What is metal sandblasting. Technology of sandblasting and metal cleaning. Sandblasting surface preparation

Sandblasting metal Is a technology of mechanical cleaning obtained as a result of the action of abrasive materials on a metal surface (substrate). The energy of the abrasive particles is set by the compressed air flow, and then the air-abrasive mixture is supplied to the treated surface.

The very name "sandblasting" came to us from the English language from sand blasting. The inventor is Benjamin Chu Tilgman, who patented this technology in the USA in 1870. In modern technical literature, the term is now more commonly used abrasive blasting(abrasive blasting), since since the end of the 19th century the number of abrasives used in the technique has grown significantly, and the sand itself is prohibited for use in most developed countries for a number of reasons.

In various sources, there are other names for this technology, for example, abrasive blasting, abrasive blasting, shot blasting, metal sandblasting, metal sandblasting, etc. - all this is nothing more than one method of surface preparation, in which an air-abrasive mixture under pressure is sprayed onto the substrate, and the abrasive particles transfer the kinetic energy of the surface and the substances on it.

The purpose of metal sandblasting is to remove corrosion products, mill scale, carbon deposits, molding compounds on casting, old coatings and various types of contaminants, as well as to obtain a characteristic roughness that improves adhesion (adhesion of the substrate to the applied protective coatings).

There is a common misconception that sandblasting metal will degrease the surface. In fact, the cleaning of non-degreased metal in advance only leads to negative consequences: the microparticles of fat are "clogged" by the abrasive deep into the profile and negatively affect the adhesion of protective coatings, reducing the quality of work performed and the service life.

Technology advantages

Sandblasting is the preferred method of cleaning metal and preparing it for protective coatings. This is due to a number of advantages of this method, such as: efficiency, high speed and quality of cleaning.

In addition, the resulting surface roughness increases the area of interaction between the metal and the protective coating and improves adhesion at the physical and chemical level.

Numerous studies carried out all over the world have long confirmed the fact that the service life of protective coatings depends to a greater extent on the quality of surface preparation than on the quality of the applied coating and the method of its application.

Leading global and domestic manufacturers of paints and varnishes also recommend preparing a metal surface before sandblasting.

Sandblasting of metal has gained high popularity due to the widespread use of steel as the main structural material susceptible to various types of corrosion during operation.

The mobility of sandblasting equipment and low complexity of application allow the method to be used almost everywhere, including high-rise and underground work, as well as the geographical remoteness of objects.

Recently high-quality abrasives and technologies for collecting and cleaning them for reuse have made the method even more economical and reduced the environmental burden on the environment.

Equipment for sandblasting metal

Sandblasting equipment can be mobile and stationary, and according to the technology of forming an abrasive jet, it is divided into pressure and ejection.

Mobile equipment typically includes mobile sandblasting machines and hand-held ejector sandblasting guns. Stationary systems include large installations for several work stations or sandblasting chambers.

Pressure sandblasting equipment

In pressure-type sandblasting equipment, the supply of abrasive is controlled by a metering valve, into which the abrasive is supplied from a sealed container under pressure, and, mixing with a jet of compressed air, is fed through a sandblasting hose (hose) to a nozzle, in which the jet is accelerated and at the exit from it sprayed onto the surface.

This type of equipment, with the correct layout, is characterized by high productivity and cost-effectiveness, since it allows you to effectively adjust the supply of abrasive and form a large volume of air-abrasive mixture under high pressure. Pressurized sandblasting equipment consumes a large amount of compressed air, due to which, in part, high performance is achieved. Typically, the air flow is 2 to 20 m3 / min at a pressure of 5 to 12 bar.

The pressure apparatus for sandblasting metal is recommended to be used for large volumes of work, for equipping inhabited cleaning chambers, for cleaning metal from old thick-layer coatings and mill scale.

Ejection sandblasting equipment

Typically, ejection equipment is in the form of sandblasting guns and uninhabited sandblasting chambers.

The vacuum generated in the ejector allows the abrasive material to be supplied through the suction sleeve to the contact zone with the compressed air jet, where the air-abrasive mixture is formed.

The performance of ejection sandblasting equipment with equal provision of compressed air and the use of the same abrasives is inferior to pressure units. But in some conditions, the use of this type of equipment is more expedient, for example, an ejection sandblasting gun, due to its mobility and low weight, makes it possible to more efficiently perform work at a height or in confined spaces. In such cases, the performance of ejection sandblasting equipment may even surpass pressure-type installations.

