Your blast nozzle is probably the second most important blasting item you will address after your air supply regardless of the type of equipment you are using.  Choosing the right blast nozzle for each application is simply a matter of of understanding the variables that affect cleaning performance and job costs.  There are Four Basic questions to answer for optimum cost/performance.

1. What Blast pattern do you want?
A nozzle’s bore shape determines its blast pattern.  Nozzles generally have either a straight bore or a restricted, venturi bore.|
-Straight Bore Nozzles create a tight blast pattern for spot blasting or blast cabinet work.  These are best for smaller jobs such as parts cleaning, weld seam shaping, cleaning handrails, steps, grillwork or carving stone and other materials.

-Venturi Bore Nozzles create a wide blast pattern and increase abrasive velocity as much as 100% for a given pressure.  Ventui nozzles are the best choice for greater productivity when blasting larger surfaces.  Long Venturi style Nozzles yield about a 40% increase in productivity compared to straight bore nozzle while abrasive consumption can be cut approximately 40%. The new XL Long Venturi Nozzles provide an even more increased abrasive velocity and production while maintaining a lightweight nozzle for the operator to hold.

-The double venturi Style nozzle can be thought of as two nozzles in a series with a gap and holes in between to allow the insertion of atmospheric air into the downstream segment of the nozzle.  The exit end is also wider than a conventional nozzle.  Both modifications are made to increase the size of the blast pattern and minimize the loss of abrasive velocity. 

-Wide Throat nozzles(wide entry) feature a large entry throat and a large diverging exit bore. When matched with the same sized hose, they can provide a 15% increase in productivity over nozzles with a smaller throat. When wide throat nozzles also feature as larger diverging exit bore, they can be used at higher pressures to yield up to a 60% larger pattern with lower abrasive use.

Its also a good idea to have angle nozzles, banana nozzles, fan nozzles and other specialty nozzles on hand for tight spots like bride lattice, behind flanges, or inside pipes.  Why waste time waiting for the abrasive to ricochet to get the job done?  Angle nozzles are available in 1, 2, or 3 outlets in both 45 or 90^o Angles.

2. Can you air supply support the nozzle?
Your air supply should be able to provide 50% more air volume (cfm) than a new nozzle would need to develop the required working blasting pressure, whether that is 100 psi or 140 psi.  The ensures a nozzle can continue to provide good service even after it is slightly worn. Note: Productivity decreases dramatically if excessive wear happens...  Also the nozzle entry throat must match the inside diameter of your air supply hose.  The wrong size combo can lead to wear points, pressure drop and excessive internal turbulence.

Matching Nozzle Size and Compressor Size for Required Production Rate Production Rate req. (sq. ft/hr) Blast Nozzle Orifice Production Rate @ 100 psi Nozzle Pressure Production Rate @ 90 psi nozzle pressure Production rate @ 80 psi nozzle pressure Compressor size CFM at 100 psi nozzle pressure Up to 100 1/4” 100 85 70 185 cfm 40-50 h.p. 101-160 5/16” 160 136 112 250 cfm 60-75 h.p. 161-230 3/8” 230 195 161 375 cfm 75-100 h.p. 231-317 7/16” 317 270 222 450 cfm 125 h.p. 318-400 1/2” 400 340 280 600 cfm 150 h.p. This chart is estimated and based upon use of a long venturi nozzle, SSPC-6 commercial blast specification

3. What Bore size do you need?
For maximum productivity, select the nozzle bore size based on the desired blast pressure and the available air pressure and flow. For example, assume you are running a 375 cfm compressor at 80% capacity.  In addition to the blast cleaning nozzle the compressor is supplying air to an air fed helmet and other components such as air motors and pneumatic controls, leaving 250 cfm available for the nozzle.  Referring to a nozzle air and pressure requirements chart, you can see that 250 cfm is sufficient for a 7/16” nozzle operating at 100 psi.  A larger nozzle, or worn 7/16” nozzle will require more air flow to maintain 100 psi. This extra flow requirement will either overwork your compressor or decrease productivity.  On the other hand, choosing a nozzle with a bore size smaller than your compressor can supply will result in less than maximum productivity from the system.

Also keep in mind that in order to supply the nozzle with the correct amount of air, the air line from the compressor to the pressure pot must be a minimum size depending on the nozzle size in order to deliver enough air. The bigger the nozzle, the larger the air supply line! Blast helmets and devices running off of compressed air will also ‘steal’ from your air supply so that must be taken into account. 

Click here for the Air Requirements Chart which shows the amount of air required for nozzles

4. What are the best nozzle material choices?
-Aluminum oxide (alumia) nozzles - offer good service life at a low cost compared to other materials.  A good choice for low usage applications where price is a factor and wear is not.

-Tungsten Carbide nozzles - offer long life and economy when rough handling can’t be avoided and mineral or slag abrasives are being used. Remember, All Tungeten Carbide nozzles are not equal. 

-Boride Sialon Tungsten Composite nozzles - offers longer life than standard tungsten carbide nozzles. Very light weight (about 1/3 that of standard tungsten carbide nozzles) which reduces operator fatigue.

-Silicon Carbide Composite nozzles - offer service life and durability very near tungsten carbide nozzles but these nozzles are about 1/3 the weight of standard tungsten carbide nozzles.

-Boron Carbide Nozzles - provide the longest life with optimum air and abrasive use. Boron Carbide nozzles is ideal and should be used with aggressive abrasives such as aluminum oxide, garnet, silicon carbide and selected mineral aggregates when rough handling can be avoided.  Boron carbide will outlast tungsten carbide nozzles by 5 to 10 times and silicon carbide 2-3 times when aggressive medias are used.

-Rotect

Service Life Comparisons Approximate Service life in Hours Nozzle Material Sand/Slag Steel Grit/Shot Aluminum Oxide/Garnet Aluminum Oxide 10-30 20-40 1-4 Tungsten Carbide 300-400 500-800 20-40 Silicon/Tungsten Composite 300-400 500-800 50-100 Boron Carbide 750-1500 1500-2500 200-1000 Rotect Longer than Boron Carbide Longer than Boron Carbide Longer than Boron Carbide Estimated values for comparison. Actual service life will vary depending on blast pressure, media size and particle shape.

Things to consider/provide to Metal Finishing when ordering:

1. Application Type - Nozzle Type/Pattern (venturi, straight bore, wide entry, angle, etc...)
2. Bore Size of the Nozzle
3. Thread Type of Nozzle - 1-1/4” Fine Threaded, 50 MM Contractor Coarse Thread, Flanged/Tapered, Insert
4. Material Type of Nozzle - Aluminum Oxide, Tungsten or Boron Carbide, Tungsten or Silicon Composite
5. Nozzle Washer - Nozzle washers should always be used and changed/checked frequently.  A good nozzle washer prevents premature wear on the nozzle holder and nozzle.