PRESSURE BLASTING:  In pressure blasting, abrasive feeds into a moving stream of compressed air via a metering valve mounted beneath a pressure vessel.  Pressure blast systems are easily distinguishable from suction systems by the single hose feeding the nozzle.  Air and abrasive travel through this blast hose at high pressure and speed, exiting the nozzle at about four times the velocity produced by suction blasting.  Pressure blast machines are used in structural steel blasting, for the high production rates, and in lightweight media blasting, for their precise regulation of media flow.

SUCTION BLASTING:  Suction blasting, sometimes called venturi blasting, draws abrasive from a non-pressurized container into a gun chamber, then propels the abrasive particles out of a nozzle.  A suction system consists of a blast gun, an air hose, a media hose, and an abrasive container.  Compressed air flows through an air jet in the blast gun to create suction.  This suction brings abrasive up through the media hose into the gun body where it is accelerated out of the nozzle with the air.  The volume of compressed air required for suction blasting is determined by the I.D. of the air jet orifice in the back of the blast gun, not the I.D. of the suction gun nozzle.  A typical suction gun air jet is half the sized of a typical nozzle orifice for pressure blasting.  This means it will use about one-fourth the volume of air, and propels abrasive to about one-fourth the velocity created by pressure blasting.   This less-forceful blast is appropriate for light to moderate cleaning and touchup applications.  Suction blasting is used on softer, delicate metals for mild deburring, light shot peening, and scale removal without penetrating the base metal.  Such metals include aluminum, titanium, and magnesium.

SHOT PEENING:  To make a metal product or component, manufacturers must cast, cut, bend, stamp, roll, or weld metal stock to produce the desired shape.  Sometimes these processes leave residual stresses in the metal that, if not removed, can cause parts to fail when stressed.  Shot peening increases the strength and durability of high-stress components by bombarding the surface with high-velocity, spherical media --- including steel shot, ceramic shot, glass beads, and other spherical media.  Shot peening produces an effect similar to that left by pounding a surface with a ball peen hammer, except that the dimples left by shot peening are much smaller and the impacts more consistent in intensity.  This bombardment creates a uniformly compressed surface, diffusing the stress forces over a larger area and leaving the surface less likely to crack.  Shot peening is a precise science, requiring adherence to exacting specifications for media hardness, blast duration, nozzle angle and pressure.  Under- or over-peening a part may cause premature failure.    Gear manufacturers peen to eliminate burrs and sharp edges, and to strengthen gear teeth.  Spring manufacturers peen their products to combat stress.  Shot peening metal castings and forgings cleans the surface, exposes defects, and improves appearances.  Peening threaded parts removes sharp edges while increasing thread holding power.  It is often used with airless machines to remove mill scale from new steel.

TUMBLE BLAST:  Allows large volumes of small parts to be blasted simultaneously while being rotated in an area confined to the blast from the gun.

VIBRATORY:  Vibratory machines, spindle machines, and tumbling barrels, designed primarily for deburring, descaling, burnishing, surface finishing and preparation of metal components. 

COMPRESSED AIR REQUIREMENTS & ABRASIVE CONSUMPTION CHART
Consumption rates are based on abrasives that weigh 100 pounds per cubic foot.

• For nozzle sizes 3/8" to 1/2", blast machines should be equipped with 1-1/4" or larger piping and inlet valve to prevent pressure loss.
• Air requirements were measured by a flow meter under actual blasting conditions, and are therefore lower than figures for air alone, with no abrasive.
• Horsepower requirements are based on 4.5 cfm per horsepower.
• Figures are for reference only, and may vary for different working conditions.   Several variables, including metering valve adjustment, can affect abrasive flow.