Ejection sandblasting chambers are designed for processing small parts with low production workload or intermittent work.

A feature of the technology is a more "gentle" surface treatment, which in some cases is also the main criterion for choosing equipment.The requirements for the provision of compressed air for such equipment are significantly lower than for pressure vessels.

Dustless sandblasting machines

Dust-free sandblasting equipment has a number of advantages compared to conventional ejection and pressure open cleaning devices.

The essence of the technology lies in the supply of an air-abrasive jet to the surface and the simultaneous parallel intake of the used abrasive by a vacuum system, its cleaning from contamination and collection for reuse.

The closed cycle of movement of the abrasive in such devices allows the use of abrasive materials with a high turnover, which leads to a decrease in cleaning costs. The need to collect waste abrasive at the cleaning site almost completely disappears, and the absence of dust in the work area makes it possible to use dust-free sandblasting machines in places where people are without special protective equipment, for example, in settlements, in residential and industrial premises.

Improving efficiency

The efficiency of sandblasting metal directly depends on the technically competent layout of equipment and tooling, the correct selection of abrasive material that meets the objectives, sufficient provision of the complex with prepared compressed air, as well as, to a large extent, on the professional training of the working personnel.

Unfortunately, too little attention is paid to training and professional development of employees. Such savings only lead to a deterioration in the quality of cleaning, a decrease in labor productivity and an increase in costs.

When choosing abrasives and equipment for sandblasting metal, they often make a common mistake, considering the price as the main criterion, and not the technical capabilities of the equipment and the suitability of the abrasives for the tasks at hand. In most cases, this choice leads to higher cleaning costs, lower surface preparation quality and labor productivity, and the planned savings turn into real financial losses.

The main indicator that should be guided by when selecting equipment and abrasives is not their price, but the cost of cleaning a unit of area and the ability to perform work with a given quality within a certain period of time.

An increase in efficiency and, as a consequence, competitiveness in the market for sandblasting metal cleaning services should be sought precisely in reducing the cost of work, increasing the professional competence of personnel and labor productivity.

Actions aimed at increasing the efficiency of sandblasting metal give a very quick economic effect in the form of reducing the cost of work and increasing the profits of enterprises.

conclusions

If you are looking for a suitable method for cleaning the metal or preparing it before painting, then sandblasting will be optimal in most cases. Due to its high productivity and economy, sandblasting metal has been the most popular method of cleaning and preparation before applying protective coatings for many years.

With the development of technologies, hand tools are being improved and new types of equipment for cleaning metal surfaces appear, perhaps some of them will occupy their niche in the future and be able to compete with sandblasting. However, the sandblasting technology itself does not stand still: new and old technological solutions appear and are improved, allowing to increase labor productivity and increase the efficiency and safety level of equipment. A wide selection of modern abrasives makes it possible to select the optimal materials for a wide variety of tasks.

Do not forget that the efficiency and economic result of your work will directly depend on the correct choice of equipment, its layout, selection of the appropriate abrasive and professional training of personnel.

Experts have long puzzled over how to clean metal products from corrosion without using chemicals and without exerting significant physical effort. As a result, a new technology appeared - sandblasting of metal, which became widespread due to its simplicity. We will talk about it in our article.

What is metal sandblasting used for?

The range of application of sandblasting is not very wide, but, despite this, in modern production this technology is considered one of the most popular. Most often it is used for the purpose of:

cleaning metal surfaces from rust, scale, paintwork residues;

removing the fatty film. Such preparation is necessary in the case of using electroplating and gas-thermal painting methods;

creating a notch (rough texture) on the metal surface for better adhesion of paint to it.

In everyday life, we are faced with sandblasting technologies when repairing and maintaining a car (using this method, they clean car wheels, process the body before painting), replace pipes (cleaning before priming), etc.

The essence of sandblasting

Sandblasting of metal consists in the action of small abrasive particles blown out under high pressure from a sandblasting machine, which is popularly called "sandblasting", on the surface to be treated.

