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Types of grit blasting explained

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Abrasives

What is grit blasting and how does it work?

Grit blasting, also known as abrasive blasting or sandblasting, is a surface preparation technique in which a stream of abrasive material is propelled at high speed to clean, smooth, or roughen the surface of a material. It is commonly used for cleaning, creating an anchor profile, deburring, desanding or creating a desired surface finish.

Grit blasting involves the use of compressed air, water or a rotating wheel (turbine) to propel abrasive particles (grit or shot) at a surface. When these abrasive particles hit the surface, they remove contaminants such as rust, old paint, scale, or they can create an anchor profile for the coating system to adhere to. It can also be used to smoothen surfaces, strengthening steel (peening) or delicately remove contaminants.

Different media can be used depending on the desired result, the equipment to be used and the base material to be blasted.

Steel shot and steel grit. The most economical way of blasting when there is a possibility to recycle the media and the surface is of normal steel. Excellent life time, can be reused many times.
Stainless steel shot and grit. An expensive but durable abrasive in cases where recycling is possible and iron contamination is an issue.
Fused alumina / corundum. The hardest commonly available abrasive (9 Mohs), for an angular surface profile and quick and aggressive cleaning.
Glass Beads. A delicate media used to smoothen and clean the surface and esthetically improve it.
Like copper slag and coal slag are used on location, where there is no possibility to recycle the blasting media. Inexpensive but creates a lot of dust, because it only lasts one cycle.
A mineral that can be uses for multiple application, it can be recycled a couple of times and creates less dust than slags
Delicate blasting media. Such as plastic blast media, walnut shell blasting media and soda blasting media are used to keep the base material intact and delicately clean the surface.

Types of blasting

Compressed Air Blasting

It is often revered to as sandblasting, because historically they used sand as the abrasive blasting media. Although the blasting principle hasn’t changed much since the first patent in 1870, the type of abrasives have changed through the years and the use of media containing free silica (like sand) have been prohibited in many countries (since 1957 in Holland), due to health hazards.Compressed air blasting involves the cleaning, smoothing or shaping of a surface by striking it with abrasive blast media, through a stream of compressed air. This method basically requires a blast pot, blast hose, blast nozzle, compressor and protective clothing for the operator. This method can be done in the following set ups:

Open blasting. When the abrasive blasting needs to be performed on location out in the open. Often done for the maintenance of bridges, ships, offshore platforms, pipelines, boilers, large vehicles or equipment etc. But also the cleaning of concrete, stones / bricks or monuments.
Blast room. In a blast room the dust is contained and collected and the abrasive blast media can be recycled. This offers cost savings in terms of abrasive costs and disposal of the spend abrasive. Using a recyclable abrasive creates less dust and blasters have a better visibility on the work to be done. In a blast room the work can also be fully automated by robotic blasting. Especially when large surfaces needs to be blasted continuously, the return on investment on a robot is very short.
Blast cabinet. When blasting smaller work pieces a blast cabinet is used in many work places. The blaster stands outside the small blasting chamber and reaches in with his hands to use the nozzle and blast the small objects. Blast cabinets can also be completely automated to save costs when big quantities need to be blasted in a factory environment.

Bead Blasting

Glass bead blasting is a type of compressed air blasting that uses small, spherical beads made of glass as the abrasive material to clean, smoothen, or finish surfaces. This method is particularly valued for its ability to create a smooth, polished surface, without significantly altering the shape or profile of the surface. As it is nonmetallic blasting media it can be used on many base materials and is often used to esthetically improve stainless steel work pieces. With the right abrasive and equipment, the specifications for food grade and medical industry can be met.

Wet Abrasive Blasting

Wet abrasive blasting is a surface preparation technique that combines water with abrasive materials to clean, descale, or prepare surfaces for coating. It is often used in façade cleaning, removal of graffiti and soft cleaning monuments. Wet abrasive blasting involves mixing water with abrasive particles and propelling the mixture at high or low velocity to remove coatings, rust, contaminants, graffiti and other surface imperfections. It is slower than traditional dry sandblasting and doesn’t create as much surface profile, but wet abrasive blasting minimizes dust, which is the main advantage.

Vapour blasting is a form of wet blasting except that pressurized air is added to the water in the nozzle, creating a mist or “vapour”. Also a finder abrasive media is normally used. This allows for a milder blasting operation to create a smoother surface.

Wheel Blasting

Wheel blasting or shot blasting is an abrasive blasting process used for surface preparation, cleaning, and finishing of metal components. It involves the use of a rotating wheel or turbine that propels abrasive media (mainly high carbon steel shot or grit) at high velocity onto the surface of the workpiece. The impact removes contaminants, rust, mill scale, or old coatings, creating a clean and textured surface. The dust is extracted from the working mix of abrasives and the clean blasting media come back into the system for another cycle.

Stationary wheel blast machines are mainly used to blast steel plates, beams, pipes and small structures, but also for deburring and cleaning casted products in the foundry industry. The blasting costs per m2 is relatively low, because the turbines (blasting wheels) run on electricity and costs for compressed air and labor are saved. Besides that the most cost efficient blasting media can be used, high carbon steel shot and grit. Unfortunately not all work pieces are suitable for a wheel blast machine and initial investment is rather high.

Portable wheel blast machines use the same principle and can be used on location, mainly on large flat steel surfaces, like ship decks, oil platforms, helicopter decks and bridge decks.

Dry-Ice Blasting

Dry ice blasting is a nonabrasive cleaning process that uses solid dry ice pellets as a blasting media. The ice particles enter a compressed air stream and impact the surface at high velocity, without damaging the base material and without leaving a residue. When the dry ice strikes the surface, the material instantly turns into gas, creating a micro explosion that lift dirt, coating and debris. The extremely cold temperature (-78 C) makes contaminants brittle, causing it to crack and break away from the surface.

The technique is slow and dry ice as a media is not easily available or storable. But dry ice blasting can be suitable for some cases, since it is nonabrasive and leaves no residue, making it suitable for machine cleaning, possibly without downtime.

Bristle Blasting

Is a mechanical blasting method that uses an handheld tool with a brush like rotating disc made form carbon steel wire. These rotating bristle tips create an impact to clean and coarsen surfaces. It can be useful addition to a set of blasting equipment, using it for spot repairs. Only really suitable for touch up work, because of the slow cleaning rate .

Vacuum Blasting

Vacuum blasting equipment combines the traditional compressed air blasting technique with a built-in vacuum extraction system. This method is designed to clean, strip, and prepare surfaces for further treatment, while minimizing dust, debris, and environmental impact. Because the media is automatically separated from the dust and loose particles, it can be reused several times. Thus reducing costs related to blast media consumption and disposal of spend media. The solution is slower and less versatile than normal compressed air blasting, but it creates no dust and it reuses abrasives. Strong machines like the AB1070 can use the cost efficient media steel grit, for very low abrasive consumption.

Conclusion

Grit blasting is a powerful technique used for a variety of applications ranging from cleaning to surface preparation. The choice of blasting media- and equipment are critical for achieving the desired result. Each type of grit blasting is optimized for specific tasks, from general cleaning to delicate finishing or industrial applications. The choice of method and abrasive will ultimately depend on the material being treated and the desired outcome.

Find out if vacuum blasting is suitable for your application and contact our sales department for more information.