Steel shot vs. silica sand

Sand is the most widely available and lowest-cost natural abrasive: historically it was “the abrasive”, and it gives its name to the whole process —sandblasting. The type used is silica sand (never calcareous), because it has the hardness the job requires. Being a natural material, it must be analyzed for the contaminants it carries from its source (dunes, rivers, quarries) and, before use, it has to be screened —to remove fines and oversize— and dried, since it absorbs moisture.

Its main limitation is fragility: projected by high-output equipment, it can be used only once, because over 80% turns to dust on the first impact. This generates huge volumes of very fine dust (below 300 mesh) and heavy pollution in the work environment.

Moreover, as it fractures it releases free silica, the cause of silicosis, an irreversible lung disease. For this reason the use of sand as an abrasive is banned or heavily restricted in most technologically advanced countries, and demands extreme safety measures where it is still used.

Steel abrasive is produced by melting, with controlled chemical composition. The process yields rounded particles —steel shot— which, when the larger diameters fracture, give rise to steel grit.

In jobs where it replaces sand, steel grit is used almost exclusively, sometimes with a small percentage of shot: the angular particle has edges and points and, on impact, works like a tool that bites and tears into the surface. It can be selected to suit the job not only by size —uniform across all particles— but also by hardness, within defined ranges.

Its great advantage is recyclability: depending on diameter, type and hardness, a single charge is projected between 700 and 5,000 times. Being quenched-and-tempered steel, it does not contaminate the work surface. As it does not absorb moisture, it needs no prior drying, and its uniform grain size produces a completely even finish. The dust it generates comes almost entirely from the material removed from the part, not from the abrasive.

Beyond the abrasive cost per m², there are operational differences that affect the initial investment, maintenance and work quality. The main ones are the following.

Equipment wear

• Both abrasives use similar projection and operator-protection equipment.
• But sand is more abrasive and wears out the transport line, hoses, couplings and nozzle far faster.

Dust and filtration system
• Sand generates far more dust, so it requires extraction and filtration systems 3 to 5 times larger than those for steel abrasive.
• These are the most expensive part of the installation and raise the maintenance cost of the filter elements.

Recovery vs. disposal

• With steel abrasive, a recovery and cleaning system is installed to reuse the abrasive efficiently.
• With sand, only a collection and final-disposal system is possible.

Resulting roughness

• Steel abrasive produces an absolutely uniform roughness across the whole surface.
• With sand, roughness varies from one area to another.

In enclosed spaces and with compressed-air equipment, steel abrasive is clearly more advantageous than sand. The reasons that support this:

• Higher productivity and lower abrasive cost per m² cleaned (on the order of 14 to 18 times).
• Lower maintenance cost and lower investment in dust-collection systems.
• Better work quality: uniform consistency, roughness and cleanliness.
• Less waste and dust generation, and less environmental pollution.
• Greater operator safety: better visibility and no silicosis risk associated with free silica.