Abrasive materials (fr. "Abrasif" - "grinding", from Latin "abradere" - "to scrape") are materials with high hardness and are used for surface treatment of metal, ceramics, rocks, minerals, glass, leather, rubber and others. Wikipedia

Comprises:

tank (container) with sandblasting (abrasive) material;

a compressor that builds up pressure;

hoses through which air and abrasive material flows;

atomizer, also called a pistol, since it is from its nozzle that fine particles are emitted.

Under the pressure of the air generated by the compressor, particles of abrasive material through hoses enter the atomizer and fly out of its nozzles at a speed of up to 650 m / s. Contacting the surface to be treated, they remove the top layer of the coating from it, cleaning it from rust, oil stains, cement, etc.

Sand is most often used as abrasive materials when working with metal. When a more delicate stripping is needed, experts use starch and plastic. The strength of the impact depends not only on the composition of the abrasive, but also on the speed with which it flies out of the sandblasting gun. Indeed, it is at this moment that a charge of kinetic energy is formed, the effect of which leads to the removal of the upper layer from the metal surface.

This technology is very dangerous, because the abrasive, flying off the surface and still having a charge of kinetic energy, can seriously injure parts of the body that are not covered by protective clothing. In addition, the constant inhalation of air saturated with fine dust leads to pneumoconiosis, a lung disease popularly called "dusting".

Therefore, the abrasive blast (sandblaster) work in special suits and gloves and use a protective helmet with a forced air supply system. At home, when you are dealing with low-power sandblasting and resorting to their help irregularly, clothes made of dense fabric that cover the body as much as possible, gloves, goggles and a mask or respirator will be enough.

Portable sandblasting machines can be found on store shelves today. But it is much cheaper to manufacture do it yourself sandblasting machine... How to do this, see the video:

Advantages and disadvantages of technology

Sandblasting metal has a number of indisputable advantages:

allows you to penetrate even the most inaccessible places. Abrasive particles are so small that they easily pass even in micro-crevices;

wide range of applications. The technology can be used wherever it is necessary to clean the surface from rust, fragments of varnish and paint;

mobility. Most of the devices are compact and can be easily transported over any distance;

high quality cleaning. Products processed in this way do not corrode for a long time, since the micro-furrows formed by the abrasive significantly improve the adhesion of the paintwork.

Adhesion (from Lat. "Adhaesio" - "sticking") in physics - adhesion of surfaces of dissimilar solid and / or liquid bodies. Wikipedia

The disadvantages of this method include the following:

production hazard. The profession of an abrasive blaster belongs to the category of "harmful";

inefficiency. In the course of work, a huge amount of abrasive material is used, therefore this type of activity cannot be attributed to energy-saving technologies.

Take it for yourself, tell your friends!

Technology

In abrasive blasting, abrasive particles are accelerated from the blast machine using the energy of compressed air. Effective cleaning with abrasive particles and compressed air requires professional skill, high-end equipment and quality control. Each element affects the result of the entire system. Cleaning removes unnecessary materials, hardening the surface of the material and making it ready for coating. Abrasive blast cleaning removes old paint, rust and other contaminants from metal structures. In addition, secondary scale that forms on new steel is removed during blast cleaning.

Angular abrasive particles roughen the surface and create a profile, or notch. Most paint manufacturers specify what profiles should be in order to ensure effective application of their products.

Uses International Standards ISO 8501-01-1988 and ISO 8504-1992 when determining the exact removal of rust and cleaning of steel surfaces prior to painting. ISO 8501-01 applies to scale. This means the following levels of rust infestation:

A - steel surface heavily scaled, but with little or no rust.
B - a steel surface that began to rust and from which the scale began to crumble.
C is the steel surface from which the scale has fallen off and from where it can be removed, but with slight visible pitting (pitting).
D - steel surface, from which the scale fell off, but with a slight pitting visible to the naked eye.

Surface preparation grades The ISO standard defines seven surface preparation grades. The following standards are often used in specifications: Surface preparation by hand and with power tools: scraping, wire brushing, power brushing and sanding - denoted by the letters "St".

ISO-St1. Processing by hand and power tools

Thick layers of rust must be stripped off before cleaning by hand or power tools. Visible contamination from oil, grease and dirt must also be removed. After cleaning by hand and power tools, the surface must be free of loose paint and dust.

ISO-St2. Thorough cleaning by hand and power tools

When viewed superficially with the naked eye, the substrate should appear free from visible traces of oil, grease and dirt and from loose scale, rust, paint and foreign matter.

