Abrasive Blasting

Abrasive Blasting

Abrasive blasting is the operation of forcibly propelling a stream of abrasive material against a surface under high pressure to smooth a rough surface, roughen a smooth surface, shape a surface, or remove surface contaminents. A pressurized fluid, typically compressed air, or a centrifugal wheel is used to propel the blasting material (often called the media). The first abrasive blasting process was patented by Benjamin Chew Tilghman on 18 October 1870.

There are several variants of the process, using various media; some are highly abrasive, whereas others are milder. The most abrasive are shot blasting (with metal shot) and sandblasting (with sand). Moderately abrasive variants include glass bead blasting (with glass beads) and media blasting with ground-up plastic stock or walnut shells and corncobs. A mild version is sodablasting (with baking soda). In addition, there are alternatives that are barely abrasive or nonabrasive, such as ice blasting and dry-ice blasting.

Types

Wet abrasive blasting

One of the original pioneers of the wet abrasive (vapourmatting) process was Norman Ashworth who found the advantages of using a wet process a strong alternative to sandblasting—which is banned in many countries.

Common features include: the ability to use extremely fine or coarse media with densities ranging from plastic to steel, the ability to use hot water and soap to allow simultaneous degreasing and blasting, elimination of dust—so silicacious materials can be used without worry, hazardous material or waste can be removed without danger—e.g., removal of asbestos, radioactive, or other poisonous products from components and structures leading to effective decontamination.

The process is available in all conventional formats including hand cabinets, walk-in booths, automated production machinery and total loss portable blasting units.

Process speeds can be as fast as conventional dry sand blasting when using the equivalent size and type of media. However the presence of water between the media and the substrate being processed creates a lubricating cushion that can protect both the media and the surface from excess damage. This has the dual advantage of lowering media breakdown rates and preventing impregnation of foreign materials into the surface. Hence surfaces after wet blasting are extremely clean, there is no embedded secondary contamination from the media or from previous blasting processes, and there is no static cling of dust to the blasted surface. Subsequent coating or bonding operations are always better after wet blasting than dry blasting because of the cleanliness levels achieved. The lack of surface recontamination also allows the use of single equipment for multiple blasting operations—e.g., stainless steel and carbon (mild) steel items can be processed in the same equipment with the same media without problems.

Bead blasting

Bead blasting is the process of removing surface deposits by applying fine glass beads at a high pressure without damaging the surface. It is used to clean calcium deposits from pool tiles or any other surfaces, remove embedded fungus, and brightengrout color. It is also used in auto body work to remove paint. In removing paint for auto body work, bead blasting is preferred over sand blasting, as sand blasting tends to invite rust formation under re-painted surfaces. It’s additionally used in cleaning mineral specimens, most of which have a Mohs hardness of 7 or less and would thus be damaged by sand.

Wheel blasting

In wheel blasting, a wheel uses centrifugal force to propel the abrasive against an object. It is typically categorized as an airless blasting operation because there is no propellant (gas or liquid) used. A wheel machine is a high-power, high-efficiency blasting operation with recyclable abrasive (typically steel or stainless steel shot, cut wire, grit, or similarly sized pellets). Specialized wheel blast machines propel plastic abrasive in a cryogenic chamber, and is usually used for deflashing plastic andrubber components. The size of the wheel blast machine, and the number and power of the wheels vary considerably depending on the parts to be blasted as well as on the expected result and efficiency. The first blast wheel was patented by Wheelabrator in 1932.

Hydro-blasting

Hydro-blasting, commonly known as water blasting, is commonly used because it usually requires only one operator. In hydro-blasting, a highly pressured stream of water is used to remove old paint, chemicals, or buildup without damaging the original surface. This method is ideal for cleaning internal and external surfaces because the operator is generally able to send the stream of water into places that are difficult to reach using other methods. Another benefit of hydro-blasting is the ability to recapture and reuse the water, reducing waste and mitigating environmental impact.

Micro-abrasive blasting

Micro-abrasive blasting is dry abrasive blasting process that uses small nozzles (typically 0.25 mm to 1.5 mm diameter) to deliver a fine stream of abrasive accurately to a small part or a small area on a larger part. Generally the area to be blasted is from about 1 mm2 to only a few cm2 at most. Also known as pencil blasting, the fine jet of abrasive is accurate enough to write directly on glass and delicate enough to cut a pattern in an eggshell.The abrasive media particle sizes range from 10 micrometres up to about 150 micrometres. Higher pressures are often required.

The most common micro-abrasive blasting systems are commercial bench-mounted units consisting of a power supply and mixer, exhaust hood, nozzle, and gas supply. The nozzle can be hand-held or fixture mounted for automatic operation. Either the nozzle or part can be moved in automatic operation.

Automated blasting

Automated blasting is simply the automation of the abrasive blasting process. Automated blasting is frequently just a step in a larger automated procedure, usually involving other surface treatments such as preparation and coating applications. Care is often needed to isolate the blasting chamber from mechanical components that may be subject to dust fouling.

Dry-ice blasting

In this type of blasting, air and dry ice are used. Surface contaminants are dislodged by the force of frozen carbon dioxide particles hitting at high velocity, and by slight shrinkage due to freezing which disrupts adhesion bonds. The dry ice sublimates, leaving no residue to clean up other than the removed material. Dry ice is a relatively soft material, so is less destructive to the underlying material than sandblasting.

Bristle blasting

Bristle blasting, unlike other blasting methods, does not require a separate blast media. The surface is treated by a brush-like rotary tool made of dynamically tuned high-carbon steel wire bristles. Repeated contact with the sharp, rotating bristle tips results in localized impact, rebound, and crater formation, which simultaneously cleans and coarsens the surface.