Reference Guides, Shot Blasting

Metallic Blast Media – Choice And Use

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Abrasive blast medias
These metallic blast medias are of a hardness on MOH’s scale 8 / 9

Cast Chilled Iron (CI) MOH Scale 9

Chilled iron grit

Chilled iron grit is produced from  (alloy-free) scrap iron, that is  re-smeltered in a hot blast furnace.  Shot made during this process is then crushed into grit.

Chilled iron grit will shatter on impact rather than wearing round. Continuously formed new edges , combined with a high hardness, density/ mass result in fast cutting/cleaning action.

Chilled iron grit is used in blast rooms and lined (against abrasion) pressure blast cabinets with abrasive reclaim recirculation systems.

CI grit blasting is ideal for aggressive cleaning applications.

CI grit will quickly strip many types of surface contaminants from steel and other cast and forged metals.

CI grit produces an etched surface on metal for a superior adhesion of paint, epoxy, enamel, rubber and other coatings.

Grit Size and Hardness

Depending on the size and hardness of the grit, chilled iron makes it ideal for quick stripping of hard scale oxides and keys the surfaces of most normally grades of steel.

CI grit hardness is between 55-65 HRC and breaks down, shatters and looses its size much quicker than steel as it is very hard and brittle.  After muliple use and recycles, it does not round up!

Application provides quick and easy scale removal from steel plate, steel profiles and fabrications. Provides for a good surface key for the adhesion of many applied coatings. Mainly used through a compressed air pressure delivery system within a blast cabinet or blast room.  If used in an automated Wheel / Turbine abrasive delivery system, chilled iron grit will destroy the internal wear components at a very much increased rate, due to the hardness and density of the chilled iron grit.

 

Cast Steel Shot MOH Scale 8

Steel shot blasting is very widely used for cleaning, stripping and shot peening to improve a metal surface. The grade and size of the steel shot will determine the finish achieved on the surface of the metal. The roundness and ball shape of the steel shot produces a clean, smooth and polished surface through a peening action created by the impact of the shot. In a peening application, steel shot is also used to impart a compressive strength and to stress relieve , load bearing metal components such as crankshafts, engine turbine blades and heavy-duty springs and many other.

  • its density is not less than 7gms/cc
  • there are three (3) hardness ranges available to choose from standard hardness 40 -51 Rc, Intermediate hardness 45 -52 Rc, or hardest 52 -62 Rc.
  • is close to spherically round in shape, and graded according to size
  • SAE standard sizes available range from S050 (0.18mm to S930 (3.0mm)
  • Peening grades of higher tolerance and to specification are also readily available

Sizes for different applications

The use of smaller steel shot will result in a smoother and more polished surface. Larger shot will clean more aggressively and produce a rougher surface on softer substrates. Both air powered and wheel blast systems can be used to accelerate the steel shot onto the surface of components. Due to the hardness and density of steel shot, it can be recycled as many as 3000 times before being replaced.

Cast Steel Grit – is angular, with sharpe cutting edges, its density is the same as shot, as not less than 7gms /cc

  • SAE standard sizes available range from G 120 (0.125 mm) to G10 (2.8mm)
  • Steel grit blasting is ideal for aggressive cleaning applications. Steel grit will quickly strip many types of surface contaminants from steel and other cast metals. Steel grit is softer than aluminum oxide and does not fracture as easily, making it ideal for so many an applications. (Sometimes even a 50 -50% mix of steel shot and steel grit work together to produce both a fast descaling process and produce the finess of the required surface profile.) Angular steel grit produces an etched surface on metal and provides addition surface area for the adhesion of paint, epoxy, enamel, rubber and other coatings.

Steel Grit Size and Hardness

  • different chemistries will lead to different operating results depending on the size and hardness of the grit. Multiple chemistries of steel grit are available. Steel grit that is formulated as a softer (40-51 Rc) metal will round off rapidly, making it ideal for quick stripping of oxides and cleaning of moulds. Harder steel grit (54-60 Rc) will maintain the angular nature of the grit for much longer to provide continued cutting action
  •  its density is not less than 7gms/cc
  • there are three (3) hardness ranges available to choose from standard hardness 40 -51 Rc, Intermediate hardness 47 -56 Rc, or hardest 54-60 Rc.
  • is multi faced and angular in shape, then graded according to size
  • SAE standard sizes available range from G50 (0.18mm to G16 (2.8mm)

 

The more commonly used medias are:

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Haydn Kitchen New APost written by
Haydn Kitchen
Shot Blasting Technical Manager