ISO-St3. Very thorough cleaning by hand and power tools

Same as for St2, but the substrate must be cleaned much more thoroughly before a metallic sheen appears.

ISO-Sa. Sandblasting

Surface preparation by sandblasting is indicated by the letters "Sa". Thick layers of rust must be removed by stubbing before proceeding with sandblasting. Visible oil, grease and dirt must also be removed. After sandblasting, the substrate should be free of dust and debris.

ISO-Sa1. Light sandblasting

When checked with the naked eye, the surface should appear free from visible oil, grease and dirt and from poor adhesion scale, rust, paint and other foreign matter.

ISO-Sa2. Thorough sandblasting

When inspected with the naked eye, the surface should appear free from visible oil, grease and dirt and from most of the scale, rust, paint and other foreign matter. Any residual contamination must have a snug fit.

ISO-Sa2.5. Very thorough sandblasting

When inspected with the naked eye, the surface should appear free from visible oil, grease and dirt and from most of the scale, rust, paint and other foreign matter. All residual traces of infection should appear only in the form of subtle spots and stripes.

ISO-Sa3. Sandblast to visually clean steel

When inspected with the naked eye, the surface should appear free from visible oil, grease and dirt and from most of the scale, rust, paint and other foreign matter. The surface should have a uniform metallic luster.

Main areas of application

cleaning metal blanks from scale, old paint, rust and other contaminants
degreasing of metal workpieces before painting, thermal spraying, electroplating, etc. operations
cleaning the fittings of electrovacuum devices before assembling and pumping out the cylinder
decorative glass matting
creating a decorative "roughness" of the surface

Recently, sandblasting has been frequently used to roughen surfaces. When cleaning and repairing old brickwork, the decorative look is preserved, and new wood surfaces, with the help of air and sand, can take on an "old", "worn" look as an effect.

Historically, sandblasting has used ordinary sand, washed and sieved to a uniform grain size. Silicate dust formed by crushing grains of sand on the surface to be treated is the cause of an occupational disease - silicosis. Therefore, when sandblasting in stationary conditions, effective exhaust and ventilation are required, in construction conditions, wearing respirators.

In addition to sand, steel shot, glass balls, corundum powder and other synthetic abrasives can be used as an abrasive.

Modern sandblasting technologies use the following technologies:

gas-dynamic cleaning with the acceleration of the abrasive in a jet stream up to a speed of 300 m / s
water jet cleaning with a stream of water at various pressures (from 100 to 7500 bar)
water jet cleaning with a stream of water with different pressures carrying an abrasive and / or inhibitor
dry ice cleaning

All modern paints and varnishes require mandatory sandblasting of the surface to roughen it and remove dirt. Sandblasting extends the service life of coatings up to six times, which can significantly save on capital and current repairs of metal structures.

Sandblasting of metal is intended for cleaning metal bases from greasy inclusions, corrosion, burn-on and residues from molding. What is metal abrasive cleaning and why is it carried out?

When ordering this type of service, it is noted that every year the price for it decreases. This is facilitated by unique technologies, the perfection of equipment and materials. Moreover, the number of offers is greater than the number of orders.

Undeniable advantages

Before coating metal substrates with paints, in order to adhere to the surface of the paintwork material, it is necessary to carry out preparatory operations. Sandblasting services are relevant today and are in demand among consumers.

A unique technology is provided for the flawless processing of metal products, buildings, structures and elements, before painting them. The use of this method is enshrined in regulatory documents, including the requirements of GOST.

According to the technological sequence, it is necessary to wash metal structures with specialized equipment with parallel cleaning of the bases.

The use of an abrasive allows for an easy, superficial and deep cleaning technology. In this case, a large number of square meters (m2) can be processed.

Cleaning degrees:

The surface treatment of the products ensures a medium level of cleanliness, that is, grease and scale marks can remain on the substrate.
Deep processing allows you to completely clean from corrosion or scale after welding, or to clean the surface until a metallic sheen appears.
Gentle cleaning removes shallow spots of corrosion and scale delamination, which gives the treated surface a relative cleanliness.

Equipment for sandblasting metal, along with the main purpose, is used, inter alia, for degreasing metal surfaces. Removal of the oil layer is necessary before painting facades and other surfaces before thermal spraying or electroplating. The price of the device is not high, so this method is affordable.

