Shot blasting uses a variety of media for cleaning and abrasion. This article discusses some of those media types.
Types of abrasive media used in blast cleaning should be selected to suit the material to be cleaned and the kind of contaminant that must be removed.
Sand is the most common abrasive media used during shot blasting for cleaning a variety of materials, especially stone buildings, walls and sculptures. But sand blasting is becoming rarer as the silica dust created during the cleaning processes can cause breathing problems.
Abrasive blasting at shipyards commonly uses coal and smelter slag, especially if they are located close to coal-fired power plants or iron smelters. The main advantage of the slag is its low silica content and so a lower dust creation. But lead, cadmium, copper and mercury particles can be released during the process.
Steel shot, cast iron shot and cast iron grit are some metallic media commonly used in abrasive blasting. Iran shot and grit are hard materials with sharp edges that are ideal for cleaning painted or rusted steel parts. Steel shot is not as hard as iron shot but works well for surface preening on metals. It produces little dust and has applications in the aircraft and space industries where it can increase the fatigue life of metals. Metallic abrasives are reclaimed and reused during the blasting process.
Silicon carbide and aluminium oxide are popular substitutes for sand as abrasive media. They are very durable, create little dust and can be collected and reused. Aluminium oxide has sharp edges and is used for fast cleaning in blast cabinets. Calcium silicate is a fine material that produces no silica and is used to clean stonework, wood and masonry and to remove graffiti.
Garnet is a very hard, natural material that produces a high performance cleaning and creates little dust. Coarser grades of garnet can be reused two or three times while the fine grades can be used in water jet cutting operations.
Glass beads are more of a soft abrasive material used for polishing and finishing and on plastics and soft metals. They are usually made from a lead free soda lime a mixture of calcium and sodium hydroxides produce a smooth finish and can be reused 30 times. They do not produce and corrosion or contamination on the surface of the material being cleaned.
There are natural compounds, metals and synthetic abrasive media that can be adapted to every job that needs abrasive blasting. Some of these media can be collected and reused.