters are prescribed in the documents for abrasive material: marginal fraction, the largest faction, base fraction, complex fraction and the smallest fraction and their ratio in percent. The fractional composition of the material is often in the range from 0,125 to 4 millimeters and its choice is of particular importance in the selection of abrasives. The choice of fraction will depend on the surface material, which is processed, the diameter of the nozzle and the pressure used in the apparatus.
- Hardness - the ability of the abrasive not to undergo destructive processes when pressing another material with higher hardness, on a specialized installation. The degree of hardness of the abrasive material is described by a hardness scale of ten classes, natural material is used as standards. Soft materials belong to the 1st class, which can be compared in hardness with talc, to the 2nd - plaster, 3-class - calcite, 4-th class - fluorite, 5-th class - apatite, 6-th class - feldspar, 7-th class - quartz, 8-th class - topaz, 9-th class - corundum, 10-th class - diamond.
- The abrasive ability of the material is determined by the area of the treated surface for the standard segment.
- Mechanical stability is the property of abrasive materials to withstand mechanical loads, without destruction. It is determined by the level of compressive strength, which is derived experimentally, by crushing the abrasive grain, fixing the force of the load at the beginning of its destruction.
- Chemical resistance is the ability of abrasive powder not to change its basic properties in contact with water, as well as with solutions of alkalis, acids and various solvents.
We should not forget, that when working with all abrasive materials, when there is a collision with the surface, the abrasive is gradually destroyed to a state of dust, mixing with surface waste, treatable. The material is fed under considerable pressure and ricocheted in different directions, forming a suspension of fine dust, it constantly settles on all surfaces. In connection with the above, When working with abrasive materials, be sure to use personal protective equipment not only for the skin, but also the respiratory system.
Choice of sand for sandblasting
- Corundum is one of the strongest abrasives, with its help it is possible to clean even the surfaces of metals badly damaged by a rust. It can be reused, which makes its use the most effective in the design of dust-free cleaning, in special sandblasting chambers or cabins. Corundum particles are lighter, than a metal fraction and are most often used in sandblasting chambers of the injector type.
- Nickel slag and garnet also make it possible to obtain a result of sufficient quality, but these materials are used infrequently, mainly because of their high cost.
- Use of cooper slag (kuproshlak) and nickel slag is most appropriate when working in open conditions, when the ability to collect spent abrasive for secondary use is limited.
- Metal fraction. The most accurate fractionation of the fraction makes it possible to obtain a predictable and homogeneous profile of the working surface (notch), which has a good effect on adhesion, avoids overspending of paint and varnish when painting and improves the quality of the protective layer.
- Cast iron and steel fraction are well suited for removing scale from metal, cleaning and surface preparation for painting. The greatest efficiency in metal cleaning is often achieved, if crushed steel fraction is used.
- Consumption of particles per 1 m? at shot blasting one of the lowest. The greatest economic effect of fractions can give when used in the design of dust-free cleaning and shot blasting chambers. The use of cast iron and steel shot for sandblasting / shot blasting allows to achieve the lowest cost of the surface, being cleaned.
- Quartz sand is one of the most available abrasive options. This material is characterized by low cost, it allows to process surfaces from various types of metal.
You need to keep that in mind, that quartz sand for sandblasting equipment has a significant disadvantage. Fine dust is very harmful to human health, therefore, under certain conditions, the use of quartz sand is significantly limited.
Independent production of abrasive material
The cost of sand for sandblasting equipment is quite high, that is why folk craftsmen often make the abrasive mixture themselves.
To do this, the following operations are performed:
- First, the white gravel sand is dried, which has a fine fraction.
- Using a sieve, with the smallest cell size, prepared material, sifting, large inclusions are emitted.
- The resulting fine composition is once again thoroughly dried.
If this method of saving is unacceptable, you need to be willing to give at least 20 rubles per kilogram of material.
Pricing of abrasive materials
Prices for materials for sandblasting are formed depending on many factors, such as the type of material, method of production, methods and quality of cleaning, country of manufacture, acquired volumes, etc.. d.
But conditionally the cost, compared to species, can be divided as follows: quartz sand - low cost; Cooper slag and nickel slag - average; garnet, corundum, cast iron shot and steel chip shot - high.