Surface cleaning works are carried out quite quickly, so in a short time it is possible to process more than one square of the area (m2).

The technology of sandblasting metal is performed for different purposes, for example, for processing machine discs. Work is carried out in an equipped room. Grinding is provided with shot or fine-grained sand under compressed air pressure.

Cast and forged structures after processing with sandblasting equipment serve for a long time. After the work, the surfaces are painted in several layers.

About the rules of sandblasting

Metal processing with a sandblasting technical device is carried out in strict accordance with the route outlined in the technological process. The sequence of operations is developed individually for one part or a batch of similar products.

For example, to prepare the surface of the facade, when we process the surface, the following nuances are taken into account:

An abrasive mixture is supplied under pressure, which is then removed independently, manually. For this, a rag is used.
The moisture content of the sand should not exceed 2%, otherwise there will be no effect from this operation.
The sand is sifted through a sieve with a mesh size ranging from 1 to 1.2 mm.
The principle of air supply is carried out through a special hose from the compressor unit to the unit. In the container, the air mass is combined with abrasive grit.
The resulting mass from sandblasting under pressure is fed to the surface to be processed.
The created pressure should not exceed 4 kgf / cm2. This condition must be met, since otherwise the surface may be deformed.
When cleaning the facades of the initial 3 floors, it is necessary to provide a pressure supply of no more than 3 kgf / cm2.
If the pressure drops, then the productivity drops. The increased consumption of sand and components per square meter of treated area (m2) confirms the need to replace the nozzle.
At the end of the work, the surface is subject to blowing with compressed air. This removes dust and sand residues.

Domestic use

Sandblasting and shot blasting of surfaces has become relevant in production and at home. For metal processing, you can purchase a Karcher unit, the price is affordable, and the quality of the processed surface is impeccable. However, the number of processed square meters (m2) may vary.

The advantage of the machine is that the surface can be processed not only smooth, but also embossed. Low weight and overall dimensions allow for easy movement of the device.

Shot-blasting of metal is performed with easy readiness of the tool, without the use of much effort. Used materials for work: quartz sand or crumbs from walnut shells. The size of the grain fraction should not exceed 1.5 mm.

The compressed air supply is adjusted manually, taking into account the consumption of abrasive, air and water. It is not difficult to choose the optimal tuning mode. To create a working condition, it is necessary to connect to a water source, a compressor and an abrasive tank.

Video: sandblasting metal.

An increase in productivity can be achieved through a water flow rate supplied at a pressure of no more than 2 bar. The maximum water consumption should not exceed 120 liters per hour, and so that there is not a lot of dust from processing, then 50 liters per hour is enough. The pressure from the compressor unit is adjustable between 3-12 bar.

For the preparation of difficult surfaces, it is provided to move the abrasive into the sandblasting gun using a valve. It is not recommended to use the abrasive for the second time, since it has exhausted its resource at the first stage. Sand consumption can reach from 50 to 200 kg per hour. This unit fully complies with accepted safety standards.

With this technical device, you can organize your business, while the number of squares of the cultivated area (m2) is not limited. Russia today widely uses these units for production purposes to fulfill government orders, as well as for private entrepreneurship.

Any contaminated surface will be ideal if sandblasting is used to clean it using special equipment and high quality materials.

1

Among all modern methods of cleaning various surfaces, characterized by high efficiency, a special place is occupied by sandblasting of metal, metal structures, pipes, car supports, structures, industrial and automotive equipment. Such processing, often called shot blasting or simply sandblasting, in a matter of minutes removes the surface from carbon deposits, oil products (including strongly hardened ones), layer scale, and multi-layer paint and varnish coatings.

The development of technology has led to the fact that today, with its help, among other things, cleaning is performed:

road and construction equipment;
industrial and building metal structures;
building facades made of granite, concrete, brick, reinforced concrete;
steel tanks, cisterns, as well as many other volumetric containers;
pipelines and oil pipelines, railways and motorways, water pipelines, sluice gates and other hydraulic structures;
wooden houses.

A patent for such processing was obtained in 1870 by Chu Tilgman, a military inventor from the United States. At first, the processing was carried out exclusively using sand of uniform size, but over time it was replaced by better and safer materials. They will be discussed below.

