As shotblasting is used for such a diverse array of applications—roughening surfaces, polishing surfaces, cleaning surfaces, and so on—it requires the use of many different kinds of blasting media. The type shape, size, and hardness of the shotblasting media used affect the blasting process and which materials may be blasted. Generally, blasting media is either spherical or angular in nature. Spherical medias are used for peening (a process in which metal is blasted with shot that acts like countless tiny ball peen hammers, treating the surface via plasticity rather than abrasion) and produce smoother surface finishes. Angular medias are used to more actively remove surface materials, such as paint, rust and scale; they can do so more quickly and with better results than round medias. Angular medias are used to “prime” surfaces as well, as they create a rough surface finish that is ideal for paint and coating adhesions to grip onto.
Blast pressure is another consideration when shotblasting; most blasting media is meant to be recoverable (i.e. collected after being applied so it may be reused). Using a high blast pressure will increase production but will negatively affect the media’s lifespan for reuse. Working with hard surfaces also reduces media life.
Understanding the Different Varieties of Shotblasting Media
Both angular and spherical media come in a variety of types, such as:
Silicon Carbide (SIC): This extremely sharp, hard (rating a 9.5 on the mohs scale) abrasive is used to blast similarly hard surfaces, such as steel, glass, and ceramics. It creates a dull matte finish. Silicon carbide may be used to blast at pressures up to 90 psi and generally has a lifespan of about 9-12 iterations. Silicon carbide is commonly used to treat metals, to etch glass, in ceramic recast removal, in the removal of very tough scale, and prior to brazing and welding applications (usually ones where aluminium oxide contamination is allowable).
Glass Beads and Glass Grit: Glass bead and glass grit are not one in the same; glass bead is a round glass used in peening and in finishing surfaces that require a bright matte sheen with no surface contamination or damage. They are not suited to use in removing paint, rust, or scale. Glass grit, on the other hand, is angular, and as such is very aggressive on a blasted surface, and more suitable for removing materials.
Glass blast media is usually used at pressures between 40-80 psi, and also typically lasts through 9 – 12 iterations.
Ceramic Blast Media: Ceramic Beads are a robust form of spherical media with high mechanical strength and high wear rates. This type of media produces very little dust, the beads tend to keep their round consistency, and the media is chemically inert. This form of media produces a smooth bright satin finish, and is useful for deburring and peening (particularly peening titanium parts). Blast pressures used with ceramic beads are usually a bit lower than those used with the materials above, averaging between 40-65 psi, and the media has an amazing lifespan of 70-90 iterations.
Ceramic blast may also be used with a wide variety of blast delivery systems, including air, wheel, and, water. Ceramic media is also available in a grit form, which is angular and known for being excellent at etching parts.
Stainless Steel Blast Media: Steel media is available in both shot and grit form. Stainless steel media is a bit softer than the types described above, but it is typically heavier. These factors make it a good choice when one is using short blasting times, in deburring, and when working with rust free-surfaces. It is especially useful for creating a bright finish while reducing blast machine wear rates. Stainless shot is also among the most reusable of all blasting media, boasting high media recovery rates and lasting a staggering 150-200 iterations. This makes it a very economical media. Plus, it may be used with blasting pressure that is as high as 90 PSI.
Stainless steel blasting media is generally used for blast cleaning, de-burring, surface refinement, and surface finishing. It may be used when working with aluminium castings and forgings, zinc pressure die castings, various non-ferrous metals, stainless steel castings and forgings, stainless steel equipment and tools, and when working with granite or stone.
Steel Shot and Grit Media: Plain steel blast media is incredibly durable, making it the favoured choice in blast rooms and automated wheel applications. Rounded steel shot is often mixed with steel grit so as to achieve anchor patterns with good finishes, as rounded steel media alone does not produce an ideal finish. Steel shot can be blasted at the extremely high pressure of 110 PSI, and usually lasts for 80-100 iterations. This type of media is also often used to prepare steel parts for painting and for scale and rust removal, in aluminum casting and weldment blasting, and in pipe blasting.