2

The essence of sandblasting is that the surfaces are cleaned by applying abrasive powder or special sand to them in an air stream. If the medium for spraying is water and not air, this is already a water jet cleaning. Compressed air, which has considerable energy, "pushes" sharp and hard grains of abrasive to the surface, which leads to the removal of scale and other surface elements from it.

If a soft abrasive material is used for sandblasting, there is a slight work hardening on the surface, since metal and dirt are removed only slightly. In some cases, the workpiece becomes polished. But when the abrasive is characterized by hard grains, a lot of dents and work-hardening, roughness are formed on the surface. Their size and total number depend on the distance at which the product is processed, the angle of application of the abrasive, air pressure, surface structure and some other factors.

In order to perform high-quality sandblasting, the master who carries out it must be a real professional, know many subtleties and nuances. In addition, a special cleaning effect cannot be achieved if the quality of the work performed is not constantly monitored and high-quality equipment is used. And it doesn't matter at all what is being cleaned - the processing of car calipers or the facade of an ordinary building requires adherence to technology and practically "jewelry" possession of a sandblasting machine.

The quality and technical capabilities of the sandblasting machine will of course also influence the results of the event. If air from the compressor is supplied at a low speed, the productivity of work decreases significantly. Low efficiency will also be observed in situations where the master cannot achieve the correct dosage of abrasive material in the air stream.

3

The procedure is optimal for removing all "unnecessary" contaminants from the metal surface, from secondary scale and burn-on, and ending with rust. In addition, the processing of metal structures, which is carried out using special equipment, allows you to degrease steel products, which creates ideal conditions for their subsequent welding or paint application. it will also be of better quality if its surface has been thoroughly cleaned beforehand. Cleaning, by the way, allows you to increase the time of use of metal structures.

Processing of pipes and metal structures is carried out with such abrasive compositions as sand, electrocorundum, steel slag. The choice of the size of the abrasive grain depends directly on the thickness of the product. For example, for thin sheet metal, 1–1.5 mm grains are quite enough, but it is better to clean more massive parts with sand with a grain of at least 2 mm.

The technology of cleaning metal with a sandblasting installation, in addition, makes it possible for granules of abrasive material to fall into the deep layers of the surface due to a powerful air flow, the speed of which can be equal in some cases to 730 m / s. It is clear that under such conditions, or other type of rolled products, they completely get rid of any type of contamination, ingrained rust, and scale.

There are several levels of cleaning steel surfaces, the requirements for which are regulated by GOST 9.402-2004 and international standards:

commercial cleaning: after processing on the metal, stripes and scratches are allowed, while there are completely no traces of rust, old paint, scale residues;
processing to pure metal: a rough relief is obtained, there is no pollution;
Removal cleaning: Paint and rust residues are possible if they do not interfere with good paint application on the steel base.

4

Quartz sand for sandblasting with a grain size of 0.5 to 5 mm is suitable for high-quality preparation of surfaces for painting, for cleaning forgings and castings, large containers and hulls of watercraft (watercraft). When using this abrasive material, a lot of dust is emitted, and the graininess of the sand decreases during operation, since it tends to crumble.

Cast iron shot has greater hardness, and hence a longer service life. But it cannot be used for processing structures made of non-ferrous metals and stainless steel (microscopic cast-iron particles remaining after work are covered with rust). But after such cleaning, the phenomenon of hardening of products is recorded. Cast iron shot can have a grain of no more than 3 mm (the minimum indicator is 0.2 mm).

In some cases, sandblasting aluminum oxide is used. It has a very narrow application. It is used to clean automotive spark plugs, metal-ceramic dentures. The grain of aluminum oxide is measured in micrometers, and its size is 50–250 microns. Metallized surfaces, structures made of non-ferrous metals and stainless steel (for example, pipes) are recommended to be processed with crushed plastics, which are classified as soft abrasives. After such cleaning, the surface becomes shiny or matte.

Nowadays, the film for sandblasting processing of granite, steel, stone, mirror and glass surfaces, which is produced under the popular brands "ADVERblast", "ORAMASK", "ORAFOL", has also begun to be actively used.

Most often it is used to perform artwork. In general, the choice of grit and the specific type of abrasive depends on the purpose of the treatment - to remove fouling, old paint, scale, and so on.